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Loss of labile organic carbon from subsoil due to land-use changes in subtropical China

Loss of labile organic carbon from subsoil due to land-use changes

in subtropical China

Hao Sheng a,*,Ping Zhou b,Yangzhu Zhang a,Yakov Kuzyakov c,d,Qing Zhou a,Tida Ge b, Cuihong Wang a

a College of Resources&Environment,Hunan Agricultural University,Changsha410128,China

b Key Laboratory of Agro-ecological Processes in the Subtropical Region,Institute of Subtropical Agriculture,the Chinese Academy of Sciences,Changsha 410125,China

c Department of Soil Science of Temperate Ecosystems,University of G€o ttingen,G€o ttingen37077,Germany

d Institut

e o

f Environmental Sciences,Kazan Federal University,Kazan420008,Russia

a r t i c l e i n f o

Article history:

Received27November2014 Received in revised form

14May2015

Accepted16May2015

Available online2June2015

Keywords:

Subsoil carbon

Soil organic matter Permanganate oxidation Chloroform fumigation

Land degradation

Deforestation

Agricultural management practices a b s t r a c t

Topsoil carbon(C)stocks are known to decrease as a consequence of the conversion of natural ecosys-tems to plantations or croplands;however,the effect of land use change on subsoil C remains unknown. Here,we hypothesized that the effect of land use change on labile subsoil organic C may be even stronger than for topsoil due to upward concentration of plantations and crops root systems.We evaluated soil labile organic C fractions,including particulate organic carbon(POC)and its components[coarse POC and ?ne POC],light fraction organic carbon(LFOC),readily oxidizable organic carbon,dissolved organic carbon(DOC)and microbial biomass down to100cm soil depth from four typical land use systems in subtropical China.Decrease in?ne root biomass was more pronounced below20cm than in the over-lying topsoil(70%vs.56%for plantation and62%vs.37%for orchard.respectively)driving a reduction in subsoil labile organic C https://www.wendangku.net/doc/e01316307.html,nd use changes from natural forest to Chinese?r plantation,Chinese chestnut orchard,or sloping tillage reduced soil organic C stocks and that of its labile fractions both in top and subsoil(20e100cm).POC reduction was mainly driven by a decrease in?ne POC in topsoil,while DOC was mainly reduced in subsoil.Fine POC,LFOC and microbial biomass can be useful early indicators of changes in topsoil organic C.In contrast,LFOC and DOC are useful indicators for subsoil.Reduced proportions of?ne POC,LFOC,DOC and microbial biomass to soil organic C re?ected the decline in soil organic C quality caused by land use changes.We conclude that land use changes decrease C seques-tration both in topsoil and subsoil,which is initially indicated by the labile soil organic C fractions.

1.Introduction

Land use and land use changes(LULUC)in tropical and sub-tropical areas,including forest conversion,capitalized agricultural intensi?cation and animal husbandry expansion,represent major anthropogenic contributions to greenhouse gas emissions(Harris et al.,2012;IPCC,2013).Tropical and subtropical Asia concen-trates the fastest and most dramatic LULUC in the world,mainly as consequences of rapid agricultural expansion and increasing pop-ulation pressure(Houghton,2002;Carlson et al.,2012).The average rate of deforestation in tropical Asia during the1990s reached up to 5.6?106ha yrà1,resulting in the emission of1.0Pg C yrà1into the atmosphere(Houghton,2002).

Tropical and subtropical aboveground biomass has received much research attention because these regions are highly pro-ductive with dense C stocks(Lewis et al.,2009;Huntingford et al., 2013).However,comprehensively studies regarding underground soil organic C(SOC)content and fractions,lability and response to land use change remain scarce.

Highly weathered tropical and subtropical soils present the deepest pro?les and largest volumes among soils worldwide,ac-counting for nearly half of the global soil C stock in the top3m of soil(Richter and Markewitz,1995;Jobb a gy and Jackson,2000). Unfortunately,most studies on the effect of LULUC on SOC have focused on the topsoil layer(0e20cm)being the layer of soil containing the highest levels of SOC and the greatest microbial

*Corresponding author.Tel./fax:t8673184617803.

E-mail address:shenghao82@https://www.wendangku.net/doc/e01316307.html,(H.

Sheng).

Contents lists available at ScienceDirect Soil Biology&Biochemistry

journal ho mep age:

https://www.wendangku.net/doc/e01316307.html,/locate/soilbio

https://www.wendangku.net/doc/e01316307.html,/10.1016/j.soilbio.2015.05.015

Soil Biology&Biochemistry88(2015)148e157

activity(e.g.,Saha et al.,2011;Nahrawi et al.,2012;Wang et al., 2013;Umrit et al.,2014).In contrast,the response of SOC and its fractions in subsoil to land use change has received less attention (Rumpel and K€o gel-Knabner,2011;Schmidt et al.,2011;Harper and Tibbett,2013),mainly because subsoil SOC has been assumed to be old,stable,inert and insensitive to LULUC.Several recent studies have focused on the level of SOC lability in subsoil and its dynamic response to land use and management practices in tropical and subtropical regions(e.g.,Veldkamp et al.,2003;Conti et al.,2014; Mobley et al.,2015).

Soil labile organic C(LOC)is more sensitive to short term land use change than SOC(Degryze et al.,2004;Yang et al.,2009a;Liang et al.,2012);however,the magnitude and characteristics of each LOC fractions,vary depending on the direction of land use change and the fractionation approach used(Strosser,2010).Measured LOC fractions are heterogeneous in terms of turnover times,chemical compositions,and functions(von Lützow et al.,2007),and there-fore,they may respond differently to short term LULUC and man-agement practices.To date,several studies have analyzed the response of topsoil LOC fractions to land use change in tropical and subtropical Asia(e.g.,Deng et al.,2009;Yang et al.,2009a;Wang et al.,2013);however,comparatively fewer studies have focused on the response of subsoil C fractions.

Subsoil LOC stocks can be affected by LULUC in different ways: (i)new aboveground vegetation can in?uence root distribution, litter fall quality,phenology,and litter layer depth,affecting fresh C supplies and soil C stability in the subsoil(Fontaine et al.,2007; Wang et al.,2014a);(ii)intensive management,including site preparation,terracing tillage,and irrigation can turn over soil ho-rizons,destroy aggregates,and expose subsoil C to air and de-composers(Salom e et al.,2010;Wei et al.,2013);(iii)common agricultural practices such as fertilization,prescribed burning,and weeding may provide fresh C and nutrients to subsoil microbial communities inducing a priming effect(Kuzyakov,2010);and(iv) strong erosion,a common consequence of land use change in hilly regions with abundant rainfall and non-stable aggregates,may lead to the exposure of subsoil and the erosion of lighter organic com-pounds(van Noordwijk et al.,1997;Wang et al.,2014b).

The subtropical region of China extends over250million hect-ares,presenting evergreen broadleaved forests as the climax https://www.wendangku.net/doc/e01316307.html,mercial timber exploitation,cash crop production and the animal husbandry industry have developed rapidly in this region over the past few https://www.wendangku.net/doc/e01316307.html,rge areas of evergreen broad-leaved forest have been slashed,burned and subsequently replaced by highly productive plantations,orchards,and sloping tillage. These rapid land use changes have led to serious environmental problems,including water-induced soil erosion,soil fertility decline,productivity loss,and decrease in ecosystem resilience (Yang et al.,2009b;Sheng et al.,2010).In addition,subtropical China is characterized by widespread mountain and hilly landforms with steep slopes,frequent heavy rainfall,and severe soil erosion. As a consequence,Chinese subtropical ecosystems are highly vulnerable to human disturbance.The nature,extent and driving forces of land use change may differ signi?cantly between sub-tropical mountainous areas and tropical plains and lowlands(e.g., the Amazon Basin).Yet,only a few studies have focused to date on the response of SOC and its labile fractions in soil,in particular in the subsoil,to land use change in subtropical regions.

In this study,we assessed the predominant land use trajectories of four land use systems(natural forest,Chinese?r plantation, Chinese chestnut orchard and sloping tillage)with well-known site history in the east of the Hunan Province.The speci?c objectives of this study were to(i)quantify the responses of SOC,in particular LOC fractions,to land use change in topsoil(0e20cm)and subsoil (20e100cm);(ii)assess the sensitivity of LOC fractions isolated by various fractionation methods as early indicators of SOC alterations due to land use change;and(iii)use LOC/SOC ratios to evaluate the effect of land use change.We tested the following hypotheses:(i) land conversion into plantations decreases SOC stock,in particular the labile fractions,in topsoil and subsoil below20cm;(ii)LOC fractions can be used as sensitive indicators of SOC alterations due to land use change;and(iii)?ne root C input controls LOC stocks in subsoil.

2.Materials and methods

2.1.Site description

The study site is located in the Dawei Mountain National Forest Park,Liuyang City,Hunan Province,central China(113 560E, 28 250N).The Forest Park covers5053ha.It adjoins Mufu Mountain on the northeast and Xuefeng Mountain on the southwest.The site climate is humid middle subtropical monsoon,with a mean annual air temperature of17.7 C(ranged from2.5 C in January to28.0 C in July)and a mean annual relative air humidity of83%.The mean annual rainfall is1800e2000mm(~55%occurring from March to July)and the mean annual potential evapotranspiration(Pen-man e Monteith equation)is1450mm(Xu and Lu,2002).In this study,we chose four typical land use systems:1)natural forest (control),2)Chinese?r(Cunninghamia lanceolata(Lamb.)Hook) plantation,3)Chinese chestnut(Castanea mollissima)orchard,and 4)sloping tillage.The plantation,orchard,and sloping tillage areas were transformed from natural forest in2004.The sites selected were distributed adjacently within a small watershed in the Forest Park.All sites were similar in topography,regional climate,and soil type,and their elevations varied from150m to165m and the slopes ranged from20 to30 .For all sites in the four land uses,the soil was classi?ed as red soil using the Chinese Soil Classi?cation System(State Soil Survey Service of China,1998),equivalent to hapludult in the USDA Soil Taxonomy(Soil Survey Staff of USDA, 2010)and Chromic Acrisol in the World Reference Base for Soil Resources(IUSS Working Group WRB,2014).The soil was acidic, and developed on deeply weathering product of medium grain granodiorite from the Sinian Period(Sheng et al.,2014).The soil pro?le was well developed and characterized by a B t horizon with accumulation of low activity clays,reddish in color due to the accumulation of iron oxides.All sites were located on well-drained uplands with a soil pro?le deeper than1.0m.Table1shows the main characteristics and properties of the topsoil of the studied sites.

The natural forest was considered as the climax vegetation, known to have followed continuously its natural ecological suc-cession for>300years.The forest plant community was dominated by Camphor trees(Cinnamomum camphora(L.)J.Presl),mixed with Liquidamba formosana Hance,among others.The plantation,or-chard,and sloping tillage sites were transformed from partially abandoned land after a natural forest clearing.No heavy machinery was involved in the land transformation process.After clear-cutting,all sites were prescribed burned and prepared for each speci?c land use.In2004,a section of the main site was afforested with Chinese?r,another section was terraced along a ridge-less contour and divided into an orchard and an area of sloping tillage.The orchard was planted with Chinese chestnut,while sweet potatoes were grown annually in the sloping tillage area. Only the orchard and sloping tillage were regularly managed and treated with chemical fertilizers.The application rate of N,P,and K was380,32,and66kg haà1yrà1in the orchard and135,26,and 96kg haà1yrà1in the sloping tillage area,respectively.Fertilizers were applied three times per year(May,late June,and early November)in the orchard,and twice a year(early April and late

H.Sheng et al./Soil Biology&Biochemistry88(2015)148e157149

August)in the sloping tillage area.Both orchard and sloping tillage were weeded and hoed by hand twice a year and irrigated peri-odically using a handheld sprinkler during prolonged drought seasons.

2.2.Experimental setup and sampling

We used a space-for-time substitution methodology which as-sumes that spatial and temporal variations are equivalent (Pickett,1986).The experimental setup comprised triplicate 20?30m ?xed plots randomly distributed across each land use area in 2012.

The litter layer was carefully removed by hand from the surface before soil sampling.We collected ten soil cores (3.5cm diameter)randomly from each experimental plot using a customized soil auger.The soil samples were obtained from a depth of 100cm at a sampling interval of 20cm,and subsequently mixed into a sub-sample for each layer.Visible plant debris and stones larger than 2mm were removed immediately after sampling.In addition,3soil pro ?les were dug randomly in each plot,and 100-cm 3columns at each sampling interval were sampled to determine soil bulk density.

Each soil subsample was divided into three portions.One portion was sieved at high moisture levels through a 2-mm mesh to ensure uniformity and homogeneity,and subsequently stored at 4 C for microbial biomass (MBC)and dissolved organic C (DOC)analyses.A second portion was air-dried,crushed,and sieved through a 2-mm mesh before measuring particulate organic C (POC),light fraction organic C (LFOC)and readily oxidizable organic C (ROC).The remaining portion was sieved through a 0.149-mm mesh for SOC and total N analyses.

With the exception of the sloping tillage area,all trees of diameter at breast height (DBH)!4cm in each plot were identi ?ed to the species level and measured using standard diameter measuring tapes.Fine root (<2mm in diameter)biomass at 0e 60cm depth was determined using soil coring (Sheng et al.,2014).In addition,we measured thickness and standing stock of the litter layer in 3randomly selected 1.0?1.0m subplots in each land use plot.

https://www.wendangku.net/doc/e01316307.html,boratory analyses

The light fraction material was extracted using NaI (Janzen et al.,1992).Brie ?y,20g of air-dried soil samples (<2mm)were sus-pended in 50ml NaI solution (1.70g cm à3),and shaken (250rpm)for 6h and subsequently centrifuged (4000rpm)for 10min.The

supernatant was then ?ltered using 0.45m m glass-?ber micro-?ltration membrane,and the remaining solution was collected for reuse.The separation method described above was repeated until no visible ?oating particles were left on the membrane.The par-ticles on the membrane were collected,washed with 75ml 0.1mol L à1CaCl 2solution followed by a wash with 200ml deion-ized water to remove any residual NaI,dried at 60 C for 48h,weighed,and stored as the light fraction material.

Particulate organic matter was separated as described by Cambardella and Elliott (1992):20g of air-dried soil samples (<2mm)were dispersed in 100ml 5g L à1sodium hexameta-phosphate and shaken for 18h.The suspension was then ?ltered through a 250-m m sieve followed by a 53-m m sieve.The material remaining on the sieves were thoroughly rinsed with deionized water,dried at 60 C overnight,weighed,and stored as coarse (>250m m)and ?ne (250e 53m m)particulate organic matter samples.

ROC was measured as described by Blair et al.(1995).Brie ?y,soil samples containing 15mg C were weighed into plastic screw top centrifuge tubes and 25ml 1/3mol L à1KMnO 4were added to each tube.All tubes were tightly sealed,tumbled for 1h and centrifuged for 5min at 2000rpm (RCF ?815g).The supernatant was subse-quently diluted with deionized water,and the C content was determined by colorimetry (Model SP-723,Spectrum Co.,Shanghai,China)at 565nm wavelength.

For measuring MBC,humid soil samples (25g on an oven-dried basis)were fumigated with CHCl 3vapor in a desiccator for 24h.After removing any residual CHCl 3by evacuation,the fumigated soils were extracted with 0.5M K 2SO 4for 30min.Non-fumigated soils were extracted following the same procedure.All soil ex-tracts were ?ltered and the organic C concentration in the extracts was determined using a TOC-analyzer (Phoenix 8000,Teledyne Tekmar Co.,Mason,OH,USA).MBC per sample was estimated as MBC ?2.22E C ,where E C ?(organic C extracted from fumigated soil)e (organic C extracted from non-fumigated soil).Organic C extracted from non-fumigated soil was also considered as DOC (Wu et al.,1990).

Organic C and total N in bulk soil,light fraction materials,and POM were determined using an elemental analyzer (Vario EL III,Elementar Analysensysteme GmbH,Hanau,Germany).Soil pH was determined in 1mol L à1KCl solution at a soil-to-solution ratio of 1:2.5(w/v)using a pH meter (Delta 320,Mettler-Toledo in-struments Ltd.,Shanghai,China).Soil bulk density was measured using the clod method (Blake and Hartge,1986).Soil particle size distribution was estimated following the sieve-pipette method

Table 1

Site characteristics and topsoil (0e 20cm)physicochemical properties in different land use systems in subtropical China.Properties

Land use systems NF

CF CO ST Elevation (m)165160150150Slope ( )

30282020Forest average DBH (cm)11.28.29.1nd Mean tree height (m)10.49.89.6nd Tree density (ha à1)260023001200nd Basal area (m 2ha à1)

94.3a 66.7b 38.4c nd Depth of litter layer (cm)

4.0 2.5 3.00.5Standing stock of litter layer (t ha à1)

7.64a 3.63b 4.05b 0.10c Fine root biomass at 0e 60cm depth (t ha à1)8.78a 3.23b 4.40b 0.11c Bulk density (g cm à3) 1.05c 1.12b 1.20ab 1.32a pH (KCl)

3.9a 3.7a 3.7a 3.8a Soil organic C (g kg à1)19.12a 13.39b 13.48b 12.31b Total nitrogen (g kg à1) 1.61a 1.16b 1.54a 1.33ab d 13C (‰)

à26.35

à26.39

à20.74

à24.78

NF,CF,CO,ST,DBH,and nd represent natural forest,Chinese ?r plantation,Chinese chestnut orchard,and sloping tillage and mean tree diameter at breast height,and no data available,respectively.Different letters in the same row indicate signi ?cant difference among land use systems (P <0.05).

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150

(Gee and Bauder,1986),and classi?ed by the American Soil Texture Taxonomy,considering as sand the particle sizes within the 20e2000m m range,silt as those in the2e20m m range,and clay for <2m m(Soil Survey Staff of USDA,2010).

2.4.Calculation of C stocks and sensitivity index

C stocks in bulk soil and labile fractions for each layer were calculated using equation(1)(Pan et al.,2003):

D?OC?g?h?e1àdT?10à1(1) where D represents to organic C stock(t haà1),OC is the average organic C content in bulk soil and labile fractions(g C kgà1),g is the soil bulk density(g cmà3),h is the sampling depth(20cm),and d is the gravel content(%).

Sensitivity index(SI)was de?ned as the reduction of LOC frac-tions after land use change,and was calculated as de?ned in equation(2)(Liang et al.,2012):

SI?elabile C fractions in treatment

àlabile C fractions in controlT

?100=labile C fractions in control(2) 2.5.Statistical analysis

All statistical analyses were performed using SPSS software (SPSS13.0for Windows,SPSS Inc.,Chicago,IL,USA).Each plot was considered as an experimental unit,and the replicated data were averaged by plots for the analyses.Prior to conducting one-way repeated-measures(ANOVA)analysis,all variables were checked for normal distribution(Kolmogorov e Smirnov test)and homoge-neity(Levene's test).Data of stocks of SOC and labile organic C were transformed to natural logarithms to achieve homogeneity.ANOVA were performed to compare SOC and LOC stocks among land use systems using Turkey's HSD test.The relation between subsoil LOC fractions with?ne root biomass at20e60cm depth,and SOC in subsoil was examined using linear regression.All results were represented as mean value±standard error and the statistical signi?cance was calculated at5%level unless otherwise mentioned.

3.Results

3.1.Plant biomass and soil basic properties

Total plant biomass decreased signi?cantly following land use change.Basal area,standing stock in the litter layer,and?ne root biomass at0e60cm depth decreased signi?cantly following the conversion from natural forest to Chinese?r plantation,by29%, 53%and63%,respectively,and to Chinese chestnut orchard,by59%, 47%and50%,respectively(Table1).For the sloping tillage plots, standing stock of the litter layer and?ne root biomass at0e60cm depth decreased by up to99%compared with natural forest.Fine root biomass below20cm decreased more strongly compared to that in the topsoil(70%vs.56%for plantation and62%vs.37%for orchard)(Fig.1).

Topsoil bulk density increased by0.2and0.3g cmà3following the conversion from natural forest to orchard and sloping tillage, respectively(Table1).Total N content also decreased by28%after natural forest conversion to plantation.

3.2.SOC stocks in top and subsoil

SOC stock in topsoil markedly decreased following land use change,by35%(plantation),32%(orchard)and25%(sloping tillage) (Fig.1).SOC stock below20cm depth was also signi?cantly reduced by23%with the conversion to plantation,29%to orchard,and40% to sloping tillage.In total,after conversion,SOC stock in0e100cm soil decreased by26%(plantation),30%(orchard),and35%(sloping tillage).These results show a remarkable loss of SOC following land use changes not only in the topsoil,but also in subsoil deeper than 20cm down to100cm.

3.3.LOC fraction stocks in top and subsoil

The stocks associated with the different LOC fractions in topsoil and subsoil responded differently to land use changes.POC decreased by15%,38%,and33%at0e20cm depth,and by10%,12%, and18%at20e100cm depth following natural forest conversion to plantation,orchard,and sloping tillage,respectively(Fig.2). Consequently,POC stock in topsoil was more sensitive to land use change than that in subsoil(Fig.3).Regarding the different POC components,only fPOC stock in0e20cm topsoil decreased by21%, 53%,and51%after natural forest conversion to plantation,orchard, and sloping tillage,respectively(Fig.2).This implied that the reduction of POC stock after land use change mainly resulted from the loss of topsoil fPOC,which,consequently,could be used as a sensitive indicator to detect SOC changes.Noticeably,fPOC stock in subsoil below40cm increased by11e74%following the land use change,indicating that changes in POC fractions in subsoil may follow the opposite direction to those in topsoil(Fig.3).

Signi?cant loss of LFOC occurred not only in topsoil,but also in subsoil below20cm following land use change(Fig.4).The topsoil showed a greater reduction in LFOC stock than did subsoil following the conversion of natural forest to orchard and sloping tillage.LFOC appeared to be more sensitive to land use changes than SOC both in top and subsoil(Fig.3).The decrease in ROC stock through the

soil

Fig.1.Fine root biomass(left)and soil organic C stocks(right)in relation to depth and land use systems in subtropical China.Letters indicate signi?cant differences among land use systems(P<0.05).

H.Sheng et al./Soil Biology&Biochemistry88(2015)148e157151

depth pro ?le following land use change was smaller than that of LFOC (Fig.4).ROC stocks did not differ signi ?cantly between natural forest and sloping tillage areas,suggesting that ROC stock was relatively insensitive to land use change.The DOC stock in the topsoil decreased by 29%and 78%following the conversion of natural forest to plantation and or-chard,respectively,and subsoil DOC stocks decreased even more dramatically following land use change (Fig.4).MBC stock

decline

Fig.2.POC stocks and those of its components (cPOC,fPOC)in relation to depth and land use systems in subtropical China.POC,cPOC,and fPOC represent particulate organic C,coarse particulate organic C,and ?ne particulate organic C,respectively.Letters represent signi ?cant differences among land use systems (P <

0.05).

Fig.3.Sensitivity index of LOC fractions in relation to subtropical land use changes across soil depth pro ?les.LOC,SOC,POC,ROC,fPOC,cPOC,LFOC,DOC,and MBC represent labile organic C,soil organic C,particulate organic C,readily oxidizable organic C,?ne particulate organic C,coarse particulate organic C,light fraction organic C,dissolved organic C,and microbial biomass,respectively.

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was more pronounced in topsoil (49e 86%)than in subsoil (21e 61%)following land use change.DOC and MBC were the most sensitive indicators to land use change (Fig.3).Noticeably,no signi ?cant reduction in MBC was observed in subsoil following the conversion from natural forest to orchard.This could be partially explained by the deep ?ne root distribution of Chinese chestnut (Fig.1).

The stocks of SOC and its fractions (POC,LFOC and DOC)in subsoil showed a signi ?cant positive correlation (R 2>0.94)with ?ne root biomass present in the soil subsurface (20e 60cm)across all land use systems (Fig.5).In addition,the stocks of LOC fractions tended to be positively linearly correlated with SOC stocks in sub-soil (20e 100cm)(Fig.6).

3.4.Proportions of LOC fractions to SOC

The proportion of the different LOC pools in relation to SOC can be used to detect changes in SOC quality.In the topsoil,the ratios

fPOC,LFOC,and MBC to SOC decreased,while those of ROC and cPOC increased following land use change (Fig.7).In subsoil,only the ratio of DOC to SOC decreased,the ratios POC,fPOC and ROC to SOC increased,and those of LFOC and MBC remained constant following land use change.In the topsoil,ratios fPOC,LFOC,DOC and MBC to SOC were more sensitive to conversion from natural forest to sloping tillage than SOC (Fig.7).4.Discussion

https://www.wendangku.net/doc/e01316307.html,anic C losses in top and subsoil following land use change Land use change could dramatically affect the balance between soil C input and output,and consequently alter SOC content and composition regarding labile https://www.wendangku.net/doc/e01316307.html,nd use change mark-edly reduced SOC and labile fractions both in topsoil (upper 20cm)and subsoil (20e 100cm),which was consistent with our

initial

Fig.4.LOC fraction stocks in relation to depth and land use systems in subtropical China.LOC,LFOC,ROC,DOC and MBC represent labile organic C,light fraction organic C,readily oxidizable organic C,dissolved organic C,and microbial biomass,respectively.Letters indicate signi ?cant differences among land use systems (P <

0.05).

Fig.5.Relation between SOC,LFOC (red),DOC (blue),and POC subsoil stocks (20e 100cm)and ?ne root biomass in 20e 60cm soil across land use systems in subtropical China.All regression lines are signi ?cant at P <0.05,and R 2values are above 0.94.SOC,POC,LFOC,and DOC represent soil organic C,particulate organic C,light fraction organic C,and dissolved organic C,respectively.Vertical and horizontal bars represent standard error for spatial variation (n ?[3plot]).(For interpretation of the references to color in this ?gure legend,the reader is referred to the web version of this article.)

H.Sheng et al./Soil Biology &Biochemistry 88(2015)148e 157153

predictions.The depletion of SOC and labile components in topsoil observed after land use change was consistent with most previous observations in the tropics and subtropics (e.g.Deng et al.,2009;Don et al.,2011;Umrit et al.,2014).However,the direction and magnitude of SOC and labile fraction stocks in topsoil following land use change can signi ?cantly differ among biomes and geographical regions.For example,MBC content in topsoil increased,while SOC and other labile fractions (DOC and ROC)did not appear to be affected by the conversion of a subtropical natural forest to plantations even after three decades (Wang et al.,2013).This could be partly explained by the relative short duration of natural succession (50years)for the referred natural forest.Different tree plantations could also differ in the quantity and quality of SOC input to the soil.In Malaysia,topsoil LOC content (0e 15cm)increased by 18%and 6%after forest conversion to oil palm plantations and pineapple orchards,respectively (Nahrawi et al.,2012).In Sergipe,Brazil,SOC content and active humic acid concentration in surface soil did not differ between a 12-year-old integrated coconut plantation and an adjacent remnant native

Atlantic Forest (Guimar ~a

es et al.,2013).These observations could be related to the presence of leguminous cover crops,fertilization and management strategies for crop residues in the

plantation.

Fig.6.Relation between POC,LFOC,and DOC (blue)stocks and SOC stocks in subsoil (20e 100cm)across land use systems in subtropical China.All regression lines are signi ?cant at P <0.1,and R 2values are above 0.80.POC,LFOC,DOC,and SOC represent particulate organic C,light fraction organic C,dissolved organic C,and soil organic C,respectively.Vertical and horizontal bars represent standard error for spatial variation (n ?[3plot]).(For interpretation of the references to color in this ?gure legend,the reader is referred to the web version of this

article.)

Fig.7.Proportions of labile organic C fractions to soil organic C in relation to depth and land use systems in subtropical China.cPOC,fPOC,LFOC,ROC,DOC,and MBC represent coarse particulate organic C,?ne particulate organic C,light fraction organic C,readily oxidizable organic C,dissolved organic C,and microbial biomass,respectively.

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SOC and labile components also decreased in subsoil below 20cm following land use change,highlighting that substantial stable SOC in subsoil could be mobilized and destabilized as a consequence of land conversion.At global and regional scales, change from forest to cropland also signi?cantly reduced SOC content at0e60cm depth(Guo and Gifford,2002;Don et al.,2011). To this end,we re-analyzed data from previous studies focused on issues other than the effect of land use change on subsoil SOC,and found that SOC stock in subsoil(20e100cm)could be reduced by 26e61%after native forest conversion to secondary forests,plan-tations,and agricultural land in the tropics and subtropics (Pibumrung et al.,2008;Yang et al.,2009b).These values were similar to our results of23e40%reduction in SOC stock in subsoil following land use change.SOC content also decreased by63%and 73%in the?rst0.2e0.5m and0.5e1m of soil,respectively, following tropical forest conversion to sugarcane?eld(Deng et al., 2009).In the Amazon region,20%or more of the C stock in subsoil found at0.3e3m depth could be mobilized by tropical forest clearing after25years of pasture growth(Veldkamp et al.,2003).

LFOC,POC and MBC stocks below20cm decreased after16years following the conversion of a subtropical old growth native forest to plantations(Yang et al.,2009a).In the Amazon plain,however, SOC stock below10cm depth is not affected by the conversion from lowland primary forest to agroforestry and monoculture planta-tions after7years(Schroth et al.,2002).This is probably thanks to the relatively?at terrain experiencing less severe soil erosion than the steep slopes considered in our study.

4.2.Causes of organic C losses in subsoil following land use change

Subsoil C stock depends on the delicate balance between C input and output.Following land use change,fresh C input to subsoil may be sharply reduced by the decline of soil and litter C stocks.In our study sites,plant species were altered,reducing and scattering plant cover,and a plant community dominated by deep-rooted trees and shrub species(Camphor)was replaced by shallow-rooted conifer trees(Chinese?r)and herbaceous vegetation (Fig.1).These aboveground changes led to decrease in C input and C allocation in the subsoil linked to root turnover and rhizodeposition (Hafner et al.,2014).Stem density,basal area and?ne root biomass also dramatically declined following natural forest conversion to plantation and orchard(Table1).Fine root turnover decreased by 5e45%following a subtropical native forest conversion to planta-tions,and by45%after tropical forest conversion to agroforest (Hertel et al.,2009;Sheng et al.,2010).Here,SOC stock and its fractions(POC,LFOC and DOC)in subsoil(20e100cm)were signi?cantly correlated with?ne root biomass in subsurface soil (20e60cm)across different land use systems(Fig.5),showing that the decrease in subsoil C input(mainly through?ne root biomass) were the dominant factors leading to the loss of SOC and labile components from subsoil after land use change.

Following land use change,litter and topsoil SOC stocks decreased by47e99%and25e35%,respectively(Table1).In a previous study,we also found a decrease in fresh C input from plant litter by32e63%following the conversion of a subtropical natural forest into plantations and orchards(Sheng et al.,2010).This pro-cess may also contribute to the reduction in subsoil C input(e.g., through leaching DOC,clay-combined C,etc.)from overlying topsoil and ground litter.

Organic C output might also be altered through land use change. In our previous study,the mean annual topsoil temperature increased by7.8 C after a subtropical natural forest was converted into sloping tillage,due to an increase in direct sunlight reaching the soil surface(Sheng et al.,2010).Increased soil temperatures can drive faster decomposition rates,including those of plant residues and topsoil SOC,leading to a reduced C input to the subsoil.In addition,decomposition rate in subsoil may be enhanced through targeted management practices(e.g.,clear-cutting,burning,fertil-ization,irrigation,and deep plowing)(Wairiu and Lal,2003). Furthermore,continuous cultivation in C-rich topsoil can supply fresh C input to subsoil(Chaopricha and Marín-Spiotta,2014), which may enhance microbial decomposition of stable C in subsoil (Fontaine et al.,2007;Wang et al.,2014a;de Graff et al.,2014).

Soils exposed to harsh physical environments(e.g.,those exposed to frequent heavy downpours,in steep slopes,or formed by loose soils)are often very vulnerable to surface erosion.Severe soil and water loss frequently occurred in the initial stage of land use change(van Noordwijk et al.,1997;Don et al.,2011).A large amount of?ne,low-density and dissolved C in topsoil may be preferentially transported by runoff after young trees are renewed or planting of cash-crops.In the?rst4years after slash-and-burn, water-induced soil erosion,substantial soil(3740kg haà1)and SOC(591kg C haà1)loss in situ were observed in our study(Sheng et al.,2010).Thereafter,the low density A h horizon disappeared, and the high density B t horizon was closer to the surface(Table1). Through soil erosion,subsoil C may also be destabilized through physical exposure at the surface and be open to O2-rich air(Salom e et al.,2010).Additionally,fresh C input and mobilized nutrients may also stimulate C decomposition in the subsoil(Kautz et al., 2013).In subsoil,stocks of LOC fractions tended to be positively correlated with SOC stock(Fig.6).

4.3.Sensitive indicators of SOC alterations following land use change

LOC fractions,determined through different fractionation ap-proaches,are widely considered as early indicators of SOC response to short term land use change(Dungait et al.,2012).However,the sensitivity of LOC fractions to land use change depends on soil depth.In topsoil,fPOC,LFOC,DOC and MBC stocks were more sensitive to land use change than was SOC.In subsoil,on the other hand,only LFOC and DOC are sensitive enough to represent useful indicators of SOC changes.Similar to POC stocks and those of its different components,MBC in subsoil below40cm can increase after land conversion(Fig.4),indicating that changes of LOC frac-tions may follow opposite patterns to those in topsoil.In another example,soil C accumulation was almost entirely from LFOC in topsoil(0e7.5cm),and C loss was mainly from C fractions associ-ated with silt and clay-size particles in the subsoil(35e60cm)48 years after the conversion of old?elds into secondary forest (Mobley et al.,2015).Consequently,the effects of land use change on LOC fractions observed in the topsoil may not directly affect the subsoil.

The response of LOC fractions to land conversion also depends on the type of land use change.The insensitive response of ROC stocks to land use changes observed in this study,partly due to there being a large proportion of passive SOC,is consistent with several previous studies(Mendham et al.,2002;Tirol-Padre and Ladha,2004).In addition,the KMnO4oxidation method was very sensitive to the presence of lignin or lignin-like compounds and therefore to the nature of the vegetation present,which may also explain the insensitivity of ROC to land use change(Skjemstad et al., 2006).POC stock can not be used either as a sensitive indicator of SOC change because it is masked by the insensitive response of the cPOC component(Fig.4).Although fPOC is relatively recalcitrant and more stable than cPOC(Jolivet et al.,2003),it consists of?ner particles,and therefore,it can be easily translocated downwards by preferential?ow through soil pores and cracks between aggregates.

Following land use change,the reduced proportions of POC, LFOC,DOC,and MBC to SOC indicated a reduction in the proportion

H.Sheng et al./Soil Biology&Biochemistry88(2015)148e157155

of readily available substrates and a lower SOC quality(Yang et al., 2009b).These results further imply that these four ratios can be considered as active indicators to detect alterations in SOC quality due to land use change(Fig.7).Furthermore,the decreased DOC to SOC ratio in subsoil following land use change showed that the main DOC loss occurred in the subsoil,highlighting the importance of DOC sorption in the subsoil.Similarly,land use and fertilization practices induced changes in the DOC to SOC ratio,which were even higher in subsoil than in topsoil(Zhang et al.,2006;Liang et al.,2012).The increased ratios of POC,cPOC and fPOC to SOC in subsoil may also be largely associated with DOC leaching.

5.Conclusions

The sites selected in this study were representative of the most common land use changes occurring in subtropical China.SOC stocks and those of the labile fractions decreased in topsoil and subsoil below20cm following land conversion.The LOC fractions to SOC ratios also decreased,indicating a reduction in C quality as a consequence of land use change.Reduced LOC fraction stocks in subsoil could partially be explained by the decrease in?ne root biomass in subsoil,with consequences for SOC stock.However,not all labile fractions could be useful early indicators of SOC alterations due to land use change.In fact,only fPOC,LFOC,and MBC in topsoil, and LFOC and DOC in subsoil were highly sensitive to land use change in subtropical China.We conclude that land use changes can in?uence both top and subsoil,consequently leading to decrease in C sequestration over long term.Therefore,long-term effects of land use on SOC stocks should be considered at soil depths greater than20cm.

Acknowledgments

Many thanks extend to the anonymous reviewers for valuable suggestions.This study was?nancially supported by the Natural Science Foundation of China(31100381),the Natural Science Foundation of Hunan Province(13JJ4066),and the Introduction of Talent Project of Hunan Agricultural University(11YJ20). References

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The way 的用法 Ⅰ常见用法： 1)the way+ that 2)the way + in which（最为正式的用法） 3)the way + 省略（最为自然的用法）举例：I like the way in which he talks. I like the way that he talks. I like the way he talks. Ⅱ习惯用法：在当代美国英语中，the way用作为副词的对格，“the way+ 从句”实际上相当于一个状语从句来修饰整个句子。 1)The way =as I am talking to you just the way I’d talk to my own child. He did not do it the way his friends did. Most fruits are naturally sweet and we can eat them just the way they are—all we have to do is to clean and peel them. 2）The way= according to the way/ judging from the way The way you answer the question, you are an excellent student. The way most people look at you, you’d think trash man is a monster. 3）The way =how/ how much No one can imagine the way he missed her. 4）The way =because

网络文明演讲稿3篇

本文目录络文明演讲稿络文明演讲稿英语之星的演讲稿: 络文明计算机互联作为开放式信息传播和交流的工具，已经走进了我们的学习和生活。从它刚刚兴起直到现在的风靡一时，年青的我们凭着对新鲜事物特有的接受能力，一直都是它忠实的应用者，无论是学习、休闲还是交流，络都发挥了不可替代的作用。络是把“双刃剑”在给我们带来利处的同时，由于我们辨别是非的经验不足，一些络糟粕也随之侵袭着我们的心灵。到底怎么样才算是文明上 ?反过来络最大的文明又应该是什么? 其实，关于络所出现的问题，早已引起了家长、学校和社会的关注，年11月，团等8个单位发布了《全国青少年络文明公约》，提倡"要善于上学习，不浏览不良信息; 要诚实友好交流，不侮辱欺诈他人;要增强自我保护意识，不随意约会友;要维护络安全，不破坏络秩序;要有益身心健康，不沉溺虚拟时空。"只要我们正确健康地上，络就会成为我们学习知识、交流思想、休闲娱乐的重要平台。现在，我们不仅学校有电脑，而且很多家庭都有了电脑，那我们在使用络时该注意什么呢? 善于上学习，不浏览不良信息。现在人们对我们中学生上有一种普遍的看法：即不是玩游戏就是聊天。其实，上学习，天地宽广。在上学习，可以查关于学习的资料，也可以在bb 上与同学交流学习的经验。这样好的条件，何乐而不为呢?但凡是不良信息的站，不应该浏览;不健康的聊天室，都应该马上离开;如果不小心点击出了不健康的页面，应该马上关闭。络语言尤其是对于正处于青春期与成长期的我们而言具有强烈的吸引力。青少年永远是时尚和流行的载体与传播者，络上的个性也在我们身上表现的淋漓尽致。络语言这些独特的表达方式，反映了我们的个性和联想能力。这从一个侧面反映了我们的特征——年轻的心态和不拘一格的想法。但是自从“第四媒体”互连出现以后，任何一个连接到互连的人都能够把自己的言论传播到络上去。络在带来发表言论，表达思想机会的同时，也导致了“滥言时代”。络的虚拟性，使的埋藏在人们心底的许多东西都迸发了出来，特别是许多不健康，不文明的东西，“反正都不认识现实的我，我想怎么说就怎么说”，许多人正是抱着这种想法，成为了不文明事物和行为的传播者，甚至是始作俑者。作为我们青少年应严格规范要求自己，坚决抵制上使用不文明用语，在络上不讲脏话不带粗口，做到时时使用络文明语言，在无限宽广的络天地里，倡导青少年络文明新风，为营造健康的络道德环境做己的努力。上时文明守法是我们在场的每一位红岭人必需做到的。我们应遵守络道德规范，懂得基本的对与错、是与非，增强络道德意识，辨明上的善恶、美丑，在上不应随便发表不负责任的言论。前段时间在《高楼坠落玻璃块砸死过路小学生》一文登出后，福田某中学高三学生胡某发帖自称“肇事者”，经民和警方一路追踪发现竟是恶作剧。尽管只是场恶作剧，但是18岁的胡某还是为他的行为付出了代价。由于其发布帖子后，一方面造成了严重的社会影响，同时也干扰了警方对案件的正常侦查。根据《治安管理处罚法》的有关规定，警方依法对胡某采取了治安拘留。这也给我们敲响了警钟。尊敬的老师，同学们：大家好!

The way的用法及其含义(二)

The way的用法及其含义（二）二、the way在句中的语法作用 the way在句中可以作主语、宾语或表语： 1.作主语 The way you are doing it is completely crazy.你这个干法简直发疯。 The way she puts on that accent really irritates me. 她故意操那种口音的样子实在令我恼火。The way she behaved towards him was utterly ruthless. 她对待他真是无情至极。 Words are important, but the way a person stands, folds his or her arms or moves his or her hands can also give us information about his or her feelings. 言语固然重要,但人的站姿,抱臂的方式和手势也回告诉我们他(她)的情感。 2.作宾语 I hate the way she stared at me.我讨厌她盯我看的样子。 We like the way that her hair hangs down.我们喜欢她的头发笔直地垂下来。 You could tell she was foreign by the way she was dressed. 从她的穿著就可以看出她是外国人。 She could not hide her amusement at the way he was dancing. 她见他跳舞的姿势，忍俊不禁。 3.作表语 This is the way the accident happened.这就是事故如何发生的。 Believe it or not, that's the way it is. 信不信由你, 反正事情就是这样。 That's the way I look at it, too. 我也是这么想。 That was the way minority nationalities were treated in old China. 那就是少数民族在旧中

文明网络演讲稿4篇

文明网络演讲稿4篇Civilized network speech document 编订：JinTai College

文明网络演讲稿4篇小泰温馨提示：演讲稿是在较为隆重的仪式上和某些公众场合发表的讲话文稿。演讲稿是进行演讲的依据，对演讲内容和形式的规范和提示，体现着演讲的目的和手段，用来交流思想、感情，表达主张、见解；也可以用来介绍自己的学习、工作情况和经验等等；同时具有宣传、鼓动、教育和欣赏等作用，可以把演讲者的观点、主张与思想感情传达给听众以及读者，使他们信服并在思想感情上产生共鸣。本文档根据演讲稿内容要求展开说明，具有实践指导意义，便于学习和使用，本文下载后内容可随意修改调整及打印。本文简要目录如下：【下载该文档后使用Word打开，按住键盘Ctrl键且鼠标单击目录内容即可跳转到对应篇章】 1、篇章1：文明网络演讲稿 2、篇章2：网络文明演讲稿 3、篇章3：文明网络演讲稿 4、篇章4：英语之星的演讲稿网络文明篇章1:文明网络演讲稿遵守网络文明公约争做文明上网人

计算机互联网作为开放式信息传播和交流的工具，已经走进了我们的学习和生活。从它刚刚兴起直到现在的风靡一时，年青的我们凭着对新鲜事物特有的接受能力，一直都是它忠实的应用者，无论是学习、休闲还是交流，网络都发挥了不可替代的作用。网络是把“双刃剑”在给我们带来利处的同时，由于我们辨别是非的经验不足，一些网络糟粕也随之侵袭着我们的心灵。到底怎么样才算是文明上网？反过来网络最大的文明又应该是什么？其实，关于网络所出现的问题，早已引起了家长、学校和社会的关注，XX年11月，团中央等8个单位发布了《全国青少年网络文明公约》，提倡"要善于网上学习，不浏览不良信息；要诚实友好交流，不侮辱欺诈他人；要增强自我保护意识，不随意约会网友；要维护网络安全，不破坏网络秩序；要有益身心健康，不沉溺虚拟时空。"只要我们正确健康地上网，网络就会成为我们学习知识、交流思想、休闲娱乐的重要平台。现在，我们不仅学校有电脑，而且很多家庭都有了电脑，那我们在使用网络时该注意什么呢？善于网上学习，不浏览不良信息。现在人们对我们中学生上网有一种普遍的看法：即不是玩游戏就是聊天。其实，网上学习，天地宽广。在网上学习，可以查关于学习的资料，也

(完整版)the的用法

定冠词the的用法：定冠词the与指示代词this ,that同源,有“那(这)个”的意思,但较弱,可以和一个名词连用,来表示某个或某些特定的人或东西. (1)特指双方都明白的人或物 Take the medicine.把药吃了. (2)上文提到过的人或事 He bought a house.他买了幢房子. I've been to the house.我去过那幢房子. (3)指世界上独一无二的事物 the sun ,the sky ,the moon, the earth (4)单数名词连用表示一类事物 the dollar 美元 the fox 狐狸或与形容词或分词连用,表示一类人 the rich 富人 the living 生者 (5)用在序数词和形容词最高级,及形容词等前面 Where do you live?你住在哪? I live on the second floor.我住在二楼. That's the very thing I've been looking for.那正是我要找的东西. (6)与复数名词连用,指整个群体 They are the teachers of this school.(指全体教师) They are teachers of this school.(指部分教师) (7)表示所有,相当于物主代词,用在表示身体部位的名词前 She caught me by the arm.她抓住了我的手臂. (8)用在某些有普通名词构成的国家名称,机关团体,阶级等专有名词前 the People's Republic of China 中华人民共和国 the United States 美国 (9)用在表示乐器的名词前 She plays the piano.她会弹钢琴. (10)用在姓氏的复数名词之前,表示一家人 the Greens 格林一家人(或格林夫妇) (11)用在惯用语中 in the day, in the morning... the day before yesterday, the next morning... in the sky... in the dark... in the end... on the whole, by the way...

文明上网,从我做起(主题班会演讲稿)

男：同学们，在开班会之前，我们想问大家几个熟悉的问题：你的QQ号是多少？你的农场几级了？牧场呢？梦幻西游呢？女:现在随着中国社会的不断发展，人们的生活也逐渐富裕起来，网络也跟着在社会中流行，融入到了我们的生活中去，而且扩张的范围极大，尤其是对于中学生来说更是对“网络”爱不释手。男：上个星期，我就问过几个中学生对告别网吧的看法，他们中的一些坚定的摇了头，并说出了一大堆上网的好处，而且反问我：“你不是也经常上网吗？”，于是，我产生了几个思考：告别网吧，是不是就等于告别了网络呢？告别网吧，这现实吗？我们的中学生在接触网络时，该如何把持自己呢？女：老师曾经说过，21世纪是知识经济的时代，是网络的时代，是人类数字化生存的时代，电脑和网络，是每一个学生都尽可能掌握的一门课程。在美国等西方国家，四五年级的学生都能够熟练地使用电脑、网络来查阅资料，学习知识。相比之下，让我们中学生告别网络的做法，我想在坐的同学没有一个会同意。男：但我们的法律为什么又规定“禁止未成年人进入网吧” 呢？首先，我们不能把“网络”等同于“网吧”。第二，表面禁止的同时，深含对我们未成年人的身心保护。我们中

学生自制能力差，一旦迷恋网吧便不能自拔，导致学业无成，甚至是猝死网吧。这类的现象时有耳闻，如果事件发生，我们便总认为这是因无知而犯下的错误，但也为时已晚了。女：“禁止未成年人进入网吧”是为了让我们的学生少犯或不犯相同的错误，让更多的人来关爱我们这些未成年人。不接触网吧，我们同样可以接触网络，比如：通过家庭的个人电脑、学校电脑室的电脑等。男：当然，作为孩子的我，完全能够理解为什么有的人家里有电脑，但他还要去网吧。刚才也说到我们自制能力差，只要用上电脑，便会觉得时间如白驹过隙，不管用多久，都觉得不够。所以，每当感到刚玩了一会，就会听到父母说“你都玩了几个小时了！该去写写作业了吧！”“你看看都几点了，还在玩？明天不用上学啊？” “你玩什么呢？这么聚精会神？要是学习也这样，还至于几百多名吗”“你作业写完了也不能玩这么久啊！复习去！”“作业写完了吧？来，别玩了，考考你学过的英文单词。”“哎呀......忙了一天了，累死我了，别玩了，去把衣服晾一下，然后扫一下地，再把碗刷了！”等。父母喋喋不休的唠叨，真的可以让人发疯！但是大家有没有想过，他们为什么要这样做？难道真的是因为看你不顺眼、想拿你撒气？

“the way+从句”结构的意义及用法

“tｈｅwａｙ+从句”结构的意义及用法首先让我们来看下面这个句子: Ｒead the foｌloｗｉnｇpassagｅａnd talkａbout ｉt wi ｔh your classmaｔes．Try tｏｔeｌl whaｔyｏu thiｎk ｏf Tom aｎd ｏｆｔhe ｗay the chiｌｄrenｔrｅated ｈim. 在这个句子中，ｔhe waｙ是先行词,后面是省略了关系副词that或in whｉch的定语从句。下面我们将叙述“the ｗaｙ+从句”结构的用法。 1.tｈe wａy之后，引导定语从句的关系词是tｈat而不是hoｗ,因此，<<现代英语惯用法词典＞＞中所给出的下面两个句子是错误的：Ｔhｉs is ｔｈeｗayｈowｉtｈａppened. This is the way how he ａlwａｙs treats me. 2．在正式语体中,thaｔ可被in which所代替;在非正式语体中，ｔhat则往往省略。由此我们得到theｗay后接定语从句时的三种模式：1) tｈe ｗaｙ＋ｔhａt-从句２）the way +ｉn whiｃh－从句3) the ｗay +从句例如：Ｔｈe way(in whiｃh ，thａt) ｔhｅｓｅｃomｒade ｓloｏｋａｔｐrobｌems is wrong．这些同志看问题的方法

不对。Ｔｈｅｗａy(that ,ｉn ｗhiｃh)yoｕ’ｒe doinｇit is comple ｔeｌy crａzy.你这么个干法,简直发疯。 Wｅａdmiｒｅd him for thｅｗay ｉｎｗhｉch he fａｃeｓdiｆficultieｓ． Waｌlａｃe ａｎd Ｄarwiｎｇreed ｏn the way ｉｎwhi ｃh ｄｉfｆｅrｅnt forms ｏf life had ｂegｕn.华莱士和达尔文对不同类型的生物是如何起源的持相同的观点。 Thｉs is ｔｈe ｗaｙ（tｈａｔ) hｅdｉd it. I lｉkeｄｔhe waｙ(ｔhat) ｓｈeｏｒganized ｔhe ｍeetｉng． 3.theｗay(tｈat)有时可以与hｏw(作“如何”解）通用。例如： That’s tｈe ｗaｙ(tｈaｔ) shｅspoke. = Tｈat’s how shｅspoke.

INTERNET演讲稿

so there are more and more people who have became internet users. do you know how many internet users in the world? let’s see the chart! 3 this is a questionnaire [?kw?st??n??r, ?kwest???ne?] (调查卷) about world internet users and population stats in 2009. the users has grown [gr?un] at a remarkable [ri?mɑ:k?bl] rate 。the rising line(上升的曲线） is not this ,not this ,is this. let us see the next pictures. 4 who is he？yes .our respectable premier [?premi?] wen .how old is he? a ha .this i dont know ,but i know he is very old , he is also surfing the internet and caring about current events and politics .so how we do ? 5 yes .the man may be watch a funny movie. the mother is telling her children learning some knowledge through the internet. in this picture .the people from different nations also learn the same thing-------how to use the internet. even the lovely dog is also want to use the internet. why are many people attracted by internet? now im not surprised to see the results, for i can find the reason just from my own life. 6 the internet changed my life; there is no doubt about that. to spend a part of our day on the internet is quite normal for many people. 7 second. the internet is a database ?deit?beis] full of latest information and offers me a lot of services. i can read the daily newspapers, movies and music from all over the world. 8 when i saw this news, my mood just like this picture—angry birds .how cruel the passed people are .ok, let me back to the topic .this is an online game--- angry birds. that’s another important part for internet .the online games are always attractive and challenging. in my opinion its more exciting to play with friends than playing alone. 9 third. to improve our english, through internet i often find professional english learning methods. is internet good or bad we should admit that there are so many advantages brought by the internet. firstly, the internet affords us lots of convenience. for example, we can shop, have meetings and even study on-line. furthermore, the internet has improved our working efficiency. we can contact colleagues on the other side of the world to talk about the working project via the internet easily. piles of files can be sent by e-mails with the help of the internet. in addition, the internet makes information conveyance much easier. just clipping “google”, related information will boom out explosively within several seconds. while applauding for those benefits the internet brings to us, we need to worry about disadvantages of the internet as well. to begin with, it is easy for the young to indulge themselves in the so-called “cyber romance”, which is full of dangers, cheatings

way 用法

表示“方式”、“方法”，注意以下用法： 1.表示用某种方法或按某种方式，通常用介词in(此介词有时可省略)。如： Do it (in) your own way. 按你自己的方法做吧。 Please do not talk (in) that way. 请不要那样说。 2.表示做某事的方式或方法，其后可接不定式或of doing sth。如： It’s the best way of studying [to study] English. 这是学习英语的最好方法。 There are different ways to do [of doing] it. 做这事有不同的办法。 3.其后通常可直接跟一个定语从句(不用任何引导词)，也可跟由that 或in which 引导的定语从句，但是其后的从句不能由how 来引导。如：我不喜欢他说话的态度。正：I don’t like the way he spoke. 正：I don’t like the way that he spoke. 正：I don’t like the way in which he spoke. 误：I don’t like the way how he spoke. 4.注意以下各句the way 的用法： That’s the way (=how) he spoke. 那就是他说话的方式。 Nobody else loves you the way(=as) I do. 没有人像我这样爱你。 The way (=According as) you are studying now, you won’tmake much progress. 根据你现在学习情况来看，你不会有多大的进步。 2007年陕西省高考英语中有这样一道单项填空题： ——I think he is taking an active part insocial work. ——I agree with you_____. A、in a way B、on the way C、by the way D、in the way 此题答案选A。要想弄清为什么选A，而不选其他几项，则要弄清选项中含way的四个短语的不同意义和用法，下面我们就对此作一归纳和小结。一、in a way的用法表示：在一定程度上，从某方面说。如： In a way he was right.在某种程度上他是对的。注：in a way也可说成in one way。二、on the way的用法 1、表示：即将来(去)，就要来(去)。如： Spring is on the way.春天快到了。 I'd better be on my way soon.我最好还是快点儿走。 Radio forecasts said a sixth-grade wind was on the way.无线电预报说将有六级大风。 2、表示：在路上，在行进中。如： He stopped for breakfast on the way.他中途停下吃早点。 We had some good laughs on the way.我们在路上好好笑了一阵子。 3、表示：(婴儿)尚未出生。如： She has two children with another one on the way.她有两个孩子，现在还怀着一个。 She's got five children，and another one is on the way.她已经有5个孩子了，另一个又快生了。三、by the way的用法

精选请文明使用网络演讲稿3篇(最新)

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“健康上网文明上网”演讲稿

“健康上网文明上网”演讲稿 “健康上网文明上网”演讲稿亲爱的老师、同学们，大家好！这里是九中青春校园广播站，我是高一6班的董晓骐。今天我演讲的题目是《远离网吧，健康上网、文明上网》现在互联网越来越普及当今社会已进入以互联网为标志的信息时代。网络给我们带来许多方便，我们可以在网上查阅资料；看最新的消息还可以开阔我们的视野促进我们的学业。我们的老师也充分地利用网上资源努力提高我们的学习成绩。但网络也是一把双刃剑，有的同学过度依赖电脑整天沉迷于网络游戏之中，课也不上学习成绩直线下降有的同学做了网络的俘虏成了“小网虫”还

有的同学因整天看着电脑眼睛受到严重损坏成了高度近视。甚至有的同学上网的目的只是打游戏或者聊天，一刻也不停歇地上网、上瘾甚至酿成了惨剧。 17岁的少年吴x治2001年第一次在网吧接触了电脑游戏后就不可收拾从自己省钱发展到主动要钱最后就是偷钱，2004年6月15日吴x治想打游戏向奶奶要钱，奶奶没有答应他就残忍地将自己奶奶杀害。最近某县城也发生了一件类似的事件，一位女孩因父母不在家连续上网四天四夜，最后昏倒在电脑旁幸好抢救及时避免了悲剧的发生。当前青少年上网人数较多，在我国2650万上网者中25岁以下的青少年占了百分之八十五以上，并且正在以每年翻一番的惊人速度增长。这当中约2/3的人在网吧上网，在网吧上网的人中99%以上的都是沉迷于网络游戏，绝大多数学生因此学业荒废，毁掉了自己美好的前程。在我看来我们学生应当上好现代信息技术课，掌握基本的电脑技能，

条件允许的话在家长或老师的监督和指导下可适度上网，并做到“五要五不要”即：要善于网上学习，不浏览不良信息；要诚实友好交流，不侮辱欺诈他人；要增强自我保护意识，不随意约会网友；要维护网络安全，不破坏网络秩序；要有益身心健康，不沉溺虚拟时空。但决不能到网吧上网要相信只要你学业有成将来是一定能在网上冲浪和遨游的。所以希望同学们远离网吧在家长和老师的指导下健康上网、文明上网，使网络成为我们成长的好帮手而不是扼杀我们生命的毒瘤。今天九中青春广播到此结束，谢谢大家收听。

“健康上网文明上网”演讲稿

“健康上网文明上网”演讲稿尊敬的读友您好：本文由网络收集而来，分享到本网站是为了能够帮助到大彖大家如果雕之后是自己需要的文档可以点击下载本文档，下我文档是收费的（所以请先阅读再下载■谢谢各位读友’本人在此祝各位读友工作顺利’事事如意。健康上网文明上网”演讲稿亲爱的老师、同学们，大家好！这里是九中青春校园广播站，我是咼一一6 班的董晓骐。今天我演讲的题目是《远离网吧，健康上网、文明上网》现在互联网越来越普及当今社会已进入以互联网为标志的信息时代。网络给我们带来许多方便，我们可以在网上查阅资料；看最新的消息还可以开阔我们的视野促进我们的学业。我们的老师也充分地利用网上资源努力提高我们的学习成绩。但网络也是一把双刃剑，有的同学过度依赖电脑整天沉迷于网络游戏之中，课也不上学习成绩直线下降有的同学做了网络的俘虏成了小网虫”还有的同学因整天看着电脑眼睛受到严重

损坏成了高度近视。甚至有的同学上网的目的只是打游戏或者聊天，一刻也不停歇地上网、上瘾甚至酿成了惨剧。仃岁的少年吴x治2001年第一次在网吧接触了电脑游戏后就不可收拾从自己省钱发展到主动要钱最后就是偷钱，2004年6月15日吴x治想打游戏向奶奶要钱，奶奶没有答应他就残忍地将自己奶奶杀害。最近某县城也发生了一件类似的事件，一位女孩因父母不在家连续上网四天四夜，最后昏倒在电脑旁幸好抢救及时避免了悲剧的发生。当前青少年上网人数较多，在我国2650万上网者中25岁以下的青少年占了百分之八十五以上，并且正在以每年翻一番的惊人速度增长。这当中约2/3的人在网吧上网，在网吧上网的人中99%以上的都是沉迷于网络游戏，绝大多数学生因此学业荒废，毁掉了自己美好的前程。在我看来我们学生应当上好现代信息技术课，掌握基本的电脑技能，条件允许的话在家长或老师的监督和指导下可适度上