Maintenance of diversity within plant communities soil pathogens as agents of negative feedback

Ecology,79(5),1998,pp.1595–1601

?1998by the Ecological Society of America

MAINTENANCE OF DIVERSITY WITHIN PLANT COMMUNITIES:SOIL PATHOGENS AS AGENTS OF NEGATIVE FEEDBACK

K ATHERINE E.M ILLS AND J AMES D.B EVER1

Department of Botany,Duke University,Durham,North Carolina27708-0338USA

Abstract.The effect of soil pathogens on plant communities was investigated using four old-?eld perennial plant species and?ve isolates of a pathogenic oomycete in the

genus Pythium.These Pythium strains were isolated from the roots of two of the plant

species,Danthonia spicata and Panicum sphaerocarpon,used in a previous experiment on

the consequences of changes in the soil community on plant growth.In this previous experiment,

Danthonia and Panicum changed the soil community in a manner that reduced their growth

relative to that of a third plant species,Anthoxanthum odoratum.In the current experiments,

we found that inoculation with Pythium reduced overall plant mass and root:shoot ratios,

but Danthonia and Panicum were more susceptible to the presence of Pythium than the

other two plant species,Anthoxanthum and Plantago lanceolata.In addition,Pythium ac-

cumulates at different rates on different plant species,with a greater than tenfold higher

population observed in association with Panicum compared to Anthoxanthum.The results

of these experiments suggest that the accumulation of species-speci?c soil pathogens could

account for the previous observation of negative feedback on plant growth through changes

in the soil community.As negative feedback may act to maintain plant species diversity

within a community,these results suggest that soil pathogens may themselves contribute

to the maintenance of plant species diversity.

Key words:Anthoxanthum;community dynamics;Danthonia;diversity;feedback;host speci?city;

old?eld;Panicum;Plantago;Pythium;pathogen;soil community.

I NTRODUCTION

It has traditionally been assumed that the mainte-nance of plant community diversity results from the partitioning of abiotic resources(reviewed by Grace and Tilman1990,Tilman and Pacala1993).Models of competition reveal that competing species will coexist when intraspeci?c competition exceeds interspeci?c competition,a situation that has generally been pre-sumed to result from abiotic niche differentiation. However,the generality of this view has recently been challenged(e.g.,Silvertown and Law1987,Aarssen 1989)and a potential role of pathogens in mediating species interactions,and particularly plant–plant co-existence,has been suggested(Holt and Pickering 1985,Burdon1987,Alexander1990).The importance of pathogens is supported by their ubiquitous occur-rence and major impacts on agricultural plant popu-lations.Moreover,recent work in natural communities has found substantial impacts of pathogens on plant demography(Weste1974,Augspurger1984,1988, 1990,Burdon1987,Alexander et al.1996)and even suggests a role of pathogens in the course of dune succession(Van der Putten et al.1993).Nevertheless, the overall role of pathogens in the maintenance of Manuscript received31January1997;revised16July 1997;accepted20July1997.

1Author and present address for correspondence:Depart-ment of Ecology and Evolution,The University of Chicago, 1101East57th Street,Chicago,Illinois60637-1573.diversity in natural plant communities is not known. This is particularly true for soil pathogens,a group known to be important in agricultural systems(Bruehl 1987,Agrios1988)but which are unusually dif?cult to study because of the confounding effects of,and complexity of interactions with,other components of the soil community(e.g.,Larkin et al.1993,Newsham et al.1995,De Rooij-van der Goes1995,Bever et al. 1997).

We have found evidence that the soil community,as a whole,can contribute to the maintenance of diversity within plant https://www.wendangku.net/doc/5417102843.html,ing a phenomenological experimental approach,we have found strong negative feedbacks on plant growth through changes in the com-position of the soil community(Bever1994,Bever et al.1997).Negative feedback occurs when the presence of a plant changes the soil community in a manner that decreases the growth of that particular plant species relative to other species.Models of this process have shown that negative feedback can maintain diversity of a plant community provided that the sign of an in-teraction coef?cient is negative(Bever et al.1997). This interaction coef?cient can be estimated in exper-imental studies where plants of a particular species are transplanted into soil communities that have previously been‘‘cultured’’by plants of the same(‘‘home’’)or a different(‘‘away’’)species;thus,the coef?cient can be estimated using a‘‘home vs.away’’contrast(Bever 1994).In previous studies we found evidence for the existence of negative feedback between Anthoxanthum

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KATHERINE https://www.wendangku.net/doc/5417102843.html,LS AND JAMES D.BEVER

odoratum and Danthonia spicata and between A.odor-atum and Panicum sphaerocarpon in an old-?eld com-munity in Durham,North Carolina(Bever1994).Spe-ci?cally,Bever(1994)found that growth of D.spicata and P.sphaerocarpon was signi?cantly reduced with soil communities that had been previously‘‘cultured’’by plants of the same species,while A.odoratum did well in these soils but exhibited reduced growth with soil communities that had previously supported plants of its own species.In independent experiments,we also found evidence of negative feedback between the pairs Anthoxanthum and Plantago,and Panicum and Plan-tago(Bever et al.1997).

The agents of negative feedbacks in these studies have not been identi?ed,but initial observations in-dicated that accumulation of species-speci?c soil pathogens may be responsible. D.spicata and P. sphaerocarpon both had low root:shoot ratios,likely the result of observed root necrosis(Bever1994).Sev-eral species of soil pathogens,including species of the genus Pythium,were subsequently isolated from their roots.It is possible that the observed accumulation of Pythium on these two plant species causes more severe effects on D.spicata and P.sphaerocarpon than on other plant species,suggesting that soil pathogens con-tribute to the observed negative feedback and thereby play an important role in the maintenance of diversity within this plant community.

In this study,we used these isolates of Pythium spp. to test whether the accumulation of species-speci?c soil pathogens may contribute to the negative feedback ob-served between certain plant species.Although Pyth-ium spp.are known to have substantial impacts on plant survival and growth(reviewed in Hendrix and Camp-bell1973,Abad et al.1994,Larkin et al.1995),the impact of Pythium on unmanaged plant communities has rarely been investigated(but see Augspurger1990). To investigate the role of soil pathogens in affecting plant community diversity,we tested the effect of Pyth-ium spp.on the growth of the plant species in which negative feedback through the soil community had pre-viously been observed(Bever1994).We then discuss these results in light of the observations of whole-soil community feedback to provide insight into the poten-tial impacts of soil pathogens on plant community di-versity.

M ETHODS

In order to investigate the role of Pythium in feed-back processes within the soil community,we focused on two questions:(1)Do different species of plants exhibit differential responses to the presence of Pyth-ium and(2)Do Pythium spp.accumulate differentially under these plant species?These objectives were eval-uated in two experiments.A full factorial experiment in which four plant species were grown in six treat-ments consisting of?ve isolates of Pythium and a ster-ile control allowed us to test differential responses of each plant species to the presence of Pythium and to speci?c Pythium isolates.Host-speci?c differences in rates of accumulation of Pythium were assessed using a series of serial dilutions of soil from A.odoratum and P.sphaerocarpon.

Study system

The plants,pathogens,and soil used for this exper-iment were obtained from a well-studied old?eld in Durham,North Carolina.The plant community in this ?eld is diverse and lacks any distinctly dominant spe-cies(Fowler and Antonovics1981).Four common, short-lived perennial plant species were used in this study—three grasses,Anthoxanthum odoratum L., Danthonia spicata(L.)Beauv.,and Panicum sphaer-ocarpon Ell.,and a herbaceous species,Plantago lan-ceolata L.Hereafter,all plant species will be referred to by generic name only.Negative feedback on plant growth through changes in the soil community had pre-viously been observed between four of the six pairs of plant species:Anthoxanthum and Danthonia,Antho-xanthum and Panicum,Anthoxanthum and Plantago, and Panicum and Plantago(Bever1994,Bever et al. 1997).However,in three separate test experiments,no feedback was observed between Danthonia and Pan-icum(Bever1994).

The isolates of Pythium(a genus popularly regarded as fungal but accurately classi?ed as an oomycete in the Kingdom Chromista)used in this experiment were cultured from roots of Danthonia and Panicum re-maining from a previous experiment that demonstrated negative feedback between these species and Antho-xanthum(Bever1994).We were not able to obtain isolates of Pythium from Anthoxanthum roots.Five iso-lates identi?ed as four different Pythium species were cultured in a manner described below—Pythium aris-tosporum,P.arrhenomanes,and P.macrosporum from Danthonia and P.arrhenomanes and P.volutum from Panicum(G.Abad,personal communication).The spe-cies of Pythium isolates used in this study infect a wide variety of hosts(Abad et al.1994,Deep and Lipps 1996,Magarey1996).In addition,P.aristosporum,P. arrhenomanes,and P.volutum have all been classi?ed as‘‘highly aggressive’’species due to their severe im-pacts on growth and survival of grasses(Abad et al. 1994).

Experiment1:Plant response to Pythium Isolation of Pythium.—Isolates of Pythium were ob-tained from root tissues of Danthonia and Panicum using techniques similar to those described by Martin (1992).Samples of roots from these grasses were rinsed thoroughly with water,surface sterilized with50% ethyl alcohol,and then dried with sterile paper towels before being placed onto selective media(PARP—pen-tachloronitrobenzene ampicillin rifampicin pimaricin medium)(Jeffers and Martin1986).Following incu-bation at room temperature for48h,isolates were trans-

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ferred to fresh plates of PARP,and isolate purity was con?rmed by growing on corn-meal agar(CMA)(Difco Laboratories,Detroit,Michigan).Species identity of the isolates was determined using sterile grass blade cultures with assistance from M.Cubeta and G.Abad, and stock cultures were stored as agar plugs in test tubes containing sterile deionized water at room tem-perature.

Preparation of Pythium inoculum.—Pythium inoc-ulum containing active mycelia and oospores that could survive in and infest the soil of treatment plants was prepared by growing the?ve Pythium isolates in sterile grass blade cultures(Martin1992).For each of the Pythium isolates,two plugs(each0.5cm3)of CMA with mycelium were placed in separate sterile tissue culture dishes(Falcon3025,150?25mm style).Ster-ile deionized water was added to the dishes to a level where the layer of water just covered the agar plugs, and50pieces(each1.0–1.5cm long)of autoclaved tall fescue grass leaves were placed into each dish.Five replicate dishes containing the grass blade cultures of each isolate were incubated at room temperature under continuous light for4d(Abad et al.1994).Infection of the grass blades by the Pythium mycelia was mon-itored under the dissecting scope,and the experiment was planted4d after the grass blade cultures were started,at which time most blades of grass had been infected by the mycelia.

Planting and harvesting processes.—Seedlings of Anthoxanthum,Panicum,and Plantago were started from seeds of greenhouse-grown plants that were pre-viously collected from the?eld.Danthonia seeds were collected from plants in our study?eld.All seeds were planted in sterile seedling mix and were allowed to grow until small seedlings of each species were avail-able.In April1996,between seven and ten replicates of each of the six treatments were planted with each plant species.All plants for this experiment were grown in385-mL pots?lled with sterile background soil.To prepare the background soil,?eld soil was?rst crum-bled until it passed through a1-cm mesh.Equal amounts of the sieved?eld soil and sand were then thoroughly mixed and autoclaved for1.5h.

Each Pythium treatment was inoculated with one of the isolates of Pythium by placing four colonized grass blades from the sterile grass blade culture beneath the top70mL of soil in each pot.Control treatments were planted in the same manner with sterile uninoculated grass blades being used in place of the Pythium in-oculum.Two seedlings of one of the plant species were planted in each pot.The entire experiment was then arranged into two randomized blocks within a green-house(10.0?–32.2?C)and pots were spaced suf?ciently to prevent cross-contamination by water splash during the course of the experiment.All pots were kept well watered during the?rst few days of the study to allow initial establishment of the seedlings and Pythium.Af-ter the1st wk,the pots were watered as needed.

The?rst block of the experiment was harvested5 wk after planting,while the second block grew for7 wk.During the harvesting process,whole plants were removed from the soil and washed.Roots and leaves were cut apart to be dried and weighed separately. Small root samples were also taken from select pots of the?rst block and from all pots in the second block to con?rm the presence of Pythium using the same process described previously.

Data analysis.—Masses of the leaves and roots from both plants in each pot were summed,and the effect of the Pythium treatments and plant species on total plant mass and root:shoot ratios was analyzed with an analysis of variance using the general linear models procedure of SAS(SAS1986).The treatment and in-teraction sums of squares were decomposed into or-thogonal tests(1)of the control treatment against the average effects of the Pythium isolates and(2)among the Pythium isolates.This technique allows us to sep-arate effects caused by the presence of Pythium in gen-eral from speci?c effects of individual isolates.We were particularly concerned with whether differences in susceptibility could explain the previous observation of negative feedback through the soil community be-tween these plant species(Bever1994).In the earlier studies,the feedbacks were tested using pairwise home vs.away contrasts(Bever1994,Bever et al.1997). Feedbacks between the plant species could result from the accumulation of Pythium in association with one of these plant species,followed by that plant species being more susceptible to the presence of Pythium than other plant species in the community.Therefore,in this experiment,we were speci?cally interested in evalu-ating pairwise differences between the four plant spe-cies in susceptibility to the Pythium isolates.These differences were tested as the single degree of freedom interaction between two plant species and the presence of Pythium.Because the pairwise contrasts were not orthogonal,their signi?cance was adjusted by the Dunn-Sida′k method to control for multiple tests(Sokal and Rohlf1981).In testing for interspeci?c differences in response to speci?c isolates of Pythium,we were also interested in the a priori hypothesis of local ad-aptation of the Pythium isolates from Panicum and Danthonia to their hosts.This hypothesis was tested by contrasting the average response of Danthonia to isolates cultured from Danthonia,and Panicum to iso-lates cultured from Panicum,against the average re-sponse of these two grass species to isolates from the other species.

Experiment2:Pythium infection of

various plant species

Differential growth rates of Pythium on two of the plant species,Anthoxanthum and Panicum,were tested in this experiment.Field soil was collected from be-neath the two plant species,diced,and homogenized to create soil communities that were initially similar

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BEVER F IG . 1.Average effect of Pythium isolates on plant growth.The average response of the four plant species to the Pythium isolates and the control are presented for plant mass (a)and root :shoot ratios (b).The least square means and 1SE are presented.Different letters indicate signi?cant differ-ences in means among the treatments as tested using Tukey’s test for multiple comparisons.For these graphs,isolates of Pythium are abbreviated as follows:‘‘P.arr.’’for P.arrhen-omanes,‘‘P.aris.’’for P.aristosporum,‘‘P.mac.’’for P.macrosporum,and ‘‘P.vol.’’for P.volutum.‘‘P.arr.(Pa )’’indicates that this isolate of P.arrhenomanes obtained from roots of Panicum,and ‘‘P.arr.(Da )’’indicates that this isolate was obtained from roots of Danthonia.

(as in Bever 1994).This fresh soil mixture was dis-tributed into replicate pots into which were planted six soil-microbe-free tillers (as in Bever 1994)of either Anthoxanthum or Panicum.The plants were watered as needed but were not fertilized while growing in a Duke University Phytotron controlled environment chamber under 12h light and at 25?C during the day and 10?C at night.After 7mo,three cores (1cm diameter)were taken from each of the nine replicate culture pots,and the soil from the cores of each pot was homogenized to obtain one pooled sample per culture pot.For each homogenized sample,two replicates of three serial di-lutions were evenly spread onto selective media (PARP).Pythium colonies were counted after 48h.Colony-forming units per gram soil were estimated based on plate counts.The average inoculum density for each pot was analyzed in an ANOVA using the general linear models procedure of SAS (SAS 1986).

R ESULTS

Experiment 1:plant response to Pythium The presence of Pythium reduced plant mass and root :shoot ratios.Plants grown with four of the ?ve Pythium isolates had plant masses (Fig.1a)and root :shoot ratios (Fig.1b)that were signi?cantly lower than the control treatment.Further,plant species varied in their susceptibility to the presence of Pythium in general (as tested by the Plant spp.?Pythium inter-action,Table 1).Speci?cally,Danthonia and Panicum were more susceptible to Pythium than Anthoxanthum and Plantago (pairwise contrasts in Table 1,Fig.2).This was demonstrated by the fact that masses (Fig.2a)and root :shoot ratios (Fig.2b)of Danthonia and Panicum infected by Pythium were less than those spe-cies under control conditions,while the masses of An-thoxanthum and Plantago did not seem affected by Pythium infection.

Although the plants differed in their response to the presence of Pythium in general,they did not differ in their response to speci?c isolates of Pythium (as tested by the Plant spp.?Pythium spp.interaction,Table 1).Of particular interest,we did not ?nd a difference in susceptiblilty between Danthonia and Panicum to their own or each other’s isolates.Thus,there is no evidence of differential adaptation of the isolates from Dan-thonia and Panicum on their respective hosts (Dan-thonia vs.Panicum,Table 1).

Experiment 2:Pythium infection of

various plant species

Results of colony formation assays for serial dilu-tions of Anthoxanthum and Panicum soil con?rmed that Pythium populations reached higher densities in the soil of Panicum than Anthoxanthum (F 1,16?41.11,P ?0.0001).The mean number of colony-forming units of Pythium from Anthoxanthum pots was 161.1,while the mean colony-forming units from the Panicum pots was 2411.1.

D ISCUSSION

This study indicates that soil pathogens may play a role in maintaining plant community diversity by pref-erentially infecting and subsequently inhibiting the growth of certain species.Some plant species were more susceptible to harmful effects of Pythium infec-tion than others,with Danthonia and Panicum being more negatively impacted than Anthoxanthum and Plantago.These host-speci?c effects may explain the previous observations of negative feedback through the soil community between these plant species (Bever 1994,Bever et al.1997).For example,the negative feedback observed between Panicum and Anthoxan-thum (Bever 1994,Bever et al.1997)may result from the increase in density of Pythium in response to cul-turing with Panicum as evidenced by root necrosis,

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T ABLE1.Analyses of covariance of plant masses and root:shoot ratios for the comparison of Pythium treatments.

Source of variation?df

Plant mass

SS P

Root:shoot ratios

SS P

Block Plant spp.1

3

6.002

4.257

0.0001

0.0001

0.032

7.918

NS

0.0001

Treatment50.3900.00010.3960.0001

Control vs.Pythium Among Pythium spp.1

4

0.147

0.237

0.0010

0.0016

0.254

0.136

0.0001

0.0321

Plant spp.?Treatment150.3250.06180.3910.0134

Plant spp.?Pythium

An–Da?Pythium

An–Pa?Pythium

An–Pl?Pythium

Da–Pa?Pythium

Da–Pl?Pythium

Pa–Pl?Pythium

Plant spp.?Pythium spp.

3

1

1

1

1

1

1

12

0.230

0.019

0.145

0.004

0.060

0.039

0.195

0.103

0.0007

NS

0.0020

NS

NS

NS

0.0004

NS

0.260

0.101

0.155

0.000

0.006

0.102

0.157

0.141

0.0002

0.0052

0.0012

NS

NS

0.0100

0.0010

NS

Danthonia vs.Panicum10.003NS0.000NS

Error167 2.169 2.101

Note:The Plant spp.?Treatment interaction tests for differences in responses of the four plant species to the control treatment or the?ve Pythium treatments.This overall interaction term was decomposed into two orthogonal interaction components:the Plant spp.?Pythium interaction and the Plant spp.?Pythium spp.interaction.The Plant spp.?Pythium interaction speci?cally tests for differences among the four plant species in their average response to the?ve Pythium isolates compared to the sterile control.This interaction component was itself decomposed into six pairwise tests for differential response to the presence of Pythium.The Plant spp.?Pythium spp.interaction component tests for differences in host-speci?c effects among the?ve Pythium isolates.

?Plant species abbreviations are as follows:‘‘An’’?Anthoxanthum,‘‘Da’’?Danthonia,‘‘Pa’’?Panicum,‘‘Pl’’?Plantago.

reduced root:shoot ratios,and isolation of Pythium spp.in the whole-soil feedback experiment(Bever 1994),and the empirical comparison of Pythium col-ony-forming units isolated from Anthoxanthum and Panicum in this experiment.This increased density of Pythium may then decrease the growth of Panicum in its local Pythium-enriched soil relative to the growth of Anthoxanthum in the same soil.The?rst experiment also provides evidence that Pythium may be an agent of negative feedback observed previously between An-thoxanthum and Danthonia,Anthoxanthum and Pani-cum,and Panicum and Plantago(Bever1994,Bever et al.1997).Our results further suggest that these strains of Pythium do not contribute to the negative feedback on plant growth previously observed between Anthoxanthum and Plantago(Bever et al.1997).The host-speci?c effects of Pythium found in our study combined with observations of greater competitive ability of Danthonia(Kelley and Clay1987)and Pan-icum(Westover1995)may work together to maintain these plant species in the community.In addition,other environmental factors,such as aphid-transmitted vi-ruses in Anthoxanthum(Kelley1994)and the aerially transmitted fungal pathogen Fusarium mono?liforme in Plantago(Alexander1984)may limit plant popu-lation densities in this community.As negative feed-back leads to the maintenance of diversity within a community and this study identi?es soil pathogens as potentially important agents of this feedback,we sug-gest that soil pathogens may contribute to the main-tenance of diversity within a plant community.

The differential response of the four plant species to Pythium was not isolate speci?c.This,in part,may re?ect a generalized resistance or tolerance of Antho-xanthum and Plantago to these root pathogens.How-ever,even Danthonia and Panicum,the more suscep-tible plant species,did not differ in their responses to individual isolates of Pythium.In fact,there was no evidence that the pathogens isolated from Danthonia exerted a greater effect on that species than the patho-gens isolated from Panicum or vice versa(as tested by the Danthonia vs.Panicum contrast,Table1).This lack of difference among the isolates is consistent with the absence of a differential response of Danthonia and Panicum to each other’s soil communities in three sep-arate measurement attempts(Bever1994).

While the consistency of results between this ex-periment and previous observations of feedback through the whole-soil community provides strong ev-idence that Pythium contribute to the observed feed-back,we cannot rule out important roles for other com-ponents of the soil community.Other potential patho-gens(e.g.,a Fusarium species was also isolated from Panicum;J.D.Bever and S.P.Bentivenga,personal observations)may be important.Moreover,the com-munities of rhizosphere bacteria(Westover1995)and the arbuscular mycorrhizal fungi(Bever et al.1996) also exhibited striking host-speci?c differentiation on these plant species,and the differentiation of these communities may contribute to the whole-soil feedback on the plant growth.It is also possible that mycorrhizal fungi and rhizosphere bacteria,which were excluded

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BEVER F IG .2.The response of four plant species to the presence of Pythium.The average responses to the ?ve Pythium isolates [hatched bars],and to the sterile control [open bars],are pre-sented for each of the four plant species.The least square mean plant mass (a)and root :shoot ratios (b)and 1SE are presented.

from the present study,could modify the effects of the soil pathogens (Newsham et al.1995),though this pos-sibility is not supported by the consistency of the re-sults of the present study and the whole-soil tests of feedback.

This experiment provides evidence that Pythium can be detrimental to the growth of certain species within a diverse plant community.Previous studies have large-ly focused on disease and mortality effects of Pythium on agronomically important plants (reviewed in Hen-drix and Campbell 1973,Larkin et al.1995,Pankhurst et al.1995,Deep and Lipps 1996,Magarey 1996,Rizvi and Yang 1996).Only ?ve plants died during the period of this study,and those deaths cannot be conclusively related to the presence of Pythium.In fact,as observed previously by Larkin and others (1995),most of the plants inoculated with Pythium in this experiment re-mained asymptomatic throughout the course of the study.Although no disease was obvious,the pathogen decreased plant productivity and inhibited root system development in two of the four plant species.Newsham and others (1994)also suggested that asymptomatic levels of root pathogen infection can alter plant fecun-

dity in the ?eld.Furthermore,four of the ?ve isolates of Pythium used in our experiment were identi?ed as species of Pythium (G.Abad,personal communication )that have been classi?ed as ‘‘highly aggressive’’(Abad et al.1994)due to their disease-causing potential on other plant species.However,in this seminatural grass-land the two isolates of the ‘‘aggressive’’Pythium ar-rhenomanes differed in their aggressiveness,with one isolate not producing signi?cant reductions in growth (Fig.1).The other isolates did not differ in their effects on plant size.

This study indicates that while Pythium reduces the growth and root development of plants overall,certain plant species proved more susceptible to Pythium in-fection,and this differential susceptibility to the patho-gens studied suggests that soil pathogens may be agents of negative feedback.These results further support ob-servations of negative feedback between these same plant species.Previous work indicates that this feed-back is mediated through changes in their whole-soil communities and,in combination with the present study,indicates that the host-speci?c effects of these pathogens may not be substantially modi?ed by other components of the soil community.Together these studies suggest that soil pathogens may strongly in?u-ence plant community composition and contribute to the maintenance of plant diversity.

A CKNOWLEDGMENTS

We thank K.Westover,P .Thrall,A.Pringle,J.Antonovics,J.Mihail,H.Alexander,J.Holah,https://www.wendangku.net/doc/5417102843.html,ler,and two anon-ymous reviewers for helpful comments on this manuscript.We are particularly grateful to G.Abad,M.Cubeta,and S.Bentivenga for advice and assistance in the isolation,cultur-ing,and identi?cation of the Pythium isolates.This work was made possible by USDA grants 92-37101-7461and 94-37101-0354,and by NSF grant DEB-9615941.

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【CN109782630A】自动泊车仿真测试方法及系统【专利】

(19)中华人民共和国国家知识产权局 (12)发明专利申请 (10)申请公布号 (43)申请公布日 (21)申请号 201910228709.X (22)申请日 2019.03.25 (71)申请人 北京经纬恒润科技有限公司 地址 100101 北京市朝阳区安翔北里11号B 座8层 (72)发明人 王珍　王胜华　康驭涛　 (74)专利代理机构 北京集佳知识产权代理有限 公司 11227 代理人 赵兴华　王宝筠 (51)Int.Cl. G05B 17/02(2006.01) (54)发明名称 自动泊车仿真测试方法及系统 (57)摘要 本发明提供自动泊车仿真测试方法及系统， 以降低测试成本、提高工作效率。在本发明实施 例中，利用动画仿真平台搭建测试场景，利用自 动测试平台搭建测试脚本，在自动测试阶段，由 自动测试平台根据测试脚本和泊车控制器的车 辆控制命令，通过人机交互平台对车辆动力学模 型的运行参数进行控制，并生成测试报告，可实 现仿真测试的自动化。使用本发明实施例所提供 的技术方案，并不需要实车参与，同时测试过程 是由自动测试平台自动执行的，因此可在降低测 试成本的同时， 提高工作效率。权利要求书2页 说明书10页 附图10页CN 109782630 A 2019.05.21 C N 109782630 A

权　利　要　求　书1/2页CN 109782630 A 1.一种自动泊车仿真测试方法，其特征在于，用于对泊车控制器进行仿真测试；所述方法基于自动泊车仿真测试系统，所述自动泊车仿真测试系统包括：自动测试平台、动画仿真平台和人机交互平台； 所述方法包括： 使用所述动画仿真平台搭建与测试用例相应的虚拟测试场景； 使用所述自动测试平台搭建与所述测试用例相应的测试脚本； 在自动测试阶段，所述自动测试平台根据所述测试脚本和泊车控制器的车辆控制命令，通过所述人机交互平台操控车辆动力学模型的运行参数，并在所述测试脚本执行完毕后生成测试报告；所述测试报告至少包括表征泊车成功或失败的信息；所述车辆动力学模型为真实车辆的虚拟仿真模型；在所述自动测试阶段，所述动画仿真平台至少用于在所述虚拟测试场景中根据运行参数显示所述车辆动力学模型。 2.如权利要求1所述的方法，其特征在于，在所述自动测试阶段，所述方法还包括： 所述自动测试平台通过所述人机交互平台模拟生成目标传感器信号，所述目标传感器信号用于所述泊车控制器生成车辆控制命令。 3.如权利要求2所述的方法，其特征在于，在所述自动测试阶段之前，所述方法还包括： 将输入输出I/O模型加载至所述人机交互平台； 将所述车辆动力学模型加载至所述人机交互平台； 将所述车辆动力学模型的运行参数与所述人机交互平台的车辆控制信号进行映射，以实现通过所述人机交互平台操控所述车辆动力学模型的运行参数。 4.如权利要求3所述的方法，其特征在于，还包括： 在所述自动测试阶段，由所述人机交互平台运行所述I/O模型以监测所述车辆动力学模型的目标运行参数；所述目标运行参数包括需监测的运行参数； 所述测试报告还包括所述目标运行参数。 5.如权利要求1-4任一项所述的方法，其特征在于，在所述自动测试阶段之前，所述方法还包括： 将人机交互工程文件加载至所述自动测试平台；所述人机交互工程文件包括车辆控制信号和需监测的运行参数。 6.如权利要求5所述的方法，其特征在于，所述自动泊车仿真测试系统的硬件架构包括：上位机、硬件在环HIL下位机和所述泊车控制器； 至少所述自动测试平台部署在所述上位机中。 7.如权利要求6所述的方法，其特征在于，所述HIL下位机包括实时处理器和I/O板卡，所述泊车控制器与所述I/O板卡具有通信连接； 在所述自动测试阶段之前，所述方法还包括：将车辆动力学模型和I/O模型加载至所述实时处理器。 8.一种自动泊车仿真测试系统，其特征在于，用于对泊车控制器进行仿真测试；所述系统包括自动测试平台、人机测试平台和动画仿真平台； 其中： 所述人机交互平台用于：操控车辆动力学模型的运行参数；所述车辆动力学模型为真实车辆的虚拟仿真模型； 2

泊车辅助系统

从APA到AVP，四代泊车辅助系统技术剖析 前言 在汽车智能化的浪潮中，车载传感器发展迅速，越来越多搭载了先进传感器的汽车进入了我们的视野。比如能够在高速公路上实现单车道巡航的凯迪拉克CT6，以及交通严重拥堵时解放驾驶员时间的奥迪A8，以及能够轻松实现高速公路自动驾驶、上下匝道的特斯拉Model系列的车型。 公众对自动驾驶的认识主要集中在高速、环路，解决的是“开车”的问题。其实自动驾驶技术除了能开得一手好车外，还可以帮助解决新老司机都比较头痛的停车问题。泊车辅助系统目前已经发展至第三代，从最开始的驾驶员必须在车内配合挂挡完成泊车，发展到驾驶员可以站在车外5米使用手机控制泊车，最后到汽车自己学习泊车路线，完成固定停车位或自家车库的泊车。 下面，我就来盘点一下已经成熟的这三代泊车辅助系统的传感器配置以及典型的应用场景，随后我会对将在一两年内量产的第四代泊车辅助系统做一个技术分析。 目前市面上已量产的泊车辅助系统主要有三类。最早普及也是最为常见的第一代叫做APA自动泊车，随后出现的是将泊车与手机结合的第二代RPA远程遥控泊车，最后是最先进的第三代叫做自学习泊车。在未来一到两年内将会出现更为先进的泊车解决方案——AVP代客泊车，也就是暂未量产的第四代泊车辅助系统。 泊车辅助一代：APA自动泊车 APA（Auto Parking Asist）自动泊车是生活中最常见的泊车辅助系统。泊车辅助系统在汽车低速巡航时，使用超声波雷达感知周围环境，帮助驾驶员找到尺寸合适的空车位，并在驾驶员发送泊车指令后，将汽车泊入车位。 APA自动泊车所以依赖的传感器并不复杂，包括8个安装于汽车前、后的UPA 超声波雷达，也就是大家常说的“倒车雷达”，和4个安装于汽车两侧的APA超声波雷达，雷达的感知范围如下图所示。 APA超声波雷达的探测范围远而窄，常见APA最远探测距离为5米；UPA超声波雷达的探测范围近而宽，常见的UPA探测距离为3米。不同的探测范围决定了他们不同的分工。 APA超声波雷达的作用是在汽车低速巡航时，完成空库位的寻找和校验工作。如下所示，随着汽车低速行驶过空库位，安装在前侧方的APA超声波雷达的探测距离有一个先变小，再变大，再变小的过程。一旦汽车控制器探测到这个过程，可以根据车速等信息得到库位的宽度以及是否是空库位的信息。后侧方的APA在汽车低速巡航时也会探测到类似的信息，可根据这些信息对空库位进行校验，避免误检。

360度全景泊车辅助系统解析

360度全景泊车辅助系统—使用说明书

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图2 摄像头

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毕业设计开题报告 学生姓名系部汽车交通与工程学院专业、班级 指导教师姓 名职称实验师 从事 专业 汽车运用是否外聘□是□ √否 题目名称汽车泊车辅助系统设计 一、课题研究现状,选题的目的、依据和意义 设计目的和意义： 随着我国经济的快速发展，交通运输车辆及私家用车的不断增加，不可避免的交通问题瞬时成为人们关注的问题。其中由于泊车事故发生的频率高，已引起了社会和交通部门的高度重视。泊车事故发生的原因是多方面的，造成泊车时的事故率远大于汽车正常行驶时的事故率，尤其是非职业驾驶员以及女性更为突出。而泊车事故给车主带来许多麻烦，不仅经济上，更有人身伤害，例如撞上别人的车，如果伤及儿童更是不堪设想，基于此基础，汽车高科技产品中，专为汽车泊位设置的“汽车泊车辅助系统”应运而生，汽车泊车辅助系统的加装可以解决司机的不少麻烦，大大降低了泊车事故的频率。由于存在视觉盲区，无法看清车附近状况，司机在泊车时很容易发生事故。为了减少带来的损失，需要有一种专门帮助司机安全泊车的装置。目前市场上用于辅助司机泊车的装置主要有：语音告警装置、后视系统以及倒车雷达等。语音告警装置用于播放提示语以提醒车后的行人注意避让正在泊车的汽车。这种装置价格便宜且使用方便，缺点是只能对车后的行人起告警作用，对于其他障碍物则不起作用，所以其应用范围有限。后视系统是由视频捕捉装置和视频播放装置组成，通过视频司机可以很直接地看到车后的障碍物。由于这类装置的价钱较高，目前还没有普及。 汽车泊车辅助系统，是汽车泊车安全辅助装置，能以声音或者后视镜的显示通告司机车附近的状况，解除了司机泊车和启动车辆时前后左右探视所引起的麻烦，并帮助司机解决由视觉引起的缺陷，提高驾驶的安全性，泊车辅助系统的原理与普通雷达一样，是根据蝙蝠在黑夜里高速飞行而不会与任何障碍物相撞的原理设计开发的。通过感应装置发出超声波来判断前方是否有障碍物，以及障碍物的距离、大小、方向、形状等。只不过由于倒车雷达体积大小及实用性的限制，目前其主要功能仅为判断障碍物与车的距离，并做出提示。司机在倒车时，启动倒车雷达，在控制器的控制下，由车尾保险杠上的探头发送超声波，遇到障碍物，产生回波信号，传感器接收到回波信号后经控制器进行数据处理，从而计算出车体与障碍物之间的距离，判断出障碍物的位置，再由显示器显示距离并发出警示信号，从而使司机倒车时不至于撞上障碍物。

自动泊车系统设计

___________________________________________________信息记录材料2019年5月第20卷第5期［信息：技术与应? 自动泊车系统设计 秦学义，郝家多，黄家兵 （皖西学院电子与信息工程学院安徽六安237012） 【摘要】一种用于实现车辆在泊车过程中的自动化、降低车主人工停车难度的智能泊车系统。通过雷达、距离传感器、GPS定位系统及图像采集设备釆集到的数据传输到中央处理器，经中央处理器运算后得到车辆当前位置和目标位置及周围环境情况，并通过处理器将采集处理后的信息转换为相应的控制电信号，用电信号控制车辆的机动装置进行方向及速度调节，或者将电信号转换为数据反馈给司机以辅助进行车辆停靠，由此实现车辆的自动泊车. 【关键词】智能化；自动化；传感器；单片机 【中图分类号】TP23【文献标识码】A【文章编号】1009-5624（2019）05-0167-02 1引言 随着社会的发展，汽车普及化程度越来越高，由于汽车的大范围普及，导致一些停车位十分拥挤，停车难度增加，这给停车技术欠缺的司机师傅带来很大的困扰，在这种情况下，我们提出自动泊车系统的构想。 2自动泊车系统总体方案设计 自动泊车系统，是基于各种传感器采集数据以高速率 传送给主控，通过STM32单片机，处理运算数据，得到车辆此时周围环境、当前位置及方向以此向机动装置发送控制命令控制车辆车速、转弯半径及前后位置实现车辆自动泊车或辅助车主泊车。该系统可分为信号检测部分、数据处理部分以及机动控制部分。信号检测部分包括超声波雷 达、OPENMV图像采集模块、速度检测模块。数据处理部分包括处理器；机动控制部分包括转向电机切、刹车电 机。采用多模块信息采集的方式，通过信息融合技术，规 划出更加的有效的路径。为用户提供快速安全有保障的自 动泊车服务。环境检测模块：用于实时釆集车辆周围环境 信息，如后方障碍物检测、行人体红外检测、周围车辆位置信息等，并汇集各种信号传送给单片机。GPS定位模块：用于车辆定位，寻找距离车辆最近的停车位，快速解决停车问题。速度检测模块：主要用于在泊车过程中实时检测车速，并发出刹车命令，避免车速过快，造成不必要的损失。OLED屏幕：通过单片机驱动，显示在停车过程中的各种数据，方便车主判断车辆位置。机动控制装置：通过对各项数据的分析，得到车辆当前所需车速及方向盘转向角度B1o 3系统模块组成 整个自动泊车系统由各种传感器、OLED屏幕、stm32fl03zet6单片机、机动控制电机、倒车警示器几部分组成。安装在汽车车身周围的各种传感器，这些传感器包括人体红外传感器、速度传感器、超声波传感器、GPS 定位传感器等，采集车辆运动的各项数据。OPENMV摄像头用于采集地面信息，获取地面白线位置，并预处理图像得到清晰图片数据，与采集数据的单片机进行数据传输。OLED屏幕用于显示车辆实时位置，以及距离障碍物距离、车速大小等各项数据。 3. 1单片机模块 单片机采用的是意法半导体集团推出的32位ARM微控制器，其内核是Cortex-M3,内置高速存储器，其主要实现过程如下：（1）通过对应传感器驱动代码驱动各传感器。（2）通过端口复用PA2和PA3,也就是串口3分别与OPENMV的P0和P1也就是RXD1和TXD1串口相连，通过串口接收OPENMV采集到的数据信息。（3）通过单片机端口驱动OLED屏幕，显示实时车速，车辆位置。 4自动泊车系统软件设计及实现 自动泊车软件部分主要包括：主程序、人体红外传感器驱动程序、OLED屏幕驱动程序、超声波传感器驱动程序、速度传感器驱动程序、串口通信子程序及OPENMV图像处理程序。 4.1泊车系统主程序设计 该部分主要完成系统的初始化，串口初始化，驱动各传感器，驱动机动控制电机等功能。单片机自动与OPENMV 连接获取图像信息。 4.2OPENMV机器视觉程序设计 该模块主要完成地面白线检测，处理采集的图像，发送处理数据给单片机。 5系统工作流程 图1自动泊车系统工作流程 系统工作时，超声波传感器向水平方向发送超声波⑶，根据超声波反弹时间得出车辆此时位置离物体或车 辆的距离并同时将数据发送给STM32数据处理器；同时工作的还有图像传感器，图像传感器主要采集车身与车尾部分的位置信息，该图像传感器会按低频率的工作方式采集照片，以每0.5s传输一次图像数据的速率给数据处理芯片传输数据，处理器通过运算可以得到此时车辆尾部距离停车白线的位置，从而控制车辆的机动装置。考虑到安全性，另外在车轮上装有轮速传感器用以实时监测车辆的速度，轮速传感器正常工作时，当车轮转速达到设定的阈值时，车辆启动刹车系统，降低车速，稳定车速在10km/lho 6结语 基于STM32fl03zet6的自动泊车系统在搭建系统成本 167

自动泊车系统关键技术的智能化发展

自动泊车系统关键技术的智能化发展 〔摘要〕：自动泊车技术是目前智能车辆技术研究的一个热点问题。通过介绍自动泊车系统的基本概念,结合自动泊车系统国内外相关研究进展。进而研究分析了自动泊车系统关键技术，提出了目前技术缺陷，并展望了未来发展。 〔关键词〕：自动泊车；系统；技术；展望 1 自动泊车系统概述 随着科技的不断进步，汽车逐渐向智能化发展，声音提示及影像已经满足不了安全泊车的需求，更具智能化的自动泊车系统（Automatic Parking System，APS）应运而生。 自动泊车系统主要由人机交互系统、环境数据采集系统、中央处理器和控制策略执行系统四部分组成。人机交互系统显示车辆的环境情况，通过驾驶者是否启动泊车的操作，来决定是否启动自动泊车系统，并且实时显示车辆的泊车过程。环境数据采集系统用来确定车辆处于环境中的位置，对于自动泊车系统而言，是非常重要的。为了使车辆可以准确泊车，需要如超声波传感器、陀螺仪、CCD摄像头等传感器。中央处理器将采集到的环境信息数据分析处理后，得出汽车的当前位置、目标位置以及周围的环境参数，依据以上参数计算判断车辆能否入该车位所提供的空间，作出自动泊车策略，生成相应的控制命令（包括车速命令和转向盘转角命令）。执行系统接收到由控制命令产生的信号，依据指令控制电动助力转向系统（Electric Power Steering，EPS），进而控制车辆转向盘转动，与此同时，控制车辆的行驶速度，完成泊车操作。 自动泊车的实际工况主要有两种形式，分别为平行泊车（俗称路边停车）和垂直泊车（俗称倒库）。 图1 平行泊车简图 图2 垂直泊车简图 2 自动泊车系统的技术发展概况

泊车辅助系统的作用

泊车辅助系统的作用 一、定义 泊车辅助系统于车前、左右后视镜和车尾分别安装了4个超广角摄像头，这四个摄像头分别采集了汽车车身前后左右四个区域的实时画面，然后通过全景视觉泊车辅助装置合成为鸟瞰全景图象，显示在屏幕上。实时提供给驾驶员泊车所需要的汽车全景图像，消除了车四周的视觉盲区，来帮助驾驶员更加精确的泊车。 二、作用 1、提供实时的全景图像 泊车辅助系统最初的研发目的就是为了解决盲区问题。这套系统以鸟瞰方式提供了车身周围360度的场景图像。通过中控台的显示屏实时的显示在驾驶员面前。解决了倒车时的盲区问题。 2、倒车轨迹 泊车辅助系统的功能已不在是单一的，更是将许多新的功能集中到一起。倒车轨迹线就是其中之一。以道可视的智能倒车轨迹线为例。在倒车泊车时利用这些轨迹线的提示作用，能够给驾驶员可以看到的，非常直接的参考。在当前角度的方向盘下，倒车，会不会与周围的障碍物，标示物或其他车辆发生碰撞。 3、行车记录 今年发生的几起别车撞人事件中，行车记录仪的作用非常的耀眼。但是如果泊车辅助系统和行车记录仪同时安装，在车内就会显得空间特别小。因此厂家把行车记录功能整合到泊车辅助系统中。这也成为今年许多车主在选择泊车辅助系统时是否带有行车记录功能作为其中一个选择的标准。

4、驻车监控 驻车监控就是在我们泊车后的防护监控功能。在开车外出时，经常会遇到需要停车去处理一些临时性的问题，去上个厕所，去吃个饭。去银行办点业务等等。这些时候经常是把车停在马路边上。这时如果别刮了，被蹭了该什么办？驻车监控的功能就是为了解决这个难题而出现的。 驻车监控系统有两个高灵敏的震动感应装置，当收到震动感应时，能够快速启动录像功能，四路摄像头能同时启动记录下当时所发生的所有事。人不在车内也能知道自己的爱车是否收到伤害。

(完整版)自动泊车系统的设计毕业论文

内蒙古科技大学 本科生毕业设计说明书（毕业论文） 题目：自动泊车系统的设计 学生姓名：xxx 专业：电子信息工程 班级：2011-2班 指导教师：xxx

自动泊车系统 摘要 随着车辆的普及度、保有量越来越高，街道、小区、公路、停车场等拥挤不堪，人们对车辆的可操作性和智能性也提出了更多的要求，所以智能的自动泊车的研发迫在眉睫。本设计以蓝牙模块与单片机最小系统通过串口相连接，并与电脑端蓝牙连接实现下位机与上位机之间的通信过程,从而实现自动泊车的功能。 本设计由上位机、蓝牙模块、STC15F2K61S2单片机最小系统、GY-26电子指南针模块、光电避障模块、超声波模块、电机驱动模块、舵机组成系统。主要包括以下几个方面：第一，硬件电路设计，硬件电路通过Altium Designer软件进行硬件电路设计，主要包括包括电源系统和单片机最小系统，第二，STC15F2K61S2单片机最小系统设计，最小系统可以实现超声波数据、光电避障模块数据、电子指南针模块数据的接受，由上位机端发送命名实现对小车的相应控制。第三，上位机软件设计，上位机由C Sharp语言在Visual Studio 2010平台编写，主要实现对由下位机说发送的数据进行处理并实时显示出来的，并且对自动泊车系统进行整体控制，通过蓝牙向单片机最小系统发送数据，单片机接收到数据后控制小车完成侧位泊车或倒车入库动作。 关键词：上位机；单片机最小系统；自动泊车

Automatic parking system Abstract With the popularization of vehicle, retains the quantity is more and more high, streets, communities, roads, parking lots and other crowded. People of the vehicle can also put forward more requirements for the operation and intelligent, so the research and development of intelligent automatic parking is imminent. This design takes the Bluetooth module and the microcontroller smallest system through the serial port, and realizes the communication process between the lower computer and the upper computer with the Bluetooth connection of the computer terminal. The design of the PC and Bluetooth module, STC15F2K61S2 MCU minimum system, GY-26 electronic compass module, photoelectric obstacle avoidance module, ultrasonic module, motor drive module, servo system. Mainly includes the following aspects: first, hardware circuit design, hardware circuit through Altium designer software were hardware circuit design, including including power supply system and the smallest single-chip system. Second, STC15F2K61S2 smallest single-chip system design, the minimum system can realize ultrasonic data, photoelectric obstacle avoidance module data, electronic compass module data received, sent by the host computer end named the corresponding control of the car.Third, PC software design and PC by C sharp language on the platform of Visual Studio 2010 prepared, mainly to achieve by the slave computer said transmitted data for processing and real-time display, and the automatic parking system integrated control, via Bluetooth to send data to the MCU minimum system, MCU receives the data control the car lateral parking or reversing storage action. Key words: PC, minimum single-chip microcomputer, automatic parking

自动泊车系统技术解析 Automatic parking system

自动泊车系统Automatic parking system I believe that many just a "cottage" new drivers for side range parking a thing very headache, but one of the subjects of this skill is also essential for everyday driving in. But auto makers are for everyone to consider this point, and the development of the automatic parking system, this system can make the vehicle automatically into the fixed parking spaces, eliminate you met in the parking problems in (scratch, stop to do not come in and wait), let us work together to learn about automatic parking system. The working principle of automatic parking system The radar probe all over the vehicle appearance to measure its distance and angle between the objects around, and then through the on-board computer to calculate the operation process, and automatically adjust the direction of rotation of the steering wheel, the driver only needs to control the speed and replacement of forward and reverse gear can be completed. The operation steps of automatic parking system is introduced At present, equipped with automatic parking system models, most only support side range parking a function, the Mercedes B class models of automatic parking system as an example, do the operation steps and function of a detailed introduction for everybody. When driving a Mercedes Benz B - class along the road, as long as the speed below 36 km / h (each vehicle speed set value will be different), the system will think that the drivers with parking intention, vehicle began to use surrounding radar probe automatically detects whether there is a suitable parking position. Available parking area length of general automatic vehicle parking system set to be larger than the body is more than 1.2 meters, can confirm this region belonged to stop range. When the automatic parking system to find a suitable parking position, when reverse gear is engaged, the system will prompt the driver whether to start the active park assist function, confirmed after the start, now the driver can both hands off the steering wheel, the steering wheel will rotate automatically adjusts the vehicle reversing direction, the driver only needs to control the throttle and brake master speed (when the driver hands grip the steering wheel, the system will be suspended from work). In the process of reversing the car, the driver needs to properly control the speed and the attention of reversing radar tone, when hearing the alarm, that have been in after the car very close. At this time the need to hang into forward gear, the car on the move at the same time, the system will automatically return to the wheel, put the location of the car, the screen prompt information update for parking has been completed, hang into neutral, complete the parking task easily. (hint: there's a part of the equipment of automatic parking system models into the parking, no automatic back wheel, drivers need to manually complete yourself) It is worth mentioning that, Lexus LS and Toyota crown high allocation of vehicles equipped with intelligent parking assist system, this system in addition to curb side parking outside the