Effects Of Water And Fertilizer Stress On Species Interaction In Annual Plant Communities

By using outdoor potted cultivation,and 4 annual plant species(Avena sative,Amaranthus hypochondriacus,Lolium multiflorum,Vicia sativa)as experimental material,the effects of resourc change on positive relationship among species were investigated by compareing biomass and functional trait aboveground and belowground in monocultures and polycultures.The main results are:1.Water and fertilizer stress had significant effects on above-and bolow-ground biomass of four plants.Four plants all had the highest biomass in normal water and fertilizer treatment,and the higher and lowest biomass in water stress and fertilizer stress respectively.In normal treatment,A stivea had the hightest biomass,and A hypochondriacus has the lowest one.In fertilizer stress treatment,the biomass of A.sativa,L.multiflorum,V.sativa and A.hypochondriacus declined10.4%,8.1%,5.3%,and 23.7% respectively.In water stress treatment,however,the biomass of A.sativa,L.multiflorum,V.sativa and A.hypochondriacus declined 16.2%,19.4%%,10.7%,and37.98% respectively.Similar to above-ground biomass,the below-ground biomass of four plants also had significant difference.In normal treatment,V.stivea had the hightest biomass,and A.stivea has the lowest one.In fertilizer stress treatment,the biomass of A.sativa,L.multiflorum,V.sativa and A.hypochondriacus declined 12.7%,24.39%,27.98% and 15.92% respectively.In water stress treatment,however,the biomass of A.sativa,L.multiflorum,V.sativa and A.hypochondriacus declined 30.36%,37.91%,35.47%,and 32.45% respectively.2.Resours stress had significant effects on abovegroud functional trait,including plant height,relative growth rate,and specific leaf area.In normal treatment,plant height ranked as follows: A.sativa > L.multiflorum>V.sativa >A.hypochondriacus.In water stress treatment,the height of A.sativa,L.multiflorum,V.sativa and A.hypochondriacus declined 29.01%,16.16%,14.35%,and 32.74% respectively.In fertilizer stress treatment,the height of A.sativa,L.multiflorum,V.sativa and A.hypochondriacus declined 14.88%,7.85%,8.02%,and 15.85%respectively.Relative growth rate had the similar change like that of plant height.The negetive effects of water stress on relative growth rate were greater than that of fertilizer.The rank order of relative growth rate in three treatments was:V.sativa >L.multiflorum > A.sativa>A.hypochondriacus.V.sativa had the greatest value of specific leaf area in normal treatment,and A.sativa had the minimum value.Water and fertilizer strees only had significant effects on specific leaf area of V.sativa,but had no significant effects on that of A.sativa,L.multiflorum,and A.hypochondriacus.The specific leaf areas of V.sativa declined 12.05% and 19.26% in water stress and fertilizer treaa respectivily.3.Resours stress had different effects on belowgroud functional trait,including root length,root area.As for root length,L.multiflorum had the greatest value,and A.sativa had the minimum value in normal treatment.In fertilizer stress treatment,the root length of four plants all reduced significantly,among which A.sativa reduced 21.65%,L.multiflorum reduced 17.89%,V.sativa reduced 4.48% and A.hypochondriacus reduced 9.67%.In water stress treatment,the root length of four plants all incraesed sinificantly,among which A.sativa increased 13.12%,L.multiflorum increased 6.81%,V.sativa increased 19.04% and A.hypochondriacus increased 20.51%.The root area,however,changed differently with resouce strees.Four plants all had the greatest value of root area in normal treatment,next rank was for fertilizer stress treatment,and then was water stress treatment.As for root weight,V.sativa had the greatest value and A.sativa had the smalest one in normal treatement.In fertilizer stress treatment,the root weight of four plants all reduced significantly.In water stress treatment,the root wieght of four plants reduced mour than that of in water stress treatment.4.Compared with normal treatment,resource tress had significant effects on functional diversity of above-ground communitis.The FD value ranked as 0.4601,0.4497 and 0.4173 in water strss,fertilizer stress and normal treatment respectively.This result indicated that both fertilizer and water stress increased the intensity of positive interaction in plant community.The change patterns of functional diversity in below-ground communities were different.There was the greatest value of functional diversity in normal treatement,the middle one in fertilizer stress treatment and smalest on in water stress treatment.These rusults suggest that the responses of functional diversity to resource tress are different between above-ground and below-ground communities.5.The calculation of Relative Yield Totals(RYTs)indicated that the values of RYTs are greater than 1 in all aboveground communitis.This indicated that there exist positive interactions in all communities treated with different factors.In the conditions of resource stress,however,the positive interaction intensity was stronger than that of normal treatment communities.In normal treatment,the value of RYT was the lowest,the fertilizer stress communities had the middle one,and the water stress communities had the greatest one.In underground communities,however,the relative yield total are all smaller than 1.This indicated that there were no positive interactions in belowground communities.