Effects Of Plant Functional Group Diversity On Productivity In Experimental Communities

Using nine annaul and twelve perennial forage grasses we constructed plant communities containing different levels of fuctional group diversity in out-door pot experiment to investigate the effect of the plant functional groups diversity on community productivity and underlaying mechanisms.The results showed that monocuhures of different plant functinal groups varied greatly in their productivities(P＜0.05).The productivity of annaual species fluctuated between 337.33 g/m² and 2078.67 g/m²,and the highest pruductive one was C₄ grass,Sorghum sudanense.The productivities of perennial species fluctuated between 706.33 g/m² and 2398.50 g/m², and the highest one was Lolium perenne,belonging to C₃ plants.The plant functional diversity had defferent effects on productivity in two different communities.The relationship between the functinial group divercity and productivity in annual communities can be described as a unimodal curve,and represented by a eqution of Y= -173.19x2 + 1078.7x + 169.45(R²=0.3501).In perennial communities,however,the productivity increased significantly with the increase of functional group diversity,and there was a positive linear relationship between functional group diversity and productivity,which could be represented by a equation of Y= 409.93x + 944.85,(R²= 0.3738).The species diversity within functional group also had different effect in different communities.In annaual communities,the productivity linearly increased with the increase of the species divicity within two functional group communities.When the number of functional groups was one,three or four,this positive promotion effect could not be found.In perennial communities,in contrast,as species diversity within functional group increased,the productivity increased significantly whether the functinoal groups were high or low.The calculation of relative yield total showed that,more than 80%of mixture communities have RTR＞1,indicated that there existed complementary effect in most mixtures.Like the productivity,functional group diversity also had significant effect on complementarity effect.In annual communities,the relationship between functional group diversity and complementarity was unimodel,while in perennial communitie;it showed a positive linear relationship.The analysis of relationship between RYT and productivity indicated that complementarity had different impact to productivity in different communities.Productivity and RYT had no conspicuous correlation in annaual communities,which indicated that the increase of productivity was not completely due to resources complematary utilization.But in perennial communities, the prodoctivity of mixtures incresed remarkably as the increase of the RYT in these communities(Y= 493.12x + 486.91,R²= 0.4564),which signified that in thses situations the increase of productivity mainly caused by the fact of the complementarity utilization of resources.The correlation among species diversity,complementarity effect and productivity analysis showed that complementarity effect had no significant effect on productivity in annaual communities,but it was the mainly mechanism in perennial communities.These results demonstrated that mechanisms drive both diversity-productivity relationships in different communities(here,annual and perennial)may differ.Therefore,in the study of relationship between biodiversity and ecosystem functioning,cautious must be paid when extrapolates conclusions from one ecosystem to others.