The Interactive Effects Of Parasitic Plants And Abiotic Factors On Structure And Biomass Of Plant Communities

Parasitic plants are a unique group of angiosperms,and depend partially or completely on host plants for essential resources(e.g.water,nutrients and photosynthates)to complete their life cycles.Parasitic plants can preferentially inhibit the growth of some plant species,and further alter species composition and productivity of plant communities.Moreover,such effects may depend on environmental conditions such as soil nutrient and water availability.While many studies have examined the interaction effect of parasitic plants and environmental conditions on plant growth,few have tested how parasitic plants interact with abiotic factors to influence the structure and functions of plant communities.In this study,five greenhouse experiments were conducted to investigate the interaction effects of the parasitic plant Cuscuta australis with soil nutrient and water availability and heterogeneity on species/functional group composition and biomass of artificial plant communities.The main results are as follows:(1)C.australis parasitism significantly decreased aboveground biomass and relative abundance of forbs,and thus reduced aboveground biomass and changed functional composition of the artificial plant communities.Biomass of grasses was greater in heterogeneous soils with small patches than in heterogeneous soils with large patches,but such an effect did not depend on C.australis parasitism.In the presence of C.australis,biomass of grasses was greater in heterogeneous soils with high contrast patches than in heterogeneous soils with low contrast patches,and the reverse was true in the absence of C.australis.(2)Soil nutrient pulse or its interaction with C.australis parasitism had little effect on aboveground biomass of the artificial plant communities or aboveground biomass and biomass ratio of the three functional groups(grasses,forbs and legumes)(3)Both drought and C.australis infection significantly decreased aboveground biomass of the artificial plant communities.However,drought reduced the negative effects of C.australis parasitism on biomass of the artificial plant communities(4)With increasing nitrogen availability,the interaction between grasses and legumes changed from facilitation to competition.Moreover,nitrogen availability interacted with parasitism by C.australis to affect the interaction between legumes and grasses.C.australis parasitism decreased the facilitative effect of legumes on grasses under low nutrient availability and the competitive effect of legumes on grasses under high nutrient availability.(5)Nutrient fluctuation significantly decreased aboveground biomass of native plant communities,but such an effect was stronger when nutrient availability was higher.There was a significant three-way interaction effect of parasitism,nutrient availability and nutrient fluctuation on the invasibility of the native plant communities.When nutrient availability was low and also nutrients were supplied in fluctuation,the invasibility of the native plant communities was lower in the presence than in the absence of C.australis.In other treatments,however,C.australis parasitism did not affect the invasibility of the native plant communitiesIn conclusion,parasitic plants can influence the productivity,structure and invasibility of plant communities by altering their functional groups,but such an effect can vary with external environmental conditions such as soil nutrient and water availability and their spatiotemporal heterogeneity.