Effects On Species Diversity And Genetic Diversity On Litter Decomposition Of Wetland Plants

Plant litter decomposition is an important ecosystem function and plays a key role in biogeochemical cycle.The loss of multi-level and multi-dimensional biodiversity has an important impact on litter decomposition.However,most studies on the relationship between biodiversity and litter decomposition are performed at the level of species diversity,while the lack of studies on litter decomposition at the level of genetic diversity limits our understanding of mixed litter decomposition.It is urgent to compare the effects of different levels of biodiversity on plant litter decomposition.Wetland ecosystem is an important carbon pool and sensitive region of global change.Phragmites australis is a wetland plant widely distributed in the world.It is an important constructive species of wetland ecosystem with high genetic diversity as well as the most widely used plant species in constructed wetland.In this study,the litters of eight wetland plant species and eight P.australis genotypes in the Yellow River Delta were used as research materials,and four richness levels(1,2,4,8)were designed at the level of species diversity and genetic diversity respectively in the form of microcosm control experiment.Finally,a total of 501 microcosm systems were obtained.An 8-month control experiment was conducted to explore the effects of species diversity and genetic diversity on litter decomposition of wetland plants.At the same time,different diversity dimension indicators were used to estimate the effects of diversity changes on litter decomposition,and the impact mechanism was preliminarily studied.The main results and conclusions are as follows:(1)The decomposition rate of different litters of wetland plant species or P.australis genotypes was lower than that of litter alone,but the initial chemistry characteristics of litter decomposition rate and interaction were different between these two diversity levels.The actual decomposition rates of different litter mixtures of wetland plant species or P.australis genotypes were significantly lower than the expected decomposition rates without any non-additive effect(T test,t=2.838,P<0.01,Ttest,t=3.491,P<0.001),indicating a negative interaction among the mixed litters(i.e.antagonistic effect).At the level of species diversity,the decomposition rate of mixed litter increased with the increase of initial phosphorus content(linear regression analysis,R2=0.247,P<0.001).At the level of genetic diversity,there was no significant correlation between initial chemistry characteristics and decomposition rate of mixed litter.At the level of species diversity,the antagonistic effect of mixed litter increased with the increase of initial nitrogen and phosphorus contents(linear regression analysis for introgen,R2=0.038,P=0.001);linear regression analysis for phosphorus,R2=0.020,P=0.014),decreased with the increase of initial carbon content and lignin content(linear regression analysis for carbon,R2=0.035,P=0.001;linear regression analysis for lignin,R2=0.012,P=0.057).At the level of genetic diversity,the antagonism between mixed litter decreased with the increase of initial lignin content(Linear regression analysis,R2=0.139,P=0.009).(2)At the level of species diversity,taxonomic diversity and phylogenetic diversity can predict the impact of diversity change on litter decomposition,but they cannot predict it well at the level of genetic diversity].Based on Pearson correlation analysis,we found that at the level of species diversity,the decomposition rate decreased significantly with the increase of taxonomic diversity index(linear regression analysis,R2=0.018,P<0.01).With the increase of initial phosphorus content,the decomposition rate increased significantly(linear regression analysis,R2=0.161,P<0.001).When the species richness was 4,the decomposition rate significantly increased with the increase of the species diversity(linear regression analysis,R2=0.108,P<0.001).Through the phylogenetic conservation analysis of the initial phosphorus content,it was also found that the initial phosphorus content had a significant significant signal(Blomberg's K value test,P=0.07,K=0.95),suggesting little effect of the local environmental selection on litter phosphorus content during the evolution process..At the level of genetic diversity,there was no significant correlation between taxonomic or phylogenetic diversity and litter decomposition rate.In conclusion,the increase of both species and genetic diversity of wetland plants had a negative impact on litter decomposition,but the dimension indexes that can estimate the impact of diversity changes on litter decomposition are different at the level of species and genetic diversity.The dimension indexes of taxonomic and phylogenetic diversity can predict the impact of species diversity changes on litter decomposition,but cannot predict the impact of genetic diversity changes.The change of initial chemistry characteristics is a potential pathway for species diversity and genetic diversity to influence litter decomposition,but at the level of species and genetic diversity,the initial chemistry characteristics are not exactly same.In the process of wetland ecosystem management and restoration,plant species and genetic diversity can be reasonably adjusted to improve the carbon sequestration function of wetland ecosystem,but at the same time,the effects of different levels and dimensions of biodiversity changes on ecosystem function and their potential mechanisms need to be comprehensively considered.