The Importance Of Spatial Patterns And Drought For The Biodiversity-Productivity Relationship And Trait Variability In Herbaceous Plants

Context:In nature,plant populations and communities often occur in spatially random and non-random patterns,such as spatially aggregated and dispersed patterns at different scales.Quantifying the spatial patterns of population and community attributes and inferring the processes behind these patterns is one of the fundamental tasks of spatial or landscape ecology.Meanwhile,the spatial arrangement of plants that shapes the spatial pattern of plants can significantly alter the pattern of species interactions,such as competition,mutualism,and niche complementarity,which alter intra-and interspecific trait variation.On the other hand,changes in plant interactions and traits can alter biodiversity-productivity relationships by changing the intensity of niche complementarity and selection effects.However,changes in intra-and interspecific trait variation and diversity-productivity relationships caused by the impact of spatial patterns on plant interactions are less considered in community ecology.Moreover,drought stress is likely to affect species interactions,trait variation,and plant productivity in different spatial patterns.However,the specific effects and mechanisms are still obscure.Therefore,considering plant spatial patterns and drought stress to reveal its effects on species trait variation and diversity-productivity relationships will help us better understand the ecosystem functions and processes.Objective:In this study,I used three herbaceous species as research objects and established field experiments on the spatial arrangement of three species.Then.I set up a split-plot factorial experiment between drought and control（permissive well-watered）.Population and community productivity data under different spatial patterns and diversity were used to systematically test the relationship between well-watered and drought on plant biodiversity-productivity relationship.The intra-and interspecific trait variation and trait-trait covariation were quantified with the functional trait data of herbaceous plants.This study will deepen our understanding of the effects of spatial patterns on ecosystem functions and processes in community ecology and spatial ecology and provide a theoretical basis for understanding the ecological applications of spatial patterns in the landscape.This thesis aims to answer the following scientific questions:（1）How does the diversity-plant productivity relationship vary with spatial patterns and drought?（2）What are the consequences of plant spatial patterns and drought on trait variability in plant populations and communities?Methods:Three herbaceous plants widely used in urban landscapes（Trifolium repens L,Zinnia elegans Jacq,and Portulaca grandiflora Hook）were selected to establish a three species-level spatial pattern-biodiversity experiment based on Moran’I spatial autocorrelation map.The experiment was set up as a split-plot factorial design with drought and normal water treatment,three plant spatial patterns:aggregation（positive autocorrelation）,regular（negative autocorrelation）and random;three species richness levels:three monocultures,two species mixtures,three species mixtures,a total of seven different species composition with five replications of each,a total of 210 1m×1m planting units,and each unit was planted with 18 plant individuals with same density controlling.All aboveground,belowground and overall biomass of each planting unit were collected to compare the effects of different spatial patterns,biodiversity and drought on community productivity.The biodiversity effects based on biomass data were also calculated to further explain the effects of spatial patterns on biodiversity-productivity relationships.In addition,intra-and interspecific plant trait variation(CV_{Intraspecific}and CV_{Interspecific})under different spatial patterns,different species richness,and drought,and trait covariance were quantified based on five functional traits of different plants in each planting plot:leaf area（LA）,specific leaf area（SLA）,leaf dry matter content（LDMC）,leaf thickness（LT）,and chlorophyll content（SPAD）.In this empirical study,I aimed to describe whether different spatial patterns,species richness,and drought affect plant productivity and trait variation.This study used factorial ANOVAs with plant productivity,biodiversity effects,and trait variation as response variables and plant spatial patterns and species richness,with the interaction between these three factors as predictor variables.Analyses were repeated separately for permissive and drought plots and for including environmental stress as a factor in the model.The data were naturally log-transformed to satisfy statistical assumptions regarding the normality of residuals and chi-square between groups.Further Tukey post hoc tests were conducted for significant effect factors.Results:Through ANOVAs,spatial patterns and drought significantly affect herbaceous diversity-productivity relationships and intra-and interspecific trait variation within plants,and varied at the community level and population level:（1）Effects of plant spatial pattern and environmental stress on biodiversity-productivity relationships:At the community level,the spatial pattern didn’t significantly affect community productivity,while species richness and drought did.Community aboveground,belowground and net productivity increased with richness.Drought significantly negatively impacted community productivity.However,the spatial pattern of plants had a significant effect on the belowground productivity of the community under the drought.The belowground productivity was higher in the random spatial pattern compared with the aggregated or regular,indicating that the random pattern was more favorable to promote a positive diversity-productivity relationship in this experiment.At the population level,spatial pattern,species richness and drought significantly affected species productivity.The productivity of Zinnia elegans Jacq increased overall with species richness,but the productivity of Triforlum repens L and Portulaca grandiflora Hook decreased with increasing richness.Drought significantly reduced the productivity of each species,and both Triforlum repens L and Zinnia elegans Jacq exhibited higher overall productivity in a random spatial pattern.In comparison,Portulaca grandiflora Hook exhibited higher overall productivity in aggregated pattern,indicating a significant variations of spatial patterns effects on species productivity.The spatial pattern of plants and interaction effects of pattern and richness and drought significantly impacted complementarity and net effects.In control,the niche complementarity and net effect increased significantly with richness when plants were in a random pattern.The net effect also increased significantly with increasing richness in drought in the random pattern,which indicates that compared with aggregated（increased interspecific competition）or regular（with reduced interspecific competition）pattern,the random spatial pattern is more favorable for plants to access and utilize resources and increase productivity in this experiment.（2）Effects of plant spatial patterns and environment stress on plant trait variation:At the community level,intraspecific trait variation was on average 9%and 5%lower for positively and negatively correlated plants than for randomly occurring plants and was not affected by species richness.Interspecific trait variation increased with plant richness but was not affected by plant spatial arrangement.The magnitude of intraspecific trait variation under the drought was 12%higher than in well-watered,while the interspecific trait variation was 8%lower,indicating that increased species competition for water resources under drought may produce trait variation among individuals,resulting in increased intraspecific trait variation and decreased interspecific trait variation.At the population-level,intraspecific trait variation and trait-trait covariance of Trifolium repens L was lower under aggregated and regular patterns at high diversity levels than in random patterns.Intraspecific trait variation of Zinnia elegans Jacq was consistently higher but decreased under drought.For Portulaca grandiflora Hook,drought significantly increased intraspecific trait variation in leaf thickness,indicating that this species is more sensitive to drought.Conclusion:This paper verifies the significant effects of spatial patterns and drought on diversity-productivity relationships and trait variation in herbaceous plants and their differences at the community and population levels,which clarifies the importance of plant spatial patterns for studying ecosystem functions and processes.This study shows that herbaceous plant spatial patterns and drought affect species interactions,alter intra-and interspecific trait variation and diversity-productivity relationships,and contribute to a deeper understanding of ecosystem functions and processes from the perspective of spatial patterns.