Effects Of Community Species Composition And Traits On Canopy Rainfall Storage Capacity In Loess Hilly-Gully Region

Rainfall is the primary source of soil water replenishment in semi-arid Loess Plateau.Vegetation canopy interception leads to partial interception of rainfall,affecting the soil-vegetation-atmosphere rainfall hydrological process.Canopy storage capacity indicates the maximum amount of rainwater that can be intercepted and maintained by the vegetation canopy,reflecting the maximum effect of the plant community on rainwater interception.A systematic investigation of the rainfall storage capacity of grassland vegetation canopy and its intrinsic linkage with community structure is important for revealing the restoration potential of grassland vegetation and ecohydrological processes.This study was carried out on different dominant species of grassland communities in the Loess Hills area.The main objectives are:1)to investigate the differences in rainfall interception characteristics of grassland communities under different rainfall characteristics;2)to elucidate the relationship between community species diversity and functional diversity and canopy rainfall storage capacity;3)to clarify the influence of spatial structure and species composition of grassland communities on canopy rainfall storage capacity.Some of the key results are as follows:（1）The artificial rainfall simulation method was used,with simulated rainfall intensities of 0.5,0.7 and 0.9 mm·min^-1 and rainfall durations of 15 min.Canopy interception depth were measured for the three dominant communities（Bothrichloa ischaemum,Lespedeza dahurica and Artemisia gmelinii）.The results show that the canopy interception depth and interception ratios of the three dominant communities gradually decreased with increasing rainfall intensity.There were no significant differences between canopy interception depth at different rainfall intensities.The canopy interception ratio at 0.5 mm·min^-1 rainfall intensity was significantly higher than at 0.7 and 0.9 mm·min^-1.Moreover,no significant differences were found in canopy interception depth and interception ratios between the community types at the same rainfall intensity.The cumulative interception depth of the three dominant communities increased gradually as rainfall duration increased,and the changes in interception depth with rainfall duration mainly showed three stages,namely the rapid increase stage,the slow increase stage,and the stabilization stage.The interception ratios also went through three stages of rapid decline,slow decline and gradual zeroing with the extension of rainfall duration.（2）The plant individual storage capacity of 31 common species was measured by immersion method.the results showed that the interception capacity of 31 common grass species in loess hills ranged from 0.47 to 3.73 g·g^-1,with an average storage capacity of 1.60g·g^-1,and the leaf individual storage capacity of all species was higher than the stem individual storage capacity.The leaf individual storage capacity ranged from 0.60 to 4.37 g·g^-1,with an average values of 2.14 g·g^-1.The stem individual storage capacity ranged from 0.25 to 2.26 g·g^-1,with an average values of 0.72 g·g^-1.Classifying all species by family,the Rosaceae species had the highest average storage capacity among all families.The species of Compositae,Gramineae and Leguminosae contributed 78.2～92.2%of the canopy storage capacity of the grassland communities,among which the average interception percentage of Compositae species in the three different dominant communities was about 36.4%.Compositae species played a major role in the canopy rainfall interception process of the grassland communities in this area.（3）The species diversity and functional diversity of the B.ischaemum,L.dahurica and A.gmelinii community were analysed using the sample survey method.The results for species diversity show that fourα-diversity indices（Shannon-Wiener index,Simpson index,Patrick index and Pielou index）were not significantly related to community storage capacity and interception ratio.The community storage capacity and interception ratio were significantly and linearly positively correlated with community leaf area index,cover and leaf biomass.The stem individual storage capacity of the plants in the community was not significantly related to the functional traits,and the leaf individual storage capacity and total plant individual storage capacity showed significant negetive correlations with leaf length,leaf area and leaf fresh weight.The functional richness FRic index,functional evenness FEve index,functional dispersion FDis index and Rao Q index differed among the three dominant communities,but the community storage capacity and interception ratio were not significantly related to each functional diversity index as well as the weighted trait values.（4）Analysis of the relationship between community stem and leaf fractions and canopy storage capacity using a leaf removal method.The results show that the leaf storage capacity is higher than the stem storage capacity in the B.ischaemum,L.dahurica and A.gmelinii community.The stratified removal method was used to analyse the vertical spatial structure of the community and its relationship with the canopy storage capacity.The results show that the number of species,stem biomass,leaf biomass,total biomass and leaf area index with plant height at 0-20 cm,20-40 cm and>40 cm decreased sequentially in the three dominant communities.And the storage capacity of plants with plant heights of 0-20 cm,20-40 cm and>40 cm accounted for 63.9%,30.3%and 5.8%of the total storage capacity of the community,respectively.Analysis of community horizontal spatial distribution and their relationship to canopy storage capacity using the pattern method.The results showed that the spatial heterogeneity indices of the three dominant species were 0.93,0.74 and 0.71 for B.ischaemum,L.dahurica and A.gmelinii,respectively.Correspondingly,the spatial heterogeneity indices for the three dominant communities were 20.14,18.20 and 16.76,respectively.These indicate that all three dominant species and their dominant grassland communities show an aggregated distribution.However,the horizontal spatial heterogeneity index of grassland communities was not significantly related to community storage capacity.