| Grassland ecosystem is one of the most important ecosystem types in the Loess Plateau,which plays an important role in ensuring the ecological security and animal husbandry production in the region.The interannual variation of its carbon storage is the most important variable for the change of terrestrial carbon storage.However,grassland ecosystem is sensitive to changes in climate environment and ecosystem carbon storage,which will not only reduce the carbon fixation ability,but also lead to a large loss of carbon stored by vegetation and soil.In the loess hilly region,the topographic changes have a strong redistribution effect on soil nutrients and water,and have an important effect on carbon density,plant species diversity and functional traits expression under different microtopographic gradients.In the context of realizing the goal of"double carbon",it is of great significance to improve and maintain the stability of carbon storage in grassland ecosystem.In this study,the grassland ecosystem of Yanhe River Basin in the typical hilly area of the Loess Plateau was selected as the research object.Five representative complete sections were selected to distinguish the slope direction and slope position,plant and soil samples were collected,14 functional traits such as plant height,leaf traits and fine root traits were determined,and plant species diversity and carbon density of each component were calculated.To analyze the patterns of changes in community-level plant species diversity,functional traits and each component carbon density across microtopographic gradients;to explore the correlations between community-level plant species diversity and functional traits;to explore the correlations between community-level plant species diversity and functional traits and each component carbon density;and to perform standardized principal axis analysis(SMA)to test whether the relationships between community-scale plant species diversity and functional traits and each component carbon density change across microtopographic gradients.Multiple linear regression model was established to comprehensively analyze the effects of plant species diversity and functional traits on carbon density of each component at community level.The results show that:(1)Vegetation carbon density and total carbon density decreased significantly(p<0.05)on the sunny slope,increased slowly and tended to be flat on the negative slope,and were higher on the sunny slope than on the negative slope.Soil carbon density in the upper part of the sunny slope was significantly higher than that in the lower part of the sunny slope,and it gradually decreased with the decrease of the slope position.The minimum carbon density of vegetation was 42.4 g C/m~2,the maximum carbon density of soil was 125.3 g C/m~2,and the maximum carbon density of soil was 222.8 g C/m~2;(2)The diversity index and richness index increased significantly(p<0.05)with the decrease of slope position;there was no significant difference between the evenness index and the dominance index.Specific leaf area,leaf phosphorus content,leaf carbon-nitrogen ratio(LC/LN),plant height,root nitrogen content,root carbon content and root carbon-nitrogen ratio(RC/RN)had significant differences on the microtopographic environmental gradient.There was significant correlation between plant species diversity and functional traits at community level.Both diversity index and dominance index were negatively correlated with leaf carbon content and plant height.The richness index was negatively correlated with leaf carbon content,root nitrogen content and root nitrogen-phosphorus ratio(RN/RP),and positively correlated with specific leaf area and root carbon-nitrogen ratio(RC/RN);(3)There was significant correlation(p<0.05)between plant species diversity at community level and functional traits and carbon density of each component.Vegetation carbon density and total carbon density were significantly negatively correlated(p<0.01)with diversity index,richness index and dominance index.Soil carbon density was significantly negatively correlated with diversity index,and negatively correlated with richness index,evenness index and dominance index.Vegetation carbon density and total carbon density were significantly positively correlated with plant height and root nitrogen content,soil carbon density was significantly negatively correlated with root carbon content,carbon density of each component was significantly positively correlated with leaf carbon content and leaf nitrogen-phosphorus ratio(LN/LP),and significantly negatively correlated with root tissue density and root carbon-nitrogen ratio(RC/RN).The relationship between leaf carbon content,leaf nitrogen-phosphorus ratio(LN/LP),plant height,root tissue density,root nitrogen content,root carbon content,root carbon-nitrogen ratio(RC/RN),root nitrogen-phosphorus ratio(RN/RP)and carbon density of each component was significantly different on the microtopographic gradient;(4)The vegetation carbon density model included diversity index,evenness index,leaf carbon content,leaf phosphorus content and root carbon-nitrogen ratio(RC/RN),and the explanatory degree reached 29%.The evenness index,leaf carbon content,leaf nitrogen content,leaf phosphorus content,root carbon content,leaf carbon-nitrogen ratio(LC/LN),root carbon-nitrogen ratio(RC/RN)and root nitrogen-phosphorus ratio(RN/RP)were included in the soil carbon density model,and the explanatory degree reached 50%.The total carbon density model included diversity index,leaf carbon content,leaf phosphorus content,root carbon content,root carbon-nitrogen ratio(RC/RN),root nitrogen-phosphorus ratio(RN/RP)and plant height,and the interpretation reached 56%.Leaf carbon content,leaf phosphorus content,root carbon content,root carbon-nitrogen ratio(RC/RN),root nitrogen-phosphorus ratio(RN/RP)and plant height had great influence on the carbon density of grassland ecosystem.In this study,the grassland ecosystem in the loess hilly region was taken as the research object.Based on estimating the carbon density of each component of the grassland ecosystem,the effects of plant species diversity and functional traits on the carbon density of each component of the grassland ecosystem at the community level were discussed from the perspective of plant species diversity and functional traits.This study provided theoretical support for the change and driving mechanism of grassland carbon density on microtopographic gradient,and provided an important basis for improving and maintaining the stability of grassland ecosystem carbon storage. |
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