Ecological Stoichiometry Of Plant-litter-soil In Five Typical Forests In Luo Mountains Of NingXia

The Luo Mountains is the only ecological security barrier in the central arid zone of Ningxia.However,due to climate change and human activities,the soil and vegetation in the protected area have been severely damaged,resulting in a fragile ecological environment.In recent years,the implementation of ecological protection and restoration measures has led to the recovery of the ecological environment in the Luo Mountains.The restoration of the ecological environment affects nutrient cycling,thus affecting the ecological stoichiometry of forest communities.Therefore,studying the ecological stoichiometric characteristics of forest communities in the Luo Mountains can help to identify the main limiting nutrients and nutrient cycling mechanisms of vegetation growth and development in this region,providing a theoretical basis for the selection of communities and forest management practices for vegetation restoration.This study selected five forest communities in the Luo Mountains(Pinus tabuliformis forest,Populus davidiana forest,Populus davidiana-Pinus tabuliformis mixed forest,Picea crassifolia forest,Picea crassifolia-Pinus tabuliformis mixed forest)as our research objects.We analyzed the nutrient content and chemical stoichiometry of different plant organs,litter and soil in each forest community and discussed the correlation and internal stability of ecological stoichiometric characteristics among plant leaves,litter and soil.Our main research results are as follows:(1)The average C content of the plants in the five forest communities ranged from highest in the P.tabuliformis forest(465.63 g/kg)to lowest in the P.tabuliformis-P.davidiana mixed forest(424.52 g/kg).The average N and P content of the plants were highest in the P.tabuliformis-P.davidiana mixed forest(14.44 g/kg and 1.1 g/kg)and lowest in the P.tabuliformis forest(10.56 g/kg and 0.62 g/kg).The C/N ratio in the P.tabuliformis and P.crassifolia forests was highest(47.79 and 41.88),while the C/N ratio in the P.davidiana and P.tabuliformis-P.davidiana mixed forests was lowest(40.21 and 34.93).The C/P ratio in the P.crassifolia forest(725.45)was higher than that in other forest communities.The N/P ratio in the P.tabuliformis and P.crassifolia forests was highest(17.79 and 17.38),while it was lowest(12.43)in the P.crassifolia-P.tabuliformis mixed forest.Among plant organs,the highest C,N and P content was found in leaves,while roots had the lowest content.In different forest communities,the highest C/N and C/P ratios were found in branches and roots,while the lowest were found in leaves.The highest N/P ratio was found in plant leaves in all forest communities.(2)The C content of litter was significantly highest in P.crassifolia forest(468.42 g/kg)and significantly lowest in the P.tabuliformis-P.davidiana mixed forest(354.13 g/kg)(P<0.05).The N content of litter was significantly highest in the P.crassifolia-P.tabuliformis mixed forest(16.05 g/kg)and significantly lowest in the P.tabuliformis and P.crassifolia forests(P<0.05).The P content of litter was significantly highest in the P.tabuliformis-P.davidiana mixed forest(1.21 g/kg)and significantly lowest in the P.davidiana and P.crassifolia forests(0.68 g/kg and 0.71 g/kg)(P<0.05).In different forest communities,the C/N ratio was significantly highest in the P.crassifolia forest(37.53)and significantly lowest in the P.tabuliformis-P.davidiana mixed forest(20.15)(P<0.05).The C/P ratio was significantly higher in the P.crassifolia and P.davidiana forests than in other forest communities(661.73 and 540.41)(P<0.05).The N/P ratio was significantly higher in the P.crassifolia-P.tabuliformis mixed forest,P.crassifolia forest and P.davidiana forest than in other forest communities(20.63,17.67,and 17.31)(P<0.05).(3)Analysis of the ecological stoichiometric characteristics of the 0-10cm,10-20cm and 20-30cm soil layers in different forest communities revealed that changes in soil C,N,P content and C/N and N/P ratios were significantly influenced by forest communities(P<0.05)in the same soil layer;soil depth significantly affected soil C,N,P content,and C/P and N/P ratios(P<0.05)in the same forest community;when forest communities and soil depth interacted,there was no significant effect on soil nutrient content and chemical stoichiometry ratios(P>0.05).Soil C,N and P content decreased with increasing soil depth,and the content of soil C,N and P was mainly concentrated in the surface soil layer.Soil C/N ratio increased with soil depth,while soil C/P and N/P ratios decreased with increasing soil depth in all forest communities.(4)The C,N and P contents of leaves in the five forest communities were significantly correlated(P<0.05).Plant N content was significantly positively correlated with litter N and P content(P<0.05);litter N content was significantly positively correlated with soil C,N and P content(P<0.05).The P content of litter was significantly positively correlated with soil P content(P<0.05).Plant C/N was significantly positively correlated with litter C/P,while plant C/P was significantly positively correlated with litter C/P and N/P ratios(P<0.05);plant N/P was significantly negatively correlated with soil C/N(P<0.05).The internal stability of nutrient content of different organs of plants and litter was stronger than that of soil for the five forest communities.(5)The C and N nutrient resorption rates of P.davidiana forest were relatively high,while the N and P nutrient resorption rates of P.tabuliformis-P.davidiana mixed forest were higher.The efficiency of C utilization was lowest,while the efficiency of N and P utilization was higher in P.crassifolia and P.tabuliformis forests.Overall,the nutrient resorption rates of C and N were higher than those of P;the P nutrient utilization efficiency was highest,while the C nutrient utilization efficiency was lowest in all forest communities.