高寒矮嵩草群落退化演替系列氮、磷生态化学计量学特征

Abstract

Alpine Kobresia humilis meadows are one of dominant vegetation types in Qinghai-Tibet Plateau.In the past decades,increasing human activities have resulted in dramatic changed in these alpine meadows.As a result,alpine meadows are experiencing different degrees of degradation.The degradation succession stages have been identified as six stations: gramineous grass-Kobresia humilis community,Kobresia humilis community,thickening in mattic epipedon Kobrecia pygmaea community,cracks in mattic epipedon Kobrecia pygmaea community,collapse in mattic epipedon Kobrecia pygmaea community,and forbs-"black soil beach ".Kobresia humilis alpine meadows degradation processes involved variations in soil elements and community structure and composition.Ecological stoichiometry has been developed to understand the relationships between organisms and ecosystem structure and function.Because nitrogen(N) and phosphorus(P) are the two most important elements limiting plant growth in a variety of ecosystems,biomass N ∶ P stoichiometry is most used in this respect.In this study,we investigated N/P ratios of soil and plants in a degradation series of the Kobresia humilis alpine meadows in Qinghai-Tibetan Plateau.Furthermore,we analyzed the relationships between of the key factors to affect community succession process and N/P ratios of plant and soil.We found that total N and total P content of soil decreased firstly and then increased with increasing degradation.The maximum values appeared in the Kobresia humilis community or in the thickening in mattic epipedon Kobrecia pygmaea community.Available N and available P of soil decreased with increasing degradation.Soil N ∶P ratio also decreased with the degradation process,and thus the highest soil N/P values appeared in the gramineous grass-Kobresia humilis community.By comparison,no significant difference in biomass N/P ratios were observed at community level among succession stages.This indicates that soil N and P cycling decoupled during grassland successional process and led to more P accumulation than N.Consequently,the unbalance of plant nutrition occurs in degraded soils.Insignificant biomass N/P ratios between different plant communities could be ascribed to their homeostasis.These findings provide important implications that soil available N content and available P content as well soil N/P ratios were more sensitive indexes to represent plant community degradation succession process while biomass N/P ratios cannot be used as the index because of it inertness.