Elevational trends of root traits for alpine grassland are weakly dependent on grazing-related degradation

Abstract

Studying the variation of root traits along the elevational gradients can offer valuable insights into plant adaptations to environmental changes. However, the coupled effect of grazing-related degradation and elevation on root traits at the community level remains underexplored, especially in alpine grasslands. To investigate how increased degradation severity affects root traits along the elevational gradient in an alpine grassland, we sampled 51 sites across the Tibetan Plateau, and measured five root traits including root diameter (RD), specific root area (SRA), specific root length (SRL), root length density (RLD), root tissue density (RTD), as well as vegetation, and soil components. We found that RD, RTD, RLD increased while SRL, SRA decreased with elevation increasing. RD slightly increased while RLD decreased with increasing degradation severity. However, increased degradation severity had no effects on SRL, SRA, RTD. Moreover, the interaction of degradation severity and elevation had no effect on RD, SRL, SRA, RTD, but it significantly influenced RLD. Structural equation modeling (SEM) showed that mean annual temperature (MAT), the proportion of grass, soil nitrate nitrogen (SNN), soil bulk density (SBD), soil pH directly or indirectly influenced root traits variation. Our findings suggest that root traits tend to adopt a resource-conservative strategy, and except for RLD, increased degradation severity has no influence on other root traits variation as elevation increases. This provides novel insights into belowground strategies in response to the interactive effects of grazing-related degradation and elevation. Specifically, grazing-related degradation should be considered when comprehensively evaluating the effects of elevation on RLD.