Plant response to N availability in permafrost-affected alpine wetlands in arid and semi-arid climate zones

Abstract

Nutrient cycling in alpine permafrost-affected wetlands remains insufficiently studied, as it is influenced by a complex network of interrelated climatic and environmental factors, at both regional and local scale. Therefore, we applied mathematical models to examine relationship between environmental factors and plant functional traits reflecting N availability in wetland communities developed under locally variable conditions in a geographic and climatic gradient of high-altitude habitats. Moreover, we assessed impact of local differences in soil chemistry on plant fractionation of N isotopes as a response to N availability. Based on environmental data and chemistry of biomass from 192 study sites from the Pamir Mountains (Tajikistan) and Khangai and Khentei Mountains (Mongolia), a matrix of rank correlations was prepared for regional and local factors and community level plant functional traits. For the traits that were highly correlated either with regional or with local drivers (that is plant N:P ratio and plant δ¹⁵N), linear models were built, with a limited set of predictors selected according to the Risk Inflation Criterion and the SOS algorithm. The models were fitted for each of the studied regions. Presented regional models indicated significant influence of soil NH₄⁺ and/or PO₄^3- content on plant N:P ratio, which showed increase with altitude and lowering precipitation. Thus, its values clearly distinguished between the Pamir Mountains (high N:P) and the Mongolian ranges (low N:P). Models for plant δ¹⁵N showed its strong positive correlations with soil δ¹⁵N and soil salinity. Average values of plant δ¹⁵N were comparable for both study areas. The studied plant functional traits showed different response to regional and local drivers. Plant N:P ratio was controlled by regional drivers via their influence on soil NH₄⁺ content. Contrastingly, plant δ¹⁵N was significantly affected by local factors, namely soil δ¹⁵N and soil salinity expressed as Na:EC.

Keywords: Central Asia; Nitrogen; Plants; Stable isotopes.