Biologic and Abiotic Factors Regulate Dissolved Organic Nitrogen With Low and High Nutrient Concentrations on Tibetan Plateau, Respectively

Shaoyu Li,Lin Zhang,Tiancai Zhou,Nan Cong,Mengli Zhao,Jian Sun

doi:10.3389/fenvs.2021.702713

Abstract

Although dissolved organic nitrogen (DON) plays an important role in the dynamic processes of nitrogen mineralization, fixation, and leaching, the ecological driving forces of DON across the Tibetan Plateau remain largely unknown. Here, we measured climate, soil, plant indicators, and DON concentration on the Tibetan Plateau, and used “change-point” analysis to determine DON patterns. Then correlation analysis was applied to analyze the relationship between DON and each index. Finally, the structural equation modelling (SEM) is used to explain the overall effect between DON and environmental factors. Our results showed that two DON patterns were presented across the Tibetan Plateau, that is, low-DON (5.43 g/mg) and high-DON (16.36 g/mg) patterns. In the low-DON pattern, biologic factors such as microbial carbon, microbial nitrogen, and productivity were the main influencing factors of DON concentration. In the high-DON pattern, DON was strongly governed by hydrothermal synchronization and superior soil environment. This study can help us to have a more comprehensive understanding of the response mechanism of soil soluble nitrogen pool in alpine ecosystems under climate change.

Highlights

Soil dissolved organic nitrogen (DON) is an important component of soil nitrogen (N) pool and plays a crucial role in regulating N cycling and plant productivity in terrestrial ecosystems (Chapin et al, 1993; Raab et al, 1996; Jiang et al, 2020)
In the low DON (LDON) pattern, our results showed that aridity index (AI) indirectly regulated the DON concentration through a positive effect on aboveground biomass and plant diversity (Gleason diversity index) (Figure 5A)
In the high DON (HDON) pattern with the warm and wet climate (high AI (Supplementary Figure S3) and hydrothermal synchronization) conditions, our results demonstrated that soil factors (SBD, Soil water content (SWC), and soil organic matter (SOM)) made greater contributions to DON (Figure 4B)

Summary

Introduction

Soil dissolved organic nitrogen (DON) is an important component of soil nitrogen (N) pool and plays a crucial role in regulating N cycling and plant productivity in terrestrial ecosystems (Chapin et al, 1993; Raab et al, 1996; Jiang et al, 2020). DON in the form of low molecular amino acids can be utilized directly by plant roots and some mycorrhiza, which increase the cycling of N by reducing the reliance of plants on soil microorganisms turning soil organic matter into inorganic nitrogen (Streeter et al, 2015). Previous studies demonstrated that the rate of ammonification and nitrification in soil can be regulated directly by the LMW-DON pool (Jahnel et al, 1994) while indirectly by HMW-DON through nonspecific inhibition of enzymes like proteases (Stepanauskas et al, 1999)

Objectives

Methods

Discussion

Conclusion