Nitrogen controls the net primary production of an alpine Kobresia meadow in the northern Qinghai-Tibet Plateau.

Licong Dai,Yikang Li,Qian Li,Guangmin Cao,Yangong Du,Xun Ke,Kai Shu,Xiaowei Guo,Li Lin,Fawei Zhang,Cuoji Peng

doi:10.1002/ece3.5442

Abstract

Net primary production (NPP) is a fundamental property of natural ecosystems. Understanding the temporal variations of NPP could provide new insights into the responses of communities to environmental factors. However, few studies based on long‐term field biomass measurements have directly addressed this subject in the unique environment of the Qinghai‐Tibet plateau (QTP). We examined the interannual variations of NPP during 2008–2015 by monitoring both aboveground net primary productivity (ANPP) and belowground net primary productivity (BNPP), and identified their relationships with environmental factors with the general linear model (GLM) and structural equation model (SEM). In addition, the interannual variation of root turnover and its controls were also investigated. The results show that the ANPP and BNPP increased by rates of 15.01 and 143.09 g/m2 per year during 2008–2015, respectively. BNPP was mainly affected by growing season air temperature (GST) and growing season precipitation (GSP) rather than mean annual air temperature (MAT) or mean annual precipitation (MAP), while ANPP was only controlled by GST. In addition, available nitrogen (AN) was significantly positively associated with BNPP and ANPP. Root turnover rate averaged 30%/year, increased with soil depth, and was largely controlled by GST. Our results suggest that alpine Kobresia meadow was an N‐limited ecosystem, and the NPP on the QTP might increase further in the future in the context of global warming and nitrogen deposition.

Highlights

Net primary productivity (NPP) is a vital component of the global carbon cycle and a fundamental property of terrestrial ecosys‐ tems
Studies of the temporal variations in NPP can greatly improve our understanding of biosphere–atmosphere interaction, of the terrestrial carbon cycle, and of how terrestrial ecosystems respond to climate change (Cramer et al, 1999)
The general linear model indicated that both growing season temperature (GST) and growing season precipitation (GSP) were significantly positively correlated with belowground net primary productivity (BNPP) (r2 = 0.50, p < 0.01 for GST; r2 = 0.49, p = 0.03 for GSP; Figure 3a,c), whereas mean annual air temperature (MAT) and mean annual precipitation (MAP) had no significant effect on BNPP (p > 0.05; Figure 3b,d)

Summary

| INTRODUCTION

Net primary productivity (NPP) is a vital component of the global carbon cycle and a fundamental property of terrestrial ecosys‐ tems. A large number of stud‐ ies have explored the temporal variability of grassland production and its controlling factors (Niklaus, Leadley, Schmid, & Körner, 2001; Nippert, Knapp, & Briggs, 2006), and many methods have been es‐ tablished to examine the response of NPP to climate change: These include long‐term monitoring, ecological modeling, and controlled experiments (Gao et al, 2009; Piao et al, 2006). Despite these ef‐ forts, general responses of NPP to climate change have not yet been reached regarding the key controlling factors that affect the grass‐ land NPP, due to the complex interactions between environmen‐ tal conditions as well as herbivorous animal populations and plant community composition (Zhang, Lal, Zhao, Jiang, & Chen, 2017). The objectives of this study are to (a) explore the interannual dynamics of ANPP and BNPP and their key controlling factors and (b) examine the interannual dynam‐ ics of turnover rate and its relationship with climate factors, par‐ ticularly focus on the patterns of root turnover with depth, based on grassland productivity and environmental data collected during 2008–2015, and we hypothesized that the effects of air tempera‐ ture on grassland productivity were mainly via altering soil available nitrogen

| MATERIALS AND METHODS

| DISCUSSION

Findings

| CONCLUSIONS