PS 4-47 - Effects of N addition on the carbon balance in temperate grassland in Inner Mongolia, China

Monday, August 7, 2017
Exhibit Hall, Oregon Convention Center
Jirui Gong1, Qinpu Luo2, Min Liu2 and Lili Yang2, (1).College of Resources Science& Technology, Beijing Normal Univercity, (2)College of Resources Science& Technology, Beijing Normal University

Nitrogen (N) deposition may have a substantial impact on structure and function of N-limited grassland ecosystem as well as the ecophysiological processes across the systems. Carbon (C) cycle is one of the important ecological processes for ecosystem. N addition can play a key role in regulating C cycle and C balance in grassland. The semiarid temperate grassland in Inner Mongolia is a significant component of China's grassland. However, there is very limited information on the responses of C cycle and C balance to multi-level N addition in the N-deficient grassland ecosystem. We conducted a field N addition experiment in the temperate grassland in Inner Mongolia in 2014 and 2015. Six N-addition treatments were established as: the control, N1 (0 g N m−2 yr−1), N2 (2 g N m−2 yr−1), N5 (5 g N m−2 yr−1), N10 (10 g N m−2 yr−1), and N25 (25 g N m−2 yr−1). We measured net ecosystem CO2 exchange (NEE), net ecosystem production (NEP), and C sequestration rates in treatments with N addition. The main objective of the study was to evaluate the responses of grassland C balance to different levels of N addition at the ecosystem scale.


Vegetation, soil and whole-ecosystem C sequestration rates tended to increase with N addition. The N25 and N10 significantly increased the whole-ecosystem C sequestration rate compared to the control. The values ranged from 106.8 g C m−2 (N1) to 258.8 g C m−2 (N25). Cumulative NEE during the growing season decreased significantly at the N5, N10 and N25, ranging from –91.52 g C m−2 (N25) to 5.73 g C m−2 (N5). The N25 slightly increased cumulative heterotrophic soil respiration compared to the control, but the effect was only significant at the highest N level in 2014 growing season. N addition significantly increased cumulative NEP in both years, with values ranging from ‒5.8 g C m−2 (control) to 128.3 g C m−2 (N10). The C input from litter decomposition was significant, and must be quantified to estimate NPP. Measuring C sequestration rates and NEP together may allow tracking of the effect of N addition on grassland C budgets. Adding 25 or 10 g N m−2 yr−1 increased C sequestration and improved the C balance of the ecosystem, and increased grassland C sequestration. Overall, our results demonstrate that N addition is an important mechanism for maintaining C balance within the temperate grassland.