Abstract
Forest soil respiration plays an important role in global carbon (C) cycling. Owing to the high degree of C and nitrogen (N) cycle coupling, N deposition rates may greatly influence forest soil respiration, and possibly even global C cycling. Soil microbes play a crucial role in regulating the biosphere–atmosphere C exchange; however, how microbes respond to N addition remains uncertain. To better understand this process, the experiment was performed in the Castanopsis kawakamii Hayata Nature Reserve, in the subtropical zone of China. Treatments involved applying different levels of N (0, 40, and 80 kg ha−2 year−1) over a three-year period (January 2013–December 2015) to explore how soil physicochemical properties, respiration rate, phospholipid fatty acid (PLFA) concentration, and solid state 13C nuclear magnetic resonance responded to various N addition rate. Results showed that high levels of N addition significantly decreased soil respiration; however, low levels of N addition significantly increased soil respiration. High levels of N reduced soil pH and enhanced P and C co-limitation of microorganisms, leading to significant reductions in total PLFA and changes in the structure of microbial communities. Significant linear relationships were observed between annual cumulative respiration and the concentration of microbial biomass (total PLFA, gram-positive bacteria (G+), gram-negative bacteria (G−), total bacteria, and fungi) and the microbial community structure (G+: G− ratio). Taken together, increasing N deposition changed microbial community structure and suppressed microbial biomass, ultimately leading to recalcitrant C accumulation and soil C emissions decrease in subtropical forest.
Highlights
Anthropogenic reactive nitrogen (N) production originated primarily from agricultural activities, fossil fuel combustion, and the growing popularity of biofuels, and has increased three- to five-fold over the past century [1]
No significant differences in soil organic C (SOC), total N (TN), ammonium N (NH4 + -N), or nitrate N (NO3 − -N) were detected after three years of N deposition (Table 1)
We found strong evidence to indicate that N addition significantly reduces Rs in subtropical forests as observed in all examined studies (n = 58, p = 0.011; Figure 6, Table S4)
Summary
Anthropogenic reactive nitrogen (N) production originated primarily from agricultural activities, fossil fuel combustion, and the growing popularity of biofuels, and has increased three- to five-fold over the past century [1]. By 2050, N deposition is projected to reach 200 Tg N year−1 , especially in forest ecosystems [1,2]. Twice as much C is stored in soils compared to that in the atmosphere. Soil respiration (Rs) is the primary pathway through which C is released from the soil system into the atmosphere [3]. Given the nature of the relationship between the C and N cycles, which are highly coupled in terrestrial ecosystems [4,5], it is likely that increasing N deposition will greatly influence Rs
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