Abstract
Elevated nitrogen (N) deposition alters the terrestrial carbon (C) cycle, which is likely to feed back to further climate change. However, how the overall terrestrial ecosystem C pools and fluxes respond to N addition remains unclear. By synthesizing data from multiple terrestrial ecosystems, we quantified the response of C pools and fluxes to experimental N addition using a comprehensive meta-analysis method. Our results showed that N addition significantly stimulated soil total C storage by 5.82% ([2.47%, 9.27%], 95% CI, the same below) and increased the C contents of the above- and below-ground parts of plants by 25.65% [11.07%, 42.12%] and 15.93% [6.80%, 25.85%], respectively. Furthermore, N addition significantly increased aboveground net primary production by 52.38% [40.58%, 65.19%] and litterfall by 14.67% [9.24%, 20.38%] at a global scale. However, the C influx from the plant litter to the soil through litter decomposition and the efflux from the soil due to microbial respiration and soil respiration showed insignificant responses to N addition. Overall, our meta-analysis suggested that N addition will increase soil C storage and plant C in both above- and below-ground parts, indicating that terrestrial ecosystems might act to strengthen as a C sink under increasing N deposition.
Highlights
Period, soil C storage may even decrease due to an increased litter decomposition rate enhanced by increases in high quality plant litter[13]
When the effects of the moderators were considered, the effects of N addition were only significant in the grassland and wetland ecosystems, where the C contents of the aboveground plant parts were increased by 30.46% [7.12%, 58.88%] and 28.20% [9.43%, 50.19%], respectively
Experimental N addition was found to stimulate the growth of both above- and below-ground plant parts, indicating an increase in the size of the plant C pools (Fig. 1a,b). These results is consistent with a previous meta-analysis investigating the effects of N addition on plants conducted by Xia & Wan[9] who noticed the differences between N-only and multi-nutrient addition effects
Summary
Period, soil C storage may even decrease due to an increased litter decomposition rate enhanced by increases in high quality plant litter[13]. Decreases in microbial abundance and activity would sustain greater ecosystem production, i.e., increasing soil C storage Such diverse responses create a more complex and dynamic relationship between C budgeting and ecosystem N enrichment. Fornara et al found that C storage was minimally affected by the addition of multi-nutrient fertilizer, suggesting that the positive N-only effect on soil C storage could be reduced by the simultaneous addition of other nutrients[25] Such paradoxical results make it important to synthesize the N-only effect on terrestrial C dynamics. The main objective of this study was trying to gain an overall perspective on the effects of N deposition on terrestrial ecosystem C storage by evaluating how N-only addition may influence C pools and fluxes between aboveground and belowground compartments. Treatments using mixed fertilizers were not included in our study, but we discuss our results in the context of previously published works reporting such case studies such as Liu & Greaver[21] and Fornara et al.[25]
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