A meta‐analysis of experimental warming effects on terrestrial nitrogen pools and dynamics

Abstract

SummaryGlobal warming may have profound effects on terrestrial ecosystems. However, a comprehensive evaluation of the effects of warming on ecosystem nitrogen (N) pools and dynamics is not available.Here, we compiled data of 528 observations from 51 papers and carried out a meta-analysis of experimental warming effects on 13 variables related to terrestrial N pools and dynamics.We found that, on average, net N mineralization and net nitrification rate were increased by 52.2 and 32.2%, respectively, under experimental warming treatment. N pools were also increased by warming, although the magnitude of this increase was less than that of N fluxes. Soil microbial N and N immobilization were not changed by warming, probably because microbes are limited by carbon sources. Grassland and shrubland/heathland were less responsive to warming than forest, probably because the reduction of soil moisture by warming offset the temperature effect in these areas. Soil heating cable and all-day treatment appeared to be the most effective method on N cycling among all treatment methods.Results of this meta-analysis are useful for better understanding the response of N cycling to global warming and the underlying mechanism of warming effects on plants and ecosystem functions.

A meta-analysis of the effects of experimental warming on soil carbon and nitrogen dynamics on the Tibetan Plateau

“…Forests show stronger responses to warming than grasslands in terms of soil respiration and soil nitrogen availability (Bai et al, 2013;Lu et al, 2013a;Rustad et al, 2001), which may be related to the fact that most observations in forests were conducted in more temperature-limited areas (Bai et al, 2013). However, grasslands may generally have lower air temperatures than forests in alpine regions on the Tibetan Plateau (Luo et al, 2010;Shen et al, 2014;Yin et al, 2013).…”

“…The increase in MBC caused by warming also implies that warming may accelerate organic matter decomposition in soil , while inconsistent responses of MBC and MBN to warming have been reported on this Plateau (Chen et al, 2010;Fu et al, 2012;Wang et al, 2011). Warming-induced increases in the net nitrogen mineralization and nitrification rates increased the nitrogen availability in soil (Bai et al, 2013;Rustad et al, 2001), which in turn increased plant biomass accumulation (Fu et al, in press;Rustad et al, 2001) and soil microbial biomass Yu et al, 2014). Furthermore, a warming-induced increase in plant biomass may more or less counterbalance the warming-induced increases in R s and decreases in litter quantity (Lu et al, 2013a).…”

“…The compiled database included biomass parameters [plant biomass (PB) and root length], soil carbon pools (soil carbon, MBC, and DOC), soil nitrogen pools [soil nitrogen, MBN, dissolved organic N (DON), ammonium nitrogen (NH 4 + -N) and nitrate nitrogen (NO 3 À -N)], R s , net nitrogen mineralization and nitrification rates, and soil enzymes (polyphenol oxidase, catalase, invertase, urease and protease) ( Table 1). Our criteria were as follows: only studies conducted on the Tibetan Plateau were included; at least one of the variables considered here was measured; studies with laboratory incubation, temperature gradients and growth chambers were excluded and only field warming experimental studies were included; only data from control and warming treatments were used for multifactor experiments; only the latest results were used for multiple observations at different times from the same study site because the observations should be independent in the metaanalysis (Hedges et al, 1999;Rosenberg et al, 2000); means, standard deviations (or standard errors), and sample sizes were directly provided or could be calculated from the studies; multiple soil depths, warming magnitudes or ecosystem types were treated as independent variables (Bai et al, 2013;Lu et al, 2013a).…”

“…The microbial biomass in soil responds quickly to changes in the soil temperature (Alvarez et al, 1995). MBC is likely to be more responsive to warming than MBN across all terrestrial ecosystems (Bai et al, 2013;Lu et al, 2013a). The nonsignificant response of MBN to warming may result from the limited availability of carbon sources (Bai et al, 2013), while warming significantly increases the dissolved organic carbon (DOC), an important carbon source for soil microorganisms (Lu et al, 2013a).…”

“…The microbial biomass of carbon (MBC) and nitrogen (MBN) in soil are important components in terrestrial ecosystem carbon and nitrogen cycling and serve as sources (mineralization) or sinks (immobilisation) of labile carbon and nitrogen pools (Bai et al, 2013;Lu et al, 2013a). The microbial biomass in soil responds quickly to changes in the soil temperature (Alvarez et al, 1995).…”