Simple additive simulation overestimates real influence: altered nitrogen and rainfall modulate the effect of warming on soil carbon fluxes

Abstract

Experiments and models have led to a consensus that there is positive feedback between carbon (C) fluxes and climate warming. However, the effect of warming may be altered by regional and global changes in nitrogen (N) and rainfall levels, but the current understanding is limited. Through synthesizing global data on soil C pool, input and loss from experiments simulating N deposition, drought and increased precipitation, we quantified the responses of soil C fluxes and equilibrium to the three single factors and their interactions with warming. We found that warming slightly increased the soil C input and loss by 5% and 9%, respectively, but had no significant effect on the soil C pool. Nitrogen deposition alone increased the soil C input (+20%), but the interaction of warming and N deposition greatly increased the soil C input by 49%. Drought alone decreased the soil C input by 17%, while the interaction of warming and drought decreased the soil C input to a greater extent (-22%). Increased precipitation stimulated the soil C input by 15%, but the interaction of warming and increased precipitation had no significant effect on the soil C input. However, the soil C loss was not significantly affected by any of the interactions, although it was constrained by drought (-18%). These results implied that the positive C fluxes-climate warming feedback was modulated by the changing N and rainfall regimes. Further, we found that the additive effects of [warming × N deposition] and [warming × drought] on the soil C input and of [warming × increased precipitation] on the soil C loss were greater than their interactions, suggesting that simple additive simulation using single-factor manipulations may overestimate the effects on soil C fluxes in the real world. Therefore, we propose that more multifactorial experiments should be considered in studying Earth systems.

Accumulation of soil carbon under elevated CO2 unaffected by warming and drought

“…However, as the warming treatment also lengthened the growing season (Albert et al, ), it may be that the potential for plant growth over a longer period of time has compensated for the increased C loss caused by the higher microbial activity. Warming has similarly been found to have no net effect on soil C stocks in some meta‐analyses (Dieleman et al, ; Ni et al, ; van Gestel et al, ), whereas other meta‐analyses have predicted soil C stocks across the globe to decrease with increasing temperatures (Crowther et al, ; Yue et al, ).…”

Increased microbial sequestration of soil organic carbon under nitrogen deposition over China’s terrestrial ecosystems

“…Weighted effect sizes were used to quantify the overall influence of N addition on soil microbial necromass C following our previous procedures (Ni et al 2017). The mean values (X N for N addition and X c for control), standard deviations (S N for N addition and S c for control), and sample sizes (n N for N addition and n c for control) at both the N addition and control plots were employed to calculate the individual effect size (lnE; Eq.…”

Interactive global change factors mitigate soil aggregation and carbon change in a semi‐arid grassland

“…The ongoing global change is multi‐faceted (IPCC, 2013) and interactions of multiple environmental change factors may enhance or offset the effects of individual factors on soil C (Rillig et al., 2019). While some studies documented additive effects of multiple global change drivers on soil C storage (Dietzen et al., 2019; Yue et al., 2017), other results suggest that direct extrapolation of single‐factor effects to the multi‐faceted reality based on the “additive effect” assumption may overestimate or underestimate the impacts on soil C fluxes (Ni et al., 2017; Zhou et al., 2016). For example, warming effects on soil CO 2 efflux were significantly dependent on water availability in a semi‐arid Mongolian grassland (Zhou et al., 2012).…”