Temperature sensitivity of soil organic matter mineralization decreases with long‐term N fertilization: Evidence from four Q₁₀ estimation approaches

Abstract

Climate warming and anthropogenic nitrogen (N) loads are two major global change components interactively affecting carbon cycling. However, the effects of N forms and amounts on temperature sensitivity (Q10) of soil organic matter (SOM) mineralization remain incomplete. With this goal, soil was sampled after 23 years of mineral and (or) organic N fertilization, and then incubated for one year at 10, 20, and 30°C. For the first time, we compared four approaches (Equal time, Equal C, 1‐C pool, and 2‐C pool model) to evaluate the Q10 of SOM mineralization. All approaches showed that the Q10 decreased by more than one third with N fertilization compared to unfertilized control at low temperatures. The '1‐C pool model' was not adequate for Q10 estimation with various C availability. The Q10 estimated by '2‐C pool model' was strongly depended on incubation duration. The 'Equal C' approach was more powerful for separating SOM pools and it revealed the decreased Q10 of the recalcitrant pool at high N rates. The impact of N fertilization on Q10 was more evident at high N than at low N. Notably, the Q10 decreased more by mineral N compared to organic fertilizers (~60% vs. ~40% decreased in Q10) at 10–20oC. The added benefit of N fertilization in protecting SOM under climate warming was demonstrated by decreased Q10. Such one‐third reduction of temperature sensitivity by N fertilization is large enough to be considered in predictions of global SOM stocks under warming and anthropogenic N loads.

Bioclimate and arbuscular mycorrhizal fungi regulate continental biogeographic variations in effect of nitrogen deposition on the temperature sensitivity of soil organic carbon decomposition

“…In general, the magnitude of N deposition effects on Q 10 was greater than 1.0 across all sites (Figure 1), which was contrary to our hypothesis and some previous studies (Mo et al, 2008; Zang et al, 2020). Together with the observation of Coucheney et al (2013), our results suggest that N deposition increased the sensitivity of SOC decomposition to elevated temperature.…”

“…In general, the magnitude of N deposition effects on Q 10 was greater than 1.0 across all sites (Figure 1), which was contrary to our hypothesis and some previous studies (Mo et al, 2008;Zang et al, 2020).…”

“…Furthermore, previous studies used the same incubation temperature for all soils at large scales (e.g., Fierer et al, 2006; Gutiérrez‐Girón et al, 2015), which would bias the realized Q 10 estimation in situ. Different from previous studies with a standardized and constant temperature (e.g., Coucheney et al, 2013; Fierer et al, 2006; Wang, Liu, Wang, et al, 2018; Zang et al, 2020), this study used a novel incubation method with periodically varying temperature based on the MAT of soil original site to quantify the biogeographic variation in N deposition effects on the Q 10 of SOC decomposition and reveal the underlying mechanisms. Therefore, we can report the response of SOC decomposition to temperature change in an ecologically realistic context (Li et al, 2020) and provide an improved estimation of Q 10 and its biogeographic response to N deposition across sites experiencing different temperatures.…”

“…Recently, the response of Q 10 to increased N input has generated increasing concern with respect to global warming and increasing N deposition scenarios, and some experiments at individual sites have been conducted (e.g., Coucheney, Strömgren, Lerch, & Herrmann, 2013; Mo et al, 2008; Wang, Liu, Wang, Tian, & Sun, 2018). However, no consensus on the effects of increased N input on Q 10 has been achieved (e.g., Hasselquist, Metcalfe, & Högberg, 2012; Li, Liu, Wu, Niu, & Tian, 2015; Wang, Liu, Wang, et al, 2018; Zang et al, 2020); this is partially attributed to differences in incubation methods and site characteristics such as climate and soil property. These individual studies conducted at specific sites are useful, but inconsistencies in incubation methods and site characteristics limit our ability to make robust generalizations of how Q 10 responds to elevated N input across broad geographic scales.…”

“…Most previous incubation studies on the N‐input effect on Q 10 used constant temperatures during the entire incubation period (e.g., Coucheney et al, 2013; Guo et al, 2017; Wang, Liu, Wang, et al, 2018; Zang et al, 2020). However, the estimation of Q 10 values at a constant temperature would bias the realized Q 10 in situ because of inaccuracy simulating real field conditions with general periodic and continuous change in soil temperature (Wang, Liu, & Tian, 2018).…”