A field incubation approach to evaluate the depth dependence of soil biogeochemical responses to climate change

Abstract

Soil biogeochemical processes may present depth‐dependent responses to climate change, due to vertical environmental gradients (e.g., thermal and moisture regimes, and the quantity and quality of soil organic matter) along soil profile. However, it is a grand challenge to distinguish such depth dependence under field conditions. Here we present an innovative, cost‐effective and simple approach of field incubation of intact soil cores to explore such depth dependence. The approach adopts field incubation of two sets of intact soil cores: one incubated right‐side up (i.e., non‐inverted), and another upside down (i.e., inverted). This inversion keeps soil intact but changes the depth of the soil layer of same depth origin. Combining reciprocal translocation experiments to generate natural climate shift, we applied this incubation approach along a 2200 m elevational mountainous transect in southeast Tibetan Plateau. We measured soil respiration (Rs) from non‐inverted and inverted cores of 1 m deep, respectively, which were exchanged among and incubated at different elevations. The results indicated that Rs responds significantly (p < .05) to translocation‐induced climate shifts, but this response is depth‐independent. As the incubation proceeds, Rs from both non‐inverted and inverted cores become more sensitive to climate shifts, indicating higher vulnerability of persistent soil organic matter (SOM) to climate change than labile components, if labile substrates are assumed to be depleted with the proceeding of incubation. These results show in situ evidence that whole‐profile SOM mineralization is sensitive to climate change regardless of the depth location. Together with measurements of vertical physiochemical conditions, the inversion experiment can serve as an experimental platform to elucidate the depth dependence of the response of soil biogeochemical processes to climate change.

Carbon sequestration in the subsoil and the time required to stabilize carbon for climate change mitigation

“…Ahrens et al., 2020): the slow downward transport of carbon fractions that are either very recalcitrant or recurrently recycled by microbes (Elzein & Balesdent, 1995; Gleixner, 2013; Kaiser & Kalbitz, 2012; Roth et al., 2019); decreasing microbial activity along the profile (Jenkinson & Coleman, 2008; Koven et al., 2013; Persson et al., 2000; Wang et al., 2021), and the increasing role of organo–mineral associations with depth (Cotrufo & Lavallee, 2022; Eusterhues et al., 2003; Georgiou et al., 2022; Hicks Pries et al., 2023; Rasmussen et al., 2018; Rumpel & Kögel‐Knabner, 2011). The reason for this gradient is not fully understood yet and needs further exploration (Guo et al., 2023). It may be caused by the selective preservation of recalcitrant compounds combined with downward transport (Elzein & Balesdent, 1995; Luo et al., 2020) as well as nonlinear interactions among C fractions such as priming (Guenet et al., 2013; Liang et al., 2018; Wang et al., 2021).…”