High microbial diversity stabilizes the responses of soil organic carbon decomposition to warming in the subsoil on the Tibetan Plateau

Abstract

Soil microbes are directly involved in soil organic carbon (SOC) decomposition, yet the importance of microbial biodiversity in regulating the temperature sensitivity of SOC decomposition remains elusive, particularly in alpine regions where climate change is predicted to strongly affect SOC dynamics and ecosystem stability. Here we collected topsoil and subsoil samples along an elevational gradient on the southeastern Tibetan Plateau to explore the temperature sensitivity (Q10) of SOC decomposition in relation to changes in microbial communities. Specifically, we tested whether the decomposition of SOC would be more sensitive to warming when microbial diversity is low. The estimated Q10 value ranged from 1.28 to 1.68, and 1.80 to 2.10 in the topsoil and subsoil, respectively. The highest Q10 value was observed at the lowest altitude of forests in the topsoil, and at the highest altitude of alpine meadow in the subsoil. Variations in Q10 were closely related to changes in microbial properties. In the topsoil the ratio of gram‐positive to gram‐negative bacteria (G+:G−) was the predominant factor associated with the altitudinal variations in Q10. In the subsoil, SOC decomposition showed more resilience to warming when the diversity of soil bacteria (both whole community and major groups) and fungi was higher. Our results partly support the positive biodiversity‐ecosystem stability hypothesis. Structural equation modeling further indicates that variations in Q10 in the subsoil were directly related to changes in microbial diversity and community composition, which were affected by soil pH. Collectively our results provide compelling evidence that microbial biodiversity plays an important role in stabilizing SOC decomposition in the subsoil of alpine montane ecosystems. Conservation of belowground biodiversity is therefore of great importance in maintaining the stability of ecosystem processes under climate change in high‐elevation regions of the Tibetan Plateau.

Soil Organic Carbon Mineralization and its Temperature Sensitivity Along a Vegetation Restoration Gradient in Subtropical China

“…In a modeling study,Moyano et al (2012) showed that the decomposition of SOC response to moisture depends on soil properties. Thus, these results also partly support the positive biodiversity-ecosystem stability hypothesis(Xu et al 2021).…”

“…Soil microbial biomass C (MBC), dissolved organic C (DOC), microbial community composition and evolved CO 2 -C were measured throughout the incubation. On the basis of our knowledge, we predicted that (1) greater SOC mineralization would be found with vegetation restoration age; (2) increased soil moisture and temperature would enhance SOC mineralization in all vegetation restoration stages; (3) lower Q 10 would be found with vegetation restoration age, but soil moisture would have a less effect on Q 10 in the SFS than that in the DS, due to soils with longer vegetation restoration years always have a greater biodiversity and might be more adaptive to changes in environmental conditions such as soil moisture (Yang et al 2018;Xu et al 2021).…”

“…But, due to higher labile SOC in the forest plantation which supported larger populations of soil microbes, Huang et al (2019) found that SOC mineralization was greater in the plantation forest than in the natural forest. The effects of soil properties on the Q 10 of SOC mineralization are also highly inconsistent (Wang et al 2019;Li et al 2021;Xu et al 2021). It was shown that the ratio of actinomycetes to bacteria (Liu et al 2017) and fungal phospholipid fatty acid (Qin et al 2019) were positively correlated with Q 10 , whereas the abundance of gram-negative bacteria decreased with the increasing Q 10 (Wang et al 2018).…”

Kinetic Properties of Microbial Exoenzymes Vary with Soil Depth but Have Similar Temperature Sensitivities Through the Soil Profile

“…Consequently, temperature can directly affect relative substrate depolymerization and nutrient acquisition potential, effectively decoupling enzyme relative activities from other regulatory factors, such as nutrient demand and substrate availability. Although microbial trait spaces are not static, as microbiomes adapt to changing conditions, they are likely to constrain both immediate responses and the trajectory of longer-term responses to environmental changes (Bradford, 2013;Conant et al, 2011;Xu et al, 2021). Therefore, it is essential to identify and validate key microbial traits and their environmental constraints in order to build a mechanistic understanding that can be generalized across spatiotemporal scales, and combine theory, measurements and models to improve the representation of microbial processes in Earth system models (Blankinship et al, 2018;Wieder et al, 2015).…”

“…Moreover, optimal enzyme temperatures are broadly correlated with the optimal growth temperatures of their organisms, as well as with the frequency of specific metabolic pathways, reflecting a concerted evolutionary adaptation to temperature and associated selective pressures (Engqvist, 2018;Somero, 2004). Therefore, variation in substrate and temperature regimes through the soil profile is likely to select for microbiomes producing enzymes with distinct kinetic and thermal properties, which may impose depth-dependent constraints on SOM turnover and responses to warming (Allison and Treseder, 2008;Carrillo et al, 2018;Cavicchioli et al, 2019;Isobe et al, 2019;Nunan et al, 2020;Xu et al, 2021). Microbial community composition and functional potential have indeed been shown to vary strongly with soil depth, reflecting selective adaptation to distinct niches (Blume et al, 2002;Brewer et al, 2019;Diamond et al, 2019;Dove et al, 2021;Eilers et al, 2012;Fierer et al, 2003b;Hansel et al, 2008;Hartmann et al, 2009;Jiao et al, 2018;Liu et al, 2019;Turner et al, 2017;Yan et al, 2019;Zosso et al, 2021).…”