Shrubification decreases soil organic carbon mineralization and its temperature sensitivity in alpine meadow soils

• Published in: Soil biology & biochemistry Vol. 168; p. 108651
• Main Authors: Jia, Bin, Jia, Li, Mou, Xiao Ming, Chen, Jie, Li, Fen-Can, Ma, Qiu-jin, Li, Xiao Gang
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.05.2022
• Subjects: Grasslands; Microbial necromass; Non-cellulosic carbohydrates; Shrubification; Soil organic matter decomposition; Temperature sensitivity; Soil organic matter decomposition; Grasslands; Microbial necromass; Shrubification; Temperature sensitivity; Non-cellulosic carbohydrates
• ISSN: 0038-0717; 1879-3428
• DOI: 10.1016/j.soilbio.2022.108651

Shrubification is widespread in global grasslands. However, whether shrubification promotes the mineralization of soil organic carbon (SOC) remains uncertain. We compared sizes and compositions of soil non-cellulosic and amino sugar pools, soil stoichiometry, SOC decomposition and its temperature sensitivity between herbaceous and shrubby patches in alpine meadows on the Qinghai-Tibetan Plateau. The SOC content and soil stoichiometric C/P and N/P ratios in shrubby patches markedly increased with increasing plant size compared with herbaceous areas, indicating the increased P limitation to microorganisms relative to C and N with SOC accumulation under shrubs. The mass ratio of galactose plus mannose to arabinose plus xylose in the non-cellulosic carbohydrate pool of plant input was higher under shrubs than under grasses but was generally similar in soils between herbaceous and shrubby patches. This suggests the retarded microbial transformation of plant-derived carbohydrates under shrubs. Shrubs decreased accumulation of microbial necromass in SOC but increased the proportion of fungal origin in the microbial necromass. Lower total CO2 efflux per unit mass of SOC at either 15 °C or 25 °C from shrubby than from herbaceous patches over the 76-day incubation was mainly associated with the increased soil C/P or N/P ratio under shrubs. Shrubs decreased temperature sensitivity of SOC decomposition compared with grasses only at 20–40 cm soil depth, where microbial-synthesized substances had greater dominance over organic matter than at 0–20 cm depth and were less abundant under shrubs relative to grasses. Our findings show that increased P limitation to microorganisms in shrubification resulted in the decreased SOC decomposability and indicate that microbial-synthesized substances determined the temperature sensitivity of SOC mineralization. Therefore, shrubification mitigates CO2 emissions in grasslands by decreasing SOC mineralization and its temperature sensitivity in the context of global warming. •Soil C/P and N/P ratios markedly increase with increasing plant size.•Shrubs retard microbial transformation of plant residues compared with grasses.•Shrubs decrease microbial necromass accumulation in SOM compared with grasses.•Increasing P limitation by shrubification reduces SOM decomposition.•Smaller microbial necromass in SOM under shrubs lowers decomposition temperature sensitivity.