Moderate grazing optimizes the allocation and microbial fate of recently assimilated carbon in an alpine grassland

doi:10.1093/jpe/rtag165

J Plant Ecol ›› Advance articles DOI:10.1093/jpe/rtag165

Moderate grazing optimizes the allocation and microbial fate of recently assimilated carbon in an alpine grassland

Mingxue Xiang^1,2, Junxi Wu^2,3*, Lha Duo³, Ben Niu², Ying Pan², Xianzhou Zhang^2,6*, Zhaoqi Wang¹, Xinquan Zhao¹, Yakov Kuzyakov^4,5

1 State Key Laboratory of Plateau Ecology and Agriculture, Qinghai University, Xining 810016, China;
2 Lhasa Plateau Ecosystem Research Station, Key Laboratory of Ecosystem Network Observation and Modeling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China;
3 School of Ecology and Environment, Tibet University, Lhasa 850000, China;
4 Department of Soil Science of Temperate Ecosystems, Department of Agricultural Soil Science, University of G?ettingen, 37077 G?ttingen, Germany;
5 Peoples Friendship University of Russia (RUDN University), 117198 Moscow, Russia;
6 College of Resources and Environment, University of Chinese Academy of Sciences, Beijing 101408, China
^*Corresponding author: wujx@igsnrr.ac.cn (J.W.); zhangxz@igsnrr.ac.cn (X.Z.).

Received:2026-01-14 Revised:2026-05-24 Accepted:2026-06-20 Published:2026-07-22
Supported by:
This work was supported by the National Natural Science Foundation of China (Grant No. 32501446), the Chief Scientist Program of Qinghai Province (Grant No. 2024-SF-102), the Tibet Autonomous Region Science and Technology Planning Project (Grant No. XZ202201ZY0016G), the National Key Research and Development Program of China (Grant No. 2021YFD1000303), the Second Tibetan Plateau Scientific Expedition and Research (STEP) Program (Grant No. 2019QZKK1002), and the RUDN University Strategic Academic Leadership Program.

中度放牧优化了高寒草地新近光合碳分配与微生物周转

Abstract

Abstract: Alpine grasslands are crucial carbon (C) reservoirs, facing strong disruptions from intensified grazing. However, how grazing intensity regulates the allocation of recently assimilated C belowground and its utilization by soil microorganisms remains uncertain. Using in-situ ¹³CO₂ pulse labeling in an alpine steppe, we compared the effects of non-grazing (NG), moderate grazing (MG), and heavy grazing (HG) on the allocation and cycling of recently assimilated C in shoots, roots, soil, and soil microorganisms. The initially assimilated ¹³C in shoots were highest under MG (245 mg C m^-2). Root δ¹³C peaks were also highest under MG (28.5 mg C m^-2), yet their mean residence time (MRT) was shortest (3.1 days), indicating rapid uptake and downward transport of newly fixed C through roots under MG. In contrast, HG delayed shoot δ¹³C peaks (to day 14) and produced the only pronounced soil δ¹³C peak (4‰), followed by a rapid decline, suggesting accelerated but short-lived belowground C allocation after severe defoliation. Despite phospholipid fatty acid (PLFA) profiles remaining stable, the share of ¹³C-PLFA held by Gram- positive bacteria increased from 30% to 40% under HG, indicating they became the dominant consumers of rhizodeposits. Besides, increasing grazing intensity exponentially shortened MRT across plant, soil, and microbial C pools. These results demonstrate that MG optimizes C allocation belowground and the microbial fate of plant-derived C, but HG accelerates plant-soil C fluxes and alters microbial consumer of rhizodeposits. Our study emphasizes the need to track where C flows and how long it resides in grazing grasslands.

Key words: alpine grassland, ¹³C pulse labeling, grazing intensity, PLFAs, Qinghai-Tibet Plateau

摘要：
高寒草地是重要的碳（C）库，正面临因放牧加剧而带来的强烈干扰。然而，放牧强度如何调控新近光合碳向地下的分配及其被微生物利用的过程，尚不清楚。本研究在高寒草地采用原位¹³CO₂脉冲标记技术，比较了禁牧（NG）、中度放牧（MG）和重度放牧（HG）对新近光合碳在植物茎叶、根系、土壤及土壤微生物中的分配与周转的影响。结果表明，茎叶最初固定的¹³C在中度放牧下最高（245 mg C m^-2）；根系δ¹³C峰值同样在中度放牧下最大（28.5 mg C m^-2），但其平均滞留时间（MRT）最短（3.1天），表明中度放牧下新近光合碳通过根系被快速吸收并向下运输。相比之下，重度放牧使茎叶中δ¹³C峰值延迟至第14天，且是唯一在土壤中产生明显δ¹³C峰值（4‰）的处理，随后该峰值迅速下降，这表明重度放牧后地下碳分配加速但持续时间短暂。尽管磷脂脂肪酸（ PLFA）的组成在各放牧强度间保持稳定，但重度放牧下革兰氏阳性菌所持有的¹³C-PLFA比例由30%提升至40%，表明其成为根际沉积物的主要消费者。此外，放牧强度的增加使植物、土壤和微生物碳库的MRT呈指数缩短。这些结果表明，中度放牧优化了地下碳分配及植物源碳在微生物间的利用，而重度放牧加速了植物–土壤碳通量并改变了根际沉积物的微生物消费格局。本研究强调了新近光合碳在不同放牧强度草地中流向何处及其滞留时间的重要性。

关键词: 高寒草地, ¹³C脉冲标记, 放牧强度, 磷脂脂肪酸, 青藏高原

Mingxue Xiang, Junxi Wu, Lha Duo, Ben Niu, Ying Pan, Xianzhou Zhang, Zhaoqi Wang, Xinquan Zhao, Yakov Kuzyakov. Moderate grazing optimizes the allocation and microbial fate of recently assimilated carbon in an alpine grassland[J]. J Plant Ecol, DOI: 10.1093/jpe/rtag165.

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Moderate grazing optimizes the allocation and microbial fate of recently assimilated carbon in an alpine grassland

中度放牧优化了高寒草地新近光合碳分配与微生物周转

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