Divecha Centre for Climate Change, Indian Institute of Science, Bangalore 560012, India.
Centre for Ecological Sciences, Indian Institute of Science, Bangalore 560012, India.
Proc Natl Acad Sci U S A. 2022 Oct 25;119(43):e2211317119. doi: 10.1073/pnas.2211317119. Epub 2022 Oct 17.
Grazing by mammalian herbivores can be a climate mitigation strategy as it influences the size and stability of a large soil carbon (soil-C) pool (more than 500 Pg C in the world's grasslands, steppes, and savannas). With continuing declines in the numbers of large mammalian herbivores, the resultant loss in grazer functions can be consequential for this soil-C pool and ultimately for the global carbon cycle. While herbivore effects on the size of the soil-C pool and the conditions under which they lead to gain or loss in soil-C are becoming increasingly clear, their effect on the equally important aspect of stability of soil-C remains unknown. We used a replicated long-term field experiment in the Trans-Himalayan grazing ecosystem to evaluate the consequences of herbivore exclusion on interannual fluctuations in soil-C (2006 to 2021). Interannual fluctuations in soil-C and soil-N were 30 to 40% higher after herbivore exclusion than under grazing. Structural equation modeling suggested that grazing appears to mediate the stabilizing versus destabilizing influences of nitrogen (N) on soil-C. This may explain why N addition stimulates soil-C loss in the absence of herbivores around the world. Herbivore loss, and the consequent decline in grazer functions, can therefore undermine the stability of soil-C. Soil-C is not inert but a very dynamic pool. It can provide nature-based climate solutions by conserving and restoring a functional role of large mammalian herbivores that extends to the stoichiometric coupling between soil-C and soil-N.
食草哺乳动物的放牧可以作为一种气候缓解策略，因为它影响着一个大型土壤碳（世界草地、草原和热带稀树草原中超过 500 皮克碳）库的大小和稳定性。随着大型食草哺乳动物数量的持续减少，食草动物功能的丧失可能对这个土壤碳库，最终对全球碳循环产生重大影响。虽然食草动物对土壤碳库大小的影响以及它们导致土壤碳增加或减少的条件越来越清楚，但它们对土壤碳同样重要的稳定性方面的影响仍然未知。我们使用跨喜马拉雅放牧生态系统中的一个复制的长期野外实验来评估食草动物排除对土壤碳年际波动的影响（2006 年至 2021 年）。与放牧相比，土壤碳和氮的年际波动在食草动物排除后增加了 30%至 40%。结构方程模型表明，放牧似乎调节了氮对土壤碳的稳定和不稳定影响。这也许可以解释为什么在没有世界各地的食草动物的情况下，氮的添加会刺激土壤碳的损失。因此，食草动物的减少，以及随之而来的食草动物功能的下降，可能会破坏土壤碳的稳定性。土壤碳不是惰性的，而是一个非常活跃的库。它可以通过保护和恢复大型食草哺乳动物的功能作用来提供基于自然的气候解决方案，这种作用延伸到土壤碳和土壤氮之间的化学计量耦合。
