放牧可增加亚热带草原的地下碳分配，微生物生物量和土壤碳,Global Change Biology

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放牧可增加亚热带草原的地下碳分配，微生物生物量和土壤碳
Global Change Biology ( IF 10.8 ) Pub Date : 2018-02-24 , DOI: 10.1111/gcb.14070
Chris H. Wilson ₁ , Michael S. Strickland ₂ , Jack A. Hutchings ₃ , Thomas S. Bianchi ₃ , S. Luke Flory ₄

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尽管牧场和牧场对全球土壤有机碳（SOC）存量有很大贡献，但大型草食动物放牧对SOC的影响仍存在很大的不确定性，尤其是对亚热带牧场而言。众所周知，根系输入是大多数草地SOC的来源，但是与细根渗出相比，放牧对碳分配对根组织生产的分配的影响尚不清楚。鉴于根C的不同形式对SOC合成和分解具有不同的含义，因此这代表了知识上的重大空白。根系分泌物应主要在微生物同化后对SOC产生贡献，从而在稳定微生物坏死的基础上促进微生物对SOC的贡献，而根凋落物的沉积则是微生物分解后直接作为植物来源的SOC贡献的。在这里，我们使用了原位同位素脉冲追踪方法，并结合了植物和土壤采样，以将植物碳分配模式与美国佛罗里达亚热带牧场的长期放牧复制品中的SOC库联系起来。我们量化了碳在根组织中的分配，并测量了放牧和未耕作地块中的根系渗出量，并对木质素酚进行了量化，以评估微生物与植物产品对总SOC的相对贡献。我们发现，放牧排斥与地下总分配显着减少，根生物量，细根分泌物和微生物生物量较低有关。同时，放牧的草场的总SOC更高，SOC的较大部分源自植物组织的沉积，这表明放牧条件下较高的根凋落物沉积促进了更大的SOC。我们得出结论，放牧对SOC的影响取决于根系生物量，这种模式可能会推广到其他以C4为主的草原，特别是在亚热带。更好地理解根系生物量背后的生态因素可能是预测SOC和优化放牧管理以增强SOC积累的关键。

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Grazing enhances belowground carbon allocation, microbial biomass, and soil carbon in a subtropical grassland

Despite the large contribution of rangeland and pasture to global soil organic carbon (SOC) stocks, there is considerable uncertainty about the impact of large herbivore grazing on SOC, especially for understudied subtropical grazing lands. It is well known that root system inputs are the source of most grassland SOC, but the impact of grazing on partitioning of carbon allocation to root tissue production compared to fine root exudation is unclear. Given that different forms of root C have differing implications for SOC synthesis and decomposition, this represents a significant gap in knowledge. Root exudates should contribute to SOC primarily after microbial assimilation, and thus promote microbial contributions to SOC based on stabilization of microbial necromass, whereas root litter deposition contributes directly as plant‐derived SOC following microbial decomposition. Here, we used in situ isotope pulse‐chase methodology paired with plant and soil sampling to link plant carbon allocation patterns with SOC pools in replicated long‐term grazing exclosures in subtropical pasture in Florida, USA. We quantified allocation of carbon to root tissue and measured root exudation across grazed and ungrazed plots and quantified lignin phenols to assess the relative contribution of microbial vs. plant products to total SOC. We found that grazing exclusion was associated with dramatically less overall belowground allocation, with lower root biomass, fine root exudates, and microbial biomass. Concurrently, grazed pasture contained greater total SOC, and a larger fraction of SOC that originated from plant tissue deposition, suggesting that higher root litter deposition under grazing promotes greater SOC. We conclude that grazing effects on SOC depend on root system biomass, a pattern that may generalize to other C4‐dominated grasslands, especially in the subtropics. Improved understanding of ecological factors underlying root system biomass may be the key to forecasting SOC and optimizing grazing management to enhance SOC accumulation.

更新日期：2018-02-24

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