The effects of burning and grazing on soil carbon dynamics in managed Peruvian tropical montane grasslands
The effects of burning and grazing on soil carbon dynamics in managed Peruvian tropical montane grasslands
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DOI：
10.5194/bg-14-5633-2017
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发表时间：
2017-12
期刊：
影响因子：
4.9
通讯作者：
V. Oliver;I. Oliveras;J. Kala;R. Lever;Y. Teh
中科院分区：
文献类型：
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作者：
V. Oliver;I. Oliveras;J. Kala;R. Lever;Y. Teh
摘要。山地热带土壤是一个巨大的碳(C)储存库，既是二氧化碳的来源，也是二氧化碳的汇。二氧化碳排放量的增加在很大程度上源于人为干扰后土壤有机质（SOM）的分解和损失。因此，为了理解、评估和预测热带土地管理的影响，有必要定量了解土壤有机质的稳定和分解。特别是，不稳定的土壤有机质是土壤有机质如何响应土地利用和管理实践变化的早期敏感指标，这可能对长期碳储存和大气二氧化碳浓度上升产生重大影响。本研究的目的是调查放牧和火灾历史对秘鲁山地草原土壤C动态的影响，这是一个尚未得到充分研究的生态系统，覆盖了秘鲁约四分之一的土地面积。采用密度分馏法对土壤中稳定和不稳定的有机质库进行量化，并对土壤CO2通量和分解量进行量化。放牧和燃烧一起显著增加了土壤二氧化碳通量和分解率，并降低了作为驱动因素的温度。虽然不同土地利用方式对土壤总碳储量的影响不显著，但燃烧与放牧组合降低了自由光照部分（LF）中碳的比例，特别是在10-20 cm和20-30 cm的较低深度。在对照土壤中，20%的回收物质为游离LF，其含碳量占土壤碳含量的30%。与之相比，烧牧土壤的游离LF恢复最小（10%），C含量显著降低（14%）。与未烧焦的土壤（7%）相比，烧焦土壤在被封冻的LF中所占的C比例（12%）要高得多，而重组分(F)（~ 70%）在不同处理之间没有显著差异。燃烧和放牧的协同效应引起了土壤碳动态的变化。CO2通量增加，主要的温度驱动因子被植物C和N分配变化等其他过程所掩盖。此外，当这两种人为活动发生在同一地点时，游离LF减少-很可能是由于碎屑被纳入土壤的减少。本研究的一个积极发现是，土壤总碳储量没有受到显著影响，长期（+10年）碳储量在被封冻的LF和重F中没有受到负面影响。这可能是因为低强度的火灾，具有防火能力的草，因为放牧压力低于导致严重退化所需的阈值。
Abstract. Montane tropical soils are a large carbon (C) reservoir, acting as both a source and a sink of CO2. Enhanced CO2 emissions originate, in large part, from the decomposition and losses of soil organic matter (SOM) following anthropogenic disturbances. Therefore, quantitative knowledge of the stabilization and decomposition of SOM is necessary in order to understand, assess and predict the impact of land management in the tropics. In particular, labile SOM is an early and sensitive indicator of how SOM responds to changes in land use and management practices, which could have major implications for long-term carbon storage and rising atmospheric CO2 concentrations. The aim of this study was to investigate the impacts of grazing and fire history on soil C dynamics in the Peruvian montane grasslands, an understudied ecosystem, which covers approximately a quarter of the land area in Peru. A density fractionation method was used to quantify the labile and stable organic matter pools, along with soil CO2 flux and decomposition measurements. Grazing and burning together significantly increased soil CO2 fluxes and decomposition rates and reduced temperature as a driver. Although there was no significant effect of land use on total soil C stocks, the combination of burning and grazing decreased the proportion of C in the free light fraction (LF), especially at the lower depths (10–20 and 20–30 cm). In the control soils, 20 % of the material recovered was in the free LF, which contained 30 % of the soil C content. In comparison, the burnt–grazed soil had the smallest recovery of the free LF (10 %) and a significantly lower C content (14 %). The burnt soils had a much higher proportion of C in the occluded LF (12 %) compared to the not-burnt soils (7 %) and there was no significant difference among the treatments in the heavy fraction (F) ( ∼ 70 %). The synergistic effect of burning and grazing caused changes to the soil C dynamics. CO2 fluxes were increased and the dominant temperature driver was obscured by some other process, such as changes in plant C and N allocation. In addition, the free LF was reduced when these two anthropogenic activities took place on the same site – most likely a result of reduced detritus being incorporated into the soil. A positive finding from this study is that the total soil C stocks were not significantly affected and the long-term (+10 years) C storage in the occluded LF and heavy F were not negatively impacted. Possibly this is because of low-intensity fire, fire-resilient grasses and because the grazing pressure is below the threshold necessary to cause severe degradation.