Ecological Indicators：土壤微生物对土地利用变化和土壤资源可利用性的响应特征

中国科学院西双版纳热带植物园生态水文研究组博士后Singh Ashutosh Kumar团队测定了干旱热带环境下土壤微生物指数随土地利用变化（自然林、轮歇地、农田）、季节更替、土壤资源（C、N、P）可利用性的响应特征。相关成果发表于Ecological Indicators（IF=4.49）。

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Highlights

·Forest conversion to fallow and agriculture altered soil biological responses.

·Response of oxidative enzymes and specific enzyme activities were distinct from other variables.

·Seasonal differences in biological responses were consistent irrespective of LUC.

·Soil resources (C, N and P) were coupled with the majority of biological responses.

·Oxidative enzymes showed weaker coupling with these soil resources.

Abstract

Land use change (LUC) in tropics, explicitly from forest to conventional agriculture, is negatively affecting soil health and productivity. However, effect of such LUC on soil biological properties are poorly known in dry tropical environment. This study aimed to determine the impact of such LUC and climate seasonality on soil biological properties (microbial and enzyme activities), and to also explore the role of soil resources (C, N and P) in driving soil biological properties during this environmental change. Soil biological indicators of topsoil (0–15 cm) were measured on a seasonal basis in the natural forest, fallow and agricultural land. Soil microbial biomass C (C_mic), CO₂ efflux (C_efflux) and hydrolytic enzyme activities (acid phosphatase, alkaline phosphatase, β-glucosidase, dehydrogenase, fluorescein diacetate) were generally higher in the forest followed agriculture and fallow. The lower level of these biological variables in agriculture soils were possibly due to lower total soil organic carbon (SOC), labile SOC (particulate OC; POC), total N and P, and cropping disturbance (i.e., fertilization) induced higher inorganic N and P. Whereas, lower biological activities in fallow soils were mainly attributed lower plant activity (i.e. litter production and root activity). In contrast, oxidative enzyme (particularly peroxidase) activities were higher in agriculture followed by the forest and fallow, which might be attributed to higher soil oxygenation from tillage in agriculture and higher persistent SOC (non-particulate OC; NPOC). Seasonal variation in soil biological properties was identical among land uses, though its extent was greater in the forest than fallow and agriculture, indicating LUC can alter the degree of seasonality in biological properties. In addition, the higher specific enzyme activities (i.e., enzyme activities per unit of C_mic) and microbial metabolic quotient (qCO₂) in the fallow followed by agriculture and forest, indicating the higher degree of stress on soil microbes after the deforestation than cropping. Whereas, the higher specific enzyme activities and qCO₂ in agriculture possibly attributed to higher microbial nutrients demand and lower SOC accumulation. Collectively, our results reveal the significant effects of deforestation and agriculture on soil biological activities and improve our understanding of the potential mechanism driving these effects.

土壤是陆地生态系统的重要组成部分，它直接贡献了诸多生态服务功能，包括净初级生产力、气候和水分调节、养分循环与碳封存等，这种服务功能从根本上取决于地上植物群落、地下土壤微生物的多功能性发挥程度。因此，对地下土壤微生物过程的深入认知，将有助于制定合理有效的土地利用和管理措施、充分发挥生态系统的服务功能。然而，对干旱热带环境下土地利用变化导致的土壤生物响应尚不明确。

为此，中国科学院西双版纳热带植物园生态水文研究组博士后Singh Ashutosh Kumar测定了干旱热带环境下土壤微生物指数随土地利用变化（自然林、轮歇地、农田）、季节更替、土壤资源（C、N、P）可利用性的响应特征。研究结果表明：土壤微生物生物量碳、二氧化碳释放量（C_efflux）、水解酶活性（磷酸酶、β-葡萄糖苷酶、脱氢酶、荧光素二乙酸酯）对土地利用变化的反应非常敏感，敏感顺序是自然林> 农田> 轮歇地，这与农田较低的有机碳（SOC、OC、POC）、总氮和磷及耕作施肥引起的高无机氮和磷有关，而轮歇地较低的土壤微生物活动则与其较低的枯落物量和根系有关。氧化酶活性（酚氧化酶、过氧化物酶）则是农田>自然林>轮歇地，这与农田耕作导致的土壤高氧化、高持续有机碳（NPOC）有关。季节变化对不同土地利用类型土壤微生物指数的影响大致相似，其中以自然林的变化最大，表明土壤微生物对多年生植物响应的重要性。在不同土地利用类型中，轮歇地的单位土壤微生物指数和微生物代谢率（qCO₂）最高。以上结果表明，森林砍伐后土壤微生物受到的胁迫压力最大，而农业活动对土壤微生物活性的影响最显著。