Microbial activity and soil respiration under nitrogen addition in Alaskan boreal forest
Microbial activity and soil respiration under nitrogen addition in Alaskan boreal forest
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DOI：
10.1111/j.1365-2486.2008.01549.x
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发表时间：
2008-05-01
影响因子：
11.6
通讯作者：
Treseder, Kathleen K.
中科院分区：
文献类型：
--
作者：
Allison, Steven D.;Czimczik, Claudia I.;Treseder, Kathleen K.
气候变暖会增加土壤有机质周转和养分矿化的速率，特别是在北部高纬度生态系统。然而，人们对这些生态系统中养分供应增加对微生物过程的影响知之甚少。为了确定土壤微生物对养分增加的反应，我们测量了阿拉斯加中部北方森林中施氮土壤中的微生物生物量、胞外酶活性、土壤呼吸作用和活性真菌的群落组成。我们预测，与细菌相比，氮素的添加会抑制真菌的活性，但会刺激碳(C)降解酶的活性和土壤呼吸。相反，我们没有发现真菌活性受到抑制的证据，尽管真菌孢子果产量显著下降，而且两个真菌分类群的相对丰度随着施氮量的增加而发生显著变化。氯仿熏蒸测定的微生物生物量对受精没有反应，定量聚合酶链式反应测定的真菌与细菌的比率也没有反应。而施肥量C/N比值从16.0+/-1.4显著缩小到5.2+/-0.3。施氮显着增加了纤维素降解酶的活性，抑制了蛋白质和甲壳素降解酶的活性，但对土壤呼吸速率和C-14特征没有影响。这些结果表明，施氮改变了微生物群落组成和胞外酶的分配，而不影响土壤呼吸作用。因此，我们的结果没有提供证据表明，在气候变暖或氮添加下，微生物对北方C循环有强烈的反馈作用。然而，由于以含氮化合物为靶标的酶活性降低，有机氮循环可能会下降。
Climate warming could increase rates of soil organic matter turnover and nutrient mineralization, particularly in northern high-latitude ecosystems. However, the effects of increasing nutrient availability on microbial processes in these ecosystems are poorly understood. To determine how soil microbes respond to nutrient enrichment, we measured microbial biomass, extracellular enzyme activities, soil respiration, and the community composition of active fungi in nitrogen (N) fertilized soils of a boreal forest in central Alaska. We predicted that N addition would suppress fungal activity relative to bacteria, but stimulate carbon (C)-degrading enzyme activities and soil respiration. Instead, we found no evidence for a suppression of fungal activity, although fungal sporocarp production declined significantly, and the relative abundance of two fungal taxa changed dramatically with N fertilization. Microbial biomass as measured by chloroform fumigation did not respond to fertilization, nor did the ratio of fungi : bacteria as measured by quantitative polymerase chain reaction. However, microbial biomass C : N ratios narrowed significantly from 16.0 +/- 1.4 to 5.2 +/- 0.3 with fertilization. N fertilization significantly increased the activity of a cellulose-degrading enzyme and suppressed the activities of protein- and chitin-degrading enzymes but had no effect on soil respiration rates or C-14 signatures. These results indicate that N fertilization alters microbial community composition and allocation to extracellular enzyme production without affecting soil respiration. Thus, our results do not provide evidence for strong microbial feedbacks to the boreal C cycle under climate warming or N addition. However, organic N cycling may decline due to a reduction in the activity of enzymes that target nitrogenous compounds.