Subalpine grassland carbon balance during 7 years of increasedatmospheric N deposition
Subalpine grassland carbon balance during 7 years of increasedatmospheric N deposition
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DOI：
10.5194/bg-13-3807-2016
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发表时间：
2016-07
期刊：
影响因子：
4.9
通讯作者：
M. Volk;J. Enderle;S. Bassin
中科院分区：
文献类型：
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作者：
M. Volk;J. Enderle;S. Bassin
摘要。空气污染因子在影响大气CO2的生物汇时相互作用，例如草地生态系统的土壤有机碳（SOC）含量。有利于植物生产力的因素，如大气氮沉降，通常被认为有利于有机碳的储存。在N和o3沉降处理下，对亚高山草地进行了为期7年的碳通量和碳库测定。总氮沉降量分别为4、9、14、29和54 kg N ha−1 yr−1 （N4、N9等）；年平均植物毒性O3剂量分别为49、65和89 mmol m−2投影叶面积。我们假设在不同年份间，该成熟生态系统的有机碳在对照处理中不会发生变化，并且空气污染物对植物产量、净生态系统生产力（NEP）和有机碳含量的影响相似，导致有机碳含量随氮沉降而增加。累积植株产量表现出显著的N和N × N效应（N54 + 38%），而O3效应不显著。在对照处理中，SOC在7年内显著增加9%。累积NEP确实对N沉降表现出强烈的驼峰型响应模式，N14增加了62%，而N54只增加了39% （N效应统计上不显著，N × N相互作用不可检验）。SOC对N有相似但不显著的响应，在中等N沉积速率下，碳增益最高，表明其单峰响应具有边际（P = 0.09） N × N相互作用。我们假设强大的、与污染物无关的土壤碳汇是管理方式从放牧转变为砍伐的结果。氮沉降下有机碳和新土壤养分与植物产量相比的非平行响应可能是由于呼吸性有机碳损失增加，微生物氮限制或启动效应减轻，以及植物碳分配的转变导致根系碳输入减少。
Abstract. Air pollution agents interact when affecting biological sinks for atmospheric CO2, e.g., the soil organic carbon (SOC) content of grassland ecosystems. Factors favoring plant productivity, like atmospheric N deposition, are usually considered to favor SOC storage. In a 7-year experiment in subalpine grassland under N- and O3-deposition treatment, we examined C fluxes and pools. Total N deposition was 4, 9, 14, 29 and 54 kg N ha−1 yr−1 (N4, N9, etc.); annual mean phytotoxic O3 dose was 49, 65 and 89 mmol m−2 projected leaf area. We hypothesized that between years SOC of this mature ecosystem would not change in control treatments and that effects of air pollutants are similar for plant yield, net ecosystem productivity (NEP) and SOC content, leading to SOC content increasing with N deposition. Cumulative plant yield showed a significant N and N × N effect (+38 % in N54) but no O3 effect. In the control treatment SOC increased significantly by 9 % in 7 years. Cumulative NEP did show a strong, hump-shaped response pattern to N deposition with a +62 % increase in N14 and only +39 % increase in N54 (N effect statistically not significant, N × N interaction not testable). SOC had a similar but not significant response to N, with highest C gains at intermediate N deposition rates, suggesting a unimodal response with a marginal (P = 0.09) N × N interaction. We assume the strong, pollutant-independent soil C sink developed as a consequence of the management change from grazing to cutting. The non-parallel response of SOC and NEP compared to plant yield under N deposition is likely the result of increased respiratory SOC losses, following mitigated microbial N-limitation or priming effects, and a shift in plant C allocation leading to smaller C input from roots.