Interannual variability in carbon dioxide fluxes and flux-climate relationships on grazed and ungrazed northern mixed-grass prairie
Interannual variability in carbon dioxide fluxes and flux-climate relationships on grazed and ungrazed northern mixed-grass prairie
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DOI：
10.1111/j.1365-2486.2008.01599.x
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发表时间：
2008-07-01
影响因子：
11.6
通讯作者：
Phillips, Rebecca L.
中科院分区：
文献类型：
--
作者：
Polley, H. Wayne;Frank, Albert B.;Phillips, Rebecca L.
草地的年度碳(C)收支是高度动态的，取决于放牧历史和气候年际变化(IAV)对二氧化碳(CO2)通量的影响。气候驱动因素的可变性可能直接影响通量，但也可能通过改变生物群对环境的反应间接影响通量，这种效应被称为“功能变化”。测定了美国北达科他州放牧和非放牧混草草原5个生长季节的净生态系统CO2交换(NEE)及其昼夜生态系统CO2交换(P-D)和夜间呼吸(R-E)。我们的主要目标是确定气候异常如何影响二氧化碳交换的可变性。我们使用回归分析来区分气候中IAV对通量的直接影响和功能变化。功能变化被量化为对一个模型的回归的改进，在该模型中，通量-气候关系的斜率随年份变化，而不是保持不变。功能变化和气候变化的直接影响共同解释了NEE、P-D和R-E周平均值约20%的变化。功能变化占气候变异性直接影响通量变化的两倍以上。放牧并不一致地影响功能变化对通量变异性的贡献，但改变了最能解释通量-气候斜率年际差异的环境变量，降低了通量的季节平均值的IAV，减弱了通量-气候相关性的强度，并通过相对比P-D更大程度地降低R-E来增加NEE。这些趋势大多与放牧降低了植物对生态系统通量的影响的解释是一致的。由于通量周值和气候调节器之间的关系每年都会改变，仅凭气候方面的IAV知识不能预测这些生态系统碳平衡的年际差异。
The annual carbon (C) budget of grasslands is highly dynamic, dependent on grazing history and on effects of interannual variability (IAV) in climate on carbon dioxide (CO2) fluxes. Variability in climatic drivers may directly affect fluxes, but also may indirectly affect fluxes by altering the response of the biota to the environment, an effect termed 'functional change'. We measured net ecosystem exchange of CO2 (NEE) and its diurnal components, daytime ecosystem CO2 exchange (P-D) and night-time respiration (R-E), on grazed and ungrazed mixed-grass prairie in North Dakota, USA, for five growing seasons. Our primary objective was to determine how climatic anomalies influence variability in CO2 exchange. We used regression analysis to distinguish direct effects of IAV in climate on fluxes from functional change. Functional change was quantified as the improvement in regression on fitting a model in which slopes of flux-climate relationships vary among years rather than remain invariant. Functional change and direct effects of climatic variation together explained about 20% of variance in weekly means of NEE, P-D, and R-E. Functional change accounted for more than twice the variance in fluxes of direct effects of climatic variability. Grazing did not consistently influence the contribution of functional change to flux variability, but altered which environmental variable best explained year-to-year differences in flux-climate slopes, reduced IAV in seasonal means of fluxes, lessened the strength of flux-climate correlations, and increased NEE by reducing R-E relatively more than P-D. Most of these trends are consistent with the interpretation that grazing reduced the influence of plants on ecosystem fluxes. Because relationships between weekly values of fluxes and climatic regulators changed annually, year-to-year differences in the C balance of these ecosystems cannot be predicted from knowledge of IAV in climate alone.