Interannual, seasonal, and diel variability in the carbon isotope composition of respiration in a C3/C4 agricultural ecosystem
Interannual, seasonal, and diel variability in the carbon isotope composition of respiration in a C3/C4 agricultural ecosystem
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DOI：
10.1016/j.agrformet.2011.09.018
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发表时间：
2012-02
影响因子：
6.2
通讯作者：
J. Fassbinder;T. Griffis;J. Baker
中科院分区：
文献类型：
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作者：
J. Fassbinder;T. Griffis;J. Baker
稳定碳同位素比值，CO 132/CO 122，是研究生态系统呼吸的自养（FRa）和异养（FRh）过程以及光合作用对呼吸的影响的重要示踪剂。因为它包含了呼吸源的信息，是使用稳定同位素方法划分净生态系统CO2交换的重要参数。本研究利用涡度相关、通量梯度、自动化箱和稳定碳同位素技术对C3/C4农业生态系统中FR和δ R的时间变化进行了定量分析，并进一步加深了对这一变化的理解。6年（2004-2009年）的同位素通量梯度测量表明，由于FRa的显著贡献，δ R在C3（大豆）和C4（玉米）生长季具有非常一致的年变化模式，FRa受近期光合产物同位素组成的强烈影响。而在春季，无论上一季种植何种作物，δ R均表现为C3信号。这种异常的一个假设是，在这些低土壤温度下，微生物活性主要依赖于C3底物。在2009年玉米生长季节早期，开始了土壤呼吸（[公式：见正文]）及其同位素组成（[公式：见正文]）的自动室测量，以帮助解释δR的变化。这些测量结果与EC测量的FR（在0.5μ molm 2s −1以内）和同位素通量梯度测量的δR（在2‰以内）在夜间接近裸露土壤条件下（LAI<0.1）的结果吻合良好。在生长高峰期，玉米冠层上方的夜间δ R始终比[公式：见正文]高1-6‰。冠层上方相对富集的信号表明δ R受地上植物呼吸（FR，ag）的强烈影响，约占FR的40%。自动箱数据和分析还揭示了[公式：见正文]中的强昼夜模式。在生长早期，[公式：见正文]显示上午急剧富集高达4‰，然后在整个下午和晚上逐渐耗尽。[公式：见文字]的日间富集在干燥条件下最为明显，而当上层土壤接近饱和时则未观察到。我们提供的轶事证据表明，在早期生长的昼夜变化可能受到湍流（平流/非扩散运输），减少了动力分馏效应的影响。在生长高峰期，有证据表明，玉米植株的遮蔽作用减少了湍流对[公式：见正文]的室测量的影响。需要进一步的研究来评估和区分生物和非生物（平流和非稳态效应）对电离室观测结果的影响。
The stable carbon isotope ratio, CO132/CO122, is a valuable tracer for studying the processes controlling the autotrophic (FRa) and heterotrophic (FRh) contributions to ecosystem respiration (FR) and the influence of photosynthesis on FR. There is increasing interest in quantifying the temporal variability of the carbon isotope composition of ecosystem respiration (δR) because it contains information about the sources contributing to respiration and is an important parameter used for partitioning net ecosystem CO2exchange using stable isotope methods. In this study, eddy covariance, flux gradient, automated chambers, and stable carbon isotope techniques were used to quantify and improve our understanding of the temporal variability in FRand δRin a C3/C4agricultural ecosystem. Six years (2004–2009) of isotope flux-gradient measurements indicated that δRhad a very consistent annual pattern during both C3(soybean) and C4(corn) growing seasons due to significant contributions from FRa, which was strongly influenced by the isotope composition of the recent photosynthate. However, in the spring, δRexhibited a C3signal regardless of the crop grown in the previous season. One hypothesis for this anomaly is that at these low soil temperatures microbial activity relied predominantly on C3substrates. Automated chamber measurements of soil respiration ( [Formula: see text] ) and its isotope composition ( [Formula: see text] ) were initiated in the early corn growing season of 2009 to help interpret the variability in δR. These measurements showed good agreement with EC measurements of FR(within 0.5μmolm2s−1) and isotope flux gradient measurements of δR(within 2‰) at nighttime for near-bare soil conditions (LAI<0.1). At peak growth, nighttime δRabove the corn canopy was consistently 1–6‰ more enriched than [Formula: see text] . The relatively enriched signal above the canopy indicates that δRwas strongly influenced by aboveground plant respiration (FR,ag), which accounted for about 40% of FR. The automated chamber data and analyses also revealed a strong diel pattern in [Formula: see text] . In the early growth period, [Formula: see text] showed a sharp morning enrichment of up to 4‰ followed by a gradual depletion throughout the afternoon and evening. Daytime enrichment in [Formula: see text] was most pronounced during dry conditions and was not observed when the upper soil was near saturation. We provide anecdotal evidence that the diel variability during early growth may have been influenced by turbulence (advection/non-diffusive transport), which reduced the kinetic fractionation effect. At peak growth, there is evidence that the sheltering effect of the corn plants diminished the influence of turbulence on the chamber measurement of [Formula: see text] . Further research is needed to evaluate and separate the contributions of biotic and abiotic (advection and non-steady state effects) influences on chamber [Formula: see text] observations.