The kinetic characteristics of the main sources of ecosystem respiration are quite unknown, partly because of methodological constraints. Here, we present a new open-top chamber (OTC) apparatus for continuous 13C/12C labelling and measurement of ecosystem CO2 fluxes, and report the tracer kinetics of nighttime respiration of a temperate grassland. * The apparatus includes four dynamic flow-through OTCs, a unit mixing CO2-free air with 13C-depleted CO2, and a CO2 analyser and an online isotope ratio mass spectrometer. * The concentration (367 +/- 6.5 micromol mol(-1)) and carbon isotopic composition, delta13C, (-46.9 +/- 0.4 per thousand) of CO2 in the OTCs were stable during photosynthesis as a result of high air through flux and minimal incursion through the buffered vent. Soil CO2 efflux was not affected by pressure effects during respiration measurements. The labelling kinetics of respiratory CO2 measured in the field agreed with that of excised soil + vegetation blocks measured in a laboratory-based system. The kinetics fitted a two-source system (r(2) = 0.97), with a rapidly labelled source (half-life 2.6 d) supplying 48% of respiration, and the other source (52%) releasing no tracer during 14 d of labelling. * Of the two sources supplying ecosystem respiration, one was closely connected to current photosynthesis (approximately autotrophic respiration) and the other was provided by decomposition of structural plant biomass (approximately heterotrophic respiration).
摘要
生态系统呼吸的主要来源的动力学特征尚不完全清楚，部分原因是方法上的限制。在这里，我们提出了一种新的开顶式气室（OTC）装置，用于连续 13C/12C 标记和测量生态系统 CO2通量，并报告了温带草原夜间呼吸的示踪动力学。* 该装置包括四个动态流通 OTCs，一个将 13C 贫化 CO2 与 CO2 自由空气混合的单元，以及一个 CO2 分析仪和一个在线同位素比质谱仪。* 在光合作用过程中，由于高空气通量和最小缓冲通风入侵，OTC 中的 CO2 浓度（367 +/- 6.5 micromol mol(-1)) 和碳同位素组成，δ13C，（-46.9 +/- 0.4 per thousand) 保持稳定。在呼吸测量期间，土壤 CO2 逸出不受压力影响。在野外测量的呼吸 CO2 的标记动力学与在基于实验室的系统中测量的离体土壤+植被块的标记动力学一致。动力学符合双源系统（r(2) = 0.97)，其中快速标记源（半衰期 2.6 d）供应 48%的呼吸，而另一个源（52%）在 14 d 的标记期间不释放示踪剂。* 在供应生态系统呼吸的两个来源中，一个与当前光合作用密切相关（约为自养呼吸），另一个由结构性植物生物质分解提供（约为异养呼吸）。
