Gong Xiao Ying, Schäufele Rudi, Feneis Wolfgang, Schnyder Hans
Lehrstuhl für Grünlandlehre, Technische Universität München, 85354, Freising, Germany.
Plant Cell Environ. 2015 Nov;38(11):2417-32. doi: 10.1111/pce.12564. Epub 2015 Jun 25.
Leaks and isotopic disequilibria represent potential errors and artefacts during combined measurements of gas exchange and carbon isotope discrimination (Δ). This paper presents new protocols to quantify, minimize, and correct such phenomena. We performed experiments with gradients of CO2 concentration (up to ±250 μmol mol(-1) ) and δ(13) CCO2 (34‰), between a clamp-on leaf cuvette (LI-6400) and surrounding air, to assess (1) leak coefficients for CO2 , (12) CO2 , and (13) CO2 with the empty cuvette and with intact leaves of Holcus lanatus (C3 ) or Sorghum bicolor (C4 ) in the cuvette; and (2) isotopic disequilibria between net photosynthesis and dark respiration in light. Leak coefficients were virtually identical for (12) CO2 and (13) CO2 , but ∼8 times higher with leaves in the cuvette. Leaks generated errors on Δ up to 6‰ for H. lanatus and 2‰ for S. bicolor in full light; isotopic disequilibria produced similar variation of Δ. Leak errors in Δ in darkness were much larger due to small biological : leak flux ratios. Leak artefacts were fully corrected with leak coefficients determined on the same leaves as Δ measurements. Analysis of isotopic disequilibria enabled partitioning of net photosynthesis and dark respiration, and indicated inhibitions of dark respiration in full light (H. lanatus: 14%, S. bicolor: 58%).
在气体交换和碳同位素分馏（Δ）的联合测量过程中，泄漏和同位素不平衡代表了潜在的误差和假象。本文提出了量化、最小化和校正此类现象的新方案。我们在夹式叶室（LI-6400）与周围空气之间设置了二氧化碳浓度（高达±250 μmol mol⁻¹）和δ¹³CCO₂（34‰）梯度进行实验，以评估：（1）空叶室以及叶室内有羊茅（C₃）或双色高粱（C₄）完整叶片时，二氧化碳、¹²CO₂和¹³CO₂的泄漏系数；（2）光照条件下净光合作用与暗呼吸之间的同位素不平衡。¹²CO₂和¹³CO₂的泄漏系数实际上是相同的，但叶室内有叶片时的泄漏系数约高8倍。在全光照条件下，泄漏对羊茅的Δ产生高达6‰的误差，对双色高粱产生2‰的误差；同位素不平衡导致Δ产生类似的变化。由于生物通量与泄漏通量之比小，黑暗中Δ的泄漏误差要大得多。利用与Δ测量相同叶片上测定的泄漏系数可完全校正泄漏假象。对同位素不平衡的分析能够区分净光合作用和暗呼吸，并表明全光照下暗呼吸受到抑制（羊茅：14%；双色高粱：58%）。
