Stutz Samantha S, Anderson Jeremiah, Zulick Rachael, Hanson David T
Department of Biology, University of New Mexico, MSC03-2020, 1 University of New Mexico, Albuquerque, NM 87131, USA.
J Exp Bot. 2017 May 17;68(11):2849-2857. doi: 10.1093/jxb/erx155.
High concentrations of inorganic carbon in the xylem, produced from root, stem, and branch respiration, travel via the transpiration stream and eventually exit the plant through distant tissues as CO2. Unlike previous studies that focused on the efflux of CO2 from roots and woody tissues, we focus on efflux from leaves and the potential effect on leaf respiration measurements. We labeled transported inorganic carbon, spanning reported xylem concentrations, with 13C and then manipulated transpiration rates in the dark in order to vary the rates of inorganic carbon supply to cut leaves from Brassica napus and Populus deltoides. We used tunable diode laser absorbance spectroscopy to directly measure the rate of gross 13CO2 efflux, derived from inorganic carbon supplied from outside of the leaf, relative to gross 12CO2 efflux generated from leaf cells. These experiemnts showed that 13CO2 efflux was dependent upon the rate of inorganic carbon supply to the leaf and the rate of transpiration. Our data show that the gross leaf efflux of xylem-transported CO2 is likely small in the dark when rates of transpiration are low. However, gross leaf efflux of xylem-transported CO2 could approach half the rate of leaf respiration in the light when transpiration rates and branch inorganic carbon concentrations are high, irrespective of the grossly different petiole morphologies in our experiment.
由根、茎和枝呼吸作用产生的木质部中高浓度无机碳，通过蒸腾流传输，最终以二氧化碳形式通过远处的组织排出植物体外。与以往专注于二氧化碳从根和木质组织流出的研究不同，我们关注的是叶片的流出以及对叶片呼吸测量的潜在影响。我们用13C标记了所传输的无机碳（涵盖已报道的木质部浓度范围），然后在黑暗中控制蒸腾速率，以改变供应给甘蓝型油菜和三角叶杨离体叶片的无机碳速率。我们使用可调谐二极管激光吸收光谱法直接测量相对于叶片细胞产生的总12CO2流出量而言，源自叶片外部供应的无机碳的总13CO2流出速率。这些实验表明，13CO2流出取决于供应给叶片的无机碳速率和蒸腾速率。我们的数据表明，在黑暗中当蒸腾速率较低时，木质部传输的二氧化碳的叶片总流出量可能较小。然而，当蒸腾速率和枝无机碳浓度较高时，无论我们实验中叶柄形态差异极大，木质部传输的二氧化碳的叶片总流出量在光照下可能接近叶片呼吸速率的一半。
