Diurnal variation in mesophyll conductance and its influence on modelled water-use efficiency in a mature boreal Pinus sylvestris stand

作者：Zsofia R. Stangl, Lasse Tarvainen, Göran Wallin, Nerea Ubierna, Mats Räntfors, John D. Marshall · 发表于：Photosynthesis Research · 年份：2019 · DOI：10.1007/s11120-019-00645-6 · 被引用次数：66 · 研究领域：Plant Water Relations and Carbon Dynamics、Tree-ring climate responses、Plant responses to elevated CO2

Mesophyll conductance ( g m ) is a critical variable for the use of stable carbon isotopes to infer photosynthetic water-use efficiency (WUE). Although g m is similar in magnitude to stomatal conductance ( g s ), it has been measured less often, especially under field conditions and at high temporal resolution. We mounted an isotopic CO 2 analyser on a field photosynthetic gas exchange system to make continuous online measurements of gas exchange and photosynthetic 13 C discrimination (Δ 13 C) on mature Pinus sylvestris trees. This allowed the calculation of g m , g s , net photosynthesis ( A net ), and WUE. These measurements highlighted the asynchronous diurnal behaviour of g m and g s . While g s declined from around 10:00, A net declined first after 12:00, and g m remained near its maximum until 16:00. We suggest that high g m played a role in supporting an extended A net peak despite stomatal closure. Comparing three models to estimate WUE from ∆ 13 C, we found that a simple model, assuming constant net fractionation during carboxylation (27‰), predicted WUE well, but only for about 75% of the day. A more comprehensive model, accounting explicitly for g m and the effects of daytime respiration and photorespiration, gave reliable estimates of WUE, even in the early morning hours when WUE was more variable. Considering constant, finite g m or g m / g s yielded similar WUE estimates on the diurnal scale, while assuming infinite g m led to overestimation of WUE. These result...