Barbour Margaret M, Cernusak Lucas A, Whitehead David, Griffin Kevin L, Turnbull Matthew H, Tissue David T, Farquhar Graham D
Landcare Research, PO Box 69, Lincoln 8152, New Zealand.
Research School of Biological Sciences, Australian National University, GPO Box 475, ACT 2601, Australia.
Funct Plant Biol. 2006 Jan;32(12):1107-1121. doi: 10.1071/FP05118.
Variation in the oxygen isotope composition of within-canopy CO has potential to allow partitioning of the ecosystem respiratory flux into above- and below-ground components. Recent theoretical work has highlighted the sensitivity of the oxygen isotope composition of leaf-respired CO (δ) to nocturnal stomatal conductance. When the one-way flux model was tested on Ricinus communis L. large enrichments in δ were observed. However, most species for which the isotope flux partitioning technique has been or would be applied (i.e. temperate tree species) are much more conservative users of water than R. communis. So, high stomatal conductance and very high enrichment of δ observed may not be typical for temperate tree species. Using existing gas-exchange measurements on six temperate tree species, we demonstrate significant water loss through stomata for all species (i.e. statistically significantly greater than cuticular loss alone) at some time for some leaves during the night. δ values predicted by the one-way flux model revealed that δ might be very much more enriched than when the net flux alone is considered, particularly close to sunrise and sunset. Incorporation of the one-way flux model into ecosystem respiration partitioning studies will affect model outputs and interpretation of variation in the oxygen isotope composition of atmospheric CO.
冠层内 CO₂ 的氧同位素组成变化有可能将生态系统呼吸通量划分为地上和地下部分。最近的理论研究强调了叶片呼吸产生的 CO₂ 的氧同位素组成（δ）对夜间气孔导度的敏感性。当在蓖麻上测试单向通量模型时，观察到 δ 有很大程度的富集。然而，大多数已应用或将要应用同位素通量划分技术的物种（即温带树种）在水分利用方面比蓖麻保守得多。因此，观察到的高气孔导度和 δ 的极高富集可能并非温带树种的典型特征。利用对六种温带树种现有的气体交换测量数据，我们证明了在夜间的某些时候，所有物种的一些叶片通过气孔有显著的水分损失（即统计学上显著大于仅通过角质层的水分损失）。单向通量模型预测的 δ 值表明，δ 可能比仅考虑净通量时富集得多，特别是在接近日出和日落时。将单向通量模型纳入生态系统呼吸划分研究将影响模型输出以及对大气 CO₂ 氧同位素组成变化的解释。
