Augé Robert M, Toler Heather D, Sams Carl E, Nasim Ghazala
Department of Plant Sciences, University of Tennessee, Knoxville, TN 37996-4561, USA.
Mycorrhiza. 2008 Mar;18(3):115-21. doi: 10.1007/s00572-008-0162-9. Epub 2008 Jan 29.
Stomatal conductance (gs) and transpiration rates vary widely across plant species. Leaf hydraulic conductance (k leaf) tends to change with g (s), to maintain hydraulic homeostasis and prevent wide and potentially harmful fluctuations in transpiration-induced water potential gradients across the leaf (Delta Psi leaf). Because arbuscular mycorrhizal (AM) symbiosis often increases gs in the plant host, we tested whether the symbiosis affects leaf hydraulic homeostasis. Specifically, we tested whether k leaf changes with gs to maintain Delta Psi leaf or whether Delta Psi leaf differs when gs differs in AM and non-AM plants. Colonization of squash plants with Glomus intraradices resulted in increased gs relative to non-AM controls, by an average of 27% under amply watered, unstressed conditions. Stomatal conductance was similar in AM and non-AM plants with exposure to NaCl stress. Across all AM and NaCl treatments, k leaf did change in synchrony with gs (positive correlation of gs and k leaf), corroborating leaf tendency toward hydraulic homeostasis under varying rates of transpirational water loss. However, k leaf did not increase in AM plants to compensate for the higher gs of unstressed AM plants relative to non-AM plants. Consequently, Delta Psi leaf did tend to be higher in AM leaves. A trend toward slightly higher Delta Psi leaf has been observed recently in more highly evolved plant taxa having higher productivity. Higher Delta Psi leaf in leaves of mycorrhizal plants would therefore be consistent with the higher rates of gas exchange that often accompany mycorrhizal symbiosis and that are presumed to be necessary to supply the carbon needs of the fungal symbiont.
气孔导度（gs）和蒸腾速率在不同植物物种间差异很大。叶片水力导度（kleaf）往往会随gs变化，以维持水力稳态，并防止叶片蒸腾引起的水势梯度（ΔΨleaf）出现大幅且可能有害的波动。由于丛枝菌根（AM）共生通常会增加宿主植物的gs，我们测试了这种共生关系是否会影响叶片水力稳态。具体而言，我们测试了kleaf是否随gs变化以维持ΔΨleaf，或者当AM植物和非AM植物的gs不同时，ΔΨleaf是否存在差异。用根内球囊霉（Glomus intraradices）侵染南瓜植株，相对于非AM对照，在充分浇水、无胁迫条件下，gs平均增加了27%。在NaCl胁迫下，AM植物和非AM植物的气孔导度相似。在所有AM和NaCl处理中，kleaf确实与gs同步变化（gs和kleaf呈正相关），这证实了在不同蒸腾失水速率下叶片趋向于水力稳态的趋势。然而，AM植物的kleaf并没有增加，以补偿未受胁迫的AM植物相对于非AM植物更高的gs。因此，AM叶片中的ΔΨleaf往往更高。最近在生产力较高的进化程度更高的植物类群中观察到ΔΨleaf有略微升高的趋势。因此，菌根植物叶片中较高的ΔΨleaf与通常伴随菌根共生的较高气体交换速率一致，并且被认为是满足真菌共生体碳需求所必需的。
