Binks Oliver, Cernusak Lucas A, Liddell Michael, Bradford Matt, Coughlin Ingrid, Carle Hannah, Bryant Callum, Dunn Elliot, Oliveira Rafael, Mencuccini Maurizio, Meir Patrick
Research School of Biology, The Australian National University, Canberra, ACT, 2601, Australia.
Centre for Tropical Environmental and Sustainability Science, College of Science and Engineering, James Cook University, Cairns, Qld, 4878, Australia.
New Phytol. 2022 Feb;233(4):1667-1681. doi: 10.1111/nph.17895. Epub 2021 Dec 20.
Soil-leaf hydraulic conductance determines canopy-atmosphere coupling in vegetation models, but it is typically derived from ex-situ measurements of stem segments and soil samples. Using a novel approach, we derive robust in-situ estimates for whole-tree conductance (k ), 'functional' soil conductance (k ), and 'system' conductance (k , water table to canopy), at two climatically different tropical rainforest sites. Hydraulic 'functional rooting depth', determined for each tree using profiles of soil water potential (Ψ ) and sap flux data, enabled a robust determination of k and k . k was compared across species, size classes, seasons, height above nearest drainage (HAND), two field sites, and to alternative representations of k ; k was analysed with respect to variations in site, season and HAND. k was lower and changed seasonally at the site with higher vapour pressure deficit (VPD) and rainfall; k differed little across species but scaled with tree circumference; r (1/k ) ranged from 0 in the wet season to 10× less than r (1/k ) in the dry season. VPD and not rainfall may influence plot-level k; leaf water potentials and sap flux can be used to determine k , k and k ; Ψ profiles can provide mechanistic insights into ecosystem-level water fluxes.
土壤-叶片水力传导率决定了植被模型中的冠层-大气耦合，但它通常源自对茎段和土壤样本的异地测量。我们采用一种新方法，在两个气候不同的热带雨林站点，对整棵树的传导率（k）、“功能性”土壤传导率（k）和“系统”传导率（k，从地下水位到冠层）进行了可靠的原位估算。利用土壤水势（Ψ）剖面和液流通量数据为每棵树确定的水力“功能性生根深度”，实现了对k和k的可靠测定。我们比较了不同物种、大小等级、季节、距最近排水点的高度（HAND）、两个野外站点的k，并与k的其他表示形式进行了比较；分析了k在站点、季节和HAND方面的变化。在水汽压差（VPD）和降雨量较高的站点，k较低且随季节变化；k在不同物种间差异不大，但与树周长成比例；r（1/k）在雨季为0，在旱季比r（1/k）小10倍。可能是VPD而非降雨量影响样地尺度的k；叶水势和液流通量可用于确定k、k和k；Ψ剖面可为生态系统水平的水流通量提供机理性见解。
