Data from: Sapwood capacitance is greater in evergreen sclerophyll species growing in high compared to low rainfall environments

1. The capacitative release of water from sapwood allows photosynthesis to continue for longer into dry periods, both diurnally and seasonally. However, costs of high capacitance include increased vulnerability to xylem cavitation. The degree of reliance on stored water is predicted to differ among environments as a result of this trade off 2. Xylem water potential and sapwood capacitance were measured on 32 evergreen sclerophyll shrub and tree species in eastern Australia, sampled from four sites contrasting in soil nutrients and rainfall. 3. Capacitance calculated over species’ typical shoot water potential operating range was 3-fold higher for species from high compared to low rainfall sites, and 1.5-fold higher for species from high compared to low nutrient sites. 4. To determine whether these site differences were related to extrinsic (e.g. water availability) or intrinsic (e.g. species anatomical construction) factors, we calculated capacitance at two common operating ranges; i.e. the mean range in water potential observed for low rainfall species (ΔΨlow rain) and the mean range for high rainfall species (ΔΨhigh rain). While no difference was seen between low and high rainfall species in release of stored water across ΔΨhigh rain, across ΔΨlow rain the high rainfall species released 38% more stored water than low rainfall species. Presumably these differences reflect underlying differences in anatomy, such as wood density, which was lower in high rainfall species. 5. These results accord with predictions that (i) species from wetter sites exhibit less negative stem water potentials and high sapwood capacitance, enabling them to maintain function under variable conditions characterized by many short, dry periods; while (ii) species from low rainfall sites have wood anatomies conferring tolerance to very low water potentials, with low sapwood capacitance, enabling them to survive longer through unpredictable and extended periods of low rainfall. The finding that the degree to which species rely on stem-stored water varies with site rainfall suggests that changes in drought regimes (e.g. incidence, duration and severity) under future climates could differentially affect species according to the capacitance properties of their woody tissues.1. 边材水容（sapwood capacitance）介导的释水过程可使光合作用在干旱时段（涵盖昼夜与季节尺度）得以延长维持。但高水容性存在相应代价：会提升木质部空穴化（xylem cavitation）的发生风险。基于这种权衡关系，不同生境下植物对贮藏水分的依赖程度预计存在差异。 2. 本研究针对澳大利亚东部的32种常绿硬叶灌木与乔木物种测定了木质部水势与边材水容，供试物种采自4个在土壤养分与降雨量方面存在显著差异的样地。 3. 在物种典型枝条水势工作范围内计算得到的边材水容，高降雨量样地物种较低降雨量样地物种高出3倍；高养分样地物种则较低养分样地物种高出1.5倍。 4. 为明确这类样地差异由外在因素（extrinsic，如水分可获得性）还是内在因素（intrinsic，如物种解剖结构）导致，我们在两种通用工作范围内计算了边材水容：即低降雨量物种观测到的平均水势变化范围（ΔΨlow rain），以及高降雨量物种的平均水势变化范围（ΔΨhigh rain）。在ΔΨhigh rain范围内，高低降雨量物种的贮藏水释放量无显著差异；但在ΔΨlow rain范围内，高降雨量物种的贮藏水释放量较低降雨量物种高出38%。推测这类差异反映了解剖结构的固有差异，例如木材密度——高降雨量物种的木材密度更低。 5. 本研究结果与两项预测相符：（i）湿润生境物种的茎干水势负值更小，且边材水容更高，使其可在以多次短期干旱为特征的多变环境中维持生理功能；（ii）低降雨量生境物种的木材解剖结构可耐受极低水势，且边材水容更低，使其可在不可预测的长期低降雨量时段中更久地存活。研究发现物种对茎贮藏水的依赖程度随样地降雨量发生变化，这意味着未来气候下干旱格局（如发生频率、持续时长与严重程度）的改变，可能会依据木本组织的水容特性对不同物种产生差异化影响。