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.

Usage Notes
Sapwood water potential, relative water content and cumulative water released from sapwood samples of 32 plant species measured in a thermocouple psychrometer and their wood densities.Richards_FuncEcol_DRYAD.xlsx

1. 木材韧皮部中水的电容性释放使得光合作用能够在干旱期间持续更长时间，无论是日间还是季节性。然而，高电容性带来的代价是增加了对木质部空洞化的敏感性。由于这种权衡，对储存水的依赖程度预计在不同环境中会有所差异。2. 在澳大利亚东部，对32种常绿硬叶灌木和树木物种的木质部水势和韧皮部电容进行了测量，这些物种分别来自四个土壤养分和降雨量不同的地点。3. 在物种典型枝条水势运行范围内计算出的电容，与高降雨量地点的物种相比，是低降雨量地点物种的3倍，与高养分地点的物种相比，是低养分地点物种的1.5倍。4. 为了确定这些地点差异是否与外在因素（例如水分可用性）或内在因素（例如物种解剖结构）相关，我们计算了两种常见的运行范围内的电容；即低降雨量物种观测到的平均水势范围（ΔΨlow rain）和高降雨量物种的平均水势范围（ΔΨhigh rain）。尽管在ΔΨhigh rain的储存水释放方面，低降雨量物种与高降雨量物种之间没有观察到差异，但在ΔΨlow rain的范围内，高降雨量物种释放的储存水比低降雨量物种多38%。这些差异可能反映了潜在的解剖学差异，例如木材密度，这在高降雨量物种中较低。5. 这些结果与预测相符：（i）潮湿地点的物种表现出更少的负茎水势和较高的韧皮部电容，这使得它们能够在许多短暂干旱的条件下维持功能；（ii）低降雨量地点的物种具有能够耐受极低水势的木材解剖结构，具有较低的韧皮部电容，这使得它们能够在不可预测的长期干旱期间存活更久。物种对茎部储存水的依赖程度随地点降雨量的变化而变化，这一发现表明，未来气候下的干旱期（例如发生频率、持续时间和严重程度）的变化可能会根据物种木质组织的电容特性而对物种产生不同的影响。