School of Biological Sciences, The University of Western Australia, Crawley, Australia; Earth Observation Group, Astron Environmental Services, East Perth, Australia.
School of Agriculture and Environment, The University of Western Australia, Crawley, Australia.
Sci Total Environ. 2022 Aug 15;834:155395. doi: 10.1016/j.scitotenv.2022.155395. Epub 2022 Apr 20.
Our understanding of how water dynamics determines the probability of tree mortality during drought is incomplete. Here we help address this shortcoming by coupling approaches from the disciplines of ecophysiology, geophysics and remote sensing in a woodland ecosystem undergoing protracted drying. Water uptake and use strategies varied between the dominant canopy species of the ecosystem. At one extreme were species that tightly regulate their water status, which is broadly consistent with the definition of isohydry. The higher leaf temperatures revealed by thermal imagery of these isohydric species are likely a reflection of reduced latent cooling owing to a stringent control of transpiration rate. Where silty sediments occur in the root zone, this strategy may have the effect of limiting the water sources available to these species during prolonged drought because of an insufficient hydraulic gradient for water uptake. In contrast were species that allowed their water status to fluctuate, operating in a fashion more consistent with anisohydry. For these species, latent cooling owing to relatively high transpiration rates maintained leaf temperatures near, or below, the ambient air temperature. The resulting drawdown in leaf water potential between soil and leaves in these anisohydric species may generate a sufficient hydraulic gradient to enable water uptake from silty soil during seasonal or prolonged droughts. In this way the spatial distribution of fine textured soil could indicate areas where the isohydric hydraulic control strategy is disadvantageous during prolonged droughts or where annual soil water recharge has fallen below a critical threshold.
我们对水分动态如何决定树木在干旱期间死亡的概率的理解并不完整。在这里，我们通过将生态生理学、地球物理学和遥感学的方法结合在一个经历长期干旱的林地生态系统中，来帮助解决这一不足。水分吸收和利用策略因生态系统的主要冠层物种而异。一种极端情况是那些严格调节自身水分状况的物种，这与等水合的定义大致一致。这些等水合物种的叶片温度较高，可能是由于蒸腾速率严格控制导致潜在冷却减少的反映。在根系区存在粉土沉积物的情况下，由于吸水的水力梯度不足，这种策略可能会限制这些物种在长时间干旱期间可用的水源，因为粉土沉积物的水力梯度不足。相比之下，允许自身水分状况波动的物种，其运作方式更符合非等水合的特点。对于这些物种，由于相对较高的蒸腾速率导致的潜在冷却使叶片温度接近或低于环境空气温度。在这些非等水合物种中，叶片水势在土壤和叶片之间的下降可能会产生足够的水力梯度，从而能够在季节性或长时间干旱期间从粉土中吸水。这样，细质地土壤的空间分布可以指示在长时间干旱期间等水合水力控制策略不利的区域，或者年土壤水分补给已经低于临界阈值的区域。
