School of Plant Biology and Centre of Excellence for Climate Change, Woodland & Forest Health, University of Western Australia, Crawley, WA, 6009, Australia; New Zealand Forest Research Institute (SCION), Te Papa Tipu Innovation Park, Rotorua, 3010, New Zealand.
Physiol Plant. 2014 Oct;152(2):301-15. doi: 10.1111/ppl.12170. Epub 2014 Mar 11.
Southwest Australian Banksia woodlands are highly diverse plant communities that are threatened by drought- or temperature-induced mortality due to the region's changing climate. We examined water relations in dominant Banksia menziesii R. Br. trees using magnetic leaf patch clamp pressure (ZIM-) probes that allow continuous, real-time monitoring of leaf water status. Multiple ZIM-probes across the crown were complemented by traditional ecophysiological measurements. During summer, early stomatal downregulation of transpiration prevented midday balancing pressures from exceeding 2.5 MPa. Diurnal patterns of ZIM-probe and pressure chamber readings agreed reasonably well, however, ZIM-probes recorded short-term dynamics, which are impossible to capture using a pressure chamber. Simultaneous recordings of three ZIM-probes evenly spaced along leaf laminas revealed intrafoliar turgor gradients, which, however, did not develop in a strictly basi- or acropetal fashion and varied with cardinal direction. Drought stress manifested as increasing daily signal amplitude (low leaf water status) and occasionally as rising baseline at night (delayed rehydration). These symptoms occurred more often locally than across the entire crown. Microclimate effects on leaf water status were strongest in crown regions experiencing peak morning radiation (East and North). Extreme spring temperatures preceded the sudden death of B. menziesii trees, suggesting a temperature- or humidity-related tipping point causing rapid hydraulic failure as evidenced by collapsing ZIM-probe readings from an affected tree. In a warmer and drier future, increased frequency of B. menziesii mortality will result in significantly altered community structure and ecosystem function.
西南澳大利亚 Banksia 林地是高度多样化的植物群落，由于该地区气候变化，干旱或高温导致死亡率上升，这些群落正受到威胁。我们使用磁叶贴压（ZIM-）探针检查了优势 Banksia menziesii R. Br. 树木的水分关系，这种探针允许对叶片水分状态进行连续实时监测。树冠上的多个 ZIM-探针与传统生态生理学测量方法相结合。在夏季，早期气孔蒸腾作用的下调防止了午间平衡压力超过 2.5 MPa。ZIM-探针和压力室读数的昼夜模式相当吻合，但 ZIM-探针记录了短时间内的动态变化，而使用压力室是不可能捕捉到这些变化的。均匀分布在叶片层上的三个 ZIM-探针的同时记录显示出叶片内膨压梯度，但这些梯度并没有以严格的基或顶部分化方式发展，并且随着 cardinal 方向而变化。干旱胁迫表现为每天信号幅度增加（叶片水分状况较低），偶尔在夜间出现基线上升（再水合延迟）。这些症状在局部比整个树冠更常见。叶片水分状况的小气候效应在经历早晨辐射峰值的树冠区域最强（东和北）。极端春季温度先于 B. menziesii 树木的突然死亡，这表明存在与温度或湿度相关的临界点，导致快速水力失效，这表现在受影响树木的 ZIM-探针读数崩溃。在一个更温暖和干燥的未来，B. menziesii 死亡率的增加将导致群落结构和生态系统功能发生显著变化。
