Tasmanian Institute of Agriculture, University of Tasmania, Private Bag 54, Hobart, Tasmania 7001, Australia.
Tree Physiol. 2012 Aug;32(8):958-67. doi: 10.1093/treephys/tps066.
Increased climatic variability, including extended periods of drought stress, may compromise on the health of forest ecosystems. The effects of defoliating pests on plantations may also impact on forest productivity. Interactions between climate signals and pest activity are poorly understood. In this study, we examined the combined effects of reduced water availability and defoliation on maximum photosynthetic rate (A(sat)), stomatal conductance (g(s)), plant water status and growth of Eucalyptus globulus Labill. Field-grown plants were subjected to two water-availability regimes, rain-fed (W-) and irrigated (W+). In the summer of the second year of growth, leaves from 75% of crown length removed from trees in both watering treatments and physiological responses within the canopies were examined. We hypothesized that defoliation would result in improved plant water status providing a mechanistic insight into leaf- and canopy-scale gas-exchange responses. Defoliated trees in the W+ treatment exhibited higher A(sat) and g(s) compared with non-defoliated trees, but these responses were not observed in the W- treatment. In contrast, at the whole-plant scale, maximum rates of transpiration (E(max)) and canopy conductance (G(Cmax)) and soil-to-leaf hydraulic conductance (K(P)) increased in both treatments following defoliation. As a result, plant water status was unaffected by defoliation and trees in the defoliated treatments exhibited homeostasis in this respect. Whole-plant soil-to-leaf hydraulic conductance was strongly correlated with leaf scale g(s) and A(sat) following the defoliation, providing a mechanistic insight into compensatory up-regulation of photosynthesis. Above-ground height and diameter growth were unaffected by defoliation in both water availability treatments, suggesting that plants use a range of responses to compensate for the impacts of defoliation.
气候变异性增加，包括干旱期延长，可能会影响森林生态系统的健康。食叶害虫对人工林的影响也可能会影响森林生产力。气候信号与害虫活动之间的相互作用还知之甚少。在本研究中，我们研究了减少水分供应和食叶害虫对桉树光合作用最大速率（Asat）、气孔导度（gs）、植物水分状况和生长的复合影响。在野外生长的植物中，我们进行了两种水分供应处理，即自然降雨（W-）和灌溉（W+）。在第二年生长的夏季，从两种浇水处理的树冠长度的 75%去除叶片，并检查树冠内的生理响应。我们假设，食叶会导致植物水分状况改善，从而为叶片和冠层尺度气体交换响应提供机制性的见解。与未受食叶的树木相比，受食叶处理的 W+处理的树木具有更高的 Asat 和 gs，但在 W-处理中未观察到这些响应。相比之下，在整个植物尺度上，蒸腾作用（Emax）和冠层导度（GCmax）以及土壤到叶片的水力导度（KP）的最大速率在两种处理中均增加了。因此，水分供应不受食叶的影响，受食叶处理的树木在这方面表现出了水分的自我平衡。整个植物的土壤到叶片的水力导度与食叶后的叶片尺度 gs 和 Asat 密切相关，为光合作用的补偿性上调提供了机制性的见解。在两种水分供应处理中，地上高度和直径生长均不受食叶的影响，这表明植物使用了一系列的响应来补偿食叶的影响。
