Hemlock woolly adelgid (Adelges tsugae) infestation affects water and carbon relations of eastern hemlock (Tsuga canadensis) and Carolina hemlock (Tsuga caroliniana)

Hemlock woolly adelgid (HWA) is an exotic insect pest causing severe decimation of native hemlock trees. Extensive research has been conducted on the ecological impacts of HWA, but the exact physiological mechanisms that cause mortality are not known. Water relations, anatomy and gas exchange measurements were assessed on healthy and infested eastern (Tsuga canadensis) and Carolina (Tsuga caroliniana) hemlock trees. These data were then used in a mechanistic model to test whether the physiological responses to HWA infestation were sufficiently significant to induce changes in whole-plant water use and carbon uptake. The results indicated coordinated responses of functional traits governing water relations in infested relative to healthy trees. In response to HWA, leaf water potential, carbon isotope ratios, plant hydraulic properties and stomatal conductance were affected, inducing a reduction in tree water use by >40% and gross primary productivity by 25%. Anatomical changes also appeared, including the activation of traumatic cells. HWA infestation had a direct effect on plant water relations. Despite some leaf compensatory mechanisms, such as an increase in leaf hydraulic conductance and nitrogen content, tree water use and carbon assimilation were diminished significantly in infested trees, which could contribute to tree mortality.

铁杉球蚜（HWA）是一种外来害虫，导致本地铁杉树大量死亡。人们对铁杉球蚜的生态影响进行了广泛研究，但导致树木死亡的确切生理机制尚不清楚。对健康的以及受侵染的加拿大铁杉（Tsuga canadensis）和卡罗来纳铁杉（Tsuga caroliniana）的水分关系、解剖结构和气体交换进行了测量。然后将这些数据用于一个机理模型，以测试对铁杉球蚜侵染的生理反应是否显著到足以引起整株植物水分利用和碳吸收的变化。结果表明，与健康树木相比，受侵染树木中控制水分关系的功能性状存在协同反应。受铁杉球蚜影响，叶片水势、碳同位素比率、植物水力特性和气孔导度均受到影响，导致树木水分利用减少40%以上，总初级生产力降低25%。解剖结构也出现了变化，包括创伤细胞的激活。铁杉球蚜侵染对植物水分关系有直接影响。尽管存在一些叶片补偿机制，如叶片水力导度和氮含量增加，但受侵染树木的水分利用和碳同化显著降低，这可能导致树木死亡。