Functional xylem anatomy of aspen exhibits greater change due to insect defoliation than to drought

Abstract

The study of tree rings can reveal long-term records of a tree's response to the environment. This dendroecological approach, when supplemented with finer-scale observations of the xylem anatomy, can provide novel information about a tree's year-to-year anatomical and hydraulic adjustments. Here we use this method in aspen (Populus tremuloides Michx.) to identify xylem response to drought and insect defoliation. Surprisingly, we found that precipitation influenced vessel diameter mostly in the trees' youth, while this correlation was less pronounced at maturity. This is likely due to a reduction in stress the stand experiences as it ages, and reflects an ability to mediate drought stress as trees mature. Defoliation events caused consistent and profound changes in fiber anatomy likely leading to reduced structural support to vessels. We therefore expect that in years of defoliation trees may be vulnerable to drought-induced cavitation when leaf area recovers. This study highlights how the inclusion of cellular level measurements in tree ring studies provides additional information on how stress events may alter tree functioning through alterations in structure.

Response of vessel features to witches’‐broom disease in Zizyphus Jujuba branches

“…Trees adjust the hydraulic structure to adapt to the abnormal water transport. Some pests or pathogens may alter trees response to abiotic stress factors (Hillabrand et al., 2018; Pouzoulet et al., 2014; Venturas et al., 2013). Phytoplasma infection caused the differential expression of genes related to cell division and differentiation (Liu et al., 2020), resulting in disorder of metabolic compositions (Liu et al., 2016), which might be the reason for the differences in anatomical structure of jujubes (Chu, 1986).…”

“…However, the vessel is subjected to various environmental stresses that threaten its function. The capacitive water release can help live through the cavitation against the abiotic stressors such as drought or freezing, and biotic stressors, such as insects (Hillabrand et al., 2018) and pathogens (Pouzoulet et al., 2014; Venturas et al., 2013). Some vessel features such as frequency, size and wall thickness have been positively correlated with cavitation resistance to water stress (Hacke & Sperry, 2001).…”

“…Environmentally induced differences in vessel features explain changes in tree hydraulic conductance (Kiorapostolou & Petit, 2018). Sometimes, vessel features of trees exhibits greater change due to biotic stressors than to abiotic stressors (Hillabrand et al., 2018; Venturas et al., 2013).…”

Decline of an ecotone forest: 50 years of demography in the southern boreal forest

“…) and long‐term changes in cell‐fibers with possible negative implications for structure and drought response (Hillabrand et al. ). The trees used to reconstruct the history of defoliation in the GLR were the surviving, non‐rotten cohort, and it is possible that the Populus that died before 2017 suffered additional defoliation events or died as a direct result of defoliation.…”

“…The recent, widespread die-off of Populus across the region has been documented (Michaelian et al 2011) and the defoliation years (1979)(1980)(1981)(1982)(1983)(1984)(1985)(1986)(1987)(1988) within the GLR match years of outbreaks of M. disstria across Alberta (Hogg et al 2002a). Multiple years of defoliation can cause high mortality (Moulinier et al 2014) and long-term changes in cell-fibers with possible negative implications for structure and drought response (Hillabrand et al 2019). The trees used to reconstruct the history of defoliation in the GLR were the surviving, non-rotten cohort, and it is possible that the Populus that died before 2017 suffered additional defoliation events or died as a direct result of defoliation.…”