Impact of simulated herbivory on water relations of aspen (Populus tremuloides) seedlings: the role of new tissue in the hydraulic conductivity recovery cycle

Abstract

Physiological mechanisms behind plant-herbivore interactions are commonly approached as input-output systems where the role of plant physiology is viewed as a black box. Studies evaluating impacts of defoliation on plant physiology have mostly focused on changes in photosynthesis while the overall impact on plant water relations is largely unknown. Stem hydraulic conductivity (k(h)), stem specific conductivity (k(s)), percent loss of hydraulic conductivity (PLC), CO(2) assimilation (A) and stomatal conductance (g(s)) were measured on well-irrigated 1-month-old Populus tremuloides (Michx.) defoliated and control seedlings until complete refoliation. PLC values of defoliated seedlings gradually increased during the refoliation process despite them being kept well irrigated. k(s) of defoliated seedlings gradually decreased during refoliation. PLC and k(s) values of control seedlings remained constant during refoliation. k(s) of new stems, leaf specific conductivity and A of leaves grown from new stems in defoliated and control seedlings were not significantly different, but g(s) was higher in defoliated than in control seedlings. The gradual increase of PLC and decrease of k(s) values in old stems after defoliation was unexpected under well-irrigated conditions, but appeared to have little impact on new stems formed after defoliation. The gradual loss of conductivity measured during the refoliation process under well-irrigated conditions suggests that young seedlings of P. tremuloides may be more susceptible to cavitation after herbivore damage under drought conditions.

Canopy Stomatal Conductance Following Drought, Disturbance, and Death in an Upland Oak/Pine Forest of the New Jersey Pine Barrens, USA

“…A quadrupling or doubling in G Cref after defoliation as was shown here for Q. prinus and Q. velutina , was also observed for g S in Populus tremuloides in a simulated defoliation experiment (Gálvez and Tyree, 2009). Thus, trees compensate for leaf area losses and reduced CO 2 uptake by capitalizing on higher water availability for the remaining leaves.…”

“…It is well known that stomata close under drought conditions to prevent further water loss (Alder et al, 1996; Cochard et al, 1996; Sperry et al, 1998), but less is known about how stomata respond to disturbance. Some leaf-level investigations suggest an increase in photosynthesis after defoliation as a means to compensate for lost leaf area (VanderKlein and Reich, 1999; Wallin et al, 2003; Turnbull et al, 2007; Delaney, 2008; Gálvez and Tyree, 2009). However, the scaling of individual leaf responses to the entire canopy is rarely investigated.…”

“…It is conceivable that different disturbance regimes will have differential responses in stomatal conductance ( g S ) or G C . For example, a pine bark beetle infestation limits water supply thus mimicking drought stress, whereas a defoliator such as gypsy moth limits demand, thus leaving more water available to remaining leaves (Gálvez and Tyree, 2009). In the first instance, one would expect a reduction in g S or G C and, in the latter case, an increase.…”

Phenotypic and developmental plasticity of xylem in hybrid poplar saplings subjected to experimental drought, nitrogen fertilization, and shading

“…Distal plant parts are arguably expendable; their sacrifice can help to maintain favourable plant water balance by reducing the total transpiring surface (Rood et al ., 2000). This strategy might be particularly vital in poplar which is well known for its ability to regenerate by root suckering and re-sprouting from auxiliary buds (Galvez and Tyree, 2009; Lu et al ., 2010). Nevertheless, it is questionable whether such reasoning is relevant to the relatively young saplings measured in this current study.…”

Fencing is not enough to reinstate regeneration: Evidence from a large fruited canopy tree Beilschmiedia tawa

“…cavitation), as many other studies have shown (e.g. Spooner et al, 2002;Smale et al, 2005;Gálvez and Tyree, 2009;Morales et al, 2015).…”