Relative water content consistently predicts drought mortality risk in seedling populations with different morphology, physiology and times to death

Abstract

Predicted increases in forest drought mortality highlight the need for predictors of incipient drought‐induced mortality (DIM) risk that enable proactive large‐scale management. Such predictors should be consistent across plants with varying morphology and physiology. Because of their integrative nature, indicators of water status are promising candidates for real‐time monitoring of DIM, particularly if they standardize morphological differences among plants. We assessed the extent to which differences in morphology and physiology between Pinus ponderosa populations influence time to mortality and the predictive power of key indicators of DIM risk. Time to incipient mortality differed between populations but occurred at the same relative water content (RWC) and water potential (WP). RWC and WP were accurate predictors of drought mortality risk. These results highlight that variables related to water status capture critical thresholds during DIM and the associated dehydration processes. Both WP and RWC are promising candidates for large‐scale assessments of DIM risk. RWC is of special interest because it allows comparisons across different morphologies and can be remotely sensed. Our results offer promise for real‐time landscape‐level monitoring of DIM and its global impacts in the near term.

Not Only Severe Events: Moderate Dry Periods Impact the Hydraulic Functioning and Survival of Planted Ponderosa Pine Seedlings

“…We postulate that the severe declines in tree hydraulic functioning and high inferred mortality that we found are likely due to the extended duration of our experimental period. We note that evidence of initiation of tree mortality at ∼13 days corroborates similar findings by Augustine and Reinhardt [31] but was shorter than the 29 days observed by Sapes and Sala [45] in a greenhouse study. More nuanced responses across treatments occurred during the first half of the experiment, although required destructive sampling did not allow us to progressively infer tree mortality.…”

“…Quantification of hydraulic vulnerability (either via vulnerability curves or measures of RWL) in seedlings is also particularly difficult to conduct over time as it requires destructive sampling [39]. Hydraulic vulnerability is further complicated by the fact that juvenile and adult trees often differ [28,29], and that vulnerability may often differ between populations of the same species growing in different local or regional environments [30,45]. Thus, a dichotomy remains between the fine scales of tree stress and mortality and the coarser scales at which they are currently observable.…”

Stem Photosynthesis Affects Hydraulic Resilience in the Deciduous Populusalba but Not in the Evergreen Laurus nobilis

“…Drought-induced hydraulic failure (i.e., whole blockage of the long-distance water transport system) poses a major threat to plant survival [76,77], but even carbon starvation can represent a significant challenge to plants facing water limitations [43,78]. The maintenance of basal metabolism under drought, when leaf gas exchange is strongly reduced by stomatal closure, relies on the consumption of stored NSCs [39].…”

“…Hydraulic failure caused by massive xylem embolism is a major and recurrent cause of drought-induced tree mortality [36][37][38], with an additional role suggested for carbon starvation. Interestingly, carbohydrate content decline, even when non-lethal, has been reported to impact plant hydraulic efficiency [39][40][41][42][43]. Non-structural carbohydrates (NSCs) are apparently involved in the maintenance of plant hydraulic function via different processes, which are only partially understood.…”

When Water Availability Is Low, Two Mediterranean Salvia Species Rely on Root Hydraulics

“…Changes in plant water content in response to drought have recently received a renewed attention [26]. Plant water status is linked to different key physiological mechanisms, Plants 2021, 10, 1888 2 of 14 including water transport and its regulation as well as carbon metabolism [27,28]. On this view, the relative water content (RWC) has been suggested as a simple indicator of plant mortality risk.…”