Growth & Development

Plants Can Change Their Xylem Anatomy to Maintain Conductivity

Sap must flow, so the xylem must change.

Plants have the potential to adjust the configuration of their hydraulic system to maintain its function across spatial and temporal gradients. Species with wide environmental niches provide an ideal framework to assess intra-specific xylem adjustments to contrasting climates. Ana García-Cervigón and colleagues aimed to assess how xylem structure in the widespread species Nothofagus pumilio varies across combined gradients of temperature and moisture, and to which extent within-individual variation contributes to population responses across environmental gradients.

Image: Gagea / Wikipedia

The team characterized xylem configuration in branches of N. pumilio trees at five sites across an 18° latitudinal gradient in the Chilean Andes, sampling at four elevations per site. They measured vessel area, vessel density and the degree of vessel grouping. They also obtained vessel diameter distributions and estimated the xylem-specific hydraulic conductivity. Xylem traits were studied in the last five growth rings to account for within-individual variation.

Xylem traits responded to changes in temperature and moisture, but also to their combination. Reductions in vessel diameter and increases in vessel density suggested increased safety levels with lower temperatures at higher elevation. Vessel grouping also increased under cold and dry conditions, but changes in vessel diameter distributions across the elevational gradient were site-specific. Interestingly, the estimated xylem-specific hydraulic conductivity remained constant across elevation and latitude, and an overwhelming proportion of the variance of xylem traits was due to within-individual responses to year-to-year climatic fluctuations, rather than to site conditions.

“The widespread species Nothofagus pumilio adjusted its xylem anatomy in response to both elevation and latitude, and to their combination,” write García-Cervigón and colleagues However, despite the existence of noticeable adjustments, xylem traits were coordinated to maintain the hydraulic function under a wide range of conditions. This revealed the homeostatic capacity of xylem and suggests that the hydraulic system of N. pumilio may have enough adaptive potential to face forecasted climatic trends, thus allowing this species to keep within its current elevational and latitudinal limits.

“Our results also indicate that the potential for adapting to climatic change may be strongly determined by the within-individual capacity for responding to year-to-year variability in environmental conditions. Thus, the scaling from individual trees to the forest level may strongly determine increases in forest resilience against environmental changes.”

This paper is listed on one of the authors’ ResearchGate pages.