Wood anatomy and carbon‐isotope discrimination support long‐term hydraulic deterioration as a major cause of drought‐induced dieback

Abstract

Hydraulic impairment due to xylem embolism and carbon starvation are the two proposed mechanisms explaining drought-induced forest dieback and tree death. Here, we evaluate the relative role played by these two mechanisms in the long-term by quantifying wood-anatomical traits (tracheid size and area of parenchyma rays) and estimating the intrinsic water-use efficiency (iWUE) from carbon isotopic discrimination. We selected silver fir and Scots pine stands in NE Spain with ongoing dieback processes and compared trees showing contrasting vigour (declining vs nondeclining trees). In both species earlywood tracheids in declining trees showed smaller lumen area with thicker cell wall, inducing a lower theoretical hydraulic conductivity. Parenchyma ray area was similar between the two vigour classes. Wet spring and summer conditions promoted the formation of larger lumen areas, particularly in the case of nondeclining trees. Declining silver firs presented a lower iWUE than conspecific nondeclining trees, but the reverse pattern was observed in Scots pine. The described patterns in wood anatomical traits and iWUE are coherent with a long-lasting deterioration of the hydraulic system in declining trees prior to their dieback. Retrospective quantifications of lumen area permit to forecast dieback in declining trees 2-5 decades before growth decline started. Wood anatomical traits provide a robust tool to reconstruct the long-term capacity of trees to withstand drought-induced dieback.

Retrospective Analysis of Wood Anatomical Traits Reveals a Recent Extension in Tree Cambial Activity in Two High-Elevation Conifers

“…This is a unique point of view dealing mostly with perennial and long-lived organisms and within a framework of long-term processes such as those related to climate change. There is certainly room for improvement: for example, additional anatomical or climate parameters such as cell wall thickness (Prendin et al, 2017) or precipitation could increase the quality of the information and the resulting inferences; tuning the length of the daily window could help to better relate growth processes to climate; the ring division in sectors, although it proved fairly effective (Carrer et al, 2016; Pellizzari et al, 2016; Castagneri et al, 2017a), can be considered a rigid and simplistic way to deal with the different and more plastic phenological phases. In the future, a ring partitioning that better considers individual- or species-specific physiological traits and tunes the time windows according to the yearly climate peculiarities, could provide better results.…”

“…Since both the dendroanatomical and xylogenetic approaches operate at cellular level, relating dendroanatomy to key environmental factors might also allow inferences on cambial activity to be extended from a few years to decades. However, up to now, only a few empirical studies have explored long-term effects of climate variability on the corresponding year-to-year change in wood anatomical traits and the related consequences for conifer tree physiology and growth (Olano et al, 2012; Fonti et al, 2013; Pacheco et al, 2016; Pellizzari et al, 2016). Furthermore, most of these investigations usually adopted a classical dendroclimatological approach to define the associations between climate and wood-anatomical parameters (e.g., using monthly resolved weather records and averaging the anatomical properties of the whole rings), therefore remaining disconnected from the cambium dynamics studies in terms of temporal resolution.…”

Coupled ecohydrology and plant hydraulics modeling predicts ponderosa pine seedling mortality and lower treeline in the US Northern Rocky Mountains

“…Legacy effects of prior drought stress events result from a series of responses that prevent plants from recovering their status (whether in the short or longer term) to that before the stress event once the event has ended (Anderegg et al ., ; Pellizzari et al ., ; Huang et al ., ; Serra‐Maluquer et al ., ; Wu et al ., ). For instance, hydraulic deterioration as a result of cavitation fatigue (Hacke et al ., ) has been shown to limit recovery after drought (L. D. L. Anderegg et al ., ).…”

How does climate influence xylem morphogenesis over the growing season? Insights from long-term intra-ring anatomy inPicea abies

“…Recent studies linking tree physiology with wood anatomy have demonstrated that the morphology of the xylem cells affects functional properties such as hydraulic safety and efficiency (Lachenbruch and McCulloh, 2014;Schuldt et al, 2016). Therefore, modifications in xylem anatomy strongly determine the performance and survival of trees, and consequently forests' vulnerability to climate change and their capacity to fix carbon (Anderegg, 2015;Sperry and Love, 2015;Pellizzari et al, 2016).…”