Strong hydraulic segmentation and leaf senescence due to dehydration may trigger die-back in Nothofagus dombeyi under severe droughts: a comparison with the co-occurring Austrocedrus chilensis

SCHOLZ F.G; BUCCI SJ; GOLDSTEIN G

TREES-STRUCTURE AND FUNCTION

SPRINGER

Lugar: Berlin; Año: 2014 vol. 28 p. 1475 - 1487

0931-1890

Key message Total leaf hydraulic dysfunction duringsevere drought could lead to die-back in N. dombeyi,while hydraulic traits of A. chilensis allow it to operatefar from the threshold of total hydraulic failure.Abstract Die-back was observed in South America temperateforests during one of the most severe droughts of the20th century (1998?1999). During this drought Austrocedruschilensis trees survived, whereas trees of the cooccurringspecies (Nothofagus dombeyi) experiencedsymptoms of water stress, such as leaf wilting andabscission, before tree die-back occurred. We comparedhydraulic traits of these two species (a conifer and anangiosperm species, respectively) in a forest stand locatedclose to the region with records of N. dombeyi mass mortality.We asked whether different hydraulic traits exhibitedby the two species could help explain their contrastingsurvivorship rates. Austrocedrus chilensis had wide leafsafety margins, which appear to be the consequence ofrelatively high leaf-and-stem capacitance, large storedwater use, strong stomatal control and ability to recoverfrom embolism-induced loss of leaf hydraulic capacity. Onthe other hand, N. dombeyi even though had a stemhydraulic threshold of -6.7 MPa before reaching substantialhydraulic failure (P88), leaf P88 occurred at leafwater potentials of only -2 MPa, which probably arereached during anomalous droughts. Massive mortality inN. dombeyi appears to be the result of the total loss of leafhydraulic conductance leading to leaf dehydration and leafdrop. Drought occurs during the summer and it is highlylikely that N. dombeyi cannot recover its photosyntheticsurface to produce carbohydrates required to avoid tissueinjury in the winter season with subfreezing temperatures.Strong hydraulic segmentation in N. dombeyi does notseem to have an adaptive value to survive severe droughts.