INVESTIGADORES
SCHOLZ Fabian Gustavo
congresos y reuniones científicas
Título:
Drought and hydraulic thresholds: Predicting the mortality of woody plants of Patagonian forests and deserts
Autor/es:
BUCCI SJ, GOLDSTEIN G, SCHOLZ FG
Reunión:
Congreso; 99 ESA Annual Meeting; 2014
Resumen:
Background/Question/Methods
Droughts are expected to increase in the next 50 years in temperate
areas of South America, particularly in the western slopes of the
southern Andes covered by Nothofagus and conifers species and in the
driest Patagonian ecosystems (steppes). Selective tree dieback has been
observed in these temperate forests during one of the most severe
drought of the 20th century (1998-1999) in which Austrocedrus chilensis
trees survived whereas trees of the co-occurring evergreen species
(Nothofagus dombeyi) experienced symptoms of water stress, such as leaf
wilt and abscission before die-back occurred. Similarly, some evergreen
shrubs in the steppe exhibited dieback during unusual summer droughts
while other shrub species survived. The mechanisms and plant traits
underlying or mitigating specie-specific mortality under future climate
change scenarios are poorly understand. Studies were done to understand
drought responses of trees and shrubs and to link hydraulic traits with
mortality providing a tool to predict the degree of species-specific
vulnerability within and across these ecosystems with dry summers and
cold winters. We asked whether different stem and leaf hydraulic traits
exhibited by the two forest species and by seven steppe species could
help explain the contrasting survivorship rates.
Results/Conclusions
Species experiencing die-off under severe drought have wide stem
safety margins and minimum stem water potentials (Ψ) far from the
threshold of irreversible hydraulic failure (P88), but the minimum leaf Ψ are close to leaf P88,
which probably are reached during anomalous droughts. Massive mortality
of N. dombeyi and of shrubby species appears to be the consequence of
the total loss of leaf hydraulic conductance (Kleaf) which
triggers leaf senescence and drop. Drought occurs during the summer and
it is highly likely that these species cannot recover its photosynthetic
surface to produce carbohydrates required to avoid tissue injury before
subzero temperatures occur. Species surviving the drought have wide
leaf safety margins as a consequence of high leaf-and-stem capacitance,
tight stomatal control, ability to recover Kleaf and deep
roots. Drought hydraulic limitation to carbohydrate production more than
plant hydraulic failure per se triggers die-off in N. dombeyi which
could favor the dominance of conifers in these temperate forests under
predicted climate changes. We suggest that strong hydraulic segmentation
inducing leaf drop during drought may not favor survivorship of some
species because carbon assimilation and osmotically active carbohydrate
synthesis during the summer season are required to avoid freezing damage
during winter.