Abstract
Knowledge of plant hydraulic strategies (isohydric vs anisohydric) is
crucial to predict the response of plants to changing environmental
conditions, such as climate-change induced extreme drought. Several
abiotic factors, such as evaporative demand, have been shown to
seasonally modify the isohydricity of plants, however, the impact of
biotic factors, such as plant-plant interactions on hydraulic strategies
has seldom been explored. Here, we investigated adaptations in hydraulic
strategies for two woody species in response to seasonal abiotic
conditions, experimental drought and plant invasion in a Mediterranean
cork oak (Quercus suber) ecosystem with a combined shrub invasion
(Cistus ladanifer) and rain exclusion experiment. From summer to
winter, the degree of isohydricity shifted from partial isohydric to
anisohydric in Q. suber and inversely from strict anisohydric to
partial isohydric for C. ladanifer. During drought, plant
invasion significantly modified the hydraulic strategy of invaded
Q. suber to a higher degree of anisohydricity with severe
negative consequences for tree functioning, implying progressive leaf
and xylem damage. The rain exclusion alone led to a non-significant
increase in anisohydricity for both species. We demonstrate that the
degree of isohydricity of plants is dynamically determined by the
interplay of species-specific hydraulic traits and their abiotic and
biotic environment.