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Meta-analysis of liana leaf and wood hydraulic traits reveals a competitive advantage for water acquisition in moderate drought conditions.
Meunier, F., Nguyen, L., di Porcia e Brugnera, M., Longo, M., Xu, X., Santiago, L. S., & Verbeeck, H.
Tropical forests are an essential component of the Earth system as they store and process huge quantities of carbon and water. They are estimated to account for over 50% of the global forest carbon sequestration and for 34% of global terrestrial photosynthesis. Tropical forests have been experiencing long-term and large-scale structural changes due to climate and land use, which potentially explains the observed increase in liana (woody vines) abundance. Lianas are structural parasites that take advantage of existing woody structures to climb up the top of the canopy, without the need for self supporting structures. Doing so, they strongly compete with tropical trees for above- and below-ground resources, which might further affect the dynamics of these ecosystems. Lianas dramatically differ from co-occurring trees by many aspects, one of them being their hydraulic traits, due to very contrasted xylem structure and anatomy. To evaluate the impact of such properties on liana proliferation, we first performed a literature meta-analysis to collect published data about liana hydraulic traits. We established relationships between functional (i.e. hydraulic) and structural (e.g. wood density) liana properties and compared them with similar functions for tropical trees. We observed strong statistical differences between the growth forms. In particular, for the same wood density, lianas exhibit significantly larger specific sapwood conductivities and increased risks of severe cavitation during droughts (higher P50). These hydraulic properties were then used as inputs of a dynamic cohort-based vegetation model (i.e. the Ecosystem Demography model, ED2) with novel implementations of plant hydraulics and lianas. Site simulations in a Neotropical primary growth forest (Paracou, French Guiana) were run with meteorologically realistic, drier-than-observed rainfall scenarios. Reference simulation showed excellent agreement in representing carbon and water fluxes when compared to flux tower data. Drought scenario runs revealed the competitive advantage of liana hydraulic properties for water uptake and transport in case of moderate drought conditions (i.e. Increase in liana abundance and biomass). Forest total carbon storage and productivity were dramatically reduced as lianas proliferate.
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