Physiological Significance of Hydraulic Segmentation, Nocturnal Transpiration and Capacitance in Tropical Trees: Paradigms Revisited

SANDRA J. BUCCI, GUILLERMO GOLDSTEIN, FABIAN G. SCHOLZ AND FREDERICK C. MEINZER

Tropical Tree Physiology: adaptation and responses in an changing environment

SPRINGER-VERLAG

Año: 2016; p. 205 - 225

Results from water relations and hydraulic architecture studies of treesfrom tropical savannas and humid tropical and subtropical forests were reanalyzedin view of paradigms related to the (i) physiological significance of hydraulicsegmentation across trees with different life history traits and habitats, (ii) determinantsof massive tree mortality, (iii) nocturnal transpiration, and (iv) the role ofinternal stem water storage. Stems and leaves of tropical and subtropical deciduoustree species are equally vulnerable to cavitation, whereas leaves of evergreenspecies are substantially more vulnerable than stems. Tree species from tropicalecosystems that do not experience seasonal droughts have stems and leaves withsimilar vulnerability to cavitation while trees from tropical ecosystems that experienceseasonal droughts have leaves that are more vulnerable to drought inducedcavitation compared to stems. Strong segmentation (whether hydraulic orvulnerability) during severe droughts may have an indirect negative impact on tree carbon balance. For example for Sclerolobium paniculatum, a widespread treespecies in neotropical savannas and seasonally dry forests, the decrease in total leafsurface area per plant (which impact hydraulic architecture) during droughts help tomaintain an adequate water balance but has large physiological costs: trees receive alower return in carbon gain from their investment in stem and leaf biomass. Leafhydraulic failure and carbon starvation may contribute to the massive,size-dependent mortality observed in this species. The functional significance of thewidespread phenomenon of nocturnal transpiration in tropical trees is discussed.One of the most likely functions of nocturnal sap flow in savanna trees growing innutrient poor soils appears to be enhanced nutrient acquisition from oligotrophicsoils. Large capacitance plays a central role in the rapid growth patterns of tropicaldeciduous tree species facilitating rapid canopy access as these species are lessshade tolerant than evergreen species. Higher growth rates in species with highcapacitance could be achieved by keeping the stomata open for longer periods oftime.