Atmospheric and hydraulic limitations on transpiration in Brazilian cerrado woody species

Abstract

The savannas of central Brazil (cerrado) form the second most extensive plant formation in South America. In Brazil, the 2·0 × 10 6 km 2 of land area covered by cerrado vegetation is exceeded only by the Amazonian rain forest (Ratter 1992). The cerrado is characterized by a markedly seasonal rainfall regime with a 4-5 month dry season, old oligotrophic soils and frequent fires. The fires occur either naturally, or as part of a land-management system applied to increase the abundance and palatability of the relatively shallow-rooted grasses for cattle (Skole et al. 1994). The impact of the resulting decrease in density of the more deeply rooted trees and shrubs on ecosystem water fluxes is unknown.Cerrado comprises three principal physiognomic subtypes ranging from cerradão, medium to tall woodlands with closed or semi-closed canopies, to cerrado sensu stricto, a savanna woodland with 3. The dependence of maximum whole-plant sap flow rates on sapwood area was similar among all four species during both the wet and dry seasons. When total daily sap flow on a leaf area basis was normalized by the daily average air saturation deficit (ASD), only one of the four species showed significantly greater water use during the wet season. 4. Although seasonal differences in regulation of transpiration were not pronounced, strong stomatal limitation of both maximum daily transpiration rates and total daily transpiration was evident during both the wet and dry seasons. Sap flow typically increased sharply in the morning, briefly attained a maximum value by about 09.30-10.30 h, then decreased sharply, despite steadily increasing solar radiation and atmospheric evaporative demand. 5.The total leaf area-specific apparent hydraulic conductance of the soil/leaf pathway (G t ) varied among plants and diurnally. The identical linear dependence of transpiration and stomatal conductance (g s ) on G t among the four study species suggested that stomatal adjustment to variation in G t limited transpiration over the entire range of G t observed. 6. When g s was normalized for daily variation in G t , about 80% of the remaining variation in g s was associated with variation in ASD. The results suggested that transpiration in these species was not limited by soil water availability per se, but by high atmospheric evaporative demand and hydraulic constraints possibly arising from their deep rooting habit.

Can we predict dispersal guilds based on the leaf-height-seed scheme in a disjunct cerrado woodland?

“…For cerrado trees, soil water availability per se does not limit their transpiration, but high atmospheric evaporative demand and hydraulic constraints possibly arising from their deep root habit do (Meinzer et al, 1999). Similar adaptative adjustments in SLA of the cerrado woody species studied may be a consequence of their similar canopy heights -abiotically and biotically dispersed species occupying similar stratum in the dense woodland site, which may indicate that there are no differences in their habitats regarding light availability.…”

Within-crown variation in leaf conductance of Norway spruce: effects of irradiance, vapour pressure deficit, leaf water status and plant hydraulic constraints

“…There is evidence for many plant species that variation in stomatal conductance, crown conductance and transpiration is closely associated with variation in the total hydraulic conductance of the soil-to-leaf pathway, G T [16,21,50,51]. Thus, a homeostatic balance has to exist between transpiration rate, leaf area, sapwood area, and the hydraulic capacity of the stem to supply water to leaves [53,57,58].…”

Análise da evapotranspiração por wavelet de Morlet em área de Vochysia divergens Pohl no Pantanal

“…Neste período também ocorre imitação de precipitação. Ainda durante a estação seca ocorre declínio do conteúdo de água no solo passível de limitar a evaporação e a disponibilidade de água para as plantas de raízes superficiais (Meinzer et al, 1999).…”