Partitioning of water resources among plants of a lowland tropical forest

Abstract

Source water used by plants of several species in a semi-evergreen lowland tropical forest on Barro Colorado Island, Panama, was assessed by comparing the relative abundance of deuterium, D, versus hydrogen, H (stable hydrogen isotope composition, δD) in xylem sap and in soil water at different depths, during the dry season of 1992. Ecological correlates of source water were examined by comparing xylem water δD values with leaf phenology, leaf water status determined with a pressure chamber, and rates of water use determined as mass flow of sap using the stem heat balance method. Soil water δD values decreased sharply to 30 cm, then remained relatively constant with increasing depth. Average δD values were-13‰, for 0-30 cm depth and-36.7‰ for 30-100 cm depth. Soil water δD values were negatively associated with soil water content and soil water potential. Concurrent analyses of xylem water revealed a high degree of partitioning of water resources among species of this tropical forest. Xylem water δD of deciduous trees (average=-25.3±1.4‰) was higher than that of evergreen trees (average=-36.3±3.5‰), indicating that evergreen species had access to the more abundant soil water at greater depth than deciduous species. In evergreen shade-tolerant and high-light requiring shrubs and small trees, δD of xylem water was negatively correlated with transpiration rate and leaf water potential indicating that species using deeper, more abundant water resources had both higher rates of water use and more favorable leaf water status.

Water acquisition patterns of two wet tropical canopy tree species of French Guiana as inferred from H218O extraction profiles

“…D. guianensis roots were not able to penetrate this layer, whereas E. falcata roots crossed this layer but did not reach more than ca. -2.0 m. In contrast with published studies [22,31,43], differences in rooting depth between species were not related to marked differences in leaf δ 13 C values -and thus in estimated intrinsic water-use efficiency -or in leaf water potential values (table I). For both species, soil moisture conditions and soil drainage types had almost no effect on Ψ wm , which suggests either that trees had access to sufficient water in the soil, or were able to regulate their leaf gas exchange, particularly stomata, in order to maintain high Ψ wm values or even to increase it slightly in the dry season (D.…”

“…In recent years, a non-destructive methodology based on the assessment of natural abundance of stable oxygen ( 18 O) or hydrogen ( 2 H) isotopes in water has been used to assess the differential uptake and use of water sources among plants in different ecosystems [13,14,15,16,17,22,31,36,43]. This methodology is based on the fact that (1) soil water extraction by roots does not induce isotopic fractionation of either oxygen or hydrogen isotopes of water [2,44,45] and (2) gradients in oxygen or hydrogen isotope composition (δ 18 O or δ 2 H) of soil water with soil depth may arise from seasonal variations in rainfall isotope signature [11,12] and from the isotope fractionation that occurs during surface soil water evaporation (see review in [16]).…”

“…This methodology has been widely applied in dry or arid ecosystems [17,22,36,43], but reports on the use of this method to infer water sources used by trees in dry tropical [31] or wet tropical [3,19] forest remain scarce. The infrequent use of such an approach in the wet tropics might be associated with the weakness or absence of strong differences in seasonal isotopic signature of rainfall water and with the weak atmospheric evaporative demand in the understorey [3,21].…”

“…The infrequent use of such an approach in the wet tropics might be associated with the weakness or absence of strong differences in seasonal isotopic signature of rainfall water and with the weak atmospheric evaporative demand in the understorey [3,21]. However, Jackson et al [31] found a strong gradient in δ 2 H from surface down to 1.0 m depth in a lowland tropical forest in Panama and were then able to show that trees differing in leaf phenology also differed in their depth of water extraction. Therefore, this methodology appears as potentially useful for inferring differences in soil water extraction among wet tropical canopy tree species.…”

Desenvolvimento do milho sob influência de árvores de pau-branco em sistema agrossilvipastoril

“…Outro aspecto importante é a profundidade de alcance do sistema radicular, pois se ele for profundo, há possibilidade de absorção de água e nutrientes em locais onde os cultivos agrícolas não exploram (Jackson et al, 1995). Caso o componente arbóreo apresente sistema radicular superficial, a área sob as árvores, além de sombreadas, apresentarão baixa disponibilidade de água (Schroth et al, 2002).…”