The partitioning of water uptake between growth forms in a Neotropical savanna: do herbs exploit a third water source niche?

In addition to trees and grasses, the savannas of central Brazil are characterised by a diverse herbaceous dicot flora. Here we tested whether the coexistence of a highly diversified assemblage of species resulted in stratification or strong overlap in the use of soil water resources. We measured oxygen and hydrogen isotope ratios of stem water from herbs, grasses and trees growing side by side, as well as the isotopic composition of water in soil profile, groundwater and rainfall, and predawn (Ψ(pd)) and midday (Ψ(md)) leaf water potentials. We used a stable isotope mixing model to estimate vertical partitioning of soil water by the three growth forms. Grasses relied on shallow soil water (5-50 cm) and were strongly anisohydric. Ψ(pd) and Ψ(md) decreased significantly from the wet to the dry season. Trees extracted water from deeper regions of the soil profile (60-120 cm) and were isohydric. Ψ(pd) and Ψ(md) did not change from the wet to the dry season. Herbs overlapped with grasses in patterns of water extraction in the dry season (between 10 and 40 cm), but they took up water at soil depths intermediate (70-100 cm) to those of trees and grasses during the wet season. They showed seasonal changes in Ψ(pd) but not in Ψ(md). We conclude that vertical partitioning of soil water may have contributed to coexistence of these three growth forms and resulted in a more complex pattern of soil water extraction than the two-compartment model of soil water uptake currently used to explain the structure and function of tropical savanna ecosystems.

Rossatto DR ，da Silveira Lobo Sternberg L ，Franco AC 《-》

Water economy of Neotropical savanna trees: six paradigms revisited.

Goldstein G ，Meinzer FC ，Bucci SJ ，Scholz FG ，Franco AC ，Hoffmann WA ... -  《TREE PHYSIOLOGY》

Seasonal changes in depth of water uptake for encroaching trees Juniperus virginiana and Pinus ponderosa and two dominant C4 grasses in a semiarid grassland.

Eggemeyer KD ，Awada T ，Harvey FE ，Wedin DA ，Zhou X ，Zanner CW ... -  《TREE PHYSIOLOGY》

Hydraulic lift in Acacia tortilis trees on an East African savanna.

Ludwig F ，Dawson TE ，Kroon H ，Berendse F ，Prins HH ... -  《OECOLOGIA》

Variation in soil water uptake and its effect on plant water status in Juglans regia L. during dry and wet seasons.

Sun SJ ，Meng P ，Zhang JS ，Wan X ... -  《-》