Abstract
A clear understanding of hydraulic regulation in cultivated plants is crucial for addressing challenges to forest water cycling due to climate changes in low subtropical China. Experiments were conducted to determine the hydrologic balance of a Eucalyptus urophylla plantation in response to periodic drought. Trees displayed lower stomatal conductance (GS) and leaf water potentials (ΨL) during the dry periods. A decrease of 22.4% was found for the maximum reference GS (GS at D = 1 kPa; GSref-max). Accordingly, specific hydraulic conductivity (ks) decreased by 45.3 – 65.6% from the wet to the dry season, depending on the tree size. Fairly stable leaf stomatal conductance (gs) with decreasing ΨL (ΨL < -1.6 MPa) contributed to the high water-use efficiency (WUE) of this Eucalyptus species. Additionally, the lower stomatal sensitivity (-m = 0.53) in the dry season might also be responsible for the high WUE, since we found an anisohydric behavior that was associated with photosynthetically active radiation (Q0). Larger trees were found to use water more efficiently than small trees, due to the higher sensitivity of ks to decreasing ΨL. This was also verified by the decreasing leaf carbon isotope discrimination (Δ13C) with increasing tree diameter. However, further studies are needed to determine the universality of these results for other Eucalyptus species in this region.
Highlights
Due to anthropogenic climate changes, the survival of tropical and subtropical forest communities may be threatened in a variety of ways, including increased frequency of severe droughts caused by changes in precipitation pattern (Davidson et al, 2012), especially in the southern region of China (Zhai et al, 2005; Zhou et al, 2011)
The water input was mainly contributed by precipitation in late spring and early summer, which accounted for 55.4% of the annual total, while that from October to February was only 16%
Fd was not affected by tree size, it was weakly related to diameter at breast height (DBH) in the dry season (R2 = 0.19, p = 0.06)
Summary
Due to anthropogenic climate changes, the survival of tropical and subtropical forest communities may be threatened in a variety of ways, including increased frequency of severe droughts caused by changes in precipitation pattern (Davidson et al, 2012), especially in the southern region of China (Zhai et al, 2005; Zhou et al, 2011). Eucalyptus species have been reported to have high photosynthetic capacity, WUE, and growth rate (Whitehead and Beadle, 2004), which may imply a high canopy GS. These characteristics may minimize and counteract the effects of extreme climate events, and reinforce community resilience (Lloret et al, 2012). How these species coordinate decreases in GS to avoid hydraulic failure with the demand to maximize carbon assimilation in dry conditions is poorly understood and less reported
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