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Hydraulic Balance of a Eucalyptus urophylla Plantation in Response to Periodic Drought in Low Subtropical China

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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.

No MeSH data available.


Relationship between DBH and the leaf carbon isotope discrimination (13C) of 11 trees for E. urophylla.
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Figure 8: Relationship between DBH and the leaf carbon isotope discrimination (13C) of 11 trees for E. urophylla.

Mentions: The substantial increase of transpirational demand in the dry season led to the decrease of ks and Gs (Figure 7B). We found that Gs decreased by 22.4% from the wet to dry seasons, while ks decreased by 45.3–65.6% more than Gs. If leaves in both seasons have the same demand for CO2, the WUE should be higher in the dry season. Such a water-use strategy may contribute to high water-use efficiency for E. urophylla, especially under dry conditions because water flux in the xylem is reduced more than Gs in the leaves. This possibility had been observed in some other studies (Brienen et al., 2011; Maseyk et al., 2011; Liu et al., 2012). In addition, the ks ratio of dry/wet decreased from 0.55 to 0.30 with increased tree size (Figure 7B), implying a higher decrease in water loss for large trees. This meant that E. urophylla in our stands tended to improve their WUE in the dry period. To verify this hypothesis, we conducted leaf carbon isotope analysis along the tree size gradient. Consistently, Δ13C showed a clear decrease with DBH (Figure 8). A number of studies have argued that moderate drought favors high WUE of tree species from different ecosystems, including forest and desert (Maseyk et al., 2011; Liu et al., 2012). Otto et al. (2014) argued that dominant clonal Eucalyptus grandis × urophylla trees use water more efficiently compared with native species. However, the underlying mechanism responsible for higher WUE is unclear. Our results indicated possible mechanisms for high WUE in dominant trees, which might be verified by further studies on the annual net biomass yield/annual transpiration, since isotope discrimination only provides an estimate of intrinsic WUE rather than the ratio of uptaken CO2 to actual fluxes of water vapor.


Hydraulic Balance of a Eucalyptus urophylla Plantation in Response to Periodic Drought in Low Subtropical China
Relationship between DBH and the leaf carbon isotope discrimination (13C) of 11 trees for E. urophylla.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5036442&req=5

Figure 8: Relationship between DBH and the leaf carbon isotope discrimination (13C) of 11 trees for E. urophylla.
Mentions: The substantial increase of transpirational demand in the dry season led to the decrease of ks and Gs (Figure 7B). We found that Gs decreased by 22.4% from the wet to dry seasons, while ks decreased by 45.3–65.6% more than Gs. If leaves in both seasons have the same demand for CO2, the WUE should be higher in the dry season. Such a water-use strategy may contribute to high water-use efficiency for E. urophylla, especially under dry conditions because water flux in the xylem is reduced more than Gs in the leaves. This possibility had been observed in some other studies (Brienen et al., 2011; Maseyk et al., 2011; Liu et al., 2012). In addition, the ks ratio of dry/wet decreased from 0.55 to 0.30 with increased tree size (Figure 7B), implying a higher decrease in water loss for large trees. This meant that E. urophylla in our stands tended to improve their WUE in the dry period. To verify this hypothesis, we conducted leaf carbon isotope analysis along the tree size gradient. Consistently, Δ13C showed a clear decrease with DBH (Figure 8). A number of studies have argued that moderate drought favors high WUE of tree species from different ecosystems, including forest and desert (Maseyk et al., 2011; Liu et al., 2012). Otto et al. (2014) argued that dominant clonal Eucalyptus grandis × urophylla trees use water more efficiently compared with native species. However, the underlying mechanism responsible for higher WUE is unclear. Our results indicated possible mechanisms for high WUE in dominant trees, which might be verified by further studies on the annual net biomass yield/annual transpiration, since isotope discrimination only provides an estimate of intrinsic WUE rather than the ratio of uptaken CO2 to actual fluxes of water vapor.

View Article: PubMed Central - PubMed

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.

No MeSH data available.