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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.


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(A) GSref (Gs of each tree at D = 1 kPa) normalized based on the highest value in relation to mean photosynthetically active radiation (Q0). (B) The stomatal sensitivity (–m) of each tree in relation to Q0 in dry (open symbols) and wet seasons (solid symbols). Symbols are the mean ± SD of all 15 trees for each light group. Lines are least-square fit through the entire data. Symbols with same letters shown in (a) indicate non-significant differences among light groups, where capital/lower cases refer to dry/wet season.
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Figure 5: (A) GSref (Gs of each tree at D = 1 kPa) normalized based on the highest value in relation to mean photosynthetically active radiation (Q0). (B) The stomatal sensitivity (–m) of each tree in relation to Q0 in dry (open symbols) and wet seasons (solid symbols). Symbols are the mean ± SD of all 15 trees for each light group. Lines are least-square fit through the entire data. Symbols with same letters shown in (a) indicate non-significant differences among light groups, where capital/lower cases refer to dry/wet season.

Mentions: The time lag between D and Gs was found to be 1.3 and 0.5 h in dry and wet seasons respectively. Thus, time-lagged Gs was used to calculate GSref. GSref had a linear relationship with -dGs/dLnD in both dry and wet seasons, but significant differences of the slopes were observed under different light levels (ANOVA, p < 0.01, Figure 4). Normalized GSref of all of the trees increased rapidly as Q0 rose until maximum (Figure 5A). GSref reached 90% of the maximum (GS90) when Q0 was 287.8 and 167.1 μmol m-2 s-1 in the dry and wet seasons, respectively. This revealed that GSref was more sensitive to light in wet season, leading to a lower saturation point than that in the dry season (p < 0.01). It was found that -m at different light levels had a weak relationship with tree size (not shown; p = 0.33). The effect of Q0 on –m was also quantified in both seasons (Figure 5B). –m gradually decreased with Q0 before a short increase under low light conditions (ANOVA, Duncan, p < 0.01), i.e., the sensitivity was not constant within a single day when the light intensity varied substantially. When the data under low light conditions (Q0< 200 μmol m-2 s-1) were removed, a linear decrease in -m ranging from 0.32 to 0.83 (dry season) and 0.22 to 1.10 (wet season) with radiation was observed for the 15 trees (Figure 5B). Mean -m was substantially higher in the wet season (0.58 ± 0.01) than in the dry season (0.53 ± 0.007) (p = 0.038).


Hydraulic Balance of a Eucalyptus urophylla Plantation in Response to Periodic Drought in Low Subtropical China
(A) GSref (Gs of each tree at D = 1 kPa) normalized based on the highest value in relation to mean photosynthetically active radiation (Q0). (B) The stomatal sensitivity (–m) of each tree in relation to Q0 in dry (open symbols) and wet seasons (solid symbols). Symbols are the mean ± SD of all 15 trees for each light group. Lines are least-square fit through the entire data. Symbols with same letters shown in (a) indicate non-significant differences among light groups, where capital/lower cases refer to dry/wet season.
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Related In: Results  -  Collection

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Figure 5: (A) GSref (Gs of each tree at D = 1 kPa) normalized based on the highest value in relation to mean photosynthetically active radiation (Q0). (B) The stomatal sensitivity (–m) of each tree in relation to Q0 in dry (open symbols) and wet seasons (solid symbols). Symbols are the mean ± SD of all 15 trees for each light group. Lines are least-square fit through the entire data. Symbols with same letters shown in (a) indicate non-significant differences among light groups, where capital/lower cases refer to dry/wet season.
Mentions: The time lag between D and Gs was found to be 1.3 and 0.5 h in dry and wet seasons respectively. Thus, time-lagged Gs was used to calculate GSref. GSref had a linear relationship with -dGs/dLnD in both dry and wet seasons, but significant differences of the slopes were observed under different light levels (ANOVA, p < 0.01, Figure 4). Normalized GSref of all of the trees increased rapidly as Q0 rose until maximum (Figure 5A). GSref reached 90% of the maximum (GS90) when Q0 was 287.8 and 167.1 μmol m-2 s-1 in the dry and wet seasons, respectively. This revealed that GSref was more sensitive to light in wet season, leading to a lower saturation point than that in the dry season (p < 0.01). It was found that -m at different light levels had a weak relationship with tree size (not shown; p = 0.33). The effect of Q0 on –m was also quantified in both seasons (Figure 5B). –m gradually decreased with Q0 before a short increase under low light conditions (ANOVA, Duncan, p < 0.01), i.e., the sensitivity was not constant within a single day when the light intensity varied substantially. When the data under low light conditions (Q0< 200 μmol m-2 s-1) were removed, a linear decrease in -m ranging from 0.32 to 0.83 (dry season) and 0.22 to 1.10 (wet season) with radiation was observed for the 15 trees (Figure 5B). Mean -m was substantially higher in the wet season (0.58 ± 0.01) than in the dry season (0.53 ± 0.007) (p = 0.038).

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 (&Psi;L) 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 &ndash; 65.6% from the wet to the dry season, depending on the tree size. Fairly stable leaf stomatal conductance (gs) with decreasing &Psi;L (&Psi;L &lt; -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 &Psi;L. This was also verified by the decreasing leaf carbon isotope discrimination (&Delta;13C) 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.


Related in: MedlinePlus