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https://doi.org/10.5194/bgd-12-10469-2015
https://doi.org/10.5194/bgd-12-10469-2015
09 Jul 2015
 | 09 Jul 2015
Status: this discussion paper is a preprint. It has been under review for the journal Biogeosciences (BG). The manuscript was not accepted for further review after discussion.

Water use strategies of a young Eucalyptus urophylla forest in response to seasonal change of climatic factors in South China

Z. Z. Zhang, P. Zhao, R. Oren, H. R. McCarthy, J. F. Niu, L. W. Zhu, G. Y. Ni, and Y. Q. Huang

Abstract. To depict the wet (April with a soil water content, SWC, of 37 %) and dry (October with a SWC of 24.8 %) seasonal changes in the water use and physiological response of a Eucalyptus urophylla plantation in subtropical South China characterized by monsoon climate, the whole-year (June 2012 to May 2013) transpiration of E. urophylla was monitored using the TDP method. Daily transpiration (ET) in October averaged 5.7 ± 2.9 kg d−1 and was 58.0 % higher than that in April (3.6 ± 2.3 kg d−1). The difference is consistent with that of the radiation and evaporative demand of the two months, while the nocturnal transpiration (ET-NOC) in the wet season (0.18 ± 0.021 kg d−1) was almost twice that in the dry season (0.11 ± 0.01 kg d−1). Trees displayed a higher stomatal conductance (GS) (53.4–144.5 mmol m−2 s−1) in the wet season and a lower GS (45.7–89.5 mmol m−2 s−1) in the dry season. The leaf-soil water potentials (ΨL) of the two months (April and October) were −0.62 ± 0.66 and −1.22 ± 0.10 MPa, respectively. A boundary line analysis demonstrated that the slight improvement in the GS by SWC in wet season was offset by a significant decrease in D, and the slope of GS sensitivity to D (dGS/dlnD) in response to GSref (references GS at D = 1 kPa) was affected by the variance of radiation instead of SWC. Specific hydraulic conductivity (ks) of trees of different sizes decreased by 45.3–65.6 % from the wet to the dry season. Combining the decreased maximum reference GS at D = 1 kPa (GSref-max) by 22.4 % with the constant max GS (GSmax) when ΨL < −1.2 MPa, we shed some light on the mechanism underlying the high water-use efficiency (WUE) of this Eucalyptus specie. With a slight change in GSref-max and high sensitivity of ks to decreasing ΨL, large trees used water more efficiently than small ones did. In addition, the −m in the dry season (0.53 ± 0.007) was lower than that in the wet season (0.58 ± 0.01) due to the difference in the ratio of GS to the boundary layer conductance (gb) in the two months. The negative relationship between −m (except when light is limited) and Q proved to be a plastic response to environmental changes for E. urophylla but did not change with decreased ks as expected.

Z. Z. Zhang, P. Zhao, R. Oren, H. R. McCarthy, J. F. Niu, L. W. Zhu, G. Y. Ni, and Y. Q. Huang
 
Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version Supplement - Supplement
 
Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version Supplement - Supplement
Z. Z. Zhang, P. Zhao, R. Oren, H. R. McCarthy, J. F. Niu, L. W. Zhu, G. Y. Ni, and Y. Q. Huang
Z. Z. Zhang, P. Zhao, R. Oren, H. R. McCarthy, J. F. Niu, L. W. Zhu, G. Y. Ni, and Y. Q. Huang

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Short summary
a) More dramatically decreased hydralic conductivity when stomatal conductance was decreasing may shed some light on the mechanism of the high WUE of Eucalyptus when exposed to drought conditions. b) As tree grows, ks is more sensitive to water loss. c) The decrease in stomatal sensitivity of GSref to D along the radiation gradient accounted for an important aspect of “plastic characteristics” for E. urophylla.
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