Interactive effects of elevated CO 2 and drought on nocturnal water fluxes in Eucalyptus saligna

Melanie J B Zeppel*, James D. Lewis, Belinda Medlyn, Craig V M Barton, Remko A. Duursma, Derek Eamus, Mark A. Adams, Nathan Phillips, David S. Ellsworth, Michael A. Forster, David T. Tissue

*Corresponding author for this work

Research output: Contribution to journalArticle

35 Citations (Scopus)

Abstract

Nocturnal water flux has been observed in trees under a variety of environmental conditions and can be a significant contributor to diel canopy water flux. Elevated atmospheric CO 2 (elevated [CO 2]) can have an important effect on day-time plant water fluxes, but it is not known whether it also affects nocturnal water fluxes. We examined the effects of elevated [CO 2] on nocturnal water flux of field-grown Eucalyptus saligna trees using sap flux through the tree stem expressed on a sapwood area (J s) and leaf area (E t) basis. After 19 months growth under well-watered conditions, drought was imposed by withholding water for 5 months in the summer, ending with a rain event that restored soil moisture. Reductions in J s and E t were observed during the severe drought period in the dry treatment under elevated [CO 2], but not during moderate- and post-drought periods. Elevated [CO 2] affected night-time sap flux density which included the stem recharge period, called 'total night flux' (19:00 to 05:00, J s,r), but not during the post-recharge period, which primarily consisted of canopy transpiration (23:00 to 05:00, J s,c). Elevated [CO 2] wet (EW) trees exhibited higher J s,r than ambient [CO 2] wet trees (AW) indicating greater water flux in elevated [CO 2] under well-watered conditions. However, under drought conditions, elevated [CO 2] dry (ED) trees exhibited significantly lower J s,r than ambient [CO 2] dry trees (AD), indicating less water flux during stem recharge under elevated [CO 2]. J s,c did not differ between ambient and elevated [CO 2]. Vapour pressure deficit (D) was clearly the major influence on night-time sap flux. D was positively correlated with J s,r and had its greatest impact on J s,r at high D in ambient [CO 2]. Our results suggest that elevated [CO 2] may reduce night-time water flux in E. saligna when soil water content is low and D is high. While elevated [CO 2] affected J s,r, it did not affect day-time water flux in wet soil, suggesting that the responses of J s,r to environmental factors cannot be directly inferred from day-time patterns. Changes in J s,r are likely to influence pre-dawn leaf water potential, and plant responses to water stress. Nocturnal fluxes are clearly important for predicting effects of climate change on forest physiology and hydrology.

Original languageEnglish
Pages (from-to)932-944
Number of pages13
JournalTree physiology
Volume31
Issue number9
DOIs
Publication statusPublished - Sep 2011

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    Zeppel, M. J. B., Lewis, J. D., Medlyn, B., Barton, C. V. M., Duursma, R. A., Eamus, D., ... Tissue, D. T. (2011). Interactive effects of elevated CO 2 and drought on nocturnal water fluxes in Eucalyptus saligna. Tree physiology, 31(9), 932-944. https://doi.org/10.1093/treephys/tpr024