Increase in water-use efficiency and underlying processes in pine forests across a precipitation gradient in the dry Mediterranean region over the past 30 years

Kadmiel Maseyk, Debbie Hemming, Alon Angert, Steven W. Leavitt, Dan Yakir*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

79 Scopus citations

Abstract

Motivated by persistent predictions of warming and drying in the entire Mediterranean and other regions, we have examined the interactions of intrinsic water-use efficiency (W i) with environmental conditions in Pinus halepensis. We used 30-year (1974-2003) tree-ring records of basal area increment (BAI) and cellulose 13C and 18O composition, complemented by short-term physiological measurements, from three sites across a precipitation (P) gradient (280-700 mm) in Israel. The results show a clear trend of increasing W i in both the earlywood (EW) and latewood (LW) that varied in magnitude depending on site and season, with the increase ranging from ca. 5 to 20% over the study period. These W i trends were better correlated with the increase in atmospheric CO 2 concentration, C a, than with the local increase in temperature (~0.04°C year -1), whereas age, height and density variations had minor effects on the long-term isotope record. There were no trends in P over time, but W i from EW and BAI were dependent on the interannual variations in P. From reconstructed C i values, we demonstrate that contrasting gas-exchange responses at opposing ends of the hydrologic gradient underlie the variation in W i sensitivity to C a between sites and seasons. Under the mild water limitations typical of the main seasonal growth period, regulation was directed at increasing C i/C a towards a homeostatic set-point observed at the most mesic site, with a decrease in the W i response to C i with increasing aridity. With more extreme drought stress, as seen in the late season at the drier sites, the response was W i driven, and there was an increase in the W i sensitivity to C a with aridity and a decreasing sensitivity of C i to C a. The apparent C a-driven increases in W i can help to identify the adjustments to drying conditions that forest ecosystems can make in the face of predicted atmospheric change.

Original languageAmerican English
Pages (from-to)573-585
Number of pages13
JournalOecologia
Volume167
Issue number2
DOIs
StatePublished - Oct 2011

Bibliographical note

Funding Information:
Acknowledgments Jim Burns of the Laboratory of Tree-Ring Research dated the samples and measured ring widths. Pablo Garcia of LTRR helped to prepare the α-cellulose from the rings. This research was supported by grants from the International Arid Land Consortium (IALC) and GLOWA-Jordan River, The Henry Gutwirth Fund for Research and the Philip M. Klutznick Fund for Research. DH and DY acknowledge the financial support provided through the European Community’s Human Potential Programme under contract HPRN-CT-1999-00059, NETCARB. AA was supported by a Weizmann Institute Postdoctoral Fellowship. We also thank three anonymous reviewers and the Handling Editor whose comments have helped produce a better manuscript.

Keywords

  • Aleppo pine
  • CO fertilization
  • Dryland productivity
  • Isotope dendrology
  • Stomatal conductance

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