Non-climatic variations in the oxygen isotopic compositions of plants

Authors: WANG X-F.; YAKIR D.; AVISHAI M.

Source: Global Change Biology, Volume 4, Number 8, December 1998 , pp. 853-849(15)

Publisher: Wiley-Blackwell

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Abstract:

Abstract

The ¹⁸O content of leaf water strongly influences the ¹⁸O contents of atmospheric CO₂ and O₂. The ¹⁸O signatures of these atmospheric gases, in turn, emerge as important indicators of large-scale gas exchange processes. Better understanding of the factors that influence the isotopic composition of leaf water is still required, however, for the quantitative utilization of these tracers. The ¹⁸O enrichment of leaf water relative to local meteoric water, is known to reflect climatic conditions. Less is known about the extent variations in the ¹⁸O content of leaf water are influenced by nonclimatic, species-specific characteristics. In a collection of 90 plant species from all continents grown under the same climatic conditions in the Jerusalem Botanical Garden we observed variations of about 9 permil in the delta ¹⁸O values of stem water, delta _s, and of about 14 permil in the mid-day delta ¹⁸O enrichment of bulk leaf water, delta _LW – delta _s. Differences between delta ¹⁸O values predicted by a conventional evaporation model, delta _M, and delta _LW ranged between – 3.3 permil and + 11.8 permil . The delta ¹⁸O values of water in the chloroplasts ( delta _ch) in leaves of 10 selected plants were estimated from on-line CO₂ discrimination measurements. Although much uncertainty is still involved in these estimates, the results indicated that delta _ch can significantly deviate from delta _M in species with high leaf peclet number. The delta ¹⁸O values of bulk leaf water significantly correlated with delta ¹⁸O values of leaf cellulose (directly) and with instantaneous water use efficiency (A/E, inversely). Differences in isotopic characteristics among conventionally defined vegetation types were not significant, except for conifers that significantly differed from shrubs in delta ¹⁸O and delta ¹³C values of cellulose and in their peclet numbers, and from deciduous woodland species in their delta ¹⁸O and delta ¹³C values of cellulose. The results indicated that predictions of the delta ¹⁸O values of leaf water ( delta _LW, delta _M and delta _ch) could be improved by considering plant species-specific characteristics.