Variation in the stable carbon isotope composition of needle and annual rings in pseudotsuga menziesii (mirb.) franco and its relation to water use needle nitrogen content and productivy.
Date
1996
Authors
Allan, Wendy Lynne
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Abstract
The variability of foliage stable carbon isotope composition (o13C) in relation to needle nitrogen content and biomass production in coastal Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco var. menziesii) was investigated. The objectives were 1) to determine the variability in ol3c of ten families of Douglas fir 2) to establish the relationship between needle nitrogen content and o13c 3) to establish the relationship between productivity and ol3c 4) and to establish the relationship between o13c and tree water use. Needle and wood tissue were collected for anaylsis from ten half-sib families growing at two contrasting sites in southwestern Washington as part of a wide adaptability trial. Needles were also analzyed from seedlings representing the 10 families, that were subjected to an irrigated and drought treatment.
My research has shown that:
(1) Foliage ol3c is influenced by both water and nitrogen stress. Whilst theory predicts that ol3c should increase as the trees are subjected to water stress, it was found that the foliage ol3c was more negative at the drier sites. This was because needle nitrogen had an overwhelming effect on o13c There was a positive, linear relationship between foliage ol3c and nitrogen content across all sites.
(2) There was a positive correspondence between growth and foliage ol3c within trees that were not subjected to severe water stress. The lack of any relationship between foliage ol3c and growth within droughted seedlings and the increase in the root:shoot ratio under water stress suggests that carbon allocation patterns change under water stress. No relationships were found between the oI 3c of whole annual rings and growth. However, there was a significant relationship between the late wood o 13c and latewood width. It is recommended that the annual tree ring should be delineated into its early and latewood components to evaluate relationships between o 13c and other parameters.
(3) There was consistent ranking of families in terms of foliage o13c between the irrigated and droughted seedlings and between the irrigated seedlings and the needles from the coastal Washington site suggesting that there is genetic variability in foliage b13C. Therefore, there is a potential to use foliage bl 3c as a proxy indicator of long-term water use efficiency in Douglas-fir. However, annual ring o13c was influenced more by environmental rather than genetic factors. It may be that the annual ring ol3c i a better indicator of tree water use over the long-term.