Abstract
Needles, annual rings from basal stem discs and bark of three dominant and three suppressed Pinus pinaster from a 12-year-old pine stand (naturally regenerated after a wildfire) were analysed to study the effects of climate, tree age, dominance, and growth on tree δ15N. Foliar-N concentration in dominant pines (0.780–1.474% N) suggested that soil N availability was sufficient, a circumstance that allowed isotopic discrimination by plants and (greater) differences in δ15N among trees. The δ15N decreases in the order wood (−0.20 to +6.12‰), bark (−1.84 to +1.85‰) and needles (−2.13 to +0.77‰). In all trees, before dominance establishment (years 1–8), the N stored in each ring displayed a decreasing δ15N tendency as the tree grows, which is mainly due to a more “closed” N cycle or an increasing importance of N sources with lower δ15N. After dominance establishment (years 9–12), wood δ15N values were higher in suppressed than in dominant trees (2.62 and 1.46‰, respectively; P < 0.01) while the reverse was true for needles and bark; simultaneously, the absolute amount of N stored by suppressed pines in successive rings decreased, suggesting a lower soil N assimilation. These results could be explained by lignification acting as major N source for needles in suppressed pines because products released and reallocated during lignification are 15N-depleted compared with the source. According to principal component analysis, wood δ15N appears associated with wood N concentration and precipitation during the growing season, but clearly opposed to age, basal area increment and mean temperature in spring and summer.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.