Effects of climate, tree age, dominance and growth on δ15N in young pinewoods

Abstract

. Effects of climate, tree age, dominance and growth on δ 15 N in young pinewoods. Trees 24, 507-510. AbstractNeedles, annual rings from basal stem disks and bark of 3 dominant and 3 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 δ 15 N. 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 δ 15 N among trees. The δ 15 N 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 δ 15 N tendency as the tree grows, which is mainly due to a more "closed" N cycle or an increasing importance of N sources with lower δ 15 N. After dominance establishment (years 9-12), wood δ 15 N 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 15 N-depleted compared to the source.According to principal component analysis, wood δ 15 N 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.

Effects of biotic and abiotic factors on δ15N in young Pinus radiata

“…The linear regression models showed that both biotic (dominance and tree age) and abiotic factors (temperature in spring-summer and annual precipitation) are needed to explain the wood  15 N air satisfactorily. Although Couto-Vázquez and González-Prieto (2010) found that tree age explained almost half of wood  15 N air variance of dominant and suppressed P. pinaster when separately considered, we only found a valid model for dominant trees with age or its inverse (1/age) explaining 34-39 % of the variance. In the best multiple regression model we obtained, explaining half the variance of wood  15 N air , the inverse of tree age has a higher standardized coefficient (0.578) than temperature in spring-summer (0.393).…”

“…As also reported in most ecosystems studied (see Högberg 1997), all plant material was 15 N-depleted compared with the  15 N air of the bulk soil in the 0-30 cm layer. While in suppressed pines the  15 N air was significantly higher in wood than in needles and bark, no differences were found for dominant trees; thus, no common trend for different coniferous species or sites (Nadelhoffer et al 1999;Couto-Vázquez and González-Prieto 2010) and dominance status can be derived.…”

Stem CO2 efflux in six co‐occurring tree species: underlying factors and ecological implications

“…It is also possible that the balance between the supply and use of NSC (Deckmyn et al . ), as well as the uptake and allocation of N (Couto‐Vázquez & González‐Prieto ) differ among trees of different crown classes, thus affecting NSC and N concentrations, and rates of R of dominant, co‐dominant and suppressed trees.…”

Effects of pre‐treatment on the nitrogen isotope composition of Japanese black pine (Pinus thunbergii) tree‐rings as affected by high N input

“…Unlike previous studies, we suggest that direct comparison of the total N concentration of untreated and pre‐treated ring samples is less meaningful, since the weight loss (removed non‐N components by toluene‐ethanol solution) upon removal is not evaluated. On the contrary, such a removal influences the δ 15 N values, since wood components (tannins, polyphenols, fats, waxes, resins, alkaloids, etc …”