Climate imprints on tree-ring δ15N signatures of sessile oak (Quercus petraea Liebl.) on soils with contrasting water availability

• Published in: Ecological indicators Vol. 45; pp. 45 - 50
• Main Authors: Härdtle, Werner, Niemeyer, Thomas, Fichtner, Andreas, Li, Ying, Ries, Christian, Schuldt, Andreas, Walmsley, David, von Oheimb, Goddert
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Ltd 01.10.2014; Elsevier
• Subjects: ammonium compounds; Animal and plant ecology; Animal, plant and microbial ecology; Applied ecology; available water capacity; Biological and medical sciences; Cambisols; Central European region; Climate change; climatic factors; Climatology. Bioclimatology. Climate change; Conservation, protection and management of environment and wildlife; Dendrochemistry; Dendroecology; Earth, ocean, space; Exact sciences and technology; External geophysics; Fagus; forest soils; Fundamental and applied biological sciences. Psychology; General aspects; growth rings; Isotope fractionation; Luxembourg; Meteorology; nitrates; nitrification; nitrogen; Nitrogen deposition; Parks, reserves, wildlife conservation. Endangered species: population survey and restocking; pollution; Quercus petraea; Regosols; soil horizons; spring; stable isotopes; Synecology; temperature; topsoil; trees; winter; wood; Europe; Luxembourg; Western Europe; Central European region; Climate change; Isotope fractionation; Dendroecology; Nitrogen deposition; Luxembourg; Dendrochemistry; Climate; Water supply; Environmental factor; Dicotyledones; Angiospermae; Sessile; Nitrogen-15; Isotopes; Quercus petraea; Fractionation; Atmospheric fallout; Ecology; Water availability; Fagaceae; Dynamical climatology; Soils; Tree ring; Spermatophyta; Environmental monitoring; Environmental protection
• ISSN: 1470-160X; 1872-7034
• DOI: 10.1016/j.ecolind.2014.03.015

•We analyzed climate imprints on wood δ15N signatures of Quercus petraea.•Winter and spring temperatures and precipitation positively affected δ15N values.•Maximum wood 15N values were related to climate warming in recent decades.•Climate- δ15N relationships improved with the sites’ water supply.•Wood δ15N signals constitute an indicator to trace shifts in soil N cycling. In the present study we investigated long-term climate imprints (160 year period) on tree-ring δ15N signatures of sessile oak (Quercus petraea) at sites with contrasting water availability (i.e. Cambisols vs. Regosols in Luxembourg, Central Europe, with 175mm and 42mm available water capacity, respectively). We hypothesized that tree-ring δ15N signatures constitute a sensitive indicator to long-term shifts in climatic conditions. Our findings revealed a close positive correlation between winter and spring temperatures and tree-ring δ15N signatures. These relationships were stronger for Cambisol than for Regosol sites. If entire chronologies were considered, peaks in annual mean temperatures closely corresponded with peaks in tree-ring δ15N signatures, with both annual mean temperatures and δ15N signatures reaching their maxima within the last two decades. In addition, we found a weak but significant impact of February precipitation on δ15N signatures, but only for Cambisols. We hypothesize that these findings are attributable to climate- (particularly temperature-) mediated nitrification rates in forest soils. As nitrification is a strongly fractionating process that produces 15N-depleted nitrate and higher isotopic ratios for ammonium in the topsoil, increased nitrification leads to 15N-enriched pools of Ninorg in the upper soil horizons and therefore higher δ15N signatures in plant tissues. Weaker correlations at Regosol sites were likely related to dryer and more acidic site conditions, both of which may reduce nitrification rates. Comparisons of oak and beech trees in the study area point to species-specific trajectories of wood nitrogen isotopes, likely related to the partitioning of ammonium and nitrate among species. In conclusion, tree-ring δ15N signatures may serve as an integrator of terrestrial N cycling and as such constitute a valuable tool in the identification of spatial and temporal patterns of N cycling in relation to environmental changes. Due to the mediating effects of the isotopic composition of the respective N sources, analyses of the isotopic composition of airborne N loads would support the interpretation of wood δ15N patterns, particularly in areas that are subject to high N pollution.