TY - JOUR

T1 - Climate imprints on tree-ring δ15N signatures of sessile oak (Quercus petraea Liebl.) on soils with contrasting water availability

AU - Härdtle, Werner

AU - Niemeyer, Thomas

AU - Fichtner, Andreas

AU - Li, Ying

AU - Ries, Christian

AU - Schuldt, Andreas

AU - Walmsley, David

AU - Oheimb, Goddert

PY - 2014/10

Y1 - 2014/10

N2 - 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 175 mm and 42 mm 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.

AB - 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 175 mm and 42 mm 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.

KW - Biology

KW - climate change

KW - dendrochemistry dendroecology

KW - Isotope fractionation

KW - Luxembourg

KW - nitrogen deposition

KW - Ecosystems Research

U2 - 10.1016/j.ecolind.2014.03.015

DO - 10.1016/j.ecolind.2014.03.015

M3 - Journal articles

VL - 45

SP - 45

EP - 50

JO - Ecological Indicators

JF - Ecological Indicators

SN - 1470-160X

ER -