1. Effects of soil and atmospheric drought on intra-annual δ13C patterns in tree ringsValentina Vitali, Jernej Jevšenak, Georg von Arx, Marina Fonti, Meisha Holloway Phillips, Rubén D. Manzanedo, Kerstin Treydte, Lorenz Walthert, Roman Zweifel, Matthias Saurer, 2025, original scientific article Abstract: None declared.Conflict of interestHigh-resolution carbon isotope ratio (δ13C) measurements of tree rings have the potential to provide seasonal environmental information. However, due to the complexity of the wood formation processes, the reliability of this method for intra-seasonal reconstruction of growing conditions remains unclear. We, therefore, investigated the intra-annual variation of δ13C in tree rings of three conifer species (Pinus sylvestris, Picea abies, Abies alba) across sites from the Swiss Alps to assess their response to seasonal variation of soil water potential (SWP) and vapour pressure deficit (VPD). Intra-annual δ13C values at a resolution of 10 points per year were assessed using laser-ablation isotope-ratio mass spectrometry. Seasonal δ13C patterns were analyzed for synchronicity across trees and species, and their correlation with on-site environmental variables was used to determine the driving factors of δ13C, to reconstruct growing season dynamics, and to estimate timings of the growth dynamics and allocation of carbon to xylem formation. The δ13C patterns showed high synchronicity between species, with characteristic maxima in wet and dry years occurring in the middle of the ring and at the end of the ring, respectively. Seasonal δ13C variations reliably reflected atmospheric dryness. Higher than normal soil dryness hindered integration of further fresh assimilates into the xylem, thus allowing the identification of species- and site-specific threshold conditions that disrupt wood formation. The δ13C of Scots pine shows the strongest correlations with VPD and SWP, making it an excellent indicator of environmental variability. Silver fir appears to integrate carbon into xylem structural material over a longer season than the other conifers, whilst Norway spruce shows more plastic site-specific responses to environmental conditions. In conclusion, we identify how atmospheric and soil drought jointly impact tree growth and intra-annual δ13C patterns across conifer species, offering valuable insights for climate reconstructions and wider applications on forest dynamics.
Keywords: water availability, annual growth, laser ablation, tree-ring isotopes, carbon isotopes
Published in DiRROS: 01.10.2025; Views: 411; Downloads: 228
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2. In pursuit of change : divergent temporal shifts in climate sensitivity of Norway spruce along an elevational and continentality gradient in the CarpathiansAndrei Popa, Jernej Jevšenak, Ionel Popa, Ovidiu Badea, Allan Buras, 2024, original scientific article Abstract: Across much of Europe, climate change has caused a major dieback of Norway spruce (Picea abies L.), an economically important tree species. However, the southeasternmost fringe of this tree species – the Eastern Carpathians – has not yet suffered large-scale dieback. Studying temporal shifts of climate sensitivity (TSCS) over time may elucidate the degree to which Norway spruce may be vulnerable to climate-change induced decline in upcoming decades. Under this framework, we analyzed a regional tree-ring network comprising >3000 trees, with the aim of quantifying TSCS since 1950. We mathematically defined TSCS as the slope parameter of the regression of climate sensitivity (the correlation coefficient) over time. Given the often-observed contrasting shift of climate sensitivity at low versus high elevations, we were particularly interested in studying potentially divergent TSCS along elevational and spatial gradients. Our analyses revealed several indications of TSCS for Norway spruce in the Eastern Carpathians. First, at high elevations (>1100 m a.s.l.), we found that the positive link between summer temperature and spruce growth decreased significantly over the study period. In turn, these trees, over time, featured an increasing positive relationship with late winter temperatures. At low elevations (<800 m a.s.l.), the signal of positive summer Standardised Precipitation-Evapotranspiration Index (SPEI) correlation became more frequent among sites towards 2021, while the strength of the positive winter SPEI correlation from the previous growing season weakened. Our results revealed that TSCS was driven significantly by an elevational climate gradient and a longitudinal continentality gradient. Overall, our findings indicate that Norway spruce is increasingly affected by water limitations under climate change at low elevations, highlighting a potentially rising risk of decline of this species in the Eastern Carpathians.
Keywords: temperature, water availability, climate change, tree-ring width, non-stationarity, Picea abies, daily climate-growth relationships
Published in DiRROS: 30.09.2024; Views: 1066; Downloads: 1105
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