AUTHOR=Móricz Norbert , Mészáros Ilona , Kern Zoltán , Illés Gábor Zoltán , Eötvös Csaba Béla , Berki Imre , Németh Tamás Márton 
  
TITLE=Stable isotope insights into contrasting drought-response strategies of five native broadleaf tree species in East Central Europe
  
JOURNAL=Frontiers in Forests and Global Change
  
VOLUME=Volume 9 - 2026
  
YEAR=2026
  
URL=https://www.frontiersin.org/journals/forests-and-global-change/articles/10.3389/ffgc.2026.1922886
  
DOI=10.3389/ffgc.2026.1922886
  
ISSN=2624-893X
  
ABSTRACT=Future forest dynamics under climate change will largely depend on the physiological acclimation capacity of the tree species to the increasing environmental stress. We combined carbon and oxygen stable isotope analyses with growth measurements to estimate the effects of atmospheric CO2 and drought stress on intrinsic water-use efficiency (iWUE) and secondary growth in five coexisting tree species (Acer campestre, Fraxinus ornus, Quercus cerris, Quercus pubescens, Tilia tomentosa) in Central Hungary. Generalized additive models explained most of the variation in iWUE (adjusted R2 = 0.77) and growth (adjusted R2 = 0.75). The isotope and iWUE chronologies showed that these species experienced increasing hydroclimatic stress, driven primarily by rising temperatures and vapor pressure deficit. The 12-month water balance (WB12), calculated from the previous September to the current August, was the strongest climatic predictor, showing strong correlations with both Δ13C (r = 0.55–0.73) and iWUE (r = −0.60 to −0.80). Although the species differed in their physiological adaptations, the general pattern of increased iWUE coupled with stagnant or declining growth suggests that elevated atmospheric CO2 could not fully offset the unfavorable effects of increased warming and drying on tree function. Unlike the other species, Q. cerris exhibited only a modest increase in iWUE until around 2010, followed by a more pronounced increase thereafter. The relationships between iWUE and growth reveal fundamental differences among the species in their drought-response strategies. T. tomentosa and F. ornus appear to adopt a more conservative water-use strategy with strongly increasing iWUE and declining growth which may enhance short-term survival but increase long-term vulnerability. In contrast, Q. pubescens and A. campestre maintained growth under increasing iWUE, suggesting broader hydraulic safety margins or deeper rooting. Q. cerris presented an intermediate pattern with stable growth initially, but pronounced decline under severe drought. Beyond these physiological differences, site conditions and landscape structure also appeared to modulate tree responses through local microclimate effects, including evaporative demand. These findings suggest that the forest composition may shift in the drier regions of Central Europe because coexisting species differ markedly in their capacity to withstand increasing drought stress.