Forest responses to global change drivers: insights from temperate and tropical ecosystems

Forests, often likened to the lungs of our planet, are at the forefront of climate mitigation strategies. Understanding how major changes affecting the atmosphere (i.e., climate and pollutants) affect ecological and ecophysiological processes underpinning forest functioning is paramount to the preservation of essential ecosystem services they provide. In the era of global change, this thesis encompasses three scientific studies that together contribute to advancing our understanding of the intricate ecophysiological responses of both temperate and tropical forest ecosystems to diverse global change drivers. The initial two papers, focus on the impact of atmospheric nitrogen (N) deposition on two temperate forest ecosystems. These studies employ a long-term manipulative experiment, where the application of N fertilizer simulates the increase in N deposition. The first study investigates forest health under elevated N deposition by employing foliar nutrient and photosynthetic pigment concentrations as stress indicators. The second paper integrates measurements of N concentration and its isotopic composition across various forest compartments, coupled with molecular analyses of soil nitrogen functional genes, to characterize processes underpinning the N cycle. The third paper, delves into water and nutrient balances in a tropical montane cloud forest (TMCF). It underscores the imperative to address the knowledge gap on tropical forest ecosystems, which may be compromised by climate change, such as alterations in precipitation water regimes and rising temperatures. This study utilizes carbon (C) and N stable isotopes in soil and plant tissues to evaluate water-use efficiency and nutrient dynamics, highlighting the potential vulnerability of TMCFs to evolving climatic conditions. These studies articulate the challenges faced by forests. From the effects of N deposition on nutrient concentrations and N dynamics in temperate forests to the ecohydrological balance in the TMCFs, these insights deepen our comprehension of the complex interplay between human-induced changes and the resilience of forest ecosystems.