Irrigation and drought stress effects on CO2 exchange in mountain ecosystems: The Levionaz (Gran Paradiso National Park) case study.

In the context of climate change and sustainable development, under the crucial perspective of an increasing pressure from human impacts, long-term conservation of mountain areas is a key strategy to improve ecosystem resilience to global warming. In the present study we evaluated the role of water availability on CO2 fluxes exchange, net ecosystem exchange (NEE), ecosystem respiration (ER) and gross primary production (GPP) in the Levionaz Plain, a high mountain grassland located in the Gran Paradiso National Park (Italian Alps). CO2 fluxes were measured by the accumulation chamber method, and soil volumetric water content (VWC) was used as proxy for water availability. Fluxes responses to different hydric regimes were established by comparing artificially irrigated (IN) and not irrigated (OUT) plots during two different years (2022, 2023), which showed different drought conditions. In particular, we detected that in 2022 was the most severe drought event recorded in the last 17 years. Results revealed that under drought conditions, water availability plays a key role in the ecosystem exchange of CO2. ER and GPP fluxes showed different responses in the two plots, with GPP most affected, and with significant differences detected in 2022, where higher values were measured in the IN plots for all fluxes. In 2023, only GPP and NEE showed significant differences between IN and OUT areas, while ER was not sensitive to irrigation. Generalized linear models highlighted that VWC was a dominating driver in the driest 2022 for both ER and GPP, but not in 2023. GPP demonstrated high sensitivity to VWC over the two evaluated years, being the response to water availability in the driest 2022 more pronounced than that of ER. This study provides insights for managing alpine grassland, suggesting that strategic, low-level irrigation during droughts can sustain productivity, offering a conservation strategy to mitigate extreme drought impacts.