Amplifying effects of recurrent drought on the dynamics of tree growth and water use in a subalpine forest

Abstract

Despite recent advances in our understanding of drought impacts on tree functioning, we lack knowledge about the dynamic responses of mature trees to recurrent drought stress. At a subalpine forest site, we assessed the effects of three years of recurrent experimental summer drought on tree growth and water relations of Larix decidua Mill. and Picea abies (L. Karst.), two common European conifers representative for contrasting water‐use strategies. We combined dendrometer and xylem sap flow measurements with analyses of xylem anatomy and non‐structural carbohydrates and their carbon‐isotope composition. Recurrent drought increased the effects of soil moisture limitation on growth and xylogenesis, and to a lesser extent on xylem sap flow. P. abies showed stronger growth responses to recurrent drought, reduced starch concentrations in branches and increased water‐use efficiency when compared to L. decidua. Despite comparatively larger maximum tree water deficits than in P. abies, xylem formation of L. decidua was less affected by drought, suggesting a stronger capacity of rehydration or lower cambial turgor thresholds for growth. Our study shows that recurrent drought progressively increases impacts on mature trees of both species, which suggests that in a future climate increasing drought frequency could impose strong legacies on carbon and water dynamics of treeline species.

High-resolution Carbon cycling data from 2019 to 2021 measured at six Austrian LTER sites

“…Drought effects on the ecosystem C cycle can persist for years (Kannenberg et al, 2020;Müller and Bahn, 2022) and novel approaches are being developed for assimilating high-resolution data for understanding and quantifying such legacies (Yu et al, 2022;Fu et al, 2020). In this context, the availability of long-term, high-resolution measurements of key ecosystem parameters is key for understanding and quantifying the effects of recurrent droughts (Oberleitner et al, 2022). The sites presented here are currently being upgraded towards their implementation in the European Research Infrastructure for Integrated European Long-Term Ecosystem, critical zone and socio-ecological Research (eLTER RI), together with another ~200 sites in Europe (Mirtl et al, 2018).…”

“…and Norway spruce (Picea abies (L.) H.Karst.). In former years, the plot was a pasture and it was reforested in the 1980s (Oberleitner et al, 2022).…”

“…In the grassland, land use and drought related carbon cycle research was carried out over the last two decades (Fuchslueger et al, 2014;Hasibeder et al, 2015;Ingrisch et al, 2020;. Research using the forest plot started only recently (Oberleitner et al, 2022). LTER Zöbelboden is located in the National Park Kalkalpen in the Northern Limestone Alps, Austria (Figure 1).…”

“…Stem growth limitations can, on the other hand, be closely related to soil water content, particularly at sites with relatively low precipitation such as Klausen-Leopoldsdorf (KLL) (Figure 5). For an in-depth study of drought related effects on tree growth at the treeline forest at Kasterstattalm (KAS), we refer to Oberleitner et al (2022).…”

Widespread but divergent drought legacy effects on gross primary productivity

“…Our study further advances the interest by investigating GPP at the ecosystem level. However, the linkage across different scales still remains limited 15 , highlighting the need for further research that integrates data from the individual level such as tree radial growth, tree water deficit 66 , and sap flow 67 to the ecosystem level like greenness, vegetation water content 68 , carbon and water fluxes. This holistic approach considering these different dimensions would be essential to comprehensively understand drought legacy effects across scales.…”