Wiesenberg, G. L. B. | bioRxiv Science

bioRxiv2026

Drought alters volatile profiles in European beech saplings across genetically diverse backgrounds

O_LIEuropean beech (Fagus sylvatica L.) is a widely distributed, ecologically and economically important deciduous tree species in European forests, but is increasingly threatened by drought stress. Volatile organic compounds (VOCs) are ubiquitous plant metabolites that may serve as non-invasive biomarkers of drought stress, yet they have rarely been studied in European beech. C_LIO_LIIn this study, we examined VOC responses of European beech to experimental drought across diverse genetic backgrounds in a common garden. The 72 four-year-old beech saplings represented three genetic clusters, seven provenances (geographic seed sources), and 12 maternal seed families. Half of the saplings were assigned to the drought treatment and received no water for 14 days, while the remaining saplings served as controls and were watered as required. VOC profiles, quantified as peak heights of mass spectral features, were measured for all individuals during pre-drought, drought, and rewatering periods. C_LIO_LIWe found that pre-drought VOC profiles, in particular monoterpenes, varied significantly among genetic backgrounds. Experimental drought significantly altered VOC profiles, characterized by increased green leaf volatiles and decreased monoterpenes, oxidized terpenoid derivatives, and other fatty acid derivatives. Reductions in monoterpenes persisted after rewatering, indicating a drought legacy effect. Drought responses were largely conserved across genetic backgrounds, with significant seed family-specific responses detected for only three VOC features. C_LIO_LIOur findings suggest that VOC profiles are genetically structured yet highly plastic under drought and highlight their potential as non-invasive biomarkers for monitoring drought stress in European beech under climate change. C_LI

ecology↗

bioRxiv2024

Leaf spectroscopy reveals drought response variation in Fagus sylvatica saplings from across the species' range

The common European beech (F. sylvatica), sensitive to prolonged drought, is expected to shift its distribution with climate change. To persist in novel environments, young trees rely on the capacity to express diverse response phenotypes. Several methods exist to study drought effects on trees and their diverse adaptive mechanisms, but these are usually destructive and challenging for the large sample numbers needed to investigate biological variation. We conducted a common garden experiment outdoors, but under controlled watering conditions, with 180 potted two-year-old saplings from 16 beech provenances across the species range, representing three distinct genetic clusters. Drought stress was simulated by interrupting irrigation and stomatal conductance and soil moisture were used to assess drought severity. We measured leaf reflectance of visible to short-wave infrared electromagnetic radiation to determine droughtinduced changes in biochemical and structural traits derived from spectral indices and a model of leaf optical properties. We quantified changes in pigmentation, water balance, nitrogen, lignin, epicuticular wax, and leaf mass per area in drought-treated saplings, revealing differences in likely adaptive responses to drought. Fagus sylvatica saplings from the Iberian Peninsula showed signatures of greater drought resistance, i.e., the least droughtinduced change in spectrally derived traits related to leaf pigments and leaf water content. We demonstrate that high-resolution leaf spectroscopy is an effective and non-destructive tool to assess individual drought responses that can characterize functional intraspecific variation among young beech trees. Next, this approach should be scaled up to canopy-level or airborne spectroscopy to support drought response assessments of forests. Plain language summaryThe common European beech tree, which is sensitive to prolonged droughts, is expected to experience local population declines due to climate change. To survive in a drier and warmer climate, young beech trees must show a variety of adaptive responses. Assessing this variation within the species is challenging, and traditional methods often harm the trees, limiting large-scale studies of their variability. We conducted an outdoor experiment with 180 potted young beech saplings from various European regions, simulating a severe drought by halting irrigation. Using advanced leaf reflectance measurements, we tracked biochemical and structural changes in the leaves, such as pigmentation, water content, and other traits. Our results highlight that beech saplings from the Iberian Peninsula demonstrated greater drought resistance, showing fewer changes compared to saplings from other regions. This study underscores the effectiveness of non-destructive, high-resolution leaf spectroscopy in assessing individual drought responses, revealing important insights into the adaptive capacity of beech trees under changing climatic conditions. Key PointsO_LILeaf reflectance measurements effectively track drought-induced trait changes in beech saplings in a non-destructive way. C_LIO_LIBeech saplings from the Iberian Peninsula show greater drought resistance with fewer biochemical and structural changes. C_LIO_LIHigh-resolution leaf spectroscopy reveals adaptive capacity differences within European beech populations under simulated drought stress. C_LI

ecology↗