Research Highlights: In this study, we found different regulatory mechanisms in two contrasting provenances of Norway spruce responding to progressive drought stress. Background and Objectives: In the context of climate and environmental changes, the following question of high importance in scientific studies is: How will Norway spruce, which forms a dominant component in European mountain and boreal forests, be able to cope with the increasing frequencies and intensities of drought periods? The aim of the study was to investigate the physiological responses of eight-month-old seedlings, as a most vulnerable phase of forest tree life, for different spruce provenances, to find out variable strategies in relation to controlled drought stress. Materials and Methods: We performed an experiment under controlled conditions with spruce seedlings from a climatologically warmer stand of 410 m above sea level (a.s.l.), and a moderately cool stand of 931 m a.s.l. The soil water content, leaf predawn water potential, the osmotic potential of needles, the relative water content of needles, and the photosynthetic performance and the contents of primary metabolites (proline and abscisic acid) were investigated as indicators of the spruce seedlings’ responses to water stress. The status of the indicators was analyzed at different temporal intervals, using repeated measures analysis of variance (ANOVA), reflecting the seedlings’ water conditions (early drought, drought, or recovery). On a daily basis, the differences among the indicators were tested with one-way ANOVA. A principal component analysis (PCA) was used to identify the provenance-specific responses of tree drought indicators in a multi-dimensional data set. Results: The responses to drought stress differed between the provenances. Whereas seedlings of ‘warm’ provenance from a low altitude performed a conservation strategy, with high amounts of accumulated abscisic acid and closing the stomata faster, the reactions of ‘cool’ provenance seedlings from a higher altitude were not so sensitive and the plants’ water supply and photosynthetic performance remained significantly higher. These findings indicate that a higher drought resistance in ‘cool’ provenance could be related to greater amounts of proline amino-acids, which are accumulated from the beginning of the drought simulation. Furthermore, proline accumulation resulting in increased stress tolerance is controlled through another mechanism than osmotic adjustment. Conclusions: The observed variations in the regulatory mechanisms used to develop adaptive strategies in different provenances are an important factor for seedling survival under a changing climate.

Photosynthetica covers wide range of photosynthesis research or research including photosynthetic parameters of both experimental and theoretical nature.

Heavy metals accumulate in forest soils worldwide, yet their effects on greenhouse gas dynamics remain poorly understood. Mycorrhizal fungi lie at the heart of this issue. These symbiotic organisms regulate carbon and nutrient flow between trees and soil, positioning them to influence fluxes of CO₂, N₂O, and CH₄. However, research on mycorrhizal ecology, metal toxicology, and greenhouse gas biogeochemistry has proceeded largely in isolation. This review bridges these fields through a conceptual framework built on three contamination scenarios and four mechanistic pathways. Our confidence in these mechanisms varies by gas: well-established for CO₂, developing for N₂O, and mostly inferential for CH₄. Critical gaps remain. Studies measuring mycorrhizal communities, metal availability, and gas emissions simultaneously are rare. Comparisons between ectomycorrhizal and arbuscular mycorrhizal systems are virtually absent. This framework establishes a basis for understanding how metal-contaminated forests regulate greenhouse gas exchange and identifies priority areas for future investigation.

Ten five-year-old seedlings of Norway spruce ( Picea abies L. Karst) from the Western Carpathians were subjected to drought (30 days without irrigation) in laboratory conditions (D trees). The control group (C trees) were irrigated regularly. Parameters such as stem diameter variations ( SDV ), soil water potential ( Ψ _S ), gas exchange and chlorophyll a fluorescence were measured. Stem growth of D trees was significantly reduced below Ψ _S = –0.3 MPa, and completely stopped below Ψ _S = –1.1 MPa. Tree water deficit ( TWD , calculated from SDV ) of D trees started to increase substantially below the threshold Ψ _S = –0.9 MPa, and closely correlated with Ψ _S . Photosynthetic traits of D trees reacted synchronously with TWD during drought, and recovered after rehydration. Gas exchange and most of the chlorophyll a fluorescence parameters were tightly positively related to TWD . Growth and TWD parameters, as well as those of gas exchange and most of the chlorophyll a fluorescence parameters differed against C trees during drought. Thus, the parameters derived from SDV may serve as indicators of the functionality of photosynthetic apparatus.