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During drought, a major abiotic stressor for European forests, excessive reactive oxygen species (ROS) are produced, causing oxidative damage that affects structural and metabolic tree functions. This research examines the effects of drought, phosphorus (P) fertilization, and provenance on photosynthetic pigments, malondialdehyde (MDA) concentrations, and antioxidant enzyme activities in common beech (Fagus sylvatica L.) and sessile oak (Quercus petraea (Matt.) Liebl.) saplings from two provenances. In a common garden experiment, four treatments were applied: regular watering with (+PW) and without P fertilization (−PW), and drought with (+PD) and without (−PD) P fertilization. Results showed that drought increased both MDA concentrations and antioxidant enzyme activity, particularly superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX), which are responsible for ROS scavenging. Additionally, chlorophyll a + b concentrations were lower in drought-exposed plants. Phosphorus fertilization minimally affected MDA levels but enhanced antioxidant responses, particularly APX and CAT activities in oak during drought. Provenance differences were notable, with oak and beech from the drier provenance showing better adaptation, reflected in lower MDA levels and higher enzyme activities. This study underscores the importance of antioxidant defenses in coping with drought stress, with phosphorus fertilization and provenance shaping the species’ adaptive capacity.

Forest trees compete for light and soil resources, but photoassimilates, once produced in the foliage, are not considered to be exchanged between individuals. Applying stable carbon isotope labeling at the canopy scale, we show that carbon assimilated by 40-meter-tall spruce is traded over to neighboring beech, larch, and pine via overlapping root spheres. Isotope mixing signals indicate that the interspecific, bidirectional transfer, assisted by common ectomycorrhiza networks, accounted for 40% of the fine root carbon (about 280 kilograms per hectare per year tree-to-tree transfer). Although competition for resources is commonly considered as the dominant tree-to-tree interaction in forests, trees may interact in more complex ways, including substantial carbon exchange.

Tree species through aboveground biomass and roots are a key factors influencing the quality and quantity of soil organic matter. Our study aimed to determine the stability of soil organic matter in Luvisols under the influence of five different tree species. The study areas were located 25 km north of Krakow, in southern Poland. The study included five tree species - Scots pine ( Pinus sylvestris L.), European larch ( Larix decidua Mill.), pedunculate oak ( Quercus robur L.), beech ( Fagus sylvatica L.) and hornbeam ( Carpinus betulus L.). Forest stands growing in the same soil conditions (Luvisols) with similar geological material (loess) and grain size were selected for the study. We evaluated labile and heavy fractions of soil organic matter (SOM). Additionally, basic physicochemical properties (pH, carbon and nitrogen content, base cation content) were determined in soil samples. The results of our study showed that soils under the influence of coniferous species were characterized by a higher content of carbon of free light fraction (C fLF ) and carbon of occluded light fraction (C oLF ) compared to deciduous species. Similar relationships were found with the nitrogen content of the free light fraction (N fLF ) and nitrogen of occluded light fraction (N oLF ). Higher C MAF and N MAF contents were recorded in soils influenced by deciduous species. The carbon, nitrogen and base cations content positively correlated with the C and N of free light fraction and occluded light fraction. PCA analysis confirmed the connection of C and N of heavy fractions (C MAF and N MAF ) with deciduous species. Our research shows that avoiding single-species conifer stands and introducing admixtures of deciduous species, which increase SOM, is justified in forest management. The selection of suitable species will provide greater stand stability and contribute more to the carbon accumulation in the soil.

Plant seasonal cycles alter carbon (C) and nitrogen (N) availability for soil microbes, which may affect microbial community composition and thus feed back on microbial decomposition of soil organic material and plant N availability. The temporal dynamics of these plant-soil interactions are, however, unclear. Here, we experimentally manipulated the C and N availability in a beech forest through N fertilization or tree girdling and conducted a detailed analysis of the seasonal pattern of microbial community composition and decomposition processes over 2 yr. We found a strong relationship between microbial community composition and enzyme activities over the seasonal course. Phenoloxidase and peroxidase activities were highest during late summer, whereas cellulase and protease peaked in late autumn. Girdling, and thus loss of mycorrhiza, resulted in an increase in soil organic matter-degrading enzymes and a decrease in cellulase and protease activity. Temporal changes in enzyme activities suggest a switch of the main substrate for decomposition between summer (soil organic matter) and autumn (plant litter). Our results indicate that ectomycorrhizal fungi are possibly involved in autumn cellulase and protease activity. Our study shows that, through belowground C allocation, trees significantly alter soil microbial communities, which may affect seasonal patterns of decomposition processes.

In trees, water and sugars are transported by xylem and phloem conduits which are hydraulically linked. A simultaneous study of both flows is interesting, since they concurrently influence important processes such as stomatal regulation and growth. A few mathematical models have already been developed to investigate the influence of both hydraulically coupled flows. However, none of these models has so far been tested using real measured field data. In the present study, a comprehensive whole-tree model is developed that enables simulation of the stem diameter variations driven by both the water and sugar transport. Stem diameter variations are calculated as volume changes of both the xylem and the phloem tissue. These volume changes are dependent on: (i) water transport according to the cohesion–tension theory; (ii) sugar transport according to the Münch hypothesis; (iii) loading and unloading of sugars; and (iv) irreversible turgor-driven growth. The model considers three main compartments (crown, stem, and roots) and is verified by comparison with actual measured stem diameter variations and xylem sap flow rates. These measurements were performed on a young oak (Quercus robur L.) tree in controlled conditions and on an adult beech (Fagus sylvatica L.) tree in a natural forest. A good agreement was found between simulated and measured data. Hence, the model seemed to be a realistic representation of the processes observed in reality. Furthermore, the model is able to simulate several physiological variables which are relatively difficult to measure: phloem turgor, phloem osmotic pressure, and Münch's counterflow. Simulation of these variables revealed daily dynamics in their behaviour which were mainly induced by transpiration. Some of these dynamics are experimentally confirmed in the literature, while others are not.

Microplastics have the capacity to accumulate in soil due to their high resistance to degradation, consequently altering soil properties and influencing plant growth. This study focused on assessing the impact of various types and doses of microplastics on beech seedling growth. In our experiment, we used polypropylene and styrene granules with diameter of 4.0 mm in quantities of 2.5% and 7%. The hypothesis was that microplastics significantly affect seedlings' nutritional status and growth characteristics. The research analysed seedlings' nutrition, root morphological features, above-ground growth, and enzymatic activity in the substrate. Results confirmed the importance of microplastics in shaping the nutritional status of young beech trees. Microplastic type significantly impacted N/P and Ca/Mg stoichiometry, while microplastic quantity influenced Ca/Al and Ca + K + Mg/Al stoichiometry. Notably, only in the case of root diameter were significantly thicker roots noted in the control variant, whereas microplastics played a role in shaping the leaves' characteristics of the species studied. The leaf area was significantly larger in the control variant compared to the variant with polypropylene in the amount of 2.5% and styrene in the amount of 7%. Additionally, the study indicates a significant impact of microplastics on enzyme activity. In the case of CB and SP, the activity was twice as high in the control variant compared to the variants with microplastics. In the case of BG, the activity in the control variant was higher in relation to the variants used in the experiment. Research on the impact of microplastics on the growth of beech seedlings is crucial for enhancing our understanding of the effects of environmental pollution on forest ecosystems. Such studies are integral in shaping forestry management practices and fostering a broader public understanding of the ecological implications of plastic pollution.

While photosynthetic isotope discrimination is well understood, the postphotosynthetic and transport-related fractionation mechanisms that influence phloem and subsequently tree ring δ 13C are less investigated and may vary among species. We studied the seasonal and diel courses of leaf-to-phloem δ 13C differences of water-soluble organic matter (WSOM) in vertical crown gradients and followed the assimilate transport via the branches to the trunk phloem at breast height in European beech (Fagus sylvatica) and Douglas fir (Pseudotsuga menziesii). δ 13C of individual sugars and cyclitols from a subsample was determined by compound-specific isotope analysis. In beech, leaf-to-phloem δ 13C differences in WSOM increased with height and were partly caused by biochemical isotope fractionation between leaf compounds. 13C-Enrichment of phloem sugars relative to leaf sucrose implies an additional isotope fractionation mechanism related to leaf assimilate export. In Douglas fir, leaf-to-phloem δ 13C differences were much smaller and isotopically invariant pinitol strongly influenced leaf and phloem WSOM. Trunk phloem WSOM at breast height reflected canopy-integrated δ 13C in beech but not in Douglas fir. Our results demonstrate that leaf-to-phloem isotope fractionation and δ 13C mixing patterns along vertical gradients can differ between tree species. These effects have to be considered for functional interpretations of trunk phloem and tree ring δ 13C.

Plant defensins (PDFs) are cysteine‐rich antimicrobial peptides (AMPs) that are important components of plant immunity. They occur constitutively in various plant tissues but are also upregulated upon stress. Therefore, these molecules are of great interest as markers for the diagnosis of early forest stress response in plants at the molecular level. PDFs are small peptides (~5 kDa) with a compact tertiary structure, requiring specific protocols and dedicated antibodies for detection by quantitative ELISA. We developed monoclonal recombinant antibodies using phage display in solution against the correctly folded antigen defensin FsPDF2 from beech (Fagus sylvatica) and analysed the antibody–antigen interaction in silico with AlphaFold 3. In a proof‐of‐principle study, we investigated the FsPDF2 stress response to abiotic (drought) and biotic (gall midge) stresses. Notably, we established an assay for defensin quantification in crude plant extract, detecting for the first time natively folded proteins in a specific sandwich ELISA. Our antibody generation strategy can be transferred by practitioners to other small antimicrobial peptides (AMP), paving the way to study this group of proteins and their corresponding stress response comprehensively.

Fruiting is typically considered to massively burden the seasonal carbon budget of trees. The cost of reproduction has therefore been suggested as a proximate factor explaining observed mast-fruiting patterns. Here, we used a large-scale, continuous 13 C labeling of mature, deciduous trees in a temperate Swiss forest to investigate to what extent fruit formation in three species with masting reproduction behavior (Carpinus betulus, Fagus sylvatica, Quercus petraea) relies on the import of stored carbon reserves. Using a free-air CO 2 enrichment system, we exposed trees to 13 C-depleted CO 2 during 8 consecutive years. By the end of this experiment, carbon reserve pools had significantly lower δ 13 C values compared to control trees. δ 13 C analysis of new biomass during the first season after termination of the CO 2 enrichment allowed us to distinguish the sources of built-in carbon (old carbon reserves vs. current assimilates). Flowers and expanding leaves carried a significant 13 C label from old carbon stores. In contrast, fruits and vegetative infructescence tissues were exclusively produced from current, unlabeled photoassimilates in all three species, including F. sylvatica, which had a strong masting season. Analyses of δ 13 C in purified starch from xylem of fruit-bearing shoots revealed a complete turn-over of starch during the season, likely due to its usage for bud break. This study is the first to directly demonstrate that fruiting is independent from old carbon reserves in masting trees, with significant implications for mechanistic models that explain mast seeding.

Mycorrhizal fungi have a key role in nitrogen (N) cycling, particularly in boreal and temperate ecosystems. However, the significance of ectomycorrhizal fungal (EMF) diversity for this important ecosystem function is unknown. Here, EMF taxon-specific N uptake was analyzed via 15 N isotope enrichment in complex root-associated assemblages and non-mycorrhizal root tips in controlled experiments. Specific 15 N enrichment in ectomycorrhizas, which represents the N influx and export, as well as the exchange of 15 N with the N pool of the root tip, was dependent on the fungal identity. Light or water deprivation revealed interspecific response diversity for N uptake. Partial taxon-specific N fluxes for ectomycorrhizas were assessed, and the benefits of EMF assemblages for plant N nutrition were estimated. We demonstrated that ectomycorrhizal assemblages provide advantages for inorganic N uptake compared with non-mycorrhizal roots under environmental constraints but not for unstressed plants. These benefits were realized via stress activation of distinct EMF taxa, which suggests significant functional diversity within EMF assemblages. We developed and validated a model that predicts net N flux into the plant based on taxon-specific 15 N enrichment in ectomycorrhizal root tips. These results open a new avenue to characterize the functional traits of EMF taxa in complex communities.