Plant Biology最新文献

Hydraulic redistribution is considered a crucial dryland mechanism that may be important in temperate environments facing increased soil drying-wetting cycles. We investigated redistribution of soil water from deeper, moist to surface, dry soils in a mature mixed European beech forest and whether redistributed water was used by neighbouring native seedlings. In two experiments, we tracked hydraulic redistribution via (1) ²H labeling and (2) ¹⁸O natural abundance. In a throughfall exclusion experiment, ²H water was applied to 30-50 cm soil depth around mature beech trees and traced in soils, in coarse and fine roots, and in the rhizosphere. On five additional natural plots, the ¹⁸O signal was measured in seedlings of European beech, Douglas fir, silver fir, sycamore maple, and Norway spruce at dawn and noon after a rain-free period. We found a significant enrichment in ²H in surface soil fine roots of mature beech, and an indication for transfer of this water into their rhizosphere, suggesting hydraulic redistribution from deeper, moist to drier surface soils. On four of the five additional plots, δ¹⁸O of seedlings' root water was lower at dawn than at noon. This indicated that dawn root water originated from soil layers deeper than the seedlings' rooting depth, suggesting hydraulic redistribution by neighbouring mature trees. Hydraulic redistribution equated to about 10% of daily transpiration in mature beech trees, and contributed to root water in understory seedlings, emphasizing hydraulic redistribution as a notable mechanism in temperate forests. Transport mechanisms and potential of different tree species to redistribute water should be further addressed.

Tree responses to drought are well studied, but the interacting effects of drought timing on growth, water use, and stress legacy are less understood. We investigated how a widespread conifer, Scots pine, responded to hot droughts early or late in the growing season, or to both. We measured sap flux, stem growth, needle elongation, and leaf water potential (Ψ_leaf) to assess the impacts of stress timing on drought resilience in Scots pine saplings. The early summer hot drought had peak temperatures of 36.5 °C, while the late summer hot drought peaked at 38.2 °C. Soil water content during both periods declined to ca. 50% of control values. The early-season hot drought caused growth cessation already at Ψ_leaf - 1.1 MPa, visible as an almost 30 days earlier end to needle elongation, resulting in needles 2.7 cm shorter, on average. This reduction in leaf area decreased productivity, resulting in a reduction of 50% in seasonal transpiration. However, the reduced water use of early-stressed saplings appeared to enhance resistance to a late-season drought, as reflected in a smaller decline in Ψ_leaf and lower tree water deficit compared to saplings that did not experience early-season stress. In summary, we observed persistant drought legacy effects from early-season hot-drought stress, as evident in a 35% reduction of leaf area, which impacted tree water use, stress resistance, and productivity. These structural adjustments of leaf development and reduced bud mass from early-season stress could be critical in evergreen conifers, whose long-lived foliage influences future water use and growth potential.

Some plant species produce an extraordinary diversity of specialized metabolites. The diverse class of terpenes is characteristic for many aromatic plants, and terpenes can occur as both emitted volatiles and stored compounds. Little is known about how intraspecific chemodiversity and phenotypic integration of both emitted volatile and stored terpenes differ intra-individually across plant development and between different plant parts, and studies considering both spatial and temporal scales are scarce. To comprehensively investigate this diversity, we used the aromatic plant Tanacetum vulgare that differs in foliar terpene composition, forming chemotypes. We collected emitted volatile terpenes of both young and old leaves during the rosette, elongated stem, and flowering stage as well as emitted volatiles of flower heads at the flowering stage. Moreover, at the flowering stage, stored terpenes were extracted from different plant parts, including roots. Terpene profiles were measured with (TD)-GC-MS. The composition of emitted volatile terpenes depended on the specific combination of chemotype, plant part, and time point; the chemodiversity of emitted volatiles was mainly affected by the development stage, indicating that at specific development stages individuals require a higher chemodiversity, potentially to mediate different interactions. For stored terpenes, intra-individual differences, mostly between aboveground and belowground plant parts, were found only for specific components of chemodiversity, such as richness and evenness, but not for functional Hill diversity. Phenotypic integration differed mainly across development stage and plant part for emitted volatile terpenes, and across chemotype and plant part for stored terpenes. Our results suggest that intraspecific chemodiversity of terpenes and their integration is a highly plastic trait that may be shaped in dependence of interactions with the environment, and the value that each plant part contributes to the fitness of an individual. Such variation on different scales, both spatially and temporally, should be considered in chemical ecological studies.

Assessing how dominant peatland species, such as Dasiphora fruticosa, adapt to water table decline is crucial to advance understanding of their growth and survival strategies. Currently, most studies have primarily focused on their growth and biomass, with limited knowledge on the response of non-structural carbohydrates (NSCs) and physiological adaptations of these woody plants under long-term drainage. This study assessed the response of photosynthesis and transpiration rates, biomass, and NSC concentrations (including soluble sugars and starch) in the leaves, stems, and roots of D. fruticosa to long-term drainage in a minerotrophic peatland. The aim was to elucidate the plant response and adaptation mechanisms to water table decline. Dasiphora fruticosa effectively regulated carbon (C) demand and supply by significantly enhancing photosynthesis, transpiration, and biomass accumulation, thereby maintaining stable C storage as the water table declined. There was a notable reduction in soluble sugar concentration in leaves with increasing water table decline, while starch concentrations in all three organs remained relatively constant. Although the concentration of soluble sugars in leaves was consistently higher than that in roots and stems, the relative proportion of soluble sugars and starch gradually decreased in leaves and increased in roots and stems with water table decline. Our findings reveal that D. fruticosa reduces NSC concentrations in leaves while increasing biomass to adapt to water table decline. This acclimation might significantly impact C dynamics in peatlands. Understanding these mechanisms is vital for predicting the dynamics of C sequestration and emission in peatland ecosystems under changing environmental conditions.

Temperate mixed forests are currently experiencing severe drought conditions and face increased risk of degradation. However, it remains unclear how critical tree physiological functions such as sap flow density (SFD) and tree water deficit (TWD, defined as reversible stem shrinkage when water is depleted), respond to extreme environmental conditions and how they interact under dry conditions. We monitored SFD and TWD of three co-occurring European tree species (Fagus sylvatica, Fraxinus excelsior and Acer pseudoplatanus) in dry conditions, using high temporal resolution sap flow, dendrometer, and environmental measurements. Species-specific SFD responses to soil drying did not differ significantly, while TWD was significantly higher in F. excelsior. Inter-specific differences in wood anatomy and water use strategies did not consistently explain these responses. TWD and SFD responded both to soil moisture content (SWC) during wet (SWC ≥ 0.2) and dry (SWC < 0.2) phases, with SFD responding more strongly. There was a significant correlation for TWD and vapour pressure deficit (VPD) only in the wet phase, and for SFD and VPD only in the dry phase. During the dry phase, the incoming PPFD significantly correlated with SFD in all species, and with TWD only in F. sylvatica and F. excelsior. TWD negatively responded to SFD, showing hysteresis effects from which a decreasing sigmoidal phase along the soil drying gradient was observed. The nonlinear correlations between TWD and SFD may result from a time lag between the two variables, and their different sensitivities to SWC and VPD under different drought intensities. We conclude that, under drought stress, TWD cannot be used as a proxy for SFD or vice versa.

Interspecific hybridization plays an important role in plant evolution, contributing to taxonomic uncertainty through intermediate phenotypes or the emergence of novel traits. The characterization of hybridization is important to elucidate systematic relationships and its role in the diversification of lineages. The genus Cenostigma comprises neotropical legume trees with phylogenetic inconsistencies, and individuals showing intermediate morphology between sympatric species, suggesting natural hybridization. We tested this hypothesis by investigating two endemic species from the Caatinga dry forest in northeast Brazil (C. microphyllum and C. pyramidale) using molecular markers (nuclear and plastid SSRs), geometric morphometrics, non-targeted metabolomics, and ecological analyses. We detected a high plastidial genetic structure among populations, not related to species boundaries but to their geographic distribution. The geometric morphometric analysis showed a clustering of pure individuals of both species with hybrids in an intermediate position, demonstrating the hybridization of these species in Caatinga. Nuclear DNA and metabolite diversity supported the separation of the two species into three clusters, with a subdivision of C. pyramidale in populations from the north (Pernambuco) and south (Bahia). Metabolomics revealed a fourth group formed mostly by hybrids. Later generation hybrids were detected as intermediate morphological forms, and gene flow was assumed as asymmetric among species and populations, being higher from C. pyramidale to C. microphyllum in populations from Bahia State. Ecological data indicated niche overlap. Hence, interspecific gene flow occurs among Cenostigma tree species, contributing to the evolution of the dry forest. Given the karyotypic and genomic similarity among species, as well as molecular and ecological evidence, we infer that the hybrids are fertile, allowing introgression and contributing to systematic complexity in Cenostigma. Hybridization did not significantly increase chemodiversity in terms of novel compounds but differentiated hybrids from parental species. In summary, we highlight the importance of multiple evidence, particularly genetic, morphological, and metabolomic traits, in the identification of hybrids and its evolutionary impact in natural environments.