Abstract Our knowledge about coordination of water transport at the whole-tree scale has been limited in its consideration of water storage and release from different tissues (i.e., sapwood and heartwood) along the xylem pathway. Here, we measured water transport and storage at spatially and temporally intensive scales in four tree species of contrasting hydraulic strategies (loblolly pine (Pinus taeda), southern red oak (Quercus falcata), Douglas-fir (Pseudotsuga menziesii), and trembling aspen (Populus tremuloides)) over the growing season in North Carolina (mesic) and Idaho (semi-arid), USA. We quantified the coordination of sap flow and volumetric water content at different heights along the main tree trunk and xylem tissue depths. Further, we investigated seasonal patterns of daily water storage and use in the different systems. Coordinated lags in sap flow between upper and lower heights along the trunk were present in all study species except oak. Whole-tree coordination of water transport and storage was more evident in the mesic system than in the semi-arid system. The angiosperm species displayed greater water storage use than the gymnosperm species in both systems, with water storage use patterns related to rain events in the mesic system and related to soil-moisture dry down in the semi-arid system. Our findings emphasize the importance of understanding water transport and storage at species- and ecosystem-specific levels inferred from spatially and temporally intensive tree measurements.
Abstract A long-term irrigation experiment in the dry Rhône Valley of Switzerland provides a unique opportunity to examine transgenerational environmental memory effects of persistent drought and irrigation in Scots pine (Pinus sylvestris L.). Previous work in this system showed that offspring from mother trees exposed to chronic drought (non-irrigated control) versus long-term irrigation differed markedly in growth and survival. Offspring from irrigated mothers grew faster under irrigated conditions but performed poorly under drought, whereas offspring from drought-exposed mothers showed higher growth and survival under drought conditions. While these responses suggested transgenerational environmental memory, the relative contributions of maternal provisioning versus epigenetic mechanisms could not be fully resolved. Notably, mother trees did not differ in genotype, and seed mass did not vary between treatments, indicating a limited role of maternal effects. Here, we tested whether transgenerational environmental memory effects persist after offspring were grown for 3 years under non-experimental conditions before being re-exposed to experimental hot-drought and irrigation treatments. In contrast to the earlier study, offspring from irrigated mothers did not show higher growth performance under irrigated conditions, indicating that irrigation-related memory weakened during the intervening non-treated phase. Conversely, seedlings originating from drought-exposed mothers consistently exhibited higher carbon assimilation and stem growth than those from irrigated mothers, irrespective of experimental treatment. Gene expression analyses showed differences in the number and identity of differentially expressed genes between offspring of drought- and irrigation-exposed mothers, although we lack data on DNA methylation, histone modifications or small RNAs. Patterns in primary metabolites broadly mirrored the results of gene expression, with modest differences in osmoprotectants and stress-related compounds. Overall, our results indicate that transgenerational environmental memory effects in P. sylvestris can diminish over time and, depending on the parental and offspring environments, may even result in mismatch and maladjustments.
Abstract To investigate N physiology and metabolism of different Catalpa bungei (C. bungei) genotypes in response to low N availability, saplings of a genotype (Cbu22-03) with high N uptake efficiency and a genotype (CbuGu) with low N uptake efficiency were exposed to 10, 100, or 1000 μM NH4NO3. The greater root biomass and fine-root surface area in Cbu22-03, combined with its higher net influxes of NO3- and NH4+ and upregulated transcript levels of CbuNRT1.1 and CbuAMT1.2, corresponded to the increased NO3- and NH4+ concentrations and total N amounts in roots compared with CbuGu. Accordingly, δ15N in both roots and leaves of Cbu22-03 was lower than that of CbuGu. Low N supply led to decreased net influxes of NO3- and NH4+, and reduced NO3-/NH4+ concentrations of roots and leaves, NR activities, and total N amounts, while inducing the up-regulation of CbuNRT1.1, CbuAMT1.2, and CbuAHA2 transcript levels, which likely enhanced nitrogen use efficiency (NUE) in both genotypes. These data suggest that Cbu22-03 shows greater capacities of N uptake and assimilation than CbuGu under the three N conditions, and both genotypes of C. bungei decreased the processes of N metabolism in response to low N availability.
Abstract Cadmium (Cd) contamination threatens soil ecosystems and food security. Robinia pseudoacacia is a potential candidate for phytoremediation, but the molecular responses and root-associated microbial responses accompanying rhizobial symbiosis under Cd exposure remain incompletely understood. We integrated root transcriptomic, internal-root metabolomic, and 16S rRNA gene sequencing data to characterize responses to Cd exposure and rhizobial inoculation in SX, the high shoot-Cd accumulator, and HB, the low shoot-Cd accumulator. SX and HB exhibited distinct transcriptional patterns and exploratory candidate-metabolite profiles. In SX, the transcriptional responses were associated with the greater shoot Cd translocation reported previously for this genotype. In HB, rhizobial inoculation under Cd exposure was associated with broader changes in candidate metal-transport and compartmentalization genes, consistent with its previously reported greater root Cd retention. Rhizobial inoculation was also associated with higher candidate abundances of leucine, trehalose, palmitic acid, thymine, and pantothenates in HB, whereas inoculated SX showed higher candidate abundances of leucine and isoleucine but lower internal L-malic acid. Cd exposure, rhizobial inoculation, and root compartment were associated with variation in bacterial community composition, including abundance patterns involving Pseudomonas, Devosia, and Rhizobium. Exploratory Spearman correlation analyses revealed compartment-specific patterns of covariation between candidate metabolites and bacterial genera; however, no metabolite-genus association remained statistically significant after Benjamini-Hochberg correction in the rhizoplane, endosphere, or rhizosphere. None of the compartment-specific Procrustes tests indicated significant overall concordance between bacterial community composition and root-metabolite profiles. Collectively, these findings identify candidate genes, metabolites, and bacterial taxa and provide testable hypotheses that could inform future genotype selection and microbiome-assisted phytoremediation strategies.
Abstract Atmospheric nitrogen (N) deposition can substantially alter nutrient balance and internal nutrient recycling in trees, yet how dioecious species regulate phosphorus (P) economy in a sex-specific manner under N enrichment remains poorly understood. We investigated how short-term N enrichment differentially modifies leaf functional traits, leaf stoichiometry, and nitrogen and phosphorus resorption efficiencies (NRE and PRE) in female and male Fraxinus velutina Torr. using a field canopy-spray experiment with two N addition levels. Although N addition consistently promoted leaf structural traits, neither sex nor the N × S interaction significantly affected leaf morphological traits, suggesting that sexual dimorphism in this species manifests primarily in nutrient economy rather than leaf structure. Under N enrichment, P-related traits exhibited pronounced sex-specific responses, with significant N × S interactions: under high N, females increased leaf P concentration and exhibited lower N:P, whereas males increased leaf N concentration, resulting in higher N:P. N addition reduced NRE in both sexes, but PRE responses differed markedly: PRE declined progressively in males under elevated N, while females maintained a moderate reduction in PRE. SMA and multivariate analyses further showed that nutrient resorption in males was more strongly associated with current-season stoichiometric variation, whereas in females, nutrient resorption showed a stronger association with P status. Together, these findings identify P balance as the primary axis of sex-specific nutrient regulation under N enrichment, with females maintaining more stable internal P homeostasis than males. This distinction that underscores the need to account for plant sex in assessments of dioecious tree responses to increasing atmospheric N deposition.
