Tree physiology最新文献

Ectomycorrhizal (ECM) fungi, as major carbon (C) sinks, are critical to plant-soil C cycling. Although C allocation between plants and ECM fungi has been studied extensively, C transport time, the key component of C cycling, remains poorly understood. To address this, we collected new needles (weekly), roots (monthly) and ECM fungi (sporocarps and hyphae) of three genera (Cortinarius, Lactarius and Russula) in a boreal Scots pine (Pinus sylvestris L.) forest in Finland. We analysed the natural abundance C isotope composition (δ13C) of sugars or organic matter and observed a strong vapour pressure deficit (VPD) signal in needle sucrose δ13C. We coupled VPD with the δ13C of water-soluble carbohydrates (WSC, δ13CWSC) in sporocarps to determine C transport times. We found Lactarius and Russula, with short hydrophilic mycelia that enable efficient solute uptake, had transport times of 6-13 days, peaking at 8 days. In contrast, Cortinarius, with extensive hydrophobic mycelia that limit water and solute movement, showed slower transport times of around 18 days. The different transport time is likely attributable to a more extensive mycelial network and potentially higher C demand in Cortinarius compared with Lactarius and Russula. The three genera also showed a marginally significant effect on δ13CWSC in sporocarps (P = 0.06, analysis of covariant). This study highlights that natural abundance δ13C analysis offers a practical alternative to pulse-labelling for estimating C transport time in complex plant-fungal interactions, where the latter is difficult to implement. The longer transport time of Cortinarius compared with Lactarius and Russula is critical during periods of reduced photosynthesis, when limited C supply makes fast allocation essential for sustaining belowground metabolism. Slower transport may weaken its role and reduce forest productivity in boreal forests with short growing seasons. As global warming favours Cortinarius, its longer C transport time may impede soil C cycling and nutrient turnover.

Sexual dimorphism in dioecious species can shape divergent hydraulic strategies in response to environmental stress, yet integrative studies linking anatomical and physiological traits across different plant organs remain scarce. We investigated sex-specific water-use strategies in two Mediterranean shrubs, Pistacia lentiscus L. and Rhamnus alaternus L., by analyzing leaf and wood anatomy, leaf functional traits, gas exchange and chlorophyll fluorescence. Male plants of both species exhibited conservative morpho-anatomical traits, including smaller, thicker leaves, lower specific leaf area (SLA), higher dry matter content and reduced intercellular spaces, traits typically associated with drought resistance strategies. In P. lentiscus, these traits correlated with higher photosynthetic rates and Fv/Fm values, alongside greater stomatal density and vessel frequency, suggesting coordinated investment in carbon gain and hydraulic efficiency/safety. Conversely, females displayed acquisitive traits (higher SLA, wider intercellular spaces, lower vessel frequency), potentially enhancing photosynthesis under mesic conditions but increasing vulnerability to drought-induced embolism. In R. alaternus, female individuals maintained higher net photosynthesis and instantaneous water- use efficiency, while males exhibited greater Fv/Fm and a decoupled leaf-wood coordination. These findings suggest that males may adopt safer hydraulic architectures, while females, potentially constrained by reproductive demands, pursue efficiency-driven strategies, still maintaining vessel redundancy in wood. As aridity intensifies in Mediterranean regions, such dimorphism may influence population dynamics, sex ratios and species resilience. Our results underscore the ecological significance of species-specific sex-based hydraulic variation and the necessity of incorporating sex into trait-based models of plant responses to climate change.

Photosynthesis links terrestrial carbon, water and nutrient cycles. Photosynthetic least-cost theory suggests that plants optimize photosynthesis at the lowest summed investments in nutrient and water use. The theory predicts that increasing nutrient availability should increase nutrient allocation toward photosynthetic enzymes and reduce stomatal conductance, allowing similar photosynthetic rates achieved at a lower ratio of leaf intercellular to atmospheric CO2 concentration (χ) and reduced water loss. The theory suggests similar responses to increasing soil pH in acidic soils due to common correlations between soil pH and nutrient availability. However, empirical tests of the theory outside of environmental gradients are rare. To test this theory experimentally, we measured photosynthetic traits in mature Acer saccharum Marshall trees growing in a 9-year, nitrogen-by-pH manipulation in the northeastern USA. Increasing soil nitrogen availability did not affect net photosynthesis (Anet) or stomatal conductance (gs) rates, but was associated with increased area-based leaf nitrogen content (Narea), increased photosynthetic capacity (Vcmax, Jmax) and decreased χ (i.e, increased water-use efficiency). These patterns strengthened the tradeoff between nitrogen and water use, indicated by steeper slopes of Narea-χ and Vcmax-χ with increasing soil nitrogen availability. When examined across all plots, soil pH had no effect on any traits. However, in plots without nitrogen additions, increasing soil pH increased the slopes of Narea-χ and Vcmax-χ, though did not modify χ. Supporting the theory, A. saccharum maintained Anet across the soil nitrogen availability gradient by trading less efficient nitrogen use for more efficient water use. Additionally, the effects of soil pH on nitrogen-water use tradeoffs appear to occur through indirect pH effects on soil nitrogen availability. These results indicate that elevated nitrogen deposition could stimulate photosynthesis less than commonly expected and instead reduce water losses, and conversely, that reductions in photosynthesis expected from increasing nitrogen limitation in some regions could be lessened if accompanied by increased transpiration.

Drought stress severely impacts the growth, yield and quality of apple (Malus domestica). Abscisic acid (ABA) and basic helix-loop-helix (bHLH) transcription factors play crucial roles in regulating the drought response in many plants, but the potential interactions between bHLH and ABA in response to drought in apple still need to be discovered. Herein, we identified a bHLH transcription factor, ORG2 (OBP3-responsive gene 2), from M. hupehensis, and the expression of which is induced by drought and ABA. Apple plants that overexpressed MhORG2 were more sensitive to drought stress, while silencing MhORG2 caused the opposite phenotype. Specifically, we found that MhORG2 could directly bind to the DRE element in the MhAAO3 promoter and repress its expression, thereby ultimately reducing drought tolerance. Furthermore, MhORG2 represses the expression of antioxidant enzyme genes (MhSOD, MhAPX1 and MhCAT), leading to the accumulation of reactive oxygen species (ROS) and consequently reducing the drought tolerance of apple plants. Our findings uncover a novel mechanism by which MhORG2 negatively regulates drought tolerance in apple plants, offering a potential target for the development of drought-tolerant crops via biotechnological approaches.

The success of CRISPR genome editing studies depends critically on the precision of guide RNA (gRNA) design. Sequence polymorphisms in outcrossing tree species pose design hazards that can render CRISPR genome editing ineffective. Despite recent advances in tree genome sequencing with haplotype resolution, sequence polymorphism information remains largely inaccessible to various functional genomics research efforts. The Populus VariantDB v3.2 addresses these challenges by providing a user-friendly search engine to query sequence polymorphisms of heterozygous genomes. The database accepts short sequences, such as gRNAs and primers, as input for searching against multiple poplar genomes, including hybrids, with customizable parameters. We provide examples to showcase the utilities of VariantDB in improving the precision of gRNA or primer design. The platform-agnostic nature of the probe search design makes Populus VariantDB v3.2 a versatile tool for the rapidly evolving CRISPR field and other sequence-sensitive functional genomics applications. The database schema is expandable and can accommodate additional tree genomes to broaden its user base.

Sulfate-proton co-transporters (SULTRs) mediate sulfate uptake, transport, storage and assimilation in plants. The SULTR family has historically been classified into four groups (SULTR1-SULTR4), with well-characterized roles for SULTR groups 1, 2 and 4. However, the functions of the large and diverse SULTR3 group remain poorly understood. Here, we present an updated phylogenetic analysis of SULTRs across angiosperms, including multiple early-divergent lineages. Our results suggest that the enigmatic SULTR3 group comprises four distinct subfamilies that predate the emergence of angiosperms, providing a basis for reclassifying the SULTR family into seven subfamilies. This expanded classification is supported by subfamily-specific gene structures and amino acid substitutions in the substrate-binding pocket. Structural modeling identified three serine residues uniquely lining the substrate-binding pocket of SULTR3.4, enabling three hydrogen bonds with the phosphate ion. The data support the proposed neofunctionalization of this subfamily for phosphate allocation within vascular tissues. Transcriptome analysis of Populus tremula × Populus alba revealed divergent tissue expression preferences among SULTR subfamilies and between genome duplicates. We observed partitioned expression in vascular tissues among the four SULTR3 subfamilies, with PtaSULTR3.4a and PtaSULTR3.2a preferentially expressed in primary and secondary xylem, respectively. Gene coexpression analysis revealed coordinated expression of PtaSULTR3.4a with genes involved in phosphate starvation responses and nutrient transport, consistent with a potential role in phosphate homeostasis. In contrast, PtaSULTR3.2a was strongly coexpressed with lignification and one-carbon metabolism genes and their upstream transcription regulators. PtaSULTR3.2a belongs to a eudicot-specific branch of the SULTR3.1 subfamily found only in perennial species, suggesting a specialized role in lignifying tissues. Together, our findings provide a refined phylogenetic framework for the SULTR family and suggest that the expanded SULTR3 subfamilies have undergone neofunctionalization during the evolution of vascular and perennial plants.

Understanding the biological mechanisms underlying tree responses to drought is critical for preserving forest biodiversity, as current global climate change is challenging the ability of drought-sensitive trees to cope with water shortage. In this study, we investigate how silver fir (Abies alba Mill.) responds to experimental drought stress, more specifically, atmospheric drought caused by high vapor pressure deficit (VPD), by analyzing the gene expression and DNA methylation profiles of different organs alongside physiological variables under well-watered, drought and recovery conditions. Roots exhibited a stronger transcriptomic response than leaves, with 50 times more altered transcripts, revealing their value for assessing water stress in this species through the expression of genes involved in water transport. In addition, brassinosteroid-related genes can serve as stress markers both in roots and leaves. VPD-induced drought also affected DNA methylation, which, like transcriptomic and physiological variables, begins to normalize once the stress is over, suggesting some resilience to drought. However, A. alba struggles to improve intrinsic water-use efficiency, which raises its vulnerability to VPD-induced drought. Our results suggest that silver fir forests might be able to cope with short drought events, but prolonged periods of water shortage, which are likely to increase with climate change, may surpass their resilience thresholds, increasing the likelihood of hydraulic failure and carbon starvation.

Members of the salicaceous genus Populus are primarily used by plant biologists as a model system for understanding the genetic underpinnings of woody plant growth and development. Beyond their importance to those conducting developmental research, Populus spp. are key members of ecosystems in the Northern Hemisphere and show promise as a vital renewable source of biomass for sustainable biofuel production. This genus also produces a class of signature herbivore-deterring and medicinally significant phenolic glycosides, commonly referred to as salicinoids. Although salicinoids in Populus are primarily associated with defense against biotic disturbances, they have also been implicated in structuring the chemotaxonomy of Populus and Salicaceae, shaping endophytic microbiomes, directing abiotic stress responses and participating in primary metabolism. Despite advancements in understanding these interactions through functional genomics and biotechnological techniques such as CRISPR/Cas9, much about their function and biosynthesis still remains obfuscated. Here, we summarize a global view of progress made in Populus salicinoid research, focusing particularly on studies conducted through a biotechnological lens, to elucidate the distribution, ecological significance, and biosynthesis of these compounds.

Wood fiber has been extensively used in the pulp and papermaking industries. The length of fiber cells is critical in determining the quality of paper. In our previous studies, we identified PdCel9A6, a gene encoding endo-1,4-β-glucanases expressed in the developing xylem to affect cell wall formation. In this study, we modified the PdCel9A6 expression specifically in xylem fiber cells. The results showed that the fiber-specific upregulation of PdCel9A6 resulted in increased plant height and internode length. The transgenics significantly increased the fiber cell length in the wood xylem. In wood cell wall components, the transgenics showed a reduction of lignin while increasing cellulose. Furthermore, the characteristics of the paper processed from the transgenics showed a significant improvement in paper strength. Transcriptome studies showed that upregulation of PdCel9A6 in fiber cells leads to changes in transcription related to cell wall remodeling and thickening during xylem development. Together, the study demonstrated a new strategy of fiber cell wall modification that could have the potential to improve forest trees for better pulping and papermaking.

Drought and episodic drought events are major impending impacts of climate change, limiting the productivity of plants and especially trees due to their inherent high transpiration rates. One common mechanism used by plants to cope with drought stress is to change the composition of their leaf cuticular waxes. Cuticular waxes are essential for controlling non-stomatal water loss and are typically composed of a homologous series of very-long-chain fatty acid-derived compounds, as well as flavonoids, tocopherols, triterpenoids, and phytosterols. In this study, we compared the cuticular waxes of 339 natural accessions of Populus trichocarpa (Torr. & Gray) (black cottonwood) grown under control and drought conditions in a common garden. A Genome-Wide Association Study (GWAS) was then used to identify candidate genes associated with cuticular wax biosynthesis and/or its regulation. Although no major differences were observed in total wax load when subject to drought conditions, the amounts of the individual wax constituents were indeed responsive to drought. Specifically, changes in alkenes, alcohols, esters and aldehydes were evident, and suggest that they contribute to the drought response/tolerance in poplar. GWAS uncovered several genes linked to fatty acid biosynthesis, including CER1, CER3, CER4, FATB, FAB1, FAR3, FAR4, KCS and a homologue of SOH1, as well as other candidate genes that may be involved in coordinating the drought responses in poplar trees. Our findings provide new evidence that genotype-specific shifts in wax composition, rather than total wax accumulation, contribute to drought adaptation in poplar. Additionally, we show that genetic variation in key wax biosynthetic genes drives cuticular wax plasticity in P. trichocarpa under drought, identifying putative molecular targets for improving stress resilience in trees. This study expands our understanding of the adaptive mechanisms of the cuticle and their potential for enhancing drought tolerance in poplar species.