Tree physiology最新文献

Rainfall pulses create brief but critical opportunities for carbon uptake in seasonally dry forests; however, how tree seedlings recover photosynthetic function during the establishment phase following these short-lived rewetting events under field conditions remains poorly understood. In particular, the coordination and timing of hydraulic, stomatal, and biochemical recovery processes during natural rainfall pulse-dry-down cycles are not well quantified, despite their importance for carbon-water coupling and drought resilience. Here, we investigated short-term physiological responses of establishing Eucalyptus seedlings during naturally occurring rainfall pulse-dry-down cycles. We measured leaf water potential (Ψleaf), gas exchange, and photosynthetic capacity (Vcmax, Jmax) before and after rainfall to assess recovery dynamics of diffusional and biochemical processes under contrasting atmospheric demand. Across species, Ψleaf and stomatal conductance improved rapidly following rainfall, reflecting transient hydraulic relief, while net photosynthesis increased by 40-60% within 1-3 days. In contrast, biochemical capacity responded more gradually: Vcmax declined by up to ~15% and Jmax by 20-40% during dry-down and showed limited or partial recovery after rewetting. Limitation partitioning revealed asynchronous recovery, with stomatal limitation relaxing rapidly after rainfall under low vapour pressure deficit (VPD), whereas under high VPD, biochemical recovery preceded full stomatal reopening. The xeric-origin E. cladocalyx sustained assimilation at more negative Ψleaf and exhibited greater biochemical stability, whereas intermediate and mesic species (E. grandis, E. urophylla, E. cloeziana) showed rapid but short-lived post-rain responses. Together, these results demonstrate that photosynthetic recovery during the seedling phase is asynchronous and strongly modulated by atmospheric demand, shaping short-term carbon-water coupling under increasingly pulsed hydroclimates.

Plant adaptation strategies to environmental variability encompass not only climatic factors but also the underlying subsurface structure, which are critical for the sustainability of vegetation restoration. However, the plant water use traits and their relationships across varying soil-rock structure settings for common species remain unclear, undermining the reliability of adaptation assessments in heterogeneous habitats. Current study examined five common tree species from two different bedrock types-limestone and dolomite-within Southwest China. Key plant water use traits, including root water sources, xylem hydraulic traits (P50 and wood density), and leaf stable isotope (δ18O and δ13C) as proxies for stomatal regulation and water use efficiency, were measured. Results revealed that the predominant root water uptake depths of all five species was significantly deeper in the limestone site (P<0.05), with its discontinuous, deep-pocket soil, compared to the dolomite site, where the continuous, thinner soil layer predominated. Besides, species in limestone site exhibited significantly less negative P50, lower wood density and leaf δ18O, more negative δ13C values compared to those in dolomite (P<0.05). The study also identified significant trade-offs between root water uptake patterns, xylem hydraulic traits and leaf isotopic composition (P<0.05). These relationships elucidate two contrasting adaptive strategies: an acquisition strategy with high hydraulic efficiency and carbon demands, supported by a deep and stable water supply in limestone site, and a conservative with high hydraulic safety and strict stomatal response, constrained by a fluctuating shallow water source in dolomite. Our findings underscore the profound influence of lithology on plant water use traits and highlight how the trade-off of root and xylem-leaf traits improves the adaptation assessments in such fragile, heterogenous environments.

The first summer after fire poses a high risk of drought mortality for species that rely on postfire recruitment for their persistence in fire-prone ecosystems (postfire seeders). However, little is known about how future conditions of elevated atmospheric CO2 (eCO2) and its interaction with severe drought will affect this key life history strategy in Mediterranean shrublands. We investigated the extent that eCO2 modifies plant traits and resource allocation, as well as how eCO2 and drought intensity interact to modify plant water status, water fluxes, and hydraulic behavior in eight-month-old seedlings of five seeder shrub species. Among the studied species, three regenerate postfire exclusively by seed (non-resprouting seeders), while two can also resprout after fire (resprouting seeders). We found that eCO₂ significantly reduced specific leaf area for all species and increased above- and belowground biomass for three species but had no species-specific effects on stomatal density or root-to-shoot ratios. When species were grouped by resprouting ability, eCO2 reduced root-to-shoot ratios in resprouting species but not in non-resprouting species. Importantly, eCO2 did not affect plant water relations under drought either at the species level or when grouped by resprouting ability. However, resprouting and non-resprouting seeders exhibited distinct water-use strategies under drought, independent of CO₂ treatment. Overall, eCO₂ is unlikely to mitigate drought stress for postfire seeders in future climates. Considering functional differences across life history strategies, as well as the variability of traits within them, is key to predicting future patterns of biodiversity in a drier and more fire-prone world.

The xylem and phloem anatomy of co-existing tree species provides valuable information on how different tree species face climate change and adjust their vascular structure to local weather conditions. We examined and compared annual ring widths and conduit size in earlywood and early phloem in Fraxinus ornus, Quercus pubescens and Ostrya carpinifolia in a sub-Mediterranean site in the period 2019-2021. The selected xylem and phloem traits were correlated with monthly weather conditions (precipitation and temperature). We found that phloem increment widths and conduits in earlywood and early phloem in the studied tree species showed different trends in terms of interannual variability and in relation to local weather conditions. In F. ornus, May conditions affected xylem traits, while June conditions phloem traits. In Q. pubescens, winter and March precipitation was related to phloem development. In O. carpinifolia, xylem ring width was positively correlated with June precipitation, while early phloem conduits were negatively affected by April temperature. Only two consistent patterns were detected across the species and years studied: wider xylem increments compared to phloem increments, and wider earlywood vessels compared to early phloem sieve tubes. Statistically significant differences were observed among species across all years for the size of xylem and phloem conduits and the hydraulic conductivity of earlywood vessels, which indicates great differences in the calculated hydraulic conductivity among the tree species. To summarize, hydraulic conductivity of earlywood vessels in Q. pubescens was on average for all three years 10.4 -times and 114-times larger than in F. ornus and O. carpinifolia, respectively. High interannual variability and species-specific sensitivity of xylem and phloem traits to precipitation and temperature confirm high plasticity and different radial growth strategies of the studied tree species to ensure optimal functioning under local weather conditions.

Olive branch dieback, which is caused mainly by fungal species in Neofusicoccum genus (Botryosphaeriaceae), leads to branch death and irreversible damage. This re-emerging disease in rainfed olive orchards in Spain is linked to crop intensification, the prohibition of the burning of pruning residues, and drought. Lepra disease, caused by Phlyctema vagabunda, is another re-emerging disease associated with shoot dieback in high-density olive orchards. In this study, the behavior of N. mediterraneum, N. parvum, and P. vagabunda was evaluated under laboratory and field conditions. Mycelial growth was measured across different temperatures and water potentials. Neofusicoccum species showed maximum growth at 25 °C but tolerated 30 °C and low water potentials (-15 MPa). Phlyctema vagabunda grew better at 25 °C but failed to grow at higher temperatures or under water stress. To investigate the impact on plants, branches of 10 of the main Spanish olive cultivars were inoculated with the pathogens in a 13-year-old orchard. Canker length, branch mortality, vegetative growth, stomatal conductance, chlorophyll fluorescence, and water potential were monitored upon inoculation. In a second pot experiment, using the most susceptible cultivar, 'Gordal Sevillana', we tested the effect of water stress on disease progression. Neofusicoccum species significantly reduced vegetative growth (30-70%), stomatal conductance (gsw) (5-42%), and water potential (9-16%). Despite the two species exhibiting similar virulence levels, according to canker length and branch mortality, their underlying mechanisms require further study. On the other hand, P. vagabunda inoculations were unsuccessful, and no canker symptoms were observed. In the pot experiment, water stress affected plant growth and gsw but did not influence pathogen behavior. Overall, compared with P. vagabunda, Neofusicoccum species are better adapted to high temperatures and low water availability. Their infections impair water relations in olive branches, reducing water potential and gsw and leading to branch mortality. This study highlights the complex dynamics linking woody pathogens and abiotic stress in perennial crops.

Field experiments are complex to interpret due to interactions between genotypes, environment, plant development, and cultivation practices. This complexity challenges the accurate phenotyping of individual plant traits over the season. Here, we quantified the primary sources of seasonal variation in stomatal conductance (gs) across 15 grapevine cultivar-rootstock combinations within a large-scale phenotyping platform, comprising over 6000 observations. Environment-related traits and date of measurement accounted for up to 76% of the variance, potentially obscuring cultivar-rootstock effects. Therefore, we integrated machine learning, spatiotemporal normalization of the gs response, and the use of mixed models to disentangle the influences of environmental factors, plant material, and crop performance related traits. After spatio-temporal normalization, cultivar and cultivar-rootstock interactions explained over 25% of the variation in gs, and Grenache exhibited the most conservative water use behaviour resulting in high water use efficiency. Specific rootstock-scion combinations also exhibited smaller, but still significant, differences in gs and water use efficiency, highlighting the specificity arising from the interaction within each rootstock-scion combination. The high variability in gs indicates that accurate quantification of rootstock-scion contributions to key traits in field studies is complex and requires accounting for spatial heterogeneity driven by the environment.

Tree mortality and susceptibility to pathogens often increases under drought conditions. The interactive nature of these stressors is thought to be related to the balance between sinks and sources of non-structural carbon (NSC), such as defence and osmoregulation versus photosynthesis, respectively. Here, we studied the transcriptional response of Norway spruce subjected to concurrent drought stress and H. annosum s.s. infection. Infection caused an up-regulation of defence-response genes as well as a down-regulation of photosynthesis-related genes under both drought and well-watered conditions. Genes involved in osmoregulation were highly expressed during concurrent drought and infection. The carbon (C) metabolism of well-watered inoculated (W-I) and drought-stressed inoculated (D-I) saplings was strikingly different. In W-I saplings, the up-regulated C-metabolism associated genes are considered to have a role in cell wall formation or modification, suggesting that C was involved in cell wall reinforcement as part of a defence response. By contrast, in D-I saplings, the up-regulation of C-metabolism associated genes was related to the degradation of starch and sucrose into glucose. Transcriptional data suggest that trees cope with drought and pathogen infection at the expense of depleting NSC reserves. Thus, exposure to both drought and infection is likely to exhaust C reserves and decrease the defence capacity of trees in the long run, increasing the risk of tree mortality.

Nitrogen is one of the essential nutrients for plant growth and development. The utilization of beneficial rhizosphere microorganisms is one of the effective ways to increase the nitrogen use efficiency, which is critical to achieving high yields in agricultural and forestry crops. Mollisia sp. Su100 is a novel endophytic fungus previously reported. However, colonization effects and molecular mechanisms of Su100 on the host plants remains unexplored. In this study, we found that Su100 efficiently colonized within the roots of Catalpa bungei seedlings and the inoculated group significantly outperformed the control group in terms of both growth and physiological indicators under nitrogen deficiency. The roots of the inoculated group exhibited lower ROS levels, higher AsA content, and stronger APX activity than those of the control, suggesting that Su100 enhanced the ROS scavenging capacity of the key non-enzymatic antioxidant AsA. Compared to the control group, the inoculated group had higher levels of AMT and NRT expression, as well as higher NO3- and NH4+ content and NR and GS enzyme activities. These results suggested that Su100 improved the nitrogen uptake and assimilation capacity of C. bungei seedlings under nitrogen deficiency. Furthermore, the melatonin (MT) content in the roots of the inoculated group increased, as did the expression levels of genes associated with auxin and BR signaling. Another significant effect of Su100 on C. bungei roots is the alteration of fatty acid (FA) metabolism, which is primarily manifested by promoting very-long-chain fatty acids (VLCFAs) synthesis, wax and suberin accumulation, and remodeling of phosphoglyceride (PG) metabolic pathways. In particular, the contents of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) as well as their molar ratio were altered by Su100 colonization. To our knowledge, this is the first report that root endophytic fungi enhance host plant tolerance to nitrogen deficiency stress by MT enrichment and FA metabolism remodeling.

Xylem conduits widen with distance from the treetop (dtreetop), counteracting most of the resistance to water transport which accumulates with transport pathway length. Inter-conduit pits represent the major resistance to water transport in the xylem, but we know little about their axial variation along the hydraulic path. We investigated the scaling of conduits and pits with dtreetop, the coordination of conduit and pit dimensions, the potential variability of scaling patterns under different growing conditions, and possible differences between species. We sampled Pinus sylvestris L., Picea abies (L.) Karst, and Betula pendula Roth. on two boreal sites with different tree growth rates. We sampled the xylem along the water transport pathway from treetops to coarse roots and measured conduit and pit dimensions using light and scanning electron microscopy. In all species, the mean hydraulic conduit diameter increased, and the cell wall reinforcement decreased with dtreetop. The scaling of the mean hydraulic conduit diameter was steeper in B. pendula than in conifers. In conifers, all measured pit dimensions increased with dtreetop. The pit functional properties torus overlap and valve effect increased with dtreetop in P. sylvestris and decreased in P. abies. In B. pendula, pit border area and pit membrane area increased with dtreetop. Pit traits, which correlated with dtreetop also correlated with the mean hydraulic conduit diameter. We found only small differences between the sites in scaling intercepts in conifers and in scaling exponents in B. pendula. We conclude that selection favors a coordinated widening of conduits and pits with dtreetop to ensure sufficient water supply of the canopy. Our results suggest that pits have a constant share of hydraulic resistance but varying hydraulic safety along the water transport pathway.