Tree physiology最新文献

Cell totipotency and pluripotency are the cellular basis for root regeneration in Platycladus orientalis cuttings, and the regeneration of adventitious roots is a key determinant for improving stem-cutting. However, the cellular basis and physiological regulation of adventitious root formation are still ambiguous. In this research, root primordia initiation and organogenesis were histologically observed, dynamic alterations in soluble proteins were monitored, and Tandem Mass Tag protein profiling during adventitious root development was carried out. It was explicitly shown that the root primordium primarily originated from undifferentiated xylem cells for indirect (callus) rooting and from dividing cells in the cortex for direct (cortex) rooting. During the entire process of adventitious root development, the activities of peroxidase (POD) and polyphenol oxidase (PPO) peaked, and the activity of indole acetic acid oxidase (IAAO) decreased during the prophase of adventitious root formation in both the direct and indirect rooting, suggesting the positive regulation of POD and PPO and the negative regulation of IAAO during adventitious root initiation. Compared with those of indirect rooting, the relatively greater activities of POD and PPO and lower activity of IAAO were related to direct rooting and the number of adventitious roots. A total of 4265 proteins were identified from the base of the cuttings, of which 343, 236 and 37 proteins were highly expressed before treatment, in root primordia induction to adventitious root formation, and adventitious root elongation stages, respectively. Through hierarchical cluster analysis, 23 peroxidase and endogenous hormone regulatory proteins were screened and obtained; these included 10 peroxidases, 1 auxin regulatory protein, 3 ABA regulatory proteins, 2 jasmonic acid regulatory proteins, and 3 gibberellin regulatory proteins, which were highly expressed during the late cutting period. Finally, a hypothetical model of the regulatory network of the differential proteins involved in adventitious root formation in P. orientalis was constructed.

C-repeat binding factors (CBFs) play a pivotal role in regulating cold response in higher plants. Camellia sinensis cv. Baiye 1, a representative albino tea cultivar, has been identified as temperature-sensitive based on long-term observations by tea farmers. However, it remains unclear whether CsCBFs are involved in temperature-mediated albinism and seasonal greening in 'Baiye 1', and the mechanisms by which CBFs regulate cold responses in albino leaves are unknown. In this study, we demonstrate that CsCBF2 suppresses the seasonal greening of albino leaves by inhibiting chlorophyll and carotenoid biosynthesis under cold stress. In tea plantations, the accumulation of chlorophylls and carotenoids in the albino shoots of 'Baiye 1' is closely correlated with the effective accumulated temperature during its seasonal greening process. Weighted Gene Co-expression Network Analysis revealed negative associations between CsCBF expression and chlorophylls, carotenoids, as well as their biosynthetic genes REVEILLE 1 (CsRVE1) and Zeaxanthin epoxidase 1 (CsZEP1) under temperature fluctuations during seasonal greening. Cold-induced upregulation of CsCBF2 expression and decreased chlorophylls and carotenoids under controlled climate conditions. Transient suppression of CsCBF2 by antisense oligodeoxynucleotide elevated expressions of target genes, and increased chlorophylls and carotenoids. CBF-binding cis-elements were identified in CsRVE1, Protochlorophyllide oxidoreductase A (CsPORA), and CsZEP1 promoters. Luciferase assays suggested CsCBF2 binding to the CRT/DRE cis-elements and repressing expression of CsRVE1, CsPORA, and CsZEP1. These findings highlight CsCBF2 as a key transcriptional repressor involved in the seasonal greening of albino 'Baiye 1' under cold stress, by modulating cold responses and inhibiting genes associated with chlorophyll and carotenoid biosynthesis.

Urban Heat Islands (UHI) are a common phenomenon in metropolitan areas worldwide where the air temperature is significantly higher in urban areas than in surrounding suburban, rural or natural areas. Mitigation strategies to counteract UHI effects include increasing tree cover and green spaces to reduce heat. The successful application of these approaches necessitates a deep understanding of the thermal tolerances in urban trees and their susceptibility to elevated urban temperatures. We evaluated how the photosynthetic thermal optimum (Topt), photosynthetic heat tolerance (T50), and key leaf thermoregulatory morphological traits (leaf area, specific leaf area, leaf width, thickness and LDMC) differ between conspecific trees growing in 'hot [UHI]' vs. 'cool' parts of Montreal, Canada (with a difference of 3.4 °C in air temperature), to assess the ability of seven common tree species to acclimation to higher temperatures. We hypothesized that individuals with hotter growing temperatures would exhibit higher Topt and T50, as well as leaf thermoregulatory morphological traits aligned with conservative strategies (e.g., reduced leaf area and increased leaf mass) compared to their counterparts in the cooler parts of the city. Contrary to our a priori hypotheses, leaf area increased with growing temperatures and only four of the seven species had higher T50 and only three had higher Topt values in the hotter area. These results suggest that many tree species cannot acclimate to elevated temperatures and that the important services they provide, such as carbon capture, can be negatively affected by high temperatures caused by climate change and/or the UHI effect. The ability vs inability of tree species to acclimate to high temperatures should be considered when implementing long term tree planting programs in urban areas.

Amazonian species are generally unable to adapt to long drought periods, indicating a low capacity to adjust their hydraulic traits. Secondary forests account for 20% of forest cover in the Amazon, making natural regeneration species crucial under climate change scenarios. In this study, we compared the hydraulic traits of five species, including non-pioneers (Bertholletia excelsa Bonpl., Carapa guianensis Aubl., Hymenaea courbaril L.) and pioneers (Cedrela fissilis Vell., Tabebuia rosea (Bertol.) Bertero ex A.DC.), across light conditions (understory, intermediate, gap) in a 22-year-old secondary forest in Central Amazon, Brazil. Twenty-five saplings were planted and monitored in 3 plots × 5 blocks. Five years after the plantation, we assessed growth, wood density, leaf water potential at predawn and midday, xylem embolism resistance (P50), and hydraulic safety margins (HSM). Leaf water potential ranged from -2.9 to 0 MPa. The non-pioneer species C. guianensis and H. courbaril exhibited the lowest P50 (-4.06 MPa), indicating higher embolism resistance, whereas the pioneer T. rosea had the highest P50 (-1.25 MPa), indicating lower resistance. HSM varied from -1.60 to 3.26 MPa, with lower values in gap conditions during the dry period (-1.60 MPa), especially affecting pioneer species. Wood density was influenced by both light and species type, with non-pioneers showing generally higher density, with H. courbaril reached 0.75 g cm-3 in the understory while the pioneer T. rosea showed the lowest density (0.27 g cm-3). These results highlight that light conditions affect hydraulic traits differently across species strategies, especially during early growth. Non-pioneer, slow-growing native species appear more resilient to light variation, making them suitable for future plantations aimed at climate adaptation in secondary forests.

The severity of droughts is expected to increase with climate change, leading to more frequent tree mortality and a decline in forest ecosystem services. Consequently, there is an urgent need for monitoring networks to provide early warnings of drought impacts on forests. Dendrometers capturing stem diameter variations may offer a simple and relatively low-cost opportunity. However, the links between stem shrinkage, a direct expression of tree water deficit (TWD), and hydraulic stress are not well understood thus far. In this study, we exposed two widespread conifers Pinus sylvestris and Larix decidua to lethal dehydration by withholding water and closely monitored TWD, midday water potential ($psi $), and midday stomatal conductance ($g_{s}$) under controlled greenhouse conditions. We found strong relationships between the three variables throughout the dehydration process, particularly suggesting the potential for continuous $psi $ predictions and stomatal closure assessments. However, the relationships decoupled during recovery from severe drought. We also identified TWD thresholds that signal the onset of drought stress and tissue damage, providing insights into stress impacts and recovery potential. While these findings are promising, challenges remain in practically transferring them to field set-ups by suitable TWD normalization. Importantly, we observed that midday $g_{s}$ was drastically reduced when TWD persisted overnight, providing a directly applicable drought stress signal that does not require normalization. In conclusion, while challenges remain, our results highlight the potential of dendrometers for monitoring tree water dynamics. Implementing dendrometer networks could support the development of early-warning metrics for drought impacts, enabling large-scale monitoring in diverse settings, such as urban areas and forest ecosystems.

It has long been held that tree species/leaves from shaded environments show faster rate of photosynthetic induction than species/leaves from sunlit environments, but the evidence so far is conflicting and the underlying mechanisms are still under debate. To address the debate, we compiled a dataset for 87 tree species and compared the initial increasing slope during the first 2-min induction (SA) and stomatal and biochemical characteristics between sun and shade species from the same study, and those between sun and shade leaves within the same species. In 77% of between-species comparisons, the species with high steady-state photosynthetic rate in the high light (Af) exhibited a larger SA than the species with low Af. In 67% within-species comparisons, the sun leaves exhibited a larger SA than the shade leaves. However, in only a few instances did the sun species/leaves more rapidly achieve 50% of full induction, with an even smaller SA, than the shade species/leaves. At both the species and leaf level, SA increased with increasing initial stomatal conductance before induction (gsi). Despite exhibiting reduced intrinsic water-use efficiency in low light, a large SA proportionally enhances photosynthetic carbon gain during the first 2-min induction in the sun species and leaves. Thus, in terms of the increase in absolute rate of photosynthesis, tree species/leaves from sunlit environments display faster photosynthetic induction responses than those from shaded environments. Our results call for re-consideration of contrasting photosynthetic strategies in photosynthetic adaption/acclimation to dynamic light environments across species.

Unravelling the complexities of transpiration can be assisted by understanding the oxygen isotope composition of transpired water vapour (δE). It is often assumed that δE is at steady state, thereby mirroring the oxygen isotope composition of source water (δsource), but this assumption has never been tested at the whole-tree scale. This study utilized the unique infrastructure of 12 whole-tree chambers enclosing Eucalyptus parramattensis E.C.Hall trees to measure δE along with concurrent temperature and gas exchange data. Six chambers tracked ambient air temperature and six were exposed to an ambient +3 °C warming treatment. Day time means for δE were within 1.2‰ of δsource (-3.3‰) but varied considerably throughout the day. Our observations show that E. parramattensis trees are seldom transpiring at isotopic steady state over a diel period, but transpiration approaches source water isotopic composition over longer time periods.

The process-based xylem formation model is an important tool for understanding the radial growth process of trees and its influencing factors. While numerous xylogenesis models for conifers have been developed, there is a lack of models available for non-coniferous trees. In this study, we present a process-based model designed for xylem formation and ring growth in broad-leaved trees, which we call the Broad-leaved Tree-Ring (BTR) model. Climate factors, including daylength, air temperature, soil moisture and vapor pressure deficit, drive daily xylem cell production (fibers and vessels) and growth (enlargement, wall deposition). The model calculates the total cell area in the simulated zone to determine the annual ring width. The results demonstrate that the BTR model can basically simulate inter-annual variation in ring width and intra-annual changes in vessel and fiber cell formation in Fraxinus mandshurica (ring-porous) and Betula platyphylla (diffuse-porous). The BTR model is a potential tool for understanding how different trees form wood and how climate change influences this process.

Freeze-thaw cycles (FTCs) are the major seasonal environment stress in the temperate and boreal forests, inducing hydraulic dysfunction and limiting tree growth and distribution. There are two types of FTCs in the field: FTCs with increasing temperature from winter to spring (spring FTCs); and FTCs with decreasing temperature from autumn to winter (autumn FTCs). While previous studies have evaluated the hydraulic function during the growing season, its seasonal changes and how it adapts to different types of FTCs remain unverified. To fill this knowledge gap, the eight tree species from three wood types (ring- and diffuse-porous, tracheid) were selected in a temperate forest undergoing seasonal FTCs. We measured the branch hydraulic traits in spring, summer, autumn, and early, middle and late winter. Ring-porous trees always showed low native hydraulic conductance (Kbranch), and high percentage loss of maximum Kbranch (PLCB) and water potential that loss of 50% maximum Kbranch (P50B) in non-growing seasons (except summer). Kbranch decreased, and PLCB and P50B increased in diffuse-porous trees after several spring FTCs. In tracheid trees, Kbranch decreased after spring FTCs while the P50B did not change. All sampled trees gradually recovered their hydraulic functions from spring to summer. Kbranch, PLCB and P50B of diffuse-porous and tracheid trees were relatively constant after autumn FTCs, indicating almost no effect of autumn FTCs on hydraulic functions. These results suggested that hydraulic functions of temperate trees showed significant seasonal changes, and spring FTCs induced more hydraulic damage (except ring-porous trees) than autumn FTCs, which should be determined by the number of FTCs and trees' vitality before FTCs. These findings advance our understanding of seasonal changes in hydraulic functions and how they cope with different types of FTC in temperate forests.