Trees最新文献

Key message

The high-wood-density species displays greater water limitation tolerance, as it maintains leaf transpiration under drought conditions.

Abstract

The relationship between environmental conditions and plant hydraulic safety is essential to understand species’ strategies to minimize damage to their hydraulic structure yet maintain function. In the Brazilian semi-arid, the relationships between rainfall seasonality, hydraulic conductivity, wood density, stomatal conductance, and phenology in different species still needs to be clarified. To better understand these relationships, we selected two deciduous trees species with contrasting wood density: (1) Commiphora leptophloeos (Mart.) J.B. Gillett (low wood density) and (2) Cenostigma pyramidale (Tul.) E. Gagnon & G. P. Lewis (high wood density) from the Caatinga dry forest of northeast Brazil. We tracked monthly measurements of whole-tree hydraulic conductivity, leaf stomatal conductance, leaf transpiration rate, xylem water potential, and phenology. We found that the low-wood-density species had a higher whole-tree hydraulic conductivity and an early leaf flush and fall. In addition, lower leaf transpiration rate and higher water storage capacity maintained high xylem water potential and stomatal conductance values, especially in the rainy season. On the other hand, the high-wood-density species had a lower whole-tree hydraulic conductivity and higher leaf transpiration rate, even during the dry season. These results point to the divergent hydraulic strategies employed by each species, further suggesting opposing hydraulic safety pathways during drought.

Key message

In upland forests, trunk CH₄ emissions exhibit significant intra-individual spatial variability, which was explained by variations in both CH₄ concentration and CH₄ production rates in the sapwood.

Abstract

Methane (CH₄) emissions from tree trunks in upland forests should be scaled accurately to assess the role of tree trunk in the forest CH₄ budget. As the chambers used to measure emissions cover only a small part of the large surface area of tree trunks, it is necessary to understand the intra-individual spatial variability of trunk CH₄ emissions. To assess this spatial variability, we measured trunk CH₄ flux at nine locations per individual on four trees in a cool-temperate upland forest for which microbial production of CH₄ inside the trunk is likely an important source of the emission. To know the origin of this variability and the underlying processes, we also measured the potential rate of CH₄ production and CH₄ concentrations in both sapwood and characterized wood and bark. Up to 15-fold intra-individual spatial variations in CH₄ fluxes were observed in target trees. The variability in emissions within an individual was primarily shown by the variation of the sapwood CH₄ concentration which was further explained by the variation in potential CH₄ production rate. The radial CH₄ diffusivity calculated from concentration gradients and emissions was not related to the measured characteristics of either wood or bark. We emphasized the importance of sampling trunk CH₄ flux at multiple locations on the surface of a tree trunk in order to capture the spatial variability, a prerequisite for estimating tree-level CH₄ emissions.

Key message

Eucalyptus grandis and Red-Gum hybrid plantlets differ in the photosynthetic responses to long and short-term water restriction, leading to different adaptation mechanisms to cope with stress.

Abstract

Eucalypts are the most planted forest species in Uruguay and face frequent drought events, which impact plantlet's establishment. Information needs to be included regarding the behavior of promising clones in such conditions. This work aimed to analyze the effects of short and long-term water restriction (WR) on photosynthetic parameters and whether they enable the plant to cope with water shortage. One clone of Eucalyptus grandis (GG) and interspecific hybrids of E. grandis × E. camaldulensis (GC) and E. grandis × E. tereticornis (GT) were subjected to WR defined by soil water potential. At 6 and 16 weeks after treatment imposition, chlorophyll (%Chl) carotenoids (%Carot), maximum net assimilation rate (A_max), stomatal conductance (g_S), leaf transpiration rate (E), light saturation point (LSP) and quantum efficiency (ΦPSII) were assessed. Our results showed that the clones behaved differently. GG minimized water loss significantly to avoid the stress condition through strong stomatal regulation while GC and GT adapted their photosynthetic structure and thus were able to cope with water shortage. Unexpectedly, GT increased A_max significantly under short-term WR, suggesting an early adaptation mechanism to WR. In the long-term WR condition, both hybrids increased %Chl, ΦPSII and A_max while reducing g_S and water uptake. These results suggest that Red-Gum hybrids experienced a “priming” effect of a sublethal dose of WR that enabled them to cope with drought stress in the long term.

Key message

In mixed combinations, the negative impact of water reduction and N addition is mitigated for F. sylvatica, but not for conifers.

Insight into the responses of trees in mixed and monospecific cultivation to water scarcity and nitrogen (N) excess is necessary to recommend suitable tree mixtures for future European forests. Our aim was to investigate the impact of water reduction, N addition or water reduction + N addition in comparison with control (well-watered, no excess N) on mycorrhizal roots and biomass of three temperate forest species (Fagus sylvatica Fs, Picea abies Pa, and Pseudotsuga menziesii Pm) grown in monospecific (FsFs, PaPa, PmPm) and mixed combinations (PaFs, PmFs). We predicted the probability of the responses with a Bayesian approach. Mycorrhizal colonization declined marginally for P. menziesii in PmFs under water reduction. Under water reduction and N addition combined, we found a decline in root tip vitality of F. sylvatica in PaFs and of P. abies in PaPa. F. sylvatica shoot biomass declined under water reduction + N addition in the monospecific combination. P. abies and P. menziesii had lower root biomass in mixture with F. sylvatica under water reduction + N addition and under water reduction as single factor, respectively. With water reduction and N addition, P. menziesii performed better than P. abies in terms of biomass production. F. sylvatica had a growth advantage in mixture with conifers instead of conspecifics. These findings suggest that young trees show rapid and interspecific responses to species mixing and water + N availability. The selection of suitable tree species should, therefore, consider their interactive responses to changing abiotic factors.

Key message

Cortical microtubule arrays are the primary mechanism for guiding the re-orientation of cellulose microfibrils and determining MFA in secondary cell wall of wood fibre and tracheid cells in reaction wood.

Abstract

Microtubules are directly and indirectly involved in guiding cellulose synthase complexes (CSCs) through the plasma membrane. The angle of cellulose deposition is a critical response to environmental signals and/or stress conditions, and particularly crucial during reaction wood formation, a process in which woody plants deposit additional cell wall material to counteract gravitational forces. Tubulin genes are upregulated in response to gravitational stimulus during reaction wood formation, which can result in changes to microtubule assembly. In this study, microtubules were visualised in three woody tree species (two angiosperms: Eucalyptus globulus Labill., Populus alba L., and one gymnosperm: Pinus radiata D. Don.) using immunofluorescence to quantitatively evaluate microtubule organisation during reaction wood formation. Our results suggest that reorientation of the cortical microtubule array affects secondary cell wall deposition, even across different types of reaction wood, by ensuring context-appropriate orientation of cellulose microfibrils and determining MFA in wood cells. Pharmacological studies conducted on in vitro cultured stem segments or in vivo during reaction wood formation corroborated these important roles for microtubules during wood development. This study starts to unveil the role of tubulins during wood formation by exploring cortical microtubule array organisation in trees subjected to gravitational stimulus and it sheds light on cellular and molecular mechanisms behind cellulose deposition in tree species.

Key message

The high-quality sap flow dataset of Melaleuca styphelioides could assists local councils in assessing tree water use and aids in the development of an urban tree sustainable planting management plan

Trees have a vital part to play in urban ecosystems, offering ecological, economic, and social advantages in addition to beautifying our suburbs. Knowledge of tree water use in urban environments is crucial for facilitating urban greening when there is a perception that growing trees on the street verge on expansive soils poses a risk to pavement and buildings. Information on long-term water use by individual trees in an urban environment is essential for local councils in developing urban tree management plans for sustainable planning of trees; however, this information is scarce. Micrometeorological models have commonly been used to estimate the canopy transpiration of plants in the absence of sap flow data. However, the reliability and accuracy of these models have rarely been assessed using sap flow measurements at the field site. This study aimed to provide the water use data of four individual Australian native Melaleuca styphelioides Sm. using sap flow instruments over 25 months. Tree transpiration, estimated based on three commonly used micrometeorological models using weather parameters and tree characteristics, was assessed and compared with sap flow measurements by employing the linear regression statistical analysis. The results revealed that the modified Penman–Monteith (PM) model demonstrated the highest level of accuracy among the evaluated models, consistently yielding lower errors and providing more reliable estimates of tree water use. This suggests that this model may be more appropriate for predicting plant water use in situations where sap flow data are unavailable.

Key message

Using artificial shading in reforested seedlings is recommended for different species, irrigation levels and soil treatments in semiarid ecosystems, but the application of pork sludge and horse guano are ineffective.

Abstract

Application of irrigation, artificial shade and soil amendments can increase the survival of seedlings in plant restoration processes of semiarid ecosystems, however, the effects of shade and soil amendment could occur only without or with low levels of irrigation. In this study, we tested these hypotheses in four woody species (Quillaja saponaria, Lithrea caustica, Schinus polygamus, and Colliguaja odorifera) from the Mediterranean-type climate region of Chile. By mean a factorial experiment, we evaluated different irrigation frequencies (1 L/week and 1 L/2 weeks during the five driest months, no irrigation), artificial shade types (polypropylene shelter, black mesh, deep hole, and no shade) and soil amendment types (natural soil, pork sludge, and horse guano). In 2014, a total of 720 plants per species were planted at each of two sites located in a pre-Andean and a coastal area, and monitored until September 2016. The effect of the type of artificial shade did not depend on the level of irrigation. All shade treatments produced positive effects on the survival of all the species, but the mesh and polypropylene shelter had a greater positive impact than planting in a deep hole. Irrigation treatments increased the survival of all species, although the effect of the highest frequency depended on the site and species. The soil amendment treatments did not have significant positive effects under any condition. In conclusion, the use of artificial shading may be recommended for different species, sites, irrigation and soil treatments in semiarid ecosystems, although the type of shade may depend on the species.

Failure of trees in high winds is of interest to a broad array of stakeholders: foresters, meteorologists, homeowners, insurance industry, parks and recreation management. Equally broad is the array of disciplines that contribute to understanding windthrow failure of trees: aerodynamics, forest management sciences, biomechanics, tree biology, and geotechnical engineering. This paper proposes a mechanistic model for assessing the windthrow failure of trees from a geotechnical engineering perspective. The model assumes a homogenized tree root–soil structure enclosed within a cylindrical volume characterizing the root spread and depth. The model predicts the anchorage resistance of a soil–root system by estimating the uprooting resistance of an equivalent circular footing using a 3D load failure envelope with a rotated parabolic ellipsoid shape. The proposed model was validated using the UK Forest Research Tree Pulling Database (UTPD) with 1239 conifer trees of six common species. The results show that the model successfully predicts the windthrow resistance of various tree species and sizes for different soil states. The soil type and state significantly affected the uprooting resistance, with the effective soil unit weight and water table depth being key soil parameters controlling tree anchorage. Conversely, soil friction angle and soil cohesion have only a modest influence on tree anchorage. The influence of desaturation due to negative pore water pressures was also investigated and found to have a significant effect on the uprooting resistance. Although the model shows promise, the paper concludes that further improvements could be made in form and calibration, as discussed in the paper.

TEOSINTE-BRANCHED/CYCLOIDEA/PCF (TCP) proteins are plant-specific transcription factors (TFs) that play a pivotal role in leaf development by controlling cell proliferation and differentiation. In this study, the authors systematically analyzed the phylogeny, sequence structure, domain feature and expression profiles of TCP genes in Liriodendron chinense, an ornamental tree species with peculiar leaf shape. A total of 17 LcTCP genes were identified in L. chinense genome, which could be grouped into two classes according to their features in the TCP domain. RT-qPCR analysis showed that the expression levels of four TCP genes in Class I (LcTCP21, LcTCP9, LcTCP19a, and LcTCP19b) and three genes in Class II (LcTCP4a, LcTCP4b, and LcTCP24) were consistently higher than those of the other LcTCP genes during leaf development. Degradome data analysis revealed that three LcTCP genes, LcTCP4a, LcTCP4b, and LcTCP24, are targeted by lch-miR319c. Further, LcTCP4a/b and LcTCP24 differed significantly in their expression levels between leaf buds and lobed leaves. However, the expression patterns of LcTCP21 and LcTCP9 contrasted with those of LcTCP19a and LcTCP19b, implying that leaf development in L. chinense may be regulated by a balance between the antagonistic roles of Class I and Class II LcTCP genes. Furthermore, overexpression of LcTCP4 in Arabidopsis thaliana caused a tendency of leaf margin smoothness, and down-regulated the expression levels of genes involved in cell division, AtCYCD3,1 and AtKNOLLE, indicating that LcTCP4 may influence leaf margin shape by inhibiting cell proliferation. Overall, this study provided a comprehensive assessment of the LcTCP gene family and serves as a cornerstone for subsequent functional verification of the LcTCP genes in regulating the leaf development of L. chinense.

Key message

The recurrent anthropogenic disturbances, poor regeneration potential, high carbon stocks, and restricted habitat suitability warrants effective conservation and restoration of two ecologically and economically important endemic tree species.

Abstract

Despite a growing consensus on the application of species distribution models (SDM) in predicting species distributions, the integration of community ecology of endemic species based on field studies with SDM is largely an isolated area of research. This paper presents a detailed account of the distribution, habitat preferences, population ecology and biomass of two endemic tree species, Terminalia paniculata Roth and Lagerstroemia microcarpa Wt. from 119 (0.1 ha) plots sampled in the Shettihalli landscape of the central Western Ghats, India. MaxEnt SDM was used to predict their distribution by testing the influence of environmental factors. We found a significant difference in the density, basal area and carbon stocks of T. paniculata across the dry and moist deciduous and semi-evergreen forests (p < 0.05). Both species were found to be predominant in moist deciduous forests and contributed high biomass carbon. The regeneration potential of T. paniculata was poor in dry deciduous and semi-evergreen forests, whereas L. microcarpa displayed poor to no regeneration in all the forest types. Further, SDM predicted a high probability of distribution for both species. The main factors driving the occurrence in Shettihalli were land use and land cover, precipitation amount of the driest month, soil pH and elevation. The current high suitability of T. paniculata and L. microcarpa were around 137.66 km² and 120.49 km², respectively. Variations in the population structure and regeneration in different forest types are attributed to ongoing anthropogenic disturbances in the landscape. The findings of this study can be extremely helpful in developing proper conservation strategies to protect these species and restore their habitat. We highly recommend the incorporation of SDMs in conservation studies.