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This insight article comments on: Ziegler C, Cochard, H, Stahl C, Bastien Gérard LF, Goret J, Heuret P, Levionnois S, Maillard P, Bonal D, Coste S. 2024. Residual water losses mediate the trade-off between growth and drought survival across saplings of 12 tropical rainforest tree species with contrasting hydraulic strategies. Journal of Experimental Botany 75, 4128–4147. [ABSTRACT FROM AUTHOR]

Under most conditions tight stomatal regulation in grapevines (Vitis vinifera) avoids xylem embolism. The current study evaluated grapevine responses to challenging scenarios that might lead to leaf embolism and consequential leaf damage. We hypothesized that embolism would occur if the vines experienced low xylem water potential (Ψx) shortly after bud break or later in the season under a combination of extreme drought and heat. We subjected vines to two potentially dangerous environments: (i) withholding irrigation from a vineyard grown in a heatwave-prone environment, and (ii) subjecting potted vines to terminal drought 1 month after bud break. In the field experiment, a heatwave at the beginning of August resulted in leaf temperatures over 45 °C. However, effective stomatal response maintained the xylem water potential (Ψx) well above the embolism threshold, and no leaf desiccation was observed. In the pot experiment, leaves of well-watered vines in May were relatively vulnerable to embolism with 50% embolism (P50) at –1.8 MPa. However, when exposed to drought, these leaves acclimated their leaf P50 by 0.65 MPa in less than a week and before reaching embolism values. When dried to embolizing Ψx, the leaf damage proportion matched (percentage-wise) the leaf embolism level. Our findings indicate that embolism and leaf damage are usually avoided by the grapevines' efficient stomatal regulation and rapid acclimation of their xylem vulnerability. [ABSTRACT FROM AUTHOR]

The study of vegetative and reproductive phenophases of plants is critical for understanding aspects related to plant behavior in different environments. In the tropics, there is a gap of understanding related to plant phenology since the theoretical framework on the topic has been built from perspectives of the temperate region. Furthermore, there are few studies in tropical regions influenced by anthropic conditions, which may be important for understanding these issues in the face of future climate scenarios. This study aimed to describe the vegetative and reproductive phenology of trees in an urban subtropical forest community and to test the influence of climatic variables on the tree community. In an urban forest fragment in Rio Grande do Sul, Brazil, eight individuals of locally dominant species were monitored: Allophylus edulis, Casearia sylvestris, Guarea macrophylla, Mimosa bimucronata, Myrsine coriacea, Myrsine umbellata, Schinus glandulosum, and Schinus terebinthifolia. The monitoring occurred every two weeks, for two years, with the recording of the presence of leaf flushing, leaf shedding, flowering, and fruiting phenophases for each tree. The seasonality of the species was tested using the Rayleigh test. We described the common pattern of community phenological activity by a Principal Component Analysis. Finally, we correlated the common patterns of each phenophase in the community with climatic variables of total precipitation, average temperature, and day length. All species showed a non-uniform phenological pattern for the evaluated phenophases despite the variable intensity. We evidenced common patterns for the community only for the vegetative phenophases. The reproductive phenophases of flowering and fruiting present themselves independently among species in the community. Finally, we identified influences only of temperature and day length on the vegetative phenophases. [ABSTRACT FROM AUTHOR]

During drought, trees reduce water loss and hydraulic failure by closing their stomata, which also limits photosynthesis. Under severe drought stress, other acclimation mechanisms are trigged to further reduce transpiration to prevent irreversible conductance loss. Here, we investigate two of them: the reversible impacts on the photosynthetic apparatus, lumped as non-stomatal limitations (NSL) of photosynthesis, and the irreversible effect of premature leaf shedding. We integrate NSL and leaf shedding with a state-of-the-art tree hydraulic simulation model (SOX+) and parameterize them with example field measurements to demonstrate the stress-mitigating impact of these processes. We measured xylem vulnerability, transpiration, and leaf litter fall dynamics in Pinus sylvestris (L.) saplings grown for 54 days under severe dry-down. The observations showed that, once transpiration stopped, the rate of leaf shedding strongly increased until about 30% of leaf area was lost on average. We trained the SOX+ model with the observations and simulated changes in root-to-canopy conductance with and without including NSL and leaf shedding. Accounting for NSL improved model representation of transpiration, while model projections about root-to-canopy conductance loss were reduced by an overall 6%. Together, NSL and observed leaf shedding reduced projected losses in conductance by about 13%. In summary, the results highlight the importance of other than purely stomatal conductance-driven adjustments of drought resistance in Scots pine. Accounting for acclimation responses to drought, such as morphological (leaf shedding) and physiological (NSL) adjustments, has the potential to improve tree hydraulic simulation models, particularly when applied in predicting drought-induced tree mortality.

During drought, trees reduce water loss and hydraulic failure by closing their stomata, which also limits photosynthesis. Under severe drought stress, other acclimation mechanisms are trigged to further reduce transpiration to prevent irreversible conductance loss. Here, we investigate two of them: the reversible impacts on the photosynthetic apparatus, lumped as non-stomatal limitations (NSL) of photosynthesis, and the irreversible effect of premature leaf shedding. We integrate NSL and leaf shedding with a state-of-the-art tree hydraulic simulation model (SOX+) and parameterize them with example field measurements to demonstrate the stress-mitigating impact of these processes. We measured xylem vulnerability, transpiration, and leaf litter fall dynamics in Pinus sylvestris (L.) saplings grown for 54 days under severe dry-down. The observations showed that, once transpiration stopped, the rate of leaf shedding strongly increased until about 30% of leaf area was lost on average. We trained the SOX+ model with the observations and simulated changes in root-to-canopy conductance with and without including NSL and leaf shedding. Accounting for NSL improved model representation of transpiration, while model projections about root-to-canopy conductance loss were reduced by an overall 6%. Together, NSL and observed leaf shedding reduced projected losses in conductance by about 13%. In summary, the results highlight the importance of other than purely stomatal conductance-driven adjustments of drought resistance in Scots pine. Accounting for acclimation responses to drought, such as morphological (leaf shedding) and physiological (NSL) adjustments, has the potential to improve tree hydraulic simulation models, particularly when applied in predicting drought-induced tree mortality. [ABSTRACT FROM AUTHOR]

Abstract Background Grape leaves provide the biochemical substrates for berry development. Thus, understanding the regulation of grapevine leaf metabolism can aid in discerning processes fundamental to fruit development and berry quality. Here, the temporal alterations in leaf metabolism in Merlot grapevine grown under sufficient irrigation and water deficit were monitored from veraison until harvest. Results The vines mediated water stress gradually and involving multiple strategies: osmotic adjustment, transcript-metabolite alteration and leaf shedding. Initially stomatal conductance and leaf water potential showed a steep decrease together with the induction of stress related metabolism, e.g. up-regulation of proline and GABA metabolism and stress related sugars, and the down-regulation of developmental processes. Later, progressive soil drying was associated with an incremental contribution of Ca2+ and sucrose to the osmotic adjustment concomitant with the initiation of leaf shedding. Last, towards harvest under progressive stress conditions following leaf shedding, incremental changes in leaf water potential were measured, while the magnitude of perturbation in leaf metabolism lessened. Conclusions The data present evidence that over time grapevine acclimation to water stress diversifies in temporal responses encompassing the alteration of central metabolism and gene expression, osmotic adjustments and reduction in leaf area. Together these processes mitigate leaf water stress and aid in maintaining the berry-ripening program.

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Long‐term record of leaf phenology of woody plants that have high longevity and that have been growing on the same site for a longer time could be one of the good indicators for assessing the effects of climate change on forest ecosystem functioning. Since climatic conditions could be different among locations, we need to record the phenology of forest plants growing under various climate types. Here, we report seasonal changes in leaf abundance of deciduous trees during a 13‐year period in the Sambe Forest of Shimane University located in northern Chugoku mountain range, western Japan (35°9′N, 132°37′–40′E, 300–628 m above sea level [asl]). Northern Chugoku mountain range is situated in the west end of Japan Sea side climate. Our study would provide the first record of tree phenology in this region. We examined eight species belonging to eight genera common in a secondary deciduous broad‐leaved forest in western Japan. Habitats of native trees ranged from canopy to understory in the forest and pioneers in an open site. Some of trees were exceptionally planted in an arboretum in the Sambe Forest. Leaf types included single leaf (i.e., Carpinus tschonoskii, Swida macrophylla, etc.) and pinnate leaves (i.e., Aesculus turbinata and Phellodendron amurense). We observed changes in the relative leaf abundance caused by budburst, leaf expansion and leaf shedding of the fixed shoots of targeted trees during 3‐day to 3‐week intervals from March to December each year from 2004 to 2016. Over the 13‐year period, we used a digital camera to take photographs of the shoots that were processed to estimate the leaf abundance. Our data was obtained from common tree species that have a wide habitat range and are distributed nationwide. Therefore, comparison of our data with those data in other climate types may significantly contribute to understand the effect of climate change across Japan on forest plants. The complete data set for this abstract published in the Data Paper section of the journal is available in electronic format in MetaCat in JaLTER at http://db.cger.nies.go.jp/JaLTER/metacat/metacat/ERDP-2020-20.1/jalter-en. [ABSTRACT FROM AUTHOR]

Water relations have been well documented in tree species, but relatively little is known about the hydraulic characteristics of crops. Here, we report on the hydraulic strategy of cotton (Gossypium hirsutum L.). Leaf gas exchange and in vivo embolism formation were monitored simultaneously on plants that were dried down in situ under controlled environment conditions, and xylem vulnerability to embolism of leaves, stems and roots was measured using intact plants. Water potential inducing 50% embolised vessels (P50) in leaves was significantly higher (less negative) than P50 of stems and roots, suggesting that leaves were the most vulnerable organ to embolism. Furthermore, the water potential generating stomatal closure (Pgs) was higher than required to generate embolism formation, and complete stomatal closure always preceded the onset of embolism with declining soil water content. Although protracted drought resulted in massive leaf shedding, stem embolism remained minimal even after ~90% leaf area was lost. Overall, cotton maintained hydraulic integrity during long-term drought stress through early stomatal closure and leaf shedding, thus exhibiting a drought avoidance strategy. Given that water potentials triggering xylem embolism are uncommon under field conditions, cotton is unlikely to experience hydraulic dysfunction except under extreme climates. Results of this study provide physiological evidence for drought resistance in cotton with regard to hydraulics, and may provide guidance in developing irrigation schedules during periods of water shortage. Knowledge about water relations of crops is critical for sustaining productivity and irrigation scheduling. Here, the coordination between embolism and leaf gas exchanged was measured for cotton plants, and results show that the hydraulic integrity of stem and roots was prioritised over canopy carbon gain during drought stress. These results demonstrate the hydraulic strategy of this important crop species, and suggest that irrigation should be applied shortly following stomatal closure to ensure canopy photosynthesis during and after water deficit. [ABSTRACT FROM AUTHOR]

Species are often classified along a continuum from isohydric to anisohydric, with isohydric species exhibiting tighter regulation of leaf water potential through stomatal closure in response to drought. We investigated plasticity in stomatal regulation in an isohydric ( Eucalyptus camaldulensis) and an anisohydric ( Acacia aptaneura) angiosperm species subject to repeated drying cycles. We also assessed foliar abscisic acid (ABA) content dynamics, aboveground/belowground biomass allocation and nonstructural carbohydrates. The anisohydric species exhibited large plasticity in the turgor loss point (ΨTLP), with plants subject to repeated drying exhibiting lower ΨTLP and correspondingly larger stomatal conductance at low water potential, compared to plants not previously exposed to drought. The anisohydric species exhibited a switch from ABA to water potential-driven stomatal closure during drought, a response previously only reported for anisohydric gymnosperms. The isohydric species showed little osmotic adjustment, with no evidence of switching to water potential-driven stomatal closure, but did exhibit increased root:shoot ratios. There were no differences in carbohydrate depletion between species. We conclude that a large range in ΨTLP and biphasic ABA dynamics are indicative of anisohydric species, and these traits are associated with exposure to low minimum foliar water potential, dense sapwood and large resistance to xylem embolism. [ABSTRACT FROM AUTHOR]

PREMISE OF THE STUDY:: A prevailing hypothesis in forest succession is that shade‐tolerant species grow more slowly than shade‐intolerant species, across light conditions, because they prioritize carbon (C) allocation to storage. We examined this hypothesis in a confamilial pair of species, including one of the fastest‐growing tree species in the world (Eucalyptus globulus) and a shade‐tolerant, slow‐growing species (Luma apiculata). METHODS:: Seedlings were subjected to one out of four combinations of light (high vs. low) and initial defoliation (90% defoliated vs. nondefoliated) for four months. Growth, C storage concentration in different organs, leaf shedding, and lateral shoot formation were measured at the end of the experiment. KEY RESULTS:: Eucalyptus globulus grew faster than L. apiculata in high light, but not in low light. Both species had lower C storage concentration in low than in high light, but similar C storage concentrations in each light condition. Defoliation had no effect on C storage, except in the case of the old leaves of both species, which showed lower C storage levels in response to defoliation. Across treatments, leaf shedding was 96% higher in E. globulus than in L. apiculata while, in contrast, lateral shoot formation was 87% higher in L. apiculata. CONCLUSIONS:: In low light, E. globulus prioritized C storage instead of growth, whereas L. apiculata prioritized growth and lateral branching. Our results suggest that shade tolerance depends on efficient light capture rather than C conservation traits. [ABSTRACT FROM AUTHOR]

Background: Sugarcane (Saccharum officinarum L.) is an important sugar crop which belongs to the grass family and can be used for fuel ethanol production. The growing demands for sugar and biofuel is asking for breeding a sugarcane variety that can shed their leaves during the maturity time due to the increasing cost on sugarcane harvest. Results: To determine leaf abscission related genes in sugarcane, we generated 524,328,950 paired reads with RNA-Seq and profiled the transcriptome of new born leaves of leaf abscission sugarcane varieties (Q1 and T) and leaf packaging sugarcane varieties (Q2 and B). Initially, 275,018 transcripts were assembled with N50 of 1,177 bp. Next, the transcriptome was annotated by mapping them to NR, UniProtKB/Swiss-Prot, Gene Ontology and KEGG pathway databases. Further, we used TransDecoder and Trinotate to obtain the likely proteins and annotate them in terms of known proteins, protein domains, signal peptides, transmembrane regions and rRNA transcripts. Different expression analysis showed 1,202 transcripts were up regulated in leaf abscission sugarcane varieties, relatively to the leaf packaging sugarcane varieties. Functional analysis told us 62, 38 and 10 upregulated transcripts were involved in plant-pathogen interaction, response to stress and abscisic acid associated pathways, respectively. The upregulation of transcripts encoding 4 disease resistance proteins (RPM1, RPP13, RGA2, and RGA4), 6 ABC transporter G family members and 16 transcription factors including WRK33 and heat stress transcription factors indicate they may be used as candidate genes for sugarcane breeding. The expression levels of transcripts were validated by qRT-PCR. In addition, we characterized 3,722 SNPs between leaf abscission and leaf packaging sugarcane plants. Conclusion: Our results showed leaf abscission associated genes in sugarcane during the maturity period. The output of this study provides a valuable resource for future genetic and genomic studies in sugarcane. [ABSTRACT FROM AUTHOR]

In the present study, conducted in a secondary dry-seasonal forest in the pacific lowlands of southwestern Panama over 2 years, fungal diversity is linked to plant phenology, litter, and climatic data. Agaricales fungi showed maximum species richness at the beginning of rainy seasons, probably due to the important litter accumulation during the dry season and the increase in humidity favoring fungal growth. Species richness declined during the wet season possibly due to torrential rains, moulds, and decreasing availability of nutrients. Occurrence of foliar pathogenic microfungi correlated negatively with flushing of new leaves at the beginning of the rainy season. Their incidence increased during the wet season and remained high during the dry season. Synchronization of leaf shedding in most tree species significantly reduced the yearly incidence of foliar pathogenic fungi causing an annual turn-over of fungal pathogens that probably contributes to maintain a high diversity of plant pathogenic species. [ABSTRACT FROM AUTHOR]

Key message: Sustainable stomatal opening despite xylem cavitation occurs in ring-porous species and stomatal closure prior to cavitation in diffuse-porous species during soil drought. Abstract: To elucidate the relationship between water loss regulation and vulnerability to cavitation associated with xylem structure, stomatal conductance ( g), defoliation, vulnerability curves, and vessel features were measured on seedlings of ring-porous Zelkova serrata and Melia azedarach, and diffuse-porous Betula platyphylla var. japonica, Cerasus jamasakura and Carpinus tschonoskii. Under prolonged drought conditions, the percentage loss of hydraulic conductivity (PLC) increased and g decreased gradually with decreasing predawn (Ψ) or xylem water potential (Ψ) in Z. serrata. During the gentle increase of PLC in M. azedarach, g increased in the early stages of dehydration while leaves were partly shed. A sharp reduction in g was observed before the onset of an increase in the PLC for drying plants of the three diffuse-porous species, suggesting cavitation avoidance by stomatal regulation. In the ring-porous species, xylem-specific hydraulic conductivity ( K) was higher, whereas the vessel multiple fractions, the ratio of the number of grouped vessels to total vessels, was lower than that in the diffuse-porous species, suggesting that many were distributed as solitary vessels. This may explain the gradual increase in the PLC with decreasing Ψ because isolated vessels provide less opportunity for air seeding. Different water loss regulation to soil drought was identified among the species, with potential mechanisms being sustainable gas exchange at the expense of xylem dysfunction or partial leaf shedding, and the avoidance of xylem cavitation by strict stomatal regulation. These were linked to vulnerability to cavitation that appears to be governed by xylem structural properties. [ABSTRACT FROM AUTHOR]

This study was designed to evaluate the response of 2 wild shrubs, Calotropis procera and Suaeda aegyptiaca, to salinity (100% seawater), drought, and waterlogging stresses. The 90-day-old plants were subjected to the stress treatments for 3 weeks, and growth and some physiological parameters were evaluated. The total plant dry mass of C. procera plants was reduced by 40%, whereas S. aegyptiaca was not significantly affected by salinity stress. Water deficit and waterlogging stresses significantly reduced the total dry mass of both species. Under all conditions, the root/shoot ratio in C. procera was 3-fold higher than in S. aegyptiaca. All applied stresses markedly increased leaf shedding in C. procera plants only. These plants appeared to have a higher salinity and waterlogging stress intensity index as manifested by chlorophyll levels lower than those in S. aegyptiaca. Under all conditions, Na+ levels of S. aegyptiaca were twice those of C. procera plants. All stresses reduced the K+/Na+ ratio in C. procera leaves. On the other hand, S. aegyptiaca plants were able to maintain this ratio near control levels under salinity and drought stresses. Consequently, S. aegyptiaca leaves had higher partial osmotic pressure than C. procera. The proline and total free amino acids levels in C. procera were between 1.3- and 2-fold higher than in S. aegyptiaca. Among all amino acids, the common change in both species under all stresses was an accumulation of free proline and a decrease in methionine levels. The results revealed that the response of both species to salinity and water stresses included avoidance and tolerance mechanisms with some differences between them. [ABSTRACT FROM AUTHOR]

Abstract: Here we examined the response mechanisms and the strategies adopted to cope with drought stress in Jatropha curcas L. Response mechanisms to water stress were explored in three different accessions (from Brazil, Tanzania and Suriname) of J. curcas in terms of water and osmotic relations, gas exchange, PSII photochemistry, and growth performances. Plants were exposed to 18 days of water stress (irrigation was kept at 20% of water holding capacity) followed by 13 days of relief from stress. J. curcas withstands drought stress with a drought-avoidance mechanism through a water saving strategy. These responses include selective abscission of leaves, and marked decreases in net photosynthetic rates and water use efficiency. This allows plants to maintain an “above-lethal” water potential during stress, and to recover net assimilation rate promptly when water availability to the roots is resumed. The Suriname accession displayed greater reductions in net photosynthesis, maximal efficiency of PSII photochemistry (F v/F m), total leaf area and plant dry weight, as compared with both Tanzania and, particularly, the Brazil accession, during drought stress. Impairment of PSII photochemistry was also observed in the Suriname accession at the end of the relief period. Water-stressed J. curcas, irrespective of seed source, was capable to recover net photosynthesis to the level of the well watered counterparts by the end of the relief period. Our data allow to conclude that J. curcas may survive to drought spells of moderate intensities but, at the same time pose serious concerns for its profitable cultivation in arid/semi-arid regions worldwide. [Copyright &y& Elsevier]

Leaf lifespan and phenology have important implications of plant adaptation to the environment. From January of 2008 till early May of 2009, this study tracked the marked twigs at least monthly to note the emergence of new leaves and leaf shedding in 15 dominant species of a natural hardwood forest in Chitou, central Taiwan. The leaf lifespans were then estimated from the results of observations of leaf phenology. We emphasized on the comparisons between the seedlings in the shaded understory and the larger trees on the exposed ridge. Most medium and large trees have scaled buds, and most small trees and shrubs have hypsophyllary buds. The budbreak occurred from March to May for most species. Species did not have the clean-cut difference in the dates of budbreak between the understory seedlings and ridge trees. Based on the duration of leaf emergence, 4 species belong to succeeding type, 7 species flush type, and 4 species intermediate type. 6 species in flush type have scaled buds. Most of newly emerged leaves would survive through the first year, or even the second and third years in most species except for the species with short leaf lifespans. Compared with the leaf fall of canopy trees, the leaf shedding of most ridge trees peaked at the similar time, whereas the leaf shedding of most understory seedlings peaked at the later time of the year, had multiple peaks or irregular patterns. Based on the estimation of the maximum leaf lifespans, the leaves clearly lived longer in the understory species than in the ridge species. In 3 species common to both sites, the understory seedlings also had longer-lived leaves than did the ridge trees. The differences in the leaf lifespans can be interpreted by the effect of light availability as well as by the effect of developmental stages. By contrast, the leaf lifespans cannot be determined with the limited data from the observations of the species with the succeeding type of leaf emergence. [ABSTRACT FROM AUTHOR]

Abstract: We evaluated the effects of moderate shade (43% vs. 100% of full sunlight) and irrigation with eutrophicated river water (daily vs. alternate-day watering) on growth and nitrogen economy of seedlings of three Mediterranean oak species, two evergreen (Quercus coccifera, Quercus ilex subsp. ballota) and a deciduous (Quercus faginea), grown in pots outdoors. Seedling biomass, N pool, N concentration and N losses by litter fall were measured at the beginning (March 2002) and end (November 2002) of a growing season. All species showed an increase of biomass and N pool under shade and/or high irrigation, while only Q. coccifera – from more arid regions – did the same under full sunlight and low irrigation. At the end of the experiment, biomass of the evergreens was higher in shade than in sun, and in high than in low irrigation, while Q. faginea – from more humid zones – responded to irrigation only. Shade-induced growth was accompanied by a decline in N concentration in the evergreens, but irrigation reduced N concentration only of Q. faginea. Shade, but not irrigation, reduced above-ground N loss. We conclude that both treatments differentially affected the evergreen and the deciduous oaks, probably due to differences in plant hydraulic and stomatal conductance. Although both treatments have similar effects on the growth of evergreens, they produced different effects on seedling N economy, which may have important consequences on future field seedling performance. [Copyright &y& Elsevier]

In mixed-species stands, modeling leaf litter dispersal is important to predict the physical and chemical characteristics of the forest floor, which plays a major role in nutrient cycling and in plant population dynamics. In this study, a spatially explicit model of leaf litterfall was developed and compared with two other models. These three models were calibrated for a mixed forest of oak and beech using litterfall data from mapped forest plots. All models assumed that an allometric equation described individual leaf litter production, but they strongly differed in the modeling of the probability density of leaf shedding with distance from source trees. Two models used a negative exponential function to account for leaf dispersal with distance, and this function was allowed to vary according to wind direction in one of them. In contrast, our approach was based on a simple ballistic equation considering release height, wind speed, wind direction, and leaf fall velocity; the distributions of wind speeds and wind directions were modeled according to a Weibull and a Von Mises distribution, respectively. Using an independent validation data set, all three models provided predictions well correlated to measurements (r > 0.83); however, the two models with a direction-dependent component were slightly more accurate. In addition, parameter estimates of the ballistic model were in close agreement with a foliar litter production equation derived from the literature for beech and with wind characteristics measured during leaf litterfall for both species. Because of its mechanistic background, such a spatially explicit model might be incorporated as a litterfall module in larger models (nutrient cycling, plant population dynamics) or used to determine the manner in which patch size in mixed-species stands influences litter mixture. [ABSTRACT FROM AUTHOR]

• Few studies have examined the effects of plant growth on nutrient remobilization in phenologically contrasting species. Here we evaluated the consequences of above-ground seasonality of growth and leaf shedding on the remobilization of nutrients from branches in eight evergreen Mediterranean phanaerophytes that differ widely in phenology. • Vegetative growth, flower bud formation, flowering, fruiting, leaf shedding, and the variations in nitrogen (N), phosphorus (P) and potassium (K) pools in branches throughout the year were monitored in each species. • Nitrogen and P remobilization occurred in summer, after vegetative growth and synchronously with leaf shedding. Despite the time-lag between growth and remobilization, the branches that invested more nutrients in vegetative growth also remobilized more nutrients from their old organs. Potassium remobilization peaked in the climatically harshest periods, and appears to be related to osmotic requirements. • We conclude that N and P remobilization occurs mainly associated with leaf senescence, which might be triggered by factors such as the replenishment of nutrient reserves in woody organs, the hormonal relations between new and old leaves, or the constraints that summer drought poses on the amount of leaf area per branch in summer. [ABSTRACT FROM AUTHOR]

Abstract: Halimium atriplicifolium and Thymus vulgaris are two Mediterranean woody species, which differ in growth form and may co-occur under the same climatic constraints. Both possess distinct short (SS) and long shoots (LS). The aims of this work were: (1) to compare their phenological patterns, (2) to relate plant phenology with root depth and summer water potential, and (3) to compare the structure and phenology of SS and LS. Pre-dawn and mid-day shoot water potentials ( and ) were assessed at the beginning and at the end of the driest period. SS and LS growth, flowering and fruit setting was followed every month throughout the annual cycle. Leaf shedding was followed with litter traps and leaf demography were monitored separately in SS and LS. and exhibited a sharper drop in T. vulgaris than in H. atriplicifolium along the summer. Root depth of H. atriplicifolium was more than twice T. vulgaris. Phenophases of H. atriplicifolium occurred between spring and summer, while those of T. vulgaris concentrated in spring. The latter species shed many current-year leaves in September, probably in response to water shortage. In both species, LS growth occurred during a more rainy period than SS growth and during a warmer period in H. atriplicifolium. Leaf area and leaf mass per area were smaller for SS leaves than LS, probably due to water and carbon shortage at the time of SS growth. In conclusion, T. vulgaris suffered from more severe water stress than H. atriplicifilium due to its shallower root system and arrested phenological activity earlier in the summer. The different morphological and phenological traits of LS and SS suggest a specialisation in carbon gain along different time periods of the year. [Copyright &y& Elsevier]

Trees of Juglans regia L. shed leaves when subjected to drought. Before shedding (when leaves are yellow), the petioles have lost 87 % of their maximum hydraulic conductivity, but stems have lost only 14% of their conductivity. This is caused by the higher vulnerability of petioles than stems to water-stress induced cavitation, These data are discussed in the context of the plant segmentation hypothesis. [ABSTRACT FROM AUTHOR]

Low water availability reduces the establishment of the invasive shrub Prosopis on some grasslands. Water deficit survival and traits that may contribute to the postponement or tolerance of plant dehydration were measured on seedlings of P. glandulosa Torr. var. glandulosa (honey mesquite) grown at CO2 concentrations of 370 (ambient), 710, and 1050 μmol mol−1. Because elevated CO2 decreases stomatal conductance, the number of seedlings per container in the elevated CO2 treatments was increased to ensure that soil water content was depleted at similar rates in all treatments. Seedlings grown at elevated CO2 had a greater root biomass and a higher ratio of lateral root to total root biomass than those grown at ambient CO2 concentration; however, these seedlings also shed more leaves and retained smaller leaves. These changes, together with a reduced transpiration/leaf area ratio at elevated CO2, may have contributed to a slight increase in xylem pressure potentials of seedlings in the 1050 μmol mol−1 CO2 treatment during the first 37 days of growth (0.26 to 0.40 MPa). Osmotic potential was not affected by CO2 treatment. Increasing the CO2 concentration to 710 and 1050 μmol mol−1 more than doubled the percentage survival of seedlings from which water was withheld for 65 days. Carbon dioxide enrichment significantly increased survival from 0% to about 40% among seedlings that experienced the lowest soil water content. By increasing seedling survival of drought, rising atmospheric CO2 concentration may increase abundance of P. glandulosa on grasslands where low water availability limits its establishment. [ABSTRACT FROM PUBLISHER]

Several phenological phases mark the seasonal growth pattern in temperate woody perennials. To gain further insight into the way these phases react on an altering growth environment, we tested whether vegetative and reproductive phenophases in a shrub species respond differentially among different genetic entities and between two different planting sites. We scored leaf bud burst, flower opening, leaf senescence and leaf fall on 267 ramets of Prunus padus L. belonging to 53 genotypes that were sampled in 9 local populations, and that were planted in 2 common gardens in the northern part of Belgium. The data were processed with cumulative logistic regression. The contribution of genetic and non-genetic components to the total variability varied between the four studied seasonal phenophases. The timing of flower opening displayed the smallest relative amount of intragenotypic variance (between ramets), suggesting a stronger genetic control and a lesser need at the individual plant level for plastic fine tuning to the micro-environment. In addition, whereas leaf bud burst showed the highest relative variance at the interpopulation level among all phenophases, probably at least partly attributable to local adaptation, flower opening displayed the highest intergenotypic variance, which may have been promoted more by assortative mating. Spring phenophases were strongly correlated (r = 0.89) as well as the autumnal phenophases (r = 0.72). Flower opening was not correlated with the autumnal phenophases. Timing of leaf bud burst and leaf senescence were negatively correlated, demonstrating that the length of the growing season enlarged or diminished among the studied genotypes. Although the two planting sites were only 24 km apart, all phenophases were advanced at the less exposed site, indicating a phenotypic plastic response. Together, our results suggest that in P. padus, flowering is less sensitive to environmental variation than leaf bud break and may show a lesser impact of a changing environment on this reproductive phenophase. [ABSTRACT FROM AUTHOR]

In greenhouse and field experiments, shedding of pepper leaves infected with Leveillula taurica was inhibited by treatments with indole acetic acid or butyric acid. Spraying with MnSO increased shedding in greenhouse trials. [ABSTRACT FROM AUTHOR]

Background: Grape leaves provide the biochemical substrates for berry development. Thus, understanding the regulation of grapevine leaf metabolism can aid in discerning processes fundamental to fruit development and berry quality. Here, the temporal alterations in leaf metabolism in Merlot grapevine grown under sufficient irrigation and water deficit were monitored from veraison until harvest. Results: The vines mediated water stress gradually and involving multiple strategies: osmotic adjustment, transcript-metabolite alteration and leaf shedding. Initially stomatal conductance and leaf water potential showed a steep decrease together with the induction of stress related metabolism, e.g. up-regulation of proline and GABA metabolism and stress related sugars, and the down-regulation of developmental processes. Later, progressive soil drying was associated with an incremental contribution of Ca2+ and sucrose to the osmotic adjustment concomitant with the initiation of leaf shedding. Last, towards harvest under progressive stress conditions following leaf shedding, incremental changes in leaf water potential were measured, while the magnitude of perturbation in leaf metabolism lessened. Conclusions: The data present evidence that over time grapevine acclimation to water stress diversifies in temporal responses encompassing the alteration of central metabolism and gene expression, osmotic adjustments and reduction in leaf area. Together these processes mitigate leaf water stress and aid in maintaining the berry-ripening program. [ABSTRACT FROM AUTHOR]

ABSTRACT Banded iron formations (BIF) have a particular vegetation type and provide a good model system for testing theories related to leaf phenology, due to unique stressful environmental conditions. As a consequence of the stressful conditions of BIF environment, we hypothesize that most species would retain at least some significant canopy cover, even at the end of the dry season, independently of growth form - trees, shrubs, and sub-shrubs. Considering the strong seasonality, we also hypothesize that photoperiod and rainfall act as triggers for leaf fall and leaf flushing in these environments. The majority of the fifteen studied species had a semi-deciduous behavior and shed their leaves mainly during the dry season, with a recovery at the end of this season. In general, leaf flushing increased around the spring equinox (end of the dry season and start of the rainy season). A trade-off between leaf loss and leaf maintenance is expected in a community in which most plants are naturally selected to be semi-deciduous. Our results suggest photoperiod as a dominant factor in predicting leaf phenology.