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Background: Soil salinization is one of the key factors restricting the production of cropland. Once rice is subjected to alkali stress at the bud burst stage, the yield will suffer irreparable serious loss. Compared with salt tolerance, studies on QTL mapping and candidate gene analysis of rice alkali tolerance are limited. Results: In this study, we used the F2:3 population derived from the alkali-tolerant cultivar LD21 and the alkali-sensitive cultivar WL138 to construct an alkali-tolerant DNA mixing pool, and the BSA (Bulked Segregation Analysis) method was used for re-sequencing. The main QTL qRSLB9 controlling the relative shoot length of rice under alkali stress was mapped by QTL-seq. The candidate interval was narrowed to 346.5 kb by regional linkage mapping, which containing 6 DEGs screened through transcriptome sequencing. The qRT-PCR and candidate gene sequencing showed that LOC_Os09g24260 was most likely to control relative shoot length (RSL) in rice as a major gene who encodes the WD domain, G-beta repeat domain-containing protein. Conclusions: Based on these results, LOC_Os09g24260 was the candidate gene of qRSLB9 conferring alkalinity tolerance to rice at the bud burst stage. Our study provides valuable genetic information and materials for breeding new rice varieties with alkalinity tolerance [ABSTRACT FROM AUTHOR]

Dormancy release and reactivation in temperate trees are mainly controlled by temperature and are affected by age, but the underlying molecular mechanisms are still unclear. In this study, we explored the effects of low temperatures in winter and warm temperatures in spring on dormancy release and reactivation in Larix kaempferi. Further, we established the relationships between cell-cycle genes and cambium cell division. The results showed that chilling accelerated L. kaempferi bud break overall, and the longer the duration of chilling is, the shorter the bud break time is. After dormancy release, warm temperatures induced cell-cycle gene expression; when the configuration value of the cell-cycle genes reached 4.97, the cambium cells divided and L. kaempferi reactivated. This study helps to predict the impact of climate change on wood production and provides technical support for seedling cultivation in greenhouses. [ABSTRACT FROM AUTHOR]

This scientific commentary discusses a study by Hart et al. on the origin and fate of carbon and nitrogen reserves in trees. The study focused on aspen saplings and investigated the remobilization of carbon and nitrogen reserves during spring leaf flush and after an experimental defoliation event. The researchers found that the sources and sinks of carbon and nitrogen differed between these two events, with stems being the main source of carbon during spring and roots playing a significant role in nitrogen transfer. The study also highlighted the existence of sink hierarchy in woody plants, where carbon is prioritized in certain sinks based on their proximity to the source. The findings suggest that factors other than carbon and nitrogen reserves may limit leaf mass recovery after defoliation. The study provides valuable insights into the complex dynamics of carbon and nitrogen in trees and has implications for understanding tree mortality and dieback. [Extracted from the article]

Key message: We established silver birch phenology in the Pyrenees. We highlight actual evapotranspiration as the main driver and the altitudinal effect within a north–south phenological pattern. Research into the phenology of trees is one of the most important issues in making reliable predictions of possible range shifts due to current climate change. Under the current climate change, warming and water stress can threaten tree performance by altering phenological events, specially at the edge of the southern especies distribution. We aimed at establishing bud burst, leaf and stem growth phenology of the Betula pendula in the Spanish Pyrenees, to determine the environmental cues triggering phenological events and to assess the effect of climate and soil water balance on annual growth cycle. The most important cues for bud burst are heat accumulation and long days that reduced the thermal time to bud burst. Leaf unfolding, the period of stem cambial activity, and the variation of the stem radial growth rates throughout the year are mainly regulated by the actual evapotranspiration. Leaf yellowing and abscission are advanced when hydric stress is pronounced shortening leaf longevity. The increase in spring temperatures brings forward the date of bud burst and the start of stem growth. However, the increase in the duration of hotter droughts causes an advance in the date of cessation of birch growth. From the southern Pyrenees to the boreal birch populations, there is a marked latitudinal gradient of phenological events, which are not linear except for the maximum stem growth rate. In the Pyrenees, the growing season is longer than in the boreal forests, but ring thickness is similar. [ABSTRACT FROM AUTHOR]

Plasticity is vital for plants to rapidly acclimate to environmental changes, especially under the climate change. Global warming could advance bud break and extend the growing season, but it also increases the risk of frost damage to developing leaves. In this study, we explored the phenological plasticity of bud burst of half-sib family sugar maple (Acer saccharum Marsh.) seedlings from 11 seed origins in two common gardens at the center and the northern edge of the species distribution in Quebec, Canada. Results showed that the phenological plasticity of sugar maple originating from inland was significantly higher than those from coastal areas at the beginning of leaf development. This discrepancy may result from the long-term frost change frequency of seed origins. Our study suggests that in the context of climate warming, the higher plasticity observed in sugar maple originating from inland areas may benefit from the phenological adaptation of sugar maple and the survival of local populations. It also suggests that inland populations may have a higher potential regarding to assisted migration, but this needs to be confirmed for other functional traits than phenology.

Dormancy release and reactivation in temperate trees are mainly controlled by temperature and are affected by age, but the underlying molecular mechanisms are still unclear. In this study, we explored the effects of low temperatures in winter and warm temperatures in spring on dormancy release and reactivation in Larix kaempferi. Further, we established the relationships between cell-cycle genes and cambium cell division. The results showed that chilling accelerated L. kaempferi bud break overall, and the longer the duration of chilling is, the shorter the bud break time is. After dormancy release, warm temperatures induced cell-cycle gene expression; when the configuration value of the cell-cycle genes reached 4.97, the cambium cells divided and L. kaempferi reactivated. This study helps to predict the impact of climate change on wood production and provides technical support for seedling cultivation in greenhouses.

Global changes affect the growing conditions of terrestrial ecosystems, causing a mismatch between plant phenology and local climates in Northern regions. Due to their long lifespan and irregular regeneration periods, trees cannot respond quickly enough to climate variability through long-term genetic adaptation. In this study, we explored the phenological plasticity and genetic variation among populations of bud burst in sugar maple (Acer saccharum Marsh.) seedlings from 30 Canadian provenances with contrasting climates planted in two common gardens near and at the northern limit of the species’ range. We tested the hypothesis that phenotypic plasticity and genetic variation among populations affect bud phenology. We expect that phenotypic plasticity is more important in regulating bud phenology due to the high variability in short-term weather events characterizing this part of North America. Bud development and leafing occurred in April–May, with complete bud burst lasting between 21 and 29 days. On average, bud swelling differed by 12 days between common gardens. Both factors site (common gardens) and provenance significantly affected bud burst, demonstrating phenological plasticity and genetic variation of sugar maple, respectively. A significant interaction between site and provenance was also found. Overall, the site (11.8–90.3%) contributed more than provenance (0–3.1%) to the variance in timings of bud burst, indicating a dominant role of plasticity in regulating spring phenology. Our study demonstrated the concurring effects of genetic variation and phenological plasticity of sugar maple and revealed the dominant role of the latter factor. The high plasticity observed in sugar maple has a crucial role in the phenological adaptation of maple and the survival of its local populations in a context of changing climate.

Most vegetative axes remain quiescent as dormant axillary buds until metabolic and hormonal signals, driven by environmental changes, trigger bud outgrowth. While the resumption of growth activity is well documented, the establishment and maintenance of quiescence is comparatively poorly understood, despite its major importance in the adaptation of plants to the seasonal cycle or in the establishment of their shape. Here, using the rosebush Rosa hybrida 'Radrazz' as a plant model, we highlighted that the quiescent state was the consequence of an internal and active energy control of buds, under the influence of hormonal factors previously identified in the bud outgrowth process. We found that the quiescent state in the non-growing vegetative axis of dormant axillary buds displayed a low energy state along with a high expression of the ALTERNATIVE OXIDASE 2 (AOX2) and the accumulation of the corresponding protein. Conversely, AOX2 expression and protein amount strongly decreased during bud burst as energy status shifted to a high state, allowing growth. Since AOX2 can deviate electrons from the cytochrome pathway in the mitochondrial respiratory chain, it could drastically reduce the formation of ATP, which would result in a low energy status unfavorable for growth activities. We provide evidence that the presence/absence of AOX2 in quiescent/growing vegetative axes of buds was under hormonal control and thus may constitute the mechanistic basis of both quiescence and sink strength manifestation, two important aspects of budbreak. [ABSTRACT FROM AUTHOR]

The budburst phase is one of the most temperature-sensitive parameters. The study of the morpho-physiological parameters of urban vegetation will allow a better characterization of the behavior of the tree in the city. This study concerns five woody species in the city of Setif (northeast of Algeria): Rosa sp, Euonyms japonicus, Populus tremula, Morus alba and Ligustrum vulgare. The observations were based on phenological behavior such as bud burst, leaf expansion and senescence during the period of january to april 2022 at six sites. The results obtained showed that the phenophase of the beginning of the buds took place between the beginning of february and the beginning of march for all the sites. Statistical analysis showed that the rosebush and the Japanese spindle are the first species whose appearance of buds was observed. The phenological monitoring of the expansion of the leaves shows that the rosebush and the mulberry occupy the first group followed by the other species. These results illustrate the manifestations of climate change, in particular the rise in temperatures in january and february in the city of Setif. [ABSTRACT FROM AUTHOR]

The boreal forest ecosystems of the northern hemisphere are dominated by conifers, of which Norway spruce (Picea abies (L.) H. Karst.) is one of the most common species. Due to its economic interest to the agroforestry industry, as well as its ecological significance, it is important to understand seasonal growth and biomass production in Norway spruce. Solid evidence that the circadian clock regulates growth in conifers has proved elusive, however, resulting in significant gaps in our knowledge of clock function in these trees. Here, we reassess the impact of the circadian clock on growth in Norway spruce. Using a combination of approaches monitoring the physiology of vegetative growth, transcriptomics and bioinformatics, we determined that the clock could be participating a decisive role in enabling growth, acting in specific developmental processes influenced by season and geographical location to guide bud burst and growth. Thus, evidences indicate that there is time for spruce., (© The Author(s) 2024. Published by Oxford University Press.)

Lammas growth of trees means the additional growth of the shoot after the growth cessation and bud set in late summer. In temperate tree species, lammas growth occurs irregularly and is often regarded as abnormal, disturbed growth. In subtropical tree species, however, lammas growth is a prevalent phenomenon, possibly due to the prolonged occurrence of high temperatures in the autumn. The occurrence of lammas growth extends the growing season of trees, but its influence on subsequent dormancy phenomena and bud burst phenology remains largely unexplored. By comparing seedlings showing lammas growth with others not showing it, we carried out an experimental study of how lammas growth affects the bud burst phenology and the underlying dormancy phenomena under both ambient and controlled chilling, forcing, and warming conditions in four subtropical tree species: Carya illinoinensis, Cinnamomum japonicum, Phoebe chekiangensis, and Torreya grandis. With the exception of C. illinoinensis, lammas growth delayed bud burst in all the species under ambient conditions. In a chilling experiment, the delay appeared to be due to higher minimum forcing requirement, higher dormancy depth, and in T. grandis, also to lower chilling sensitivity in the lammas-growth seedlings than in the non-lammas-growth ones. However, a spring warming experiment showed that the sensitivity of bud burst to spring temperatures was higher in the lammas-growth seedlings than in the non-lammas-growth ones. Because of this, the difference between the two phenotypes in the timing of bud burst vanished with increasing warming. Our findings elucidate the significant impact of lammas growth on the dormancy dynamics of subtropical tree species, highlighting the necessity to better understand how the physiological phenomena causing lammas growth change the trees' subsequent environmental responses under changing climatic conditions., (© The Author(s) 2024. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permission@oup.com.)

pH of xylem sap (pHx) was determined in three trees (Malus domestica (apple tree), Picea abies and Pinus cembra) in response to seasonal changes. Conifer trees from lowland (600 m) were compared to trees growing at the alpine timberline (1950 m a.s.l.). Xylem sap was extracted with a Scholander pressure bomb and pHx was measured with a pH microsensor. In all species, pHx changed markedly with season. In spring, pHx was acidic; during winter, the pHx was more alkaline. In apple trees, the pHx did not show a significant correlation with temperature but was rather affected by developmental stage. During flushing in spring, xylem sap acidification took place concomitant to the developmental stage "tight cluster", when foliar development enables a significant transpiration and a consequent movement of water in the xylem. The xylem sap of the two studied conifers showed a significantly larger seasonal alkalinisation (+2.1) than found in apple trees (+1.2) and was significantly more pronounced at the timberline. Xylem sap acidification took place before bud break. pHx had a significant negative correlation with soil temperatures and corresponded to already reported pHx of angiosperms. Overall, pHx appears to be a sensitive stress marker and indicator of activity status in tree xylem. [ABSTRACT FROM AUTHOR]

Abstract Background Entering and exiting winter dormancy present important trade-offs between growth and survival at northern latitudes. Many forest trees display local adaptation across latitude in traits associated with these phenology transitions. Transfers of a species outside its native range introduce the species to novel combinations of environmental conditions potentially requiring different combinations of alleles to optimize growth and survival. In this study, we performed genome wide association analyses and a selection scan in a P. trichocarpa mapping population derived from crossings between clones collected across the native range and introduced into Sweden. GWAS analyses were performed using phenotypic data collected across two field seasons and in a controlled phytotron experiment. Results We uncovered 584 putative candidate genes associated with spring and autumn phenology traits as well as with growth. Many regions harboring variation significantly associated with the initiation of leaf shed and leaf autumn coloring appeared to have been evolving under positive selection in the native environments of P. trichocarpa. A comparison between the candidate genes identified with results from earlier GWAS analyses performed in the native environment found a smaller overlap for spring phenology traits than for autumn phenology traits, aligning well with earlier observations that spring phenology transitions have a more complex genetic basis than autumn phenology transitions. Conclusions In a small and structured introduced population of P. trichocarpa, we find complex genetic architectures underlying all phenology and growth traits, and identify multiple putative candidate genes despite the limitations of the study population.

Climate warming is modifying the movement of air masses over Northern latitudes, producing warming and cooling events across the boreal regions. These new conditions changes may mismatch plant phenology from weather conditions, and affect the growing period of trees. Understanding the processes of local adaptation in bud phenology can help to predict the response of plants to these rapid and unexpected environmental changes.Our study monitored bud burst and bud set weekly during four growing seasons in black spruce [Picea mariana (Mill.) B.S.P.] saplings planted in a common garden and originating from five provenances representing the whole latitudinal distribution of the closed boreal forest in Quebec, Canada. We compared the variance in bud phenology among populations and years, and analysed the relationships with temperatures at the origin sites.Bud burst and bud set occurred in mid‐May and mid‐July, respectively, with a large variability among provenances and between the study years. A delayed bud phenology was observed in the provenances from warmer sites, with bud burst and bud set being 1.1 and 1.4 days later for every additional degree in mean annual temperature at the origin site respectively. Populations with earlier bud bursts also showed earlier bud sets, thus the growing season was similar among provenances. The heritability of bud set was higher than that of bud burst, with estimates of 0.26 and 0.21 respectively. On average, variance in bud phenology among provenances reached 5.3%, which was higher than that within provenances (2.6%). The factor year explained 37.7%–69.7% of the variance in bud phenology.Synthesis. The findings demonstrate the evolutionary response to climate variations in the boreal biome. Endogenous and environmental components have different effects on the phases of bud burst and bud set. This complex interaction among drivers of bud phenology may prevent reliable predictions of changes in the growing season under changing climate. An earlier growth reactivation due to higher spring temperatures could result in higher frost risks to the developing buds. Despite a longer period for photosynthesis expected for the evergreen black spruce under warmer conditions, the period spent for bud development could remain unchanged. [ABSTRACT FROM AUTHOR]

Understanding species-specific responses to climate change allows a better assessment of the possible impact of global warming on forest growth. We studied the responses of the shrub species Corylus avellana L., Corylus maxima Mill. and intermediate forms, together stated as the Corylus taxa, and Cornus sanguinea L. upon periodically elevated temperatures in spring and/or in summer–autumn. Experiments were performed in a common garden, with Belgian and Pyrenean provenances for Corylus avellana and Cornus sanguinea. In the Corylus taxa, a warmer spring resulted in a reduction in height and diameter growth. Remarkably, the reduced diameter increment was restored with full compensation in the following year. The height increment for Cornus sanguinea was larger upon a warmer summer–autumn, concurring with a later leaf senescence. Our results suggest that Corylus is more sensitive to spring warming, influencing growth negatively, whereas Cornus is more sensitive to summer–autumn warming, influencing height growth positively. These deviating responses can be explained, at least partly, by their diverging ecological niches, with the Corylus taxa being more shade-tolerant compared to Cornus sanguinea. The warm spring conditions advanced bud burst in all studied taxa, whereas the warm summer–autumn advanced leaf senescence but prolonged its duration in the Corylus taxa, as well as delayed this phenophase in Cornus sanguinea. Little to no after-effects of the temperature treatments were detected. Although Corylus avellana and Cornus sanguinea plants originated from similar origins, their growth and phenological responses in the common garden diverged, with Corylus being more stable and Cornus displaying more variation between the Belgian and Pyrenean provenances. [ABSTRACT FROM AUTHOR]

Background: Entering and exiting winter dormancy present important trade-offs between growth and survival at northern latitudes. Many forest trees display local adaptation across latitude in traits associated with these phenology transitions. Transfers of a species outside its native range introduce the species to novel combinations of environmental conditions potentially requiring different combinations of alleles to optimize growth and survival. In this study, we performed genome wide association analyses and a selection scan in a P. trichocarpa mapping population derived from crossings between clones collected across the native range and introduced into Sweden. GWAS analyses were performed using phenotypic data collected across two field seasons and in a controlled phytotron experiment. Results: We uncovered 584 putative candidate genes associated with spring and autumn phenology traits as well as with growth. Many regions harboring variation significantly associated with the initiation of leaf shed and leaf autumn coloring appeared to have been evolving under positive selection in the native environments of P. trichocarpa. A comparison between the candidate genes identified with results from earlier GWAS analyses performed in the native environment found a smaller overlap for spring phenology traits than for autumn phenology traits, aligning well with earlier observations that spring phenology transitions have a more complex genetic basis than autumn phenology transitions. Conclusions: In a small and structured introduced population of P. trichocarpa, we find complex genetic architectures underlying all phenology and growth traits, and identify multiple putative candidate genes despite the limitations of the study population. [ABSTRACT FROM AUTHOR]

Between-branch nitrogen competition is expected to be important during spring in temperate deciduous trees as nitrogen allocation would be higher in branches from earlier budburst than in those from later budburst. Such phenology-induced branch interaction would influence plant photosynthesis, but this has not been evaluated. Warming experiments were conducted on whole crowns (warmed trees; trunks and all branches of the same tree were warmed) or parts of the crowns (warmed branches with unwarmed control branches in the same tree), with unwarmed control trees, in saplings of the deciduous species Fraxinus lanuginosa. Spring leaf phenology and leaf photosynthetic traits were investigated to determine how the difference in temperature affects leaf phenology and photosynthetic traits. The timing of budburst was influenced by temperature—budburst was earlier in warmed trees and warmed branches than in control trees and control branches, but budburst timing did not differ between control trees and control branches or between warmed trees and warmed branches. In contrast, leaf traits were affected by the variation in phenology within crowns—nitrogen content and photosynthetic capacity were greater in the leaves of the warmed branches than in the control branches, but they did not differ between the leaves of warmed trees and control trees. Thus, branch warming altered the distribution of nitrogen between warmed and unwarmed branches as warmed branches developed faster, resulting in intracrown variation in leaf photosynthetic traits. [ABSTRACT FROM AUTHOR]

A field-based experiment was carried out in Rukum (East), Nepal, from February to June 2020, to assess the effect of different methods and dates of grafting on the graft take rate of Persian walnut (Juglans regia L.) in field condition. The experiment comprised ten treatments with combination of two factors. The two factors included the grafting dates including: 13th, 19th, and 26th of February, 4th and 11th of March and grafting methods including: outdoor grafting and bench grafting (tongue grafting in both). The experiment was laid out in a Randomized Complete Block Design with three replications. The findings revealed that bench grafting resulted in significantly better outputs than outdoor method for length of scion (at 30 and 60 days after grafting) and graft take rates. Bench grafting showed 44% graft take followed by outdoor grafting (38% graft take). Plants grafted on 13th and 19th of February showed statistically better results for growth performance over the other dates. Plants grafted on 19th of February showed 67% graft take with 53% saleable plants, but statistically similar to the plants grafted on 13th and 26th of February. The earliest bud burst was observed in plants grafted on 13th and 19th of February in 31 and 33 days, respectively. Bench grafting on 19th February showed significantly higher length of scion (16.4 cm) at 60 days after grafting. However, non-significant results were seen for other parameters due to the interaction. Therefore, bench grafting on 13th,19th and 26th of February led to the best graft take in Persian Walnut. [ABSTRACT FROM AUTHOR]

pH of xylem sap (pHx) was determined in three trees (Malus domestica (apple tree), Picea abies and Pinus cembra) in response to seasonal changes. Conifer trees from lowland (600 m) were compared to trees growing at the alpine timberline (1950 m a.s.l.). Xylem sap was extracted with a Scholander pressure bomb and pHx was measured with a pH microsensor. In all species, pHx changed markedly with season. In spring, pHx was acidic; during winter, the pHx was more alkaline. In apple trees, the pHx did not show a significant correlation with temperature but was rather affected by developmental stage. During flushing in spring, xylem sap acidification took place concomitant to the developmental stage “tight cluster”, when foliar development enables a significant transpiration and a consequent movement of water in the xylem. The xylem sap of the two studied conifers showed a significantly larger seasonal alkalinisation (+2.1) than found in apple trees (+1.2) and was significantly more pronounced at the timberline. Xylem sap acidification took place before bud break. pHx had a significant negative correlation with soil temperatures and corresponded to already reported pHx of angiosperms. Overall, pHx appears to be a sensitive stress marker and indicator of activity status in tree xylem.

The role of stress relieving enzymes during bud sprouting in grapevines has already been established in different varieties. However, data on 'Red Globe' variety under tropical conditions are not reported. The present study was conducted to generate data on stress relieving enzymatic activities during bud sprout in 'Red Globe' on different rootstocks under arid conditions of India. Influence of different rootstocks on stress relieving enzymes (catalase, peroxidase, ascorbic acid oxidase and polyphenol oxidase) involved in bud sprouting under tropical conditions with double pruning and single cropping pattern was evidenced. Positive interactions were observed between enzymatic activities of stress relieving enzymes, increased bud break (64.25 %) and reduction in days taken to bud sprout (8.43 days). Among the rootstocks under study, vines on 110R and own rooted vines have strong impact on stress relieving enzymes that resulted into early and increased bud sprouting. Also, the dynamics of enzymatic activity can be used as biological indicators for forecasting the end of bud dormancy and recommencement of growth. [ABSTRACT FROM AUTHOR]

Low-cost phenological experiments with cut twigs are increasingly used to study bud development in response to spring warming and photoperiod. However, a broader variety of species needs to be tackled and in particular the influence of insufficient winter chilling deserves more attention. Therefore, we investigated if and how chilling requirements can be efficiently investigated by cut twigs and how this low-tech approach could be successfully implemented as a citizen science or school project. We conducted an experiment on bud burst and leaf development of Corylus avellana L. twigs, with natural chilling outdoors on a shrub (S) and another chilling treatment as cut twigs in containers (C), and subsequent forcing indoors. Subsampling of the number of cutting dates and number of twigs was used to infer minimum required sample sizes. Apart from insufficiently chilled twigs, ~80% of the twigs (both S and C) reached leaf out. For multiple definitions of chilling and forcing, a negative exponential relationship was revealed between chilling and amount of forcing needed to reach certain developmental stages. At least 5 out of 15 cutting dates or alternatively half of the 10 twig repetitions, but especially those mirroring low chilling conditions, were needed to describe the chilling-forcing relationship with some degree of robustness. In addition, for cutting dates with long chilling, i.e., from January onwards, freshly cut twigs (S) required significantly more forcing to reach bud burst than twigs from containers (C), although the effect was small. In general, chilling conditions of mature shrubs were well captured by cut twigs, therefore opening the possibility of chilling through refrigeration. We conclude that experimental protocols as outlined here are feasible for citizen scientists, school projects, and science education, and would have the potential to advance the research field if carried out on a large scale. We provide an easy-to-use Shiny simulation app to enable citizen scientists to build up a bud development model based on their own experimental data and then simulate future phenological development with winter and/or spring warming. This may encourage them to further study other aspects of climate change and the impacts of climate change.

The frequency of sudden, strong warming events is projected to increase in the future. The effects of such events on spring phenology of trees might depend on their timing because spring warming has generally been shown to advance spring budburst while fall and winter warming have been shown to delay spring phenology. To understand the mechanism behind timing-specific warming effects on spring phenology, I simulated warming events during fall, mid-winter and at the end of winter and quantified their effects on bud dormancy depth and subsequently on spring leaf out. The warming events were carried out in climate chambers on tree seedlings of Betula pendula and Fagus sylvatica in October, January, and February. Control seedlings were kept at photoperiod and temperature matching the daily fluctuating field conditions. Warmed seedlings were kept 10°C warmer than the control seedlings for 10 days during the respective warming periods. Warming in October increased bud dormancy depth and decreased spring leaf-out rate only for F. sylvatica, whereas warming in February reduced bud dormancy depth and advanced spring leaf-out rate only for B. pendula. Neither bud dormancy depth nor spring leaf out rate were affected by January warming. The results indicate that warming-induced changes in bud dormancy depth may explain species- and timing-specific warming effects on spring phenology. The extent to which the timing of bud dormancy phases is species-specific will influence among-species variation in future spring leaf out times.

The use of single-node cuttings of shoots as explants to study bud dormancy and its physiology under controlled conditions is a common practice in grapevine (Vitis vinifera L.) or other perennial plant research. In particular, this method has been extensively used to understand the effect of different chemicals on bud dormancy and bud burst. However, the soil water content in those experiments is usually not reported and its relevance is often neglected. Here, we observed that an unevenly distributed soil water content in a tray containing multiple explants results in an uneven pattern of bud burst within the same treatment. Thus, we hypothesised that soil water content can dramatically affect bud burst. To investigate this, we first established that fresh single-node cuttings were able to transport water into the buds. We then tested the rate of bud burst at different water treatments (35%, 55%, 70%, 85%, and 100% of field capacity; FC). We observed a clear dependence of bud burst on water, in which, at very low levels of water, bud burst does not occur; after 35% FC, bud burst rate increases with water content until around 85% FC; and, from 85% FC, bud burst rate becomes independent of water content. These data highlight the critical importance of monitoring soil water content in any bud burst assay in perennials. Finally, we provide a detailed protocol for determining and controlling field capacity and other soil water content indicators.

Future predictions of forest ecosystem responses are a challenge, as global temperatures will further rise in the coming decades at an unprecedented rate. The effect of elevated temperature on growth performance and phenology of three Prunus spinosa L. provenances (originating from Belgium, Spain, and Sweden) in a common garden environment was investigated. One-year-old seedlings were grown in greenhouse conditions and exposed to ambient and elevated temperatures in the spring (on average 5.6 °C difference) and in the late summer/autumn of 2018 (on average 1.9 °C difference), while they were kept hydrated, in a factorial design. In the following years, all plants experienced the same growing conditions. Bud burst, leaf senescence, height, and diameter growth were recorded. Height and radial growth were not affected in the year of the treatments (2018) but were enhanced the year after (2019), whereas phenological responses depended on the temperature treatments in the year of the treatments (2018) with little carry-over effects in the succeeding years. Spring warming enhanced more height growth in the succeeding year, whereas summer/autumn warming stimulated more radial growth. Spring warming advanced bud burst and shortened the leaf opening process whereas summer/autumn warming delayed leaf senescence and enlarged the duration of this phenophase. These results can help predict the putative shifts in species composition of future forests and woody landscape elements.

Premise: Boreal and northern temperate forest trees possess finely tuned mechanisms of dormancy, which match bud phenology with local seasonality. After winter dormancy, the accumulation of chilling degree days (CDD) required for rest completion before the accumulation of growing degree days (GDD) during quiescence is an important step in the transition to spring bud flush. While bud flush timing is known to be genetically variable within species, few studies have investigated variation among genotypes from different climates in response to variable chilling duration. Methods: We performed a controlled environment study using dormant cuttings from 10 genotypes of Populus balsamifera, representing a broad latitudinal gradient (43–58°N). We exposed cuttings to varying amounts of chilling (0–10 weeks) and monitored subsequent GDD to bud flush at a constant forcing temperature. Results: Chilling duration strongly accelerated bud flush timing, with increasing CDD resulting in fewer GDD to flush. Genotypic variation for bud flush was significant and stratified by latitude, with southern genotypes requiring more GDD to flush than northern genotypes. The latitudinal cline was pronounced under minimal chilling, whereas genotypic variation in GDD to bud flush converged as CDD increased. Conclusions: We demonstrate that increased chilling lessens GDD to bud flush in a genotype‐specific manner. Our results emphasize that latitudinal clines in bud flush reflect a critical genotype‐by‐environment interaction, whereby differences in bud flush between southern vs. northern genotypes depend on chilling. Our results suggest selection has shaped chilling requirements and depth of rest as an adaptive strategy to avoid precocious flush in climates with midwinter warming. [ABSTRACT FROM AUTHOR]

Low-cost phenological experiments with cut twigs are increasingly used to study bud development in response to spring warming and photoperiod. However, a broader variety of species needs to be tackled and in particular the influence of insufficient winter chilling deserves more attention. Therefore, we investigated if and how chilling requirements can be efficiently investigated by cut twigs and how this low-tech approach could be successfully implemented as a citizen science or school project. We conducted an experiment on bud burst and leaf development of Corylus avellana L. twigs, with natural chilling outdoors on a shrub (S) and another chilling treatment as cut twigs in containers (C), and subsequent forcing indoors. Subsampling of the number of cutting dates and number of twigs was used to infer minimum required sample sizes. Apart from insufficiently chilled twigs, ~80% of the twigs (both S and C) reached leaf out. For multiple definitions of chilling and forcing, a negative exponential relationship was revealed between chilling and amount of forcing needed to reach certain developmental stages. At least 5 out of 15 cutting dates or alternatively half of the 10 twig repetitions, but especially those mirroring low chilling conditions, were needed to describe the chilling-forcing relationship with some degree of robustness. In addition, for cutting dates with long chilling, i.e., from January onwards, freshly cut twigs (S) required significantly more forcing to reach bud burst than twigs from containers (C), although the effect was small. In general, chilling conditions of mature shrubs were well captured by cut twigs, therefore opening the possibility of chilling through refrigeration. We conclude that experimental protocols as outlined here are feasible for citizen scientists, school projects, and science education, and would have the potential to advance the research field if carried out on a large scale. We provide an easy-to-use Shiny simulation app to enable citizen scientists to build up a bud development model based on their own experimental data and then simulate future phenological development with winter and/or spring warming. This may encourage them to further study other aspects of climate change and the impacts of climate change. [ABSTRACT FROM AUTHOR]

The frequency of sudden, strong warming events is projected to increase in the future. The effects of such events on spring phenology of trees might depend on their timing because spring warming has generally been shown to advance spring budburst while fall and winter warming have been shown to delay spring phenology. To understand the mechanism behind timing-specific warming effects on spring phenology, I simulated warming events during fall, mid-winter and at the end of winter and quantified their effects on bud dormancy depth and subsequently on spring leaf out. The warming events were carried out in climate chambers on tree seedlings of Betula pendula and Fagus sylvatica in October, January, and February. Control seedlings were kept at photoperiod and temperature matching the daily fluctuating field conditions. Warmed seedlings were kept 10°C warmer than the control seedlings for 10 days during the respective warming periods. Warming in October increased bud dormancy depth and decreased spring leaf-out rate only for F. sylvatica , whereas warming in February reduced bud dormancy depth and advanced spring leaf-out rate only for B. pendula. Neither bud dormancy depth nor spring leaf out rate were affected by January warming. The results indicate that warming-induced changes in bud dormancy depth may explain species- and timing-specific warming effects on spring phenology. The extent to which the timing of bud dormancy phases is species-specific will influence among-species variation in future spring leaf out times. [ABSTRACT FROM AUTHOR]

The objective of this study was to develop a model to estimate the chilling requirements of 10 oriental pear cultivars by standardizing dormancy depth. The dormancy depth of these cultivars was standardized to a range of 0–100 by setting the lowest bud burst rate during endodormancy as 0 and the bud burst rate immediately after the completion of endodormancy as 100. The endodormancy period was divided into periods. Stage I represented continuously increasing dormancy depth until the deepest dormancy was reached. Stage II represented the period of decreasing dormancy depth following the deepest dormancy; this stage included the breaking of dormancy. In addition, the 10 studied cultivars were classified into three types according to their dormancy depth changing pattern: stage I drop type, stage II leap-up type, and stage I·II symmetric type. A chilling accumulation model was derived based on both the endodormancy period and the dormancy depth of each cultivar. The results showed that − 1.9 to 12.0 °C was an effective range for chilling accumulation and that 2.1–4.0 °C was the most effective range for chilling accumulation. The results also revealed that negative accumulation, the reverse reaction of chilling accumulation, occurred under high-temperature conditions (above 14 °C). The results of the model verification process confirmed that the high-temperature conditions (above 14 °C) exhibited negative accumulation values due to an inverse relationship with dormancy depth during endodormancy stage I and that the chilling accumulation for the actual dormancy break mostly occurred during endodormancy stage II. [ABSTRACT FROM AUTHOR]

The physiological constraints on bud burst in woody perennials, including vascular development and oxygenation, remain unresolved. Both light and tissue oxygen status have emerged as important cues for vascular development in other systems; however, grapevine buds have only a facultative light requirement, and data on the tissue oxygen status have been confounded by the spatial variability within the bud. Here, we analysed apoplastic development at early stages of grapevine bud burst and combined molecular modelling with histochemical techniques to determine the pore size of cell walls in grapevine buds. The data demonstrate that quiescent grapevine buds were impermeable to apoplastic dyes (acid fuchsin and eosin Y) until after bud burst was established. The molecular exclusion size was calculated to be 2.1 nm, which would exclude most macromolecules except simple sugars and phytohormones until after bud burst. We used micro-computed tomography to demonstrate that tissue oxygen partial pressure data correlated well with structural heterogeneity of the bud and differences in tissue density, confirming that the primary bud complex becomes rapidly and preferentially oxygenated during bud burst. Taken together, our results reveal that the apoplastic porosity is highly regulated during the early stages of bud burst, suggesting a role for vascular development in the initial, rapid oxygenation of the primary bud complex. [ABSTRACT FROM AUTHOR]

Several studies reported the beneficial effect of Dormex (Hydrogen Cyanamid) on compensating the lack of chilling hours required for a normal vines budburst. It was recently prohibited in many countries due to its toxicity on plants and humans. The objective of this study was to find alternatives for Dormex. Gibberellic acid plays a role as endogenous hormone on budburst. Nano-fertilizers (Amino25) are known to prevent biotic and abiotic stresses in plant. No studies were conducted on the effect of both products on vines in warm winter climate. Two experiments will be discussed in this paper and compared to previous result of Dormex applied at the same location. The treatments were: Openfield /Without Products, Greenhouse/Without Products, Open-field!Gibberellic acid, Greenhouse/Gibberellic acid, Open-field/Amino25 and Greenhouse/ Amino25. The study was conducted on three ARRA seedless cultivars. Gibberllic acid was applied at 2ppm and Amino25 were applied at 1.5 g L- 1 for several times before budburst. Giberellic acid enhanced bud formation under greenhouse as Dormex did and induced earliness of 2 weeks in budburst while its effect on fruits, flowers and yield was less efficient than Dormex. It did not have effect in open-field conditions as well as Amino25 in both cultivation systems. Gibberellic acid could replace Dormex to resolve bud burst problem. Since Gibberellic acid and Nano-fertilizers are non-toxic and could be used on organic farming, advanced research should take place to enhance the effects of Gibberellic acid in open-field conditions and additional studies are recommended regarding the effect of Nanofertilizers on grapevines. [ABSTRACT FROM AUTHOR]

There is evidence that the ongoing climate change is happening through nighttime rather than daytime warming. How such a daily-asymmetric warming modifies plant phenology is still unclear. We investigated the effects of asymmetric warming on bud break by daily monitoring seedlings belonging to 26 black spruce [Picea mariana (Mill.) BSP.] and 15 balsam fir [Abies balsamea (L.) Mill.] provenances from the native range in Canada. Seedlings were subjected to either daytime or nighttime warming in three growth chambers at temperatures ranging between 10 and 24 °C. On average, a warming of 4 °C advanced the timings of bud break in both species by 2.4 days, with the later phases being more sensitive to the treatment. Bud break of both species responded more strongly to daytime warming, with the bud break occurred 1.2 and 3.2 days earlier under daytime than nighttime warming in black spruce and balsam fir, respectively. A marked ecotypic differentiation was only observed in black spruce that originated from provenances distributed broadly across Canada, with seedlings from the warmest provenance completing bud break 8.3 days later than those from the coldest one. However, no significant effect of provenance was observed for balsam fir, the narrowly distributed species. Overall, the above results suggest that a higher temporal resolution such as temperatures during daytime and nighttime, and higher spatial resolution should be taken into account to improve the accuracy of phenological model predictions under global change scenarios. Phenological models based on daily average temperature should take into account the diverging impacts of asymmetric warming on plant phenology. Our findings may indicate that the influence of warming on plant phenology may be less dramatic than expected. [ABSTRACT FROM AUTHOR]

Global change increases the risk of extreme climatic events. The impact of extreme temperature may depend on the tree species and also on the provenance. Ten provenances of Fagus sylvatica L. were grown in a common garden environment in Belgium and subjected to different temperature treatments. Half of the one year old seedlings were submitted to a high thermal stress in the spring of the first year, and all plants were exposed to a late spring frost in the second year. The high-temperature treated plants displayed reduced growth in the first year, which was fully compensated (recovery with exact compensation) in the second year for radial growth and in the third year for height growth. Frost in the spring of the second year damaged part of the saplings and reduced their growth. The frost damaged plants regained the pre-stress growth rate one year later (recovery without compensation). The high temperature treatment in the first year and the frost damage in the second year clearly influenced the phenological responses in the year of the event and in the succeeding year. Little population differentiation was observed among the provenances for growth and for phenological responses. Yet, a southern provenance, a non-autochthonous provenance (original German provenance that was planted in Belgium about a century ago) and a more continental provenance flushed earlier than the local Atlantic provenances in the year of the frost event, resulting in more frost damage. Some caution should therefore be taken when translocating provenances as an anticipation of the predicted climate warming.

Light and temperature are crucial factors for the annual growth rhythm of tree seedlings of the boreal and temperate zone. Dormant, vegetative winter buds are formed under short days (SD) and altered light quality. In the conifer Norway spruce, expression of FTL2 increases and PaCOL1-2 and PaSOC1 decrease under light regimes, inducing bud set. Although temperature is known to modulate the timing of bud set, information about combined effects of light climate and temperature on bud phenology and gene expression is limited. We studied the interactive effects of temperature (18, 22/24 °C) and day extension with blue (B), red (R) or far-red (FR) light or different R:FR ratios compared to SD on growth–dormancy cycling and expression of FTL2, PaCOL1-2 and PaSOC1 in Norway spruce seedlings. Day-extension with B light and all treatments involving FR light sustained shoot elongation, with increased growth at higher temperature. The R light treatment resulted in delayed/prevented bud set compared to SD, with more delay/prevented bud set at 24 °C than 18 °C. This was associated with lower PaFTL2-transcript levels at 24 °C and more rapid subsequent bud burst. For the growth-sustaining treatments (long days, FR and B light), the PaFTL2-transcript levels were generally lower and those of PaCO1-2 and PaSOC1 higher compared with SD and R light. In conclusion, our results demonstrate more reduced/prevented bud set and faster bud burst with increased temperature under day extension with R light, indicating less deep dormancy than at lower temperature. Also, sustained shoot elongation under the B light treatment (27 µmol m−2 s−1) in contrast to the lower B light-irradiances tested previously (≤13 µmol m−2 s−1), demonstrates an irradiance-dependent effect of day extension with B light.

Main conclusion: The roles of microRNA-mediated epigenetic regulation were highlighted in the bud dormancy–activity cycle, implying that certain differentially expressed miRNAs play crucial roles in apical bud burst, such as csn-miR319c/TCP2. microRNAs (miRNAs) are a class of small non-coding RNAs that regulate gene expression by targeting mRNA transcripts for cleavage or directing translational inhibition. To investigate whether miRNAs regulate bud dormancy–activation transition in tea plant, which largely affects the yield and price of tea products and adaptability of tea trees, we constructed small RNA libraries from three different periods of bud dormancy–burst transition. Through sequencing analysis, 262 conserved and 83 novel miRNAs were identified, including 118 differentially expressed miRNAs. Quantitative RT-PCR results for randomly selected miRNAs exhibited that our comprehensive analysis is highly reliable and accurate. The content of caffeine increased continuously from the endodormancy bud to flushing bud, and differentially expressed miRNAs coupling with their targets associated with bud burst were identified. Remarkably, csn-miR319c was downregulated significantly from the quiescent bud to burst bud, while its target gene CsnTCP2 (TEOSINTE BRANCHED/CYCLOIDEA/PROLIFERATING CELL FACTOR 2) displayed opposite expression patterns. Co-transformation experiment in tobacco demonstrated that csn-miR319c can significantly suppress the functions of CsnTCP2. This study on miRNAs and the recognition of target genes could provide new insights into the molecular mechanism of the bud dormancy–activation transition in tea plant. [ABSTRACT FROM AUTHOR]

• Transmittance and phenology data were collected in oak stands during leaf unfolding. • Modelling transmittance provided parameters characterizing tree foliage development. • Growing season onset can continuously be monitored with light sensors. • The relationship between observed bud burst date and transmittance is complex. • Indices based on transmittance could be used to give an estimate of bud burst date. Better knowledge and a more complete long-term monitoring of tree species phenology and tree foliage development are crucial to accurately estimating the impact of climate change on forest ecosystems functioning and on forest species distribution. We set up global solar radiation sensors under the forest canopy and continuously recorded solar radiation in order to follow the development of sessile oak (Quercus petraea L.) foliage in pure stands over four consecutive years and for two levels of stand density. At the same time, we made phenological observations to determine bud burst date. One of our goals was to link observed bud burst dates and transmittance measurements. Our results show that solar radiation transmittance during the leaf unfolding period followed a sigmoid-shaped curve; and that it was possible to fit a generalized logistic model to determine a set of parameters characterizing tree foliage and its development during the unfolding period. Among these parameters, we suggest that the date at which solar radiation interception by foliage reaches 50% could be used to monitor the beginning of the growing season over the long term. The relationship between observed bud burst date and the transmittance model parameters was more complex than we expected. We tested several indices to deduce the date of bud burst from transmittance. We showed that when radiation interception due to foliage reached 10%, this indicated the observed bud burst date. Finally, a linear model including parameters from the generalized logistic models of transmittance as predictors explained 57% of the variability in bud burst date. Complementary research combining light measurements and phenological observations over a longer period of time is needed to know whether these relationships could help estimate bud burst date regardless of the year or the stand density. [ABSTRACT FROM AUTHOR]

Fagaceae can be found in tropical and temperate regions and contain species of major ecological and economic importance. In times of global climate change, tree populations need to adapt to rapidly changing environmental conditions. The predicted warmer and drier conditions will potentially result in locally maladapted populations. There is evidence that major genera of the Fagaceae are already negatively affected by climate change‐related factors such as drought and associated biotic stressors. Therefore, knowledge of the mechanisms underlying adaptation is of great interest. In this review, we summarise current literature related to genetic adaptation to abiotic environmental conditions. We begin with an overview of genetic diversity in Fagaceae species and then summarise current knowledge related to drought stress tolerance, bud burst timing and frost tolerance in the Fagaceae. Finally, we discuss the role of hybridisation, epigenetics and phenotypic plasticity in adaptation. [ABSTRACT FROM AUTHOR]

A complete diallel cross was made among nine Betula pendula trees growing in a natural population and a trial was planted on agricultural soil at one site. This exceptional trial has provided estimates of genetic parameters that can only be estimated in complete diallels. Traits measured were height and diameter during a period of 37 years, and assessments were made of bud burst, leaf abscission and rust infection at the early ages. All traits showed genetic variation and the variance components of general combining ability (GCA) effects were dominating, with heritability estimates of 0.16 and 0.23 for height and diameter at age six years. The best-growing families could be identified at that age. At age 37 years, when the trial had been thinned twice, the offspring from the highest and lowest ranked parent for growth contributed with 19% and 6% of the total volume of the stand, respectively. The GCA effects were also highly significant for the assessment traits, but with an interaction with year for bud burst. High values of estimates of genetic correlations proved that bud burst, leaf abscission and rust infection are interrelated, and also to some extent with growth traits. Families with an early bud burst were tallest, were less affected by the rust fungus and kept their leaves later in the autumn. [ABSTRACT FROM AUTHOR]

Highlights • The timing of bud phenology is the result of internal and external cues. • Bud burst and bud set mirror the temperature of their provenance. • Ecotypes with later growth in spring could be sensitive to autumn frosts. • Ecotypes selection can aim to avoid early or late frosts, but not both. Abstract Forest managers use artificial regeneration to influence tree species composition and productivity. The selection of plant material could assume a leading role in forest planning, mainly when aiming to increase the adaptation of stands within a context of climate change. In this study, we investigated the timing of bud burst and bud set in five black spruce [ Picea mariana (Mill.) B.S.P.] ecotypes growing in a common garden and originating from a latitudinal range in the boreal forest of Québec, Canada. Bud phenology was monitored weekly during the 2015, 2017 and 2018 growing seasons. On average, the bud burst process lasted 23 days, occurring 1.2 days later for each degree Celsius of increase in mean annual temperature at the provenance site. Bud set duration was 55 days and occurred 1.8 days later for each degree Celsius of increase in mean annual temperature at the provenance site. We demonstrated that both bud burst and bud set occurred earlier in individuals from colder sites, which resulted in similar lengths of the growing season among provenances. This clinal variation in the timings of growth resumption and cessation confirms the ecotypic differentiation of black spruce populations and reflects a long-lasting adaptation to the local temperatures in the sites of origin. The findings of this study demonstrate that ecotype selection in black spruce can aim to avoid damage from either early or late frosts, but not both. [ABSTRACT FROM AUTHOR]

In boreal and temperate trees, air temperature is a major environmental factor regulating the timing of spring phenological events, such as vegetative bud burst, through underlying physiological processes. This has been established by experimental research, and mathematical process-based tree phenology models have been developed based on the results. The models have often been applied when assessing the effects of climate change. Currently, there is an increasing trend to develop process-based tree phenology models using only observational phenological records from natural conditions. We point out that this method runs a high risk of producing models that do not simulate the real physiological processes in the trees and discuss experimental designs facilitating the development of biologically realistic process-based models for tree spring phenology. Highlights Studies addressing spring phenology of trees are increasingly topical because of the ongoing climate change. Spring phenology of trees is often studied with process-based mathematical models, which simulate physiological processes underlying the timing of phenological events, such as vegetative bud burst. Process-based tree phenology models are often used in computer simulations for projecting the effects of future climate warming on trees and forest ecosystems. Traditionally models have been developed with the aid of growth chamber and greenhouse experiments, which have facilitated the determination of environmental responses of the physiological processes. However, nowadays models are often developed without experimental research, using observational long-term phenological records, or remote-sensed data, gathered in natural conditions as the only biological information. [ABSTRACT FROM AUTHOR]

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The control of bud burst process depending on temperature is crucial factor in woody perennial plants to survive in unfavorable ecological conditions. Although it has important economic and agronomic values, little information is available on the molecular mechanism of the bud burst process in Corylus avellana. Here for the first time, we conducted a de novo transcriptome-based experiment using eco-dormant leaf bud tissues. Four transcriptome libraries were constructed from the leaf bud tissues and sequenced via Illumina platform. Transcriptome analysis revealed 86,394 unigenes with a mean length of 1189 nt and an N50 of 1916 nt. Among these unigenes, 63,854 (73.78%) of them were annotated by at least one database. De novo assembled transcripts were enriched in phenylpropanoid metabolism, phytohormone biosynthesis and signal transduction pathways. Analyses of phytohormone-associated genes revealed important changes during bud burst, in response to gibberellic acid, auxin, and brassinosteroids. Approximately 2163 putative transcription factors were predicted, of which the largest number of unique transcripts belonged to the MYB transcription factor family. These results contribute to a better understanding of the regulation of bud burst genes in perennial plants. [ABSTRACT FROM AUTHOR]

The University of Tokyo Hokkaido Forest (UTHF) has accumulated phenology data of woody plants since 1930: bud burst, flowering, foliage coloring, and natural defoliation. However, the original data for the 13 years from 1938 to 1950 have been lost. In this paper, means for the lost 13 years were estimated using original datasets from before and after the 13 years. Two different series of mean values, both including the 13 years were digitized from hand-drawn figures. In the process, some incorrect data in the original figures were detected. The results of this paper could enhance the value of the long-term plant phenology data by connecting data from 1930 to 2010. [ABSTRACT FROM AUTHOR]