Timing Of Bud Burst Research Articles

Dormancy characteristics of lammas-growth seedlings of subtropical trees and their phenological responses to experimental warming.

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.

Contrasting temperature and light sensitivities of spring leaf phenology between understory shrubs and canopy trees: Implications for phenological escape

Spring leaf phenology influences plant fitness and is highly sensitive to environmental changes. The spring phenological escape hypothesis posits that deciduous understory plants generally leaf out earlier than canopy trees to access a period of high light before the canopy closes. However, plants in different forest layers may respond differently to climate warming, which could lead to phenological mismatch between the understory and canopy species. Therefore, exploring the phenological sensitivities of plants from different forest layers is crucial for anticipating the effects of climate-driven phenological shifts. However, these types of studies are still scarce. Here, we conducted a twig experiment in climate chambers for eight tree species and seven shrub species growing in subtropical deciduous forests in the Shennongjia Mountains, central China. Specifically, we set up three treatments (control, warming, and shading) for five weeks to test the responses of the timing of bud burst and leaf unfolding, and the duration of bud development to different temperatures and light intensities. For shrubs, bud burst and leaf unfolding occurred earlier and the duration of bud development was shorter than these of trees. For both shrubs and trees, warming significantly advanced the timing of leaf unfolding and shortened the duration of bud development. Shading significantly delayed the timing of bud burst for both shrubs and trees. Shading also delayed the timing of leaf unfolding and lengthened the duration of bud development for trees, but did not significantly influence the two phenological metrics for shrubs. Tree phenology, as measured by all three metrics, was more sensitive to temperature than was shrub phenology. The timing of bud burst of shrubs was slightly more sensitive to light than that of trees. Our results indicate that shrubs leaf out earlier than trees in the same forest, which allows understory species to take advantage of the high-light resources before canopy closure. However, in our study, trees were more responsive to warming temperatures, suggesting that spring warming could advance canopy closure relative to shrub leaf phenology, potentially resulting in phenological mismatch between understory shrubs and canopy trees.

Unpunctual in diversity: The effect of stand species richness on spring phenology of deciduous tree stands varies among species and years.

Climatic drivers alone do not adequately explain the regional variation in budburst timing in deciduous forests across Europe. Stand-level factors, such as tree species richness, might affect budburst timing by creating different microclimates under the same site macroclimate. We assessed different phases of the spring phenology (start, midpoint, end, and overall duration of the budburst period) of four important European tree species (Betula pendula, Fagus sylvatica, Quercus robur and Tilia cordata) in monocultures and four-species mixture stands of a common garden tree biodiversity experiment in Belgium (FORBIO) in 2021 and 2022. Microclimatic differences between the stands in terms of bud chilling, temperature forcing, and soil temperature were considerable, with four-species mixtures being generally colder than monocultures in spring, but not in winter. In the colder spring of 2021, at the stand level, the end of the budburst period was advanced, and its overall duration shortened, in the four-species mixtures. At species level, this response was significant for F. sylvatica. In the warmer spring of 2022, advances in spring phenology in four-species stands were observed again in F. sylvatica and, less markedly, in B. pendula but without a general response at the stand level. Q. robur showed specific patterns with delayed budburst start in 2021 in the four-species mixtures and very short budburst duration for all stands in 2022. Phenological differences between monocultures and four-species mixtures were linked to microclimatic differences in light availability rather than in temperature as even comparatively colder microclimates showed an advanced phenology. Compared to weather conditions, tree species richness had a lower impact on budburst timing, but this impact can be of importance for key species like F. sylvatica and colder springs. These results indicate that forest biodiversity can affect budburst phenology, with wider implications, especially for forest- and land surface models.

Effect of Micro Climate on Flowering Characteristics in Grapes (Vitis vinifera L.)

The study aimed to find out the effect of micro climate on flowering characteristics in grapes varieties viz. Perlette, Flame Seedless, Superior Seedless and Punjab Purple. The experiment was conducted in Punjab-Ludhiana during 2018-19 fruiting seasons. Grape varieties were grown in both protective covering (Greenhouse) and open field. The data recorded showed that temperature and relative humidity was higher in protective covering with comparison to open field. The result of the experiment showed advancement in flowering characteristics viz. time of bud-burst, flowering initiation and fruit set in grape varieties grown under protective covering as compared to those grown in open field condition. Maximum advancement in bud burst was observed in Perlette variety (9 and 5 days earlier). Flower initiation was advanced by 4 days in Flame Seedless and Superior Seedless varieties and fruit set by 3-10 days in Punjab Purple variety grown in protective covering.

Feasting on the ordinary or starving for the exceptional in a warming climate: Phenological synchrony between spongy moth (Lymantria dispar) and budburst of six European tree species.

Global warming is affecting the phenological cycles of plants and animals, altering the complex synchronization that has co-evolved over thousands of years between interacting species and trophic levels. Here, we examined how warmer winter conditions affect the timing of budburst in six common European trees and the hatching of a generalist leaf-feeding insect, the spongy moth Lymantria dispar, whose fitness depends on the synchrony between egg hatch and leaf emergence of the host tree. We applied four different temperature treatments to L. dispar eggs and twig cuttings, that mimicked warmer winters and reduced chilling temperatures that are necessary for insect diapause and bud dormancy release, using heated open-top chambers (ambient or +3.5°C), and heated greenhouses (maintained at >6°C or >10°C). In addition, we conducted preference and performance tests to determine which tree species the larvae prefer and benefit from the most. Budburst success and twig survival were highest for all tree species at ambient temperature conditions, whereas it declined under elevated winter temperature for Tilia cordata and Acer pseudoplatanus, likely due to a lack of chilling. While L. dispar egg hatch coincided with budburst in most tree species within 10 days under ambient conditions, it coincided with budburst only in Quercus robur, Carpinus betulus, and, to a lesser extent, Ulmus glabra under warmer conditions. With further warming, we, therefore, expect an increasing mismatch in trees with high chilling requirements, such as Fagus sylvatica and A. pseudoplatanus, but still good synchronization with trees having low chilling requirements, such as Q. robur and C. betulus. Surprisingly, first instar larvae preferred and gained weight faster when fed with leaves of F. sylvatica, while Q. robur ranked second. Our results suggest that spongy moth outbreaks are likely to persist in oak and hornbeam forests in western and central Europe.

Warming nondormant tree roots advances aboveground spring phenology in temperate trees.

Climate warming advances the onset of tree growth in spring, but above- and belowground phenology are not always synchronized. These differences in growth responses may result from differences in root and bud dormancy dynamics, but root dormancy is largely unexplored. We measured dormancy in roots and leaf buds of Fagus sylvatica and Populus nigra by quantifying the warming sum required to initiate above- and belowground growth in October, January and February. We furthermore carried out seven experiments, manipulating only the soil and not air temperature before or during tree leaf-out to evaluate the potential of warmer roots to influence budburst timing using seedlings and adult trees of F. sylvatica and seedlings of Betula pendula. Root dormancy was virtually absent in comparison with the much deeper winter bud dormancy. Roots were able to start growing immediately as soils were warmed during the winter. Interestingly, higher soil temperature advanced budburst across all experiments, with soil temperature possibly accounting for c. 44% of the effect of air temperature in advancing aboveground spring phenology per growing degree hour. Therefore, differences in root and bud dormancy dynamics, together with their interaction, likely explain the nonsynchronized above- and belowground plant growth responses to climate warming.

The Survival Rate and Growth of Grafted-Seedling of Durian (Durio zibethinus Murr.) Using 3 Rootstocks Ages and 3 Levels of Scion Buds

This experiment was performed to determine the survival rate of grafted-seedling growth of durians using various ages of rootstocks and different numbers of scion buds. The study was arranged in a two-factorial randomized block design with three replications. The first factor was rootstock age (4, 6, and 8 weeks) and the second factor was the number of buds on the scion (1, 2, and 3 buds). The percentage of the successful grafting and several growth parameters, i.e., time of bud break, length and diameter of new shoots were evaluated for three months. Data were analysed using analysis of variance and continued with the post-hoc Tukey’s test. The results showed that age of rootstock did not affect percentage of successful grafting, time of budburst, shoot length and shoot diameter. Likewise, the number of shoots did not affect the percentage of successful grafting, shoot length, and shoot diameter, but had a significant effect on bud bursting time (P<0.05). Scion that had three buds resulted in the fastest time of bud break (28.45 days). The highest percentage of successful graft union was in the 4-week-old rootstock and scion with 2 and 3 buds (100%), the maximal successful also obtained in the 6-week-old rootstocks with 3 buds. The four-week-old rootstocks also gave the best result in the new shoot length and diameter. Nevertheless, there was no interaction between rootstock age and the number of buds on scion in survival rate of grafted seedlings of durian.

Phenological mismatch affects individual fitness and population growth in the winter moth.

Climate change can severely impact species that depend on temporary resources by inducing phenological mismatches between consumer and resource seasonal timing. In the winter moth, warmer winters caused eggs to hatch before their food source, young oak leaves, became available. This phenological mismatch changed the selection on the temperature sensitivity of egg development rate. However, we know little about the fine-scale fitness consequences of phenological mismatch at the individual level and how this mismatch affects population dynamics in the winter moth. To determine the fitness consequences of mistimed egg hatching relative to timing of oak budburst, we quantified survival and pupation weight in a feeding experiment. We found that mismatch greatly increased mortality rates of freshly hatched caterpillars, as well as affecting caterpillar growth and development time. We then investigated whether these individual fitness consequences have population-level impacts by estimating the effect of phenological mismatch on population dynamics, using our long-term data (1994-2021) on relative winter moth population densities at four locations in The Netherlands. We found a significant effect of mismatch on population density with higher population growth rates in years with a smaller phenological mismatch. Our results indicate that climate change-induced phenological mismatch can incur severe individual fitness consequences that can impact population density in the wild.

Severe Drought Still Affects Reproductive Traits Two Years Later in a Common Garden Experiment of Frangula alnus

Longer periods of intensified droughts in Western Europe are predicted due to ongoing climate change. Studying the responses of woody species during intense drought events can help toward understanding the consequences for forest ecosystems. We studied the effects of an intense summer water limitation on several reproductive traits, two years after the treatment, in Frangula alnus Mill. shrubs grown in a common garden. Drought-treated shrubs produced more berries one and two years after the drought event, while the height increment of the second post-treatment year was still significantly retarded. The mean weight of stones from berries picked two years after the drought treatment and their germination percentage, which was corrected for mean stone weight, were higher for the treated shrubs. These results indicate a resource re-allocation toward reproduction, rather than toward growth, which was still in action two years after the water limitation. The higher germination success, which is a transgenerational effect, and which has already been suggested to be an adaptation to survival in more stressful growth conditions, is also still detectable two years after the severe drought. F. alnus produces mature berries continuously during the whole summer. From the middle of July till the end of August, the counts of mature berries, the mean stone weight and the germination percentage, corrected for mean stone weight, decreased, whereas the timing of seedling emergence, also corrected for stone weight, advanced slightly. The timing of seedling emergence correlated weak but significantly with the timing of bud burst in the mother shrubs, with a variance analysis indicating a stronger genetic control for bud burst in comparison to seedling emergence. Several results corroborated previous findings. Population differentiation in the common garden was observed for mature berry counts and for several phenological traits. In conclusion, longer-term effects of drought on reproductive traits in woody species may add more complexity to the consequences of climate change on tree species distributions and survival of forest ecosystems.

Untangling winter chilling and spring forcing effects on spring phenology of subtropical tree seedlings

Global warming is having an unprecedented impact on plant phenology and vitality worldwide, potentially leading to significant changes in the food web, carbon, water cycling and ecosystem functions. Environmental drivers explaining spring phenology, mainly including temperature (chilling in late autumn and winter and forcing in late winter and spring) and photoperiod, have been extensively investigated in temperate trees, but these factors have been rarely studied in subtropical forests and their potential effects are therefore relatively unknown. This knowledge gap is especially important to fill because these ecosystems harbor the largest portion of the world's biodiversity. In this study, we sought to test the effects of chilling (low vs. high) and forcing temperatures (20 vs. 25 °C) on spring phenology for seedlings of five subtropical woody species using six climate chambers. We compared forcing requirements for budburst and leaf-out in the different treatments by calculating the number of degree days achieved from the start of the experiment to the time of budburst and leaf-out, and we examined seedlings’ survival under the different treatments. Although the survival of subtropical seedlings was found to be little affected by variation in chilling or forcing, longer chilling duration and warmer forcing temperature led to a lower forcing requirement for budburst, which advanced both budburst and leaf-out. This suggests that the seedlings experienced a non-linear accumulation of forcing with generally a higher efficiency at 25 °C than at 20 °C. Interestingly, shorter exposure to chilling conditions disrupted the sequence of budburst / leaf-out timings among the study species. This study confirms that the sensitivity of spring leaf phenology to forcing and chilling is not only found in temperate perennial plants but also in subtropical trees that undergo a dormancy period. It offers new perspectives for a comprehensive analysis of subtropical plant phenology in response to global climate change.

Genetic Differentiation of Budburst Timing in Fagus crenata Populations along a Spatial Gradient in Late Frost Timing in the Hakkoda Mountains, Northern Japan

We studied the genetic differentiation in budburst timing among Fagus crenata populations along spatial gradients in late frost timing in the Hakkoda Mountains, northern Japan, by focusing on last fatal frost day and topography. For budburst timing, we analyzed interpopulation variations in habitats, genetic variations in a nursery, and the relationships between these variations and environmental conditions in the habitats. Analyses of interpopulation variation showed that the day and the temperature sum of budburst positively correlated with the last fatal frost day in the habitats. Analyses of genetic variation showed significant genetic variations among provenances and families for both traits. For all provenances, the heritability for these traits were 0.7–0.8. The genetic variations were significantly associated with variations in the last fatal frost day among the provenances, suggesting that natural selection due to late fatal frost causes genetic differentiation in the traits along the spatial gradient in late frost timing. These results demonstrate that late frost is a key factor driving genetic differentiation of leaf-out phenology within a regional tree population.

Plant height determines phenological variation in Quercus suber L.

Phenological traits of vegetative apical buds were monitored in a Quercus suber L. (cork oak) montado near Lisbon during 2015. Natural regeneration plants, growing at a fenced plot, and mature trees (MT) from the surrounding montado were selected and divided in six groups (n=8) according to height (H): Sd1 (small seedlings, H<0.1 m); Sd2 (seedlings, 0.1<H<0.5 m); Sp (saplings, 1<H<2 m); Jv1 (small juveniles, 3<H<6 m); Jv2 (juveniles, H>6 m); MT (mature trees). Observations included budburst date, apical shoot elongation and leaf production. Vegetative phenology patterns of Q. suber changed according to height/age group. Average budburst dates occurred between early-April (day 99, Sd1) and mid-May (after day 120, mature and juvenile trees), at day lengths between 12.8 (Sd1) and 13.7 hours (Jv2). Height was positively related with average budburst dates, degree day sums and daylength at budburst. Shoot elongation followed different patterns according to size/age group. In seedlings, cumulative growth was smaller and restricted to the weeks immediately after budburst, whilst taller/older trees phenological patterns were more variable, with vegetative growth often maintained until mid-summer. The differences in budburst timing and vegetative growth patterns may be reflecting the different strategies to cope with resource limitation and maximize the length of the growing season among groups.

Effect of bud position on the seedling growth of five citrus species

This research aimed to evaluate the bud position in the vegetative phase of seedling growth derived from five citrus species. The research was carried out from April to July 2018 at the Tlekung Agricultural Research Installation. Factorial Randomized Block Design with two factors is the method in this study. The bud position taken as the propagation material was the first factor consisting of the top (36-50 cm from the base part of tree), middle (16-35 cm from the base part of tree), and bottom (0-15 cm from the base part of tree). The second factor was the citrus species consisting of mandarin cv. Madura, tangerine cv. Pontianak, pummelo cv. Giri Matang, lime cv. Sweet, and orange cv. Punten. There was no significant interaction between the bud position and species on all variables. However, regardless of bud position, citrus species showed significantly different in vegetative growth. The best average of 100% for the success of bud grafting, 36.89 days after bud grafting for the budburst time, 4.5 mm for the shoot diameter, 29.81 cm for the shoot length, and 19.55 leaves for the number of leaves was shown by orange cv. Punten. The results of this research sugges that the use of buds taken from different positions is recommended for citrus grafted bud.

Estimating the potential threat of increasing temperature to the forests of Turkey: a focus on two invasive alien insect pests

Rising temperature can affect forests negatively through its impact on insect pests. The present study focused on two invasive alien insect species (Dryocosmus kuriphilus and Leptoglossus occidentalis) to understand how rising temperature might affect their damage in Turkish forests. For D. kuriphilus, the timing of chestnut budburst, gall induction and emergence of its introduced parasitoid, Torymus sinensis, were monitored between 2015 and 2019, and each phenological event was compared annually with fluctuations in temperature to observe the parasitoid-host synchrony. For L. occidentalis, cumulative degree days (CDD) were calculated, and the possible number of generations produced in 2020 in different regions of Turkey were predicted. The CDD calculations were repeated under increasing temperature and different photoperiod-diapause induction scenarios. Evaluation of the monitoring data on the D. kuriphilus system showed that gall induction occurred at the same time as budburst, whereas T. sinensis emergence was independent from the budburst, and that the parasitoid-host synchrony was disrupted after the abnormally warm winter in 2018. The CDD calculations estimated that L. occidentalis produced one to five generations from north to south in 2020. They also suggested a significant increase in the number of generations in the southern Turkey under temperature increase scenarios. Including photoperiod as a time-limiting factor reduced the highest possible number of generations from five to two. In conclusion, rising temperature has a potential to threaten the biocontrol against D. kuriphilus, and it can increase voltinism in L. occidentalis.

Does ontogeny matter for the spring temperature requirement for bud burst of two coniferous species in cool temperate forests?

Spring leaf phenology is an important event for trees to determine carbon fixation during the growing season. However, less is understood about the intraspecific variation in spring leaf phenology and its relationship with the spring temperature requirements of conifers, which is problematic for accurately predicting the influence of spring climate warming on conifers. I monitored bud burst timing and the degree days required for bud burst for seedlings and large individuals of Abies sachalinensis (fir) and Larix kaempferi (larch) over two seasons in northern Japan. Contrary to my expectation, the degree days required for the bud burst of small individuals were similar to or larger than those of the large individuals for fir and larch. Consequently, the bud burst timing of small individuals was similar to or later than that of large individuals for fir and larch. Even when conifer species are in their early stage, the spring temperature requirement for bud burst is not necessarily less than that for large individuals, which is not the case for many broad-leaved species. These results indicate that for these two coniferous species, ontogenetic differences in temperature requirements are not necessary to be considered for the response of communities to spring climate change.

Higher spring phenological sensitivity to forcing temperatures of Asian compared to European tree species under low and high pre-chilling conditions

Winter chilling, spring forcing temperature and photoperiod are the most important drivers explaining the spatial and temporal variability of spring phenology in temperate trees. However, how these factors interact with each other on dormancy release and spring budburst date remains unclear and varies greatly depending on species. Our knowledge is also limited as to whether heat accumulation of forcing temperatures that trigger bud break in spring is a linear or non-linear process. Here, we aimed at experimentally quantifying the effect of chilling, forcing, photoperiod and their interactions on the budburst dates of nine different temperate tree species from East Asia (near Beijing, China) and Central Europe (near Zurich, Switzerland), including six phylogenetically related species (same genus). We conducted a full factorial experiment in climate chambers using two chilling (low and high, i.e., 0 vs. 56 days at 2°C after sampling at the end of December), four forcing (5, 10, 15, and 20°C), and two photoperiod (8 vs. 16 h) treatments simultaneously in Beijing and Zurich. We found that species growing near Beijing responded more readily to forcing conditions than species of the same genus growing near Zurich regardless of chilling treatment. Budburst timing of most species but European beech was marginally, if at all, affected by photoperiod. Furthermore, our results suggest that linear heat accumulation, as commonly used with the growing degree hours (GDH) model, could result in accurate prediction of budburst date depending on the temperature threshold used as a basis for heat accumulation. Our results also demonstrate the important role of chilling in shaping the sensitivity and rate of forcing accumulation to trigger budburst and suggest that species-specific sigmoid relationship for accumulating heat that accounts for prior chilling exposure may yield better predictions of budburst dates. Our results suggest that deciduous trees may have adapted their chilling and forcing requirements in regards to the predictability of winter-spring transition and late spring frosts. A less predictable winter-spring transition, as observed in Central Europe, could have driven species evolution towards higher chilling and forcing requirements compared to species growing in a more predictable climate of Northeastern Asia. Our cross-continental experiment therefore suggests that the spring phenology of East Asian species is tighter coupled to spring forcing temperature than Central European forests.

Spatial and Temporal Trends in the Timing of Budburst for Australian Wine Regions

Background and Aims. This research investigates spatial and temporal trends in budburst timing across Australian wine regions from 1910–2019. The potential drivers of these observed trends were then identified, including anthropogenic climate change and large-scale climate drivers (El Nino–Southern Oscillation (ENSO), Indian Ocean Dipole (IOD), and Southern Annular Mode (SAM)). Methods and Results. The timing of budburst was approximated using accumulation measurements applied to Australia wide gridded temperature data. We show that the modelled budburst date has been gradually shifting to earlier in the year for most (95%) Australian wine regions, at an average rate of one day every 24 years. This linear trend in budburst timing is likely to be associated with steadily increasing air temperatures due to anthropogenic climate change. Significant interannual variability was also observed and was correlated with IOD and SAM; however, no significant relationship was found with ENSO. Positive IOD phases result in budburst occurring on average four days earlier than the long-term average; however, this can be as high as eight days. Conclusions. The results of this study highlight that budburst timing for wine grapes is not a stationary phenomenon and is influenced by both natural and anthropogenic conditions. Significance of the Study. Understanding variability and trends in modelled budburst timing will assist tactical and strategic management practices and improve phenological modelling and adaptation planning for climate change.

Seasonal variations of cold hardiness and dormancy depth in five temperate woody plants in China

Woody plant species in temperate regions must withstand a cold winter and freezing events through cold acclimation and dormancy in autumn and winter. However, how seasonal changes in dormancy depth and cold hardiness affect the frost risk of temperate species is unclear because few studies have assessed dormancy depth and cold hardiness simultaneously. In this study, an experiment was conducted to estimate the dormancy depth and cold hardiness of five common woody temperate plant species during the winter of 2018/2019 in Beijing, China. Twigs of each species were collected at different dates during winter and the timing of budburst was monitored under the same forcing conditions. The dormancy depth was quantified as growing degree day (GDD) requirements of spring events. Simultaneously, the cold hardiness of buds at each sampling date was determined based on the electrical conductivity of the holding solution. Two indices (chilling accumulation and cold hardiness index) were used to simulate the past dynamics of dormancy depth, spring phenology, and cold hardiness from 1952 to 2021. The maximum dormancy depth of the study species was observed between early October and early December, and thereafter decreased exponentially. The cold hardiness peaked in mid-winter (end of December) through cold acclimation and thereafter decreased in spring (deacclimation). During the past 70 years, the budburst date (first flowering date or first leaf date) of five species was estimated to have advanced significantly, and dormancy depth in early spring was predicted to have increased owing to the warming-associated decrease in chilling accumulation. However, cold hardiness has decreased because of weakened acclimation and accelerated deacclimation under a warming climate. The frost risk before and after budburst remained unchanged because of the reduction in occurrence and severity of low-temperature events and earlier late spring frosts. The present methods could be generalized to estimate and predict the seasonal changes in dormancy depth and cold hardiness of temperate species in the context of climate change.

Statistical Approach to Assess Chill and Heat Requirements of Olive Tree Based on Flowering Date and Temperatures Data: Towards Selection of Adapted Cultivars to Global Warming

Delineating chilling and forcing periods is one of the challenging topics in understanding how temperatures drive the timing of budburst and bloom in fruit tree species. Here, we investigated this question on olive trees, using flowering data collected over six years on 331 cultivars in the worldwide collection of Marrakech, Morocco. Using a Partial Least Squares approach on a long-term phenology (29 years) of ‘Picholine Marocaine’ cultivar, we showed that the relevance of delineating the chilling and forcing periods depends more on the variability of inter-annual temperatures than on the long-term datasets. In fact, chilling and forcing periods are similar between those delineated by using datasets of 29 years and those of only 6 years (2014–2019). We demonstrated that the variability of inter-annual temperatures is the main factor explaining this pattern. We then used the datasets of six years to assess the chill and heat requirements of 285 cultivars. We classified Mediterranean olive cultivars into four groups according to their chill requirements. Our results, using the Kriging interpolation method, indicated that flowering dates of most of these cultivars (92%) were governed by both chilling and forcing temperatures. Our investigations provided first insights to select adapted cultivars to global warming.

Growth-Development, Yield and Quality Characteristics of Aronia Varieties Grown in Pots

This study was carried out to determine the growth, development, yield and some quality characteristics of Nero and Viking Aronia varieties grown in open field and pot in Samsun ecological conditions. Three-year-old Aronia plants were planted in 80-liter pots containing a 1:1:1 (v/v) mixture (barnyard manure+soil+sand) and 5 plants were included in each replication. Number of shoots, flower buds and clusters, berry weight (g), yield (g/plant), firmness (N), number of fruits per cluster, must yield (ml/100g), TSSS (%) and pH values were measured in Aronia cultivars. In addition, monthly shoot growth rate (cm/month) was determined and phenological observations recorded. According to Viking and Nero Aronia varieties, the number of shoots (7.8 and 7.6 pieces), the number of flower buds (22.63 and 22.85 pieces), the number of clusters (45.06 and 44.80 pieces), the weight of berry (0.82 and 0.79 g), the fruit number in the bunch (21.45 and 21.53 pieces), berry firmness (4.90 and 5.35 N), amount of must (49.67 and 54.00 ml/100 g) and TSS (17.07 and 16.47) and pH values (3.65 and 3.52) were found to be close to each other. Bud burst (10 March), flowering (26 April), berry set (12 May) and harvest time (24 August) were also similar in cultivars. It was also revealed that while the shoot length was 97.47 cm and 95.47 cm on March 11, respectively, in Viking and Nero varieties, it reached 124.73 and 120.73 cm in August, five months later.