Plasticity plays a dominant role in regulating the phenological variations of sugar maple populations in Canada

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

The early bud gets the cold: spring phenology drives exposure to late frost

International audienc

The early bud gets the cold: Diverging spring phenology drives exposure to late frost in a Picea mariana [(Mill.) BSP ] common garden

Under climate change, the increasing occurrence of late frost combined with advancing spring phenology can increase the risk of frost damage in trees. In this study, we tested the link between intra-specific variability in bud phenology and frost exposure and damages. We analysed the effects of the 2021 late frost event in a black spruce (Picea mariana (Mill.) BSP) common garden in Québec, Canada. We hypothesised that the timing of budbreak drives the exposure of vulnerable tissues and explains differences in frost damage. Budbreak was monitored from 2015 to 2021 in 371 trees from five provenances originating between 48°and 53°N and planted in a common garden at 48°N. Frost damages were assessed on the same trees through the pro-portion of damaged buds per tree and related to the phenological phases by ordinal regressions. After an unusually warm spring, minimum temperatures fell to -1.9°Con May 28 and 29, 2021. At this moment, trees from the northern provenances were more advanced in their phenology and showed more frost damage. Provenances with earlier budbreak had a higher probability of damage occurrence according to ordinal regression. Our study highlights the importance of intra-specific variability of pheno-logical traits on the risk of frost exposure. We provide evidence that the timings of bud phenology affect sensitivity to frost, leading to damages at temperatures of -1.9°C. Under the same conditions, the earlier growth reactivation observed in the northern provenances increases the risks of late frost damage on the developing buds

The Role of Organ and Leaf Habit on the Secondary Xylem Anatomy Variation across 15 Species from Brazilian Cerrado

Xylem is a complex tissue connecting the organs of plants and it performs multiple functions, including water transport, mechanical support, and storage. Because of the interaction between structure and function, xylem anatomy can provide useful information about its role in plant strategies. However, knowledge of how xylem anatomical traits change across organs and species functional groups is still limited. Here, we tested the role of different plant organs (stem and roots) and leaf habits (deciduous, semi-deciduous, and evergreen) on xylem anatomy variation across 15 woody species from the Brazilian Cerrado. Vessels, fibers, and parenchyma traits were measured on 45 individuals sampled in 2014 in Botucatu, São Paulo, Brazil. Our results revealed a higher parenchyma fraction and less fiber fraction in roots than in stems across species. Differences in wood anatomical traits between organs were mainly species-specific in parenchyma traits rather than vessel and fiber traits. Across leaf habits, only the root ray fraction was higher in evergreen species compared to deciduous species. These findings highlight a potential role of organs and leaf habits in xylem storage across Cerrado woody species

Hydraulic architecture of crown in three Brazilian species

The hydraulic limitation hypothesis postulates an increase in resistance to water conductivity as trees become taller. Accordingly, we expect that the hydraulic architecture of trees shares a close relationship with the crown architecture and that anatomical traits can directly or indirectly influence hydraulic conductivity. The aim of this work was to investigate the variations in vessels, hydraulic properties and wood density of three native Brazilian tree species. We selected 40-year-old Balfourodendron riedelianum, Cariniana legalis and Handroanthus vellosoi trees and measured maximum vessel length, specific hydraulic conductivity, the percentage loss of conductivity, leaf hydraulic conductivity, and density of branches at three different positions of the crown. Variability in anatomical and hydraulic properties was mostly explained by differences between species, while small differences were related to the position of the branch along the crown-position gradient. Within the measured variables, only the maximum vessel length differed between one crown position and the other. We posit that poor differences between anatomical and hydraulic positions in the crown-position gradient could be related to sample positions within the crown, which were relatively close to each other, with branches having similar ages and diameters. Our findings demonstrate that despite growing in the same environment and having the same age, our species deploy contrasting carbon allocation and hydraulic species-specific strategies. These strategies mirror different growth performances resulting from a different trade-off between hydraulic capacity and safety

Phenology of black spruce populations, implications and perspectives in the context of climate change

International audienceForest managers use artificial regeneration to modify 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 in the context of climate change. These studies aimed to test the effect of provenance on height growth and timing of both bud burst and bud set in five black spruce [Picea mariana (Mill.) B.S.P.] provenances growing in a common garden and originating from a latitudinal range in the boreal forest of Québec, Canada. Bud phenology and shoot extension were monitored weekly during the growing seasons 2015-2021. We demonstrated that both bud burst and bud set occurred earlier in individuals from colder sites. Moreover, variance in bud phenology among provenances was higher than that within provenances and the heritability of bud set was higher than that of bud burst. Despite the lag in timing, provenances from colder sites highlighted a longer duration of the shoot extension than provenances originated from warmer sites. However, in northern provenances the growth rate was lower, resulting in a smaller increment of height growth than in Southern provenances. We also provide evidence that the timings of bud phenology affect sensitivity to frost. Phenological timings and height growth are key adaptive traits strongly associated with local environmental conditions. Endogenous and environmental components have different effects on height growth and phenological timing. This clinal variation in growth and phenological traits confirms the ecotypic differentiation of black spruce populations and reflects a long-lasting adaptation to the local temperatures at the origin sites. Our findings represent a useful tool providing further information about the growth dynamics under future climate change scenarios, and for artificially regenerated forests and assisted migration for one of the most distributed and economically exploited species of the Canadian boreal forest