Foliar Senescence Research Articles

Early leaf senescence under drought conditions in the Northern hemisphere

Changes in the dates of autumn foliar senescence (DFS) have significant impacts on regional carbon uptake, while current approaches for the estimation of DFS are still lacking. The most important issue is that there are complicated factors that affect the DFS, among which drought effects probably have contributed the most. Using long-term DFS observations derived from the third-generation normalized difference vegetation index dataset (NDVI3g), we found a wider spread of earlier DFS trends over the Northern Hemisphere from 1999 to 2015, three times larger than that from 1982 to 1998. The five multivariate analysis of variance approaches consistently suggest the key role of drought in regulating these changes. We therefore derived a new DFS algorithm with the standardized precipitation evapotranspiration index (SPEI) to characterize these drought effects, and validations from both NDVI3g and MODIS data demonstrated that our new algorithm provided significantly improved estimates of DFS for all plant functional types, with higher accuracy for water-limited ecosystems. We further applied this new algorithm to predict DFS under various shared socioeconomic pathways (SSPs) by the end of this century, and we found overall earlier DFS than the current expectations. Our results therefore highlight the importance of drought in the modeling of plant phenology using remote sensing observations and thus are highly important for understanding the relationships between land carbon sinks and climate change, especially given that droughts are projected to be more severe and frequent in the future.

Drivers and dynamics of foliar senescence in temperate deciduous forest trees at their southern limit of distribution in Europe

Research on autumn phenology is very important for understanding and simulating the future growth of temperate deciduous forests. This is especially needed at the southern edge of the temperate zone, where climate change impacts are particularly intense. We studied foliar senescence timing for mature stands of Fagus sylvatica L., Populus tremula L., Betula pendula Roth, Quercus petraea (Matt.) Liebl. and Quercus robur L. at the southern edge of European temperate forests. First, we analysed long-term series (1997–2019) of senescence timing in southern France. Then, we compared a more detailed four-year dataset (2017–2020) of senescence dynamics and its correlations to meteorological conditions for stands in northern Spain and Belgium, with the latter area representing the core distribution of the species. In contrast to other temperate regions, no significant delaying trends in the timing of autumn phenology were detected in the long-term in southern temperate forests, which were characterized by high inter-site variability. In the short-term (4 years), species-specific correlations with meteorological conditions were found, with, for example, the senescence of F. sylvatica being affected by temperature while the senescence of Q. petraea was affected by both temperature and precipitation. Autumn dynamics differed between the core and southern areas of distribution of the species in the study period. In particular, while late season conditions affected senescence timing in the southern populations, the senescence dynamics of the core populations was mostly influenced by the legacy of spring – early summer conditions and, overall, more affected by precipitation than southern populations. Our data fill important knowledge gaps on the functioning of temperate deciduous forests at the southern limit of distribution in Europe.

Functional roles of nematodes associated with the walnut twig beetle and eastern black walnut in the inland northwest

AbstractBeetles (Scolytinae) form intimate associations with a taxonomically and functionally diverse suite of nematodes that are phytopathogens, fungal feeders, and entomoparasites. Despite their ubiquity, the ecological significance of nematodes in the lifecycles of economically important bark and ambrosia beetle species (Curculionidae: Scolytinae) and associated plant diseases remains largely unexplored. Thousand cankers disease (TCD) is caused by the walnut twig beetle (WTB, Pityophthorus juglandis Blackman) and the fungus Geosmithia morbida (Kolařík, Freeland, Utley & Tisserat; Ascoymycota: Hypocreales) and causes foliar senescence, progressive crown dieback, and mortality in black walnut (Juglans nigra L.) throughout western North America. In this study, nematodes recovered from P. juglandis and J. nigra in Idaho (ID) and Washington (WA) were identified morphologically and by constructing multilocus phylogenies to infer taxonomic relationships to taxa for which molecular data were available. We conducted assays to determine the extent to which nematodes feed and reproduce on G. morbida and other fungi commonly found in galleries of P. juglandis. Inoculation experiments were conducted to determine the effect of nematodes on the area of subdermal necrotic lesions (cankers) caused by G. morbida in branches of mature J. nigra and stems of seedlings. The phoretic nematode Bursaphlenhus juglandis (Ryss, Parker, Alvarez‐Ortega, Nadeler & Subbotin) was frequently found under elytra of WTB in all locations, and a free‐living nematode (Panagrolaimus sp.) was also widespread and found in the bark of mature trees. Both B. juglandis and Panagrolaimus sp. reduced the size of cankers caused by G. morbida in seedlings and branches of mature trees, respectively. However, these species may play opposite roles as disease synergists and antagonists based on the observation that exudates and/or microbiota associated with Panagrolaimus sp., but not B. juglandis destroyed G. morbida colonies in culture. Furthermore, B. juglandis contributed to foliar symptoms in seedlings inoculated with G. morbida. An entomoparasitic nematode (Aphelenchoididae), most closely resembling an Ektaphelenchus sp., was also found in the haemocoel of WTB. Infection rates were positively related to beetle population sizes as inferred from emergence rates. Ditylenchus sp. was also found in incubated walnut wood in WA and Rhabtidolaimus sp. was phoretic on P. juglandis and found in incubated walnut wood in WA and ID. The community of nematodes in J. nigra in WA and ID differed substantially from what has been observed associated with J. nigra in its native range.

Wood growth phenology and its relationship with leaf phenology in deciduous forest trees of the temperate zone of Western Europe

Wood growth phenology of temperate deciduous trees is less studied than leaf phenology, hindering the understanding of their interaction. In order to describe the variability of wood growth and leaf phenology across locations, species and years, we performed phenological observations of both xylem formation and leaf development in three typical temperate forest areas in Western Europe (Northern Spain, Belgium and Southern Norway) for four common deciduous tree species (Fagus sylvatica L., Betula pendula Roth., Populus tremula L. and Quercus robur L.) in 2018, 2019 and 2020, with only beech and birch being studied in the final year.The earliest cambial reactivation in spring occurred at the Belgian stands while the end of cambial activity and wood growth cessation generally occurred first in Norway. Results did not show much consistency across species, sites or years and lacked general patterns, except for the end of cambial activity, which occurred generally first in birch. For all species, the site variation in phenophases (up to three months) was substantially larger than the inter-annual variability (up to six weeks). The timeline of bud-burst and cambium reactivation, as well as of foliar senescence and cessation of wood growth, were variable across species even with the same type of wood porosity. Our results suggest that wood growth and leaf phenology are less well connected than previously thought. Linear models showed that temperature is the dominant driver of wood growth phenology, but with climate zone also having an effect, especially at the start of the growing season. Drought conditions, on the other hand, have a larger effect on the timing of wood growth cessation. Our comprehensive analysis represents the first large regional assessment of wood growth phenology in common European deciduous tree species, providing not only new fundamental insights but also a unique dataset for future modelling applications.

Increased drought effects on the phenology of autumn leaf senescence

Global warming delays the autumn date of foliar senescence (DFS) in recent decades, with positive implications for growing season length and therefore global carbon storage. However, warming-associated drought, leading to water limitation, may conversely stimulate earlier DFS. Using ground observations since 1940s and 34 years of satellite greenness data (1982‒2015) over the Northern Hemisphere (>30° N), we show the increased impact of drought on DFS. Earlier DFS is linked to decreased precipitation under warming and weaker drought resistance associated with various plant functional traits. For example, isohydric plants with strict regulation of water status may drop leaves fast during droughts. We derive an improved set of phenology models based on this influence and project earlier DFS by the end of the century, particularly at high latitudes (>50° N). Our results limit uncertainties in the later end of plant growth with warming, aiding estimation of carbon uptake of terrestrial ecosystems. The authors use long-term ground and satellite data to reveal the impact of drought on autumn date of foliar senescence (DFS). They link increased drought impacts to precipitation changes and plant functional traits and project earlier DFS by the end of the century, particularly at high latitudes.

The genetic architectures of vine and skin maturity in tetraploid potato.

The genetic architectures of potato vine and skin maturity, as well as the correlation between the traits, were investigated using multiple techniques from quantitative genetics and genomics. Potato vine and skin maturity, which refer to foliar senescence and adherence of the tuber periderm, respectively, are both important to production and therefore breeding. Our objective was to investigate the genetic architectures of these traits in a genome-wide association panel of 586 genotypes, and through joint linkage mapping in a half-diallel subset (N = 397). Skin maturity was measured by image analysis after mechanized harvest 120days after planting. To correct for the influence of vine maturity on skin maturity under these conditions, the former was used as a covariate in the analysis. The genomic heritability based on a 10K SNP array was 0.33 for skin maturity vs. 0.46 for vine maturity. Only minor QTLs were detected for skin maturity, the largest being on chromosome 9 and explaining 8% of the variation. As in many previous studies, S. tuberosum Cycling DOF Factor 1 (CDF1) had a large influence on vine maturity, explaining 33% of the variation in the panel as a bi-allelic SNP and 44% in the half-diallel as a multi-allelic QTL. From the estimated effects of the parental haplotypes in the half-diallel and prior knowledge of the allelic series for CDF1, the CDF1 allele for each haplotype was predicted and ultimately confirmed through whole-genome sequencing. The ability to connect statistical alleles from QTL models with biological alleles based on DNA sequencing represents a new milestone in genomics-assisted breeding for tetraploid species.

Increased drought effects on the phenology of autumn foliar senescence

Increased drought effects on the phenology of autumn foliar senescence

Increased drought effects on the phenology of autumn foliar senescence

Increased drought effects on the phenology of autumn foliar senescence

Increased drought effects on the phenology of autumn foliar senescence

Increased drought effects on the phenology of autumn foliar senescence

Increased drought effects on the phenology of autumn foliar senescence

Increased drought effects on the phenology of autumn foliar senescence

Bacterial diacetyl suppresses abiotic stress-induced senescence in Arabidopsis.

Premature plant senescence induced by abiotic stresses is a major cause of agricultural losses worldwide. Tools for suppressing stress-induced plant senescence are limited. Here, we report that diacetyl, a natural compound emitted by the plant-beneficial bacterium Bacillus amyloliquefaciens, suppresses abscisic acid -mediated foliar senescence in Arabidopsis thaliana under various abiotic stress conditions. Our results establish diacetyl as an effective protector against stress-induced plant senescence and reveal a molecular mechanism for bacteria-enhanced plant stress resistance.

Effect of Potassium Supply and Water Stress on Potato Drought Tolerance and Water Productivity

ABSTRACT Potato (Solanum tuberosum L.) is one of major food crops grown worldwide and in Lebanon. The response of field grown potato to 0, 200, 300 kg of potassium (K) ha−1 was examined under deficit irrigation (imposed water stress). Trials were conducted under Near East-North Africa (NENA) pedo-climatic conditions found in the semiarid central Bekaa of Lebanon. Irrigation water was provided by a drip irrigation system. A mild deficit irrigation, corresponding to 68% of calculated ET0 in 2015 and 85% of it in 2016, was started at the flowering stage and lasted till foliar senescence. Canopy temperature, at maximum development, showed a slight decrease with the increase of potassium levels. During physiological maturity, the midday leaf temperature was significantly lower at the higher K dose, indicating improved leaf water potential. The highest K dose showed a non-significant, higher, chlorophyll content in the leaves, notably in the first year. A significant increase in the weight of one commercial tuber was found in K300 (247.6 g). The commercial yield ranged between 33.05 and 34.78 Mg ha−1 (K300) and 23.31 and 25.53 Mg ha−1 (K0) in 2015 and 2016 respectively. During the 2016 trial, 8 plots out of 16 had an agronomic water yield between 9 and 13 kg.m−3 against 12 out of 16 plots in 2015, competing with the reported values for potato in the region. Optimizing nutrient and water input in the NENA region can contribute to food security with minimal environmental impact.

Severe drought can delay autumn senescence of silver birch in the current year but advance it in the next year

Historically, the autumn dynamics of deciduous forest trees have not been investigated in detail. However, autumn phenological events, like onset of loss of canopy greenness (OLCG), onset of foliar senescence (OFS) and cessation of wood growth (CWG), have an important impact on tree radial growth and the entire ecosystem's seasonal dynamics. Here, we monitored the leaf and wood phenological events of silver birch (Betula pendula) at four different sites in Ås, southeastern Norway: (a) a natural mature stand, (b) a plantation on former agricultural ground, (c) young natural trees, and (d) young trees in pots under different fertilization levels. The study took place over four consecutive years (from 2017 to 2020), with a particular focus on 2018, a year in which there was a severe summer drought, and the next year, 2019, which featured more normal conditions. First, we provided a description of birch phenology within its mid-north distributional. Second, we showed that drought advanced CWG by about 5 to 6 weeks and it delayed OLCG and OFS up to 30 days. Third, we observed an unexpected advance in OLCG in 2019 compared to 2018 (30 days) and 2020 (14 days). OFS presented similar dynamics as OLCG, whereas CWG was advanced only in 2018. These findings might indicate lag-effects of severe drought on the next year autumn leaf phenology but not on wood growth. On the other hand, the comparison between the natural stand and the plantation showed that, under drought conditions, wood growth is more sensitive to site fertility than autumn leaf phenology. In summary, our study elucidated the autumn dynamics of an important deciduous forest species in the northern temperate zone and showed unexpected impacts of a severely dry and warm summer on the current and next year leaf phenology.

Increased drought effects on the phenology of autumn foliar senescence

Increased drought effects on the phenology of autumn foliar senescence

Drivers and Dynamics of Foliar Senescence in Temperate Deciduous Trees at Their Southern Limit of Distribution in Europe

Drivers and Dynamics of Foliar Senescence in Temperate Deciduous Trees at Their Southern Limit of Distribution in Europe

The functional roles of psyllid abundance and assemblage on bird-associated forest defoliation.

Fluctuations in the abundance of insect herbivores and the severity of damage they cause to their hosts are key factors affecting tree health and trophic interactions. Bell miner associated dieback (BMAD) is a trophic cascade involving eucalypt trees, psyllids and bell miners. Bell miners are a territorial species of bird that reduce insectivorous bird diversity, thereby increasing psyllid abundances. The role of psyllids in BMAD is debated, primarily because psyllid host specificity, genus, defoliation potential and/or lerp composition have been conflated or unexplored. This study documented psyllid communities and canopy structure of four eucalypt hosts (Eucalyptus bridgesiana, E. caliginosa, E. propinqua and E. siderophloia) in BMAD and non-BMAD-affected forests in northern New South Wales. Psyllid abundances were significantly higher in BMAD-affected forests. However, psyllid assemblages did not differ between forest types which contrasts with an influential hypothesis concerning bell miner farming of psyllids that produce sugary lerps (Glycaspis species). Importantly, psyllid communities differed among species of eucalypt host. Hosts supporting higher abundances of Cardiaspina tended to have a stronger negative relationship between canopy health and psyllid abundances than other host trees. Cardiaspina were also found on older leaves and associated with more leaf damage than other psyllids. Unlike most other psyllid genera, Cardiaspina initiate premature foliar senescence leading to defoliation which ultimately changes the age structure of leaves of the canopies of affected trees. Our study supports the functional linkage between psyllid assemblages, their relative abundances and defoliation potential to bottom-up mechanisms behind a bird-associated trophic cascade.

Widespread decline in winds delayed autumn foliar senescence over high latitudes.

The high northern latitudes (>50°) experienced a pronounced surface stilling (i.e., decline in winds) with climate change. As a drying factor, the influences of changes in winds on the date of autumn foliar senescence (DFS) remain largely unknown and are potentially important as a mechanism explaining the interannual variability of autumn phenology. Using 183,448 phenological observations at 2,405 sites, long-term site-scale water vapor and carbon dioxide flux measurements, and 34 y of satellite greenness data, here we show that the decline in winds is significantly associated with extended DFS and could have a relative importance comparable with temperature and precipitation effects in contributing to the DFS trends. We further demonstrate that decline in winds reduces evapotranspiration, which results in less soil water losses and consequently more favorable growth conditions in late autumn. In addition, declining winds also lead to less leaf abscission damage which could delay leaf senescence and to a decreased cooling effect and therefore less frost damage. Our results are potentially useful for carbon flux modeling because an improved algorithm based on these findings projected overall widespread earlier DFS than currently expected by the end of this century, contributing potentially to a positive feedback to climate.

Divergent responses of phenology and growth to summer and autumnal warming.

Plant phenology is highly sensitive to climate change, and shifts in autumnal foliar senescence are critical for plant productivity and nutrient cycling. Global warming has delayed the timing of foliar senescence, but the response of autumnal foliar senescence to nonuniform seasonal warming remains poorly understood, with experimental evidence in trees especially scarce. We therefore conducted a field experiment on seasonally asymmetric warming on 2-year-old larch (Larix principis-rupprechtii) seedlings in two hydrologically contrasting years (wet 2018 and dry 2019). Autumnal and year-round warming significantly delayed the timing of foliar senescence by 6 and 7 d in 2018, the wet year, with corresponding temperature sensitivities of 6.73±1.47 and 8.26±1.00d/°C, respectively. Interestingly, the dates of senescence did not change across the warming treatments in 2019, the dry year. However, there was no significant effect of summer warming on the timing of foliar senescence neither in the wet nor dry year. The delayed autumnal foliar senescence was responsible for an increase in biomass only in the wet year, 2018. In contrast, summer warming, but not autumnal warming, increased the mortality of the seedlings in both 2018 and 2019. These results suggest that the hydrological conditions substantially modify the response of autumnal phenology and growth to seasonal warming. Autumnal warming increases growth, whereas summer warming could cause carbon starvation/hydraulic failure, reduce growth, and lead to higher mortality. Our results suggest that the functioning, ecosystem services, and sustainability of forests in the future depend on the strength and pattern of nonuniform seasonal warming. This study can inspire new research in phenology and tree growth in experiments with asymmetric warming.

Florística e fenologia de dez espécies do extrato arbustivo-arbóreo em torno do Apiário-Escola da Universidade Estadual de Alagoas (UNEAL)

RESUMO: Os padrões fenológicos predominantes para a Caatinga são marcados pela rápida reposição das copas durante o início do período chuvoso e por hábito caducifólio no início do período seco. O processo de floração e frutificação está diretamente relacionado ao período de chuvas e principalmente em um ambiente com muitas variações como a Caatinga. O presente trabalho teve por objetivo caracterizar a flora da área onde o apiário/escola está localizado, bem como a fenologia de dez espécies representativas do extrato arbustivoarbóreo de ocorrência em área de Caatinga na mesorregião do Semiárido alagoano. O estudo foi conduzido na estação experimental Curral do Meio (Sementeira), situada no município de Santana do Ipanema, mesorregião do Sertão alagoano. As observações foram realizadas mensalmente no período de abril de 2019 a janeiro de 2020, onde foram registrados dados de floração (botões florais e flores em antese), frutificação (frutos em desenvolvimento e frutos maduros prontos para dispersão), brotamento (surgimento de folhas novas) e queda foliar. Foram constatados nas 50 parcelas amostradas da área experimental 1.626 indivíduos, os quais estão distribuídos em 18 famílias, 36 gêneros, 40 espécies e dois indivíduos indeterminados. Durante o presente estudo e de acordo com os dados obtidos, pode-se verificar que, para as dez espécies, a produção de folhas novas ocorreu durante o período chuvoso e início da estação seca, o que indica que a fase de brotamento está diretamente relacionada com a precipitação. Porém, quando se observa a senescência foliar, pode-se analisar que algumas espécies concentraram as quedas das folhas no período seco e início da estação chuvosa, a exemplo da Catingueira, Baraúna e Umburana de Cheiro, enquanto que no Pereiro esta fenofases foi registrada praticamente ao longo de quase todo o período, o que indica que a espécie apresenta substituição gradual das folhas.
 PALAVRAS-CHAVE: apicultura, flora nativa, Caatinga, atividade sustentável.

Selection of tree species for forests under climate change: is PSI functioning a better predictor for net photosynthesis and growth than PSII?

A chlorophyll fluorescence (ChlF) assessment was carried out on oak seedlings (Quercus ilex L., Quercus pubescens Willd., Quercus frainetto Ten.) of Italian and Greek provenance, during the years 2017 and 2018, in a common garden in central Italy planted in 2017. This trial aimed to test the relative performances of the oak species in the perspective of assisted migration as part of the actions for the adaptation of forests to climate change. The assessment of the photosynthetic performance of the tree species included the analysis of the prompt chlorophyll fluorescence (PF) transient and the modulated reflection (MR) at 820nm, leaf chlorophyll content, leaf gas exchange (net photosynthesis, stomatal conductance), plant growth (i.e., height) and mortality rate after 2 years from the beginning of the experiment. The assessment of the performance of the three oak species was carried out 'in vivo'. Plants were generated from seeds and exposed to several environmental factors, including changing seasonal temperature, water availability, and soil biological and physical functionality. The results of PF indicate a stable functionality of the photosynthetic system PSII (expressed as FV/FM) across species and provenances and a decline in photochemistry functionality at the I-P phase (ΔVIP) in Q. frainetto, thus indicating a decline of the content of PSI in this species. This result was confirmed by the findings of MR analysis, with the speed of reduction and subsequent oxidation of PSI (VRED and VOX) strongly correlated to the amplitude of ΔVIP. The photosynthetic rates (net photosynthesis, PN) and growth were correlated with the parameters associated with PSI content and function, rather than those related to PSII. The low performance of Q. frainetto in the common garden seems to be related to early foliar senescence with the depletion of nitrogen, due to suboptimal climatic and edaphic conditions. Chlorophyll fluorescence allowed discrimination of populations of oak species and individuation of the less (or/and best) suitable species for future forest ecology and management purposes.