Shaded Branches Research Articles

Bark beetles on logging residues of European larch: Effects of shading and diameter of logging residues on infestation density

Abstract Ips cembrae, an important pest of European larch (Larix decidua), has caused local outbreaks in the last two decades and is becoming increasingly important as the proportion of European larch in forests increases. In 2021–2023, larch logs and piles of branches were placed into shaded forest and sunlit areas every month to study bark beetle species on logging residues. After adult emergence, the logs and branches were debarked, and the infestation density of bark beetles was analysed. The results indicate that shading, log diameter and top/bottom parts of log had a significant effect on infestation density of I. cembrae on logs. The infestation density of I. cembrae was higher on logs felled between December and June than on logs felled between July and November. Shading of branches was the most significant variable affecting the bark beetle species composition on branches. All four of the bark beetle species recorded were affected by diameter of the branches. Ips cembrae primarily infested sunlit branches while Cryphalus intermedius preferred shaded branches. In contrast, the infestation densities of Pityogenes chalcographus and Pityophthorus pityographus seemed to be affected primarily by moisture content of the branches.

Microclimatic gradients cause phenological variations within temperate tree canopies in autumn but not in spring

Tree crowns experience strong vertical microclimatic gradients, particularly in light availability. Surprisingly, little is known about whether these gradients cause within-crown variation in leaf phenology and whether such variations represent different light-use strategies of sun- and shade leaves.In a temperate mixed forest at the Swiss Canopy Crane II site in Switzerland, we measured over three years the annual leaf phenology in the upper and lower crowns of mature trees from six broadleaved and three conifer species. We further recorded the microclimate (temperature, humidity, light) continuously in various positions within the canopy.We found microclimatic canopy gradients to be strongest during summer, but negligible in winter and spring, indicating that any phenological gradients in autumn, but not in spring, might be driven by microclimatic differences. Budbreak timing did not differ within the crowns of any of the broadleaved trees. However, in the three species with deeper crowns, leaf unfolding was up to 10 days faster in the lower crown but showed no difference in the more shallow-crowned species. Surprisingly, only the evergreen conifers Abies alba and Picea abies showed earlier bud break in the lower crowns. In autumn, senescence in all broadleaved species progressed from the upper crown downwards, resulting in up to two weeks longer vegetation seasons in the lower crown.With this first broad assessment of within-tree phenology, we show how microclimatic gradients and different light-use strategies lead to a considerable variability of within-crown phenological gradients. We interpret the faster leaf unfolding in the lower crown of three broadleaved species as a shade avoidance strategy, allowing shade branches to improve their C balance early in the season. In contrast, longer retention of lower leaves in autumn is unlikely to significantly improve the C balance, and more likely caused by higher summer temperature and irradiance in the upper leaves.

Late-season biosynthesis of leaf fatty acids and n-alkanes of a mature beech (Fagus sylvatica) tree traced via 13CO2 pulse-chase labelling and compound-specific isotope analysis.

Leaf cuticular waxes play an important role in reducing evapotranspiration via diffusion. However, the ability of mature trees to regulate the biosynthesis of waxes to changing conditions (e.g., drought, light exposition) remain an open question, especially during the late growing season. This holds also true for one of the most widely distributed trees in Central Europe, the European beech tree (Fagus sylvatica L.). In order to investigate the ongoing formation of wax constituents like alkanes and fatty acids, we conducted a 13CO2 pulse-chase labelling experiment on sun-exposed and shaded branches of a mature beech tree during the late summer 2018. The 13C-label was traced via compound-specific δ13C isotope analysis of n-alkanes and fatty acids to determine the de-novo biosynthesis within these compound classes. We did not observe a significant change in lipid concentrations during the late growing season, but we found higher n-alkane concentrations in sun-exposed compared to shaded leaves in August and September. The n-alkane and fatty acid composition showed ongoing modifications during the late growing season. Together with the uptake and following subsequent decrease of the 13C-label, this suggests ongoing de-novo biosynthesis, especially of fatty acids in European beech leaves. Moreover, there is a high variability in the 13C-label among individual branches and between sun-exposed and shaded leaves. At the same time, sun-exposed leaves invest more of the assimilated C into secondary metabolites such as lipids than shaded leaves. This indicates that the investigated mature beech tree could adjust its lipid production and composition in order to acclimate to changes in microclimates within the tree crown and during the investigated period.

On Combining DeepSnake and Global Saliency for Detection of Orchard Apples

For the fast detection and recognition of apple fruit targets, based on the real-time DeepSnake deep learning instance segmentation model, this paper provided an algorithm basis for the practical application and promotion of apple picking robots. Since the initial detection results have an important impact on the subsequent edge prediction, this paper proposed an automatic detection method for apple fruit targets in natural environments based on saliency detection and traditional color difference methods. Combined with the original image, the histogram backprojection algorithm was used to further optimize the salient image results. A dynamic adaptive overlapping target separation algorithm was proposed to locate the single target fruit and further to determine the initial contour for DeepSnake, in view of the possible overlapping fruit regions in the saliency map. Finally, the target fruit was labeled based on the segmentation results of the examples. In the experiment, 300 training datasets were used to train the DeepSnake model, and the self-built dataset containing 1036 pictures of apples in various situations under natural environment was tested. The detection accuracy of target fruits under non-overlapping shaded fruits, overlapping fruits, shaded branches and leaves, and poor illumination conditions were 99.12%, 94.78%, 90.71%, and 94.46% respectively. The comprehensive detection accuracy was 95.66%, and the average processing time was 0.42 s in 1036 test images, which showed that the proposed algorithm can effectively separate the overlapping fruits through a not-very-large training samples and realize the rapid and accurate detection of apple targets.

Critical role of air and soil temperature in the development of primary and secondary physical dormancy inAlbizia julibrissin(Fabaceae)

AbstractPhysical dormancy (PY) is typically induced by seed coat impermeability that develops once the moisture content of seeds drops below a species-specific threshold. Considering this, we utilizedAlbizia julibrissin(Fabaceae) to ask (i) whether seeds that mature on the outer branches of trees (directly exposed to sunlight) are more likely to be impermeable than seeds matured under canopy cover; (ii) whether this difference might be explained by the maternal environment in which the seeds mature; and (iii) which conditions impose secondary dormancy following dispersal? Temperature was tracked in both shaded and sun-exposed seed pods throughout the growing season using data-loggers. Temperatures remained lower in pods under canopy cover than those exposed to direct sunlight. Consequently, the moisture content of seeds collected from sun-exposed branches were significantly lower than seeds matured under canopy cover, thereby producing a higher percentage of impermeable seeds. A dispersal-mimicking experiment revealed that seeds matured in sun-exposed branches and subsequently dispersed to an open site for 4 months were more likely to develop impermeability (i.e. secondary dormancy). The opposite was found to be true for seeds matured in shaded branches and subsequently dispersed to a canopy-covered site. We conclude that the microclimate of both the maternal environment in which seeds mature, and the site to which they disperse, determines the development of primary and secondary dormancy, respectively.

Вплив системи догляду за кроною на декоративність і довговічність рослин сортів Syringa vulgaris L.

Досліджено вплив способів обрізування крони рослин Syringa vulgaris L. на їхню декоративність і довговічність. Встановлено, що досягти найкращого результату можна тільки за регулярного догляду за кроною. Спонукає до цього, щонайперше, дихотомічне (несправжнє) гілкування, за яким кожна однорічна гілка продукує навесні два пагони з верхівкової пари бруньок та ще кілька – з бруньок, що розташовані нижче по осі цієї гілки. Отже, щороку загальна їхня кількість щонайменше потроюється. Коренева система не зможе за цей час збільшити в таких обсягах свою масу і фізіологічну активність, що корелятивно спричиняє значне зменшення розмірів пагонів і суцвіть. Якщо догляд був нерегулярний або відсутній, виникає потреба інтенсивного прорідження або кардинального омолодження крони. Доведено, що цими заходами можна поліпшити декоративність рослин, але на довговічність вони вплинуть негативно. Зумовлює це дві причини. Перша – запобігання ран внаслідок видалення гілок на кільце. Встановлено, що навіть 1,5-2,0-сантиметрові зрізи на стовбурі чи скелетних гілках ніколи не загояться, а за 10-15 років їхня деревина струхліє, утворивши порожнину. Деревина великих ран руйнується швидше, що призводить до виникнення дупел та повільного відмирання всієї рослини. Другою причиною вкорочення довговічності є раптово порушений функціональний корелятивний коренево-листковий зв'язок, що є наслідком різкого зменшення в омолодженій рослині надземної частини. Спочатку це призведе до сповільнення фотосинтезу (крона майже відсутня), а потім, корелятивно, й до затухання кореневого синтезу: через мізерне надходження асимілятів до коренів. Унаслідок цього загальна маса фізіологічно активної частини кореневої системи теж значно зменшиться, що негативно вплине на довговічність рослини загалом. Декоративність кущів через це з року в рік погіршується. Також встановлено, що до обрізування крони змушує й загущена посадка бузків. Для відновлення її декоративності спочатку варто видалити кволі рослини, а в решти – знизити крону приблизно на третину аби наблизити її до кореневої системи, що забезпечить рослинам фізичну витривалість та дещо внормує в них функціональний коренево-листковий зв'язок. Здійснити цей захід треба якомога раніше в часовому вимірі, бо, окрім згаданого, рослини почнуть страждати й від хвороб. Потужні гілки потрібно вкорочувати, а не вирізати на кільце, аби не нанести стовбурам і гілкам першого порядку великих ран. За такого підходу до обрізування крони бузки будуть декоративними й здебільшого випадків – довговічними.

A STUDY OF CO2 GAS EXCHANGE IN KARELIAN BIRCH UNDER LOW SOLAR RADIATION CONDITIONS IN PLANTATIONS WITH DIFFERENT LEVELS OF SOIL FERTILITY

Comparative estimation of CO 2 gas exchange in leaves of shaded branches of Karelian birch ( Betula pendula var. сarelica ) was carried out in two 40-50 years old plantations with different levels of mineral nutrition. On both plantations, comparison of parameters of CO 2 gas exchange was also made between sunlit and shaded leaves. Characteristics of CO 2 gas exchange in shaded leaves differed depending on the content of mineral substances (N, P, K) in the soil. With increasing of soil fertility, mean values of photosynthesis of shaded leaves increased from 1.22 to 2.74 mmol·m -2 ·c -1 , dark respiration – from 0.43 to 0.69 mmol·m -2 ·c -1 . Mean values of photosynthesis of sunlit leaves did not differ significantly (p>0.05) between these two plantations, but respiration has changed from –1.54 to –2.63 mmol·m -2 ·c -1 . With increasing of soil fertility, parameters of photosynthetic light-curves changed: constant of saturation decreased from 100-120 to 20-60 mmol·m -2 ·c -1 , light compensation point – from 12-20 to 6-8 mmol·m -2 ·c -1 , which is evidence of more effective operating of photosynthetic apparatus when nutrition was not a limiting factor. Significant differences in parameters of photosynthetic light-curves were revealed between sunlit and shaded leaves in both plantations. In plantation with a higher level of NPK, index of usage of photosynthetically active radiation ( PhAR ) for photosynthesis was equal to 6.1 and 53.1 mmol СО 2 · (mmol photons) -1 in sunlit and shaded leaves, respectively. Dark respiration was -2.63 and -0.66 mmol · m -2 ·c -1, a light compensation point – 45.8 and 5.91 mmol·m - 1 ·c -1 for sunlit and shaded leaves, respectively. Based on fresh weight, amounts of carotenoids ( c ) and chlorophyll хл (a+b) in the shaded and sunlit leaves had no significant differences. Mean values of the хл (a+b)/с ratio in shaded leaves were 1.5 times more than in the sunlit leaves. Based on leaf area, because of decreasing of thickness of the shaded leaves, amount of хл (a+b) was 1.4 times more in the shaded leaves in comparison of the sunlit leaves. Assessment of the carbon balance of the shaded branches showed that the balance remains positive when the daily mean values of the photosynthetically active radiation are equal to 18-25 mmol·m -2 ·s -1 . The Karelian birch, growing on the comparatively fertile soil, utilises the low values of solar radiation more effectively than on soil with a low nutrient content, and owing to morphological and physiological adaptations the short-stemmed and shrubby birches with a figured wood can survive in environment of a heavy shade.

Hanging in the treetops: anin situexperiment in ancient hemlock assessing outbreak defoliator performance among crown levels

1. Past studies have shown that both egg lay and larval feeding of a generalist defoliator, pale-winged gray (Iridopsis ephyraria Walker) (Lepidoptera: Geometridae), are concentrated in the mid-lower crown of eastern hemlock [Tsuga canadensis (L.) Carr.]. 2. Using tree-climbing techniques, we carried out in situ bioassays in large hemlock trees (∼25 m) to determine whether the observed foraging preferences are adaptive and how they reflect associated intra-tree variations in microhabitat quality associated with temperature and foliage nutritional quality. 3. In 1 of 2 years, larval survival was significantly higher in the shaded lower versus sunlit upper crown; however, in both years, groups that fed in the sunlit upper crown branches had larger male and female moths and more female-biased sex ratios. 4. Differences in pale-winged gray performance among crown levels were somewhat supported by trends in foliage nutritional chemistry but not well-correlated with variation in temperature. 5. The present study is one of only a few to carry out bioassays on large mature trees and results reinforce the idea that foraging patterns of herbivores are likely to reflect trade-offs among several factors that vary between sunlit and shaded branches within forest canopies.

Functional ratios among leaf, xylem and phloem areas in branches change with shade tolerance, but not with local light conditions, across temperate tree species.

Leaf, xylem and phloem areas drive the water and carbon fluxes within branches and trees, but their mutual coordination is poorly understood. We test the hypothesis that xylem and phloem areas increase relative to leaf area when species are selected for, or branches are exposed to, higher levels of light intensity. Trees of 10 temperate, broadleaved and deciduous, tree species were selected. Fifty-centimetre-long branches were collected from shaded and exposed conditions at a height of 3-4m. We measured the total leaf area, xylem area, phloem area and leaf traits, as well as the area of the constituent cell types, for a stem section at the branch base. Xylem area:leaf area and phloem area:leaf area ratios did not differ consistently between sun and shade branches, but, as expected, they decreased with species' shade tolerance. Similar trends were observed for conductive cell areas in xylem and phloem. Trees of light-demanding species maintain higher water loss and carbon gain rates per leaf area by producing more xylem area and phloem area than shade-tolerant species. We call for more comparative branch studies as they provide an integrated biological perspective on functional traits and their role in the ecology of tree species.

Bud vigor, budburst lipid peroxidation, and hormonal changes during bud development in healthy and moribund beech (Fagus sylvatica L.) trees

Key message Despite meristem totipotency, epicormic branches from moribund trees produce buds with less vigor and increased lipid peroxidation compared to those of healthy trees. Abstract A better understanding of the factors governing bud vigor and development, and their underlying mecha- nisms is essential for management of broad-leaved stands, of which oaks and beeches are among the most important species. This study investigated possible differences in leaf bud vigor and development in healthy and moribund beech trees. Leaf buds on shaded branches found in the under- story of a natural beech stand in Catalonia (NE Spain) were used for comparison. The vigor, extent of lipid peroxida- tion, and hormonal profile of leaf buds of healthy and moribund beech trees were investigated. Results showed less bud vigor in moribund trees than in healthy ones. In the former, there was increased lipid peroxidation at bud- burst. Although endogenous levels of gibberellins, cytoki- nins, and auxin were significantly influenced by bud development in both tree types, buds of moribund trees showed markedly different dynamics in the endogenous concentrations of auxin, abscisic acid and the ethylene precursor, 1-aminocyclopropane-1-carboxylic acid. We conclude that moribund trees (a) are less efficient in pro- ducing new leaves, as indicated by less bud vigor and greater lipid peroxidation at budburst than healthy trees and (b) show a marked differential hormonal pattern during bud development compared to healthy trees.

Partial shading of lateral branches affects growth, and foliage nitrogen- and water-use efficiencies in the conifer Cunninghamia lanceolata growing in a warm monsoon climate.

The degree to which branches are autonomous in their acclimation responses to alteration in light environment is still poorly understood. We investigated the effects of shading of the sapling crown of Cunninghamia lanceolata (Lamb.) Hook on the whole-tree and mid-crown branch growth and current-year foliage structure and physiology. Four treatments providing 0, 50, 75 and 90% shading compared with full daylight (denoted as Treatment(0), Treatment(50%), Treatment(75%) and Treatment(90%), and Shaded(0), Shaded(50%), Shaded(75%) and Shaded(90%) for the shaded branches and Sunlit(0), Sunlit(50%), Sunlit(75%) and Sunlit(90%) for the opposite sunlit branches under natural light conditions, respectively), were applied over two consecutive growing seasons. Shading treatments decreased the growth of basal stem diameter, leaf dry mass per unit leaf area, stomatal conductance, transpiration rate, the ratio of water-soluble to structural leaf nitrogen content, photosynthetic nitrogen-use efficiency and instantaneous and long-term (estimated from carbon isotope composition) water-use efficiency in shaded branches. Differences between shaded and sunlit branches increased with increasing severity and duration of shading. A non-autonomous, partly compensatory behavior of non-shaded branches was observed for most traits, thus reflecting the dependence between the traits of sunlit branches and the severity of shading of the opposite crown half. The results collectively indicated that tree growth and branch and leaf acclimation responses of C. lanceolata are not only affected by the local light environment, but also by relative within-crown light conditions. We argue that such a non-autonomous branch response to changes in light conditions can improve whole-tree resource optimization. These results contribute to better understanding of tree growth and utilization of water and nitrogen under heterogeneous light conditions within tree canopies.

Sunlight Causes Skin Blackening in ‘Fuyu’ Persimmon Fruits during Storage

과피흑변은 '부유' 단감(Diospyros kaki, 'Fuyu') 과실의 저장 중에 발생하는 주요 생리적 장해의 하나이다. 부유 과실의 과피에서 페놀화합물의 함량, PPO와 POD의 활성, 지질 포화도를 분석하였다. 페놀화합물은 일광의 방향에 따라 과피에 불균등하게 분포하였는데, 일광 노출면에 축적량이 가장 많았고 그 반대면에서는 가장 적었다. 그러나 수관 내부의 음지 가지에서 수확한 과실의 경우 페놀화합물은 과피에 비교적 고르게 분포되어 있었다. PPO와 POD의 활성 또한 과피에서 고르지 않았으나, 이는 과피흑변이 발생한 과실에서만 그러하였으며, 흑변 부위는 PPO 활성은 가장 높고 POD 활성은 가장 낮았다. 수확 시에 일광면에 표식을 한 과실을 저온에 저장하였을 때, 저장 중 과피흑변의 증상인 운형 흑반은 정확히 표식 부위에 발생하였다. 게다가, 일광면은 높은 지질포화도를 보였는데, 이는 일광에 의해 야기된 고온에 대한 적응을 의미한다. 따라서 이러한 결과로 미루어 볼 때, 부유 과실의 과피흑변 장해는 일광에 노출된 과실의 고온 순화 과피 조직에서 나타나는 저온장해 증상의 일종인 것으로 간주할 수 있을 것이다. Skin blackening is a serious postharvest disorder occurring in 'Fuyu' persimmon fruits (Diospyros kaki, 'Fuyu'). Phenolic content, polyphenol oxidase (PPO) and peroxidase (POD) activity, and lipid saturation were investigated in skin tissue of 'Fuyu' fruits. The phenolic compounds were accumulated unevenly on fruit skin depending on sunlight exposure, i.e., the most accumulation on sunny side and the least on the opposite, shaded side. The fruits harvested from shaded branches inside the canopy showed relatively even distribution of phenolic compounds in the skin. The activity distribution of PPO and POD were also uneven but only in fruits suffering f rom skin b lackening disorder, w ith the h ighest and the lowest a ctivity of PPO and P OD, respectively, in the blackened area of the fruit. When the sunny, southern sides of fruits were marked at harvesting time and fruits were stored at low temperature, a round black spot, as a symptom of skin blackening disorder, developed during storage exactly on the marked region. In addition, the sunny side of fruit showed higher lipid saturation, thus indicating adaptation to high temperature caused by the sunlight. These results suggest that the skin blackening disorder of 'Fuyu' fruits can be considered as a kind of chilling injury symptom that develops on the high-temperature-acclimated skin tissue of sunlight-exposed fruits when they are later exposed to low temperature.

Variability of BVOC emissions from a Mediterranean mixed forest in southern France with a focus on <i>Quercus pubescens</i>

Abstract. We aimed at quantifying biogenic volatile organic compound (BVOC) emissions in June from three Mediterranean species located at the O3HP site (southern France): Quercus pubescens, Acer monspessulanum and C. coggygria (for isoprene only). As Q. pubescens was shown to be the main BVOC emitter with isoprene representing ≈ 99% of the carbon emitted as BVOC, we mainly focused on this species. C. coggygria was found to be a non-isoprene emitter (no other BVOCs were investigated). To fully understand both the canopy effect on Q. pubescens isoprene emissions and the inter-individual variability (tree to tree and within canopy), diurnal variations of isoprene were investigated from nine branches (seven branches located to the top of canopy at ≈ 4 m above ground level (a.g.l.), and two inside the canopy at ≈ 2 m a.g.l.). The Q. pubescens daily mean isoprene emission rate (ERd) fluctuated between 23 and 98 μgC gDM−1 h−1. Q. pubescens daily mean net assimilation (Pn) ranged between 5.4 and 13.8, and 2.8 and 6.4 μmol CO2 m−2 s−1 for sunlit and shaded branches respectively. Both ERd and isoprene emission factors (Is), assessed according to Guenther et al. (1993) algorithm, varied by a factor of 4.3 among the sunlit branches. While sunlit branches ERd was clearly higher than for shaded branches, there was a non-significant variability of Is (59 to 77 μgC gDM−1 h−1). Diurnal variations of isoprene emission rates (ERs) for sunlit branches were also investigated. ERs were detected at dawn 2 h after Pn became positive and were mostly exponentially dependent on Pn. Diurnal variations of ERs were not equally well described throughout the day by temperature (CT) and light (CL) parameters according to G93 algorithm. Temperature had more impact than photosynthetically active radiation (PAR) on the morning emissions increase, and ER was no longer correlated to CL × CT between solar noon (maximum ER) and mid-afternoon, possibly due to thermal stress of the plant. A comparison between measured and calculated emissions using two isoprene algorithms (G93 and MEGAN – Model of Emissions of Gases and Aerosols from Nature) highlighted the importance of isoprene emission factor Is value used, and some weakness in assessing isoprene emissions under Mediterranean climate conditions (drought) with current isoprene models.

Structural development of redwood branches and its effects on wood growth

Redwood branches provide all the carbohydrates for the most carbon-heavy forests on Earth, and recent whole-tree measurements have quantified trunk growth rates associated with complete branch inventories. Providing all of a tree's photosynthetic capacity, branches represent an increasing proportion of total aboveground wood production as trees enlarge. To examine branch development and its effects on wood volume growth, we dissected 31 branches from eight Sequoia sempervirens (D. Don) Endl. and seven Sequoiadendron giganteum Lindl. trees. The cambium-area-to-leaf-area ratio was maintained with size and age but increased with light availability, whereas the heartwood-deposition-area-to-leaf-area ratio increased with size and age but was insensitive to light availability. The proportion of foliage mass arrayed in <1-cm-diameter epicormic shoots increased with decreasing light and was higher in Sequoia (20-60%) than in Sequoiadendron (3-16%). Well-illuminated branches concentrated leaves higher and distally, while shaded branches distributed leaves lower and proximally. In similar light environments, older branches distributed leaves lower and more proximally than younger branches. Branch size, light, species, heartwood area, a heartwood-area-species interaction, and ovulate cone mass predicted 87.5% of the variability in wood volume growth of branches. After accounting for the positive effects of size and light, wood volume growth declined with heartwood area and age. The effect of age was trivial compared to the effect of heartwood area, suggesting that heartwood expansion caused the age-related decline in wood volume growth. Additionally, Sequoiadendron branches of similar size and light environment with more ovulate cones produced less wood, even though these cones were long-lived and photosynthetic, reflecting the energetic cost of seed production. These results contributed to a conceptual model of branch development in which light availability, injury, heartwood content, gravity, and time interact to produce the high degree of branch structural variation evident within redwood crowns.

Variation of photosynthesis and pigment concentration relative to irradiance and nitrogen content for two coexisting desert shrubs

Variation of light within canopies directly influences foliage photosynthetic acclimation and hence is important for determining the fitness of plants growing in fragile arid ecosystems. This study was conducted at Gurbantünggüt desert in the hinterland of the Eurasian continent, Xinjiang, China. Gas exchange, pigment concentration and nitrogen (N) content were measured in the sun-lit and shaded assimilating branches/leaves of two coexisting desert species during an annual growing season. Photo-saturated photosynthesis was higher in Tamarix ramosissima but light compensation points were lower compared to Haloxylon ammodendron. T. ramosissima exhibited a higher efficiency and sustained highest maximum net photosynthesis (PN) toward the end of the growing season, while H. ammodendron had a higher efficiency earlier in the growing season. Both species exhibited significantly higher (P<0.05) PN in sun-lit branches compared to shaded branches throughout the growing season. T. ramosissima recorded higher pigment concentration and N content compared to H. ammodendron during the growing season. Although pigment concentrations decreased with seasonal courses regardless of light conditions, they were significantly higher (P<0.001) in sun-lit branches compared to shaded branches of T. ramosissima but completely opposite results were obtained in H. ammodendron. Seasonal N content was influenced by variation in precipitation with age-related changes in assimilating branches affecting the allocation of N content along light gradients in both species. The observed differences in PN between the sun-lit and shaded canopy fractions were caused by N import of the leaves, which varied slightly with the gradient in irradiance due to N reallocation within photosynthetic apparatus. T. ramosissima revealed a higher potential for irradiance acclimation through plasticity in photosynthetic apparatus, and hence an important attribute for colonizing wider ecological range compared to H. ammodendron.

Concentrative nitrogen allocation to sun-lit branches and the effects on whole-plant growth under heterogeneous light environments

We investigated the nitrogen and carbohydrate allocation patterns of trees under heterogeneous light environments using saplings of the devil maple tree (Acer diabolicum) with Y-shaped branches. Different branch groups were created: all branches of a sapling exposed to full light (L-branches), all branches exposed to full shade (S-branches), and half of the branches of a sapling exposed to light (HL-branches) and the other half exposed to shade (HS-branches). Throughout the growth period, nitrogen was preferentially allocated to HL-branches, whereas nitrogen allocation to HS-branches was suppressed compared to L- and S-branches. HL-branches with the highest leaf nitrogen content (N(area)) also had the highest rates of growth, and HS-branches with the lowest N(area) had the lowest observed growth rates. In addition, net nitrogen assimilation, estimated using a photosynthesis model, was strongly correlated with branch growth and whole-plant growth. In contrast, patterns of photosynthate allocation to branches and roots were not affected by the light conditions of the other branch. These observations suggest that tree canopies develop as a result of resource allocation patterns, where the growth of sun-lit branches is favoured over shaded branches, which leads to enhanced whole-plant growth in heterogeneous light environments. Our results indicate that whole-plant growth is enhanced by the resource allocation patterns created for saplings in heterogeneous light environments.

Changes of xylem sap ionic content and stem hydraulics in response to irradiance in Laurus nobilis

This study reports experimental evidence for light-mediated changes of stem hydraulic conductance (K(stem)) in field-grown laurel plants. Field measurements based on the evaporative flux method revealed that sun-exposed branches had 60% higher K(stem) with respect to shade-exposed branches. Xylem sap potassium concentration was approximately 3 mM as recorded in shaded branches and up to 12 mM in illuminated ones. Such a difference in [K(+)] proved to induce significant increase in xylem hydraulic conductance of excised twigs when artificially perfused with various solutions, as a likely consequence of the interaction of cations with the pectic matrix of pit membranes (the so-called 'ionic effect'). We propose that this mechanism provides plants with a large potential for fine regulation of water flow towards different parts of the canopy exposed to different environmental conditions with the result of optimizing light and water utilization.

A METHODOLOGY TO STUDY THE POST-HARVEST RIPENING BEHAVIOR OF MANGO (CV. COGSHALL) ACCORDING TO AGRONOMIC CONDITIONS

The post-harvest ripening of ?Cogshall? mango fruit was analyzed in two contrasted conditions of light environment (sunny and shaded branches). Cold storage at 13°C was compared to this at 20°C. A Maturity Index was suggested to consider the ripening and senescence rate regardless of storage conditions. Harvest date and fruit position had an incidence on the content of sugars and organic acids. A cold storage during two weeks reduced but did not stop fruit evolution and fruit ripened normally when they were transferred at 20°C. The use of a Maturity Index could be interesting to improve the representation of fruit quality changes during storage. (Resume d'auteur)

THE ENGLISH BEECH MASTING SURVEY 1980–2007: VARIATION IN THE FRUITING OF THE COMMON BEECH (FAGUS SYLVATICA L.) AND ITS EFFECTS ON WOODLAND ECOSYSTEMS

Summary 1. Study of annual production of beech mast at twelve main sites including closed canopy beechwood, shelter belts, avenues and an isolated tree in a park, as well as intermittent observations at others, has now continued for twenty-eight years. 2. During this period beech mast was sampled from up to 100 trees by seven-minute samples collected from the ground. Aerial samples have also been collected from low-growing branches. 3. Production of full seed varies greatly from year to year, and all trees produce empty pericarps as well as full mast, especially on lower or shaded branches. 4. The proportion of full nuts consumed or damaged by the moth Cydia fagiglandana Z., birds and small mammals, in English sites, can become significant especially in non-mast years. 5. Good masting occurred in 1980, 1982, 1984, 1987, 1990, 1995, 1997, 2000, 2002, 2004 and 2006: after each of these good years, one year of very poor masting normally followed. The best year recorded so far was 1990. In both 1981 and 2005, no full mast was found, and singularly very little in 1991 and 2001. 6. Regional variation within England is much less than the annual variation, but over the period the northern trees have produced on average fewer full nuts but rather more empty and total nuts. In 2007, however, northern trees produced markedly less full and total nuts than their southern counterparts. 7. Over such a long period it was inevitable that site changes would occur. In some instances the substrate beneath particular trees is now less favourable for rapid nut collection. As some trees have died, additional younger trees are now being assessed. In 1996, far more viable seed was formed in certain Scottish sites than at those we observed in England, so it is highly desirable that Scottish and Welsh sites be monitored in the future.

Vertical foliage distribution determines the radial pattern of sap flux density in Picea abies

Understanding the causes determining the radial pattern of sap flux density is important both for improving knowledge of sapwood functioning and for up-scaling sap flow measurements to canopy transpiration and ecosystem water use. To investigate the anatomical connection between whorls and annual sapwood rings, pruning-induced variation in the radial pattern of sap flux density was monitored with Granier probes in a 35-year-old Picea abies (L.) Karst tree that was pruned from the crown bottom up. Modifications in the radial pattern of sap flux density were quantified by a shape index (SI), which varies with the relative contribution of the outer and inner sapwood to tree transpiration. The SI progressively diminished during bottom up pruning, indicating a significant reduction in sap flow contribution of the inner sapwood. Results suggest that the radial pattern of sap flux density depends mainly on the vertical distribution of foliage in the crown, with lower shaded branches hydraulically connected with inner sapwood and upper branches connected with the outer rings.