Ecophysiological analysis of woody species in contrasting temperate communities during wet and dry years

This study employed an intensive sampling regime in which leaf gas exchange and tissue-water relations were measured simultaneously on the same leaf at midday on 19 tree species from three distinct forest communities during wet (1990) and dry (1991) growing seasons. The study sites were located on a xeric barrens, a misic valley floor, and a wet-mesic floodplain in central Pennsylvania, United States. The xeric, mesic, and wetmesic sties had drought-related decreases in gravimetric soil moisture of 53, 34 and 27%, respectively. During the wet year, xeric and mesic communities had high seasonal mean photosynthetic rates (A) and stomatal conductance of water vapor (g _wv) and low midday leaf water potential (), whereas the wet-mesic community had low A and g _wv and high midday . The mesic and wet-mesic communities had dry year decreases in predawn , g _wv and A with the greatest drought effect occurring in the mesic community. Regression analysis indicated that species from each site that exhibited high wet-year A and g _wv tended to have low midday . This trend was reversed only in the mesic community in the drought year. Despite differences in midday , all three communities had similar midday leaf turgor pressure (_p) in the wet year attributable to lower osmotic potential at zero turgor ( ⁰ ) with increasing site droughtiness. Lower wet year ⁰ in the xeric community was due to low symplast volume rather than high solute content. Species with the lowest ⁰ in the wet year often did not have the lowest ¹⁰⁰ possibly related to differences in tissue elasticity. Moreover, increased elasticity during drought may have masked osmotic adjustment in ¹⁰⁰ but not in ⁰ , via dilution of solutes at full hydration in some species. Despite the sampling regime used, there were no relationships between gas exchange and osmotic and elastic parameters that were consistently significant among communities or years. This result questions the universal, direct effect of osmotic and elastic adjustments in the maintenance of photosynthesis during drought. By including a large number of species, this study provided new insight to the ecophysiology of contrasting forest communities, and the community-wide impact of drought on contrasting sites.     

Use of an analytical model to study limitations on net photosynthesis in Arbutus unedo under field conditions

Summary From field gas-exchange measurements on Arbutus unedo growing in Portugal, parameter values necessary to apply an analytical, physiologicallybased model of C ₃ photosynthesis were obtained. The model successfully simulated measured diurnal photosynthetic responses in Arbutus during periods without water stress, under both natural and CO₂-saturating conditions. The model was used to analyze those factors limiting primary productivity during each of the experimental days. Due to a large investment in ribulose bisphosphate (RuBP) regeneration capacity, irradiance was rarely limiting, even during cloudy periods, but the limitation imposed by stomatal conductance was quite large, averaging over 30%. The fact that experimental leaves were maintained in a horizontal position is at least partially responsible for these results. Possible other reasons for this apparent excess of RuBP regeneration capacity visa-vis RuBP carboxylase-oxygenase concentration are discussed.     

Changes in gas exchange, proline accumulation and antioxidative enzyme activities in three olive cultivars under contrasting water availability regimes

Changes in photosynthetic performance, osmolyte accumulation and the activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT) and polyphenol oxidase (PPO) were investigated in one-year-old olive cultivars (Chemlali, Meski and Picholine) subjected to contrasting water availability regimes under arid climatic conditions in Tunisia. Shoot elongation rates (SER) and photosynthetic performance were markedly reduced by the water deficit regime (WD) in all cultivars except for Chemlali, which proved to be superior to the other two cultivars with respect to drought tolerance. Higher photosynthetic performance (net photosynthesis (P_n), stomatal conductance (g_s) and transpiration rates (E)) in the Chemlali and Meski cvs. compared to Picholine olive allowed them to maintain better plant water status and shoot elongation rates. Under WD conditions, Chemlali showed a greater capability for proline accumulation. Leaves grown under WD conditions showed signs of oxidative stress such as reduced chlorophyll and carotenoid concentrations. Nevertheless, different cultivars developed certain antioxidative defense mechanisms, including elevated SOD, APX and CAT activities. In contrast, PPO activity decreased under WD circumstances. Comparatively, Chemlali olive displayed better antioxidative enzyme activity, and thus better protection against oxidative stress. These results show that the ability of olive trees to up-regulate the enzymatic antioxidative system might be an important attribute linked to drought tolerance. These findings demonstrate that the association of higher P_n, proline accumulation and antioxidative defenses could be effective in a water-limited environment and may be useful selection criteria in breeding programs with the objective of improving drought tolerance and growth of olive trees, at least under the described environmental conditions.     

Antifungal activity of the dill (Anethum graveolens L.) seed essential oil against strawberry anthracnose under in vitro and in vivo conditions

Strawberry anthracnose, caused by Colletotrichum nymphaeae, is mainly controlled by the application of synthetic chemical fungicides. The present study assessed the antimicrobial activity of essential oils (EOs) from dill (Anethum graveolens L.) seed against C. nymphaeae. The antifungal effects of dill seed EO on C. nymphaeae was initially evaluated in vitro and further extended as in vivo condition. The results indicate that in the contact and volatile assays, dill seed EO significantly inhibited mycelial growth of C. nymphaeae at all concentrations tested. Conidia germination was also significantly inhibited at concentrations of 250 – 1000 ppm. Disease incidence and severity of anthracnose on strawberry fruits were significantly reduced compared with infected control, from concentrations of 500 and 50 ppm, respectively. The results confirm the efficacy of dill seed EO against C. nymphaeae, which may represent an alternative to synthetic chemical fungicides to control strawberry anthracnose pre- and post-harvest.     

Morphological and physiological variation in western redcedar (<Emphasis Type="Italic">Thuja plicata</Emphasis>) populations under contrasting soil water conditions

Adaptation to precipitation conditions may induce genetic diversity that changes morphological and physiological traits. This hypothesis was investigated in the seedlings of seven western redcedar (Thuja plicata Donn ex D. Don) populations, which were collected along a precipitation transect from the Pacific coast to the southern interior of British Columbia, Canada. The experimental seedlings were either well-watered or soil-droughted and measured for growth, gas exchange rates, transpiration efficiency, and carbon isotope discrimination during or at the end of the third growing season. Significant variation was found in most of these morphological and physiological traits among the populations. Much of this variation occurred under well-watered, but not so much under droughted conditions. Mean height increments and transpiration efficiency showed a significant linear relationship, but biomass increments exhibited a quadratic relationship with precipitation on the origin site of these populations. Measurements of water use efficiency obtained from instantaneous gas exchange measurements, carbon isotope discrimination, and transpiration efficiency were intercorrelated in the seedlings. However, neither did any of these measurements consistently rank the populations, nor were they indicative of adaptation to climatic precipitation conditions in these western redcedar populations.     

Seed provenance for changing climates: early growth traits of nonlocal seed are better adapted to future climatic scenarios,but not to current field conditions

The urgency to repair degraded ecosystems is challenged by the need to future‐proof populations to deal with changing climates. Therefore, it is necessary to know if source gene‐pools are resilient to both current and future climatic conditions. We tested this question with the pioneer shrub Hardenbergia violacea (Fabaceae), an important species for restoration in eastern Australia. We evaluated in situ and ex situ performance of seed from eight provenances, two local and six from regions receiving hotter and wetter spring to autumn conditions and/or drier winters and we included wild and commercial collections. We compared survivorship of seedlings in climate‐houses that emulated current and predicted temperature and rainfall. In the field, we measured germination and seedling survivorship. We used neutral codominant markers to provide inbreeding and heterozygosity estimates to evaluate against health and survivorship. All provenances survived the current conditions, but local provenances were the poorest performers in the predicted hotter and wetter scenario compared with nonlocal provenances. No provenance survived more than a fortnight of a climate‐house simulated, but predicted, extreme weather event of a drought (35/22°C 12 hours day/night, 50 mL/week = 220 mm rainfall). Heterozygosity was positively associated with plant health in surviving plants, and plants in poor condition had high inbreeding estimates. In the field, nonlocal provenances performed poorly and most survivors were from local provenances. The contribution of individual genetic variation to stress tolerance will be an important consideration when selecting provenances for future climates.     

Physiological performance of silver-fir (Abies alba Mill.) populations under contrasting climates near the south-western distribution limit of the species

Silver-fir (Abies alba Mill.) populations located at the south side of the main Pyrenean axis and Pre-Pyrenees constitute the south-western distribution limit of the species and, therefore, may be responding more noticeably to climate change than those in the centre of the range. The increasing aridity detected in the Pyrenees during the 20th century should affect more negatively the physiological performance of the southernmost silver-fir stand growing under more xeric conditions in comparison with stands growing within the main distribution area under mesic conditions. To evaluate the climatic influence on the performance of silver fir near its distribution limit, we studied several physiological and growth variables in shoots and needles from two silver fir populations located in nearby but climatically contrasting sites: Paco Ezpela (site E) and Gamueta (site G). Site E showed a stronger Mediterranean influence than site G, i.e. the former site was characterized by higher temperatures and leaf-to-air water vapour pressure difference and lower precipitation in summer than the latter site. Silver firs from site E showed lower values of primary and secondary growth, needle length, stomatal conductance, net photosynthesis and photosystem II (PSII) efficiency than individuals from site G. The reduction in net photosynthesis could be ascribed to a low CO₂ availability and to a lower PSII efficiency. We conclude that the physiological differences found between both sites were caused by the more xeric conditions of site E as compared with the more mesic environment in site G. The predicted increase of severe droughts in the southern Pyrenees might cause a decrease in photosynthesis and growth in those silver-fir stands located near the ecological limit of the species.     

The effect of air pollution on the mechanism of stomatal control

Summary A long-term field experiment permanently measuring gas exchange in the top of a 70-year-old spruce, continued for through the 1990 growing season. Two gas exchange chambers were run simultaneously under identical climatic conditions. One of two similar twigs was exposed to ambient air whereas the other received pure air. These experiments aimed to examine the ability of the stomata to control water balance, comparing pure and ambient air. This was done not only in natural climatic conditions but also in experimental, specifically maintained stress situations. Special care was taken to ensure that only steady state values of stomatal responses are related to the environmental stimuli. During a drought period lasting several weeks, overshooting transpiration values were documented for the ambient air. The two twigs do not merely differ in their control capacity, but the behaviour of the stomata in ambient air deviates from the norm. The increasingly uncontrolled water losses during the drought period have a negative effect on photosynthetic capacity. The influence of water deficit on stomatal response to other environmental factors (light, CO₂) is shown. Due to deficient control quality of the stomata lower stress tolerance in the face of drought is suggested in ambient air as compared with pure air. By tracing dysfunctions to structural changes in the cell walls of the stomatal apparatus, a mechanism is described explaining forest decline under the combined influence of air pollutants and drought stress.     

Phenology and seed setting success of snowbed plant species in contrasting snowmelt regimes in the Central Pyrenees

Plant growth and performance in snowbed communities are strongly influenced by the length of the growing period remaining after the snowmelt date. Under the scenario of climate change, studying the phenological responses of snowbed species to variations in snowmelt date might be crucial to understand their ability to adapt and survive under changing conditions. We studied 13 plant species from contrasting biological and ecological groups (i.e. ‘snowbed specialists’, ‘preferential species’ and ‘generalist species’) growing in four snowbed plots with siliceous substrates in the Central Pyrenees. These species were monitored for two consecutive years and in two different microsites, namely the central part and the peripheral part of each snowbed plot. We characterised their phenological cycle and length and their success in seed setting, measured as the number of individuals succeeding in dispersing their seeds.     

The role of the storage carbon of cotyledons in the establishment of seedlings of Hymenaea courbaril under different light conditions

BACKGROUND AND AIMS: Hymenaea courbaril (Leguminosae-Caesalpinioideae) is a tree species with wide distribution through all of the Neotropics. It has large seeds (approx. 5 g) with non-photosynthetic storage cotyledons rich (40 %) in a cell wall polysaccharide (xyloglucan) as a carbon reserve. Because it is found in the understorey of tropical forests, it has been considered as a shade-tolerant, late-secondary species. However, the physiological mechanisms involved in seedling establishment, especially regarding the interplay between storage and light intensity, are not understood. In this work, the ecophysiological role of this carbon cotyledon reserve (xyloglucan) is characterized, emphasizing its effects on seedling growth and development during the transition from heterotrophy to autotrophy under different light conditions. METHODS: Seedlings of H. courbaril were grown in environments with different light intensities, and with or without cotyledons detached before xyloglucan mobilization. Development, growth, photosynthesis and carbon partitioning (dry mass and [14C]sucrose) were analysed in each treatment. KEY RESULTS: The detachment of cotyledons was not important for seedling survival, but resulted in a strong restriction (50 % less) of shoot growth, which was the main sink for the cotyledon carbon reserves. Carbon restriction promoted an early maturation of the photosynthetic apparatus without changes in the net CO2 fixation per unit area. The reduced surface area of the first leaves in seedlings without cotyledons was evidence of limited growth and development of seedlings in low light conditions (22 micromol m(-2) s(-1) photon flux). CONCLUSIONS: There is an increase in the importance of storage xyloglucan in cotyledons for H. courbaril seedling development as light intensity decreases, confirming that this polymer plays a key role in the adaptation of this species to establish successfully in the shadowed understorey of the forest.     

The role of cytokinins in root development of pea seedlings

Endogenous cytokinin-like activity was detected in pea seedlings usingthe soybean callus bioassay. Higher levels of activity were found in two-day-oldseedling roots and in the root free zone of four-day-old seedlings compared tothe lateral root zone of four-day-old seedlings. By day six, the levels ofendogenous cytokinin-like activity was greatly reduced in both the lateral rootzone and root free zone. Decapitation of the root tip disrupted the spatialorganization of the root. Lateral roots were subsequently found along the entirelength of the root rather than in a discreet lateral root zone. Application of10^–3 M dihydrozeatin to decapitated root tipsovercame the effect of root tip removal and restored the situation to what isnormally found in intact roots. There was little mobility of dihydrozeatin inthe root, with applied ³H-DHZ not moving from the root free zone,even 24 h after application.     

Plastid development in seedlings of Echinochloa crus-galli var. oryzicola under anoxic germination conditions

Plastid development in the primary leaf of Echinochloa crus-galli (L.) Beauv. var. oryzicola (Vasing.) Ohwi was followed during 5 d of anoxic germination and growth. Plastids develop slowly from simple spheroidal proplastids into larger pleomorphic plastids with several stromal membranes and many peripheral membrane vesicles. A small prolamellar body is present at 96 h with perforated (pro)thylakoids extending into the stroma. Changes in starch grains and plastoglobuli are evidence of carbohydrate and lipid metabolism. Plastid division is indicated by dumbbell plastid profiles after 4 d of anoxia. These results demonstrate that plastids not only maintain their integrity during anaerobic germination but also show developmental changes involving an increase in internal membrane complexity, although to a lesser extent than in etiolated shoots.Abbreviation PLB prolamellar body Scientific paper No. 6167. College of Agriculture, Washington State University, Pullman     

From seed to seed: the role of photoreceptors in Arabidopsis development

As sessile organisms, plants have evolved a multitude of developmental responses to cope with the ever-changing environmental conditions that challenge the plant throughout its life cycle. Of the many environmental cues that regulate plant development, light is probably the most important. From determining the developmental pattern of the emerging seedling, to influencing the organization of organelles to best maximize energy available for photosynthesis, light has dramatic effects on development during all stages of plant life. In plants, three classes of photoreceptors that mediate light perception have been characterized at the molecular level. The phytochromes recognize light in the red portion of the spectrum, while cryptochromes and phototropins perceive blue and UVA light. In this review, we discuss the different aspects of development that are regulated by these photoreceptors in the model plant species Arabidopsis thaliana and how the phytochromes, cryptochromes, and phototropins bring about changes in development seen in the growing plant.     

The role of fleshy pericarp in seed germination and dispersal under flooded conditions in three wetland forest species

In flooded habitats, inundations affect important forest regeneration processes, such as seed dispersal and germination. The main seed dispersal mechanism used by species in Austral South American temperate swamp and riparian forests is endozoochory, which releases seeds from the fleshy pericarp. Endozoochory could be favorable or unfavorable in wetland habitats, since this mechanism exposes seeds directly to water and can, in some cases, be detrimental to germination. In this study, we studied whether or not the fleshy pericarp favors germination after the flooding period's end. Furthermore, we quantified if the number of days which the fruit was found to be floating related to its germination success. We used the seeds of three common fleshy fruit species of flooded habitats from southern Chile, the trees Luma apiculata and Rhaphithamnus spinosus, and the vine Luzuriaga radicans. We simulated flooding periods of 7, 15, 30 and 45 days submerging seeds, with and without pericarps, in water. We found that the pericarp's presence significantly increased Luma's germination success and significantly decreased that of Luzuriaga. The germination of Rhaphithamnus was low after periods of flooding in both seed treatments, with no significant differences found between them. The fruits could float for an average of one to four weeks, depending on the species, which did not relate to their germination success. These results show that germination was affected by the presence of fleshy pericarps in flooded conditions and furthermore, that flotation allows for hydrochory from one week to one month. We suggest that in swamp forests multiple seed dispersal mechanisms are advantageous, especially for fleshy-fruited species.     

The role of biofouling development in the loss of seed mussels in aquaculture

The efficient seeding of juvenile mussels is critical to the sustainability and profitability of mussel aquaculture. However, seeding mussels is highly inefficient, with many juveniles being lost in the following few months. One possible cause of these losses could be the development of biofouling assemblages. Therefore, the relationships between biofouling accumulation and losses of juveniles were assessed. Losses of juvenile mussels were initially high (42.9–49.1% over approximately one to two weeks), with lower rates of loss over the following four to five months. Biofouling development followed a successional pattern beginning with colonisation by amphipods, subsequent establishment of macroalgae, and the formation of an assemblage dominated by mussels and sessile invertebrates. However, biofouling development did not play a major role in the loss of juveniles. Rather, large-scale losses of mussels occurred shortly after seeding when biofouling was scant, suggesting alternative causes of loss were in operation.     

土壤水分变化对长白山主要树种蒙古栎幼树生长的影响

选择长白山红松阔叶林主要优势树种蒙古栎为研究对象,人工控制3种施水量研究蒙古栎幼树形态、生物量效应和光合生理特征对土壤含水量变化的响应．结果表明,不同土壤含水量变化显著影响蒙古栎叶片、枝、根的生物量及其分配格局和叶片光合气体交换特征．水分胁迫改变幼树树冠结构,抑制幼树树高、地径、叶片大小、地上和地下生物量;同时,蒙古栎幼树根冠生物量比随着土壤水分含量的减少显著提高;供水量减少对幼树净光合速率、CO2利用率和碳利用率等特征有显著的负向影响;而叶片气孔导度、蒸腾速率和水分利用率对不同土壤含水量反应较复杂,只在土壤含水量较低时,幼树气孔导度、蒸腾速率明显降低,叶片水分利用率升高,表现出蒙古栎树种是干旱可变植物,长期水分胁迫可提高树种的耐旱能力．     

Non-redundant functions of sHSP-CIs in acquired thermotolerance and their role in early seed development in Arabidopsis

Heat-shock proteins (HSPs) are a group of evolutionarily conserved polypeptides whose expression is induced in all organisms in response to environmental stresses and during various developmental processes. In this work, we show that the rose (Rosa hybrida) cytoplasmic 17.5-kDa Class I small HSP (sHSP17.5-CI, accession number: BQ103946) increases dramatically during flower development, and accumulates in closed bud petals and leaves only in response to heat stress. mRNA for a putative ortholog of this protein is also found in petals, but not leaves, of Arabidopsis (Arabidopsis thaliana) plants grown under optimal conditions, and it accumulates in leaves in response to heat stress. Analysis of Arabidopsis T-DNA insertion lines affected at three homologous genes revealed that their acquired thermotolerance, as measured by hypocotyl-elongation assay, is impaired. The correlation between sHSP-CI accumulation and expansion of rose petal cells, impairment of acquired thermotolerance, and defects in early embryogenesis of the double mutants (hsp17.4/hsp17.6A), all suggest that sHSP-CI proteins play a role in protecting cell proteins at various developmental stages, whereas in hypocotyl elongation they have a non-redundant function in acquired thermotolerance but have a redundant function in early embryogenesis.     

Influence of short‐term drought conditions and subsequent re‐watering on the physiology and proteome of Lolium multiflorum/Festuca arundinacea introgression forms,with contrasting levels of tolerance to long‐term drought

Festuca arundinacea is a drought tolerant species. Lolium multiflorum has better forage quality but lower tolerance to abiotic stresses. Their hybrids offer an opportunity to perform research on the molecular basis of tolerance to drought. The aim of this work was to recognise the mechanisms of response to short‐term drought (11 days) in a glasshouse in two L. multiflorum/F. arundinacea introgression forms with distinct levels of tolerance to long‐term drought (14 weeks) in the field. Measurements of physiological parameters, analyses of protein accumulation profiles using two‐dimensional gel electrophoresis, and mass spectrometry identification of proteins, which were accumulated differentially between the selected genotypes during short‐term drought, were performed. Genotype 7/6, with lower yield potential during 14 weeks of drought, and lower ability to re‐grow after watering, had a higher capacity for photosynthesis during 11 days of drought. Genotype 4/10, more tolerant to long‐term drought, was able to repair damaged cell membranes after watering and was also characterised by lower transpiration during short‐term drought. A total of 455 proteins were analysed, and the 17 that were differentially accumulated between the two genotypes were identified. The results of physiological and proteomic research led to a hypothesis that the higher photosynthetic capacity of genotype 7/6 could be due to a more efficient Calvin cycle, supported by higher accumulation of crucial proteins involving chloroplast aldolase.     

The role of the pod in seed development: strategies for manipulating yield

Pods play a key role in encapsulating the developing seeds and protecting them from pests and pathogens. In addition to this protective function, it has been shown that the photosynthetically active pod wall contributes assimilates and nutrients to fuel seed growth. Recent work has revealed that signals originating from the pod may also act to coordinate grain filling and regulate the reallocation of reserves from damaged seeds to those that have retained viability. In this review we consider the evidence that pods can regulate seed growth and maturation, particularly in members of the Brassicaceae family, and explore how the timing and duration of pod development might be manipulated to enhance either the quantity of crop yield or its nutritional properties.