Does endophyte influence resource acquisition and allocation in defoliated tall fescue as a function of microsite conditions?

Tall fescue [Lolium arundinaceum (Schreb.) Darbysh.] often benefits in terms of productivity and persistence when infected with Neotyphodium coenophialum ([Morgan-Jones and Gams], Glenn, Bacon, and Hanlin) endophyte, but the influence of novel non-ergogenic endophytes is unclear. We conducted a field experiment using container-grown tall fescue plants to determine how plants allocated resources when clipped repeatedly in microsites differing in the amount of available light associated with open (full sun), and partially shaded (about 20 or 40% of full sun) conditions. Plants of the same tall fescue cultivar (Jesup) were host to either a native or novel non-ergogenic fungal endophyte (MaxQ™), or were devoid of endophyte. Seedlings of plants infected with the novel endophyte had slower germination, germinated later, and allocated more photosynthate to shoots than roots, when compared to J− or J+ plants. Herbage production of undisturbed canopies was not influenced by host–endophyte association within a microsite, with more herbage produced at the open than at the heavily shaded site. Clipping plants to a 5- or a 10-cm residue height tended to accentuate differences, with diminished productivity and greater variability occurring when plants were maintained at 5 cm. This trend was supported by allometric resource allocation patterns, and in terms of vegetative propagule mass relative to the number of propagules. Tall fescue, irrespective of host–endophyte association, grown as forage in silvopastoral situations should be managed to maintain no less than a 10-cm residual plant height. Trends in photosynthate allocation and plant size might influence persistence and should be investigated for more than two growing seasons.     

Effect of drought and low light on growth and enzymatic antioxidant system of Picea asperata seedlings

The combined effects of drought and low light on biomass partition, foliar nitrogen concentration, membrane stability and active oxygen species (AOS) and antioxidant system were investigated in dragon spruce (Picea asperata Mast.) seedlings grown at two watering regimes (well-watered, 100% of field capacity and drought, 30% of field capacity) and light availabilities (HL, 100% of full sunlight and low light, 15% of full sunlight). Under high light condition drought not only reduced foliar nitrogen concentration (Nmass) and membrane stability index (MSI) but also significantly increased biomass partitioning to roots, AOS, ascorbic acid (AsA) content and antioxidant enzyme activities including superoxide dismutase (SOD, EC 1.15.1.1), peroxidase (POD, EC 1.11.1.7), catalase (CAT, EC 1.11.1.6), ascorbate peroxidase (APX, EC 1.11.1.11) and glutathione reductase(GR, EC 1.6.4.2). However, no prominently drought-induced differences in biomass partitioning to root, SOD, GR activities, hydrogen peroxide (H₂O₂) and MSI were observed in low light seedlings. On the other hand, significant interaction of drought and low light was found on MSI, the antioxidant enzymes activities (SOD, POD, CAT, APX, GR), H₂O₂ and superoxide radical (O₂ ⁻). These results suggested that seedlings grown at the understory were more sensitive to drought than low light.     

阳生植物和阴生植物的叶黄素循环与非辐射能量耗散X

自然条件下阳生植物和阴生植物的光合速率存在着明显的差距,它们拥有不同的适应强光胁迫的能力,前者明显强于后者。从叶黄素组分来看,阳生植物拥有更大的叶黄素库[紫黄质（V）＋单环环氧玉米黄质（A）＋玉米黄质（Z）],其中Z和[Z＋A]的含量更明显高于阴生植物;从阳生植物或阴生植物内部来看,不同物种间,Z1[Z＋A]和[V＋A＋Z]含量的差异相对较小,A则基本相同;不论是阳生植物还是阴生植物,非光化学猝灭值与Z、[Z＋A]及[V＋A＋Z]含量均呈现较好的正相关关系,后三者含量越高,非光化学猝灭值越大,而且[V＋A＋Z]库的大小与Z含量基本上是成比例增另的。说明在不同植物种间,[Z＋]（主要是Z）仍然是影响非辐射能量耗能的主要因素。     

Exposure to low levels of photosynthetically active radiation induces rapid increases in palisade cell chloroplast volume and thylakoid surface area in sunflower (Helianthus annuus L.)

Summary Sudden changes in photoactive radiation (PAR) (wavelength, 400–700 nm) induces rapid surface area changes in chloroplast thylakoid membranes. Although this response may have important photo-acclimative functions for the plant, little is known about the mechanisms by which changes in irradiance are detected or how thylakoid membranes actually increase or decrease surface area. Knowledge of the time required for significant changes in thylakoid area would help eliminate or support several possible mechanisms that may be involved in this aspect of photo-acclimation in plants. Leaf tissues were acclimated to a PAR of 500 mol quanta per m² per s then exposed to low irradiance (PAR, 50 mol quanta per m² per s) and sampled at 5, 15, 30, and 60 min post exposure. Tissue and cell structure were quantified and results showed a significant increase in the surface-to-volume ratio and surface area per unit of standard leaf volume for both appressed and nonappressed thylakoids within 5 min of exposure to low irradiance. On the basis of the ratios of appressed to nonappressed thylakoids, the surface area of the nonappressed thylakoids was found to increase faster than that of the appressed thylakoids throughout the sample period. The portion of the appressed thylakoids in contact with the stroma was defined as margin thylakoids. Margin thylakoid surface-to-volume ratio did not change relative to the high-irradiance control during the sample period but did remain significantly lower than the low-irradiance control during the sample period. The ratio of appressed to margin thylakoids indicated a broadening and shortening of the appressed thylakoid stack within the first 5 min of low-irradiance exposure. The rapidity of the shade response indicates that the early events in this response probably do not directly involve gene activation pathways.Abbreviations PAR photosynthetically active radiation - Sv surface to volume density - Vv volume density - UV-B ultraviolet B radiation     

UV hazard on a summer’s day under Mediterranean conditions, and the protective role of a beach umbrella

Mediterranean beaches are very crowded during summer and, because of the high values of solar UV radiation, the potential risk for human health is relevant. In this study, all-day measurements of biologically effective global and diffuse UV radiation for skin (UVBE_eryt) and eye (UVBE_pker, UVBE_pconj, UVBE_cat) disorders were carried out on differently tilted surfaces on a summers day on a Mediterranean beach. The role played by beach umbrellas in protection from excessive sun exposure was also investigated. Erythema, photokeratitis and cataract seem to require almost the same exposure time to reach the risk threshold dose. Under full sunlight, the highest global and diffuse UV values are reached on surfaces normally oriented towards sunlight and on horizontal surfaces, respectively. Over vertical surfaces, at this northern hemisphere site, global and diffuse UV radiation reaches maxima values in the south-facing direction around noon, while maxima values are reached early in the morning and late in the afternoon over surfaces facing east and west, respectively. The quality of the beach umbrellas protection (efficiency in blocking solar UV radiation) varies with surface orientation; the highest efficiency for our specific site and geometrical conditions occurs over horizontal surfaces, with efficiency being least over vertical surfaces when incident radiation values are still relevant.     

Life history and population dynamics of the Japanese Yam,Dioscorea japonica thunb.

Shoot morphology at the emergence ofDioscorea japonica Thumb. could be classed into the following three types: (1) a seedling emergence with only one leaf (Se type), (2) a plant consisting of one stem and one leaf, which has emerged from a small tuber (rhizophore) or bulbil less than 50 mg in dry weight (S type) and (3) a twiner with many leaves, which has emerged from a tuber or a bulbil of more than 50 mg in dry weight (L type). The Se type failed to develop beyond the second leaf stage in 1.5% sunlight exposure. The effects of initial plant (seeds, bulbils and tubers) size and light intensity on plant growth were analyzed. The larger the initial plant size was, the greater the growth in height and leaf area was. The distribution ratio of assimilated substances in leaves was high in smaller plants at the early growth stage. The distribution ratio in the tubers of larger plants became high at the early stage of growth. In all three types at over 3% sunlight exposure, the switch-over from the vegetative to reproductive growth phase occurred simultaneously at a later growth stage, but the Se type at 1.5% sunlight exposure showed a very early switch-over in its development; this switch-over may be related to shade tolerance capacity. The L type showed shade avoidance by forming a large productive structure as a twiner     

Efficiency of asbestos shading for growth of Barki rams during hot summer

Twenty-four growing Barki rams, 5–6 months old with an average body weight of 22 kg, were divided into asbestos shaded and unshaded groups during summer. Ad libitum feeding on roughage with 0.5 kg of concentrates per head per day was practiced. Drinking water was available twice daily in the early morning and afternoon. Biweekly observations included rectal temperature (RT; °C), and respiration rate (RR; breaths per minute) at 06:00 h and 14:00 h were recorded. Meteorological data, plasma glucose, calcium, inorganic phosphorus and packed cell volume were also measured. Results indicated that experimental animals developed hyperthermia during June to September, as evidenced by higher (P < 0.01) RT and RR than normal (40 ± 0.05 and 103.9 ± 3.87 vs. 38.9 ± 0.10 and 40 ± 6.56, respectively). Diurnal variations in these physiological phenomena were closely associated (P < 0.05) with ambient temperature changes. As compared with the unshaded group, providing an asbestos shed reduced (P < 0.05) RT and RR in the hyperthermic animals during the day (39.9 ± 0.07 and 94.7 ± 3.75 vs. 40.1 ± 0.08 and 113.1 ± 4.74, respectively), but it increased (P < 0.05) these parameters during summer nights (39.5 ± 0.05 and 82.4 ± 0.95 vs. 39.2 ± 0.07 and 71.6 ± 2.41, respectively). It also increased (P < 0.05) packed cell volume 1 h after morning drinking (35 ± 0.97 vs. 33.2 ± 0.60); reduced (P < 0.05) plasma glucose (43.3 ± 5.88 vs. 53.2 ± 6.31); caused hypocalcemia (10.9 ± 0.35 vs. 11.5 +- 0.43; P < 0.05) and hypophosphatemia (3.9 ±0.35 vs. 4.6 ± 0.34; P < 0.05) as a result of hyperthermia. Monthly variations in all parameters studied were higher (P < 0.01) during early summer. It is concluded that providing an asbestos shed for growing Barki rams under Egyptian summer conditions will not protect the animals from hyperthermia by day and night, as it interferes with extra body heat dissipation to the surroundings during summer nights. Although the unshaded animals were more hyperthermic during summer days, they tended to be normal during the night.     

Clonal growth in Ailanthus altissima on a natural site in West Virginia

Abstract. : The exotic tree Ailanthus altissima is usually confined to open sites. As an exception, Ailanthus established in a densely closed forest in West Virginia, which was analyzed with the aim to elucidate possible pathways of persistence in forest succession of this light-demanding pioneer species. Demographic analysis revealed a seedling mortality of 100 %. Instead, the understory is populated by clonal ramets, ranging from one to more than 19 yr of age, with a mean of 5 yr. Growth averages only 0.11 m/yr, and height is correlated with age. This clonal growth contrasts with the performance of Ailanthus on open sites. The possible ecological benefits of establishing a ramet bank in a resource-poor habitat are considered in terms of space occupation of a pioneer species.     

Eco-physiological studies on the response of taxodiaceous conifers to shading with special reference to the behavior of leaf pigments

The effects of light intensity on the content and composition of leaf pigments, especially of carotenoids, were studied with mature current-year leaves of Taxodiaceous saplings grown under different grades of shade in summer. Both chlorophyll and total carotenoid contents increased with decreasing light intensity, maintaining approximately linear relations between each other, over a range of relative solar radiation of 100% to 7% of full daylight. The regression of total chlorophyll content on mean solar radiation could be well approximated by Shinozaki-Kira's reciprocal equation. The ratio of chlorophyll a to chlorophyll b was smaller in the shade than in the sun. The percentage of α-carotene and violaxanthin in the total carotenoid content tended to increase with increasing degree of shade, while those of β-carotene and lutein were reduced. The eco-physiological meanings of the pigments were considered based on this evidence. The order of shade tolerance among the four species tested is also discussed taking the responses of leaf weight and chlorophyll content to incident light intensity into consideration.     

Leaf dynamics of seedlings of rain forest species in relation to canopy gaps

Summary Leaf dynamics of eight tropical rain forest species seedlings was studied in three environments: the shaded forest understorey, a small gap of ±50 m², and a large gap of ±500 m². Leaf production rate and leaf loss rate were enhanced in gaps, and a large gap resulted in larger increases than a small gap. For most species net leaf gain rate was larger in gaps, although this rate was not always largest in the large gap. Leaf loss decreased, and leaf survival percentages increased with increasing shade tolerance of species, indicating a slower leaf turnover for more shade tolerant species. Leaf area growth rate was only partly determined by net leaf gain rate. Ontogenetic effects on leaf size were also important, especially in the large gap. Species which possessed leaves with high specific leaf weight (SLW) showed lower leaf loss rates and higher leaf survival percentages than species with low SLW leaves. Leaf life span seemed to be related to leafcost per unit area. The relation of specific patterns in leaf production and leaf loss to the regeneration mode of the species is briefly discussed.