Sun Plants Research Articles

Corn Response to Competition: Growth Alteration vs. Yield Limiting Factors

Competition mechanisms among adjacent plants are not well understood. This study compared corn growth and yield responses to water, N, and shade at 74,500 plants ha−1 (1×) with responses to water and N when planted at 149,000 plant ha−1. Plant biomass, leaf area, chlorophyll content, reflectance, and enzyme expression (transcriptome analysis) were measured at V‐12. Grain and stover yields were measured with grain analyzed for 13C isotopic discrimination (Δ) and N concentration. At V‐12, 60% shade plants had increased chlorophyll and reduced leaf area and height compared to full sun plants. In the 2× treatment, plants had 11% less chlorophyll than 1× plants with leaf area and height similar to 60% shade plants. At harvest, plants in the 2× treatment were smaller, had increased water and N use efficiency, and an 11% per hectare yield increase compared with the 1× unstressed treatment. Per‐plant yields from 60% shade and 2× treatments were 50% less than 1× unstressed treatment. Yield reduction in shaded plants was attributed to light stress. Lower yield in the 2× treatment was attributed to a population‐density induced 20% decrease in the red/near‐infrared (NIR) ratio, which resulted in downregulation of C4 carbon metabolism enzymes (phosphoenolpyruvate carboxykinase, phosphoenolpyruvate carboxylase, and pyruvate orthophosphate dikinase). Although the net impact of high plant density and shade stress on per‐plant yield were similar, the stress compensation mechanisms differed.

Water deficit affects mesophyll limitation of leaves more strongly in sun than in shade in two contrasting Picea asperata populations

The aim of this study was to examine the response of internal conductance to CO(2) (g(i)) to soil water deficit and contrasting light conditions, and their consequences on photosynthetic physiology in two Picea asperata Mast. populations originating from wet and dry climate regions of China. Four-year-old trees were subjected to two light treatments (30% and 100% of full sunlight) and two watering regimes (well watered, drought) for 2 years. In both tested populations, drought significantly decreased g(i) and the net photosynthesis rate (A) and increased carbon isotope composition (delta(13)C) values in both light treatments, in particular in the sun. Moreover, drought resulted in a significantly higher relative limitation due to stomatal conductance (L(s)) in both light treatments and higher relative limitation due to internal conductance (L(i)) and abscisic acid (ABA) in the sun plants. The results also showed that L(i) (0.26-0.47) was always greater than L(s) (0.12-0.28). On the other hand, drought significantly decreased the ratio of chloroplastic to internal CO(2) concentration (C(c)/C(i)), photosynthetic nitrogen utilization efficiency (PNUE) and total biomass in the sun plants of the wet climate population, whereas there were no significant changes in these parameters in the dry climate population. Our results also showed that the dry climate population possessed higher delta(13)C values with higher ratio of internal conductance to stomatal conductance (g(i)/g(s)), suggesting that increasing the g(i)/g(s) ratio enhances water-use efficiency (WUE) in plants evolved in arid environments. Thus, we propose that the use of the g(i)/g(s) parameter to screen P. asperata plants with higher water deficit tolerance is certainly worthy of consideration. Furthermore, g(i) is an important variable, which reflects the population differences in PNUE, and it should thus be included in plant physiological investigations related to leaf economics.

Differential induced response to generalist and specialist herbivores by Lindera benzoin (Lauraceae) in sun and shade

Theoretically, induced defenses should be prevalent within low resource environments like the forest understory where constitutive defenses would be costly. Also, the induced response should be stronger when the herbivore is a generalist rather than a specialist, which often have mechanisms to avoid or overcome plant defenses. These ideas have been previously tested for herbaceous species, and we examined these predictions in Lindera benzoin (spicebush), a common woody shrub of the eastern deciduous forest. Lindera benzoin plants in contrasting light environments served as control plants or were subjected to one of four treatments: application of jasmonic acid, clipping, herbivory by the specialist Epimecis hortaria (tulip tree beauty) and herbivory by the generalist Spodoptera exigua (beet armyworm). Following treatment, we assessed induced responses by measuring leaf chemistry (C/N ratio, protein content, and peroxidase activity), and by using insect bioassays with E. hortaria larvae. We found no difference in peroxidase activity between light environments in controls, plants treated with clipping or jasmonic acid. In plants subject to insect herbivory, peroxidase activity was greater in shade plants than in sun plants. The magnitude of this increase in the shade varied between the herbivores, with a 32 fold increase in plants exposed to the generalist S. exigua and a 9 fold increase in plants exposed to the specialist E. hortaria. Leaves from shade plants had more protein and lower C/N ratios than leaves from sun plants, regardless of induction treatment. In control plants, E. hortaria larvae consumed more leaf biomass and achieved greater final weights in the sun than in the shade, but these differences disappeared with induction treatments were applied. These results are among the first to show rapid induction in a woody plant, and different levels of induction with light environments and with specialist versus generalist herbivores.

Antioxidant defences and oxidative damage in salt-treated olive plants under contrasting sunlight irradiance

The interactive effects of root-zone salinity and sunlight on leaf biochemistry, with special emphasis on antioxidant defences, were analysed in Olea europaea L. cv. Allora, during the summer period. Plants were grown outside under 15% (shade plants) or 100% sunlight (sun plants) and supplied with 0 or 125 mM NaCl. The following measurements were performed: (1) the contribution of ions and soluble carbohydrates to osmotic potentials; (2) the photosystem II (PSII) photochemistry and the photosynthetic pigment concentration; (3) the concentration and the tissue-specific distribution of leaf flavonoids; (4) the activity of antioxidant enzymes; and (5) the leaf oxidative damage. The concentrations of Na(+) and Cl(-) were significantly greater in sun than in shade leaves, as also observed for the concentration of the 'antioxidant' sugar-alcohol mannitol. The de-epoxidation state of violaxanthin-cycle pigments increased in response to salinity stress in sun leaves. This finding agrees with a greater maximal PSII photochemistry (F(v)/F(m)) at midday, detected in salt-treated than in control plants, growing in full sunshine. By contrast, salt-treated plants in the shade suffered from midday depression in F(v)/F(m) to a greater degree than that observed in control plants. The high concentration of violaxanthin-cycle pigments in sun leaves suggests that zeaxanthin may protect the chloroplast from photo-oxidative damage, rather than dissipating excess excitation energy via non-photochemical quenching mechanisms. Dihydroxy B-ring-substituted flavonoid glycosides accumulate greatly in the mesophyll, not only in the epidermal cells, in response to high sunlight. The activity of antioxidant enzymes varied little because of sunlight irradiance, but declined sharply in response to high salinity in shade leaves. Interestingly, control and particularly salt-treated plants in the shade underwent greater oxidative damage than their sunny counterparts. These findings, which conform to the evolution of O. europaea in sunny environments, suggest that under partial shading, the antioxidant defence system may be ineffective to counter salt-induced oxidative damage.

Morphological variation of Aechmea distichantha (Bromeliaceae) in a Chaco forest: habitat and size‐related effects

Plants show different morphologies when growing in different habitats, but they also vary in their morphology with plant size. We examined differences in sun- and shade-grown plants of the bromeliad Aechmea distichantha with respect to relationships between plant size and variables related to plant architecture, biomass allocation and tank water dynamics. We selected vegetative plants from the understorey and from forest edges of a Chaco forest, encompassing the whole size range of this bromeliad. Plant biomass was positively correlated with most architectural variables and negatively correlated with most biomass allocation variables. Understorey plants were taller and had larger diameters, whereas sun plants had more leaves, larger sheath area, sheath biomass and sheath mass fraction. All tank water-related variables were positively correlated with plant biomass. Understorey plants had a greater projected leaf area, whereas sun plants had higher water content and evaporative area. Plasticity indices were higher for water-related than for allocation variables. In conclusion, there were architectural and biomass allocation differences between sun- and shade-grown plants along a size gradient, which, in turn, affected tank water-related variables.

Effects of smoke, heat, darkness and cold stratification on seed germination of 40 species in a cool temperate zone in northern Japan

The effects of smoke, heat, darkness and cold stratification on seed germination were examined for 40 species with various life history attributes. These species establish in early successional stages on a volcano and are distributed in cool temperate zones of northern Japan. Smoke decreased seed germination in 11 species and increased it in one species, Leucothoe grayana. Germination of Polygonum longisetum was enhanced by a combination of smoke and cold, and that of Aralia elata by smoke and heat. Heat increased germination for three species and decreased it for one. Cold stratification broke dormancy in seeds of 11 species. Continuous darkness decreased germination of 22 species and did not increase germination for any species, showing that approximately half of the species require light for maximum germination. Although most species are sun plants that establish in early stages of succession and/or in disturbed areas, smoke and heat do not enhance germination of these species after disturbance, even when the disturbance is fire. Germination of slender and/or large seeds tends to be decreased more by smoke, probably because of their larger surface area. Light is more important than smoke and heat for detection of disturbance and for seed germination in this region. However, despite the low fire frequency in the region, germination of a few species was increased by fire-derived stimuli.

Assessment of Photosynthesis Tolerance to Herbicides, Heat and High Illumination by Fluorescence Imaging

Fluorescence imaging represents a non-invasive tool for revealing and understanding spatial heterogeneity in leaf performance caused by external factors, such as abiotic stress. Sun (Rosa meillandina and Chrysanthemum morifo- lium) and shade (Spathiphyllum wallisii) plants were used to study their tolerance to heat and high illumination. Fluores- cence yield, effective PSII quantum yield and non-photochemical quenching were analysed in leaves attached to plants by fluorescence imaging. The control plants of all species showed homogeneous images of the fluorescence parameters throughout the leaf. The fluorescence yield (F) was 0.1 or less, the effective PSII quantum yield (Y(II)) around 0.75 and non-photochemical quenching (NPQ) less than 0.3. The two sun plants showed higher tolerance to stress conditions. Few variations were observed in F and Y(II) images after stress photoperiods and some leaf regions showed an increase in NPQ, indicating more thermal energy dissipation in these zones than in other leaf regions. The images of the fluorescence parameters were similar to those of control plants after one recovery photoperiod without stress conditions. Shade plant showed lower tolerance and irreversible damage was observed after the first photoperiod, particularly at the base of the leaf and in the areas adjacent to the ribs. The centre and top of the leaf were less damaged, and effective PSII quantum yield remained high because the leaf curved to reduce the incident radiation. Incubation with the herbicides DCMU and paraquat led to differences in the fluorescence parameter images. The effect of DCMU (0.1 mM) was visible after 30 min incubation, beginning at the ribs and adjacent areas of the leaf. The three species studied showed different degree of sensi- tivity to paraquat (0.2 mM), and the effective quantum yield in each species was affected at different incubation times.

High-nitrogen and low-irradiance can restrict energy utilization in photosynthesis of successional tree species in low subtropical forest

Responses of photosynthesis and the partition of energy utilization to high-nitrogen importation and high-light intensity in leaves of three dominant tree species of subtropical forest, including sun plant or early-successional species Schima superba, mesophyte or intermediate-successional species Canstanopsis hystrix, and shading-tolerant plant or late-successional species Cryptocarya concinna were studied by using the CO(2) exchange system and chlorophyll fluorescence method. Our results showed that, regardless of plant species, net photosynthetic rate (P (n)) was higher in high-nitrogen supply and high irradiance (HNHL) plants than in low-nitrogen supply and high irradiance (LNHL) plants, implying that low-nitrogen importation would limit P (n) of plants grown under high irradiance. However, high-nitrogen supply and low irradiance (HNLL) plants had a lower P (n). Insignificant change of quantum yield (F (v)'/F (m)') in opened PS II was found in leaves of HNHL, LNHL or HNLL plants of S. superba and C. hystrix, while a higher F (v)'/F (m)' occurred in HNHL plants of C. concinna in comparison with LNHL or HNLL plants. The HNHL plants of C. concinna also had a higher photochemical quantum yield (DeltaF/F (m)') than LNHL or HNLL plants, however no similar responses were found in plants of S. superba and C. hystrix (P <0.05). In the irradiance range of 0-2000 mumol photon.m(-2) .s(-1), the fraction of energy consumed by photochemistry (varphi (PSII)) was 18.2% in LNHL plants of S. superba which was higher than that in HNHL plants (P>0.05) and it was significantly higher than in HNLL plants (P<0.05). C. hystrix also had a similar response in varphi (PSII) to nitrogen supply and irradiance. Regardless of species HNLL plants had a significant varphi (PSII) and higher heat dissipation in light, and this effect was more severe in C. concinna than in S. superba or C. hystrix. The results may mean that high-nitrogen importation by nitrogen deposit and low irradiance caused by changing climate or air pollution would more severely restrict photosynthetic processes in the late-successional species C. concinna than in the early-successional species S. superba and intermediate-successional species C. hystrix. The continuous high-nitrogen precipitation in the future and the over cast mist or pollution smoke could induce late-successional species to degrade, however, early-successional species would be more adapted to competition for more resources to keep their dominance in ecosystems. In this sense, the zonal vegetation may accelerate degradation caused by high nitrogen precipitation and low irradiance, while the early-successional and mesophytic vegetations can remain longer. Thus, nitrogen precipitation may play an important role in plant community succession.

Interactions of water stress and solar irradiance on the physiology and biochemistry of Ligustrum vulgare

We studied the interactive effects of water stress and solar irradiance on physiological and biochemical traits in Ligustrum vulgare L., with special emphasis on antioxidant enzymes and flavonoids. Water relations, photosynthetic performance, plant growth, activities of antioxidant enzymes and of phenylalanine-ammonia-lyase, and concentrations of nonstructural carbohydrates and phenylpropanoids were measured in plants growing in 12% (shade) or 100% (sun) sunlight and supplied with 100 or 40% of daily evapotranspiration-demand over a 4-week period. The mild water stress treatment caused leaf water potential and relative water content to decline on average by -0.22 MPa and 4.5%, respectively. In response to the water stress treatment, photosynthetic rates decreased more in sun plants than in shade plants, likely because of declines in photosystem II photochemistry, apparent maximum rate of carboxylation and apparent maximum electron transport rate coupled with significant reductions in stomatal conductance. Antioxidant enzymatic activities, which were much greater in sun leaves than in shade leaves under well-watered conditions, increased (particularly the enzymatic activities associated with hydrogen peroxide removal) in response to water stress only in shade leaves. Antioxidant phenylpropanoids, particularly quercetin and luteolin derivatives, markedly increased in response to full sunlight irrespective of water treatment; however, antioxidant phenylpropanoid concentrations increased in response to water stress only in shade leaves. We suggest that: (1) assimilated carbon in sun plants was used largely to support an effective antioxidant system capable of countering water-stress-induced oxidative damage--an example of cross tolerance; and (2) in shade plants, carbon was also diverted from growth to counter oxidative damage driven by the mild water-stress treatment. Both findings are consistent with the nearly exclusive distribution of L. vulgare in well-watered, partially shaded Mediterranean areas.

Photoperiod, light quality, and irradiance effects on flowering in the alpine and prairie ecotypes of Stellaria longipes

Plants growing in vegetative shade are subjected to reductions in both red to far-red (R/FR) light ratio and in irradiance levels of photosynthetically active radiation (PAR). In this report we have attempted to uncouple the reduced R/FR ratio- and low PAR-mediated effects of shade on flowering in the ramets of Stellaria longipes Goldie s.l. (Caryophyllaceae) ecotypes collected from alpine “sun” and lower elevation prairie “shade” habitats. Both ecotypes were also tested for their flowering response (defined as the number of open flowers per ramet) to daylength. The alpine ecotype plants can best be classified as day-neutral, whereas prairie ecotype plants require long-days (LD). Under a low PAR of 115 μmol m–2·s–1 given under LD conditions at a reduced (0.7) R/FR ratio, alpine ecotype plants flowered significantly later relative to plants grown under the low PAR at a normal (1.22) R/FR ratio. In contrast, plants of the prairie ecotype flowered earlier under the reduced R/FR ratio combined with the same low PAR. Flower number per ramet differed significantly between the two ecotypes, with alpine ecotype plants developing fewer flowers under a low PAR (109 μmol m–2·s–1 irradiance) relative to a high PAR of 611 μmol m–2·s–1 (both given at a normal R/FR ratio). The prairie ecotype plants responded differently and had similar flower numbers under both low and high PARs at the normal (1.22) R/FR ratio. However, growing the prairie ecotype plants under a reduced R/FR ratio at a low PAR showed a significant increase in number of flowers. In contrast, plants grown under high (2.7) and normal (1.9) R/FR ratios combined with low PAR produced many more flowers than the alpine ecotype. Thus, the two components of shade, reduced R/FR ratio and low PAR can cause distinctly different flowering responses in sun and shade plants of S. longipes.

Effects of moderate high-temperature stress on photosynthesis in three saplings of the constructive tree species of subtropical forest

During the exposition to moderate high-temperature stress, photosynthetic rates and fluorescence of chlorophyll a were measured with a photosynthetic measurement system (Li-Cor 6400) and leaf chamber fluorometer (Li-Cor6400 LCF), respectively, in leaves of saplings, sun-adapted species ( Schima superba), shade-adapted species ( Cryptocarya concinna), and in mesophytic plant ( Castanopsis hystrix) (42°C). The results showed that moderate high-temperature stress led to a decrease in F v/ F m, namely the primary photochemical quantum efficiency, indicating that moderate high-temperature stress causes a partial inhibition of PSII. It also showed that such an effect was more severe in the shade-adapted plant C. concinna than in the sun-adapted species S. superba. However, except for the sun-grown leaves of C. concinna, the moderate high-temperature stress increased the photosynthetic rate of leaves at high light intensity. Simultaneously, less photoinhibition was found to occur under high-light intensity, suggesting that the capacity of resistant-photoinhibition was stimulated by moderate high-temperature stress. The quantum yield of PSII (ϕ PSII) decreased in the sun-grown leaves of S. superba and C. hystrix but did not show any significant change in leaves of the shade plant C. concinna and shade-grown leaves of sun plant S. superba or the mesophytic plant C. hystrix because they already had a very low ϕ PSII under this condition. Moderate high-temperature stress led to a decrease in ϕ PSII/ϕ CO 2 ratios, an estimate of the quantum requirement for CO 2 assimilation, in the sun plant S. superba and the mesophytic plant C. hystrix because they were associated with the dissipation of a lower fraction of excitation energy. However, no significant changes were found in shade plant C. concinna and in shade-grown leaves of the other examined plants. The effect of moderate high-temperature (42°C) on photosynthesis depends on species and leaf type (sun and shade leaves) in the saplings of subtropical broad-leaved trees.

Pigment apparatus in Ajuga reptans plants as affected by adaptation to light growth conditions

Mechanisms of adaptation of the photosynthetic apparatus at the level of pigment complex in a shade-tolerant bugle plant (Ajuga reptans L.) grown at full solar irradiation in an open plot were studied. In “sun” plants, the content of photosynthetic pigments decreased markedly as compared to “shade” plants grown under a forest canopy at 5–10% of the full solar irradiation. In leaves of sun plants, the portion of β-carotene and lutein in the carotenoid spectrum was higher than in shade plant leaves, antheraxanthin and zeaxanthin were present, and de-epoxidation of violaxanthin was by an order of magnitude higher in sun plant leaves reaching 40%. The data obtained indicate the role of the violaxanthin cycle in the protection of photosynthetic apparatus in a shade-tolerant plant against destruction under excessive irradiation.

Photosynthetic light responses of a widespread moss, Sanionia uncinata, from contrasting water regimes in the high Arctic tundra, Svalbard, Norway

Photosynthetic responses to light intensity were investigated under field conditions in Sanionia uncinata growing in contrasting water regimes in the high arctic tundra. Carbon dioxide exchange measurements were made using an infra-red gas analyser under ambient environmental conditions (CO2 concentration, 363–370 p.p.m.; air temperature, 12–15°C) at near optimum hydration on sunny days. The sunlight was reduced using layers of shade cloth. The photosynthetic photon flux density required to saturate net photosynthesis (PPFDsat) of Sanionia growing in a dry and wet site was 484 and 990 μmol m−2 s−1, respectively. The PPFD at which there was zero net exchange of CO2 (PPFDcomp) in dry and wet sites was 34 and 100 μmol m−2 s−1, respectively, and the PPFD at the point of 50% of the light saturated net photosyntheric rate (PPFDhalf) in dry and wet sites was 138 and 306 μmol m−2 s−1, respectively. The findings suggest that Sanionia growing in the wet site appears to require high radiation for photosynthesis. The light-saturated net photosynthetic rate (Pmax) in dry and wet sites was 0.84 and 1.42 mg CO2 g−1 s−1, respectively, and dark respiration rates (Rdark) were 0.21 and 0.57 mg CO2 g−1 s−1, respectively. NPmax and Rdark were >1.5-fold lower in the dry site than the wet site. These results suggest that Sanionia found in dry habitats is shade plants (sciophilous) while Sanionia in wet habitats is sun plants heliophilous.

Stem and leaf growth of alpine sun and prairie shade ecotypes of Stellaria longipes under different photoperiods: role of ethylene

Plant ecotypes of Stellaria longipes Goldie from competitive, shade-adapted prairie habitat and less competitive, nonshaded alpine habitat were subjected to shortened or extended photoperiod conditions. Increasing daylength was positively correlated to increased stem elongation in both ecotypes. Leaf length and area for shade (prairie) plants was significantly altered with increased photoperiods, whereas sun (alpine) plants exhibited minimal leaf expansion in response to increased photoperiod. Increased ethylene evolution in the alpine genotype during rapid stem elongation and extended photoperiods suggests that ethylene plays a growth regulatory role in this sun-adapted genotype. The prairie genotype evolved less ethylene during these same periods, indicating either a diminished requirement for elevated ethylene to effect elongation and leaf expansion responses or possibly increased ethylene sensitivity because of interactions with other hormones, such as gibberellin or auxin. The sun genotype consistently produced more ethylene than the shade genotype under all photoperiod treatments. We conclude that photoperiod alters stem elongation and leaf expansion responses; similar trends were observed for extended photoperiods as were observed for shaded conditions, specifically low light intensity (photosynthetically active radiation) conditions. Further, ethylene levels altered during these responses, especially in sun-adapted alpine plants, which suggests that ethylene is involved in these growth responses.

Photosynthesis, transpiration and water use efficiency of six (6) indigenous tree seedlings for two (2) years in a nursery in the Philippines

Ecophysiological assessment of seedlings of six (6) indigenous were conducted in the nursery for two years. Light compensation point ranges from 10 to 20 μmol m-2 s-1 which is in the boundary between shade and sun plants. A. thurifera and H. plagata consistently exhibited the highest photosynthetic rates, while S. almon and S. contorta had the lowest rates. Transpiration was relatively high from P. malaanonan, A. thurifera and H. plagata. Water use efficiency was high in A. thurifera, H. plagata and P. nodosa. The implications of the ecophysiological performance of the species to site selection (dry vs. moist sites), use of nurse trees and silvicultural treatments like thinning were explained. H. plagata and P. nodosa would have higher chances of survival and growth in drier sites than the other species. The rest of the species would require planting them in sites with high soil moisture or the provision of nurse trees temper evapo‐transpiration in case of dry sites. The study showed the potential of using ecophysiological parameters in designing improved silvicultural management for indigenous trees in the Philippines for plantation development.

Niche characteristics of dominant populations of vegetation in Mian Mountain, Shanxi

Mian Mountain is located in the northern of Taiyue Ranges and the middle south of Shanxi,at 36°50′N,112°5′E.In this paper,the niche breadth and niche overlapping of 25 dominant populations of vegetation in Mian Mountain,Shanxi,were studied by using Shannon-Weaver index and Portraits's method.The result indicated that the niche breadth of Quercus liaotungensis(2.458 7),Prunus davidiana(2.342 2),Spiraea,pubescens(2.306 1),Carex lanceolata(2.518 7) and Artemisia brachyloba(2.218 2) were more than that of other species because these species had wide ecological amplitude,and extensive adaptation to environment,which were constructive or dominant species in the communities.There was not completely general overlapping among all 25 species because of their different biological characters and different adaptation to environment.In the arborous layer,there was less niche overlapping between species-pairs except Q.liaotungensis.The niche overlapping between Abelia biflora and S.pubescens(0.663),P.davidiana and Lespedeza bicolor(0.587) were more than that of other species-pairs in the shrub layer. The niche overlapping between C.lanceolata and Phlomis umbrosa(0.339),A.gmelinii and A.brachyloba(0.245) were more than that of the other species-pairs in the herb layer.The species-pairs having more niche overlapping had similar biological characters and similar adaptation to environment;on the contrary,those having less niche overlapping had different biological traits and different adaptation to environment.For example,A.biflora and S. pubescens,C.lanceolata and Phlomis umbrosa were shade-tolerant plants and had some shade tolerance,otherwise P.davidiana and L.bicolor,A.gmelinii and A.brachyloba were sun plants.

Morphological and physiological responses of Cedrela Fissilis Vellozo (Meliaceae) seedlings to light

Seeds of Cedrela fissilis Vellozo were planted and maintained under two distinct conditions: at east border of a forest with red: far-red ratio of 1.15 and under canopy with photosynthetic photon flux density of 0.22-7% of full sun radiation and red: far-red ratio of 0.21-0.36. Seedling growth (height and stem diameter) was faster under sun, the development of roots more continuous and the number of leaves almost twice of that of shade plants. The leaf area was 10 times greater in sun plants with 15-25 leaflets per leaf while under shade only 5 to 10 leaflets were found per leaf. In shade plants, a higher proportion of dry mass was found in aerial parts. Leaves of sun plants had the capacity of gas exchange to respond to high light radiation, but leaves adapted to shade presented a lower response to light changes. When shade plants were transferred and maintained under the sun for 15 days, only the young leaves were adapted to increased light radiation, reaching the same photosynthetic rate as sun plants, while old leaves were shed. Sun plants transferred to shade conditions did not lose leaves, but did not reach the same photosynthetic rate attained by shade plants.

LEAF ANATOMY OF DOMINANT PLANT SPECIES IN THE SUCCESSIONAL COMMUNITIES OF XIANGSHAN MOUTNAIN, HUAIBEI, CHINA

The results of eco_anatomical observations on the leaf blades of 5 dominant species in a mixed forest of Xiangshan Mountain, Huaibei, China, indicated that these species share some xeromorphic characteristics such as a developed epidermal cuticle or hairs, total_palisade or flourishing palisade tissue, and developed vascular tissue in middle vein. Ziziphus jujuba var. spinosa and Vitex negundo var. cannabifolia, the two dominant species widely distributed throughout Xiangshan Mountain, show great plasticity in their lamina structure in two aspects: 1) Within the same community, the lamina structure shows temporal developmental plasticity with leaves collected at the beginning of May being more characteristic of sun plants as compared to those in mid September; 2) In different successional community, lamina structure are indicative of environmental plasticity. The shrub_herb communities tend to have xeromorphic/sun leaves, shrub communities have xeromorphic/sun leaves, the sparse mixed forest has mesophytic/sun leaves, and the Platycladus orientalis forest has mesophytic/shade leaves. These differences in leaf anatomy reflect both the ability for plants to adapt heterogeneous habitats as well as differences in the environment of the different communities. The results of non_parameter correlation analysis showed that the lamina structure was influenced by many environment factors, with soil water content, relative humidity and wind velocity being the principle factors. Lamina anatomical characteristics, such as cuticle thickness of the upper epidermis, stomatal density, thickness of the palisade tissue, leaf thickness, xylem thickness and bundle thickness of the middle vein, all were negatively correlated to soil water content and relative humidity and positively correlated to wind velocity.

Shade tolerance, photoinhibition sensitivity and phenotypic plasticity of Ilex aquifolium in continental Mediterranean sites

Shade tolerance, plastic phenotypic response to light and sensitivity to photoinhibition were studied in holly (Ilex aquifolium L.) seedlings transported from the field to a greenhouse and in adult trees in the field. All plants were growing in, or originated from, continental Mediterranean sites in central Spain. Seedlings tolerated moderate but not deep shade. Mortality was high and growth reduced in 1% sunlight. Survival was maximal in 12% sunlight and minimal in full sunlight, although the relative growth rate of the seedlings surviving in high light was similar to that of plants in moderate shade. Maximum photochemical efficiency at predawn was significantly lower in sun plants than in shade plants in the field, revealing chronic photoinhibition that was most pronounced in winter. Plasticity in response to available light varied according to the variable studied, being low for photosynthetic capacity and stomatal conductance, and high for specific leaf area, root:shoot ratio and leaf area ratio, particularly in seedlings. Differences in water relations and hydraulic features between sun and shade plants in the field were marginal. High water potential at the turgor loss point of field-grown plants suggested that holly is sensitive to drought during both the seedling and the adult stage. Low relative growth rates in both high and low light with low physiological plasticity in response to light indicate the existence of a stress-tolerance mechanism. We conclude that holly is a facultative understory plant in areas of oceanic and relatively mild climate, but an obligate understory plant in dry continental areas such as the study site. The impact of abandonment of traditional management practices and climate change on these Mediterranean populations is discussed.

Physiological responses to drought and shade in two contrasting Picea asperata populations

The responses of photosynthetic gas exchange, chlorophyll fluorescence, activities of antioxidant enzymes and lipid membrane peroxidation of two contrasting Picea asperata Mast. populations to 30% of full sunlight (shade) and full sunlight (sun) were investigated under well‐watered and drought conditions. Two contrasting populations were from the wet and dry climate regions in China, respectively. For both populations tested, drought resulted in lower needle relative water content (RWC), CO2 assimilation rate (A), stomatal conductance (gs) and effective PSII quantum yield (Y), and higher non‐photochemical quenching (qN), superoxide dismutase (SOD), ascorbate peroxidase (APX) activities as well as malondialdehyde (MDA) levels and electrolyte leakage in sun plants, whereas these changes were not significant in shade plants. For the wet climate population, shade plants showed higher chlorophyll contents (Chla, Chlb and Chla + b) than sun plants under both well‐watered and drought conditions. Our study results implied that shade, applied together with drought, ameliorated the detrimental effects of drought. On the other hand, compared with the wet climate population, the dry climate population was more tolerant to drought in the sun treatment, as indicated by less decreases in A and mass‐based leaf nitrogen content (Nmass), more responsive stomata, greater capacity for non‐radiative dissipation of excitation energy as heat (analysed by qN), and higher level of antioxidant enzyme activities as well as lower MDA content and electrolyte leakage. These results demonstrated that the different physiological strategies were employed by the P. asperata populations from contrasting climate regions when the plants were exposed to drought and shade.