Lower Dark Respiration Rates Research Articles

Changes in Photosynthetic Characteristics between Green-Leaf Poplar Linn. "2025" and Its Bud-Sporting Colored-Leaf Cultivars.

Colored-leaf poplar is increasingly popular due to its great ornamental values and application prospects. However, the photosynthetic characteristics of these colored-leaf cultivars have not been well understood. In this study, the photosynthetic differences between green-leaf poplar Populus deltoids Linn. "2025" (L2025) and colored-leaf cultivars 'Zhonghong poplar' (ZHP), 'Quanhong poplar' (QHP), and 'Caihong poplar' (CHP) were investigated on several levels, including chloroplast ultrastructure observation, photosynthetic physiological characteristics, and expression analysis of key genes. The results showed that the photosynthetic performance of ZHP was basically consistent with that of L2025, while the ranges of light energy absorption and efficiency of light energy utilization decreased to different degrees in CHP and QHP. A relatively low water use efficiency and high dark respiration rate were observed in QHP, suggesting a relatively weak environmental adaptability. The differences in chloroplast structure in different colored-leaf poplars were further observed by transmission electron microscopy. The disorganization of thylakoid in CHP was considered an important reason, resulting in a significant decrease in chlorophyll content compared with other poplar cultivars. Interestingly, CHP exhibited extremely high photosynthetic electron transport activity and photochemical efficiency, which were conductive to maintaining its relatively high photosynthetic performance. The actual quantum yield of PSII photochemistry of ZHP was basically the same as that of QHP, while the relatively high photosynthetic performance indexes in ZHP suggested a more optimized photosynthetic apparatus, which was crucial for the improvement of photosynthetic efficiency. The differential expressions of a series of key genes in different colored-leaf poplars provided a reasonable explanation for anthocyanin accumulation and specific photosynthetic processes.

Chlorophyll Fluorescence Parameter as a Tool in Selecting Heat-tolerant Summer-flowering Chrysanthemum (Dendranthema ×grandiflorum)

Chrysanthemum ‘Bai Tian Xing’, ‘Huang Ching Chin’, ‘Pink Pearl’, and ‘NCHU-001’ plants were preheated at 35 °C for 24 hours to induce heat tolerance. The recently fully expanded leaves were detached, kept in a moist Ziploc bag, and then subjected to 35, 40, 45, 47.5, 50, 52.5, 55, 60, or 65 °C for 20 minutes. After dark-acclimatized at room temperature for 30 minutes, leaves were measured for Fv/Fm value with a chlorophyll fluorescence parameter. Results showed that ‘Bai Tian Xing’ had the highest critical (Tcrit) and midpoint temperature (Tmid). Mean Tcrit and Tmid were shown to be 47 and 50 °C, respectively, and Tmid gave greater distinguishment of Fv/Fm value among cultivars. Plants of four cultivars were acclimatized at 15 to 40 °C for 3 days and 35 °C being the most effective temperature to induce a heat-tolerant response in chrysanthemum. Required inducing time to reach a stable leaf Fv/Fm value ranged from 4.6 to 11.1 hours among cultivars. All cultivars had similar required time to reach visible bud between summer and autumn crops (except NCHU-001), but all had delayed flowering in the summer crop. There is a negative linear relationship between flowering heat delay and leaf Fv/Fm value (R2 = 0.93). Progenies from reciprocal crossing of ‘Bai Tian Xing’ × ‘NCHU-001’ and ‘Huang Ching Chin’ × ‘Pink Pearl’ were also subjected to treatments for Fv/Fm measurements and observed for time to flowering in the summer crop. All combinations showed negative linear relationship between time to flowering and leaf Fv/Fm value (R2 = 0.70–0.87). Two plants, 109-W001Y and 109-W003Pi, showed early flowering habit and good flower performance under heat conditions were selected. All four cultivars and the two selected lines were measured for photosynthetic parameters under day/night temperatures of 35/30 or 25/20 °C in growth chambers. All cultivars and lines showed decreased net photosynthetic rate and dark respiration rate under 35/30 °C when compared with 25/20 °C. Relatively higher net photosynthetic rate and lower dark respiration rate in ‘Bai Tian Xing’, ‘109-W001Y’, and ‘109-W003Pi’ under 35/30 °C, when compared with the other three cultivars, might have contributed to better flowering performance in the summer.

Higher temperature, increased CO2, and changing nutrient ratios alter the carbon metabolism and induce oxidative stress in a cosmopolitan diatom

AbstractPhytoplankton are responsible for about 90% of the oceanic primary production, largely supporting marine food webs, and actively contributing to the biogeochemical cycling of carbon. Yet, increasing temperature and pCO2, along with higher dissolved nitrogen: phosphorus ratios in coastal waters are likely to impact phytoplankton physiology, especially in terms of photosynthetic rate, respiration, and dissolved organic carbon (DOC) production. Here, we conducted a full‐factorial experiment to identify the individual and combined effects of temperature, pCO2, and N : P ratio on the antioxidant capacity and carbon metabolism of the diatom Phaeodactylum tricornutum. Our results demonstrate that, among these three drivers, temperature is the most influential factor on the physiology of this species, with warming causing oxidative stress and lower activity of antioxidant enzymes. Furthermore, the photosynthetic rate was higher under warmer conditions and higher pCO2, and, together with a lower dark respiration rate and higher DOC exudation, generated cells with lower carbon content. An enhanced oceanic CO2 uptake and an overall stimulated microbial loop benefiting from higher DOC exudation are potential longer‐term consequences of rising temperatures, elevated pCO2 as well as shifted dissolved N : P ratios.

PHOTOSYNTHETIC RATES HELP EXPLAIN THE DISTRIBUTION OF ARBUTUS XALAPENSIS (TEXAS MADRONE) POPULATIONS

Light response curves were generated using photosynthetic rates measured for mature canopy leaves and leaves from juvenile plants below the canopy of Arbutus xalapensis Kunth (Texas Madrone, Ericaceae) plants in central Texas. We hypothesize that understory juvenile plants will have higher photosynthetic rates at lower light levels and larger leaf areas; and saturate at lower light levels, lower light compensation points, lower dark respiration rates than canopy leaves. Plants were measured in a Juniperus ashei J. Buchholz/Quercus fusiformis Small (Ashe Juniper/Live Oak) hilltop woodland. In the area, A. xalapensis tree density was 2 ± 3 plants/ha x̄ ± 1 standard deviation) and basal area was 210 ± 190 cm2/plant. The photosynthetic flux density (PFD) on a clear sunny day at midday with sun at its zenith was 1870 ± 11 µmol/m2/s at the upper canopy edge; below the canopy light levels were 36 ± 4 µmol/m2/s, indicating the dense shade of the community. No differences were found in maximum photosynthetic rates (Amax), which were ∼ 16 µmol CO2/m2/s, between canopy and subcanopy leaves. Light saturation was slightly over 400 µmol/m2/s for both canopy and subcanopy leaves. Light levels below the canopy were 8.3% of the light saturation point of A. xalapensis, which means the plants were fixing carbon at less than 10% of their potential maximum rate. As indicated by light response curves, photosynthetic rates of leaves below the canopy or in light gaps would increase to the same level as canopy leaves, suggesting that recruitment in shade is possible for this species. However, leaves appear to be adapted to high light, having similar photosynthetic characteristics as high light canopy leaves, suggesting juveniles can respond to light gaps quickly in various community types.

Low Light Increases the Abundance of Light Reaction Proteins: Proteomics Analysis of Maize (Zea mays L.) Grown at High Planting Density.

Maize (Zea mays L.) is usually planted at high density, so most of its leaves grow in low light. Certain morphological and physiological traits improve leaf photosynthetic capacity under low light, but how light absorption, transmission, and transport respond at the proteomic level remains unclear. Here, we used tandem mass tag (TMT) quantitative proteomics to investigate maize photosynthesis-related proteins under low light due to dense planting, finding increased levels of proteins related to photosystem II (PSII), PSI, and cytochrome b6f. These increases likely promote intersystem electron transport and increased PSI end electron acceptor abundance. OJIP transient curves revealed increases in some fluorescence parameters under low light: quantum yield for electron transport (φEo), probability that an electron moves beyond the primary acceptor QA− (ψo), efficiency/probability of electron transfer from intersystem electron carriers to reduction end electron acceptors at the PSI acceptor side (δRo), quantum yield for reduction of end electron acceptors at the PSI acceptor side (φRo), and overall performance up to the PSI end electron acceptors (PItotal). Thus, densely planted maize shows elevated light utilization through increased electron transport efficiency, which promotes coordination between PSII and PSI, as reflected by higher apparent quantum efficiency (AQE), lower light compensation point (LCP), and lower dark respiration rate (Rd).

Intraspecific, ecotypic and home climate variation in photosynthetic traits of the widespread invasive grass Johnsongrass.

Despite their near ubiquity across global ecosystems, the underlying mechanisms contributing to the success of invasive plants remain largely unknown. In particular, ecophysiological traits, which are fundamental to plants’ performance and response to their environment, are poorly understood with respect to geographic and climate space. We evaluated photosynthetic trait variation among populations, ecotypes and home climates (i.e. the climates from the locations they were collected) of the widespread and expanding invader Johnsongrass (Sorghum halepense). We found that populations vary in the maximum net photosynthetic flux and the light-saturated net photosynthetic rate, and that agricultural and non-agricultural ecotypes vary in apparent quantum yield and water-use efficiency (WUE). We also found that populations from warmer home climates had lower dark respiration rates, light compensation points and WUEs. As Johnsongrass expands across the USA the abiotic and biotic environments are driving variation in its genetics, phenotypes and its underlying physiology. Our study demonstrates the importance of evaluating physiological traits in invasive plants, especially as they relate to home climates.

Surviving in the shadows: Light responses of co-occurring Rubiaceae species within a tropical forest understory

The question of how closely related species coexist in the heavily shadowed understory of tropical forests is still not properly clarified. We studied the magnitude of trait variation in twelve morphological, nutritional, and physiological traits related to light response in 85 individuals belonging to nine co-occurring Rubiaceae species in the understory of a tropical forest in Southeast Brazil. Three topographic habitats were chosen from shadowed and more fertile soils in the valley to more open canopies and less fertile soils at slopes and ridge, which were characterized using soil and canopy cover variables. Light curves (A/PAR) were adjusted in five leaves (one leaf per individual plant) for each species and habitat. We compared soil and canopy variables among the topographic habitats, quantified trait dispersion among the nine species, and tested for differences in trait values among habitats and species. Ridge habitat showed the lowest resource availabilities, soil nutrients and water, and a more open canopy. Species distributions in the gradient were best explained by specific leaf area (SLA) and leaf thickness. The Rubiaceae species showed a great investment in leaf nitrogen, regardless of habitat or species. Ridge species maintained low dark respiration rates and light compensation points. Higher SLA values for valley plants allowed greater light-saturated net photosynthetic rates on a mass basis, providing higher positive net carbon balance when compared to the plants in the slope and ridge. Living and survival of these shade plants are possible by very low mean light compensation points. We show that trait differences among topographic habitats in coexisting species of Rubiaceae are important to understanding the organization of tropical forests understory “species swarms”.

Growth, yield formation, and inulin performance of a non-food energy crop, Jerusalem artichoke (Helianthus tuberosus L.), in a semi-arid area of China

Jerusalem artichoke is an important crop that is used as a foodstuff, animal feed, and an energy crop. However, there has been little fundamental research on its breeding, and a lack of elite cultivars has seriously limited its industrial use. This study was conducted to characterize Jerusalem artichoke’s yield formation mechanism based on its growth and photosynthetic characteristics, to identify reliable criteria for high yield cultivar screening, and to guide the breeding of new high yield cultivars. High yield group (MH) cultivars exhibited vigorous aboveground and root growth, higher photosynthetic capacities (especially in terms of their ability to utilize weak light and minimize dark respiration) and lower rates of sexual reproduction than low yield group (ML) cultivars. Traits associated strongly with high yields included a high leaf area index (LAI), plant height, and stem diameter; a low dark respiration rate (Rd), light compensation point (LCP), and light saturation point (LSP); and late maturation with a long vegetative period. In addition, high yields were due more to increases in tuber number than tuber size, and growth under elevated CO2 conditions was identified as a potentially effective way of increasing yields. The tubers of high yield cultivars exhibited elevated inulin contents, and the inulin content depended more on the total sugar content than the reducing sugar content. Because high yield cultivars have low rates of sexual reproduction, it may be necessary to complement hybrid breeding efforts with mutation breeding, molecular breeding, and other breeding strategies to improve Jerusalem artichoke yields.

Photoperiod mediates the effects of elevated CO2 on the growth and physiological performance in the green tide alga Ulva prolifera

Ulva spp., an increasingly important food, are the dominant species of the large-scale green tides. In this study, both the growth and the physiological responses of the Ulva prolifera were studied after cultured in three different light and dark regimes (12:12, 14:10 and 16:8-h light/dark) in combination with current (420 μatm; LC) and increased (1000 μatm; HC) levels of atmospheric CO2. Grown rate of U. prolifera was significantly enhanced by increased CO2 under the three light:dark regimes, especially under 16:8 h-light:dark, indicating that growth was C-unsaturated at present CO2 levels. U. prolifera showed a significantly higher growth rate and lower dark respiration rate (Rd) at 16:8 h-light:dark treatment than at 12:12 h-light/dark treatment, regardless of the CO2 treatment. The photochemical performance was largely unaffected by elevated CO2 and daylength. These results suggest that U. prolifera in a future CO2 enriched coastal water, seems to be resilient to higher CO2 concentrations, and this could be enhanced by longer daylength.

Effects of different rootstocks on the weak light tolerance ability of summer black grape based on 4 photo-response models

The photo response curves of 11 rootstock-scion combinations including summer black/Beta, summer black/1103P, summer black/101-14, summer black/3309C, summer black/140Ru, summer black/5C, summer black/5BB, summer black/420A, summer black/SO4, summer black/Kangzhen No.1, summer black/Huapu No.1 were fitted by rectangular hyperbola mo-del, non-rectangular hyperbola model, modified rectangular hyperbola model and exponential model respectively, and the differences of imitative effects were analyzed by determination coefficiency, light compensation point, light saturation point, initial quantum efficiency, maximum photosynthetic rate and dark respiration rate. The result showed that the fit coefficients of all four models were above 0.98, and there was no obvious difference on the fitted values of light compensation point among the four models. The modified rectangular hyperbola model fitted best on light saturation point, apparent quantum yield, maximum photosynthetic rate and dark respiration rate, and had the minimum AIC value based on the akaike information criterion, therefore, the modified rectangular hyperbola model was the best one. The clustering analysis indicated that summer black/SO4 and summer black/420A combinations had low light compensation point, high apparent quantum yield and low dark respiration rate among 11 rootstock-scion combinations, suggesting that these two combinations could use weak light more efficiently due to their less respiratory consumption and higher weak light tolerance. The Topsis comparison method ranked summer black/SO4 and summer black/420A combinations as No. 1 and No. 2 respectively in weak light tolerance ability, which was consistent with cluster analysis. Consequently, summer black has the highest weak light tolerance in case grafted on 420A or SO4, which could be the most suitable rootstock-scion combinations for protected cultivation.

Impact of Carbon Dioxide and Increasing Nitrogen Levels on Growth, Photosynthetic Capacity, Carbohydrates and Secondary Metabolites in Kacip Fatimah (Labisia pumila)

Aims: This study was designed to investigate how CO2 and nitrogen availability alters growth, leaf gas exchange, primary and secondary metabolites production (total phenolics and flavonoid) in three varieties of L. pumila. namely var alata, var pumila and var lanceolata. under CO2 enrichment (1200 µmol mol-1) combined with four levels of nitrogen fertilization (0, 90, 180 and 270 kg N ha-1) for 15 weeks. Study Design: Three-month old L. pumila seedlings of var. alata, var. pumila and var. lanceolata were left for a month to acclimatize in a nursery until ready for the treatments. Carbon dioxide enrichment treatment started when the seedlings reached 4 months old where plants were exposed to 1200 µmol-1 mol-1 CO2 and fertilized with four levels of nitrogen concentrations viz. 0, 90, 180 and 270 kg N Ha-1. The fertilization with nitrogen levels were split into three applications. A control at ambient CO2 (400 µmol-1 mol-1) with standard N fertilization (180 kg N ha-1) was included to compare plant responses to high CO2 combined with different levels of N. Place and Duration of Study: Faculty of Agriculture Glasshouse Complex, Universiti Putra Malaysia from February to May 2011. Methodology: The seedlings were raised in specially constructed growth houses receiving 12-h photoperiod and average photosynthetic photon flux density of 300 µmol m-2 s-1. Carbon dioxide at 99.8% purity was supplied from a high–pressure CO2 cylinder and injected through a pressure regulator into fully sealed 2 m x 3 m growth houses at 2-h daily and applied continuous from 800 to 1000. Total plant biomass was taken by calculating the dry weight of root, stem and leaf per seedling. Total leaf area per plant was measured using a leaf area meter (LI-3100, Lincoln Inc, USA). The measurement of photosynthesis was obtained from a closed system of infra-red gas analyzer LICOR 6400 Portable Photosynthesis System. The response of net CO2 exchange (A) to changing intercellular CO2 concentration (Ci) was conducted at 27°C, 50% relative humidity and at light saturating conditions of 800 µmol m-2s-1. Anthrone method was used to determine the content of total available carbohydrate. Follin–Ciocalteau reagent was used to determine total phenolics and flavonoid using spectrophotometer. Results: In all parameters measured there were no significant was observed in the three varieties. As the levels of nitrogen increased from 0 to 270 kg N ha-1, plant growth, photosynthesis and total chlorophyll content was enhanced. However, carbohydrate, total phenolics and flavonoid was reduced with the increase in nitrogen fertilization. It was found that the high application of nitrogen can increased the photosynthetic capacity of L. pumila by having high Vcmax (RuBisCO CO2 fixation capacity), A sat (CO2 saturation point) and low dark respiration rate in the analysis of A/Ci curves. The production of secondary metabolites was related to increased total non-structural carbohydrate (TNC) under low nitrogen condition. Photosynthesis, displayed a significant negative relationship with secondary metabolites production. Total chlorophyll content exhibited very significant negative relationships with total soluble sugar, starch and total non-structural carbohydrate. Conclusion: This study demonstrated that enrichment with high levels of CO2 is able to enhance the production of plant secondary metabolites. However, increased nitrogen fertilization can reduce the production of these plant secondary metabolites under CO2 enrichment. When there were accumulation of TNC in plant leaves and reduction in photosynthesis, the production of plant secondary metabolites might be up-regulated. The increase in the production of plant secondary metabolites was indicated by reduction in chlorophyll contents.

Sunfleck limits the small-scale distribution of endangered Kingdonia uniflora in the natural habitat of subalpine forest proved by its photosynthesis

The physiological effects of sunflecks on understory plants are poorly understood. Kingdonia uniflora is an endemic and endangered species in China, with a patchy distribution over much of its range. Sunflecks are reportedly the likely dominant factor in determining its patchy distribution. We studied the photosynthesis of K. uniflora in the field to test whether understory sunflecks result in photoinhibition and, thereby, potentially influence its patchy distribution. K. uniflora exhibited the low dark respiration rates, low light compensation points, and low light saturation points characteristic of shade-tolerant plants, allowing maintenance during the long periods of low understory light. Moreover, K. uniflora was able to regulate light energy utilization by non-photochemical quenching in low light. Gas exchange parameters were measured in six treatments (sunfleck-enriched, sunfleck-enriched with added saturation light, sunfleck-enriched with filtered ultraviolet-B (UV-B) radiation , sunfleck-limited, sunfleck-limited with added saturation light, and sunfleck-limited with filtered UV-B). The sunfleck-enriched treatment caused photoinhibition in K. uniflora, in part due to a UV-B-induced decrease in Pn. In addition, the application of simulated sunflecks indicated that K. uniflora leaves do not need continuous light. The photosynthetic responses of K. uniflora to sunflecks indicate that the sunflecks are a limiting factor in the small-scale distribution of K. uniflora.

Light compensation points in shade-grown seedlings of deciduous broadleaf tree species with different successional traits raised under elevated CO2.

We measured leaf photosynthetic traits in shade-grown seedlings of four tree species native to northern Japan, raised under an elevated CO2 condition, to investigate the effects of elevated CO2 on shade tolerance of deciduous broadleaf tree species with different successional traits. We considered Betula platyphylla var. japonica and Betula maximowicziana as pioneer species, Quercus mongolica var. crispula as a mid-successional species, and Acer mono as a climax species. The plants were grown under shade conditions (10% of full sunlight) in a CO2 -regulated phytotron. Light compensation points (LCPs) decreased in all tree species when grown under elevated CO2 (720 μmol·mol(-1) ), which were accompanied by higher apparent quantum yields but no photosynthetic down-regulation. LCPs in Q. mongolica and A. mono grown under elevated CO2 were lower than those in the two pioneer birch species. The LCP in Q. mongolica seedlings was not different from that of A. mono in each CO2 treatment. However, lower dark respiration rates were observed in A. mono than in Q. mongolica, suggesting higher shade tolerance in A. mono as a climax species in relation to carbon loss at night. Thus, elevated CO2 may have enhanced shade tolerance by lowering LCPs in all species, but the ranking of shade tolerance related to successional traits did not change among species under elevated CO2 , i.e. the highest shade tolerance was observed in the climax species (A. mono), followed by a gap-dependent species (Q. mongolica), while lower shade tolerance was observed in the pioneer species (B. platyphylla and B. maximowicziana).

Response of invasive Chromolaena odorata and two coexisting weeds to contrasting irradiance and nitrogen

Chromolaena odorata is a widespread exotic weed in southern China and other regions of the world. To better understand its invasive strategies, we compared leaf pigment contents and gas-exchange traits of the invader with its two coexisting species (native Urena lobata and invasive Bidens pilosa) under combined conditions of irradiance (full, medium, and low) and nitrogen (full, medium, and low) supplies. The chlorophyll (Chl) a+b content of U. lobata was the highest and the Chl a/b ratio of C. odorata was the lowest among the three weed species. In most treatments, leaf pigment, light-saturated photosynthetic rate (P max), and light saturation point (LSP) of all the species increased, while their Chl a/b ratios decreased with the increasing nitrogen. The P max and LSP of U. lobata were greater than those of the coexisting weeds under full irradiance (FI), but significantly declined with the decreasing irradiance. The invasive weeds, especially C. odorata, showed lower P max and LSP under FI, but they showed slight decrease under low irradiance. Compared to U. lobata, C. odorata exhibited the lower light compensation point (LCP) in most treatments, higher LSP under low and medium irradiance, and lower dark respiration rate under FI. In addition, all the three species showed similar responses to different irradiance and nitrogen conditions, mean phenotypic plasticity index (MPPI) of most photosynthetic variables of the two invasive species was lower than that of U. lobata. These results suggested that C. odorata behaved as a facultative shadetolerant weed, being able to grow in moderately sheltered environments; the lower MPPI might be one of the important competitive strategies during its invasion. However, its invasion should be limited to some very shady habitats. In the field, control should be mainly directed against populations growing in the open or nutrient-rich habitats, where its expansion speed could be much faster. Deep shade by intact canopies or luxuriant forests might be an effective barrier against its invasion.

The Growth and Establishment of Floating Turions of Potamogeton crispus Are Not Favored by Summer Climate

The dispersion of asexual propagules is an important determinant for the spread and establishment of many aquatic plant species. In order to improve the understanding of the expansion of the Potamogeton crispus population, an in situ growth experiment with P. crispus turions was performed in a 30 days period. The sinking turions produced longer seedlings and more leaves than that of floating turions during the experimental period. A lower dark respiration rate and higher activities of superoxide dismutase and peroxidase were detected in the floating turions than those in the sinking turions, indicating that the self‐protection process of the floating turions and stress condition (high sunlight exposure and temperature) in summer may influence the primary metabolites of these floating turions. Moreover, we also found that the scale leaf porosities of the floating turions would determine the buoyancy of turions. These results indicated that the sinking and floating of P. crispus turions are determined by the anatomical structures and in situ summer climatic condition is unfavorable for the establishment of P. crispus floating turions.

Primary, Secondary Metabolites, Photosynthetic Capacity and Antioxidant Activity of the Malaysian Herb Kacip Fatimah (Labisia Pumila Benth) Exposed to Potassium Fertilization under Greenhouse Conditions

A randomized complete block design was used to characterize the relationship between production of total phenolics, flavonoids, ascorbic acid, carbohydrate content, leaf gas exchange, phenylalanine ammonia-lyase (PAL), soluble protein, invertase and antioxidant enzyme activities (ascorbate peroxidase (APX), catalase (CAT) and superoxide dismutase (SOD) in Labisia pumila Benth var. alata under four levels of potassium fertilization experiments (0, 90, 180 and 270 kg K/ha) conducted for 12 weeks. It was found that the production of total phenolics, flavonoids, ascorbic acid and carbohydrate content was affected by the interaction between potassium fertilization and plant parts. As the potassium fertilization levels increased from 0 to 270 kg K/ha, the production of soluble protein and PAL activity increased steadily. At the highest potassium fertilization (270 kg K/ha) L. pumila exhibited significantly higher net photosynthesis (A), stomatal conductance (gs), intercellular CO2 (Ci), apparent quantum yield (ξ) and lower dark respiration rates (Rd), compared to the other treatments. It was found that the production of total phenolics, flavonoids and ascorbic acid are also higher under 270 kg K/ha compared to 180, 90 and 0 kg K/ha. Furthermore, from the present study, the invertase activity was also found to be higher in 270 kg K/ha treatment. The antioxidant enzyme activities (APX, CAT and SOD) were lower under high potassium fertilization (270 kg K/ha) and have a significant negative correlation with total phenolics and flavonoid production. From this study, it was observed that the up-regulation of leaf gas exchange and downregulation of APX, CAT and SOD activities under high supplementation of potassium fertilizer enhanced the carbohydrate content that simultaneously increased the production of L. pumila secondary metabolites, thus increasing the health promoting effects of this plant.

Ecophysiological analysis of moss-dominated biological soil crusts and their separate components from the Succulent Karoo, South Africa

Biological soil crusts, formed by an association of soil particles with cyanobacteria, lichens, mosses, fungi and bacteria in varying proportions, live in or directly on top of the uppermost soil layer. To evaluate their role in the global carbon cycle, gas exchange measurements were conducted under controlled conditions. Moss-dominated soil crusts were first analyzed as moss tufts on soil, then the mosses were removed and the soil was analyzed separately to obtain the physiological response of both soil and individual moss stems. Net photosynthetic response of moss stems and complete crusts was decreased by insufficient and excess amounts of water, resulting in optimum curves with similar ranges of optimum water content. Light saturation of both sample types occurred at high irradiance, but moss stems reached light compensation and saturation points at lower values. Optimum temperatures of moss stems ranged between 22 and 27°C, whereas complete crusts reached similar net photosynthesis between 7 and 27°C. Under optimum conditions, moss stems reached higher net photosynthesis (4.0 vs. 2.8μmolm(-2)s(-1)) and lower dark respiration rates (-0.9 vs. -2.4μmolm(-2)s(-1)). Respiration rates of soil without moss stems were high (up to -2.0μmolm(-2)s(-1)) causing by far lower absolute values of NP/DR ratios of soil crusts as compared to moss stems. In carbon balances, it therefore has to be clearly distinguished between measurements of soil crust components versus complete crusts. High rates of soil respiration may be caused by leaching of mosses, creating high-nutrient microsites that favor microorganism growth.

Effects of chloroplast dysfunction on mitochondria: white sectors in variegated leaves have higher mitochondrial DNA levels and lower dark respiration rates than green sectors.

Co-ordination between plastids and mitochondria is so essential that there should be extensive inter-organellar crosstalk during development of plant cells. Indeed, chloroplast dysfunction in white leaves of plastid ribosome-deficient mutant barley, albostrians, is reportedly accompanied by increases in the levels of mitochondrial DNA and mitochondrial transcripts, suggesting that (i) developmental/physiological status of plastids (or heterotrophic growth condition of albino leaves) can affect the status of mitochondrial genome, and (ii) the function of the affected mitochondria may also be up-regulated accordingly. However, functional aspects of the mitochondria affected by chloroplast dysfunction have not yet been examined in detail. Here, we examined the effects of chloroplast dysfunction on mitochondrial DNA level and dark respiration rate, by comparing white and green sectors within individual variegated leaves, using 12 ornamental plants as experimental materials. The pattern of leaf variegation differed from species to species, suggesting that different mechanisms were involved in the formation of white sectors in different species. Quantitative hybridization analysis revealed that mitochondrial DNA levels were generally higher in white sectors than in green sectors. In spite of the elevated mitochondrial DNA levels, however, dark respiration rates in white sectors were generally lower than those in green sectors. Several possible mechanisms for elevation of mitochondrial DNA level and suppression of dark respiration rates in white sectors are discussed.Electronic supplementary materialThe online version of this article (doi:10.1007/s00709-011-0325-y) contains supplementary material, which is available to authorized users.

Photosynthesis and daily metabolic carbon balance of the invasive <i>Caulerpa racemosa</i> var. <i>cylindracea</i> (Chlorophyta: Caulerpales) along a depth gradient

The photosynthetic plasticity of the invasive green alga Caulerpa racemosa v. cylindracea (hereafter C. racemosa) has been proposed as a relevant mechanism determining its successful performance on Mediterranean benthic assemblages over broad depth gradients. In the present study, the photosynthetic performance of C. racemosa was evaluated through a carbon balance approach at three invaded sites with contrasting depths (11, 18 and 26 m) and light regimes. At each sampling depth, photosynthesis vs irradiance (P vs E) curves were performed on C. racemosa fronds and daily net productivity values were obtained by the numerical integration of P vs E models with continuous recording of irradiance measured on the sea floor. Photosynthetic responses were consistent with those typically exhibited by shade-adapted macroalgal species and other Mediterranean populations of C. racemosa: a significant reduction in maximum photosynthesis (Pmax) occurring at an intermediate depth (18 m) and a higher photosynthetic efficiency (α) and lower dark respiration rate (Rd) at the deepest sampling depth. Mean values of daily net C balance obtained from the deeper site were only 15% lower than those obtained from the shallower site, despite the severe reduction in light availability. This daily net carbon gain was ca. 29% higher than would be expected if photosynthetic adjustments did not occur in the deeper algal population. The evidence provided by these data support the hypothesis of photoacclimation in C. racemosa as an effective mechanism to optimize algal productivity across depth gradients in the Mediterranean Sea.

Physiological and morphological differences in the heterophylly of Sabina vulgaris Ant. in the semi-arid environment of Mu Us Desert, Inner Mongolia, China

Sabina vulgaris is a heterophyllus tree with two leaf forms: needle leaves and scale leaves. Most seedlings establish under a tree canopy and have only needle leaves, whereas mature individuals grow in the open and have both leaf forms. To clarify the functional traits of both leaf types, we studied the leaf mass per area (LMA), nitrogen content, stable carbon isotope composition, and photosynthetic traits of the two leaf forms. Scale leaves had a larger LMA, higher leaf area-based photosynthetic rate, higher water-use efficiency, and stronger tolerance of photoinhibition compared to needle leaves. Conversely, needle leaves had a lower light compensation point and higher leaf mass-based photosynthetic rate than scale leaves. With their low light compensation point and dark respiration rate, needle leaves appeared to be more effective at maximizing photosynthetic production under light-limited conditions in the inner crown or dark seedling stage. In contrast, scale leaves appeared to be more efficient at the canopy surface due to their higher area-based photosynthetic rate, tolerance to photoinhibition, and higher water-use efficiency. These different leaf functional traits of scale and needle leaves indicate functions similar to those of sun and shade leaves, respectively, in other tree species.