Variations In Photosynthetic Activity Research Articles

Impact of airborne iron oxide nanoparticles on Tillandsia usneoides as a model plant to assess pollution in heavy traffic areas

Due to the increasing evidence of widespread sub-micron pollutants in the atmosphere, the impact of airborne nanoparticles is a subject of great relevance. In particular, the smallest particles are considered the most active and dangerous, having a higher surface/volume ratio. Here we tested the effect of iron oxide (Fe3O4) nanoparticles (IONPs) with different mean diameter and size distribution on the model plant Tillandsia usneoides.Strands were placed in home-built closed boxes and exposed to levels of airborne IONPs reported for the roadside air, i.e. in the order of 107 - 108 items m−2. Plant growth and other morpho-physiological parameters were monitored for two weeks, showing that exposure to IONPs significantly reduced the length increment of the treated strands with respect to controls. A dose-dependence of this impairing effect was found only for particles with mean size of a few tens of nanometers. These were also proved to be the most toxic at the highest concentration tested. The IONP-induced hamper in growth was correlated with altered concentration of macro- and micronutrients in the plant, while no significant variation in photosynthetic activity was detected in treated samples. Microscopy investigation showed that IONPs could adhere to the plant surface and were preferentially located on the trichome wings.Our results report, for the first time, evidence of the negative effects of airborne IONP pollution on plant health, thus raising concerns about related environmental risks.Future research should be devoted to other plant species and pollutants to assess the impact of airborne pollution on plants and devise suitable attenuation practices.

Seasonal Photosynthesis Variations of Dominant Tree Species Used in Different Urban Landscapes

Photosynthesis is the only natural process that converts photon energy into chemical energy, and it is responsible for 90–95% of plant biomass accumulation and hence growth. Environmental factors such as light, temperature, and CO2 concentration in the atmosphere are major factors that influence photosynthesis, and excess of these can cause stress on plants. The photosynthetic response of tree species is found to vary to these factors. Therefore, the photosynthetic response of tree species can be a good indicator to assess these environmental factors that are changing due to urbanization and can be used to mitigate these factors as well by cultivating suitable tree species. The present study provides information on the seasonal variations in photosynthetic activity in six tree species. In the present study during the month of May (late summer to early monsoon) most of the tree species showed higher photosynthetic rates. It is also noticed that transpiration rate and water use efficiency was more in the month of May compared to other months. An increase in net photosynthesis and transpiration is observed among the tree species under high rainfall conditions 285.2 mm. It is also observed that photosynthesis decreased where the evaporative demand is very high.

Effect of Quarry Activities on Some Morphological Parameters of Two Maize Varieties (SWAN 1 and SAMMAZ 52)

The effect of quarry activities on some morphological parameters of two maize varieties (swan 1 and sammaz 52) was investigated with the aim of determining the impact of quarry activities on some growth parameters of the maize varieties under study. The seeds were collected from the Seed Bank Department of the Ondo State Ministry of Agriculture, Akure, Ondo State. They were authenticated at the Herbarium unit of the Federal University of Technology, Akure, and the voucher was deposited. Soil samples were collected at 50m, 100m, 150m, 200m, and 250m from the quarry site and transferred to the laboratory for analysis. A screen house experiment was set up to house the pots. Seeds of SWAN 1 and SAMMAZ 52 were sown into perforated plastic pots (30 cm diameter and 33 cm depth) filled with 10 kg of quarry soil. The following morphological parameters were determined; shoot height, leaf area, plant dry weight, shoot dry weight, root dry weight, root-shoot ratio, leaf area, and determination of photosynthetic parameters especially chlorophylls a and b. The result revealed that at 50 meters from the quarry site, SAMMAZ 52, one of the maize varieties grown in soil taken from the site, had the highest shoot height (94 cm). which showed that plants growing in higher concentrations of dust pollution respond to nutrient stress by devoting more of their available carbon to shoot growth, resulting in elongated stems, were consistent with the observed higher shoot height in SAMMAZ 52, daily variations in photosynthetic activity and the rate of nitrogen uptake are to blame for these alterations in plant behavior. The efficiency with which plants use the available nutrients determines whether they will survive in an area where there is quarry dust. The observed higher biomass (3.84g) under SAMMAZ 52's management regime can be attributed to the best possible rates of photosynthesis and nutrient assimilation, as well as to the presence of more chlorophyll and larger leaf surfaces.

Photosynthetic patterns during autumn in three different Salix cultivars grown on a brownfield site

Leaf senescence at the end of the growing season is a complex process stimulated by changes in daylength and temperature that prepares deciduous trees for winter by reducing photosynthetic rates and remobilization of nutrients. Extending the duration of photosynthetic activity could have important consequences for the translocation of heavy metals in the phytoremediation of contaminated sites using deciduous trees like willow. In the present study, three Salix cultivars (‘India,’ ‘SX67,’ and ‘Fish Creek’) that were observed to maintain green leaves late into autumn were evaluated over an 11-week period extending from mid-September to mid-November on a brownfield site in Montreal, Canada. Gas exchange rates, chlorophyll fluorescence, and leaf pigments were measured weekly. A general trend of declining stomatal conductance and transpiration were observed early in the trial, followed by reductions in photosynthetic efficiency and concentrations of chl a, chl b, and carotenoids, in agreement with other studies. In particular, the cultivar ‘Fish Creek’ had higher rates of gas exchange and pigment concentrations than either ‘SX67’ or ‘India,’ but values for these parameters also declined more rapidly over the course of the trial. Both photoperiod and soil and air temperatures were strong drivers of changes in photosynthetic activity in all three of these cultivars according to correlation analyses. Further studies should focus on their biomass production and heavy metal accumulation capacity in light of the observed variation in photosynthetic activity stimulated by seasonal changes in light and temperature.

Comprehensive Assessment of the Dynamics of Banana Chilling Injury by Advanced Optical Techniques

Green-ripe banana fruit are sensitive to chilling injury (CI) and, thus, prone to postharvest quality losses. Early detection of CI facilitates quality maintenance and extends shelf life. CI affects all metabolic levels, with membranes and, consequently, photosynthesis being primary targets. Optical techniques such as chlorophyll a fluorescence analysis (CFA) and spectroscopy are promising tools to evaluate CI effects in photosynthetically active produce. Results obtained on bananas are, however, largely equivocal. This results from the lack of a rigorous evaluation of chilling impacts on the various aspects of photosynthesis. Continuous and modulated CFA and imaging (CFI), and VIS remission spectroscopy (VRS) were concomitantly applied to noninvasively and comprehensively monitor photosynthetically relevant effects of low temperatures (5 °C, 10 °C, 11.5 °C and 13 °C). Detailed analyses of chilling-related variations in photosynthetic activity and photoprotection, and in contents of relevant pigments in green-ripe bananas, helped to better understand the physiological changes occurring during CI, highlighting that distinct CFA and VRS parameters comprehensively reflect various effects of chilling on fruit photosynthesis. They revealed why not all CFA parameters can be applied meaningfully for early detection of chilling effects. This study provides relevant requisites for improving CI monitoring and prediction.

Seasonal variation in the canopy color of temperate evergreen conifer forests.

Summary Evergreen conifer forests are the most prevalent land cover type in North America. Seasonal changes in the color of evergreen forest canopies have been documented with near‐surface remote sensing, but the physiological mechanisms underlying these changes, and the implications for photosynthetic uptake, have not been fully elucidated.Here, we integrate on‐the‐ground phenological observations, leaf‐level physiological measurements, near surface hyperspectral remote sensing and digital camera imagery, tower‐based CO2 flux measurements, and a predictive model to simulate seasonal canopy color dynamics.We show that seasonal changes in canopy color occur independently of new leaf production, but track changes in chlorophyll fluorescence, the photochemical reflectance index, and leaf pigmentation. We demonstrate that at winter‐dormant sites, seasonal changes in canopy color can be used to predict the onset of canopy‐level photosynthesis in spring, and its cessation in autumn. Finally, we parameterize a simple temperature‐based model to predict the seasonal cycle of canopy greenness, and we show that the model successfully simulates interannual variation in the timing of changes in canopy color.These results provide mechanistic insight into the factors driving seasonal changes in evergreen canopy color and provide opportunities to monitor and model seasonal variation in photosynthetic activity using color‐based vegetation indices.

Elemental and Isotopic Variations of Copper and Zinc Associated with the Diel Activity of Phototrophic Biofilm.

The response in metal concentrations and isotopic composition to variations in photosynthetic activity of aquatic micro-organisms is crucially important for understanding the environmental controls on metal fluxes and isotope excursions. Here we studied the impacts of two successive diel cycles on physicochemical parameters, Cu and Zn concentrations, and isotopic composition in solution in the presence of mature phototrophic biofilm in a rotating annular bioreactor. The diel cycles induced fluctuations in temperature, pH, and dissolved oxygen concentration following the variation in the photosynthesis activity of the biofilm. Diel variations in metal concentrations were primarily related to the pH variation, with an increase in metal concentration in solution related to a pH decrease. For both metals, δ(66Zn) and δ(65Cu) in solution exhibited complex but reproducible diel cycles. Diel variations in photosynthetic activity led to alternatively positive and negative isotope fractionation, producing the sorption of light Zn (Δ(66Znsorbed-solution) = -0.1 ± 0.06‰) and heavy Cu isotopes (Δ(65Cusorbed-solution) = +0.17 ± 0.06‰) during the day at high pH and the excretion of lighter Zn isotopes (-0.4‰ < Δ(66Znexcreted-biofilm) < +0.14‰) and heavy Cu isotopes (Δ(65Cuexcreted-biofilm) = +0.7 ± 0.3‰) during the night at lower pH. We interpreted Zn and Cu diel cycles as a combination of a desorption of exopolymeric substance-metal complexes and a small active efflux during the night with adsorption and incorporation via an active uptake during the day. The hysteresis of metal concentration in solution over the diel cycle suggested the more important role of uptake compared to desorption and efflux from the biofilm. The phototrophic biofilm presents a non-negligible highly labile metal pool with important potential for contrasting isotopic fractionation at the diel scale.

Variation of photosynthetic activity during the process of green tides induced by nutrient additions in the coastal sea of Qingdao, China

Three nutrient addition experiments were conducted to induce green tides of Ulva prolifera from April to August in 2016 in the coastal waters of Qingdao, China. Photosynthetic activity (Fv/Fm), biomass, nutrients and temperature were measured.We found that Fv/Fm of U. prolifera increased to the maximum about 0.7 ∼ 0.75 under favorable environment, and declined significantly when the growth of U. prolifera was limited by nutrient and temperature. In Addition, the results showed that Fv/Fm increased to the maximum prior to occurrence of green tide and fell significantly before green tide dissipated. Fv/Fm can be used to predict the outbreak and dissipation of green tides.

Different Arabidopsis thaliana photosynthetic and defense responses to hemibiotrophic pathogen induced by local or distal inoculation of Burkholderia phytofirmans.

Pathogen infection of plant results in modification of photosynthesis and defense mechanisms. Beneficial microorganisms are known to improve plant tolerance to stresses. Burkholderia phytofirmans PsJN (Bp), a beneficial endophytic bacterium, promotes growth of a wide range of plants and induces plant resistance against abiotic and biotic stresses such as coldness and infection by a necrotrophic pathogen. However, mechanisms underlying its role in plant tolerance towards (hemi)biotrophic invaders is still lacking. We thus decipher photosynthetic and defense responses during the interaction between Arabidopsis, Bp and the hemibiotrophic bacterium Pseudomonas syringae pv. tomato DC3000 (Pst). Different Bp inoculations allowed analyzes at both systemic and local levels. Despite no direct antibacterial action, our results showed that only local presence of Bp alleviates Pst growth in planta during the early stage of infection. Molecular investigations showed that seed inoculation of Bp, leading to a restricted presence in the root system, transiently primed PR1 expression after challenge with Pst but continuously primed PDF1.2 expression. Bacterization with Bp reduced Y(ND) but had no impact on PSII activity or RuBisCO accumulation. Pst infection caused an increase of Y(NA) and a decrease in ΦPSI, ETRI and in PSII activity, showed by a decrease in Fv/Fm, Y(NPQ), ΦPSII, and ETRII values. Inoculation with both bacteria did not display any variation in photosynthetic activity compared to plants inoculated with only Pst. Our findings indicated that the role of Bp here is not multifaceted, and relies only on priming of defense mechanisms but not on improving photosynthetic activity.

Seasonal dynamics of photosynthetic activity, Microcystis genotypes and microcystin production in Lake Taihu, China

In recent years, toxic Microcystis blooms have occurred annually in Lake Taihu, China. In order to elucidate the relationships between photosynthetic activity of Microcystis, Microcystis genotypic composition, microcystin (MC) production and environmental factors, water samples and associated environmental data were collected from January to December 2014 in Lake Taihu. Seasonal variations in photosynthetic activity were measured using a Phyto-PAM Analyzer, abundances of total and toxic Microcystis genotypes were determined by quantitative real-time PCR (qPCR), and MC concentrations were quantified by HPLC. The maximum quantum yield of photosystem II (Fv/Fm) of Microcystis cells changed on a seasonal basis. Fv/Fm was not detectable in the winter, but increased from spring to early summer, after which, it gradually decreased until the winter. The level of non-photochemical quenching (NPQ) increased from March to August and then decreased until December. qPCR data showed that the abundances of total Microcystis genotypes ranged from 1.91 × 105 to 8.64 × 107 copies/mL and toxic Microcystis genotypes ranged from 2.38 × 104 to 5.67 × 107 copies/mL. The toxic proportion varied from 12.5 to 65.6%, with an average value of 27.9%. Correlation analysis revealed that there was a positive correlation between photosynthetic activity, genotypic composition and MC production. Water temperature was the only environmental factor that was positively correlated with Fv/Fm, NPQ, total and toxic Microcystis and intracellular MC. Additionally, total phosphorus was also significantly correlated with intracellular MC. These results indicate that future global warming, in addition to eutrophication, could promote Microcystis blooms in Lake Taihu and that blooms may increase in intensity and toxicity.

The Comparatively Proteomic Analysis in Response to Cold Stress in Cassava Plantlets.

Cassava (Manihot esculenta Crantz) is a tropical root crop and sensitive to low temperature. However, it is poorly to know how cassava can modify its metabolism and growth to adapt to cold stress. An investigation aimed at a better understanding of cold-tolerant mechanism of cassava plantlets was carried out with the approaches of physiology and proteomics in the present study. The principal component analysis of seven physiological characteristics showed that electrolyte leakage (EL), chlorophyll content, and malondialdehyde (MDA) may be the most important physiological indexes for determining cold-resistant abilities of cassava. The genome-wide proteomic analysis showed that 20 differential proteins had the same patterns in the apical expanded leaves of cassava SC8 and Col1046. They were mainly related to photosynthesis, carbon metabolism and energy metabolism, defense, protein synthesis, amino acid metabolism, signal transduction, structure, detoxifying and antioxidant, chaperones, and DNA-binding proteins, in which 40 % were related with photosynthesis. The remarkable variation in photosynthetic activity and expression level of peroxiredoxin is closely linked with expression levels of proteomic profiles. Moreover, analysis of differentially expressed proteins under cold stress is an important step toward further elucidation of mechanisms of cold stress resistance.Electronic supplementary materialThe online version of this article (doi:10.1007/s11105-016-0987-x) contains supplementary material, which is available to authorized users.

MODIS-based vegetation index has sufficient sensitivity to indicate stand-level intra-seasonal climatic stress in oak and beech forests

Variation in photosynthetic activity of trees induced by climatic stress can be effectively evaluated using remote sensing data. Although adverse effects of climate on temperate forests have been subjected to increased scrutiny, the suitability of remote sensing imagery for identification of drought stress in such forests has not been explored fully. The study seeks to evaluate the sensitivity of MODIS-based vegetation index to heat and drought stress in temperate forests, and to explore the differences in stress response of oaks and beech. We identified 8 oak and 13 beech pure and mature stands, each covering between 4 and 13 MODIS pixels. For each pixel, we extracted a time series of MODIS NDVI from 2000 to 2010. We identified all sequences of continuous unseasonal NDVI decline to be used as the response variable indicative of environmental stress. Neural network-based regression modelling was then applied to identify the climatic variables that best explain observed NDVI declines. Tested variables explained 84–97 % of the variation in NDVI, whilst air temperature-related climate extremes were found to be the most influential. Beech showed a linear response to the most influential climatic predictors, while oak responded in a unimodal pattern suggesting a better coping mechanism. MODIS NDVI has proved sufficiently sensitive as a stand-level indicator of climatic stress acting upon temperate broadleaf forests, leading to its potential use in predicting drought stress from meteorological observations and improving parameterisation of forest stress indices.

Variation in photosynthetic activity of phytoplankton during the spring algal blooms in the adjacent area of Changjiang River estuary

Nine cruises were undertaken in the adjacent area of Changjiang River estuary from late March to May in 2011 to investigate the variation in photosynthetic activity (Fv/Fm) of surface water during algal blooms. The time series covered the period from Skeletonema sp. bloom to Prorocentrum donghaiense bloom. The results showed that Fv/Fm ranged from 0.17 to 0.73. Temperature, turbidity and nutrients were the primary influencing factors on Fv/Fm and Fv/Fm showed a strong diel periodicity. Additionally, the change in Fv/Fm during Skeletonema sp. and P. donghaiense bloom was similar. Fv/Fm increased to more than 0.60 before bloom initiation, and then chlorophyll a (Chl a) concentration rocketed and the bloom broke out. Fv/Fm was above 0.6 during bloom development and declined to below 0.6 when bloom dissipated. Fv/Fm increasing to higher level occurred several days prior to significant increases in Chl a and outbreak of bloom, indicating Fv/Fm can be used to predict onset of algal blooms.

Comparison of leaf proteomes of cassava (Manihot esculenta Crantz) cultivar NZ199 diploid and autotetraploid genotypes.

Cassava polyploid breeding has drastically improved our knowledge on increasing root yield and its significant tolerance to stresses. In polyploid cassava plants, increases in DNA content highly affect cell volumes and anatomical structures. However, the mechanism of this effect is poorly understood. The purpose of the present study was to compare and validate the changes between cassava cultivar NZ199 diploid and autotetraploid at proteomic levels. The results showed that leaf proteome of cassava cultivar NZ199 diploid was clearly differentiated from its autotetraploid genotype using 2-DE combined MS technique. Sixty-five differential protein spots were seen in 2-DE image of autotetraploid genotype in comparison with that of diploid. Fifty-two proteins were identified by MALDI-TOF-MS/MS, of which 47 were up-regulated and 5 were down-regulated in autotetraploid genotype compared with diploid genotype. The classified functions of 32 up-regulated proteins were associated with photosynthesis, defense system, hydrocyanic acid (HCN) metabolism, protein biosynthesis, chaperones, amino acid metabolism and signal transduction. The remarkable variation in photosynthetic activity, HCN content and resistance to salt stress between diploid and autotetraploid genotypes is closely linked with expression levels of proteomic profiles. The analysis of protein interaction networks indicated there are direct interactions between the 15 up-regulation proteins involved in the pathways described above. This work provides an insight into understanding the protein regulation mechanism of cassava polyploid genotype, and gives a clue to improve cassava polyploidy breeding in increasing photosynthesis and resistance efficiencies.

Photoperiodic regulation of the seasonal pattern of photosynthetic capacity and the implications for carbon cycling

Although temperature is an important driver of seasonal changes in photosynthetic physiology, photoperiod also regulates leaf activity. Climate change will extend growing seasons if temperature cues predominate, but photoperiod-controlled species will show limited responsiveness to warming. We show that photoperiod explains more seasonal variation in photosynthetic activity across 23 tree species than temperature. Although leaves remain green, photosynthetic capacity peaks just after summer solstice and declines with decreasing photoperiod, before air temperatures peak. In support of these findings, saplings grown at constant temperature but exposed to an extended photoperiod maintained high photosynthetic capacity, but photosynthetic activity declined in saplings experiencing a naturally shortening photoperiod; leaves remained equally green in both treatments. Incorporating a photoperiodic correction of photosynthetic physiology into a global-scale terrestrial carbon-cycle model significantly improves predictions of seasonal atmospheric CO(2) cycling, demonstrating the benefit of such a function in coupled climate system models. Accounting for photoperiod-induced seasonality in photosynthetic parameters reduces modeled global gross primary production 2.5% (∼4 PgC y(-1)), resulting in a >3% (∼2 PgC y(-1)) decrease of net primary production. Such a correction is also needed in models estimating current carbon uptake based on remotely sensed greenness. Photoperiod-associated declines in photosynthetic capacity could limit autumn carbon gain in forests, even if warming delays leaf senescence.

Temporal variation in cyanobacteria species composition and photosynthetic activity in experimentally induced blooms

Temporal variation in the photosynthetic activity of bloom-forming cyanobacteria was evaluated by the maximum quantum yield of photosystem II (Fv/Fm) using a 30-(3,4-dichlorophenyl)-10, 10-dimethyl urea (DCMU) methodology. To evaluate the Fv/Fm of cyanobacteria in phytoplankton communities containing several algal groups, phycocyanin was directly excited at 590 nm, and in vivo fluorescence at 680 nm emission was measured before and after DCMU addition. Using a cultured Microcystis strain, we first tested the relevance of the method and found that Fv/Fm values measured under phycocyanin excitation approximately corresponded to those under chlorophyll a (chl a) excitation (440 nm). Second, we monitored temporal variations in Fv/Fm for induced cyanobacterial blooms in experimental ponds. Cyanobacterial Fv/Fm was usually lower than overall phytoplankton Fv/Fm measured under chl a excitation, suggesting that potential photosynthetic activity of bloom-forming cyanobacteria was lower than in other algal groups, such as green algae and diatoms. We also found that temporal variations in Fv/Fm explained the shift of dominant species from Microcystis aeruginosa to Aphanizomenon issatschenkoi. Our results consistently demonstrated that this method is simple and useful for evaluation of cyanobacterial potential photosynthetic activity in natural phytoplankton communities.

Irradiance heterogeneity within crown affects photosynthetic capacity and nitrogen distribution of leaves in Cedrela sinensis

Because light conditions in the forest understory are highly heterogeneous, photosynthetic acclimation to spatially variable irradiance within a crown is important for crown-level carbon assimilation. The effect of variation in irradiance within the crown on leaf nitrogen content and photosynthetic rate was examined for pinnate compound leaves in saplings of Cedrela sinensis, a pioneer deciduous tree. Five shading treatments, in which 0, 25, 50, 75 and 100% of leaves were shaded, were established by artificial heavy shading using shade screen umbrellas with 25% transmittance. Although the nitrogen content of leaves was constant regardless of shading treatment, ribulose 1.5-bisphosphate carboxylase/oxygenase (Rubisco) content and light-saturated photosynthetic capacity were lower in shade leaves within partially shaded crowns than within fully shaded crowns. Shade leaves within partially shaded crowns contained higher amount of amino acids. Most shade leaves died in partially shaded crowns, whereas more than half of shade leaves survived in totally shaded crowns. Assumptions on photosynthetic acclimation to local light conditions cannot explain why shade leaves have different photosynthetic capacities and survival rates in between partially and totally shaded crowns. Irradiance heterogeneity within the crown causes a distinct variation in photosynthetic activity between sun and shaded leaves within the crown.

PRI assessment of long-term changes in carotenoids/chlorophyll ratio and short-term changes in de-epoxidation state of the xanthophyll cycle

The Photochemical Reflectance Index (PRI), an index based on leaf reflectance at 531 nm, has been found suitable for tracking variations in photosynthetic activity from leaf to ecosystem levels. This suitability has been attributed to PRI correlation with xanthophyll interconversion and photosynthetic radiation-use efficiency. However, other pigments and factors may be involved in such relationships. We studied the relationship between PRI and xanthophylls and other carotenoids in saplings of two widely distributed evergreen species (Scots pine and Holm oak) submitted to experimentally changing light conditions in a field experiment. PRI was strongly correlated with the de-epoxidation state of xanthophylls (DEPS, an expression of the relative concentration of the three xanthophyll cycle pigments), but also with carotenoids/chlorophyll ratio and β-carotene/chlorophyll ratio in both species. However, following momentary decreases in light due to clouds, PRI changed following the DEPS changes, while the carotenoids/chlorophyll ratio remained constant. The results show that PRI was able to reveal short-term changes in de-epoxidation state, i.e. the signal of xanthophyll interconversion, but it also tracked long-term changes in carotenoids/chlorophyll. Carotenoids other than xanthophylls, e.g. β-carotene, are also related to photoprotective processes, thus also making PRI effective as a measure of changes in photosynthetic light-use efficiency in response to stress on a long-term level.

Gender, season and habitat: Patterns of variation in photosynthetic activity, growth and fecundity in Thymelaea velutina

Changes in the ecophysiological performance of a plant species due to different environmental conditions generally reflect adaptations to the habitat where the plant grows and are often related to its survival capacity in a particular place. We examined this with the dioecious shrub Thymelaea velutina, in two contrasting populations representing the extremes of the altitudinal gradient where the species lives (coastal dunes and mountain habitats over 1000 m). We measured net photosynthetic rates and stomatal conductance, estimated the level of plant stress by chlorophyll fluorescence, and assessed their correlations with growth rate, plant size, flower production and fruit set. We hypothesized that plants at high altitude were more photosynthetically stressed than at sea level and expected a gender × habitat interaction in performance as females need more resources than males. Plants in the mountain experienced chronic photoinhibition during winter and a reduced photosynthetic performance both in winter and spring compared to plants in coastal dunes. However, there was no association between any of the fluorescence variables and either plant growth or fecundity, suggesting that other factors are involved determining performance. Mountain plants showed also an apparent lower capacity of heat dissipation to excessive radiation than dune plants. In the dunes, the greater leaf area and mass can lead to a higher photosynthetic carbon gain by whole individuals compared to plants in the mountain. No effect of gender was detected on the ecophysiological performance of this species, which we partly attribute to the small size of fruits of the female plants.

Multiple site tower flux and remote sensing comparisons of tropical forest dynamics in Monsoon Asia

The spatial and temporal dynamics of tropical forest functioning are poorly understood, partly attributed to a weak seasonality and high tree species diversity at the landscape scale. Recent neotropical rainforest studies with local tower flux measurements have revealed strong seasonal carbon fluxes that follow the availability of sunlight in intact forests, while in areas of forest disturbance, carbon fluxes more closely tracked seasonal water availability. These studies also showed a strong seasonal correspondence of satellite measures of greenness, using the Enhanced Vegetation Index ( E VI) with ecosystem carbon fluxes in both intact and disturbed forests, which may enable larger scale extension of tower flux measurements. In this study, we investigated the seasonal patterns and relationships of local site tower flux measures of gross primary productivity ( P g) with independent Moderate Resolution Imaging Spectroradiometer (MODIS) satellite greenness measures across three Monsoon Asia tropical forest types, encompassing drought-deciduous, dry evergreen, and humid evergreen secondary tropical forests. In contrast to neotropical forests, the tropical forests of Monsoon Asia are more extensively degraded and heterogeneous due to intense land use pressures, and therefore, may exhibit unique seasonal patterns of ecosystem fluxes that are more likely water-limited and drought-susceptible. Our results show significant phenologic variability and response to moisture and light controls across the three tropical forest sites and at the regional scale. The drier tropical forests were primarily water-limited, while the wet evergreen secondary forest showed a slight positive trend with light availability. Satellite E VI greenness observations were generally synchronized and linearly related with seasonal and inter-annual tower flux P g measurements at the multiple sites and provided better opportunities for tower extension of carbon fluxes than other satellite products, such as the MODIS P g product. Satellite E VI-derived P g images revealed strong seasonal variations in photosynthetic activity throughout the Monsoon Asia tropical region.