Home About us Contact
|
Home About us Contact | ||
|
|
||
Light Capture (light + capture)
Selected AbstractsThe inherent ,safety-net' of an Acrisol: measuring and modelling retarded leaching of mineral nitrogenEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 2 2002D. Suprayogo Summary The inherent features of Acrisols with their increasing clay content with depth are conducive to reducing nutrient losses by nutrient adsorption on the matrix soil surfaces. Ammonium (NH4+) and nitrate (NO3,) adsorption by a Plinthic Acrisol from Lampung, Indonesia was studied in column experiments. The peak of the H218O breakthrough occurred at 1 pore volume, whereas the median pore volumes for NH4+ and NO3, ranged from 6.4 to 6.9 and 1.1 to 1.6, respectively. The adsorption coefficients (Ka in cm3 g,1) measured were 1.81, 1.51, 1.64 and 1.47 for NH4+ and 0.03, 0.09, 0.10 and 0.17 for NO3,, respectively, in the 0,0.2, 0.2,0.4, 0.4,0.6 and 0.6,0.8 m soil depth layers. The NH4+ and NO3, adsorption coefficients derived from this study were put in to the Water, Nutrient and Light Capture in Agroforestry Systems (WaNuLCAS) model to evaluate their effect on leaching in the context of several cropping systems in the humid tropics. The resulting simulations indicate that the inherent ,safety-net' (retardation mechanism) of a shallow (0.8,1 m) Plinthic Acrisol can reduce the leaching of mineral N by between 5 and 33% (or up to 2.1 g m,2), mainly due to the NH4+ retardation factor, and that the effectiveness in reducing N leaching increases with increasing depth. However, the inherent ,safety-net' is useful only if deep-rooted plants can recover the N subsequently. [source] Biomass allocation and leaf life span in relation to light interception by tropical forest plants during the first years of secondary successionJOURNAL OF ECOLOGY, Issue 6 2008N. Galia Selaya Summary 1We related above-ground biomass allocation to light interception by trees and lianas growing in three tropical rain forest stands that were 0.5, 2 and 3-year-old regeneration stages after slash and burn agriculture. 2Stem height and diameter, leaf angle, the vertical distribution of total above-ground biomass and leaf longevity were measured in individuals of three short-lived pioneers (SLP), four later successional species (LS) and three lianas (L). Daily light capture per individual (,d) was calculated with a canopy model. Mean daily light interception per unit leaf area (,area), leaf mass (,leaf mass) and above-ground mass (,mass) were used as measures of instantaneous efficiency of biomass use for light capture. 3With increasing stand age, vegetation height and leaf area index increased while light at the forest floor declined from 34 to 5%. The SLP, Trema micanthra and Ochroma pyramidale, dominated the canopy early in succession and became three times taller than the other species. SLP had lower leaf mass fractions and leaf area ratios than the other groups and this difference increased with stand age. 4Over time, the SLP intercepted increasingly more light per unit leaf mass than the other species. Lianas, which in the earliest stage were self-supporting and started climbing later on, gradually became taller at a given mass and diameter than the trees. Yet, they were not more efficient than trees in light interception. 5SLP had at least three-fold shorter leaf life spans than LS and lianas. Consequently, total light interception calculated over the mean life span of leaves (,leaf mass total = ,area × SLAdeath leaves× leaf longevity) was considerably lower for the SLP than for the other groups. 6Synthesis. We suggest that early dominance in secondary forest is associated with a high rate of leaf turnover which in turn causes inefficient long-term use of biomass for light capture, whereas persistence in the shade is associated with long leaf life spans. This analysis shows how inherent tradeoffs in crown and leaf traits drive long-term competition for light, and it presents a conceptual tool to explain why early dominants are not also the long-term dominants. [source] Mutation of Residue Arginine18 of Cytochrome b559,-Subunit and its Effects on Photosystem II Activities in Chlamydomonas reinhardtiiJOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 7 2007Jing-Jing Ma Abstract It has been known that arginine is used as the basic amino acid in the ,-subunit of cytochrome b559 (Cyt b559) except histidine. However, previous studies have focused on the function of histidine in the activities of photosystem (PS) II and there are no reports regarding the structural and/or functional roles of arginine in PSII complexes. In the present study, two arginine18 (R18) mutants of Chlamydomonas reinhardtii were constructed using site-directed mutagenesis, in which R18 was replaced by glutamic acid (E) and glycine (G). The results show that the oxygen evolution of the PSII complex in the R18G and R18E mutants was approximately 60% of wild-type (WT) levels and that, after irradiation at high light intensity, oxygen evolution for the PSII of mutants was reduced to zero compared with 40% in WT cells. The efficiency of light capture by PSII (Fv/Fm) of R18G and R18E mutants was approximately 42%,46% that of WT cells. Furthermore, levels of the ,-subunit of Cyt b559 and PsbO proteins were reduced in thylakoid membranes compared with WT. Overall, these data suggest that R18 plays a significant role in helping Cyt b559 maintain the structure of the PSII complex and its activity, although it is not directly bound to the heme group. [source] How can we predict the effects of elevated CO2 on the balance between perennial C3 grass species competing for light?NEW PHYTOLOGIST, Issue 1 2002F. Teyssonneyre Summary ,,Changes in the balance between mixed plant species have been reported under elevated [CO2] compared with ambient atmospheric [CO2]. We hypothesized that species response to elevated CO2 in mixture can be explained by taking into account resource partitioning between mixed species. ,,This hypothesis was tested experimentally on three perennial C3 grass species (Lolium perenne, Festuca arundinacea and Holcus lanatus) grown in monocultures and in binary mixtures (Lolium,Festuca and Lolium,Holcus) under mild (frequent cuts) or severe (infrequent cuts) competition for light and at a high N supply (40 g N m,2). ,,Under mild competition for light, the dry matter yield response to elevated CO2 of the mixed grass species was similar to that observed in monocultures. By contrast, under severe light competition, the grass species that absorbed more light per unit leaf area (Holcus and Festuca), also had a greater response to elevated CO2 in mixture compared with monoculture. ,,Under our experimental conditions, we have shown that the dry matter yield response to CO2 in mixture can be predicted from both the species response in monoculture, and the light capture per unit leaf area in ambient CO2 of the mixed compared with the pure grasses. [source] Photosynthetic Acclimation to Simultaneous and Interacting Environmental Stresses Along Natural Light Gradients: Optimality and ConstraintsPLANT BIOLOGY, Issue 3 2004ü. Niinemets Abstract: There is a strong natural light gradient from the top to the bottom in plant canopies and along gap-understorey continua. Leaf structure and photosynthetic capacities change close to proportionally along these gradients, leading to maximisation of whole canopy photosynthesis. However, other environmental factors also vary within the light gradients in a correlative manner. Specifically, the leaves exposed to higher irradiance suffer from more severe heat, water, and photoinhibition stresses. Research in tree canopies and across gap-understorey gradients demonstrates that plants have a large potential to acclimate to interacting environmental limitations. The optimum temperature for photosynthetic electron transport increases with increasing growth irradiance in the canopy, improving the resistance of photosynthetic apparatus to heat stress. Stomatal constraints on photosynthesis are also larger at higher irradiance because the leaves at greater evaporative demands regulate water use more efficiently. Furthermore, upper canopy leaves are more rigid and have lower leaf osmotic potentials to improve water extraction from drying soil. The current review highlights that such an array of complex interactions significantly modifies the potential and realized whole canopy photosynthetic productivity, but also that the interactive effects cannot be simply predicted as composites of additive partial environmental stresses. We hypothesize that plant photosynthetic capacities deviate from the theoretical optimum values because of the interacting stresses in plant canopies and evolutionary trade-offs between leaf- and canopy-level plastic adjustments in light capture and use. [source] Engineering photosynthetic light capture: impacts on improved solar energy to biomass conversionPLANT BIOTECHNOLOGY JOURNAL, Issue 6 2007Jan H. Mussgnug Summary The main function of the photosynthetic process is to capture solar energy and to store it in the form of chemical ,fuels'. Increasingly, the photosynthetic machinery is being used for the production of biofuels such as bio-ethanol, biodiesel and bio-H2. Fuel production efficiency is directly dependent on the solar photon capture and conversion efficiency of the system. Green algae (e.g. Chlamydomonas reinhardtii) have evolved genetic strategies to assemble large light-harvesting antenna complexes (LHC) to maximize light capture under low-light conditions, with the downside that under high solar irradiance, most of the absorbed photons are wasted as fluorescence and heat to protect against photodamage. This limits the production process efficiency of mass culture. We applied RNAi technology to down-regulate the entire LHC gene family simultaneously to reduce energy losses by fluorescence and heat. The mutant Stm3LR3 had significantly reduced levels of LHCI and LHCII mRNAs and proteins while chlorophyll and pigment synthesis was functional. The grana were markedly less tightly stacked, consistent with the role of LHCII. Stm3LR3 also exhibited reduced levels of fluorescence, a higher photosynthetic quantum yield and a reduced sensitivity to photoinhibition, resulting in an increased efficiency of cell cultivation under elevated light conditions. Collectively, these properties offer three advantages in terms of algal bioreactor efficiency under natural high-light levels: (i) reduced fluorescence and LHC-dependent heat losses and thus increased photosynthetic efficiencies under high-light conditions; (ii) improved light penetration properties; and (iii) potentially reduced risk of oxidative photodamage of PSII. [source] Can improvement in photosynthesis increase crop yields?PLANT CELL & ENVIRONMENT, Issue 3 2006STEPHEN P. LONG ABSTRACT The yield potential (Yp) of a grain crop is the seed mass per unit ground area obtained under optimum growing conditions without weeds, pests and diseases. It is determined by the product of the available light energy and by the genetically determined properties: efficiency of light capture (,i), the efficiency of conversion of the intercepted light into biomass (,c) and the proportion of biomass partitioned into grain (,). Plant breeding brings , and ,i close to their theoretical maxima, leaving ,c, primarily determined by photosynthesis, as the only remaining major prospect for improving Yp. Leaf photosynthetic rate, however, is poorly correlated with yield when different genotypes of a crop species are compared. This led to the viewpoint that improvement of leaf photosynthesis has little value for improving Yp. By contrast, the many recent experiments that compare the growth of a genotype in current and future projected elevated [CO2] environments show that increase in leaf photosynthesis is closely associated with similar increases in yield. Are there opportunities to achieve similar increases by genetic manipulation? Six potential routes of increasing ,c by improving photosynthetic efficiency were explored, ranging from altered canopy architecture to improved regeneration of the acceptor molecule for CO2. Collectively, these changes could improve ,c and, therefore, Yp by c. 50%. Because some changes could be achieved by transgenic technology, the time of the development of commercial cultivars could be considerably less than by conventional breeding and potentially, within 10,15 years. [source] DELLA protein function in growth responses to canopy signalsTHE PLANT JOURNAL, Issue 1 2007Tanja Djakovic-Petrovic Summary Plants can sense neighbour competitors through light-quality signals and respond with shade-avoidance responses. These include increased shoot elongation, which enhances light capture and thus competitive power. Such plant,plant interactions therefore profoundly affect plant development in crowded populations. Shade-avoidance responses are tightly coordinated by interactions between light signals and hormones, with essential roles for the phytochrome B photoreceptor [sensing the red:far red (R:FR) ratio] and the hormone gibberellin (GA). The family of growth-suppressing DELLA proteins are targets for GA signalling and are proposed to integrate signals from other hormones. However, the importance of these regulators has not been studied in the ecologically relevant, complex realm of plant canopies. Here we show that DELLA abundance is regulated during growth responses to neighbours in dense Arabidopsis stands. This occurs in a R:FR-dependent manner in petioles, depends on GA, and matches the induction kinetics of petiole elongation. Similar interactions were observed in the growth response of seedling hypocotyls and are general for a second canopy signal, reduced blue light. Enhanced DELLA stability in the gai mutant inhibits shade-avoidance responses, indicating that DELLA proteins constrain shade-avoidance. However, using multiple DELLA knockout mutants, we show that the observed DELLA breakdown is not sufficient to induce shade-avoidance in petioles, but plays a more central role in hypocotyls. These data provide novel information on the regulation of shade-avoidance under ecologically important conditions, defining the importance of DELLA proteins and GA and unravelling the existence of GA- and DELLA-independent mechanisms. [source] | ||||||||||