Variation In Photosynthetic Rate Research Articles

Diurnal Variations in Photosynthesis, Stomatal Conductance and Leaf Water Relation in Sorghum Grown with or without Silicon under Water Stress

ABSTRACT Sorghum [Sorghum bicolor (L.) Moench] was grown hydroponically with or without 50 ppm silicon (Si), and exposed to water stress from 10 days after sowing (DAS). At 15 and 23 DAS, we measured dry weight and diurnal variations in photosynthetic rate (P N), stomatal conductance (g s), transpiration rate (T), leaf water potential (ψ L), and water uptake rate (23 DAS only). The reduction in dry weight at 23 DAS caused by water stress was ameliorated by silicon. Under water stress, silicon-treated seedlings showed higher g s, P N, and T than untreated ones. ψ L remained almost constant within treatments throughout the daytime. Water uptake rate was reduced by water stress, but the reduction was ameliorated by silicon. We conclude that silicon enhanced water uptake and g s, improving water supply to the leaves. These effects of silicon occurred soon after exposure to water stress.

Nitrogen in cell walls of sclerophyllous leaves accounts for little of the variation in photosynthetic nitrogen‐use efficiency

Photosynthetic rate per unit nitrogen generally declines as leaf mass per unit area (LMA) increases. To determine how much of this decline was associated with allocating a greater proportion of leaf nitrogen into cell wall material, we compared two groups of plants. The first group consisted of two species from each of eight genera, all of which were perennial evergreens growing in the Australian National Botanic Gardens (ANBG). The second group consisted of seven Eucalyptus species growing in a greenhouse. The percentage of leaf biomass in cell walls was independent of variation in LMA within any genus, but varied from 25 to 65% between genera. The nitrogen concentration of cell wall material was 0.4 times leaf nitrogen concentration for all species apart from Eucalyptus, which was 0.6 times leaf nitrogen concentration. Between 10 and 30% of leaf nitrogen was recovered in the cell wall fraction, but this was independent of LMA. No trade-off was observed between nitrogen associated with cell walls and the nitrogen allocated to ribulose 1.5-bisphosphate carboxylase/oxygenase (Rubisco). Variation in photosynthetic rate per unit nitrogen could not be explained by variation in cell wall nitrogen.

Multi-angle remote sensing of forest light use efficiency by observing PRI variation with canopy shadow fraction

We show that observed co-variations at sub-hourly time scales between the photochemical reflectance index (PRI) and canopy light use efficiency (LUE) over a Douglas-fir forest result directly from sub-hourly leaf reflectance changes in a 531 nm spectral window roughly 50 nm wide. We conclude then, that over a forest stand we are observing the direct effects of photosynthetic down-regulation on leaf-level reflectance at 531 nm. Key to our conclusion is our ability to simultaneously measure the LUE and reflectance of the Douglas-fir stand as a function of shadow fraction from the “hot spot” to the "dark spot"dark spot” and a new finding herein, based on radiative transfer theory, that the magnitude of a normalized reflectance difference index (NDRI) such as PRI can vary with shadow fraction only in case the reflectance of the shaded and sunlit leaves differ in at least one of the NDRI bands. Our spectrometer measurements over a nearly 6 month period show that at a forest stand scale, only two NDRIs (both containing a band near 570 nm) vary with shadow fraction and are correlated with LUE; an NDRI with a band centered at 531 nm roughly 50 nm wide, and another near 705 nm. Therefore, we are able to conclude that only these two bands' reflectance differ between the sunlit and the shaded elements of the canopy. Their reflectance changes on time scales of a few minutes or less. Our observations also show that the reflectance changes at 531 nm are more highly correlated with variations in canopy light use efficiency when only sunlit canopy elements are viewed (the hot spot), than when only shaded elements (the dark spot) are viewed. Taken together then, these results demonstrate that the observed sub-hourly changes in foliage reflectance at 531 nm and 705 nm can only result from corresponding variations in photosynthetic rates. The importance of our results are as follows: (1) We show that variations in PRI with LUE are a direct result of rapid changes in foliage reflectance at 531 nm resulting from photosynthetic down-regulation, and can be observed at forest scales. (2) Our findings also suggest a new sensor and methodology for the direct retrieval from space of changes in forest LUE by measuring PRI as a function of shadow fraction using a multi-angle spectrometer simultaneously retrieving both shadow fraction and PRI.

Synecological comparisons sustained by ecophysiological fingerprinting of intrinsic photosynthetic capacity of plants as assessed by measurements of light response curves

In some literature variations in photosynthetic rates are considered to be of little relevance for fitness. This depends among other things on how one defines fitness, i.e. if one takes strictly Darwinian fitness as seed production or if one needs to evaluate particular traits and consider plant establishment. It also matters if one takes the Darwinian organism individual as the central entity in evolution (individual fitness) or the species individual in a modified Structure of Evolutionary Theory sensu Stephen Jay Gould. A phenotypically expressed trait like photosynthetic rate, even if intra- and interspecific differences may be small, can matter in habitat performance and niche acquisition. Light dependence curves (LCs) of photosynthetic rates are now readily measured under field conditions using miniaturized equipment of pulse amplitude modulated fluorometers. In contrast to actual momentary measurements of quantum yield of photosynthesis under actually prevailing ambient conditions, LC measurements reflect the expressed intrinsic capacity of photosynthesis. In this review we explore the power of LC measurements yielding cardinal points such as maximum apparent electron transport rate of photosystem II (ETRmax) and saturating photosynthetically active radiation (PARsat) in making intra- and interspecific comparisons of plant performance and synecological fingerprinting in ecophysiological studies across species, sites, habitats and ecosystems.

Variations in photosynthetic rate and associated parameters with age of oil palm leaves under irrigation

Net photosynthetic rate (P N), transpiration rate (E), and stomatal conductance (g s) in an adult oil palm (Elaeis guineensis) canopy were highest in the 9th leaf and progressively declined with leaf age. Larger leaf area (LA) and leaf dry mass (LDM) were recorded in middle leaves. P N showed a significant positive correlation with g s and a negative relationship with leaf mass per area (ALM). The oil palm leaf remains photosynthetically active for a longer time in the canopy which contributes significantly to larger dry matter production in general and greater fresh fruit bunch yields in particular.

Fotossíntese de folhas individuais de um cafeeiro

The great variability in income irradiance over a plant canopy makes difficult the comparison of photosynthesis rates among leaves in a plant and their integration. In this study, photosynthetical rates of ten different leaves of a coffee plant were obtained during a day. The daily variation in photosynthetic rates showed a peak between 7:00 h and 9:00 h with higher values measured for the leaves positioned at the sunrise direction and northern orientation. Lower values were consistently observed for leaves at inner position of the plant. After 9:00 h, despite the increase in photosynthetically active radiation, photosynthetic rates decreased steadily to reach negligible values at sunset. The reductions on photosynthesis rates can also be attributed to increasing stomatal resistance. Since number of leaves is highly variable in coffee plants, those results make evident how difficult is to integrate and estimate whole plant photosynthesis by taking the average of 10 leaves.

From thallus to communities: scale effects and photosynthetic performance in macroalgae communities

Experiments on aquatic plant photosynthesis are often performed on spatial scales much smaller than natural systems. The photosynthesis-irradiance relationship (P-I curve) depends, however, on whether photosynthesis is measured on leaves, shoots, plants or entire communities, so that results cannot be reliably extrapolated from the limited spatial scale of experiments to the larger scale of natural systems. To evaluate how the photosynthetic response changes with spatial scale for aquatic plants, we measured the photosynthetic production as a function of irradiance for thallus pieces, single-species and multi-species communities of 4 different marine algae (Fucus serratus, Chordaria flagelliformis, Enteromorpha sp. and Ahnfeltia plicata). Thallus pieces followed the well- known hyperbolic shape of P-I curves; that is, the community P-I curves approached linearity. Thal- lus pieces, thus, saturated at irradiances below 160 µmol photons m -2 s -1 , while the communities started to saturate at values 4 times higher and never became fully saturated even at 1750 µmol pho- tons m -2 s -1 . This increasing linearisation of the P-I relationship for communities influenced the pho- tosynthetic parameters, as maximum gross photosynthesis and compensation irradiances increased 3 to 8 times. The increasing linearisation of the P-I curves is attributed to the 3-dimensional structure of the communities, since communities with a low extinction per unit leaf area, and thus an even dis- tribution of irradiance among thallus parts, used their potential photosynthesis capacity more effi- ciently. Although not significantly different, multi-species communities had a slightly more linear response and a higher gross photosynthesis than single-species communities, suggesting a more effi- cient distribution and photosynthetic use of light among the photosynthetic tissue. An increase in spatial scale from thallus pieces to communities decreased variation in photosynthetic rates between species, implying that differences between species are much smaller on natural scales than experi- ments on single thallus pieces suggest. The findings imply that experiments on the thallus scale should be avoided or treated with caution when predicting the ecological performance of plants in their natural habitat.

Effect of photosynthetic efficiency and water availability on tolerance of leaf removal in Amaranthus hybridus

Summary Although substantial genetic variation in photosynthetic rate exists within natural populations, it is unclear how such variation might affect the capacity of plants to tolerate herbivore damage. I tested if decreased efficiency of electron transport, caused by a mutation that confers resistance to the herbicide triazine, affected the ability of Amaranthus hybridus to tolerate leaf removal, and if this genotypic effect interacted with water availability. Tolerance levels were compared with the root‐to‐shoot ratio and with compensatory photosynthesis, to investigate the mechanisms of tolerance. Triazine‐resistant A. hybridus was found to have lower tolerance to herbivory suggesting that herbivores should drive selection for higher photosynthetic capacity. Although interactive effects between water availability and photosynthetic genotype were not detected, reduced water availability did cause an overall increase in the ability of plants to tolerate damage. Greater tolerance of plants under low water availability and of the TS genotype was associated positively with root‐to‐shoot ratios, but there was a negative association between greater tolerance under low water availability and compensatory photosynthesis. These results suggest that photosynthetic variation is more likely to alter tolerance indirectly though changes in resource allocation, and that direct associations between physiological variables and tolerance may be uncommon in natural systems.

Reflectance assessment of seasonal and annual changes in biomass and CO 2 uptake of a Mediterranean shrubland submitted to experimental warming and drought

We aimed to evaluate how the remote sensing vegetation indices NDVI and PRI responded to seasonal and annual changes in an early successional stage Mediterranean coastal shrubland canopy that was submitted to experimental warming and drought simulating predicted climate change for the next decades. These conditions were obtained by using a new non-intrusive methodological approach that increases the temperature and prolongs the drought period by using roofs that automatically cover the vegetation after the sunset or when it rains. On average, warming increased air temperature by 0.7 °C and soil temperature by 1.6 °C, and the drought treatment reduced soil moisture by 22%. We measured spectral reflectance at the canopy level and at the individual plant level seasonally during 4 years. Shrubland NDVI tracked the community development and activity. In control and warming treatments, NDVI increased with the years while it did not change in the drought treatment. There was a good relationship between NDVI and both community and individual plant biomass. NDVI also decreased in summer seasons when some species dry or decolour. The NDVI of E. multiflora plant individuals was lower in autumn and winter than in the other seasons, likely because of flowering. Shrubland PRI decreased only in winter, similarly to the PRI of the most dominant species, G. alypum. At this community scale, NDVI was better related than PRI to photosynthetic activity, probably because photosynthetic fluxes followed canopy seasonal greening in this complex canopy, which includes brevideciduous, annual and evergreen species and variable morphologies and canopy coverage. PRI followed the seasonal variations in photosynthetic rates in E. multiflora and detected the decreased photosynthetic rates of drought treatment . However, PRI did not track the photosynthetic rates of G. alypum plants which have lower LAIs than E. multiflora. In this community, which is in its early successional stages, NDVI was able to track biomass, and indirectly, CO 2 uptake changes, likely because LAI values did not saturate NDVI. Thus, NDVI appears as a valid tool for remote tracking of this community development. PRI was less adequate for photosynthetic assessment of this community especially for its lower LAI canopies. PRI usefulness was also species-dependent and could also be affected by flowering. These results will help to improve the interpretation of remote sensing information on the structure and physiological status of these Mediterranean shrublands, and to gain better insight on ecological and environmental controls on their ecosystem carbon dioxide exchange. They also show the possibility of assessing the impacts of climate change on shrubland communities.

Models for ultraviolet radiation—dependent photoinhibition of Lake Erie phytoplankton

We calibrated a model for ultraviolet radiation (UVR) and photosynthetically active radiation‐dependent photoinhibition, with explicit damage and recovery processes (the R model), against observations of photosynthesis by Lake Erie phytoplankton exposed to natural sunlight in the summer of 1998. The model explained 74%–96% of the variation in photosynthetic rates and indicated active recovery processes at 4 of the 5 experimental stations. UVR‐dependent photoinhibition kinetics were not as well explained by two simpler models that assumed either a lack of recovery processes or an instantaneous equilibrium between damage and recovery. The 1998‐calibrated R model also provided consistently significant predictions of photoinhibition in 10 experiments done the previous year, albeit with a reduced goodness‐of‐fit, whereas simpler models did not. Biological weighting functions (BWFs) derived for UVR effects in 1998 were similar in shape throughout the UVR part of the spectrum, with an especially steep decrease from 300 to 320 nm, compared with BWFs published for other phytoplankton communities and/or species. The R model predicted photoinhibitory losses of primary production, integrated through the photic zone, that were intermediate between the two simpler models and showed that Lake Erie phytoplankton varied in both their spectral sensitivity (as expressed by the BWF) and recovery rates.

Ecophysiological characteristics of six broad-leaved agroforestry tree species

Twelve year old, six broad-leaved agroforestry tree species, growing at the same site, have revealed significant intergeneric diurnal variations in photosynthetic rate, amount of water transpired, leaf water potential (Y) and canopy temperature during the months of May and June. Significant mid-noon (13.30 hour) drop and substantial afternoon recovery up to 17.30 hour for all the physiological attributes were observed in all the six investigated tree species, namely, Grewia optiva, Morus alba, Celtis australis, Bauhinia variegata, Dalbergia sissoo and Toona ciliata.

Photosynthetic characteristics of charophytes from tropical lotic ecosystems

SUMMARY Responses of photosynthetic rates, determined by oxygen evolution using the light and dark bottles technique, to different temperatures, irradiances, pH, and diurnal rhythm were analyzed under laboratory conditions in four charophyte species ( Chara braunii Gmelin , C. guairensis R. Bicudo , Nitella subglomerata A. Braun and Nitella sp.) from lotic habitats in southeastern Brazil. Parameters derived from the photosynthesis versus irradiance curves indicated affinity to low irradiances for all algae tested. Some degree of photoinhibition, [ β = -(0.30‐0.13) mg O2 g ‐1 dry weight h ‐1 ( µ mol photons m ‐2 s ‐1 ) ‐1 ], low light compensation points (I c = 4‐20 µ mol photons m ‐2 s ‐1 ) were found for all species analyzed, as well as low values of light saturation parameter (I k ) and saturation (I s ) 29‐130 and 92‐169 µ mol photons m ‐2 s ‐1 , respectively. Photoacclimation was observed in two populations of N. subglomerata collected from sites with different irradiances, consisting of variations in photosynthetic parameters (higher values of α , and lower of I k and maximum photosynthetic rate, P max , in the population under lower irradiance). The highest photosynthetic rates for Chara species were observed at 10‐15 ° C, while for Nitella the highest photosynthetic rate was observed at 20‐25 ° C, despite the lack of significant differences among most levels tested. Rates of dark respiration significantly increase with temperature, with the highest values at 25 ° C. The results from pH experiments showed highest photosynthetic rates under pH 4.0 for all algae, suggesting higher affinity for inorganic carbon in the form of carbon dioxide, except in one population of N. subglomerata , with similar rates under the three levels, suggesting indistinct use of bicarbonate and carbon dioxide. Diurnal changes in photosynthetic rates revealed a general pattern for most algae tested, which was characterized by two peaks: the first (higher) during the morning (07.00‐11.00) and the second (lower) in the afternoon (14.00‐17.00). This suggests an endogenous rhythm determining the daily variations in photosynthetic rates.

Temperature Sensitivity of Photosynthesis in Lolium perenne Swards: A Comparison of Two Methods for Deriving Photosynthetic Parameters from in vivo Measurements

The seasonal variation in photosynthetic rate of grass swards is partly the result of changes in the environment and partly the result of changes in the photosynthetic capacity of the sward itself. We evaluated two types of photosynthesis equations regarding their capacity to analyse seasonal and short-term temperature effects on photosynthesis of ryegrass (Lolium perenne L.). Intact cores of a field-grown ryegrass sward were taken to the laboratory 10 d after cutting for measurement of photosynthesis under controlled conditions. This was done during two four-week periods, in summer and autumn. Net photosynthetic rate (PN) of the sward was lower in autumn than in summer. Both a simple negatively exponential photosynthesis irradiance-response curve and the Farquhar equations for photosynthesis were applied to the in vivo canopy measurements. Application of the irradiance-response curve showed that irradiance-saturated gross photosynthetic rate increased linearly with increasing temperature and was higher in summer than in autumn. The initial radiation use efficiency did not differ between the seasons but decreased with the temperature rise. This explains the observation that total canopy photosynthetic rate decreased after short-term temperature increases in both seasons. The parameters in Farquhar equations that represent the temperature sensitivity of the maximum electron transport rate and of the Michaelis-Menten constants for CO2 and O2 fixation could not be quantified satisfactorily. Parameterisation of the Farquhar equations was hampered by a lack of robust information on many biochemical parameters, and the use of simple empirical response-functions may be preferable in the case of in vivo canopy measurements on grass swards.

Variation in Photosynthetic Rates and Biomass Productivity among Four Mulberry Cultivars

Among four mulberry (Morus alba L.) cultivars (K-2, MR-2, BC2-59, and S-13), highest net photosynthetic rate (PN) was observed in BC2-59 while the lowest rates were recorded with K-2. Significant differences among the four cultivars were found in leaf area, biomass production, activities of ribulose-1,5-bisphosphate carboxylase and sucrose phosphate synthase, and glucose and sucrose contents. The PN and the activities of photosynthetic enzymes in the four cultivars were significantly correlated with the growth and biomass production measured as leaf yield, total shoot mass, and aerial plant biomass.

Vertical migration by the marine dinoflagellate Prorocentrum triestinum maximises photosynthetic yield.

Although vertical migration has been widely documented in many dinoflagellate species, the adaptive advantages of the strategy remain unclear. To investigate relationships between diurnal vertical migration and depth-related variation in photosynthetic yield in a marine dinoflagellate, Prorocentrum triestinum (Schiller), two experimental approaches were adopted. First, vertical distribution patterns of P. triestinum in a shallow estuary were investigated with respect to depth-related variation in photosynthetic rate. Second, changes in vertical positioning of P. triestinum in response to manipulations in incident light flux were investigated in an artificial water column. During the field experiment, changes in dissolved oxygen concentration in bottle cultures of P. triestinum indicated maximum rates of photosynthesis at 0.5m depth. Cell densities of P. triestinum in the water column were also highest at 0.5m depth and varied in accordance with photosynthetic yield. Fluorescence measurements indicated photoinhibition at super-saturating photosynthetic photon flux densities (PPFDs). Similar patterns were evident in the artificial water column. Depth distribution of P. triestinum varied significantly according to incident PPFD; the band of maximum cell density shifted downward in response to an increase in PPFD and upward in response to a PPFD decrease. Distributions of cells with respect to PPFD were very similar to those observed in the field experiment. Overall, vertical positioning of P. triestinum during the day is consistent with an active migratory mechanism for maximising photosynthetic production.

From Fluorescence to Fitness: Variation in Photosynthetic Rate Affects Fecundity and Survivorship

From Fluorescence to Fitness: Variation in Photosynthetic Rate Affects Fecundity and Survivorship

Seasonal variation in primary production of microphytobenthos at the Isshiki intertidal flat in Mikawa Bay

Seasonal variations in photosynthetic rates by microphytobenthos and phytoplankton at the Isshiki tidal flat in Mikawa Bay were measured with a 14C combustion method. In addition, diurnal variations in the photosynthetic rate and photosynthesis versus irradiance (P-I) curves were obtained through in situ incubation. The photosynthetic rate of microphytobenthos (annual average, 13.9 ± 6.4 mg C m−2 h−1) did not show a remarkable change, and they maintained a higher production rate than phytoplankton (annual average 9.0 ± 5.1 mg C m−2 h−1) throughout the year. The P-I curves from in situ experiments showed that the photosynthetic activity of microphytobenthos at the laboratory irradiance (250 μE m−2 s−1) was 56% of that at the maximum irradiance (1200 μE m−2 s−1) in situ. In the in situ experiments, the chlorophyll a concentration, photosynthetic rate, and activity of microphytobenthos varied greatly throughout the day, influenced by tidal submersion/emersion and daylight. From an analysis of these results, it is considered that microphytobenthos contributed greatly to primary production in this ecosystem throughout the year by adapting suitably to intertidal environments.

Inhibition of marine photosynthesis by ultraviolet radiation: Variable sensitivity of phytoplankton in the Weddell‐Scotia Confluence during the austral spring

To assess the potential impacts of ozone depletion on photosynthesis in the Southern Ocean, we need to know more about effects of ultraviolet radiation (UV) on phytoplankton in Antarctic waters, where, in addition to variable stratospheric ozone, temporal and regional differences in vertical mixing might influence photosynthesis and photoacclimation of phytoplankton assemblages. Toward this end, we quantified the responses to UV of Antarctic phytoplankton in the Weddell‐Scotia Confluence during the austral spring of 1993. Experimental results on spectral sensitivity of photosynthesis were fit statistically to a model that incorporated uninhibited photosynthesis as a function of photosynthetically available radiation (PAR), wavelength‐dependence of inhibition, and the kinetics of photosynthesis during exposure to UV. In contrast to previous results on UV‐induced photoinhibition in a diatom culture at 20°C natural phytoplankton from open waters of the Antarctic showed no ability to counter UV‐induced inhibition of photosynthesis during exposures of 0.5–4 h: the rate of photosynthesis declined exponentially as a function of cumulative exposure, and inhibition was not reversed during incubations for up to 3.5 h under benign conditions. The results suggest that nonlinear exposure‐response relationships are necessary for modeling UV dependent photosynthesis in the surface mixed layer of the springtime Weddell‐Scotia Confluence. Consequently, we modified our laboratory‐based model of photosynthesis and photoinhibition to describe photoinhibition as a nonlinear function of biologically weighted cumulative exposure to damaging irradiance. The model described ˜90% of the spectrally dependent experimental variation in photosynthetic rate, and yielded six biological weighting functions (BWFs) for phytoplankton in the Weddell‐Scotia Confluence. Assemblages from different stations showed substantial variability in sensitivity to UV. Tolerance of UV was generally highest in assemblages from shallower mixed layers, which presumably had experienced higher irradiance, including UV, prior to sampling. The BWFs of assemblages that seemed acclimated to low irradiance showed the highest sensitivity to UV yet seen for Southern Ocean phytoplankton. The pattern of UV sensitivity was consistent with acclimation, but also with selection against less tolerant species.

Effect of genome and ploidy on photosynthesis of wheat

We assessed (1) the effects of addition and doses of the D genome from different sources and (2) the addition of either the A genome or the D genome on the photosynthesis of synthesized hexaploid wheats. On average, the increased doses of the D genome reduced photosynthesis, but the depression was dependent on the source of the D genome. Two accessions of Aegilops squarrosa had depressed photosynthetic rates, but not another accession of Ae. squarrosa. The D genome of cv. Thatcher did not contribute to depress photosynthetic rate. Triticum monococcum had considerably higher photosynthetic rates than Ae. squarrosa. However, addition of the A genome from T. monococcum did not increase the photosynthetic rates of hexaploids. Chlorophyll a : b ratio, functional photosystem II and the core complex of photosystem II did not account for the variation in photosynthetic rate among the genotypes studied. In our experiment, photosynthesis of polyploids was not dependent on photosynthesis rates of the donor genomes.

Photosynthesis and Production of Epilithic Algal Communities in Thingvallavatn

Epilithic algal communities in Lake Thingvallavatn have different species- and depth-specific patterns for growth and for photosynthesis and respiration. The estimated specific photosynthesis (P max ) was relatively low, and decreased with increasing depth from 1.56 to 0.85 mg O 2 mg #751 chlorophyll a h #751 . A similar decrease in dark respiration rate was observed. In the laboratory experiments on natural epilithic communities 68 to 79% of the variation in photosynthetic rate (mg O 2 m #752 h #751 ) was explained by irradiance, 0.4 to 8% by temperature, and 2 to 5% by biomass (...)