Relationship between photosynthetic radiation-use efficiency of barley canopies and the photochemical reflectance index (PRI)

Some processes of excess radiation dissipation have been associated with changes in leaf reflectance near 531 nm. We aimed to study the relations between the photochemical reflectance index (PRI) derived from this signal, and photosynthetic radiation-use efficiency (defined as net CO₂ assimilation rate/incident photon flux density) in a cereal canopy. Measurements of reflectance, fluorescence, gas exchange and xanthophyll cycle pigments were made in the morning, midday and afternoon in barley canopies with two levels of nitrogen fertilization. The photosynthetic radiation-use efficiency decreased at midday, mainly in the third leaf, in both treatments, with lower values for the nitrogen deficient leaves. The zeaxanthin content showed the inverse pattern, increasing at midday and in the nitrogen deficient treatment. The photosynthetic radiation-use efficiency was well correlated with the epoxidation state, EPS (violaxanthin + 0.5 antheraxanthin)/(violaxanthin + antheraxanthin + zeaxanthin). The PRI [here defined as (R₅₃₉ - R₅₇₀)/(R₅₃₉+ R₅₇₀)] was significantly correlated with epoxidation state and zeaxanthin and with photosynthetic radiation-use efficiency. These results validate the utility of PRI in the assessment of radiation-use efficiency at canopy level.     

Nondestructive evaluation of the photosynthetic properties of micropropagated plantlets by imaging photochemical reflectance index under low light intensity

The photochemical reflectance index (PRI) of micropropagated potato leaves was estimated nondestructively from outside the culture vessel using a PRI imaging system developed by the present group. The PRI was determined under low light intensity conditions after dark treatment and compared with the chlorophyll fluorescence parameter Fv/Fm, which denotes photosystem II maximum quantum yield. Short-term high-light treatment decreased Fv/Fm of the plantlets. Culture conditions such as temperature and sucrose concentration also affected Fv/Fm. A linear relationship between the PRI and Fv/Fm was observed in both cases of high-light treatment and different culture conditions, suggesting the potential of the PRI to be used as a substitute for Fv/Fm. PRI estimated from reflection images under low light intensity conditions may be used for rapid and noninvasive evaluation of photosynthetic properties of micropropagated plantlets in a similar manner to Fv/Fm.     

Geometrical similarity analysis of photosynthetic light response curves, light saturation and light use efficiency

Light absorption and use efficiency (LAUE mol mol⁻¹, daily gross photosynthesis per daily incident light) of each leaf depends on several factors, including the degree of light saturation. It is often discussed that upper canopy leaves exposed to direct sunlight are fully light-saturated. However, we found that upper leaves of three temperate species, a heliophytic perennial herb Helianthus tuberosus, a pioneer tree Alnus japonica, and a late-successional tree Fagus crenata, were not fully light-saturated even under full sunlight. Geometrical analysis of the photosynthetic light response curves revealed that all the curves of the leaves from different canopy positions, as well as from the different species, can be considered as different parts of a single non-rectangular hyperbola. The analysis consistently explained how those leaves were not fully light-saturated. Light use optimization models, called big leaf models, predicted that the degree of light saturation and LAUE are both independent of light environment. From these, we hypothesized that the upper leaves should not be fully light-saturated even under direct sunlight, but instead should share the light limitation with the shaded lower-canopy leaves, so as to utilize strong sunlight efficiently. Supporting this prediction, within a canopy of H. tuberosus, both the degree of light saturation and LAUE were independent of light environment within a canopy, resulting in proportionality between the daily photosynthesis and the daily incident light among the leaves.     

Relationships of photosynthetic capacity to PSII efficiency and to photochemical reflectance index of Pinus taiwanensis through different seasons at high and low elevations of sub-tropical Taiwan

We investigated the relationships of photosynthetic capacity (P _nsat, near light-saturated net photosynthetic rate measured at 1,200 μmol m⁻² s⁻¹ PPFD) to photosystem II efficiency (F _v/F _m) and to photochemical reflectance index [PRI = (R ₅₃₁ − R ₅₇₀)/(R ₅₃₁ + R ₅₇₀)] of Pinus taiwanensis Hay. needles at high (2,600 m a.s.l) and low-elevation (800 m a.s.l) sites through different seasons. Results indicate that at high-elevation site, P _nsat, F _v/F _m and PRI (both measured at predawn) paralleled in general with the air temperature. On the coolest measuring day with the minimum air temperature dropping to −2°C, P _nsat could decrease to ca. 15% of its highest value, which was measured in autumn. At low-elevation site, with the minimum air temperature of 10–12°C in cooler season and almost no seasonal variation of F _v/F _m, P _nsat dropped to ca. 65% of its highest value and PRI decreased ca. 0.02 in winter. Even though seasonal variation of P _nsat was affected by many factors, it was still closely related to PRI based on statistical analyses using data from both sites, through different seasons. On the contrary, seasonal variation of F _v/F _m of P. taiwanensis needles was influenced mainly by low temperature at high elevation. Therefore, the correlation of P _nsat − F _v/F _m was lower than that of P _nsat − PRI when data combined from both high- and low-elevation sites were analyzed. It is concluded that predawn PRI could be used as an indicator to estimate the seasonal potential of photosynthetic capacity of P. taiwanensis grown at low- and high-elevations of sub-tropical Taiwan.     

Estimating photosynthetic radiation use efficiency using incident light and photosynthesis of individual leaves

It has been theorized that photosynthetic radiation use efficiency (PhRUE) over the course of a day is constant for leaves throughout a canopy if leaf nitrogen content and photosynthetic properties are adapted to local light so that canopy photosynthesis over a day is optimized. To test this hypothesis, 'daily' photosynthesis of individual leaves of Solanum melongena plants was calculated from instantaneous rates of photosynthesis integrated over the daylight hours. Instantaneous photosynthesis was estimated from the photosynthetic responses to photosynthetically active radiation (PAR) and from the incident PAR measured on individual leaves during clear and overcast days. Plants were grown with either abundant or scarce N fertilization. Both net and gross daily photosynthesis of leaves were linearly related to daily incident PAR exposure of individual leaves, which implies constant PhRUE over a day throughout the canopy. The slope of these relationships (i.e. PhRUE) increased with N fertilization. When the relationship was calculated for hourly instead of daily periods, the regressions were curvilinear, implying that PhRUE changed with time of the day and incident radiation. Thus, linearity (i.e. constant PhRUE) was achieved only when data were integrated over the entire day. Using average PAR in place of instantaneous incident PAR increased the slope of the relationship between daily photosynthesis and incident PAR of individual leaves, and the regression became curvilinear. The slope of the relationship between daily gross photosynthesis and incident PAR of individual leaves increased for an overcast compared with a clear day, but the slope remained constant for net photosynthesis. This suggests that net PhRUE of all leaves (and thus of the whole canopy) may be constant when integrated over a day, not only when the incident PAR changes with depth in the canopy, but also when it varies on the same leaf owing to changes in daily incident PAR above the canopy. The slope of the relationship between daily net photosynthesis and incident PAR was also estimated from the photosynthetic light response curve of a leaf at the top of the canopy and from the incident PAR above the canopy, in place of that measured on individual leaves. The slope (i.e. net PhRUE) calculated in this simple way did not differ statistically from that calculated using data from individual leaves.     

A relationship between carbon dioxide, photosynthetic efficiency and shade tolerance

Net photosynthesis and transpiration of seedlings from shade tolerant, moderately tolerant and intolerant tree species were measured in ambient carbon dioxide (CO₂) concentrations ranging from 312 to 734 ppm. The species used, Fagus grandifolia Ehrh. (tolerant), Quercus alba L., Q. rubra L., Liriodendron tulipifera L. (moderately tolerant), Liquidambar styraciflua L. and Pinus taeda L. (intolerant), are found co-occurring in the mixed pine-hardwood forests of the Piedmont region of the southeastern United States. When seedlings were grown in shaded conditions, photosynthetic CO₂ efficiency was significantly different in all species with the highest efficiency in the most shade tolerant species, Fagus grandifolia , and progressively lower efficiencies in moderately tolerant and intolerant species. Photosynthetic CO₂ efficiency was defined as the rate of increase in net photosynthesis with increase in ambient CO₂ concentration. When plants which had grown in a high light environment were tested, the moderately tolerant and intolerant deciduous species had the highest photosynthetic CO₂ efficiencies but this capacity was reduced when these species grew in low light. The lowest CO₂ efficiency and apparent quantum yield occurred in Pinus taeda in all cases. Water use efficiency was higher for all species in enriched CO₂ environments but transpiration rate and leaf conductance were not affected by CO₂ concentration. High photosynthetic CO₂ efficiency may be advantageous for maintaining a positive carbon balance in the low light environment under a forest canopy.     

Relationships between photosystem II efficiency and photochemical reflectance index under different levels of illumination: comparison among species grown at high- and low elevations through different seasons

Previously, we found a significant association between photosystem II efficiency (ΦPSII) and photochemical reflectance index (PRI) measured at predawn among different species at different elevations and throughout several seasons. However, this relationship has not been evaluated under varied levels of illumination. Here, we used the Taiwan species Pinus taiwanensis (a conifer distributed at 750–3,000 m a.s.l.), Stranvaesia niitakayamensis (an evergreen tree, 1,700–3,100 m) and two Miscanthus spp. (perennial C₄ Gramineae, coastline–3,200 m) to elucidate the ΦPSII–PRI relationship. We studied six levels of photosynthetic photon flux density (PPFD) (0, 200, 400, 800, 1,200 and 2,000 μmol m⁻² s⁻¹) over several growth seasons at high (2,600 m a.s.l.) and low (800 m a.s.l.) elevation sites. In comparing the same species or genus, ΦPSII and PRI were closely correlated in darkness or under the same level of PPFD, with data obtained from different seasons and elevations pooled for regression analysis. Because both the intercept and slope of the ΦPSII–PRI equation showed a negative curvilinear correlation with PPFD, we could fit an empirical regression model, ΦPSII = c + d·ln(PPFD) + e·[ln(PPFD)]² + f·PRI + g·PRI·ln(PPFD) + h·PRI·[ln(PPFD)]², for multiple regression analysis. Using this model, we found a close correlation between the estimated and measured ΦPSII (r ² = 0.842−0.937, P < 0.001) for all four species examined and for mango (Mangifera indica) measured under both artificial illumination and sunlight (data from Weng et al. 2010). This empirical regression model could simulate both seasonal and diurnal variations of leaf-scale photosynthetic efficiency at high and low elevations.     

Blue light reduces photosynthetic efficiency of cyanobacteria through an imbalance between photosystems I and II

Several studies have described that cyanobacteria use blue light less efficiently for photosynthesis than most eukaryotic phototrophs, but comprehensive studies of this phenomenon are lacking. Here, we study the effect of blue (450 nm), orange (625 nm), and red (660 nm) light on growth of the model cyanobacterium Synechocystis sp. PCC 6803, the green alga Chlorella sorokiniana and other cyanobacteria containing phycocyanin or phycoerythrin. Our results demonstrate that specific growth rates of the cyanobacteria were similar in orange and red light, but much lower in blue light. Conversely, specific growth rates of the green alga C. sorokiniana were similar in blue and red light, but lower in orange light. Oxygen production rates of Synechocystis sp. PCC 6803 were five-fold lower in blue than in orange and red light at low light intensities but approached the same saturation level in all three colors at high light intensities. Measurements of 77 K fluorescence emission demonstrated a lower ratio of photosystem I to photosystem II (PSI:PSII ratio) and relatively more phycobilisomes associated with PSII (state 1) in blue light than in orange and red light. These results support the hypothesis that blue light, which is not absorbed by phycobilisomes, creates an imbalance between the two photosystems of cyanobacteria with an energy excess at PSI and a deficiency at the PSII-side of the photosynthetic electron transfer chain. Our results help to explain why phycobilisome-containing cyanobacteria use blue light less efficiently than species with chlorophyll-based light-harvesting antennae such as Prochlorococcus, green algae and terrestrial plants.     

On the relationship between nutrient use efficiency and fertility in forest ecosystems

The concept of nutrient use efficiency is central in understanding ecosystem functioning because it is the step in which plants can influence the return of the nutrients to the soil pool and the quality of the litter. There are several ways to define nutrient use efficiency, but a common way within ecosystem ecology is as the ratio of litterfall production per unit nutrient to the litterfall nutrient content. However, this ratio is not a valid measurement to examine nutrient use efficiency in relationship to ecosystem fertility because there is a strong autocorrelation between litterfall dry mass per unit of nutrient and the amount of nutrients. More appropriate statistical analysis of the relationship between the fertility of ecosystems and the amount of nutrients in the litterfall are inconclusive, but indicate that, at least in some cases, there is (1) no pattern, (2) higher nutrient use efficiency at intermediate-fertility sites or (3) higher efficiency at higher-fertility sites. There is, however, no indication that nutrient use efficiency is greater in nutrient-poor ecosystems. This conclusion has important consequences for ecosystem nutrient cycling. Given the lack of a clear, consistent relationship between site fertility and litterfall nutrients, there is little likelihood that such a feedback mechanism plays an important role in ecosystem nutrient cycling. Received: 22 January 1996 / Accepted: 26 December 1996     

Relationships between the photochemical reflectance index (PRI) and chlorophyll fluorescence parameters and plant pigment indices at different leaf growth stages

This study aimed to evaluate the photochemical reflectance index (PRI) for assessing plant photosynthetic performance throughout the plant life cycle. The relationships between PRI, chlorophyll fluorescence parameters, and leaf pigment indices in Solanum melongena L. (aubergine; eggplant) were studied using photosynthetic induction curves both in short-term (diurnal) and long-term (seasonal) periods under different light intensities. We found good correlations between PRI/non-photochemical quenching (NPQ) and PRI/electron transport rate (ETR) in the short term at the same site of a single leaf but these relationships did not hold throughout the life of the plant. In general, changes in PRI owing to NPQ or ETR variations in the short term were <20?% of those that occurred with leaf aging. Results also showed that PRI was highly correlated to plant pigments, especially chlorophyll indices measured by spectral reflectance. Moreover, relationships of steady-state PRI/ETR and steady-state PRI/photochemical yield of photosystem II (Φ(PSII)) measured at uniform light intensity at different life stages proved that overall photosynthesis capacity and steady-state PRI were better correlated through chlorophyll content than NPQ and xanthophylls. The calibrated PRI index accommodated these pigments effects and gave better correlation with NPQ and ETR than PRI. Further studies of PRI indices based on pigments other than xanthophylls, and studies on PRI mechanisms in different species are recommended.     

The relationship between light scattering and chlorophyll a fluorescence during oscillations in photosynthetic carbon assimilation

Light scattering, which can be taken as an indicator of the transthylakoid proton gradient, and the 518-nm rise, which can be regarded as a measure of the transthylakoid membrane potential, have been followed during oscillations in chlorophyll a fluorescence, which are known to be associated with corresponding changes in photosynthetic carbon assimilation. Both components oscillated in a manner which was broadly reciprocal to chlorophyll a fluorescence. However, there was a phase shift such that the light-scattering change usually anticipated fluorescence and often also the 518-nm shift. It is concluded that the proton motive force rises and falls slightly in advance of rises and falls in carbon assimilation. The relationship of these changes to a possible underlying mechanism is discussed.     

Effects of light and elevated pCO2 on the growth and photochemical efficiency of Acropora cervicornis

The effects of light and elevated pCO₂ on the growth and photochemical efficiency of the critically endangered staghorn coral, Acropora cervicornis, were examined experimentally. Corals were subjected to high and low treatments of CO₂ and light in a fully crossed design and monitored using 3D scanning and buoyant weight methodologies. Calcification rates, linear extension, as well as colony surface area and volume of A. cervicornis were highly dependent on light intensity. At pCO₂ levels projected to occur by the end of the century from ocean acidification (OA), A. cervicornis exhibited depressed calcification, but no change in linear extension. Photochemical efficiency (F _v /F _m ) was higher at low light, but unaffected by CO₂. Amelioration of OA-depressed calcification under high-light treatments was not observed, and we suggest that the high-light intensity necessary to reach saturation of photosynthesis and calcification in A. cervicornis may limit the effectiveness of this potentially protective mechanism in this species. High CO₂ causes depressed skeletal density, but not linear extension, illustrating that the measurement of extension by itself is inadequate to detect CO₂ impacts. The skeletal integrity of A. cervicornis will be impaired by OA, which may further reduce the resilience of the already diminished populations of this endangered species.     

The consequences of chlorophyll deficiency for photosynthetic light use efficiency in a single nuclear gene mutation of cowpea

The light harvesting and photosynthetic characteristics of a chlorophyll-deficient mutant of cowpea (Vigna unguilata), resulting from a single nuclear gene mutation, are examined. The 40% reduction in total chlorophyll content per leaf area in the mutant is associated with a 55% reduction in pigment-proteins of the light harvesting complex associated with Photosystem II (LHC II), and to a lesser extent (35%) in the light harvesting complex associated with Photosystem I (LHC I). No significant differences were found in the Photosystem I (PS I) and Photosystem II (PS II) contents per leaf area of the mutant compared to the wildtype parent. The decreases in the PS I and PS II antennae sizes in the mutant were not accompanied by any major changes in quantum efficiencies of PS I and PS II in leaves at non-saturating light levels for CO₂ assimilation. Although the chlorophyll deficiency resulted in an 11% decrease in light absorption by mutant leaves, their maximum quantum yield and light saturated rate of CO₂ assimilation were similar to those of wildtype leaves. Consequently, the large and different decreases in the antennae of PS II and PS I in the mutant are not associated with any loss of light use efficiency in photosynthesis.Abbreviations LHC I, LHC II light harvesting chlorophyll a/b protein complexes associated with PS I and PS II - A₈₂₀ light-induced absorbance change at 820 nm - ø_{PS I}, ø_{PS II} relative quantum efficiencies of PS I and PS II photochemistry     

Enhanced photosynthetic nitrogen use efficiency and increased nitrogen allocation to photosynthetic machinery under cotton domestication

Photosynthesis Research - Domestication involves dramatic phenotypic and physiological diversifications due to successive selection by breeders toward high yield and quality. Although...     

Leaf paraheliotropism in Styrax camporum confers increased light use efficiency and advantageous photosynthetic responses rather than photoprotection

Styrax caporum is a native shrub from the Brazilian savanna. Most of its leaves are diaheliotropic, whereas some are paraheliotropic, mainly at noon. A previous study of this species revealed higher stomatal conductance (gs) and transpiration rates (E) in para- compared to diaheliotropic leaves, and a rise in CO₂ assimilation rates (A) with an increase of irradiance for paraheliotropic leaves. We hypothesized that this species exploits the paraheliotropism to enhance the light use efficiency, and that it is detected only if gas exchange is measured with light interception by both leaf surfaces. Gas exchange was measured with devices that enabled light interception on only one of the leaf surfaces and with devices that enabled light interception by both leaf surfaces. Water relations, relative reflected light intensity, leaf temperature (T_l), and leaf anatomical analyses were also performed. When both leaf surfaces were illuminated, a higher A, E, and gs were observed in para- compared to diaheliotropic leaves; however, A did not depend on gs, which did not influence CO₂ accumulation in the stomatal cavity (Ci). When only the adaxial leaf surface was illuminated, a greater A was detected for para- than for diaheliotropic leaves only at 11:00 h; no differences in T_l were observed between leaf types. Light curves revealed that under non-saturating light the adaxial side of paraheliotropic leaves had higher A than the abaxial side, but they showed similar values under saturating light. Although the abaxial leaf side was highly reflective, both surfaces presented the same response pattern for green light reflection, which can be explained by the compact spongy parenchyma observed in the leaves, increasing light use efficiency in terms of CO₂ consumption for paraheliotropic leaves. We propose that paraheliotropism in S. camporum is not related to leaf heat avoidance or photoprotection.     

Gas exchange and photosynthetic water use efficiency in response to light, CO2 concentration and temperature in Vicia faba

Light and temperature-response curves and their resulting coefficients, obtained within ecophysiological characterization of gas exchanges at the leaf level, may represent useful criteria for breeding and cultivar selection and required tools for simulation models aimed at the prediction of potential plant behaviour in response to environmental conditions.

Leaf-scale gas exchanges, by means of an IRGA open-flow system, were measured in response to light intensity (8 levels from 0 up to 2000 μmol m⁻² s⁻¹), CO₂ concentrations (ambient—350 μmol mol⁻¹ and short-term enriched—700 μmol mol⁻¹) and air temperature (from 7 up to 35 °C) on three Vicia faba L. genotypes, each representing one of the three cultivated groups: major, equina and minor. The net assimilation rate response to light intensity was well described by an exponential rise to max function. The short-term CO₂ enrichment markedly increased the values of light response curve parameters such as maximum photosynthetic rate (+80%), light saturation point (+40%) and quantum yield (+30%), while less homogenous behaviour was reported for dark respiration and light compensation point. For each light intensity level, the major and minor genotypes studied showed assimilation rates at least a 30% higher than equina.

The positive effects of short-term CO₂ enrichment on photosynthetic water use efficiency (WUE) indicate a relevant advantage in doubling CO₂ concentration. In the major and minor genotypes studied, similar assimilation rates, but different WUE were observed.

The optimum leaf temperature for assimilation process, calculated through a polynomial function, was 26–27 °C and no relevant limitations were observed in the range between 21 and 32 °C.

Analysis at the single leaf level provided both rapid information on the variations in gas exchange in response to environmental factors and selection criteria for the screening of genotypes.     

Estimating leaf photosynthesis of C3 plants grown under different environments from pigment index,photochemical reflectance index,and chlorophyll fluorescence

Photosynthesis Research - Photosynthetic rates vary depending on growth conditions, even within species. Remote sensing techniques have a great potential to predict the photosynthetic rates of...