Photosynthetic Light Response Curves Research Articles

Comparison of four light-response models using relative curvature measures of nonlinearity

Photosynthetic light response curves serve as powerful mathematical tools for quantitatively describing the rate of photosynthesis of plants in response to changes in irradiance. However, in practical applications, the daunting task of selecting an appropriate nonlinear model to accurately fit these curves persists as a significant challenge. Thus, there arises a need for a method to systematically evaluate the efficacy of such models. In the present study, four distinct nonlinear models, namely Exponential Model (EM), Rectangular Hyperbola Model (RHM), Nonrectangular Hyperbola Model (NHM), and Modified Rectangular Hyperbola Model (MRHM), were used to fit the relationship between light intensity and the rate of photosynthesis across 42 empirical datasets. The goodness of fit for each model was assessed using the root-mean-square error, and relative curvature measures of nonlinearity were employed to assess the nonlinear behavior of the models. In terms of goodness of fit, pairwise difference tests of the root-mean-square error revealed that there was little to choose among the four models, although RHM gave a marginally poorer fit. However, in terms of nonlinear behavior, EM not only provided the most favorable linear approximation performance at the global level, but also exhibited the best close-to-linear behavior at the individual parameter level among the four models across the 42 datasets. Consequently, the results strongly advocate for EM as the most suitable mathematical framework for fitting photosynthetic light response curves. These findings provide insights into the model assessment for nonlinear regression in describing the relationship between the photosynthetic rate and light intensity.

The photosynthetic uptake of inorganic carbon from Pyropia seaweed aquaculture beds: Scaling up population-level estimations

Seaweed aquaculture beds (SABs) contribute positively to CO2 removal (CDR) worldwide. Among cultivated seaweed species, Pyropia represents approximately 8% of the global seaweed production and has the capacity to sequester a significant amount of carbon from the surface layer of the coastal ocean. In this study, we evaluated the carbon uptake efficiency of Pyropia SABs by measuring their photosynthetic rates. Pyropia individuals were collected from Pyropia SABs on the south and west coasts of South of Korea from December to March (cultivation period) in 2016 to 2019, and the photosynthetic light response curves (P-E curves) were measured. Oxygen-based photosyntheses were converted into carbon-based photosynthetic rates using theoretical photosynthetic quotients. Pyropia thallus consumed an average 37 mg C g−1ww d−1, with a high ratio of gross primary production to respiration (P/R ratio; 5–14). To quantify the carbon uptake potential in the coastal areas of South Korea during the cultivation period, we extrapolated the carbon uptake rates using the estimated biomass, total area of Pyropia SABs, and meteorological irradiance data. The highest carbon uptake rate (2143 kt C month−1) was observed in the Southwestern Sea of South Korea in December. Considering all productivity data from the entire cultivation period, approximately 6789 kt C was taken up by the Pyropia SABs. Therefore, our study indicates a significant potential to mitigate climate change by reducing greenhouse gas emissions using Pyropia SABs.

Physiological differences among cryptic species of the Mediterranean crustose coralline alga Lithophyllum stictiforme (Corallinales, Rhodophyta)

ABSTRACT The crustose coralline alga Lithophyllum stictiforme is an important reef builder, forming coralligenous concretions in the Mediterranean Sea. This algal species complex is composed of eight cryptic species (or clades). The objective of our study was to compare light-dependent physiological processes within and between the two most abundant cryptic species (C1 and C4) of L. stictiforme from the Bay of Marseille (France). Physiological rates of respiration, photosynthesis and calcification were measured using incubation chambers under various irradiance levels and in the dark during the summer period. We compared the physiology of the C1 and C4 cryptic species of L. stictiforme among three algal groups: C1 (the most common in the Marseille area) from 28 m depth, C4 from the same site and depth, and C1 from a deeper site at 45 m depth. We found both interspecific (between C1 and C4) and intraspecific (within C1) physiological differences. Photosynthetic parameters showed acclimation to light (or depth) with higher values of initial slope of photosynthetic light response curve (α) and lower values of saturating irradiance (Ek) and compensating irradiance (Ec) for C1 from 45 m than for C1 and C4 from 28 m depth. At the shallower depth, significant physiological differences were observed between C1 and C4 with a higher value of maximum rate of gross photosynthesis (Pg max) in C4, suggesting better ability to grow under high irradiance. Light and dark calcification rates differed only between C4 from 28 m and C1 from 45 m depth, being intermediate in C1 from 28 m depth. On a 24 h basis, diel net calcification rates were significantly higher in specimens from the shallower waters than from the deeper waters. Physiological differences suggest physiological plasticity within the regionally dominant cryptic species C1 and species-specific physiological traits between the cryptic species C1 and C4.

Potential of agrivoltaics systems into olive groves in the Mediterranean region

Agrivoltaics systems have emerged as an approach to alleviate competition for land use between food and energy production. Conducting a thorough analysis of the impact that shading from PV modules can have on crops is crucial for the correct design of the system, as excessive shading can lead to important crop yield reductions. This paper focuses on integrating agrivoltaics systems within super-intensive olive groves in the Mediterranean region. A dual model is used to calculate the suitable transparency of PV modules, representing the area not occupied by PV cells. This model customizes the results based on the site's meteorological parameters and the photosynthetic light-response curve of the olive cultivar. The results indicate that transparency levels vary between 0.57 and 0.71, with the lowest values observed in locations with higher solar radiation, such as Egypt and Tunisia. Using these transparency values and typical 20%-efficiency monocrystalline silicon modules, the annual average energy generation per m2 in the selected locations is 65.9 kWh. Another finding reveals that optimizing the model by considering only the months corresponding to the olive growth cycle can reduce the required transparency, thereby increasing the installed PV capacity by up to 3.5%. Furthermore, the potential deployment of these systems is evaluated in terms of installed PV capacity, energy generation, CO2 emissions and job creation. The calculations show that installing agrivoltaics systems into 1% of the total olive surface area in the Mediterranean region would: (i) result in a 2.5% increase in the global PV capacity, (ii) generate 1.8% of the current electricity demand in the selected Mediterranean countries, (iii) avoid the emissions of 4 Mt. (CO2) per year, and (iv) create around 560,000 jobs.

Assessing Water Relations and Carbon Dynamics of Pinus taeda Branches Undergoing Shade-Induced Mortality

Light acts as a complex signal, influencing various plant physiological, phenological and morphogenetic traits. Although previous studies have explored the effects of varying light levels on branch growth and survival, the underlying mechanisms of branch mortality under shade conditions remain poorly understood, hindering our understanding of canopy dynamics. In this study, contrasting shade conditions were imposed on Pinus taeda branches, and the changes in their water relations and carbon dynamics were evaluated. Monthly measurements of the photosynthetic light–response curve (LRC), sap flow and water potential of the branches were conducted. Furthermore, the conditions that led to the deaths of lower branches were investigated, and principal component analysis (PCA) was used to classify branches according to their mortality status. Significant shade treatment effects were observed for all photosynthetic parameters. The assimilation at light saturation (Amax), dark respiration rate (Rd), apparent quantum yield (AQY), light compensation point (LCP) and light saturation point (LSP) all decreased from full light to deepest shade, whereas the opposite was the case for the convexity term (θ). All water relations traits also decreased from full light to deepest shade; however, although significant shade effect was observed in stomatal conductance (gs) and sap flow, the differences in the pre-dawn (Ψpre-dawn) and mid-day (Ψmid-day) water potentials among treatments were not statistically significant. The PCA classification results showed that it could be used as a reliable method to screen for branch mortality as early as four months before mortality becomes evident. Our results shed more light on branch physiology and mortality under shade and have the potential to help improve the prediction of tree crown size, ultimately improving process-based forest growth models.

Interactive effect of branch source-sink ratio and leaf aging on photosynthesis in pistachio.

Tree source-sink ratio has a predominant and complex impact on tree performance and can affect multiple physiological processes including vegetative and reproductive growth, water and nutrient use, photosynthesis, and productivity. In this study, we manipulated the branch level source-sink ratio by reduction of photosynthetic activity (partial branch defoliation) or thinning branch fruit load early in the growing season (after fruit set) in pistachio (Pistacia vera) trees. We then characterized the leaf photosynthetic light response curves through leaf aging. In addition, we determined changes in leaf non-structural carbohydrates (NSC) and nitrogen (N) concentrations. In leaves with high source-sink ratios, there was a gradual decrease in maximum net photosynthetic rate (ANmax) over the growing season, while in branches with low source-sink ratios, there was a sharp decline in ANmax in the first two weeks of August. Branches with high-sink showed an up-regulation (increase) in photosynthesis toward the end of July (at 1,500 growing degree days) during the period of rapid kernel growth rate and increased sink strength, with ANmax being about 7 μmol m-1 s-1 higher than in branches with low-sink. In August, low source-sink ratios precipitated leaf senescence, resulting in a drastic ANmax decline, from 25 to 8 μmol m-1 s-1 (70% drop in two weeks). This reduction was associated with the accumulation of NSC in the leaves from 20 to 30 mg g-1. The mechanisms of ANmax reduction differ between the two treatments. Lower photosynthetic rates of 8-10 μmol m-1 s-1 late in the season were associated with lower N levels in high-sink branches, suggesting N remobilization to the kernels. Lower photosynthesis late in the season was associated with lower respiration rates in low-source branches, indicating prioritization of assimilates to storage. These results can facilitate the adaptation of management practices to tree crop load changes in alternate bearing species.

Basil functional and growth responses when cultivated via different aquaponic and hydroponics systems.

Aquaponics is an innovative farming system that combines hydroponics and aquaculture, resulting in the production of both crops and fish. Decoupled aquaponics is a new approach introduced in aquaponics research for the elimination of certain system bottlenecks, specifically targeting the optimization of crops and fish production conditions. The aquaponics-related literature predominantly examines the system's effects on crop productivity, largely overlooking the plant functional responses which underlie growth and yield performance. The aim of the study was the integrated evaluation of basil performance cultivated under coupled and decoupled aquaponic systems compared with a hydroponic one, in terms of growth and functional parameters in a pilot-scale aquaponics greenhouse. We focused on the efficiency of the photosynthetic process and the state of the photosynthetic machinery, assessed by instantaneous gas exchange measurements as well as photosynthetic light response curves, and in vivo chlorophyll a fluorescence. Light use efficiency was estimated through leaf reflectance determination. Photosynthetic pigments content and leaf nutritional state assessments completed the picture of basil functional responses to the three different treatments/systems. The plant's functional parameters were assessed at 15-day intervals. The experiment lasted for two months and included an intermediate and a final harvest during which several basil growth parameters were determined. Coupled aquaponics resulted in reduced growth, which was mainly ascribed to sub-sufficient leaf nutrient levels, a fact that triggered a series of negative feedbacks on all aspects of their photosynthetic performance. These plants experienced a down-regulation of PSII activity as reflected in the significant decreases of quantum yield and efficiency of electron transport, along with decreased photosynthetic pigments content. On the contrary, decoupled aquaponics favored both growth and photochemistry leading to higher light use efficiency compared with coupled system and hydroponics, yet without significant differences from the latter. Photosynthetic light curves indicated constantly higher photosynthetic capacity of the decoupled aquaponics-treated basil, while also enhanced pigment concentrations were evident. Basil functional responses to the three tested production systems provided insights on the underlying mechanisms of plant performance highlighting key-points for systems optimization. We propose decoupled aquaponics as an effective system that may replace hydroponics supporting high crops productivity. We suggest that future works should focus on the mechanisms involved in crop and fish species function, the elucidation of which would greatly contribute to the optimization of the aquaponics productivity.

Comparative growth and physiological performance of American chestnuts, oaks, hickories, and sugar maple across a silvicultural gradient in overstory retention

The development of a blight-tolerant transgenic American chestnut (Castanea dentata (Marsh.) Borkh.) would provide the potential for reintroducing this species into forests it historically dominated. However, we lack a silvicultural understanding of the environmental conditions most favorable to the growth and survival of American chestnut relative to species with which it historically co-existed. We examined effects of shelterwoods with variable residual densities on the growth and physiology of blight-tolerant chestnut seedlings relative to sugar maple (Acer saccharum Marsh.), and several oak (Quercus spp.) and hickory (Carya spp.) species across a broad range of light availabilities (gap light index; GLI; of 4–50%). To assess the hypothesis that American chestnuts are more physiologically plastic and responsive to light than oaks and hickories, we measured seedling relative diameter and height growth rates and photosynthetic light-response curves across a GLI gradient. The diameter and height growth of chestnut increased with GLI, while oaks and hickories did not. All species varied aspects of their photosynthetic physiology across the GLI gradient in an approximately equivalent manner; the dark respiration rate and light compensation point increased equivalently across species in response to increases in light availability. A multivariate analysis identified three major axes of variation across ten measured traits, largely reflecting differences in species averages and phenotypic plasticity across the GLI gradient. American chestnut seedlings were spread across these multivariate dimensions more than other species, consistent with the hypothesis of higher phenotypic plasticity in this focal species. These results suggest that low residual shelterwood densities may better promote the establishment of underplanted chestnut seedlings relative to associated tree species provided it does not result in detrimental increases in the productivity of competing understory species.

Phytoplankton Primary Productionin the Coastal Water surrounding Shantar Archipelago

Our studies were carried out in July 2016, in the Uda Bay and the Academy Bay (including the Ulban Bay and Nikolay Bay). The primary production (PP) of phytoplankton in the photic zone was calculated from the thickness of the euphotic zone, as well as by the concentration of chlorophyll а, and the assimilation numbers of phytoplankton. We used for calculations a modified nonrectangular hyperbola model, for photosynthetic light-response curves of phytoplankton. The formation of PP is a function of the supply of nutrients to the photic zone from the underlying waters by intense tidal currents under conditions of weak stratification. The high concentrations of humus substances in Uda Bay limited the growth of phytoplankton. The values of integra-ted PP varied between Uda Bay to Academy Bay from 250–1000 to 1069–4268 mgC m–2 day–1.

Determining the ecophysiological limits of a narrow niche tropical conifer tree (Podocarpus trinitensis).

Many tropical species live close to their thermal limits within a narrow niche. Here, we investigate the ecophysiological limits of the tropical tree Podocarpus trinitensis, which is endemic to Trinidad and Tobago where most populations exist as isolated stands on hilltops. Five wild stands from a range of elevations were compared in the field with measurements of leaf temperature, canopy cover, stomatal conductance (gs), chlorophyll content and several chlorophyll fluorescence parameters. A parallel greenhouse experiment was used to acclimate seedlings to 'CONTROL' and 'HEAT' treatments (with mid-day air temperatures of 34.5 and 37°C respectively), after which the above parameters were measured along with photosynthetic light and temperature response curves, leaf morphology and in vitro Fv/Fm thermostability. There was a positive association between improved physiological performance and elevation. In the high elevation sites, leaf temperatures were significantly lower while most of the physiological parameters were higher (gs, chlorophyll content, ɸ PSII, ETRmax and Isat90). In the greenhouse, HEAT and CONTROL plants were similar for most parameters, except leaf temperature (which was coupled with air temperature) and leaf mass per unit area (which was higher in HEAT plants). Temperature response curves showed an optimum temperature for photosynthesis of 30±0.5°C (TOpt) and in vitro Fv/Fm indicated a critical temperature of 47.4±0.38°C for HEAT and 48.2±0.24°C for CONTROL (T50), with no indication of heat acclimation. Podocarpus trinitensis was found to be shade tolerant. In the field, seedlings established under a close canopy (>95% canopy cover) and had a low light saturation point (LCP). In the greenhouse, where more light was available, seedlings retained a low light compensation point, light saturation point (LSP) and maximum photosynthetic rate (Amax). The results suggest that P. trinitensis is moderately heat tolerant with the higher elevation sites being more habitable, but stands are also able to survive near sea level under a closed canopy. The narrow niche, along with the 30±0.5°C optimum temperature for photosynthesis and the lack of thermal plasticity in critical temperature, suggests that P. trinitensis has little room to acclimate to temperatures higher than those currently experienced.

Photosynthetic Processes and Light Response Model Fitting of Quercus acutissima Carruth. and Quercus variabilis Bl. in the Changjiang River Delta, China

Plants have the capacity to fix CO2 through photosynthesis. To reveal the photosynthetic processes of Quercus acutissima Carruth. and Quercus variabilis Bl., their net photosynthetic rates were quantified during the early and peak growing seasons. To evaluate forest photosynthetic efficiencies, the photosynthetic light response curves of Q. acutissima and Q. variabilis were fitted by the rectangular hyperbola model (RHM), non-rectangular hyperbola model (NHM), and modified rectangular hyperbola model (Ye model). The results revealed the following: (1) All daily variation curves of the net photosynthetic rate, stomatal conductivity, and transpiration rate were single-peaked. The peak times of the Q. acutissima and Q. variabilis’ net photosynthetic rates appeared at 12:00 am during the early growing season and 10:00 am during the peak growing season. (2) The photosynthetic capacities of both Q. acutissima and Q. variabilis during peak growing seasons were higher than during the early growing season. (3) The net photosynthetic rate was found to be positively correlated with stomatal conductivity, the transpiration rate, and photosynthetically active radiation, and it was negatively correlated with the intercellular CO2 concentration. (4) The Ye model provided the best fit for the light response curves of Q. acutissima and Q. variabilis when compared with the rectangular hyperbola and nonrectangular hyperbola models. The photosynthetic performance of Q. acutissima was superior to that of Q. variabilis; thus, it can be employed as a priority tree species in carbon sink forests.

Leaf chlorophyll parameters and photosynthetic characteristic variations with stand age in a typical desert species (Haloxylon ammodendron).

As a desert shrub, Haloxylon ammodendron combines ecological, economic, and social benefits and plays an important role in the ecological conservation of arid desert areas. Understanding its physiological characteristics and its mechanism of light energy utilization is important for the conservation and utilization of H. ammodendron. Therefore, we selected five stands (5-, 11-, 22-, 34-, and 46-year-old) of H. ammodendron as research objects in the study and measured their photosynthetic light response curves by a portable open photosynthesis system (Li-6400) with a red-blue light source (6400-02B). Then, we measured the leaf chlorophyll parameters in the laboratory, calculated the photosynthetic characteristics by using Ye Zipiao’s photosynthetic model, analyzed their variation patterns across stand ages, and explored the relationships between leaf chlorophyll parameters and photosynthetic characteristics. The results showed that leaf chlorophyll parameters and photosynthetic characteristics of H. ammodendron at different stand ages were significantly different. Chl content, P nmax, and LUEmax of H. ammodendron were V-shaped with the increase of stand age. The 5-year-old H. ammodendron was in the rapid growth period, synthesized more Chl a+b content (8.47 mg g−1) only by using a narrower range of light, and the Pnmax and LUEmax were the highest with values of 36.21 μmol m−2 s−1 and 0.0344, respectively. For the 22-year-old H. ammodendron, due to environmental stress, the values of Chl a+b content, P nmax, and LUEmax were the smallest and were 2.64 mg g−1, 25.73 μmol m−2 s−1, and 0.0264, respectively. For the older H. ammodendron, its Chl content, P nmax, and LUEmax were not significantly different and tended to stabilize but were slightly higher than those of the middle-aged H. ammodendron. On the other hand, the other photosynthetic parameters did not show significant variation patterns with stand age, such as R d, AQE, LSP, LCP, and I L-sat. In addition, we found that the relationships between Chl a+b content and P nmax and between Chl a+b content and LUEmax were highly correlated, except for the older H. ammodendron. Thus, using leaf chlorophyll content as a proxy for photosynthetic capacity and light use efficiency should be considered with caution. This work will provide a scientific reference for the sustainable management of desert ecosystems and vegetation restoration in sandy areas.

Photosynthesis in guar: Recovery from water stress, basic parameter estimates, and intrinsic variation among germplasm

ABSTRACT Little is known about the photosynthetic physiology of guar (Cyamopsis tetragonoloba L. Taub), a legume crop, including how photosynthetic parameters intrinsically vary among germplasm and their recovery from water stress. To address this, two greenhouse studies were conducted: Study-1 to compare photosynthetic light response (A N–I) curves and related parameters in three contrasting guar genotypes under optimal and post-water deficit conditions; and Study-2 to quantify photosynthetic parameters in 44 guar genotypes and explore inter-relationships with plant growth parameters. In Study-1, the mean net photosynthetic rate (A N) statistically peaked with 1500 μmol (photons) m −2 s −1, though the maximum A N [33.29 μmol (CO2) m−2 s−1] was modeled to occur with 1950 μmol (photons) m −2 s −1. The light compensation point (I comp), dark respiration rate (R D), and maximum quantum yield (Ф(I 0)) were modeled to be 49.9 μmol (photons) m−2 s−1, 2.62 μmol (CO2) m−2 s−1, and 0.0526 μmol (CO2) μmol −1 (photons), respectively. Photosynthesis in guar was resilient to water stress. Despite reductions in growth, specific leaf area (SLA), and other growth parameters, persistently drought-stressed guar plants, on average, exhibited rapid and full recovery of photosynthetic functions when watered. Genotypes differed in their capacity to recover to some degree. In Study-2, A N differed only between two of the 44 genotypes tested, corresponding to the minimum and maximum A N values. There were no relationships between A N and most plant growth parameters. This finding suggested there is low potential to use point measurements of A N as a selection parameter for increased guar productivity.

Limited effects of shade on physiological performances of cocoa (Theobroma cacao L.) under elevated temperature

Shade is one of the recommended management solutions to mitigate the effects of heat stress, which is a major challenge for cocoa production globally. Nevertheless, there are limited studies to verify this hypothesis. Here, we evaluate the effects of heat and shade on cocoa physiology using experimental plots with six-month old potted seedlings in a randomized complete block design. Infrared heaters were applied for one month to increase leaf temperatures by an average of 5–7 ºC (heat treatment) compared with no heat (unheated treatments), and shaded plants were placed under a shade net removing 60% of the light compared with no shade (sun treatments). Plants under heat treatments in sun and in shade showed severe reduction in photosynthesis. Measurements of chlorophyll fluorescence and photosynthetic light response curves indicated that heat caused damages at photosystem II and additionally resulted in lower rates of maximal photosynthesis. Temperature optima for photosynthesis were at 31–33 ºC with only small differences between treatments, and as light saturation was reached at low PAR levels of 325 – 380 µmol m −2 s −1 in shade and 427 – 521 µmol m −2 s −1 in sun, ambient rates of photosynthesis were comparable between sun and shade treatments. Heat treatments resulted in decreased concentrations of chlorophyll and changed pigment composition, reduced specific leaf areas, and plant biomass. While shade may benefit cocoa seedlings, our results indicate that the positive effects may not be sufficient to counteract the negative effects of increased temperatures on cocoa physiology. • Heat is imposed on six-month old cocoa seedlings and shade is provided. • Heat treated plants show severe reduction in photosynthesis and damages at photosystem II. • Heat decreases chlorophyll concentrations and pigment composition. • Shade improves cocoa physiology but has limited effects on heat.

Upscaling Gross Primary Production from Leaf to Canopy for Potato Crop (Solanum tuberosum L.)

Estimating gross primary production (GPP) is important to understand the land–atmosphere CO2 exchange for major agroecosystems. Eddy covariance (EC) measurements provide accurate and reliable information about GPP, but flux measurements are often not available. Upscaling strategies gain importance as an alternative to the limitations of the use of the EC. Although the potato provides an important agroecosystem for worldwide carbon balance, there are currently no studies on potato GPP upscaling processes. This study reports two GPP scaling-up approaches from the detailed leaf-level characterization of gas exchange of potatoes. Multilayer and big leaf approaches were applied for extrapolating chamber and biometric measurements from leaf to canopy. Measurements of leaf area index and photosynthesis were performed from planting to the end of the canopy life cycle using an LP-80 ceptometer and an IRGA Li-Cor 6800, respectively. The results were compared to concurrent measurements of surface–atmosphere GPP from the EC measurements. Big-leaf models were able to simulate the general trend of GPP during the growth cycle, but they overestimated the GPP during the maximum LAI phase. Multilayer models correctly reproduced the behavior of potato GPP and closely predicted both: the daily magnitude and half-hourly variation in GPP when compared to EC measurements. Upscaling is a reliable alternative, but a good treatment of LAI and the photosynthetic light-response curves are decisive factors to achieve better GPP estimates. The results improved the knowledge of the biophysical control in the carbon fluxes of the potato crop.

Flexible drought deciduousness in a neotropical understory herb.

PremiseAdaptive divergence across environmental gradients is a key driver of speciation. Precipitation seasonality gradients are common in the tropics, yet drought adaptation is nearly unexplored in neotropical understory herbs. Here, we examined two recently diverged neotropical spiral gingers, one adapted to seasonal drought and one reliant on perennial water, to uncover the basis of drought adaptation.MethodsWe combined ecophysiological trait measurements in the field and greenhouse with experimental and observational assessments of real‐time drought response to determine how Costus villosissimus (Costaceae) differs from C. allenii to achieve drought adaptation.ResultsWe found that drought‐adapted C. villosissimus has several characteristics indicating flexible dehydration avoidance via semi‐drought‐deciduousness and a fast economic strategy. Although the two species do not differ in water‐use efficiency, C. villosissimus has a more rapid growth rate, lower leaf mass per area, lower stem density, higher leaf nitrogen, and a strong trend of greater light‐saturated photosynthetic rates. These fast economic strategy traits align with both field‐based observations and experimental dry‐down results. During drought, C. villosissimus displays facultative drought‐deciduousness, losing lower leaves during the dry season and rapidly growing new leaves in the wet season.ConclusionsWe revealed a drought adaptation strategy that has not, to our knowledge, previously been documented in tropical herbs. This divergent drought adaptation evolved recently and is an important component of reproductive isolation between C. villosissimus and C. allenii, indicating that adaptive shifts to survive seasonal drought may be an underappreciated axis of neotropical understory plant diversification.

Photosynthetic light response curves in Eucalyptus benthamii and Eucalyptus dunnii clones

The photosynthetic light-response curve reflects the instantaneous response of the net photosynthetic rate to different gradients of photosynthetically active radiation. Genetic materials can respond differently to light and consequently alter productivity. Thus, this work aimed to compare clones of Eucalyptus benthamii and Eucalyptus dunnii by checking the CO2 assimilation rate due to the increase in photosynthetically active radiation. The evaluations were carried out in mini-stumps implanted in a clonal mini-garden system. The CO2 assimilation rate curves were determined with the aid of a portable photosynthesis meter. The curves of CO2 assimilation rate (A) in response to the increase in photosynthetically active radiation (PAR) were evaluated at values of 1500, 1000, 700, 450, 250, 120, 50 and 0 μmol m-2 s-1 for clones of E. benthamii and E. dunnii. The three Eucalyptus clones evaluated showed a similar behavior of the A/PAR curve, showing a high demand for photosynthetically active radiation. In general, the three clones were very similar in terms of CO2 assimilation rate due to the increase in photosynthetically active radiation

Interspecific variation in leaf traits, photosynthetic light response, and whole-plant productivity in amaranths (Amaranthus spp. L.).

Photosynthetic light response curve parameters help us understand the interspecific variation in photosynthetic traits, leaf acclimation status, carbon uptake, and plant productivity in specific environments. These parameters are also influenced by leaf traits which rely on species and growth environment. In accessions of four amaranth species (Amaranthus. hybridus, A. dubius, A. hypochondriacus, and A. cruentus), we determined variations in the net photosynthetic light response curves and leaf traits, and analysed the relationships between maximum gross photosynthetic rate, leaf traits, and whole-plant productivity. Non-rectangular hyperbolae were used for the net photosynthesis light response curves. Maximum gross photosynthetic rate (Pgmax) was the only variant parameter among the species, ranging from 22.29 to 34.21 μmol m–2 s–1. Interspecific variation existed for all the leaf traits except leaf mass per area and leaf inclination angle. Stomatal conductance, nitrogen, chlorophyll, and carotenoid contents, as well as leaf area correlated with Pgmax. Stomatal conductance and leaf nitrogen explained much of the variation in Pgmax at the leaf level. At the plant level, the slope between absolute growth rate and leaf area showed a strong linear relationship with Pgmax. Overall, A. hybridus and A. cruentus exhibited higher Pgmax at the leaf level and light use efficiency at the whole-plant level than A. dubius, and A. hypochondriacus. Thus, A. hybridus and A. cruentus tended to be more efficient with respect to carbon assimilation. These findings highlight the correlation between leaf photosynthetic characteristics, other leaf traits, and whole plant productivity in amaranths. Future studies may explore more species and accessions of Amaranthus at different locations or light environments.

Photosynthetic Responses of Greenhouse Ornamentals to Interaction of Irradiance, Carbon Dioxide Concentration, and Temperature

Supplemental lighting, temperature control, and CO2 enrichment can improve the productivity of greenhouse crops, but operating costs for greenhouse control systems to maintain environmental parameters at desired setpoints can be expensive. To balance operating costs with productivity, growers need to be able to predict how a crop will perform as a function of photosynthetic photon flux density (PPFD), CO2 concentration, and temperature. The objective of this study was to explore the response of net photosynthetic rate (Pn) to PPFD and CO2 concentration, for plants acclimated to different growth environment temperatures or light intensities. We measured Pn at all combinations of 14 irradiances and four CO2 concentrations of calibrachoa (Calibrachoa ×hybrida ‘Superbells Lemon Slice’), petunia (Petunia ×hybrida ‘Supertunia Mini Strawberry Pink Veined’), and verbena (Verbena ×hybrida ‘Superbena Royale Whitecap’) grown at three light intensities, and of geranium (Pelargonium ×hortorum ‘Maverick Red’), pepper (Capsicum annuum ‘California Wonder’), and sunflower (Helianthus annuus ‘Pacino Gold’) grown at three different temperatures. Sunflower, pepper, and geranium were fit to a model representing Pn as a function of PPFD, CO2 concentration, and leaf temperature. Photosynthetic light response curves, at each CO2 concentration, were fit for each species and growth environment using a nonrectangular hyperbola. These models can be used to identify multiple combinations of PPFD, CO2 concentration, and leaf temperature that would result in equivalent rates of photosynthesis, allowing the most cost-effective combination to be chosen.

Two Mechanisms Drive Changes in Boreal Peatland Photosynthesis Following Long-Term Water Level Drawdown: Species Turnover and Altered Photosynthetic Capacity

Climate change and the related increases in evapotranspiration threaten to make northern peatlands drier. The carbon sink function in peatlands is based on the delicate balance between the photosynthesis and decomposition. However, little is known about how existing and invading plant species will photosynthesize under drier conditions. The aim of this study is to quantify the long-term consequences of climate change-induced drying for peatland photosynthesis in the level of individual species and vegetation community. We measured the species-level photosynthesis of vascular plants and mosses characteristic for the three peatland types (rich fen, poor fen, bog) within a 16-year water level drawdown (WLD) experiment. Measurements were made in the laboratory from mesocosms collected from the field within the same day. We applied nonlinear mixed-effects models to test the impact of WLD on hyperbolic photosynthetic light response curve parameters. The model was then used to upscale photosynthesis to site-level. WLD impacted site-level photosynthesis through two mechanisms: species turnover and changes in species-level photosynthesis rate. The rich fen was the most sensitive and underwent major changes through both mechanisms; the vascular plant community shifted to woody plant dominance with higher rate of photosynthesis than the pre-treatment vegetation, and the rate of species-level photosynthesis increased significantly. The bog had a stable plant community with little change in photosynthesis, while the poor fen was an intermediate of the three peatland types. Our results suggest that vascular plants are the main drivers of site-level productivity changes, while mosses are more resistant to change. The change seems proportional to the availability of mineral nutrients, with higher nutrient status supporting vascular plant expansion.