Search Results (56)

The response of plants to elevated atmospheric [CO₂] is highly dynamic and influenced by developmental stage, yet its role in photosynthetic acclimation remains underexplored. This study examines the physiological and molecular responses of wheat (Triticum durum, var. Amilcar) to elevated [CO₂] (700 ppm vs. 400 ppm) at two distinct developmental stages: the vegetative stage at the end of the elongation stage and the reproductive stage at the beginning of ear emergence (Z39 and Z51, respectively). Wheat plants at the developmental stage Z39, cultivated under elevated [CO₂], maintained photosynthetic rates despite a carbohydrate build-up. However, at Z51, photosynthetic acclimation became more evident as the decline in Rubisco carboxylation capacity (Vc_max) persisted, but also stomatal conductance and diffusion were decreased. This was accompanied by the up-regulation of the CA1 and CA2 genes, likely as a compensatory mechanism to maintain CO₂ supply. Additionally, hormonal adjustments under elevated [CO₂], including increased auxin and bioactive cytokinins (zeatin and isopentenyl adenine), may have contributed to delayed senescence and nitrogen remobilization, sustaining carbon assimilation despite biochemical constraints. These findings highlight the developmental regulation of photosynthetic acclimation, emphasizing the need for the stage-specific assessments of crop responses to future atmospheric conditions. Full article

Plants are commonly exposed to fluctuating illumination under natural light conditions, causing dynamic photosynthesis and further affecting plant growth and productivity. In this context, although the vital role of potassium (K) in steady-state photosynthesis has been well-established, knowledge of the dynamic changes in photosynthesis mediated by K remains scarce. Here, the gas-exchange and chlorophyll fluorescence parameters under steady-state and dynamic photosynthetic responses were quantified in Phaseolus vulgaris L. seedlings grown under K-deficient (−K, 0.02 mM K) and normal K (+K, 2 mM K) conditions. After a transition from low to high light, the time course–induction curves of the net photosynthetic rate (A), stomatal conductance (g_s), mesophyll conductance (g_m), and maximum carboxylation rate (V_cmax) showed an obvious decline in the −K treatment. In comparison with the +K treatment, however, there were no statistical differences in the initial A and V_cmax values in P. vulgaris supplied with deficient K, suggesting that the K-deficiency-induced decreases in A and V_cmax were light-dependent. Interestingly, the time to reach 90% of the maximum A, g_s, and g_m significantly decreased in the −K treatment in comparison with the +K treatment by 27.2%, 45.6%, and 52.9%, respectively, whereas the time to reach 90% of the maximum V_cmax was correspondingly delayed by almost two-fold. The photosynthetic limitation during the induction revealed that the biochemical limitation was the dominating factor that constrained A under the −K conditions, while, under the +K conditions, the main limiting factor changed from biochemical limitation to stomatal limitation over time. Moreover, g_m imposed the smallest limitation on A during induction in both K treatments. These results indicate that a decreased K supply decreases the photosynthetic performance under fluctuating light in P. vulgaris and that improving the induction responses of biochemical components (i.e., V_cmax) has the potential to enhance the growth and productivity of crops grown in K-poor soil. Full article

Climate-change-driven elevation of atmospheric CO₂ (e[CO₂]) disrupts rice physiology by impairing nitrogen use efficiency (NUE) and leaf carbon balance. This study investigated how sodium chloride (NaCl) amendment modulates these processes in upland rice (Oryza sativa L. cv. CMG 2085) under current (400 μmol mol⁻¹) and elevated (700 μmol mol⁻¹) CO₂ concentrations. Using a randomized block design with factorial treatments (CO₂ × NaCl), we analyzed leaf nutrients, gas exchange, chlorophyll fluorescence, and yield parameters. Our findings revealed that 3 mmol L⁻¹ NaCl under ambient CO₂ (1) reduced photorespiration by half, (2) increased grain yield, and (3) enhanced leaf area despite lower leaf N content, indicating improved NUE. Conversely, under e[CO₂], NaCl supplementation decreased rice yield by 15%, demonstrating CO₂-dependent reversal of sodium benefits. Photosynthetic modeling showed higher Vcmax and J values at ambient CO₂, while e[CO₂] increased J/Vcmax, suggesting altered nitrogen allocation to photosynthetic reactions. These results demonstrate that applying low-dose NaCl (3 mmol L⁻¹) can optimize carbon and nitrogen economy under current CO₂ concentrations, although its efficacy diminishes under e[CO₂]. These findings support climate-resilient cultivation strategies for upland rice in tropical and subtropical regions where mild salinity can be used to enhance nitrogen use efficiency and yield under present-day atmospheric conditions. Full article

Nitrogen is a key element in promoting crop growth and development and improving photosynthesis. This study aimed to study the response of two rice genotypes to the restoration of N supply after varying periods of N deficiency. We used the low-nitrogen-tolerant rice Jijing 88 (JJ 88) and the nitrogen-sensitive rice variety Xinong 999 (XN 999) as test materials. The results of this study indicated that, compared to XN 999, JJ 88 has a higher content of the photosynthetic pigments. Photosynthesis in JJ 88 has strong adaptability under low-nitrogen conditions. Upon an increase in the nitrogen supply level, the maximum regeneration rate of ribulose biphosphate (RuBP, J_max) and the maximum carboxylation rate of RuBP (V_cmax) in JJ 88 showed a relatively large increase. The chlorophyll fluorescence parameters, including the effective quantum yield of photosystem II (Φ_PSII), the efficiency of excitation capture by open PSII centers (Fv′/Fm′), photochemical fluorescence quenching (qP), and the electron transfer rate (ETR) decreased slightly, while the non-photochemical fluorescence quenching (NPQ) increased slightly. Under low-nitrogen conditions, low-nitrogen-tolerant rice varieties maintain reasonable growth during the seedling stage. With an increase in the nitrogen supply level, the dry matter accumulation, photosynthetic pigment content, photosynthesis, and electron transfer ability of plants improve, but not to normal nitrogen supply levels. However, compared with XN 999, JJ 88 has a more proactive recovery ability. The research results provide valuable guidance for the breeding of nitrogen-efficient rice varieties and nitrogen fertilizer management. Full article

We explored the response of photosynthetic capacity to nitrogen (N) deposition among Larix gmelinii trees in different crown classes (e.g., suppressed, intermediate, and dominant trees) in a 12-year field experiment in a forest in the Greater Khingan Mountains in Northeast China. Four N-addition treatments were established: control (CK), low N (LN), medium N (MN), and high N (HN) (0, 25, 50, and 75 kg N·ha⁻¹·year⁻¹, respectively). Photosynthesis and its influencing factors were measured in 2023. Nitrogen addition significantly increased the maximum net photosynthetic rate (P_max), maximum carboxylation rate (V_cmax), and maximum electron transport rate (J_max) of suppressed and intermediate trees. The suppressed trees showed maximum P_max and V_cmax in MN and HN, and maximum J_max in HN. The intermediate trees showed maximum P_max, V_cmax, and J_max in MN. For dominant trees, P_max was increased in LN and MN and decreased in HN, and V_cmax was increased by N addition and peaked in MN. Nitrogen addition significantly increased the leaf N content (N_mass), chlorophyll content (Chl_m), the ratio of N to phosphorous (N:P), and photosynthetic enzyme activities in all crown classes. N_mass had significant nonlinear relationships with P_max, V_cmax, and J_max. Enzyme activity and Chl_m positively affected the photosynthetic capacity of suppressed and intermediate trees, and N:P negatively affected the photosynthetic capacity of dominant trees. The promoting effect of N addition on photosynthetic capacity was stronger in suppressed and intermediate trees than in dominant trees. Therefore, the crown class should be considered when studying the effect of N deposition on the boreal forests. Full article

Urban forests play important roles in carbon sequestration and climate change mitigation. However, their adaptive mechanisms and limitations on photosynthesis throughout the canopy are poorly understood. This study takes the most widely distributed 50-year-old camphor plantations (Cinnamomum camphora) in Shanghai as the research objects. We investigated the variations in leaf morphology and photosynthetic physiology and biochemistry at six different canopy positions during a summer and an autumn period. We discovered that on account of leaf nitrogen loss and water deficit, light-saturated photosynthesis (A_max) declined in upper sunlit leaves despite being exposed to high sunlight in the same fashion as stomatal and mesophyll conductance (g_sw, g_m), photochemical quenching coefficient and actual photochemical efficiency of PSII (Φ_PSII, q_P), and maximum rate of electron transport and carboxylation (J_max, V_cmax) during the growing season. Although seasonal change had little effect on A_max, the relative importance of limitations varied temporally. Mesophyll and biochemical limitation were the major contributors to the decline in the A_max in upper sunlit leaves between summer and autumn, respectively. Our study highlights the constraints of carbon fixation capacity in dense stands of mature camphor trees and offers technical support for the accurate prediction of canopy photosynthesis and the enhancement of carbon sequestration management in urban forests. Full article

The response of CO₂ assimilation rate (A_N) to incident light intensity reflects the efficiency of light utilization. The light intensity dependence of A_N varies widely among different plant species, yet the underlying mechanisms remain poorly understood. To elucidate this issue, we measured the light intensity dependence of gas exchange and chlorophyll fluorescence in twelve tree species. The results indicated that (1) with increasing light intensity, the variation in A_N was closely related to stomatal conductance (g_s), mesophyll conductance (g_m), the maximum velocity of Rubisco carboxylation (V_cmax), and electron transport rate (ETR); (2) compared with A_N at sub-saturating light, the increase in A_N at saturating light was more strongly associated with V_cmax and ETR than with g_s and g_m; and (3) the increase in V_cmax and A_N from 600 to 2000 μmol photons m⁻² s⁻¹ were positively correlated with the maximum capacity of V_cmax. These findings suggest that V_cmax is an energy-dependent process that significantly regulates the light intensity dependence of A_N in plants. This provides valuable insights for crop improvement through the manipulation of V_cmax. Full article

Substantial variation in the temperature dependence of parameters of the Farquhar, von Caemmerer, and Berry C₃ photosynthesis model, as well as those of in vitro Rubisco kinetic characteristics, have been observed in controlled conditions but have seldom been systematically examined in the field. In this work, A vs. C_i curves were measured over a 15 or 20 °C range of temperature in four C₃ species growing outdoors on two occasions about three weeks apart early in the growing season and also once near mid-season when air temperatures were more stable. The two early season occasions were chosen for having contrasting temperatures for 3 to 4 days preceding the measurements. Low temperatures (mean maximum/minimum temperatures of 19/11 °C) resulted in higher values of the V_Cmax of Rubisco and J_max at a given measurement temperature in most species compared with higher temperatures (max/min 31/25 °C). The apparent activation energy of V_Cmax of Rubisco ranged from 56 to 82 kJ mol⁻¹, and that of electron transport (J_max) ranged from 28 to 56 kJ mol⁻¹ across species and temperatures. In three of the four species, the activation energy of V_Cmax decreased and that of J_max increased after the cooler temperatures. Stomatal conductance measured at 20 and 25 °C increased strongly with the prior warm temperatures in all species. Measurements made near mid-season, after a period of relatively stable temperatures (mean maximum/minimum temperatures of 27/18 °C), also indicated a wide range of values of the activation energies of V_Cmax and J_max among these species. Full article

Light serves as the unique driving force of photosynthesis in plants, yet its intensity varies over time and space, leading to corresponding changes in the photosynthetic rate. Here, the photosynthetic induction response under constant and fluctuating light was examined in naturally occurring saplings of four sun-demanding woody species, Eucalyptus. Ficus macrocarpa L., Hibiscus syriacus L. and Ficus carica L. We aimed to find out the relations among gas exchange parameter adaptions among different species during photosynthetic induction. The net photosynthetic rates (A) versus time course curves were sigmoidal or hyperbolic after the dark-adapted leaves were irradiated by continuous saturated light. Compared with other species, Ficus carica L. have the largest net photosynthesis rate, stomatal conductance to CO₂ (g_sc), and the maximum carboxylation rate (V_cmax) at both the initial and steady photosynthetic state. The initial g_sc (g_sci) was as much as sixfold higher compared to the other shrub, Hibiscus syriacus L. The time required to reach 90% of A (t_A90) was 7–30 min; t_A90 of Ficus carica L. and Ficus macrocarpa L. were lower than that of the other two species. The time required to reach 90% of g_sc (t_gsc90) significantly lagged behind t_A90 among species. Biochemical induction was fast in leaves of Ficus carica L., as about 4 min were needed to reach 90% of V_cmax, while the other species needed 7–18 min. Correlation analysis showed that the t_gsc90 was the main factor in limiting t_A90, especially for Eucalyptus spp. and Hibiscus syriacus L.; g_sci was negatively correlated with t_gsc90 among species. Moreover, time-integrated limitation analysis revealed that g_sc still accounted for the largest limitation in constraining A of Eucalyptus spp. and Hibiscus syriacus L. and Ficus macrocarpa L. Overall, the findings suggest that to enhance the carbon gain by woody species under naturally dynamic light environments, attention should be focused on improving the rate of stomatal opening or initial stomatal conductance. Full article

The relative impacts of biochemical and stomatal limitations on photosynthesis during photosynthetic induction have been well studied for diverse plants under ambient CO₂ concentration (C_a). However, a knowledge gap remains regarding how the various photosynthetic components limit duction efficiency under elevated CO₂. In this study, we experimentally investigated the influence of elevated CO₂ (from 400 to 800 μmol mol^–1) on photosynthetic induction dynamics and its associated limitation components in two broadleaved tree species, Populus tomentosa and Eucalyptus robusta. The results show that elevated CO₂ increased the steady-state photosynthesis rate (A) and decreased stomatal conductance (g_s) and the maximum carboxylation rate (V_cmax) in both species. While E. robusta exhibited a decrease in the linear electron transport rate (J) and the fraction of open reaction centers in photosynthesis II (q_L), P. tomentosa showed a significant increase in non-photochemical quenching (NPQ). With respect to non-steady-state photosynthesis, elevated CO₂ significantly reduced the induction time of A following a shift from low to high light intensity in both species. Time-integrated limitation analysis during induction revealed that elevated CO₂ reduces the relative impacts of stomatal limitations in both species, consequently shifting the predominant limitation on induction efficiency from stomatal to biochemical components. Additionally, species-specific changes in q_L and NPQ suggest that elevated CO₂ may increase biochemical limitation by affecting energy allocation between carbon fixation and photoprotection. These findings suggest that, in a future CO₂-rich atmosphere, plants productivity under fluctuating light may be primarily constrained by photochemical and non-photochemical quenching. Full article

Chemical weed control is a significant agricultural concern, and reliance on a limited range of herbicide action modes has increased resistant weed species, many of which use C4 metabolism. As a result, the identification of novel herbicidal agents with low toxicity targeting C4 plants becomes imperative. An assessment was conducted on the impact of 3-cyanobenzoic acid on the growth and photosynthetic processes of maize (Zea mays), a representative C4 plant, cultivated hydroponically over 14 days. The results showed a significant reduction in plant growth and notable disruptions in gas exchange and chlorophyll a fluorescence due to the application of 3-cyanobenzoic acid, indicating compromised photosynthetic activity. Parameters such as the chlorophyll index, net assimilation (A), stomatal conductance (g_s), intercellular CO₂ concentration (C_i), maximum effective photochemical efficiency (F_v′/F_m′), photochemical quenching coefficient (q_P), quantum yield of photosystem II photochemistry (ϕ_PSII), and electron transport rate through PSII (ETR) all decreased. The A/PAR curve revealed reductions in the maximum net assimilation rate (A_max) and apparent quantum yield (ϕ), alongside an increased light compensation point (LCP). Moreover, 3-cyanobenzoic acid significantly decreased the carboxylation rates of RuBisCo (V_cmax) and PEPCase (V_pmax), electron transport rate (J), and mesophilic conductance (g_m). Overall, 3-cyanobenzoic acid induced substantial changes in plant growth, carboxylative processes, and photochemical activities. The treated plants also exhibited heightened susceptibility to intense light conditions, indicating a significant and potentially adverse impact on their physiological functions. These findings suggest that 3-cyanobenzoic acid or its analogs could be promising for future research targeting photosynthesis. Full article

Understanding photosynthetic mechanisms in different plant species is crucial for advancing agricultural productivity and ecological restoration. This study presents a detailed physiological and ultrastructural comparison of photosynthetic mechanisms between Hibiscus (Hibiscus rosa-sinensis L.) and Pelargonium (Pelargonium zonale (L.) L’Hér. Ex Aiton) plants. The data collection encompassed daily photosynthetic profiles, responses to light and CO₂, leaf optical properties, fluorescence data (OJIP transients), biochemical analyses, and anatomical observations. The findings reveal distinct morphological, optical, and biochemical adaptations between the two species. These adaptations were associated with differences in photochemical (A_MAX, E, C_i, iWUE, and α) and carboxylative parameters (VC_MAX, ΓCO₂, g_s, g_m, Cc, and AJ_MAX), along with variations in fluorescence and concentrations of chlorophylls and carotenoids. Such factors modulate the efficiency of photosynthesis. Energy dissipation mechanisms, including thermal and fluorescence pathways (ΦPSII, ETR, NPQ), and JIP test-derived metrics highlighted differences in electron transport, particularly between PSII and PSI. At the ultrastructural level, Hibiscus exhibited optimised cellular and chloroplast architecture, characterised by increased chloroplast density and robust grana structures. In contrast, Pelargonium displayed suboptimal photosynthetic parameters, possibly due to reduced thylakoid counts and a higher proportion of mitochondria. In conclusion, while Hibiscus appears primed for efficient photosynthesis and energy storage, Pelargonium may prioritise alternative cellular functions, engaging in a metabolic trade-off. Full article

The development of water-saving management relies on understanding the physiological response of crops to soil drought. The coordinated regulation of hydraulics and stomatal conductance in plant water relations has steadily received attention. However, research focusing on grain crops, such as winter wheat, remains limited. In this study, three soil water supply treatments, including high (H), moderate (M), and low (L) soil water contents, were conducted with potted winter wheat. Leaf water potential (Ψ_leaf), leaf hydraulic conductance (K_leaf), and stomatal conductance (g_s), as well as leaf biochemical parameters and stomatal traits were measured. Results showed that, compared to H, predawn leaf water potential (Ψ_PD) significantly reduced by 48.10% and 47.91%, midday leaf water potential (Ψ_MD) reduced by 40.71% and 43.20%, K_leaf reduced by 64.80% and 65.61%, and g_s reduced by 21.20% and 43.41%, respectively, under M and L conditions. Although g_s showed a significant difference between M and L, Ψ_leaf and K_leaf did not show significant differences between these treatments. The maximum carboxylation rate (V_cmax) and maximum electron transfer rate (J_max) under L significantly decreased by 23.11% and 28.10%, stomatal density (SD) and stomatal pore area index (SPI) under L on the abaxial side increased by 59.80% and 52.30%, respectively, compared to H. The leaf water potential at 50% hydraulic conduction loss (P₅₀) under L was not significantly reduced. The g_s was positively correlated with Ψ_MD and K_leaf, but it was negatively correlated with abscisic acid (ABA) and SD. A threshold relationship between g_s and K_leaf was observed, with rapid and linear reduction in g_s occurring only when K_leaf fell below 8.70 mmol m⁻² s⁻¹ MPa⁻¹. Our findings demonstrate that wheat leaves adapt stomatal regulation strategies from anisohydric to isohydric in response to reduced soil water content. These results enrich the theory of trade-offs between the carbon assimilation and hydraulic safety in crops and also provide a theoretical basis for water management practices based on stomatal regulation strategies under varying soil water conditions. Full article

Although the maximum carboxylation rate (V_cmax) is an important parameter to calculate the photosynthesis rate for the terrestrial biosphere models (TBMs), current models could not satisfactorily estimate the V_cmax of a crop because the V_cmax is always changing during crop growth period. In this study, the Breathing Earth System Simulator (BESS) and light response curve (LRC) were combined to invert the time-continuous V_m25 (V_cmax normalized to 25 °C) using eddy covariance measurements and remote sensing data in five maize sites. Based on the inversion results, we propose a Two-stage linear model using leaf age to estimate crop V_m25. The leaf age can be readily calculated from the date of emergence, which is usually recorded or can be readily calculated from the leaf area index (LAI), which can be readily obtained from high spatiotemporal resolution remote sensing images. The V_m25 used to calibrate and validate our model was inversely solved by combining the BESS and LRC and using eddy covariance measurements and remote sensing data in five maize sites. Our Two-stage linear model (R² = 0.71–0.88, RMSE = 5.40–7.54 μmol m⁻² s⁻¹) performed better than the original BESS (R² = 0.01–0.67, RMSE = 13.25–18.93 μmol m⁻² s⁻¹) at capturing the seasonal variation in the V_m25 of all of the five maize sites. Our Two-stage linear model can also significantly improve the accuracy of maize gross primary productivity (GPP) at all of the five sites. The GPP estimated using our Two-stage linear model (underestimated by 0.85% on average) is significantly better than that estimated by the original BESS model (underestimated by 12.60% on average). Overall, our main contributions are as follows: (1) by using the BESS model instead of the BEPS model coupled with the LRC, the inversion of V_m25 took into account the photosynthesis process of C4 plants; (2) the maximum value of V_m25 (i.e., PeakV_m25) during the growth and development of maize was calibrated; and (3) by using leaf age as a predictor of V_m25, we proposed a Two-stage linear model to calculate V_m25, which improved the estimation accuracy of GPP. Full article

L-cysteine, a precursor of essential components for plant growth, is synthesized by the cysteine synthase complex, which includes O-acetylserine(thiol) lyase (OAS-TL) and serine acetyltransferase. In this work, we investigated how S-benzyl-L-cysteine (SBC), an OAS-TL inhibitor, affects the growth, photosynthesis, and oxidative stress of Ipomoea grandifolia plants. SBC impaired gas exchange and chlorophyll a fluorescence, indicating damage that compromised photosynthesis and reduced plant growth. Critical parameters such as the electron transport rate (J), triose phosphate utilization (TPU), light-saturation point (LSP), maximum carboxylation rate of Rubisco (V_cmax), and light-saturated net photosynthetic rate (P_Nmax) decreased by 19%, 20%, 22%, 23%, and 24%, respectively. The photochemical quenching coefficient (q_P), quantum yield of photosystem II photochemistry (ϕ_PSII), electron transport rate through PSII (ETR), and stomatal conductance (g_s) decreased by 12%, 19%, 19%, and 34%, respectively. Additionally, SBC decreased the maximum fluorescence yield (F_m), variable fluorescence (F_v), and chlorophyll (SPAD index) by 14%, 15%, and 15%, respectively, indicating possible damage to the photosynthetic apparatus. SBC triggered root oxidative stress by increasing malondialdehyde, reactive oxygen species, and conjugated dienes by 30%, 55%, and 61%, respectively. We hypothesize that dysfunctions in sulfur-containing components of the photosynthetic electron transport chain, such as the cytochrome b₆f complex, ferredoxin, and the iron–sulfur (Fe-S) centers are the cause of these effects, which ultimately reduce the efficiency of electron transport and hinder photosynthesis in I. grandifolia plants. In short, our findings suggest that targeting OAS-TL with inhibitors like SBC could be a promising strategy for the development of novel herbicides. Full article