Plant Photosynthetic Capacity Research Articles

Vapour pressure deficit affects crop water productivity, yield, and quality in tomatoes

A high atmospheric vapour pressure deficit (VPD) hinders calcium absorption in tomatoes (Solanum lycopersicum L.), which severely reduces tomato yield, crop water productivity (WPcrop), and quality. Although reducing the VPD is effective for increasing tomato yield and water productivity, regulating the VPD is costly. Therefore, this study aimed to explore the effects of VPD regulation (high VPD=2.22 kPa, low VPD=0.95 kPa) during different growth stages on tomato WPcrop, yield, and quality to identify a VPD management method that saves costs and enhances the above parameters. The results showed that the yield was significantly positively correlated with fruit calcium absorption. Decreasing the VPD during the fruit expansion stage and increasing it during the flowering stage significantly increased calcium accumulation in the fruits, thereby improving tomato WPcrop, yield, and quality. Additionally, a high VPD during the flowering stage increased stomatal conductance and mesophyll conductance, thereby increasing intercellular and chloroplast CO2 concentrations and enhancing plant photosynthetic capacity, and reduced the stem water potential, leaf water potential, and leaf relative water content, thereby increasing the water potential difference, leaf hydraulic conductance, and calcium absorption. By integrating game theory and the technique for order of preference by similarity to ideal solution method, a comprehensive analysis of tomato appearance, nutrients, and flavour quality revealed that growing plants under a high VPD during the seedling, flowering, and fruit ripening stages and a low VPD during the fruit expansion stage not only enhanced the comprehensive tomato quality value but also maximally reduced the humidification cost. Conclusively, controlling the environmental VPD at 2.22 kPa during the seedling, flowering, and fruit ripening stages and at 0.95 kPa during the fruit expansion stage can effectively increase tomato WPcrop, yield, and quality. This study provides a theoretical basis for the environmental regulation of high-quality, efficient, and water-conserving cultivation of greenhouse tomatoes.

Plant biomass of grasses in actively restored grasslands shows stronger association with eco‐physiological properties than in degraded native grasslands

AbstractGrassland degradation levels determine plant eco‐physiological properties, and thus influences ecosystem function. However, how land degradation affects the relationship between plant biomass and eco‐physiological properties of native and artificially restored grasslands is insufficiently understood. Here, we evaluated aboveground biomass (AGB), plant photosynthetic capacity, as well as soil texture, in a series of native grasslands (non‐degraded, slightly degraded, moderately degraded, heavily degraded, and extremely degraded) and artificially restored grasslands with different growth times (5, 9, 11, 14 and 17 years) within the alpine grassland ecosystem of the Qinghai–Tibet Plateau during the plant growing season. Results showed that, in native grasslands, land degradation significantly decreased the nitrogen (N) concentration and AGB of grasses but did not impact the phosphorus (P) concentration. In actively restored grasslands, the AGB, photosynthetic rate (Pn), N and P of grasses decreased significantly after 9 years or longer of replanting time. Furthermore, the AGB of grasses in actively restored grasslands showed stronger association with eco‐physiological properties than in native grasslands. In native grasslands, degradation affected AGB directly, but also indirectly through Pn. In actively restored grasslands, degradation affected AGB directly, but also indirectly through Pn, N and P. Our findings suggest that the mechanisms by which grass species respond to degradation differ between native and actively restored grasslands. Also, compared to native grasslands, the eco‐physiological properties of grasses are more sensitive to changing environmental conditions in actively restored grasslands. More importantly, the differing response mechanisms are likely to alter the plant community dynamics and future ecosystem stability.

Comparative Morpho-Physiological, Biochemical, and Gene Expressional Analyses Uncover Mechanisms of Waterlogging Tolerance in Two Soybean Introgression Lines.

Waterlogging is one of the key abiotic factors that severely impedes the growth and productivity of soybeans on a global scale. To develop soybean cultivars that are tolerant to waterlogging, it is a prerequisite to unravel the mechanisms governing soybean responses to waterlogging. Hence, we explored the morphological, physiological, biochemical, and transcriptional changes in two contrasting soybean introgression lines, A192 (waterlogging tolerant, WT) and A186 (waterlogging sensitive, WS), under waterlogging. In comparison to the WT line, waterlogging drastically decreased the root length (RL), shoot length (ShL), root fresh weight (RFW), shoot fresh weight (ShFW), root dry weight (RDW), and shoot dry weight (ShDW) of the WS line. Similarly, waterlogging inhibited soybean plant growth by suppressing the plant's photosynthetic capacity, enhancing oxidative damage from reactive oxygen species, and decreasing the chlorophyll content in the WS line but not in the WT line. To counteract the oxidative damage and lipid peroxidation, the WT line exhibited increased activity of antioxidant enzymes such as peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT), as well as higher levels of proline content than the WS line. In addition, the expression of antioxidant enzyme genes (POD1, POD2, FeSOD, Cu/ZnSOD, CAT1, and CAT2) and ethylene-related genes (such as ACO1, ACO2, ACS1, and ACS2) were found to be up-regulated in WT line under waterlogging stress conditions. In contrast, these genes showed a down-regulation in their expression levels in the stressed WS line. The integration of morpho-physiological, biochemical, and gene expression analyses provide a comprehensive understanding of the responses of WT and WS lines to waterlogging conditions. These findings would be beneficial for the future development of soybean cultivars that can withstand waterlogging.

Warming affects leaf light use efficiency and functional traits in alpine plants: evidence from a 4-year in-situ field experiment.

Light use efficiency (LUE) is a crucial determinant of plant productivity, while leaf functional traits directly affect ecosystem functions. However, it remains unclear how climate warming affects LUE and leaf functional traits of dominant species in alpine meadows. We conducted a 4-year in-situ field warming experiment to investigate the eco-physiological characteristics for a dominant species (Elymus nutans) and a common species (Potentilla anserina) on the Tibetan Plateau. The leaf traits, photosynthesis and fluorescence characteristics were measured, along with the soil physical-chemical properties associated with the two species. Experimental warming increased the leaf LUE, maximum photochemical efficiency, non-photochemical quenching, relative water content and specific leaf area for both species. However, there was a decrease in leaf and soil element content. Different species exhibit varying adaptability to warming. Increasing temperature significantly increased the photosynthetic rate, stomatal conductance, transpiration rate, total water content, and specific leaf volume of E. nutans; however, all these traits exhibited an opposite trend in P. anserina. Warming has a direct negative impact on leaf LUE and an indirectly enhances LUE through its effects on leaf traits. The impact of warming on plant photosynthetic capacity is primarily mediated by soil nutrients and leaf traits. These results indicate that the two different species employ distinct adaptive strategies in response to climate change, which are related to their species-specific variations. Such changes can confer an adaptive advantage for plant to cope with environmental change and potentially lead to alterations to ecosystem structure and functioning.

γ-Aminobutyric acid enhances salt tolerance by sustaining ion homeostasis in apples

Soil salinization had become a global ecological problem, which restricts the plant growth, and the quantity and quality of fruits. As a signaling molecule, γ-Aminobutyric acid (GABA) mediates a series of physiological processes and stress responses. Our previous research showed that GABA could alleviate drought, low phosphorus, cadmium stresses in apples, but the further research about its physiological mechanisms under salt stress was even more needed. The present study showed that the inhibition of salt stress on plant growth might be effectively alleviated by the treatment of 0.5 mM GABA, and the osmotic balance and photosynthetic capacity of plants could be maintained. Exogenous GABA could effectively inhibit the enrichment of reactive oxygen species and the uptake of Na+, while maintaining ion homeostasis. The experiment results indicated GABA could markedly promote the expression amount of Na+ and K+ transport-related genes (e.g., HKT1, AKT1, NHX1, SOS1, SOS2, and SOS3) in apples under salt stress. Overexpression and interference (RNAi) of MdGAD1 in apple roots, which is a crucial enzyme in the GABA biosynthesis, affected the salt tolerance of plants. Transgenic apple plants with roots of overexpression MdGAD1 showed less relative electrolyte leakage and more expression level of related ion transport genes than CK group, but RNAi MdGAD1 led to the opposite results. These results indicated that GABA accumulation could effectively strengthen the resistance of apple plants to salt stress and alleviate the injury of apple seedlings resulted from salinity.

Nitrogen deposition alters drought-induced changes in biomass and nonstructural carbohydrates allocation patterns of Quercus mongolica seedlings

Water and nitrogen (N) are major constraints that affect plant growth and survival. N deposition can enhance plant photosynthetic capacity and drought tolerance. However, the ecophysiological processes of plants in response to N deposition associated with drought stress are unclear. We investigated the allocation patterns of biomass and nonstructural carbohydrates (NSC) among different organs in response to the addition of ammonium nitrate in Mongolian oak seedlings along a drought stress gradient. This study used pot experiment with three levels of N addition (CK: 0, LN: 5 and HN: 10 g N m−2 yr−1) in conjunction with three irrigated water volumes (W0: 36 L, W1: 25 L, reduction 30%, and W2: 18 L, reduction 50 %). The results showed drought stress, resulting in a decreasing trend in photosynthesis, had been reversed by N addition, and trends in water use efficiency also appeared to increase. Similarly, drought caused a decreasing trend in the biomass and the decreases in the ratio of root-to-shoot (R:S) and total biomass at the whole-seedling level. The enhancements in aboveground biomass were induced by N addition regardless of water conditions. Adversely, root biomass appeared to decrease under normal water conditions (W0) and increased under drought stress. In addition, leaf soluble sugar (SS) concentration and leaf SS: starch increased with N addition under W0 and decreased under severe drought (W2). When water and N availability were abundant, the carbon (C) use strategy of Mongolian oak seedlings focused on aboveground growth to get more carbohydrates. However, when water availability was in severe deficit, the C use strategy of seedlings shifted from growth to protection and defense by restoring more carbohydrates in stems or roots to survive the harsh environments, even when N availability was adequate. This study provided new insights into the understanding of C use strategy and drought survival mechanism in response to environmental change.

Maize GOLDEN2-LIKE proteins enhance drought tolerance in rice by promoting stomatal closure.

Drought has become one of the most severe abiotic stresses experienced in agricultural production across the world. Plants respond to water deficit via stomatal movements in the leaves, which are mainly regulated by abscisic acid (ABA). A previous study from our lab showed that constitutive expression of maize (Zea mays L.) GOLDEN2-LIKE (GLK) transcription factors in rice (Oryza sativa L.) can improve stomatal conductance and plant photosynthetic capacity under field conditions. In the present study, we uncovered a function of ZmGLK regulation of stomatal movement in rice during drought stress. We found that elevated drought tolerance in rice plants overexpressing ZmGLK1 or GOLDEN2 (ZmG2) was conferred by rapid ABA-mediated stomatal closure. Comparative analysis of RNA-sequencing (RNA-seq) data from the rice leaves and DNA affinity purification sequencing (DAP-seq) results obtained in vitro revealed that ZmGLKs played roles in regulating ABA-related and stress-responsive pathways. Four upregulated genes closely functioning in abiotic stress tolerance with strong binding peaks in the DAP-seq data were identified as putative target genes of ZmGLK1 and ZmG2 in rice. These results demonstrated that maize GLKs play an important role in regulating stomatal movements to coordinate photosynthesis and stress tolerance. This trait is a valuable target for breeding drought-tolerant crop plants without compromising photosynthetic capacity.

Validating and Developing Hyperspectral Indices for Tracing Leaf Chlorophyll Fluorescence Parameters under Varying Light Conditions

Chlorophyll a fluorescence (ChlFa) parameters provide insight into the physiological and biochemical processes of plants and have been widely applied to monitor and evaluate the photochemical process and photosynthetic capacity of plants in a variety of environments. Recent advances in remote sensing provide new opportunities for the detection of ChlFa at large scales but demand further tremendous efforts. Among such efforts, application of the hyperspectral index is always possible, but the performance of hyperspectral indices in detecting ChlFa parameters under varying light conditions is much less investigated. The objective of this study is to investigate the performance of reported hyperspectral indices for tracking ChlFa parameters under different light conditions and to develop and evaluate novel spectral indices. Therefore, an experiment was conducted to simultaneously measure ChlFa parameters and spectral reflectance of sunlit and shaded leaves under varying light conditions, and 28 reported hyperspectral indices were examined for their performance in tracking the ChlFa parameters. Furthermore, we developed novel hyperspectral indices based on various spectral transformations. The results indicated that the maximum quantum efficiency of photosystem II (PSIImax), the cumulative quantum yield of photochemistry (ΦP), and the fraction of open reaction centers in photosystem II (qL) of sunlit leaves were significantly higher than those of shaded leaves, while the cumulative quantum yield of regulated thermal dissipation (ΦN) and fluorescence (ΦF) of shaded leaves was higher than that of sunlit leaves. Efficient tracing of ChlFa parameters could not be achieved from previously published spectral indices. In comparison, all ChlFa parameters were well quantified in shaded leaves when using novel hyperspectral indices, although the hyperspectral indices for tracing the non-photochemical quenching (NPQ) and ΦF were not stable, especially for sunlit leaves. Our findings justify the use of hyperspectral indices as a practical approach to estimating ChlFa parameters. However, caution should be used when using spectral indices to track ChlFa parameters based on the differences in sunlit and shaded leaves.

A Review on Impact of Different Nitrogen Management Techniques on Maize (Zea mays L.) Crop Performance

Nitrogen (N), as a primary nutrient requirement of maize (Zea mays L.), plays a critical role in its development and productivity. Proper nitrogen management practices involve a delicate balance between providing an adequate amount of this nutrient and mitigating potential environmental impacts. When implemented effectively, these practices can significantly improve corn production. An adequate nitrogen supply promotes vigorous vegetative growth, contributing to strong stalks and an abundance of leaves, which are essential for maximizing the plant's photosynthetic capacity. This lush foliage, in turn, leads to increased photosynthesis and carbohydrate production, providing the energy maize needs throughout the reproductive stage to develop and fill its kernels. In addition, nitrogen is closely linked to kernel development. Well-timed and dosed nitrogen applications can result in larger, well-filled ears with plump kernels, ultimately increasing both the quantity and quality of the maize yield. Environmental considerations, such as reducing nitrogen runoff and greenhouse gas emissions, are important for maintaining ecosystems and mitigating climate change. Thus, this review article highlights the need for a holistic approach to nitrogen management, combining innovative techniques with sustainable agricultural practices, to ensure food security and environmental conservation in maize production systems.

Saline-Alkaline Stress Resistance of Cabernet Sauvignon Grapes Grafted on Different Rootstocks and Rootstock Combinations.

Grafting the wine grape variety Cabernet Sauvignon onto salinity-tolerant rootstocks can improve salinity tolerance and grape yields in regions with high salinity soils. In this experiment, the effects of different rootstocks and rootstock combinations on the saline-alkaline stress (modified Hoagland nutrient solution + 50 mmol L-1 (NaCl + NaHCO3)) of Cabernet Sauvignon were studied. Correlation and principal component analyses were conducted on several physiological indicators of saline-alkaline stress. Salinity limited biomass accumulation, induced damage to the plant membrane, reduced the chlorophyll content and photosynthetic capacity of plants, and increased the content of malondialdehyde, sodium (Na+)/potassium (K+) ratio, and antioxidant enzyme activities (superoxide dismutase, peroxidase, and catalase). Significant differences in several indicators were observed among the experimental groups. The results indicate that the saline-alkaline tolerance of Cabernet Sauvignon after grafting was the same as that of the rootstock, indicating that the increased resistance of Cabernet Sauvignon grapes to saline-alkaline stress stems from the transferability of the saline-alkaline stress resistance of the rootstock to the scion.

Leaf photosynthetic pigment as a predictor of leaf maximum carboxylation rate in a farmland ecosystem.

The leaf maximum rate of carboxylation (Vcmax) is a key parameter of plant photosynthetic capacity. The accurate estimation of Vcmax is crucial for correctly predicting the carbon flux in the terrestrial carbon cycle. Vcmax is correlated with plant traits including leaf nitrogen (Narea) and leaf photosynthetic pigments. Proxies for leaf chlorophyll (Chlarea) and carotenoid contents (Cararea) need to be explored in different ecosystems. In this study, we evaluated the relationship between leaf maximum rate of carboxylation (scaled to 25°C; Vcmax25) and both leaf Narea and photosynthetic pigments (Chlarea and Cararea) in winter wheat in a farmland ecosystem. Our results showed that Vcmax25 followed the same trends as leaf Chlarea. However, leaf Narea showed smaller dynamic changes before the flowering stage, and there were smaller seasonal variations in leaf Cararea. The correlation between leaf Vcmax25 and leaf Chlarea was the strongest, followed by leaf Cararea and leaf Narea (R2=0.69, R2=0.47 and R2=0.36, respectively). The random forest regression analysis also showed that leaf Chlarea and leaf Cararea were more important than leaf Narea for Vcmax25. The correlation between leaf Vcmax25 and Narea can be weaker since nitrogen allocation is dynamic. The estimation accuracy of the Vcmax25 model based on Narea, Chlarea, and Cararea (R2=0.75) was only 0.05 higher than that of the Vcmax25 model based on Chlarea and Cararea (R2=0.70). However, the estimation accuracy of the Vcmax25 model based on Chlarea and Cararea (R2=0.70) was 0.34 higher than that of the Vcmax25 model based on Narea (R2=0.36). These results highlight that leaf photosynthetic pigments can be a predictor for estimating Vcmax25, expanding a new way to estimate spatially continuous Vcmax25 on a regional scale, and to improve model simulation accuracy.

Environmental Gradients and Vegetation Types Alter the Effects of Leaf Traits on the Dominance of Woody Angiosperm Species

Leaf traits can reflect plant photosynthetic capacity, resource utilization strategy and adaptability to the environment. However, whether species’ leaf traits are tightly related to the functioning of their community and how that relationship varies with environmental gradients remain largely unexplored. We measured 6 leaf traits, including petiole fineness (PF), specific leaf area (SLA), leaf area (LA), leaf length–width ratio (LLWR), leaf nitrogen content (LN) and leaf phosphorus content (LP), of 733 populations (415 species) of 19 woody angiosperm communities in the eastern Qinghai–Tibetan Plateau across multiple climatic zones or vegetation types. Through meta-analysis and relative importance analysis, the relationship between leaf traits of species and their community dominance and its change with environments were analyzed. The results showed that species dominance was correlated positively with their LA and LP, suggesting that species with high light interception and resource utilization capacity can easily become dominant species in woody angiosperm communities. Along the altitudinal gradient, the effect of PF and SLA on species dominance increased and changed significantly in their pattern, from positive or nonsignificant in temperate forests to negative in alpine and subalpine shrubs, suggesting that increasing petiole mechanical support and lamina protection cost is a dominant leaf growth strategy in stressful high-altitude environments. Our findings demonstrate that the demand for efficient light acquisition and/or utilization and species adaptability or tolerance to specific environmental stress are key mechanisms by which leaf traits govern community composition and functioning.

Leaf optical properties and photosynthesis of fern species with a wide range of divergence time in relation to mesophyll anatomy.

For a comprehensive understanding of the mechanisms of changing plant photosynthetic capacity during plant evolutionary history, knowledge of leaf gas exchange and optical properties are essential, both of which relate strongly to mesophyll anatomy. Although ferns are suitable for investigating the evolutionary history of photosynthetic capacity, comprehensive research of fern species has yet to be undertaken in this regard. We investigated leaf optical properties, gas exchange and mesophyll anatomy of fern species with a wide range of divergence time, using 66 ferns from natural habitats and eight glasshouse-grown ferns. We used a spectroradiometer and an integrating sphere to measure light absorptance and reflectance by the leaves. The more newly divergent fern species had a thicker mesophyll, a larger surface area of chloroplasts facing the intercellular airspaces (Sc), thicker cell walls and large light absorptance. Although no trend with divergence time was obtained in leaf photosynthetic capacity on a leaf-area basis, when the traits were expressed on a mesophyll-thickness basis, trends in leaf photosynthetic capacity became apparent. On a mesophyll-thickness basis, the more newly divergent species had a low maximum photosynthesis rate, accompanied by a low Sc. We found a strong link between light capture, mesophyll anatomy and photosynthesis rate in fern species for the first time. The thick mesophyll of the more newly divergent ferns does not necessarily relate to the high photosynthetic capacity on a leaf-area basis. Rather, the thick mesophyll accompanied by thick cell walls allowed the ferns to adapt to a wider range of environments through increasing leaf toughness, which would contribute to the diversification of fern species.

The role of ectomycorrhization with Scleroderma sp. in promoting substrate nutrients mobilization under phosphorus-enriched compost amendment: A case study with Castanea henryi seedlings

Ecological forestry means continuous and sustainable management of production from the seedling to the adult stage. At present, ectomycorrhizal (ECM) fungi plays an important role in the nutrient management of seedling production in commercial forestry applications. Additionally, phosphorus-enriched compost (PEC) is considered as an environmentally cleaner soil amendment with a great potential in seedling production. However, little is known about the specific antagonistic or synergistic effects of these two sustainable practices on Castanea henryi seedling growth and nutrient uptake. An experiment was conducted to evaluate the effects of ECM inoculation (Scleroderma sp.) and three different application rates (0 %, 15 %, 35 % v:v) of phosphorus-enriched chestnut forest green waste compost (CFG; a typical form of PEC). Results indicated that CFG significantly increased the accumulation of most nutrients in plants but decreased the uptake of Cu and Zn. Without ECM inoculation, there was a significant positive correlation between soil rhizosphere bioavailable P content and aboveground seedling biomass (F = 111.570, p < 0.01). Inoculation of Scleroderma sp. significantly stimulated P mobilization in the soil rhizosphere of the low fertilization treatment (15 %) but had limited benefit in the non-fertilization (0 %) or high fertilization (35 %) treatments. The structural equation modeling indicated that the increase in activity of the rhizosphere soil acid phosphatase was the primary factor that increased soil P bioavailability and plant photosynthetic capacity in the inoculated treatments. Our results better explain the interaction of ECM on PEC sources of nutrients, and provide a low-cost and sustainable commercial propagation system underpinned by biologically regulated nutrient supply systems.

GmFtsH25 overexpression increases soybean seed yield by enhancing photosynthesis and photosynthates.

Increasing plant photosynthetic capacity is a promising approach to boost yields, but it is particularly challenging in C3 crops, such as soybean (Glycine max (L.) Merr.). Here, we identified GmFtsH25, encoding a member of the filamentation temperature-sensitive protein H protease family, as a major gene involved in soybean photosynthesis, using linkage mapping and a genome-wide association study. Overexpressing GmFtsH25 resulted in more grana thylakoid stacks in chloroplasts and increased photosynthetic efficiency and starch content, while knocking out GmFtsH25 produced the opposite phenotypes. GmFtsH25 interacted with photosystem I light harvesting complex 2 (GmLHCa2), and this interaction may contribute to the observed enhanced photosynthesis. GmFtsH25 overexpression lines had superior yield traits, such as yield per plant, compared to the wild type and knockout lines. Additionally, we identified an elite haplotype of GmFtsH25, generated by natural mutations, which appears to have been selected during soybean domestication. Our study sheds light on the molecular mechanism by which GmFtsH25 modulates photosynthesis and provides a promising strategy for improving the yields of soybean and other crops.

Citocininas no acúmulo de biomassa de Limonium sinuatum sob restrição radicular durante a fase de viveiro

Abstract It has been suggested that the response of the specialty cut flower Limonium sinuatum to different abiotic stress situations related to the plug tray cell size during nursery could be associated with the synthesis and translocation of endogenous cytokinins produced in the root tips. To validate this hypothesis, the aim of this work was to evaluate the participation of cytokinins in the process of biomass accumulation in L. sinuatum plants through foliar spraying with a synthetic cytokinin (benzyl aminopurine, BAP) and an inhibitor of the synthesis of endogenous cytokinins (dopamine). Our results indicated that spraying L. sinuatum plants with BAP increased leaf area initiation and expansion, biomass accumulation through increased plant photosynthetic capacity, and differential partitioning towards the shoot apical meristem by a positive feedback mechanism that has a threshold of optimal response close to 100 mg L-1 BAP. Dopamine spraying appeared to affect the synthesis of endogenous cytokinins, reducing the previously mentioned responses. Responses were dose-dependent, with an optimum of 100 mg L-1 BAP and 200 mg L-1 dopamine. Our results allow concluding that the level of endogenous cytokinins during the abiotic stress such as root restriction during nursery is a determining variable of the biomass accumulation process in this species.

Alleviation of iron deficiency in pear by ammonium nitrate and nitric oxide

BackgroundIron is essential for the growth and development of trace elements in plants, and iron deficiency can lead to leaf chlorosis. Ammonium and nitrate are the major forms of nitrogen present in soils. Ammonium nitrate alleviates the chlorosis of leaves caused by iron deficiency, but the mechanism is not clear in pear.ResultsAmmonium nitrate induced the increase of nitric oxide (NO) under iron deficiency. We further analyzed the effect of NO by exogenous NO treatment. The results showed that ammonium nitrate and NO increased the activity of ferric chelate reductase. NO induced the expression of multiple IRT genes and promoted the transmembrane transport of irons. Ammonium nitrate and NO promoted the activity of nitrogen assimilation-related enzymes and the nitrogen absorption capacity, and they also increased glutamine synthetase activity. Finally, ammonium nitrate and NO increased chlorophyll synthesis, with subsequent increase in the photosynthetic capacity of plants and accumulation of biomass.ConclusionAmmonium nitrate indirectly alleviates the symptoms of plant yellowing by promoting the increase of NO, which increases the response of iron transporters. Both substances increase the nitrogen accumulation in plants. This study demonstrates a new option for minimizing Fe deficiency by regulating the balance between nutrients.

Variation of yield and physiological characteristics of Lathyrus sativus L. populations under terminal drought

Grass pea is one of the oldest native crops grown in vast geographical regions of Iran, however ‎little is known about its tolerance to water shortage during post flowering period. We conducted ‎field experiments in 2018 and 2019 to study the effects of terminal drought on growth, yield, and ‎some physiological characteristics of grass pea (Lathyrus sativus L.) ecotypes. Nine local grass pea ‎ecotypes (Baft_1, Baft_2, Bardsir, Dehbakri, Kuhbanan, Rabor, Sirjan, Shiraz, and Torbat ‎Heydarieh), collected from different climatic regions in the east, southeast, and south of Iran, were ‎exposed to either normal irrigation or terminal drought (water withholding after flowering). Normal ‎irrigation was applied after 60 mm water evaporation from class A evaporation pan for the whole ‎growing season. Terminal drought decreased seed and biological yields, relative to normal ‎irrigation, with Baft_2 and Rabor the superior ecotypes in both treatments. Among yield traits, pod number per plant had very high correlation with seed and biological yields in either irrigation regime and was the highest in high yielding ecotypes. Leaf surface area, relative water content (RWC) and starch content decreased while soluble sugars and proline content increased by terminal drought. The highest yielding ecotypes, Baft_2 and Rabor had not the highest leaf area and RWC though they had the highest starch content under normal and sugars content under terminal drought. Also they had the greatest water use efficiency in both years and watering regimes. Proline content, RWC and sugar contents did not significantly correlate with seed or biological yield under terminal drought. Our results suggest that drought tolerance in ‎grass pea is closely associated with better utilization of water and plant photosynthetic capacity, as reflected in high starch ‎accumulation and conversion to sugars, perhaps as an osmotic adjustment factor. Also, high yielding ecotypes allocated higher dry matter to reproductive tissues.

Canopy nitrogen addition enhance the photosynthetic rate of canopy species by improving leaf hydraulic conductivity in a subtropical forest.

Elucidating the effects of atmospheric nitrogen (N) deposition on the photosynthetic capacity of plants is critical to understand forest growth and conservation under global change. However, studies on this topic generally consider only understory N addition, which ignores the effect of canopy interception. In this study, we conducted a field experiment in a subtropical forest to compare the effects of canopy vs. understory N addition on the photosynthetic rate of canopy and understory species. We found that canopy N addition enhanced the photosynthetic rate of canopy species by increasing leaf hydraulic conductivity and shortening the distance of CO2 transportation. In contrast, understory N addition had non-significant effects on the photosynthetic rate of canopy species. Moreover, the photosynthetic rate of understory species was not affected by canopy or understory N addition. Interestingly, changes in hydraulic conductivity contributed more to accelerating the photosynthetic rate than changes in CO2 transport distance. Our results provide important insights into the dissimilar effects of canopy and understory N addition on the photosynthetic rates of species in subtropical forests. Based on our findings, we highlighted the urgent need to consider canopy processes in future studies on N deposition.

Effects of Phosphorus Fertilization on Growth Characteristics, Fatty Acid Composition, and Seed Yields of Fengdan (Paeonia ostii T. Hong &amp; J. X. Zhang)

Paeonia ostii T. Hong &amp; J. X. Zhang is a perennial oil and medicinal plant with great importance as well as landscaping. P. ostii is being extensively planted in China, but the soil fertility limits the yield and quality. There is little information available on the effects of phosphorus fertilization on productivity, physiological characteristics, and seed yield and quality. This study investigated the influence of different phosphorus levels, 0 kg·hm−2 (CK), 90 c−2 (P1), 135 kg·hm−2 (P2), 180 kg·hm−2 (P3), 225 kg·hm−2 (P4), and 270 kg·hm−2 (P5), on the photosynthesis, morphology, physiological parameters, and yield of P. ostii. The results indicated that the net photosynthetic rate, stomatal conductance (gS), and transpiration rate of P. ostii increased significantly with the application of P4, which increased by 34.77%, 65.72%, and 21.00% compared with CK, respectively. Simultaneously, the contents of soluble sugar, soluble protein, and photosynthetic pigment in P4 were the highest compared with other treatments. In addition, thousand-grain weight (326.4 g) and seed yield per plant (37.33 g) of P4 were significantly higher than the control. However, the total amount of unsaturated fatty acids in P4 was lower compared with other treatments. The indexes of high correlation coefficients with Dim 1 and Dim 2 were gS and superoxide dismutase (SOD), respectively. The results showed that phosphorus levels improved plant photosynthetic capacity and increased antioxidant capacity as well as seed yield. Furthermore, phosphate fertilizer had significant effects on the oil composition. Moreover, the effect of phosphorus application rate on the growth index of P. ostii was greater than that of the physiological index.