Higher Rates Of Net Photosynthesis Research Articles

Variations in photoperiods and their impact on yield, photosynthesis and secondary metabolite production in basil microgreens

BackgroundThe effects of different photoperiods on plant phytochemical synthesis can be improved by adjusting the daily light integral. Photoperiod is one of the most important environmental factors that control growth, plant’s internal rhythm and the synthesis of secondary metabolites. Information about the appropriate standard in terms of photoperiod for growing basil microgreens as one of the most important medicinal plants is limited. In this study, the effects of five different photoperiods, 6 (6 h × 3 cycles), 8 (8 h × 2 cycles), 16, 18, and 24 h day− 1 on the yield, photosynthesis and synthesis of secondary metabolites of three cultivars and one genotype of basil microgreens in floating system were evaluated. The purpose of this research was to determine the feasibility of using permanent light in growing basil microgreens and to create the best balance between beneficial secondary metabolites and performance.ResultsThe results showed that the effects of photoperiod and cultivar on all investigated traits and their interaction on photosynthetic pigments, antioxidant capacity, total phenolic compounds, proline content and net photosynthesis rate were significantly different at the 1% level. The highest levels of vitamin C, flavonoids, anthocyanins, yield and antioxidant potential composite index (APCI) were obtained under the 24-h photoperiod. The highest antioxidant capacity was obtained for the Kapoor cultivar, and the highest total phenolic compound and proline contents were measured for the Ablagh genotype under a 24-h photoperiod. The highest yield (4.36 kg m− 2) and APCI (70.44) were obtained for the Ablagh genotype. The highest nitrate content was obtained with a photoperiod of 18 h for the Kapoor cultivar. The highest net photosynthesis rate was related to the Violeto cultivar under a 24-hour photoperiod (7.89 μmol CO2 m− 2 s− 1). Antioxidant capacity and flavonoids had a positive correlation with phenolic compounds and vitamin C. Yield had a positive correlation with antioxidant capacity, flavonoids, vitamin C, APCI, and proline.ConclusionsUnder continuous light conditions, basil microgreens resistance to light stress by increasing the synthesis of secondary metabolites and the increase of these biochemical compounds made basil microgreens increase their performance along with the increase of these health-promoting compounds. The best balance between antioxidant compounds and performance was achieved in continuous red + blue light. Based on these results, the use of continuous artificial LED lighting, due to the increase in plant biochemical with antioxidant properties and yield, can be a suitable strategy for growing basil microgreens in floating systems.

Optimizing One-Time Nitrogen Fertilization for Rice Production Using Controlled-Release Urea and Urease Inhibitors

One-time fertilization with controlled-release urea (CRU) is a research hotspot for its lower labor cost and stability of nitrogen (N) supply for rice growth. Yet the fertilizer formulation needs to be further improved to better adjust the N supplement to meet the demand of rice plants and obtain a higher grain yield. Therefore, the effects of novel fertilizer formulations composed of CRU, urease inhibitor (UI) and nitrification inhibitor (NI) on the rice growth and photosynthetic characteristics as well as high-yield formation were tested through a two-year field experiment. The result indicated that the combined use of CRU and UI treatment can achieve higher yields than with CRU at the same N application level. Meanwhile, with a 20% reduction of N use, one-time application of CRU + UI can obtain the same high yield as the conventional split application of urea. Compared with conventional fertilization and CRU treatment, the CRU + UI treatment had suitable leaf area and biomass accumulation at the vegetative growth stage and high effective stem tiller rate. More post-anthesis dry matter accumulation, higher net photosynthesis rate and low senescence rate were guaranteed for its high yield and nitrogen agronomic efficiency.

Suitability of Salicaceae genotypes to produce biomass using industrial wastewater

Water circularity is a challenge which must be met to guarantee the sustainability of this resource. Woody biomass is another resource of interest for the bioeconomy, which has multiple uses and acts as a carbon sink. Combining both aspects involves establishing wastewater irrigated plantations, the so-called Vegetation Filters. The aim in this research was to contribute towards assessing the suitability of different Salicaceae genotypes for enhancing the efficiency of these simultaneous processes. Twenty-three genotypes of different species and hybrids of the genera Populus and Salix were irrigated using brewery wastewater under controlled conditions (in a greenhouse using hydroponic cultivation or in pots with substrate) and in the field. Although the application of wastewater reduced the overall production, relevant differences among the genotypes were detected. Growth, physiological activity and nitrogen and electric conductivity (EC) attenuation efficiency provided good criteria for selection, although given the interaction with site conditions it is essential that plant material is selected based on its adaptation to the environment. The poplar hybrids ‘2000 Verde’ and ‘I-214’ showed the highest rates of net photosynthesis and transpiration, with high percentages of N removal and moderate biomass production, these two initially being considered of interest for the purposes outlined above. The ‘AF34’ genotype showed the highest production in the field, followed by the ‘Levante’ willow hybrid. The white poplar ‘PO-10-10-20’, which presented moderate production in the field, is also of interest due to its autochthony, which can be advantageous in certain environments.

Arbuscular Mycorrhizal Fungi Induce Changes of Photosynthesis-Related Parameters in Virus Infected Grapevine.

The negative effects of viruses and the positive effects of arbuscular mycorrhizal fungi (AMF) on grapevine performance are well reported, in contrast to the knowledge about their interactive effects in perennial plants, e.g., in grapevine. To elucidate the physiological consequences of grapevine-AMF-virus interactions, two different AMF inoculum (Rhizophagus irregularis and 'Mix AMF') were used on grapevine infected with grapevine rupestris stem pitting virus, grapevine leafroll associated virus 3 and/or grapevine pinot gris virus. Net photosynthesis rate (AN), leaf transpiration (E), intercellular CO2 concentration (Ci) and conductance to H2O (gs) were measured at three time points during one growing season. Furthermore, quantum efficiency in light (ΦPSII) and electron transport rate (ETR) were surveyed in leaves of different maturity, old (basal), mature (middle) and young (apical) leaf. Lastly, pigment concentration and growth parameters were analysed. Virus induced changes in grapevine were minimal in this early infection stage. However, the AMF induced changes of grapevine facing biotic stress were most evident in higher net photosynthesis rate, conductance to H2O, chlorophyll a concentration, total carotenoid concentration and dry matter content. The AMF presence in the grapevine roots seem to prevail over virus infection, with Rhizophagus irregularis inducing greater photosynthesis changes in solitary form rather than mixture. This study shows that AMF can be beneficial for grapevine facing viral infection, in the context of functional physiology.

Grain Yield Formation and Nitrogen Utilization Efficiency of Different Winter Wheat Varieties under Rainfed Conditions in the Huang-Huai-Hai Plain

Winter wheat production is threatened by drought stress under rainfed conditions; thus, screening high- and stable-yielding wheat varieties to ensure the sustainable development of wheat production and food security in the Huang-Huai-Hai Plain (HHHP) is vital. In this research, four-year field experiments with twelve winter wheat varieties were conducted during the winter wheat-growing seasons between 2016 and 2020 in order to: (1) screen high- and stable-yielding winter wheat varieties under rainfed conditions, (2) investigate the mechanism of high-yielding wheat yield formation and the relationships among grain-yield formation traits, and (3) investigate the nitrogen utilization efficiency (NUtE) of high-yielding wheat. The results showed that high-yield level wheat varieties (HL; Yannong999, Taimai1918 and Yannong173) obtained a higher average grain yield than medium-yield level wheat varieties (ML) and low-yield level wheat varieties (LL) by 10.1% and 29.0%, respectively. Compared with ML and LL, HL had a higher biomass at anthesis, higher spike dry matter at anthesis, higher spike partitioning index and fruiting efficiency (grain set per unit of spike dry weight at anthesis), and the highest grain number per square meter (24.2 × 103 m−2). Simultaneously, HL maintained a higher leaf area index (LAI) at anthesis and a higher net photosynthesis rate (Pn) of flag leaves after anthesis, which contributed to a higher post-anthesis biomass; HL also had higher maturity biomass, harvest index (HI), and biomass remobilization in comparison to ML and LL. The above results demonstrated that HL improved grain yield by increasing grain number per square meter, post-anthesis biomass, biomass remobilization, maturity biomass, and HI. Additionally, HL also obtained higher NUtE by improving grain yield. Therefore, screening winter wheat varieties with traits such as HL can help achieve high and stable yields and high NUtE under rainfed conditions.

POTASSIUM APPLICATION USING THE 4R NUTRIENT STEWARDSHIP APPROACH FOR IMPROVING WHEAT GROWTH AND YIELD TRAITS

Potassium (K) plays a key role in numerous plant metabolic processes, and its adequate amount is necessary for proper plant growth and development. Imbalanced fertilizer application has rapidly depleted the soil available K and harmed crops. However, the science-based K application in crops must follow the 4R nutrient stewardship approach to enhance crop yields. Therefore, a planned pot study used the 4R nutrient management technique for wheat potassium management. The evaluation of two wheat cultivars (Punjab-2008 and Barani-2011) employed two commercial K sources (MOP and SOP) with different application methods (basal and foliar) and sowing times (15 October, 15 November, and 15 December). The wheat variety Punjab-2008 performed better in root and shoot length, fresh biomass, and grain yield between 15 October and 15 November. Meanwhile, the Barani-2011, sown on 15 November, produced higher total chlorophyll contents and water use efficiency (WUE). The use of SOP (high dose), MOP (medium to high dose), and foliar spray of SOP at 1.5% and 3% resulted in maximum shoot length and the root-to-shoot ratio for both tested cultivars. Punjab-2008 produced higher grain yield when applied with a high SOP level than a high level of MOP. Similarly, a maximum leaf area index and proline contents observed in Punjab-2008 occurred with a high level of SOP applied. In contrast, a higher net photosynthesis rate and WUE emerged in Barani-2011 under a medium SOP level and a higher level of MOP. Thus, the conclusion is that medium to high rates of SOP proved a better source of K nutrition for improving yield parameters of wheat cultivars.

Genotypic variation in water relations and gas exchange of urban trees in Detroit, Michigan, USA

Increasing tree species diversity has become a key underpinning for communities to improve resilience of urban and community forests. Increasingly, urban forestry researchers are examining physiological traits to aid in selecting trees for urban sites. Knowledge of physiological responses also has implications for understanding species’ resilience to increased stresses associated with climate change. Here, we compare growth, leaf SPAD chlorophyll index, water relations, and gas exchange of seven genotypes of shade trees planted in two locations in downtown Detroit, MI, USA. Genotypes included Redpointe® maple (Acer rubrum ‘Frank Jr.’), Flashfire® maple (Acer saccharum ‘JFS-Caddo2′), Pacific Sunset® maple (Acer truncatum x platanoides ‘Warrenred’), Emerald City® tulip tree (Liriodendron tulipifera ‘JFS-Oz’), Chanticleer® pear (Pyrus calleryana ‘Glen’s Form’), swamp white oak (Quercus bicolor), and Emerald Sunshine® elm (Ulmus propinqua ‘JFS-Bieberich’). Trees were planted in either Lafayette Plaisance Park (Park), a large urban greenspace, or on the median of St. Aubin Avenue (Median), a nearby major thoroughfare. Tree height growth and leaf SPAD index were higher for trees planted in the Park location than on the Median. However, genotypic variation was larger than the effects of location or the interaction of Genotype × Location for most traits. Across measurement dates, midday leaf water potential was lowest for Pyrus trees and highest for Ulmus and Liriodendron trees. Pyrus and Quercus trees had relatively high rates of net photosynthesis (A) and stomatal conductance (gs) while Liriodendron, Acer saccharum, and Ulmus trees had low rates of A and gs. Liriodendron trees closed their stomata rapidly as leaf water potential (Ψw) declined (isohydric response), while Pyrus and Quercus trees maintained gs across a range of leaf Ψw (anisohydric response). Liriodendron trees also had the highest relative growth rates, suggesting that drought stress avoidance through isohydry is a viable drought tolerance mechanism in urban trees.

Role of LOC_Os01g68450, Containing DUF2358, in Salt Tolerance Is Mediated via Adaptation of Absorbed Light Energy Dissipation.

Salt stress affects plant growth and productivity. In this study we determined the roles of eight genes involved in photosynthesis, using gene co-expression network analysis, under salt-stress conditions using Arabidopsis knockout mutants. The green area of the leaves was minimum in the at1g65230 mutant line. Rice LOC_Os01g68450, a homolog of at1g65230, was ectopically expressed in the at1g65230 mutant line to generate revertant lines. Under salt stress, the revertant lines exhibited significantly higher net photosynthesis rates than the at1g65230 mutant line. Moreover, the operating efficiency of photosystem II (PSII) and electron transport rate of the revertant lines were higher than those of the wild type and at1g65230 mutant line after 10 days of exposure to salt stress. After this period, the protein PsbD–the component of PSII–decreased in all lines tested without significant difference among them. However, the chlorophyll a and b, carotenoid, and anthocyanin contents of revertant lines were higher than those of the mutant line. Furthermore, lower maximum chlorophyll fluorescence was detected in the revertant lines. This suggests that LOC_Os01g68450 expression contributed to the salt tolerance phenotype by modifying the energy dissipation process and led to the ability to maintain photosynthesis under salt stress conditions.

Transparent plastic film combined with deficit irrigation improves hydrothermal status of the soil-crop system and spring maize growth in arid areas

Plastic film mulching and irrigation amount greatly affect soil hydrothermal status and spring maize (Zea mays L.) productivity in arid areas. Yet the coupled effects of film mulching with different optical properties and deficit irrigation on water and temperature variation within the soil-crop system and on plant growth in arid areas have not been well-investigated. A two-year field experiment was conducted with five treatments: 1) full irrigation without mulching (FN), 2) full irrigation with transparent plastic film mulching (FT), 3) full irrigation with black plastic film mulching (FB), 4) deficit irrigation with transparent plastic film mulching (DT), and 5) deficit irrigation without mulching (DN). The results showed that plastic film mulching significantly increased soil water in the 80–120 cm soil layer and canopy air humidity. The alternating wet-dry behavior of soil water caused by plastic film mulching was an effective water utilization strategy that increased crop water productivity. DT stimulated the alternating wet-dry behavior of soil water in the 0–80 cm layer more than the FN. This alternating behavior was characterized by relatively wet soil at the 12-leaf growth stage (V12), relatively dry soil from V12 to the grain-filling growth stage (R3), and relatively wet soil again after R3. Alternating wet-dry behavior changed from wet to dry at V12 in 2019 and was earlier than V12 in 2020. Plastic film mulching significantly increased soil temperature at the six-leaf growth stage (V6) and decreased canopy air temperature during the whole maize growing seasons. The higher net photosynthesis rate was observed at the canopy air relative humidity of 78.6%. Net photosynthesis rate decreased with increasing canopy air temperature. FT, FB, DT, and FN significantly increased grain yields over DN by 39.7–45.8%, 25.5–41.8%, 18.2–33.4%, and 9.0–17.0%, respectively, and increased net income over DN by 894–1127, 436–979, 343–844, and 166–429 USD ha–1, respectively. DT decreased net income and output/input ratio by 28.1% and 10.9% in 2019, respectively, compared with FT. However, these values were 12.3% and 4.0% in the relatively wet growing season in 2020. Deficit irrigation combined with transparent plastic film mulching can ensure an acceptable maize grain yield and net income in arid areas with limited water resources, especially in growing seasons with greater rainfall.

Inconsistent changes in NPP and LAI determined from the parabolic LAI versus NPP relationship

Rapidly altering vegetation dynamics, is an aspect of global environmental change which has consequences for ecosystem structure, function, and the provision of ecosystem services. However, the responses of vegetation greenness and vegetation productivity to environmental changes may be inconsistent. Currently, we do not know how these inconsistent trends of greenness and productivity vary across the globe, nor the main causes of that variability. We used leaf area index (LAI) and net primary productivity (NPP) to represent vegetation greenness and productivity, respectively. The results showed that about 42% of the global vegetated area showed inconsistent trends of LAI and NPP from 2000 to 2015. These inconsistent trends were mainly found in humid areas. A parabolic relationship was found between the NPP and LAI of global vegetation, with a turning point in LAI of global vegetation of 4.5 ± 0.4 m2 m−2. The ratio of NPP to LAI (NPP/LAI), net primary production per unit leaf area, decreases as the LAI increases. The variability of NPP/LAI is significantly correlated with the consistency of NPP and LAI changes in different land cover types. NPP/LAI is lower in tree-dominated biomes with higher canopies (such as forests), and higher in areas dominated by short vegetation (such as shrubland and grassland). Drylands have higher NPP/LAI than humid regions which are perhaps due to high rates of net photosynthesis and narrow leaves. The results of this study not only clearly portray the relationship between vegetation greenness and productivity but also help us to understand the impact of vegetation dynamics on global carbon cycling in a changing environment.

Effects of Planting Density on Morphological and Photosynthetic Characteristics of Leaves in Different Positions on Cunninghamia lanceolata Saplings

The improvement of the stand yield and economic benefits of Cunninghamialanceolata (Lamb.) Hook, one of the most important plantation trees in China, has always been a concern. An appropriate planting density plays an important role in increasing productivity. To determine the optimum planting density of C. lanceolata, we measured leaf morphology, gas exchange parameters, and photosynthetic pigments in replicate leaves on 4-year-old saplings grown in four canopy positions under a low (D1), medium (D2), and high (D3) planting density (approximately 900, 2505, and 6660 trees·ha−1, respectively). We then ranked trait variations using the coefficient of variation to explore the influence of planting density. Planting density significantly influenced the leaf morphology, gas exchange parameters, and the photosynthetic pigment contents of C. lanceolata. Medium planting density (D2) resulted in a larger leaf area and specific leaf areas, a higher net photosynthesis rate, and higher photosynthetic pigment contents. The responses of leaf gas exchange parameters had the most plastic traits that responded to planting density. An appropriate planting density and leaf position might improve C. lanceolata leaf morphology and physiological attributes, which in turn would facilitate growth.

Nitrogen nutrition effects on triticale photosynthesis and assimilate translocation under late-season water stress conditions

In this study, photosynthesis and assimilate translocation and their contribution to improving grain yield and harvest index (HI) of triticale under different N sources and irrigation regimes in an arid climate were evaluated. There were two levels of water regimes: normal irrigation (IRN) and deficit irrigation (cutting irrigation after anthesis stage - IRD). Four N sources: Azospirillum brasilense (Bio), Azospirillum brasilense + 75 kg N ha−1 as urea (Bio + N75), 150 kg N ha−1 as urea (N150) and control unfertilized (N0) plots were used. Results showed the highest net photosynthesis rate (Pn ) was observed in Bio + N75 (24 and 20 µmol CO2 m−2 s−1 at the milking and soft dough stages, respectively) under IRN. The IRD decreased Pn in all N sources, however, the highest reduction was observed in N150 and the lowest in Bio and Bio + N75 treatments. Similar trends were observed in other photosynthetic traits and assimilate remobilization, except for the instantaneous water use efficiency (IWUE), which increased by IRD when bio-fertilizer was applied. The highest grain yield was found by N150 under IRN, which was not significantly different from Bio + N75 treatment. In contrast, application of Bio + N75 resulted in the highest grain yield compared to the other N sources under IRD. Overall, since the lowest reduction in photosynthetic traits, assimilate remobilization, and grain yield of triticale under IRD conditions occurred when bio-fertilizer was applied, this N fertilizer regime could be recommended for the arid areas where water shortage occurs frequently.

The Influence of Soil Tillage System on Changes in Gas Exchange Parameters of Pisum sativum L.

A field experiment was carried out in 2017–2019 as a split-plot design with four replicates at the Agricultural Experimental Station in Grabów, Poland. The aim of the study was to compare the gas exchange parameters of the pea depending on the use of different soil tillage systems. Physiological plant parameters as: net photosynthetic rate (PN), transpiration rate (E), stomatal conductance (gs), intercellular CO2 concentration (Ci) and relative chlorophyll content were measured in three developmental stages. The study have showed that all the measured parameters were affected by the tillage system of the soil. Net photosynthetic rate and transpiration rate were significantly lower in the treatments, where simplified-tillage was applied. Pea grown in the plough tillage (CT) showed a generally higher rate of net photosynthesis and transpiration rate compared to that of peas grown in the reduced tillage and no-tillage systems, but this was dependent on the plant development stage and the weather conditions prevailing in a given year. The highest intercellular CO2 concentration (Ci) under different cultivation methods were found in the no-tillage system, regardless of the developmental stage of legumes. The values of determination coefficients showed a positive relationship between the photosynthetic rate and seed yield of the peas tested in all the years of the research. The study also showed that a significantly higher SPAD index was found in the CT tillage system, irrespectively on the developmental stage.

Study on Morphological, Physiological Characteristics and Yields of Twenty-One Potato (Solanum tuberosum L.) Cultivars Grown in Eastern Sub-Himalayan Plains of India

The present study was conducted in the eastern sub-Himalayan plains of West Bengal, India, to evaluate 21 potato cultivars (including table- and processing-type) and assess their suitability in terms of improved physiological responses, yield performances, stability and profitability. A significant difference in various growth attributes, i.e., plant height, number of stems per plant, leaf area index (LAI), dry matter (DM) accumulation, and crop growth rate (CGR), was noted amongst different cultivars. Significant variation was also observed in net photosynthesis rate (NPR), transpiration rate (TR), and stomatal conductance rate (SCR) recorded at various stages of growth. Amongst all the cultivars, ‘Kufri Chipsona-4’ showed the highest SCR at both 60 and 80 days after planting (DAP), while ‘Kufri Pokhraj’ had the highest NPR at both 60 and 80 DAP. However, the highest TR was achieved with ‘Kufri Chipsona-3’and ‘Kufri Surya’ at 60 and 80 DAP, respectively. ‘Kufri Pukhraj’ and ‘Kufri Himsona’ achieved the maximum and minimum tuber bulking rate (TBR) values at initial growth stages (upto 60 days), respectively; however, ‘Kufri Arun’ and ‘Kufri Surya’ had significantly higher TBRs during the later part of growth (after 60 days to maturity), leading to higher tuber yields amongst the medium maturing cultivars. Among the 21 cultivars, ‘Kufri Arun’ showed the maximum total tuber yield (35.52 t/ha), followed by ‘Kufri Pukhraj’ (33.54 t/ha) with higher marketable grade tubers. In terms of production economics, ‘Kufri Arun’ achieved the maximum net return (USD 2137.4) and B:C (benefit:cost) ratio (2.17), suggesting the suitability of this cultivar in the eastern sub-Himalayan plains of West Bengal. The early maturing ‘Kufri Pukhraj’ and processing variety ‘Kufri Chipsona-3’ also showed their suitability in terms of net returns and B:C ratio. The heat-tolerant variety ‘Kufri Surya’ also achieved a tuber yield of 31 tha−1 with satisfying net return (USD 1596.9) and B:C ratio (1.88), suggesting the suitability of this cultivar in this region under terminal heat stress. However, the stability analysis showed that the cultivars ‘Kufri Khyati’ and ‘HPS II/67’ were the most stable in terms of additive main effect and multiplicative interaction (AMMI) stability value (ASV) and yield stability index (YSI), respectively.

Poplar Autophagy Receptor NBR1 Enhances Salt Stress Tolerance by Regulating Selective Autophagy and Antioxidant System.

Salt stress is an adverse environmental factor for plant growth and development. Under salt stress, plants can activate the selective autophagy pathway to alleviate stress. However, the regulatory mechanism of selective autophagy in response to salt stress remains largely unclear. Here, we report that the selective autophagy receptor PagNBR1 (neighbor of BRCA1) is induced by salt stress in Populus. Overexpression of PagNBR1 in poplar enhanced salt stress tolerance. Compared with wild type (WT) plants, the transgenic lines exhibited higher antioxidant enzyme activity, less reactive oxygen species (ROS), and higher net photosynthesis rates under salt stress. Furthermore, co-localization and yeast two-hybrid analysis revealed that PagNBR1 was localized in the autophagosome and could interact with ATG8 (autophagy-related gene). PagNBR1 transgenic poplars formed more autophagosomes and exhibited higher expression of ATG8, resulting in less accumulation of insoluble protein and insoluble ubiquitinated protein compared to WT under salt stress. The accumulation of insoluble protein and insoluble ubiquitinated protein was similar under the treatment of ConA in WT and transgenic lines. In summary, our results imply that PagNBR1 is an important selective autophagy receptor in poplar and confers salt tolerance by accelerating antioxidant system activity and autophagy activity. Moreover, the NBR1 gene is an important potential molecular target for improving stress resistance in trees.

METHYL JASMONATE EFFECT ON THE PROCESS OF COLD ADAPTATION IN WHEAT

The effect of methyl jasmonate (MeJA) on frost resistance, photosynthetic and respiratory activity, and water metabolism in wheat plants (Triticum aestivum L.) exposed to a low hardening temperature (4 °С) was studied. It was found that under hardening conditions, treatment with MeJA led to a greater increase in the plants’ frost resistance than without it, and also augmented dry shoot and root biomass gain. In addition, pretreatment with MeJA helped the seedlings maintain a higher rate of net photosynthesis and transpiration, and increased stomatal conductance during the hardening period. Also, the rate of dark respiration was observed to rise in the presence of MeJA, leading an increase in the ratio of respiration to gross photosynthesis (Rd/Pg). Based on the obtained results, it was concluded that MeJA had a positive effect on the cold adaptation of wheat plants, which is due to its regulatory effect on the main physiological processes.

Strategy by latitude? Higher photosynthetic capacity and root mass fraction in northern than southern silver birch (Betula pendula Roth) in uniform growing conditions.

Growth of northern trees is limited by short growing seasons. In multi-year trials, northern trees usually grow less than southern ones but can have higher gas exchange, whereas differences in biomass allocation and its relation to photosynthesis are less known. We characterized silver birch (Betula pendula Roth) provenances from southern (latitude 61°) and northern (latitude 67°) Finland in uniform chamber conditions. In a time-series experiment, we measured traits related to growth, biomass allocation and photosynthesis, and determined gas exchange responses to temperature and light. We found provenance differences in photosynthetic capacity and growth. The northern provenance allocated relatively more to roots, having a higher root mass fraction and lower shoot:root ratio than the southern provenance. On the other hand, the northern provenance had fewer leaves and lower total leaf dry weight (DW) than the southern provenance. The northern provenance attained higher rates of net photosynthesis (Anet) and higher stomatal conductance (gs) in all measured temperatures and higher photosynthesis at the optimum temperature (Aopt) than the southern provenance, but there was no difference in the optimum temperature of photosynthesis (Topt, 18.3 °C for the southern provenance vs 18.9 °C for the northern one). Photosynthetic light response curves showed no between-provenance differences. In a time-series, the northern provenance had higher Anet than the southern provenance, but gs was similar. The northern provenance had higher maximum quantum yield of photosystem II photochemistry (Fv/Fm) than the southern provenance. There were no differences between provenances in height, total plant DW, shoot DW, root DW or shoot mass fraction. Our results suggest that the provenances occupy a common thermal niche, or can at least relatively quickly acclimate to a common growth temperature. Thus, carbon assimilation of these northern trees may not be significantly affected by rising temperatures alone. In an equal photoperiod and optimal conditions, we found different one-season biomass accumulation strategies: southern trees grow with more leaves, while northern trees reach similar total assimilation (total DW, height) with more efficient photosynthetic capacity per leaf area (higher gas exchange, higher Fv/Fm) and relatively more investment in the below-ground fraction of the plant.

Contrasting Growth, Photosynthesis, Antioxidant Responses and Water Use Efficiency in Two Medicago sativa L. Genotypes under Different Phosphorus and Soil Water Conditions

Genotypic variations of alfalfa (Medicago sativa L.) to both phosphorus (P) deficiency and water deficiency are evident on the Loess Plateau of China. Here, we compare the adaptive mechanisms between an introduced cultivar (Arkaxiya) and a landrace (Longzhong) subjected to P- and water-limited conditions. The two genotypes were grown in a soil medium with 0, 4.2, 8.4 and 16.8 μg applied P per gram dry soil. Three water treatments were imposed (maintained at 75–90%, 45–55% and 30–35% of pot capacity (PC)) 28 days after sowing (DAS). At high soil P and high soil water content (SWC), high rates of net photosynthesis (Pn) contributed to greater plant growth and P-use efficiency (PUE) in the introduced Arkaxiya compared to the landrace Longzhong. However, at low SWC, Longzhong had enhanced antioxidative defense (mainly SOD and CAT) compared to Arkaxiya. In addition, shorter shoot length and greater branching in Longzhong than Arkaxiya may also facilitate adaptation to low SWC. The contrasting adaptive mechanisms of the two genotypes provide a number of early-screening parameters associated with plant growth for the selection and introduction of alfalfa targeted at different rainfall and available P environments.

Possibility of Increasing the Growth and Photosynthetic Properties of Precocious Walnut by Grafting

Plant growth characteristics after grafting are mainly dependent on photosynthesis performance, which may be influenced by grafting combinations with different rootstocks and scions. In this study, we used one-year-old walnut grafts to investigate the grafting compatibility between precocious (‘Liaoning 1’, L) and hybrid (‘Zhong Ning Sheng’, Z) walnut, as well as rootstock and scion impact on the growth and photosynthetic properties of walnut trees. The results showed that grafting compatibility between the two varieties is high, with survival rates upward of 86%. Overwintering survival of grafted seedlings was as high as 100%, which indicated that the allopolyploid had good resistance to low-temperature stress. The homograft of the hybrid walnut had the highest net photosynthesis rate (18.77 μmol·m−2s−1, Z/Z) and growth characteristics, which could be due to its higher transpiration rate and stomatal conductance, whereas the homograft of precocious walnut presented the lowest net photosynthesis rate (15.08 μmol·m−2s−1, L/L) and growth characteristics. Significant improvements in the net photosynthesis rate (15.97 and 15.24 μmol·m−2s−1 for L/Z and Z/L, respectively) and growth characteristics of precocious walnut were noticed during grafting of the hybrid walnut, which could have been contributed by their transpiration rate. The results of this study serve as a guide for the selection and breeding of good rootstock to improve plant growth characteristics and photosynthetic efficiency. We conclude that good rootstock selection improves plant growth potential and could play an important role in sustainable production.

Arbuscular mycorrhiza influences carbon-use efficiency and grain yield of wheat grown under pre- and post-anthesis salinity stress.

Soil salinity severely affects and constrains crop production worldwide. Salinity causes osmotic and ionic stress, inhibiting gas exchange and photosynthesis, ultimately impairing plant growth and development. Arbuscular mycorrhiza (AM) have been shown to maintain light and carbon use efficiency under stress, possibly providing a tool to improve salinity tolerance of the host plants. Thus, it was hypothesized that AM will contribute to improved growth and yield under stress conditions. Wheat plants (Triticum aestivum L.) were grown with (AMF+) or without (AMF-) arbuscular mycorrhizal fungi (AMF) inoculation. Plants were subjected to salinity stress (200mm NaCl) either at pre- or post-anthesis or at both stages. Growth and yield components, leaf chlorophyll content as well as gas exchange parameters and AMF colonization were analysed. AM plants exhibited a higher rate of net photosynthesis and stomatal conductance and lower intrinsic water use efficiency. Furthermore, AM wheat plants subjected to salinity stress at both pre-anthesis and post-anthesis maintained higher grain yield than non-AM salinity-stressed plants. These results suggest that AMF inoculation mitigates the negative effects of salinity stress by influencing carbon use efficiency and maintaining higher grain yield under stress.