Leaf Photosynthesis Rate Research Articles

Intercropping induces physiological and morphological plasticity in oilseed rape and barley under drought stress

Intercropping is an agricultural practice that can improve crop yield due to better availability of resources, including water. There are few studies, however, addressing the physiological mechanisms behind this phenomenon. In this work oilseed rape (Brassica napus L.) and barley (Hordeum vulgare L.) were cultivated either as monocrop (MC) or intercrop (IC) under well-watered (WW) or drought stress (DS) conditions in a growth chamber. After eight weeks DS, the leaf relative water content was higher in the IC compared with the MC plants in both species and the DS-induced senescence of old leaves was considerably postponed in oilseed rape. Intercropped oilseed rape showed elevated levels of leaf photosynthesis rate, superior accumulation of organic osmolytes but higher water loss compared with the MC counterparts under DS conditions. In barley, less transpiration, an increased root : shoot ratio and osmolyte accumulation was observed in the IC compared with MC plants under DS conditions. The water use efficiency was higher in the IC compared to MC barley and the plants yield was higher in the IC than in the MC oilseed rape. Our data showed that intercropping is a reliable practice for cultivation of both species under arid and semi-arid regions or under rainfed conditions.

Simulating the effects of low-temperature stress on wheat biomass growth and yield

Low-temperature stress in late spring poses a serious threat to winter wheat production. In three-year environment-controlled phytotron experiments at both elongation and booting stages, we observed that short-term low-temperature stress decreased leaf area and stem, limited leaf photosynthetic system, and severely reduced grain yield, especially in the low-temperature sensitive cultivar. To better quantify the effects of low-temperature stress on leaf photosynthesis rate (Pn), leaf area index (LAI), biomass partitioning, and grain yield, the lethal temperature at 50% mortality (LT50), low-temperature damage index (LDI), and process-based algorithms were proposed and incorporated into the WheatGrow model. The algorithms take into account the effects of low-temperature with different durations and reflected a low-temperature sensitivity of cultivars at different growth periods by using LT50. The improved WheatGrow model could reproduce well the observed dynamics of the decrease of Pn during the treatment period, recovery of Pn after cold treatments, and the damage to LAI and biomass accumulation under the low-temperature stress treatments. Compared to the original model, RMSE of Pn, LAI, total aboveground biomass, and grain yield in the improved WheatGrow model were reduced by 63 to 77% under low-temperature stress. Although the newly developed algorithms expand crop modeling capacity into quantifying the impacts of low-temperature stress on wheat productivity, further assessments with observed data under field conditions are still required, especially for obtaining suitable parameters at the regional scale.

Tomato Evapotranspiration, Crop Coefficient and Irrigation Water Use Efficiency in the Winter Period in a Sunken Chinese Solar Greenhouse

In the Northern China Plain (NCP), sunken solar greenhouses (SSG) are now increasingly being used for vegetable cultivation in winter due to low winter temperatures. Investigating plant transpiration and determining crop coefficients are helpful when developing irrigation scheduling and improving crop growth. In this study, a three-season experiment was conducted in a commercial tomato SSG to investigate changes in microclimate, sap flow (SF), photosynthesis traits and plant physiological parameters, and to calculate the crop coefficient and evaluate the irrigation efficiency using current irrigation management practices. Results show that the average transmissivity from top plastic covers was 0.69, and the inside temperature increased by approximately 10 °C in November and 15–18 °C in December, which guaranteed the growth of tomatoes in winter. The leaf photosynthesis rate (Pn) is linearly related to radiation, however, a concave quadratic function is a better fit for Pn and VPD, with the highest Pn at approximately 1.0 kPa VPD; leaf transpiration is positively and linearly related to both radiation and VPD. Therefore, increasing greenhouse transmissivity and maintaining an internal VPD of approximately 1 kPa could produce a high leaf Pn and low transpiration concurrently. Daily total SF was linearly correlated with solar radiation, VPD and temperature with determination coefficients of 0.87–0.96, 0.89–0.91 and 0.62–0.84, respectively. Correcting the slope of SF to radiation with VPD (SF = (0.12 + 0.14VPD)Rs), R2 increased by 0.08, and the root mean square error and relative error decreased by 0.047 mm day−1 and 6.53%, respectively. Therefore, this integrated equation is recommended to estimate daily tomato transpiration when plant height is approximately 1.5 m, and the leaf area index (LAI) is between 2 and 2.5. During the fruit expansion and ripening period, the average basal crop coefficients (Kcb) for greenhouse tomatoes in winter was between 0.99 and 1.11. The irrigation efficiency increased from 0.3 in the first season to 0.6–0.69 in the second and third seasons when the tensiometer method was used. Therefore, using the tensiometer method to guide tomato irrigation could markedly improve irrigation efficiency in greenhouses.

Acclimation of Ecophysiological and Agronomic Traits to Increasing Growth Temperature in Three Cowpea Genotypes Grown in Anuradhapura, Sri Lanka

The future of food crop production is uncertain due to the negative effects of global warming. Cowpea is grown in warm environments including in Sri Lanka, where less is known about the potential acclimation of ecophysiological and agronomic traits to increasing temperatures. We evaluated the acclimation potential of yield components and ecophysiological traits of three recommended cowpea genotypes to the seasonal variation in growth temperature in Anuradhapura, Sri Lanka. This study was conducted at the Faculty of Agriculture, Rajarata University of Sri Lanka, in two consecutive seasons with average daytime temperatures of 30.4°C and 33.2°C. Three genotypes, Dhawala, Waruni, and MI-35, were tested in this study, and their rates of leaf photosynthesis and respiration at the 50% flowering stage and final yield parameters were measured at their respective average growth temperatures in both seasons. The total yield per hectare showed an average decrease of 16%, 17%, and 22% in the Dhawala, Waruni, and MI-35 genotypes at high average growth temperature, respectively. These reductions were associated with the reduction in the number of seeds per pod, hundred seed weight, and number of pods per plant, suggesting that there could be an among-genotype variation in flower abscission, fertilization, and biomass partitioning during the season in which the average growth temperature was high. In the season with high average growth temperature, genotype Dhawala showed an increased carbon gain per unit carbon loss and increased water use efficiency compared to MI-35 and Waruni genotypes. Therefore, genotype Dhawala is a better candidate than MI-35 and Waruni genotypes in the face of global warming, which may be considered in further breeding programs and market preferences. More work is proposed to examine the patterns of biomass partitioning and radiation use efficiency in three cowpea genotypes at elevated temperatures.

Identifying variation for N-use efficiency and associated traits in amphidiploids derived from hybrids of bread wheat and the genera Aegilops, Secale, Thinopyrum and Triticum.

Future genetic progress in wheat grain yield will depend on increasing biomass and this must be achieved without commensurate increases in nitrogen (N) fertilizer inputs to minimize environmental impacts. In recent decades there has been a loss of genetic diversity in wheat through plant breeding. However, new genetic diversity can be created by incorporating genes into bread wheat from wild wheat relatives. Our objectives were to investigate amphidiploids derived from hybrids of bread wheat (Triticum aestivum L.) and related species from the genera Aegilops, Secale, Thinopyrum and Triticum for expression of higher biomass, N-use efficiency (NUE) and leaf photosynthesis rate compared to their bread wheat parents under high and low N conditions. Eighteen amphidiploid lines and their bread wheat parents were examined in high N (HN) and low N (LN) treatments under glasshouse conditions in two years. Averaged across years, grain yield reduced by 38% under LN compared to HN conditions (P = 0.004). Three amphidiploid lines showed positive transgressive segregation compared to their bread wheat parent for biomass per plant under HN conditions. Positive transgressive segregation was also identified for flag-leaf photosynthesis both pre-anthesis and post-anthesis under HN and LN conditions. For N uptake per plant at maturity positive transgressive segregation was identified for one amphidiploid line under LN conditions. Our results indicated that introgressing traits from wild relatives into modern bread wheat germplasm offers scope to raise biomass and N-use effciency in both optimal and low N availability environments.

The residual impact of straw mulch and biochar amendments on grain quality and amino acid contents of rainfed maize crop

The inability of humans and many farm animals to synthesize certain amino acids has long triggered tremendous interest in increasing the levels of these so-called essential amino acids in crop plants. Hence, a two-year field experiment was conducted to evaluate the effects of straw mulch (8 t ha−1) and biochar applied at various rates (0, 4, 12, 36 t ha−1) on the chlorophyll, photosynthesis, total nitrogen in soil, essential and nonessential amino acid (AA) contents of maize grain. The maize straw mulch and biochar significantly increased chlorophyll contents, photosynthesis rate of maize crop and total soil nitrogen. The application of biochar (12 t ha−1) increased the chlorophyll contents and photosynthesis rate and total soil nitrogen during both years. However, excessive biochar applications (more than 12 t ha−1) had negative effects on chlorophyll contents, photosynthesis rate of maize crop and total soil nitrogen of soil. The AAs were significantly affected by biochar, depending on the application rate. In conclusion, the application of straw mulch and biochar improved the rate of leaf chlorophyll contents, photosynthesis rate and amino acid contents in maize grain when applied at appropriate rates, but the effects were negative when biochar was overused.

LncRNA PMAT–PtoMYB46 module represses PtoMATE and PtoARF2 promoting Pb2+ uptake and plant growth in poplar

Lead (Pb2+) is one of the most toxic heavy-metal contaminants. Fast-growing woody plants with substantial biomass are ideal for bioremediation. However, the transcriptional regulation of Pb2+ uptake in woody plants remains unclear. Here, we identified 226 Pb2+-induced, differentially expressed long non-coding RNAs (DELs) in Populus tomentosa. Functional annotation revealed that these DELs mainly regulate carbon metabolism, biosynthesis of secondary metabolites, energy metabolism, and signal transduction through their potential target genes. Association and epistasis analysis showed that the lncRNA PMAT (Pb2+-induced multidrug and toxic compound extrusion (MATE) antisense lncRNA) interacts epistatically with PtoMYB46 to regulate leaf dry weight, photosynthesis rate, and transketolase activity. Genetic transformation and molecular assays showed that PtoMYB46 reduces the expression of PtoMATE directly or indirectly through PMAT, thereby reducing the secretion of citric acid (CA) and ultimately promoting Pb2+ uptake. Meanwhile, PtoMYB46 targets auxin response factor 2 (ARF2) and reduces its expression, thus positively regulating plant growth. We concluded that the PMAT–PtoMYB46–PtoMATE–PtoARF2 regulatory module control Pb2+ tolerance, uptake, and plant growth. This study demonstrates the involvement of lncRNAs in response to Pb2+ in poplar, yielding new insight into the potential for developing genetically improved woody plant varieties for phytoremediating lead-contaminated soils.

Differences in Biochar Sources for Controlled Nitrogen Loss in a Hybrid Maize Agroforestry System with Melaleuca cajuputi

Biochar is used to improve soil fertility and control nitrogen loss in soil. This study aimed to evaluate the difference between biochar sources, namely Melaleuca cajuputi waste and rice husk, for controlled nitrogen loss in hybrid maize planted between Melaleuca cajuputi stands. A split-plot design with three replications was used. The main plot was composed of biochar sources (BS), i.e., without biochar application (WB), Melaleuca cajuputi biochar (MCB), and rice husk biochar (RHB). The subplot was the urea fertilizer dosage, i.e., 0, 150, 300, and 450 kg/ha. The observation parameters were nitrate reductase activity (NRA), total chlorophyll (TC), leaf photosynthesis rate (LPR), nitrogen loss (NL), nitrogen use efficiency (NUE), and seed yield per hectare (SY). The data were analyzed with ANCOVA and LS-means. The results showed that there was no significant difference between mixing MCB or RHB in UF for all hybrid maize parameters, whereas significant differences were observed with WB. The NL values ​​of MCB and RHB were 13.85 and 13.08 kg/ha N, i.e., NL was significantly reduced by 70.90% and 72.51%, and the percentage of SY increased by 28.60% and 37.94% compared to WB, respectively.

Leaf growth, gas exchange and assimilation performance of cowpea varieties in response to Bradyrhizobium inoculation

Supplying nitrogen to crops through selecting high N fixing legumes and effective inoculant is one of the key strategies to improve crop productivity. However, studies related to the effect of Bradyrhizobial inoculation on leaf growth, its functioning in relation to photosynthesis, and transpiration efficiency (WUE) of cowpea [Vigna unguiculata (L.) Walp] varieties in the tropics were inadequate. A two-year field experiment was conducted at three sites to evaluate the effect of inoculation on leaf growth, gas exchanges and photosynthetic efficiency of cowpea varieties. The study treatments were composed of four varieties, Keti (IT99K-1122), TVU, Black eye bean, and White wonderer trailing and three levels of inoculation (non-inoculated or inoculated with Bradyrhizobium strains CP-24 or CP-37). Gas exchange was measured on live plants at 67–77 days after sowing, between 8:00 to 11:00 a.m. and 14:00 to 16:00 p.m. Leaf growth parameters (leaf number and leaf area) were measured by destructive sampling, and the yield data was determined by harvesting plants in the three central rows at physiological maturity. Variety TVU performed best in terms of leaf number, photosynthesis rate, and WUE. Whereas, Black eye bean revealed superior performances for leaf area, leaf area index, and stomatal conductance compared with the rest two varieties. The effect of inoculation was significant with 14.0, 23.8, 13.7, and 11.0% advantage in leaf area, leaf area index, net photosynthesis, and WUE, respectively. Moreover, the performance of cowpea of the 2018 cropping season showed a relative advantage over 2019 in terms of leaf number, leaf area, leaf area index, net photosynthesis, and stomatal conductance. Therefore, inoculating cowpea varieties with effective Bradyrhizobium strain can be a viable alternative to enhance growth, gas exchange, photosynthetic efficiency, and grain yield.

Evaluation of rice genotypes on seed attributes and agronomic performance for developing direct-seeded cultivar

<abstract> <p>Direct seeding of rice (DSR) may give benefit in using water and labor more efficient and reduce production costs. This study purposes to investigate the character of the seeds, their early vigor traits, the growth and development of rice plants for developing DSR cultivar. The research was conducted in four stages: the measurement of the size of the seed, endosperm, and embryo; the germination test in the laboratory; seedling test using experimental pots; and testing the agronomic performance on transplanting and direct seeding methods in a plastic house. Seed material used eight breeding lines of IPB University and two released varieties. The results of study showed that each genotype had different characteristics of seed, endosperm, and embryo in both weight and area. Seed weight becomes the most dominant in the emergence of superior EV traits, whereas the more seed weight indicates faster radicle emergence and more weight of seedling. DSR method compared to transplanting showed performance such as taller plant, higher leaf area and photosynthesis rate at early growth stage, earlier heading time, and higher plant dry weight since early growth until 65 days old. The seed characters have positively correlation to dry weight of seedlings, number of leaves, leaf area, and canopy dry weight. We also found that higher area of endosperm and embryo significantly correlated to have faster plumule emergence, higher leaf area and plant height. Candidate genotypes for DSR would be further investigated in the field trial agronomically.</p> </abstract>

Improving Grain Yield via Promotion of Kernel Weight in High Yielding Winter Wheat Genotypes.

Simple SummaryImproving plant net photosynthetic rates and accelerating water-soluble carbohydrate accumulation play an important role in increasing the carbon sources for wheat kernel growth and yield. The objective of this study was to quantify the relative yield contribution by analyzing the photosynthesis rate of flag leaf, water-soluble carbohydrate content of flag leaf, flag leaf sheath and stem, and other agronomic and physiological traits in 15 wheat cultivars released in Shandong Province, China between 1969 and 2006. Our results suggest that increase of flag leaf photosynthesis and WSC had a positive effect of 0.593 on the TKW, and thus benefit for developing high yielding wheat cultivars.Improving plant net photosynthetic rates and accelerating water-soluble carbohydrate accumulation play an important role in increasing the carbon sources for yield formation of wheat (Triticum aestivum L.). Understanding and quantify the contribution of these traits to grain yield can provide a pathway towards increasing the yield potential of wheat. The objective of this study was to identify kernel weight gap for improving grain yield in 15 winter wheat genotypes grown in Shandong Province, China. A cluster analysis was conducted to classify the 15 wheat genotypes into high yielding (HY) and low yielding (LY) groups based on their performance in grain yield, harvest index, photosynthetic rate, kernels per square meter, and spikes per square meter from two years of field testing. While the grain yield was significantly higher in the HY group, its thousand kernel weight (TKW) was 8.8% lower than that of the LY group (p < 0.05). A structural equation model revealed that 83% of the total variation in grain yield for the HY group could be mainly explained by TKW, the flag leaf photosynthesis rate at the grain filling stage (Pn75), and flag leaf water-soluble carbohydrate content (WSC) at grain filling stage. Their effect values on yield were 0.579, 0.759, and 0.444, respectively. Our results suggest that increase of flag leaf photosynthesis and WSC could improve the TKW, and thus benefit for developing high yielding wheat cultivars.

Optimal light intensity and quality increased the saffron daughter corm yield by inhibiting the degradation of reserves in mother corms during the reproductive stage

Saffron (Crocus sativus L.) two-segment (TS) cropping system, with mother corms flowering in a controlled environment first and then growing daughter corms in the field, can greatly increase stigma yield and quality, but may decrease daughter corm yield (mainly due to depletion of nutrient reserves in mother corms). Light plays crucial roles in regulation of nutrient reserve metabolism in tubers, corms, and other storage organs. However, how the metabolism of mother corm reserves, which determines the daughter corm yield, responds to light intensity and quality during the reproductive stage remains unclear. Plants grew under five light intensities (56, 200, 400, 600, and 800 μmol m−2 s−1) and three combinations of red (R) to blue (B) light (4R1B, 3R1B, and 3R2B) at 200 μmol m−2 s−1 during the reproductive stage. After flowering, the plants were transplanted to the field. Leaf growth, net photosynthesis, carbohydrate and nutrient content, stigma yield and quality, and daughter corm yield were assessed. The stigma yield and quality decreased with increasing light intensity, whereas the carbohydrate and total N, P, and K content in the mother corm showed the opposite trend. The light treatment of 200(3R2B) not only maintained the stigma yield (up to 482.4 mg (10 corms)−1) at a highest level, but also improved the apocarotenoid content (up to 33.6%) in stigma, and carbohydrate and nutrient content in mother corm. Compared with 56 μmol m−2 s−1, light 200 (3R2B) decreased the length and weight of leaves, ratio of leaf to corm weight, and starch and nutrient decomposition in corms, but increased the rate of photomorphogenesis, stomatal opening, chlorophyll concentration (up to 72.9%), net photosynthesis (up to 448.6%), and leaf sucrose concentration (up to 156.7%). A decreased demand for leaf development and increased carbon capture inhibited the decomposition of carbohydrates and nutrients in the mother corm. The high sucrose concentration in leaves served not only as a carbon substrate for leaf growth, but also as a signal for inhibiting the translocation of carbon from corm to leaves and then the decomposition of starch in corm. The increased reserves in mother corms and improved stomatal opening combined to result in large leaf area, well-developed vascular tissue, and then high rate of leaf photosynthesis in the field, which provided assimilates for achieving yield potential and a high proportion of large-size corms. This is the first report on optimizing light intensity and quality during the reproductive stage to partially eliminate daughter corm yield decreases in the TS cropping system. Furthermore, this work also contributed to understanding the metabolism of nutrient reserves and leaf growth in saffron as regulated by light intensity and quality.

Study of Genetic Analysis of Physiological Attributes under Normal and Drought Conditions in Gossypium hirsutum L.

The aim of this study was to identify the suprior cotton genotypes with improved physiological characteristics under drought conditions. On the bais of root-shoot charcteristics, five genoypes of G. hirsutum were identified as drought tolerant and three genotypes screened out as drought susceptible. The field screening experiment were carried out to validate the findigs of root-shoot screening sudy on the basis of physiological as well as agronomical chracteristics. Both drought tolerant and susceptible genotypes were grown in glass house in pots and followed line x tester mating desighn to cross these genotyps. Parents with their fiftenn offsprings were grown in field conditions in very next cotton season for further analysis. Analysis of variance showed the existence of significant variations among the accessions for all the physiological parameters i.e, osmotic potential, relative water content, cell injury, leaf water potential, excised leaf water loss, stomatal conductance, photosynthesis rate and transpiration rate. Further, among parents line, MS-64 and tester, BH-176 showed superior performance under water scarce conditions. Among the crosses COOKER-315 x Cyto-62 and GS-444 x MPS-11 were better perfomed for high yielding parametrs. The results showed that these two combinations might be helpful to develop drought resistant germplasm on large scale.

Physiological evaluation of growth and yield variation of mustard (Brassica juncea) varieties under organic products in North-Western Indo-Gangetic Plains

A field experiment was conducted for two years to analyze the physiological basis of variation in the growth and yield of popular mustard varieties under organic production. Twelve mustard varieties of varied duration and agroclimatic suitability were evaluated in a randomized complete block design. Results revealed that varieties NRCHB-506, RH-406, and RGN-229, being at par, registered significantly maximum leaf area index, photosynthesis rate, and chlorophyll content at all the crop growth stages, i.e., 30, 60 and 90 DAS. During both the intervals, i.e., 30-40 and 80-90 DAS, variety RH-406 followed by RGN-229 registered maximum crop growth rate, whereas,in NRCHB-101, the lowest crop growth rate was observed. At each crop growth stage, photosynthesis rate has a significant positive correlation with leaf area index, chlorophyll content, crop growth rate during 30-40 and 80-90 DAS. Varieties Pusa Mustard-25 (5.8) and Pusa Mustard-26 (5.7) recorded significantly higher primary branches plant-1. However, varieties Pusa Tarak, RH-406, and RGN-229 recorded the significantly highest number of secondary branches plant-1. Being at par, varieties NRCHB-506, RH-406, RGN-229, and Pusa Bold recorded a significantly higher number of silique plant-1, seed yield,and stover yield than other varieties. The seed yield was found significantly and positively correlated with the crop growth rate at 80-90 DAS (r=0.600**), chlorophyll content at 90 DAS (r=0.558**), and silique plant-1(r=0.518**).Therefore, it is inferred that varieties like RH-406, RGN-229, and NRCHB-506 are suitable to grow under organic nutrient management in the prevailing agro-climatic conditions.

Comparing different pretreatments at transplanting stage for acclimation of walnut trees to hot and dry conditions

Walnut (Juglans regia L.) is a drought and heat-sensitive plant. These sensitivities are intensified with young plants which are grown in greenhouse nurseries. We subjected one-year-old greenhouse-grown walnut 'Chandler' trees to different pretreatments [long-term water stress, controlled salinity stress, and foliar application of β-aminobutyric acid (BABA)] for acclimation to unfavorable conditions after transplantation. Then, the plants were transplanted into hot and dry conditions to evaluate efficiency of different preconditioning treatments in acclimation of the plants to deleterious environmental conditions. Investigating the plants' responses to the pretreatments for understanding activated adaptation mechanisms indicated that the pretreatments have induced osmotic adjustment (OA) in leaves. In this regard, the salinity pretreatment was the most effective treatment. For OA, proline accumulation was more effective than soluble sugars. However, glycine betaine was not involved in OA. The pretreatments sensitized stomatal responses to drought, according to limitation of water loss from detached leaves. Ninety days after transplantation, the preconditioned plants had higher biomass than the control plants. The major reasons were the prevention of leaf abscission and chlorophyll degradation. Moreover, improved water conservation ability in the preconditioned plants enhanced leaf expansion, photosynthesis rate and biomass accumulation in plants' organs. Restriction of stomatal conductance for water conservation in the control plants resulted in photosynthesis inhibition, heat accumulation, and vigor loss. The efficiency of BABA and salinity stress in acclimation of walnut to deleterious environmental conditions was higher than water stress. However, BABA foliar application as the safest and least complicated pretreatment was suggested in a drought/heat acclimation strategy in walnut.

Nitrogen forms and irrigation regimes interact to affect rice yield by regulating the source and sink characteristics

AbstractThe interaction betweennitrogen management and irrigation regimes plays important roles in regulating the rice (Oryza sativa L.) source, sink characteristic, and grain yield. However, if and how nitrogen forms could synergistically interact with irrigation methods in rice remain unclear. Herein, a soil‐grown experiment was conducted with three nitrogen forms, namely, ammonium nitrogen (AN), ammonium, nitrate mixed (ANM), and nitrate nitrogen (NN), as well as three irrigation regimes, namely, submerged irrigation (0 kPa), alternate wetting and moderate drying (−20 kPa), and alternate wetting and severe drying (−40 kPa). Results demonstrated that grain yield was the highest in the ammonium nitrate and alternate wetting and moderate drying irrigation. Nitrate nitrogen application decreased grain yield in each irrigation regime. The alternate wetting and moderate drying and ammonium nitrate treatment had higher chlorophyll content, leaf nitrogen content, leaf area index (LAI), photosynthesis rate, and chlorophyll fluorescence, superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and sucrose‐synthase activity and decreased leaf malondialdehyd (MDA) content than the other treatments at mid‐tillering, panicle initiation, heading, and maturity stages. By contrast, AN treatment exhibited very small difference between AN and ANM treatment in submerged irrigation. Besides, grain yield was positively correlated with chlorophyll content, leaf nitrogen content, LAI, photosynthesis rate, antioxidant enzymes, and sucrose‐synthase activity at main growth stages. Therefore, the adoption of ANM and alternate wetting and moderate drying can synergistically increase grain yield by promoting the leaf‐source and grain‐sink activity of rice. Results of the present investigation provided new ideas for increasing grain yield by nitrogen forms management in alternate wetting and drying irrigation.

Early growth and development of maize on sandy soils fertilised with zinc sources at different application rates

The grain yield and quality of maize is often negatively influenced by zinc (Zn) deficiencies during early growth and development. Application of Zn to soil is therefore a necessity, especially when it is sandy. Glasshouse experiments were carried out to test the effects of Zn sources and application rates on plant-available Zn and on early growth and development of maize grown in a sandy soil. Soil Zn concentration was increased most by ZnSO4 and least by ZnO. The Na2EDTA method was superior to four other methods in extracting soil Zn. For most plant parameters that were measured (leaf number, stem thickness, plant height, photosynthesis rate, leaf area, dry mass, root length and root mass) ZnEDTA was the most effective chelated source, followed by ZnHEDTA, ZnDTPA or ZnEDDHA. Regarding inorganic sources ZnSO4 was superior, followed by ZnCO3, ZnCl2 and ZnO. As a group the inorganic sources performed more poorly than the chelated sources. These rankings differed in terms of Zn concentration and uptake by the plants. The results must be verified in field trials that last for several years accommodating a wider range of climate and soil conditions to develop reliable Zn fertilisation guidelines for maize cultivated on sandy soils.

Grazing alters species relative abundance by affecting plant functional traits in a Tibetan subalpine meadow.

Domestic livestock grazing has caused dramatic changes in plant community composition across the globe. However, the response of plant species abundance in communities subject to grazing has not often been investigated through a functional lens, especially for belowground traits. Grazing directly impacts aboveground plant tissues, but the relationships between above‐ and belowground traits, and their influence on species abundance are also not well known. We collected plant trait and species relative abundance data in the grazed and nongrazed meadow plant communities in a species‐rich subalpine ecosystem of the Qinghai–Tibet Plateau. We measured three aboveground traits (leaf photosynthesis rate, specific leaf area, and maximum height) and five belowground traits (root average diameter, root biomass, specific root length, root tissue density, and specific root area). We tested for shifts in the relationship between species relative abundance and among all measured traits under grazing compared with the nongrazed meadow. We also compared the power of above‐ and belowground traits to predict species relative abundance. We observed a significant shift from a resource conservation strategy to a resource acquisition strategy. Moreover, this resource conservation versus resource acquisition trade‐off can also determine species relative abundance in the grazed and nongrazed plant communities. Specifically, abundant species in the nongrazed meadow had aboveground and belowground traits that are associated with high resource conservation, whereas aboveground and belowground traits that are correlated with high resource acquisition determined species relative abundance in the grazed meadow. However, belowground traits were found to explain more variances in species relative abundance than aboveground traits in the nongrazed meadow, while aboveground and belowground traits had comparable predictive power in the grazed meadow. We show that species relative abundance in both the grazed and the nongrazed meadows can be predicted by both aboveground traits and belowground traits associated with a resource acquisition versus conservation trade‐off. More importantly, we show that belowground traits have higher predictive power of species relative abundance than aboveground traits in the nongrazed meadow, whereas in the grazed meadows, above‐ and belowground traits had comparable high predictive power.

Efficacy of rhizobacterial exopolysaccharides in improving plant growth, physiology, and soil properties.

The current study investigated the influence of exopolysaccharides (EPSs) producing plant growth-promoting rhizobacteria (PGPR) on the growth, physiology, and soil properties. The pre-isolated and compatible EPS producing PGPR strains were first screened based on improvement in soil aggregates in an incubation study. The screened strains (Rhizobium phaseoli strain Mn-6, Pseudomonas bathysetes strain LB5, and unidentified strain R2) were then employed in pot study for assessing improvements in maize growth, physiology, and soil properties. Eight treatments including T1 = control, T2 = Mn-6, T3 = R2, T4 = LB5, T5 = Mn-6 + R2, T6 = Mn-6 + LB5, T7 = R2 + LB5, and T8 = Mn-6 + R2 + LB5 were applied in completely randomized design (CRD) hexa replicated (half for root and half for soil, and yield attributes). The results depicted that among various treatments, the application of PGPR strain Mn-6 increased plant height, root length, root fresh and dry weight, root length density, SPAD value, leaf areas index, photosynthesis rate, transpiration, and stomatal conductance by 24, 79, 72, 90, 49, 35, 23, 21, 75, and 77%, respectively, compared with non-inoculated treatment. Similarly, significant improvement in maize yield and soil physical properties was also observed in response to the application of EPS-producing PGPR. Therefore, it is concluded that the application of EPS producing PGPR is an effective strategy to improve plant growth, physiology, yield, and soil physical properties. Moreover, EPS-producing PGPR should be exploited in field studies for their potential in improving plant growth and soil properties.

Effects of different technical substitutions on reducing replant disease of Radix pseudostella-riae and the underlying mechanism.

Radix pseudostellariae is a traditional Chinese medicinical herb, with tuberous roots being used as a medicine. Serious continuous monoculture problems were suffered from process of artificial and intensive cultivation. To explore the effective technical methods to overcome the monoculture problems, the effects of different technical substitution patterns on soil environment remediation, photosynthetic physiology and yield performance of R. pseudostellariae were assessed under continuous cropping system with four technical substitution treatments in the phase between two crops after the newly harvested R. pseudostellariae (first crop): fallow (RP-F-RP), fallow treated with microbial fertilizer (RP-F-BF), water flooding (RP-WF), and water flooding treated with specific microbial fertilizer (RP-WF-BF). Results showed that RP-WF-BF pattern was the single one that could effectively restore R. pseudostellariae yield under two-year monoculture and three-year monoculture to more than 90% and 70% of the newly planted respectively. All the other patterns did not significantly improve R. pseudostellariae yield under two-year monoculture. The contents of polysaccharide and total saponin in R. pseudostellariae under RP-WF-BF treatment were significantly increased by 15.3% and 16.5% compared with those of the newly planted, respectively. The abundance of beneficial microorganisms in the rhizosphere soil of R. pseudostellariae significantly increased. A reverse pattern occurred for pathogens under RP-WF-BF pattern. Moreover, soil nitrogen cycling was improved. The expression of AOB, nosZ and nirK was increased by 931%, 124% and 100% compared with those in the RP-F-RP pattern, respectively. Soil acidification under RP-WF-BF pattern was alleviated. The alleviation of soil biological and abiotic stress enhanced the stability of the antioxidant enzyme system, thereby improving the growth and development of R. pseudostellariae at the seedling and the early expand stages. The chlorophyll content, leaf area index and photosynthesis rate of leaves were increased, with the dry matter translocation improved and accumulation of underground dry matter accelerated, which ultimately increased yield and quality under RP-WF-BF pattern. In this study, the separate water flooding treatment (RP-WF) and microbial fertilizer treatment (RP-F-BF) failed to significantly reduce the continuous cropping obstacles of R. pseudostellariae, while the combination of them could produce a multiplication effect of sustainable strengthening on rhizosphere environment. The findings suggested that effective technical substitution could reduce replant disease of R. pseudostellariae.