Leaf Photosynthetic Characteristics Research Articles

Effects of N, P, and K application rates on distribution of 13C assimilates, starch accumulation in grains and fertilizer utilization of wheat

Clarifying the appropriate application rates of N, P, and K fertilizers and the physiological mechanisms of wheat under water-saving recharge irrigation in the North China Plain would provide a theoretical basis for formulating reasonable fertilization plans for high-yield and high-efficiency wheat production. We established four treatments with different amounts of nitrogen (N), phosphorus (P2O5), and potassium (K2O) application: 0, 0, and 0 kg·hm-2 (F0), 180, 75, and 60 kg·hm-2 (F1), 225, 120, and 105 kg·hm-2 (F2), and 270, 165, and 150 kg·hm-2 (F3). During the jointing and anthesis stages of wheat, the relative water content of each treatment in the 0-40 cm soil layer was replenished to 70%, to investigate the differences in wheat flag leaf photosynthetic characteristics, distribution of 13C assimilates, grain starch accumulation, and fertilizer utilization. The results showed that the relative chlorophyll content of flag leaves, photosynthetic and chlorophyll fluorescence parameters, 13C assimilate allocation in each organ, enzyme activities involved in starch synthesis, and starch accumulation in the F1 treatment were significantly higher than that in F0 treatment, which was an important physiological basis for the 20.9% increase in grain yield. The above parameters and yield in the F2 and F3 treatments showed no significant increase compared to F1 treatment, while fertilizer productivity and agronomic efficiency of N, P, and K decreased by 17.5%-58.4% and 12.7%-50.7%, respectively. Therefore, F1 could promote flag leaf photosynthetic assimilate production and grain starch accumulation under water-saving supplementary irrigation conditions, resulting in higher grain yield and fertilizer utilization efficiency.

Nano calcium carbonate improves wheat nitrogen accumulation and grain yield by enhancing soil nitrogen supply and flag leaf photosynthetic characteristics

ContextOver-application of chemical fertilizers to attain optimal crop yields has resulted in an environmental issue of global concern. To mitigate this, reducing nitrogen (N) application and enhancing fertilizer use efficiency is crucial, and nano-fertilizers offer a promising solution. However, there is a paucity of studies examining the use of nano-fertilizers in fields. ObjectivesThis study aimed to assess the impact of different dosages of nano calcium carbonate (NCC) mixed with compound fertilizer (CF) on soil N supply, enzyme activity, microbial ecology, as well as photosynthetic characteristics, N accumulation and yield of wheat plants. MethodsThe effects were examined through a soil column leaching experiment and a two-year field experiment conducted from 2020 to 2022. Five treatment groups were established, namely CK (CF), T1 (CF + 0.15% NCC), T2 (CF + 0.30% NCC), T3 (CF + 0.45% NCC), and T4 (CF + 0.60% NCC), to determine the optimal ratio of NCC to CF. ResultsAll NCC treatments resulted in reduced leaching of soluble N. Nevertheless, the 0.45% and 0.60% NCC treatments (T3 and T4) posed a risk of migration through water runoff, leading to nutrient losses. The simultaneous application of NCC and CF increased the content of soil nitrate N (NO3--N), as well as the activity levels of urease and protease during the anthesis stage. Additionally, it elevated the abundance of various microbial communities, including Actinobacteria, Acidobacteria, Chloroflexi, Cyanobacteria, and Nitrospirae. NCC application reduced the content of Na+/K+ and malondialdehyde (MDA), while elevating the activities of flag leaf superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), nitrate reductase (NR), and glutamine synthetase (GS). Additionally, it increased stomatal conductance (Gs) and net photosynthetic rate (Pn). The 0.30% NCC treatment showed significantly higher N accumulation in the stem, leaf, and spike compared to CK at the maturity stage. Moreover, 0.30% NCC treatment exhibited a significant increase in the number of grains per spike and higher yields compared to CK. In particular, 0.30% and 0.45% NCC treatments accomplished yield boosts of 29.6–34.7% and 19.9–26.0%, respectively. ConclusionNCC enhanced wheat plant N accumulation and yield through regulation of N release rate and increased soil N content, enzyme activity, and microbial community diversity and abundance. Additionally, NCC boosted flag leaf photosynthesis rate during the anthesis to maturity stage of wheat. This research highlights the potential of NCC to improve wheat crop production. And 0.30% NCC is the optimal application concentration for NCC.

Foliar zinc spraying improves assimilative capacity of sugar beet leaves by promoting magnesium and calcium uptake and enhancing photochemical performance

Sugar beet, a zinc-loving crop, is increasingly limited by zinc deficiency worldwide. Foliar zinc application is an effective and convenient way to supplement zinc fertilizer. However, the regulatory mechanism of foliar zinc spraying on sugar beet leaf photosynthetic characteristics remains unclear. Therefore, we investigated the effects of foliar ZnSO4·7H2O application (0, 0.1%, 0.2%, and 0.4%) on the photosynthetic performance of sugar beet leaves under controlled hydroponic conditions. The results indicated that a foliar spray of 0.2% Zn fertilizer was optimal for promoting sugar beet leaf growth. This concentration significantly reduced the leaf shape index of sugar beet, notably increasing leaf area, leaf mass ratio, and specific leaf weight. Foliar spraying of Zn (0.2%) substantially elevated the Zn content in sugar beet leaves, along with calcium (Ca) and magnesium (Mg) contents. Consequently, this led to an increase in the potential photochemical activity of PSII (Fv/Fo) (by 6.74%), net photosynthetic rate (Pn) (11.39%), apparent electron transport rate (ETR) (11.43%), actual photochemical efficiency of PSⅡ (Y (Ⅱ)) (11.46%), photochemical quenching coefficient (qP) (15.49%), and total chlorophyll content (25.17%). Ultimately, this increased sugar beet leaf dry matter weight (11.30%). In the cultivation and management of sugar beet, the application of 0.2% Zn fertilizer (2.88 mg plant−1) exhibited the potential to enhance Zn and Mg contents in sugar beet, improve photochemical properties, stimulate leaf growth, and boost light assimilation capacity. Our result suggested the foliar application of Zn might be a useful strategy for sugar beet crop management.

Improving the estimation accuracy of rapeseed leaf photosynthetic characteristics under salinity stress using continuous wavelet transform and successive projections algorithm.

Soil salinization greatly restricts crop production in arid areas for salinity stress can inhibit crop photosynthesis and growth. Chlorophyll fluorescence and photosynthetic gas exchange (CFPGE) parameters are important indicators of crop photosynthesis and have been widely used to evaluate the impacts of salinity stress on crop photosynthesis and growth. Remote sensing technology can quickly and non-destructively obtain crop information under salinity stress, however, at present, the distribution of spectral features of CFPGE parameters in different regions is still unclear. In this study (2019-2020), under salinity stress conditions, the spectral data of rapeseed leaves were acquired and the CFPGE parameters were simultaneously determined. Then, continuous wavelet transformation (CWT) and standard normal variate (SNV) transformation were utilized to preprocess the raw spectral data. After that, a CFPGE parameter estimation model was constructed by using the partial least squares regression (PLSR) algorithm and the support vector machines (SVM) algorithm based on the spectral features in the red region (600-800 nm) and those in the red, blue-green (350-600 nm), and near-infrared (800-2500 nm) regions. The results showed that the spectral features of CFPGE parameters could be extracted by successive projections algorithm (SPA) based on the CWT preprocessing. The CFPGE parameter estimation model constructed based on the spectral features in the red region (675 nm, 680 nm, 688 nm, 749 nm, and 782 nm) had the highest Fv/Fm estimation accuracy on day 30, with R2c, R2p, and RPD of 0.723, 0.585, and 1.68, respectively. Based on this, the spectral features (578 nm, 976 nm, 1088 nm, 1476 nm, and 2250 nm) in the blue-green and near-infrared regions were added in the variables for modeling, which significantly improved the accuracy and stability of the model, with R2c, R2p, and RPD of 0.886, 0.815, and 2.58, respectively. Therefore, the fusion of the spectral features in the red, blue-green, and near-infrared regions could improve the estimation accuracy of rapeseed leaf CFPGE parameters. This study will provide technical reference for rapid estimation of photosynthetic performance of crops under salinity stress in arid and semi-arid areas.

Effects of microbial agents and corn protein ferment on physiological characteristics in leaves and yield of tomato.

Premature senescence in greenhouse tomato is a significant challenge under long-season cultivation, due to suboptimal nutrient management during growth periods. We investigated the effects of microbial agents (T1), corn protein ferment (T2), and their combined application (T3) on photosynthetic characteristics and antioxidant enzyme activities in 'Saint Laurent 3689' tomato leaves, normal management served as the control (CK). We explored the physiological mechanism of delaying leaf senescence. Results showed that applying microbial agents or corn protein ferment individually led to improvements in leaf photosynthetic characteristics and antioxidant enzyme activities. The combined application yielded superior outcomes. Eighty days post the combined application of microbial agents and corn protein ferment (T3), chlorophyll (a+b) content, net photosynthetic rate, and the activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) in leaves increased by 16.4%, 30.9%, 23.4%, 33.0% and 40.3%, respectively, compared with the CK. Furthermore, plant height and stem diameter increased by 8.2% and 7.0%, while the total yield exhibited a significant increase of 9.9% compared with the CK 210 days post-treatment. In conclusion, the combined application of microbial agents and corn protein ferment has promising potential in enhancing chlorophyll content, net photosynthetic rate, and the activities of SOD, POD and CAT in tomato leaves. This approach effectively delayed leaf senescence, thereby promoting tomato growth and remarkably increasing the yield.

Leaf photosynthetic characteristics of waxy maize in response to different degrees of heat stress during grain filling

BackgroundIn the context of climate change, maize is facing unprecedented heat stress (HS) threats during grain filling. Understanding how HS affects yield is the key to reducing the impact of climate change on maize production. Suyunuo5 (SYN5) and Yunuo7 (YN7) were used as materials, and four temperature gradients of 28℃ (day)/20℃ (night; T0, control), 32 °C/24°C (T1, mild HS), 36 °C/28°C (T2, moderate HS), and 40 °C/32°C (T3, severe HS) were set up during grain filling to explore the physiological mechanism of different degrees HS affecting photosynthetic characteristics of leaves in this study.ResultsResults showed that HS accelerated the degradation of chlorophyll, disturbed the metabolism of reactive oxygen species, reduced the activity of antioxidant enzymes, and caused leaf damage. Heat stress induced the down-regulation of photosynthesis-related genes, which results in the decrease of enzymatic activities involved in photosynthesis, thereby inhibiting photosynthesis and reducing yield. Integrated analysis showed that the degree of the negative influence of three HS types during grain filling on leaves and yield was T3 > T2 > T1. The increase in HS disturbed leaf physiological activities and grain filling. Meanwhile, this study observed that the YN7 was more heat tolerance than SYN5 and thus it was recommended to use YN7 in waxy maize planting areas with frequent high temperatures.ConclusionsHeat stress during grain filling caused premature senescence of the leaves by inhibiting the ability of leaves to photosynthesize and accelerating the oxidative damage of cells, thereby affecting the waxy maize yield. Our study helped to simulate the productivity of waxy maize under high temperatures and provided assistance for a stable yield of waxy maize under future climate warming.

Grain Yield, Biomass Accumulation, and Leaf Photosynthetic Characteristics of Rice under Combined Salinity-Drought Stress

Simultaneous stresses of salinity and drought often coincide during rice-growing seasons in saline lands, primarily due to insufficient water resources and inadequate irrigation facilities. Consequently, combined salinity-drought stress poses a major threat to rice production. In this study, two salinity levels (NS, non-salinity; HS, high salinity) along with three drought treatments (CC, control condition; DJ, drought stress imposed at jointing; DH, drought stress imposed at heading) were performed to investigate their combined influences on leaf photosynthetic characteristics, biomass accumulation, and rice yield formation. Salinity, drought, and their combination led to a shortened growth period from heading to maturity, resulting in a reduced overall growth duration. Grain yield was reduced under both salinity and drought stress, with a more substantial reduction under the combined salinity-drought stress. The combined stress imposed at heading caused greater yield losses in rice compared with the stress imposed at jointing. Additionally, the combined salinity-drought stress induced greater decreases in shoot biomass accumulation from heading to maturity, as well as in shoot biomass and nonstructural carbohydrate (NSC) content in the stem at heading and maturity. However, it increased the harvest index and NSC remobilization reserve. Salinity and drought reduced the leaf area index and SPAD value of flag leaves and weakened the leaf photosynthetic characteristics as indicated by lower photosynthetic rates, transpiration rates, and stomatal conductance. These reductions were more pronounced under the combined stress. Salinity, drought, and especially their combination, decreased the activities of ascorbate peroxidase, catalase, and superoxide dismutase, while increasing the contents of malondialdehyde, hydrogen peroxide, and superoxide radical. Our results indicated a more significant yield loss in rice when subjected to combined salinity-drought stress. The individual and combined stresses of salinity and drought diminished antioxidant enzyme activities, inhibited leaf photosynthetic functions, accelerated leaf senescence, and subsequently lowered assimilate accumulation and grain yield.

Variations in Leaf Functional Traits and Photosynthetic Parameters of Cunninghamia lanceolata Provenances

Studying the variation and correlation of traits among provenances is of great significance for the selection of excellent provenances and the interpretation of the acclimation mechanisms of different provenances in the context of climate change. The photosynthetic characteristic parameters and leaf functional traits of 18 Cunninghamia lanceolata provenances in a common garden were measured. Redundancy analysis combined with Pearson analysis was used to analyze the relationship among leaf photosynthetic characteristics, functional traits, and geo-climatic conditions. The results showed the following: (1) Significant differences in functional traits and photosynthetic parameters among provenances were observed, and the gsw and LDMC have the greatest variation as photosynthetic indicators and functional traits, respectively, because of the acclimation ability. (2) Leaf functional traits can better reflect the variation of photosynthetic characteristic parameters. The correlation between most photosynthetic characteristic parameters and functional traits reached a significant level (p < 0.05), and the leaf dry weight (LDW) and specific leaf area (SLA) are key trait factors that determine photosynthetic characteristic parameters. (3) Precipitation appeared to be a key factor that influences intraspecific leaf traits’ variability compared to temperature. This study can explain how provenances acclimate to the environment and which provenances are more suitable for planting in the study area under the context of climate change from a mechanistic perspective.

Coordination of leaf photosynthetic traits and chloroplast relocation of the C4 plant Setaria palmifolia

Setaria palmifolia (Poaceae), an NADP-malic enzyme type C4 grass, is distributed from the understory to the margins of forests. To reveal how this C4 plant acclimates to habitats with contrasting light regimes, we documented the behavior of chloroplast relocation and determined patterns of chloroplast relocation and photosynthetic characteristics in response to the light of S. palmifolia grown under different light regimes. Through the observation of leaf sections and measurement of leaf transmittance (T), we confirmed that mesophyll (M) cells of S. palmifolia performed avoidance and accumulation responses, resulting in an increase and decrease in T, respectively. Measurements of gas exchange revealed that the leaf photosynthetic characteristics of S. palmifolia were modulated by growth light. Shade-grown plants significantly increased dry-weight-based chlorophyll (Chl) contents and specific leaf area (SLA), indicating increased light capture. These plants, however, displayed a reduced light-saturated photosynthetic rate (Pmax) and light saturation point (LSP) compared to unshaded plants. The patterns of chloroplast relocation were closely aligned with the photosynthetic response. Shade-grown plants displayed significantly faster kinetics, a greater extent of chloroplast relocation, and lower incident light for the induction of the avoidance response than unshaded plants. The coordination patterns of chloroplast relocation and photosynthetic response suggest that chloroplast relocation in S. palmifolia complements its leaf photosynthetic responses to light availability. The ability to adjust its photosynthetic behavior and perform chloroplast relocation may enable this C4 species to thrive in habitats with various light conditions.

Low-temperature at booting reduces starch content and yield of wheat by affecting dry matter transportation and starch synthesis.

With the continuous change of global climate, the frequency of low-temperature stress (LTS) in spring increased greatly, which led to the increase of wheat yield decline. The effects of LTS at booting on grain starch synthesis and yield were examined in two wheat varieties with differing low-temperature sensitivities (insensitive variety Yannong 19 and sensitive variety Wanmai 52). A combination of potted and field planting was employed. For LTS treatment at booting, the wheat plants were placed in a climate chamber for 24h at -2°C, 0°C or 2°C from 19:00 to 07:00 then 5°C from 07:00 to 19:00. They were then returned to the experimental field. The effects of flag leaf photosynthetic characteristics, the accumulation and distribution of photosynthetic products, enzyme activity related to starch synthesis and relative expression, the starch content, and grain yield were determined. LTS at booting caused a significant reduction in the net photosynthetic rate (Pn), stomatal conductance (Gs), and transpiration rate (Tr) of the flag leaves at filling. The development of starch grains in the endosperm is also hindere, there are obvious equatorial grooves observed on the surface of the A-type starch granules, and a reduction in the number of B-type starch granules. The abundance of 13C in the flag leaves and grains decreased significantly. LTS also caused a significant reduction in translocation amount of pre-anthesis stored dry matte from vegetative organs to grains and amount of post-anthesis transfer of accumulated dry matte into grains, and the distribution rate of dry matter in the grains at maturity. The grain filling time was shortened, and the grain filling rate decreased. A decrease in the activity and relative expression of enzymes related to starch synthesis was also observed, with a decrease in the total starch content. As a result, a decrease in the grain number per panicle and 1000-grain weight were also observed. These findings highlight the underlying physiological cause of decreased starch content and grain weight after LTS in wheat.

Alternative Furrow Irrigation Combined with Topdressing Nitrogen at Jointing Help Yield Formation and Water Use of Winter Wheat under No-Till Ridge Furrow Planting System in Semi-Humid Drought-Prone Areas of China

Benefiting from the high–farmland construction program in China, one–off irrigation can be guaranteed in most fields in semi–humid drought–prone areas in China. However, little information is available on water and nitrogen (N) management in wheat production under this condition. This study aimed to explore the effects of alternative furrow irrigation (AFI) and topdressing N fertilizer (TN) on wheat productivity under a no–till ridge–furrow planting system in semi–humid drought–prone areas. The experimental design was as follows: two furrow irrigation (FI) methods, namely, EFI (every furrow irrigation) and AFI (alternative furrow irrigation) with 75 mm at the jointing stage were set as the main treatments. Two topdressing N (TN) patterns, namely, NTN (0 kg ha−1 of N) and TN (60 kg ha−1 of N) along with irrigation were set as the secondary treatments. Moreover, a traditional planting practice with no irrigation and no topdressing N (NINTN) was set as control. In 2018–2020, a field experiment was carried out to investigate the effects on soil water, leaf chlorophyll relative content (SPAD) and net photosynthetic rate (Pn), aboveground dry matter assimilates, grain yield, water use efficiency (WUE) and economic benefit. We found that both FI methods and TN patterns significantly influenced soil water content. Compared with NINTN, the soil water content in each combination of the FI method and TN pattern was effectively improved at the booting and anthesis stages, leading to the significant increase in SPAD and Pn in leaves, post–anthesis dry matter accumulation (POA), grain yield, WUE and economic benefit of winter wheat. Compared with the EFI, averaged across years and TN patterns, the AFI technique increased the soil water storage at booting and anthesis stages and significantly improved the Pn at early milk (4.9%) and early dough (7.5%) stages, POA (40.6%) and its contribution to grain (CRPOA, 27.6%), the grain yield (10.2%), WUE (9.1%) and economic benefit (9.1%). In addition, compared with the NTN, the TN pattern significantly increased the water computation by wheat from booting to maturity, enhanced leaf Pn after anthesis and POA, and finally resulted in the increase in grain yield (14.7–21.9%) and WUE (9.6–21.1%). Thus, the greatest improvement in the leaf photosynthetic characteristics, aboveground dry matter assimilates, grain yield, WUE and economic benefit was achieved under AFITN treatment. Above all, it can be concluded that the AFITN with AFI of 75 mm and TN of 60 kg ha−1 at jointing was an alternative management strategy for optimizing yield formation and water use of winter wheat. This study provided new insights into improving wheat productivity in drought–prone areas where one–off irrigation can be guaranteed.

Effects of iron oxide nanoparticles (Fe3O4) and salinity on growth, photosynthesis, antioxidant activity and distribution of mineral elements in wheat (Triticum aestivum).

Soil salinisation is one of the main abiotic stresses decreasing crop productivity. Here, we show that the plant treatment with iron oxide (Fe3O4) nanoparticles (NPs) may be a promising solution for reducing the negative impact of soil salinity on plant performance. For this purpose, effects of the NPs on growth, photosynthesis, pro-/antioxidant, redox balance and the content of mineral elements in 19-day-old wheat (Triticum aestivum) plants under soil salinity were studied. Seed treatment with NPs (200 and 500mg L-1) enhanced growth and photosynthetic rate in leaves. Moderate salinity stress (150mMNaCl) led to a decrease in plant biomass as well as the rate of photosynthesis and PSII activity; leaf photosynthetic characteristics were also suppressed by lower (75mMNaCl) salinity treatment. However, seed pre-treatment with the NPs partially eliminated the negative effect of the salt on growth, PSII activity and photosynthesis. Also, we observed a decrease in the content of malondialdehyde (MDA) and an increase in ascorbate and total peroxidase activity in the plant leaves upon combined treatment with NaCl and the NPs compared with treatment with NaCl alone. The combined treatment with the NPs and salinity also led to a noticeable increase in the content of Fe and Mn in the shoot. It was concluded that Fe3O4 NPs can enhance plant growth by improving photosynthetic characteristics, antioxidant balance and the availability of iron and manganese ions, under conditions of soil salinisation.

Yield of summer maize hybrids with different growth duration determined by light and temperature resource use efficiency from silking to physiological maturity stage.

In order to explore the physiological mechanism of different yield of summer maize (Zea mays L.) hybrids with different growth duration, a field experiment was conducted to study the growth stage, leaf photosynthetic characteristics, dry matter accumulation (DMA), transport and distribution characteristics and yield of the early maturity hybrid Denghai 518 (DH518) and the mid-late maturity hybrid Denghai 605 (DH605) from 2017 to 2021. The results showed that the yield of DH605 was significantly higher than that of DH518. The growth period of DH518 was 7-10 days shorter and the days of the growth stage of the sowing-silking stage (R1) were 5-6 days shorter compared to that of DH605. The contribution to grain dry matter by leaf and stalk dry matter remobilization (DMRC) of DH518 was significantly higher than that of DH605. There was a significant negative correlation between pre-silking growth days and harvest index (HI). The 13C distribution to grains of DH518 was significantly higher than that of DH605, and the HI and the corresponding contribution of HI to yield was also higher than that of DH605. The light and temperature resource use efficiency from silking to physiological maturity stage of DH605 was significantly higher than that of DH518. The yield per GDD of DH605 increased by 7.25% than that of DH518. At post-silking, the duration of higher leaf area index (DLAI) (>56 days) and active photosynthesis duration (APD) (>50 days) of DH605 were longer compared with that of DH518, and the average plant growth rate was 7.15% higher than that of DH518, which significantly increased the DMA of DH605. Therefore, the significant reduction of DH518 yield compared with DH605 was not due to the shortening of the growth stage of sowing-R1, but the lower light and temperature resource use efficiency from silking to physiological maturity stage.

Nitrogen Fertilizer and Sowing Density Affect Flag Leaf Photosynthetic Characteristics, Grain Yield, and Yield Components of Oat in a Semiarid Region of Northwest China

Oat has been gaining renewed interest due to its role in a healthy human diet, in animal feed, and as a source of high value compounds with industrial applications. Nitrogen fertilization and planting density are two of the most important crop management practices that affect the formation of yield components and final yield of oat. A 2 year 3 × 5 factorial field experiment was conducted to investigate the effects of nitrogen (N) fertilizer and planting density on the flag leaf photosynthetic characteristics, grain yield, and yield components under rainfed conditions. The experiment consisted of three sowing densities (60, 180, and 300 kg·ha−1) and five nitrogen fertilizer rates (0, 45, 90, 135, and 180 kg·ha−1). Results showed that the grain yield was significantly (p < 0.05) correlated with the leaf net photosynthesis rate (Pn), stomatal conductance (Gs), intercellular CO2 concentration (Ci), transpiration rate (Tr), water-use efficiency (WUE), stomatal limitation value (Ls), chlorophyll content (SPAD value), leaf area index (LAI), panicle length, number of spikelets per panicle (NSP), number of grains per panicle (NGP), weight of grains per panicle (WGP), and 1000-kernel weight. Among the yield components, grain yield was driven by number of spikelets per panicle (NSP) and number of grains per panicle (NGP) at low (or high) planting density with low N supply, whereas, at high N supply, 1000-kernel weight was also an important factor for yield. Nitrogen fertilizer and sowing density had significant (p < 0.05) effects on the flag leaf photosynthetic characteristics, grain yield, and yield components of oat. The yield components increased and then decreased with the increase in nitrogen fertilizer, while they decreased with the increase in planting density. The maximum values (p < 0.05) of grain yield were observed in the nitrogen fertilization of 90 kg·ha−1 and sowing density of 180 kg·ha−1 treatment in both growing seasons, mainly contributing to the improved leaf photosynthesis traits (Pn, Gs, Tr, Ls, SPAD, and LAI). The combination of nitrogen fertilization of 90 kg·ha−1 and sowing density of 180 kg·ha−1 is suitable for oat production on a cool semiarid plateau or other agroecozones with similar environmental conditions.

Effects of Different Soil Modifiers on Salt Improvement and Distribution, Crop Growth of the Gully Land Consolidation on Loess Plateau

Due to the strong evaporation and leakage loss, secondary saline-alkali was the main problem in the watershed of gully land consolidation on Loess Plateau. Through field farming experiments, five modifiers (maize stalk (MS), humus acid (HA), Yan Ke (YK), He Kang (HK), and nanobiochar (NB)) were studied to investigate the effects of these soil modifiers on soil water and salt distribution, leaf photosynthetic characteristics, and maize growth and yields, as well as economic benefits in secondary saline-alkali soils of gully land consolidation watershed on Loess Plateau in 2019 and 2020. The results showed that soil modifiers could increase the water-holding capacity of the soil, reduce the salt content of the soil profiles, and decompose the accumulation of salt. The maximum desalination rate obtained in 2019 and 2020 increased, respectively, by 71.57% and 46.02%, compared to that in the control treatment. Soil modifiers could increase the net photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (Gs), and decreased the intercellular CO2 concentration (Ci). The output increased by 13.63%-31.84%, and revenue increased by 6.48%-38.01%. According to analyzing the production of soil modifier application, we found that the highest net profit was achieved when HK application rate was 52.4 kg/ha. Therefore, this study suggested that 52.4 kg/ha might be recommended as an appropriate soil modifier application strategy to deal with crop growth and improve economic benefit in secondary saline-alkali soils of Northwest China.

Raised bed planting promotes grain number per spike in wheat grown after rice by improving spike differentiation and enhancing photosynthetic capacity

The yield of wheat in wheat–rice rotation cropping systems in the Yangtze River Plain, China, is adversely impacted by waterlogging. A raised bed planting (RBP) pattern may reduce waterlogging and increase the wheat yield after rice cultivation by improving the grain number per spike. However, the physiological basis for grain formation under RBP conditions remains poorly understood. The present study was performed over two growing seasons (2018/2019 and 2019/2020) to examine the effects of the planting pattern (i.e., RBP and flat planting (FP)) on the floret and grain formation features and leaf photosynthetic source characteristics of wheat. The results indicated that implementation of the RBP pattern improved the soil–plant nitrogen (N) supply during floret development, which facilitated balanced floret development, resulting in a 9.5% increase in the number of fertile florets per spike. Moreover, the RBP pattern delayed wheat leaf senescence and increased the photosynthetic source capacity by 13.9%, which produced more assimilates for grain filling. Delayed leaf senescence was attributed to the resultant high leaf N content and enhanced antioxidant metabolism. Correspondingly, under RBP conditions, 7.6–8.6% more grains per spike were recorded, and the grain yield was ultimately enhanced by 10.4–12.7%. These results demonstrate that the improvement of the spike differentiation process and the enhancement of the leaf photosynthetic capacity were the main reasons for the increased grain number per spike of wheat under the RBP pattern, and additional improvements in this technique should be achievable through further investigation.

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

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

Impact of heat stress of varying severity on papaya (Carica papaya) leaves: Major changes in stress volatile signatures, but surprisingly small enhancements of total emissions

Tropical plants are considered to be highly heat stress resistant, but heat waves of different frequency and duration induced by global climate change can exceed the plant heat stress tolerance in the tropics. To gain insight into the overall heat resistance, leaves of papaya were exposed to mild (37 and 41 °C), moderate (46 °C) and severe (49 °C) heat stress (applied for 5 min), and plant recovery was monitored for 48 h upon return to pre-stress conditions. Leaf photosynthetic characteristics were reduced immediately after stress in all cases, but photosynthesis rate almost fully recovered after mild heat treatment, and partly recovered in 48 h after moderate stress, while no recovery was observed under severe stress. Constitutive BVOC emissions dominated by long-chained aldehydes, and glucosinolate breakdown products, attained the emission maxima at 46 °C. Acute heat stress led only to a minor induction of BVOC emissions, and the greatest share of induced emissions was observed in leaves exposed to 46 °C. Induced emissions were dominated by oxygenated monoterpenes, indicating an increase in leaf oxidative status. Our results demonstrate that papaya could withstand moderately severe heat stress of up to 46 °C, but this level of stress will have negative impacts on plant carbon gain due to delayed photosynthetic recovery after heat stress. Although volatile profiles sensitively responded to heat stress, the magnitude and degree of elicitation were surprisingly small throughout the recovery, suggesting that papaya is relatively heat resistant and possess a suite of heat-protective traits. • Papaya photosynthetic recovery was rapid under mild heat stress, delayed under moderate stress and absent under severe stress. • Heat stress of different severity had only moderate effects on volatile emissions, but the composition of emitted volatiles was strongly altered. • Volatile emission blend rather than the absolute amount characterizes the impact of heat stress on leaves of papaya.

Nitrogen rate and plant density interaction enhances grain yield by regulating the grain distribution of secondary branches on the panicle axis and photosynthesis in japonica rice

Two japonica rice cultivars with different panicle trait index (PTI), HP917 (a high-PTI cultivar) and DP128 (a low-PTI cultivar) were used to investigate the effects of the nitrogen (N) rate and plant density on the grain distribution of secondary branches on the panicle axis, leaf photosynthetic characteristics, and grain yield by a split plot design. The main plots were assigned to four N rates (0, 140, 200, and 260 kg ha-1), and the subplots were assigned to two plant densities: (D20, 15 plants m-2; D10, 30 plants m-2). Results showed that the grain yield was increased by increasing N rate and plant density, reaching a peak at N200 with D10. Compared with N0 treatment, the PTIs of HP917 and DP128 increased with an increase in the N rate, respectively. The PTIs of HP917 and DP128 increased by 4% with increasing plant density from D20 to D10. The leaf capacity was significantly affected by N rate and plant density. The grain distribution characteristics of secondary branches on the panicle axis was closely related to yield. Correlation analysis showed the PTI was positively correlated with grain yield and net photosynthetic rate. These results suggested the improvement in PTI from 0.15 to 0.52 was beneficial to increase the grain yield, which might contribute to the increased grain number of secondary branches of the middle and bottom panicle.

Effects of nitrogen reduction combined with organic materials on crop yield, photosynthetic characteristics, and product quality of corn-cabbage rotation system

Nitrogen reduction combined with organic materials is an important measure to achieve or even increase crop yield retention at the background of fertilizer reduction. We conducted a pot experiment to explore the effects of nitrogen reduction combined with organic materials on yield, photosynthetic characteristics, and product quality of agricultural products of maize-cabbage rotation system in yellow soil area of Guizhou. There were five treatments, including no fertilizer (CK), conventional fertilizer (CF), nitrogen reduction (20%, the same below) combined with biochar (RF+B), nitrogen reduction combined with rapeseed cake (RF+O), and nitrogen reduction combined with both biochar and rapeseed cake (RF+BO). Leaf photosynthetic characteristics were measured in maize (seedling stage, jointing stage, heading stage, and mature stage) and cabbage (seedling stage, growing stage and harvest stage). The biological characters, yield and quality indices were investigated in the harvest period. Compared with CF, RF+BO significantly enhanced the yield of corn and cabbage by 9.7% and 39.2%, respectively, while RF+O had no effect, and RF+B did not affet maize yield. RF+BO improved the biological properties of maize and cabbage, including the 100-kernel weight of maize, and plant height, maximum leaf length and total biomass of cabbage. Furthermore, the green holding period and high photosynthetic duration of maize and cabbage were prolonged, among which, maize leaf SPAD was increased respectively by 42.7%, 11.0%, 12.8%, and 30.3% at seedling, jointing, heading, and mature stages, the cabbage leaf SPAD was increased by 13.5%, 9.2%, and 30.3% in seedling, growing and harvest stages, respectively. The net photosynthetic rate (Pn) of maize was increased by 11.1%, 10.9%, and 119.8% in seedling, jointing, and mature stages, while that of cabbage was increased by 12.7% and 14.6% in growing and harvest stages, respectively. The stomatal conductance (gs) of maize was increased by 58.3% and 41.7% in jointing and harvest stages, while that of cabbage was increased by 10%, 64.7%, and 19.2% in seedling, growing, and harvest stages, respectively. The transpiration rate (Tr) of maize was increased by 55.0%, 10.6%, 14.0%, and 143.9% in seedling, jointing, heading, and mature stages, respectively, while that of cabbage was increased by 26.1% in growing stage. The nutritional quality of maize and cabbage was significantly improved. The contents of reducing sugar, starch, and crude protein in maize were increased by 16.2%, 3.5% and 20.3%. The contents of Vc, amino acid, and reducing sugar in cabbage were increased by 26.3%, 21.0% and 27.8%, separately. In conclusion, 20% nitrogen reduction combined with biochar and rapeseed cake had positive effects on crop growth, yield increase, green retention period, high photosynthetic duration, and agricultural product quality improvement in Guizhou yellow soil maize-cabbage rotation system, the overall effect of which was the best. Nitrogen reduction combined with single organic material overally did not affect crop yield, photosynthetic characteristics, and quality.