Non-structural Carbohydrate Remobilization Research Articles

Comparison of Agronomic and Physiological Characteristics for Rice Varieties Differing in Water Use Efficiency under Alternate Wetting and Drying Irrigation

Rice (Oryza sativa L.) stands as one of the most critical staple crops globally, with its yield and water use efficiency (WUE) being pivotal for food security. This study aimed to evaluate the agronomic and physiological traits and WUE of six rice varieties under two irrigation regimes: alternate wetting and drying (AWD) and conventional irrigation (CI). The results showed the significant improvements in grain yield and WUE with variety improvement under both irrigation treatments. Under AWD, high water use efficiency varieties (HWVs) demonstrated pronounced enhancements, including tillers and spikelet production, filled grain rate, 1000-grain weight, harvest index, leaf area index, non-structural carbohydrate remobilization, photosynthesis and catalase and peroxidase activities of leaf, root and shoot biomass, and root activity. AWD was observed to synchronize and amplify grain yield (2–14%) and WUE, including both leaf-level (13.94–20.72%) and yield-level (23.20–30.87%) water use efficiencies (WUEL and WUEY). The water use potential for HWVs was substantially enhanced under AWD. The integration of variety improvement with AWD irrigation strategies effectively achieves the dual objectives of high yield and WUE, offering a promising approach for sustainable rice production.

Comparison of population photosynthesis characteristics and grain yield of wheat under various sowing dates and seeding rates

AbstractThis study investigated the effects of sowing dates and seeding rates on photosynthetic characteristics and grain yield in wheat (Triticum aestivum L.). A field experiment was conducted with three sowing dates—early sowing date (SD‐E), normal sowing date (SD‐N), and delay sowing date (SD‐D)—and three seeding rates—90 low seeding rate (SR‐L), 108 moderate seeding rate (SR‐M), and high seeding rate 126 kg ha−1 (SR‐H). The results revealed that the grain yield at SR‐L in the SD‐E regime, SR‐M in the SD‐N regime, and SR‐H in the SD‐D regime was increased by 7.48%–9.93%, 14.1%–16.7%, and 19.0%–41.6%, respectively, compared to other combinations under the same sowing date. Consistent with the yield performance, the aboveground biomass accumulation, nonstructural carbohydrates (NSC) accumulation in stems, and NSC remobilization amount from anthesis to maturity were the highest at SR‐L in the SD‐E, at SR‐M in the SD‐N, or at SR‐H in the SD‐D regime, among other treatment combinations. Improved canopy photosynthetic characteristics (i.e., leaf area index, leaf photosynthetic rate, canopy photosynthetically active radiation interception rate, and radiation use efficiency) were also observed at the SR‐M in the SD‐N or at SR‐H in the SD‐D regime. Collectively, a suitable sowing date combined with an optimum seeding rate could enhance grain yield, and increasing the seeding rate could mitigate the yield loss when sowing was delayed by optimizing traits photosynthesis in wheat.

Inferior spikelet filling is affected by T6P/SnRK1-mediated NSC remobilization in large-panicle rice (Oryza sativa L.).

Poor grain filling in inferior spikelets (IS), which is influenced by the remobilization of nonstructural carbohydrates (NSC) stored in the sheath and internode of rice plants, limits the expected high yield of large-panicle rice. NSC remobilization from the sheath to the panicle is regulated by the T6P/SnRK1 pathway. However, in large-panicle rice, it is unclear whether IS grain filling is related to the NSC remobilization mediated by T6P/SnRK1 signaling. In this study, two large-panicle cultivars-W1844 and CJ03-with distinct differences in IS grain filling were used to explore the physiological mechanism mediating IS development. Compared to W1844, CJ03 IS showed lower expression of the genes related to sucrose uploading, later sucrose peaking, and delayed starch accumulation. In the CJ03, low OsSUTs expression and NSC output, transport rate, and contribution rate were detected in the sheaths and internodes. These results suggest that poor NSC remobilization results in insufficient assimilate supply for the IS, and consequently, poor IS grain filling. Furthermore, poor NSC remobilization coincided with the increased T6P content and decreased SnRK1 activity during grain filling in CJ03 IS. The expression levels of genes related to T6P metabolism and those encoding the catalytic subunit of SnRK1 were consistent with the observed T6P content and SnRK1 activity in the sheaths and internodes. Therefore, IS grain filling is potentially affected by T6P/SnRK1 signaling-mediated NSC remobilization in large-panicle rice.

Quantifying the Individual and Combined Effects of Short-Term Heat Stress at Booting and Flowering Stages on Nonstructural Carbohydrates Remobilization in Rice

Rice production is threatened by climate change, particularly heat stress (HS). Nonstructural carbohydrates (NSCs) remobilization is a key physiological mechanism that allows rice plants to cope with HS. To investigate the impact of short-term HS on the remobilization of nonstructural carbohydrates (NSCs) in rice, two cultivars (Huaidao-5 and Wuyunjing-24) were subjected to varying temperature regimes: 32/22/27 °C as the control treatment, alongside 40/30/35 °C and 44/34/39 °C, for durations of 2 and 4 days during the booting, flowering, and combined stages (booting + flowering) within phytotrons across the years 2016 and 2017. The findings revealed that the stem’s NSC concentration increased, while the panicle’s NSCs concentration, the efficiency of NSCs translocation from the stem, and the stem NSC contribution to grain yield exhibited a consistent decline. Additionally, sugar and starch concentrations increased in leaves and stems during late grain filling and maturity stages, while in panicles, the starch concentration decreased and sugar concentration increased. The heat-tolerant cultivar, Wuyunjing-24, exhibited higher panicle NSC accumulation under HS than the heat-sensitive cultivar, Huaidao-5, which had more stem NSC accumulation. The flowering stage was the most vulnerable to HS, followed by the combined and booting stages. Heat degree days (HDDs) were utilized to quantify the effects of HS on NSC accumulation and translocation, revealing that the flowering stage was the most affected. These findings suggest that severe HS makes the stem the primary carbohydrate storage sink, and alleviation under combined HS aids in evaluating NSC accumulation, benefiting breeders in developing heat-tolerant rice varieties.

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.

Reduced Nitrogen Input Combined with Nitrogen-Saving japonica Rice Varieties Balances Yield and Nitrogen Use Efficiency in The Lower Reaches of the Yangtze River in China

Maintaining rice yield and reducing nitrogen (N) input are two important targets in sustainable agriculture practices. The adoption of a nitrogen-saving variety (NSV) provides a unique opportunity to achieve this. However, limited options in NSV japonica rice and a lack of information on their responses to N reduction make management decisions difficult. This study aims to explore the responses of yield and nitrogen use efficiency (NUE) in NSV to N reduction. Two newly released NSVs and two popular general varieties (GVs) of japonica rice were field tested in Yangzhou, located at the lower reaches of Yangtze River of China, in two consecutive years. The results showed that for NSVs, with a 40–60% reduction in common practice N rate (300 Kg ha−1), the rice yield could maintain a record average level (p < 0.05), whereas the yield for the GV would drop 20–30% (p < 0.05). This indicates that combining the practices of adoption of NSV and N reduction to 120–180 Kg N ha−1 could balance the yield and N consumption. Moderate N reduction promotes the N accumulation and NUE, and it increases the number of tillers, the productive tiller percentage and the total amount of spikelets in the population, and increases the carbon and N metabolism of the population in the NSV. Compared with GV, NSV showed higher NUE and non-structural carbohydrate re-mobilization in the reduced N rate. The results showed that the practice of N reduction has to adopt NSV at the same time in order to maintain the grain yield level in rice.

Decreased panicle N application alleviates the negative effects of shading on rice grain yield and grain quality

Light deficiency is a growing abiotic stress in rice production. However, few studies focus on shading effects on grain yield and quality of rice in East China. It is also essential to investigate proper nitrogen (N) application strategies that can effectively alleviate the negative impacts of light deficiency on grain yield and quality in rice. A two-year field experiment was conducted to explore the effects of shading (non-shading and shading from heading to maturity) and panicle N application (NDP, decreased panicle N rate; NMP, medium panicle N rate; NIP, increased panicle N rate) treatments on rice yield- and quality-related characteristics. Compared with non-shading, shading resulted in a 9.5–14.8% yield loss (P<0.05), mainly due to lower filled-grain percentage and grain weight. NMP and NIP had higher (P<0.05) grain yield than NDP under non-shading, and no significant difference was observed in rice grain yield among NDP, NMP, and NIP under shading. Compared with NMP and NIP, NDP achieved less yield loss under shading because of the increased filled-grain percentage and grain weight. Shading reduced leaf photosynthetic rate after heading, as well as shoot biomass weight at maturity, shoot biomass accumulation from heading to maturity, and nonstructural carbohydrate (NSC) content in the stem at maturity (P<0.05). The harvest index and NSC remobilization reserve of NDP were increased under shading. Shading decreased (P<0.05) percentages of brown rice, milled rice, head rice, and amylose content while increasing (P<0.05) chalky rice percentage, chalky area, chalky degree, and grain protein. NMP demonstrated a better milling quality under non-shading, while NDP demonstrated under shading. NDP exhibited both lower chalky rice percentage, chalky area, and chalky degree under non-shading and shading, compared with NMP and NIP. NDP under shading decreased amylose content and breakdown but increased grain protein content and setback, contributing to similar overall palatability to non-shading. Our results suggested severe grain yield and quality penalty of rice when subjected to shading after heading. NDP improved NSC remobilization, harvest index, and sink-filling efficiency and alleviated yield loss under shading. Besides, NDP would maintain rice’s milling, appearance, and cooking and eating qualities under shading. Proper N management with a decreased panicle N rate could be adopted to mitigate the negative effects of shading on rice grain yield and quality.

Sucrose nonfermenting-1-related protein kinase 1 regulates sheath-to-panicle transport of nonstructural carbohydrates during rice grain filling.

The remobilization of nonstructural carbohydrates (NSCs) reserved in rice (Oryza sativa) sheaths is essential for grain filling. This assimilate distribution between plant tissues and organs is determined by sucrose non-fermenting-1-related protein kinase 1 (SnRK1). However, the SnRK1-mediated mechanism regulating the sheath-to-panicle transport of NSCs in rice remains unknown. In this study, leaf cutting treatment was used to accelerate NSC transport in the rice sheaths. Accelerated NSC transport was accompanied by increased levels of OsSnRK1a mRNA expression, SnRK1a protein expression, catalytic subunit phosphorylation of SnRK1, and SnRK1 activity, indicating that SnRK1 activity plays an important role in sheath NSC transport. We also discovered that trehalose-6-phosphate, a signal of sucrose availability, slightly reduced SnRK1 activity in vitro. Since SnRK1 activity is mostly regulated by OsSnRK1a transcription in response to low sucrose content, we constructed an snrk1a mutant to verify the function of SnRK1 in NSC transport. NSCs accumulated in the sheaths of snrk1a mutant plants and resulted in a low seed setting rate and grain weight, verifying that SnRK1 activity is essential for NSC remobilization. Using phosphoproteomics and parallel reaction monitoring, we identified 20 SnRK1-dependent phosphosites that are involved in NSC transport. In addition, the SnRK1-mediated phosphorylation of the phosphosites directly affected starch degradation, sucrose metabolism, phloem transport, sugar transport across the tonoplast, and glycolysis in rice sheaths to promote NSC transport. Therefore, our findings reveal the importance, function, and possible regulatory mechanism of SnRK1 in the sheath-to-panicle transport of NSCs in rice.

Senescence-Specific Expression of RAmy1A Accelerates Non-structural Carbohydrate Remobilization and Grain Filling in Rice (Oryza sativa L.).

Remobilization of pre-anthesis NSCs (non-structural carbohydrates) is significant for effective grain filling in rice (Oryza sativa L.). However, abundant starch particles as an important component of NSCs are still present in the leaf sheath and stem at the late stage of grain filling. There are no studies on how bioengineering techniques can be used to improve the efficiency of NSC remobilization. In this study, RAmy1A was expressed under the senescence-specific promoter of SAG12, which was designed to degrade starch in the leaf sheath and stem during grain filling. RAmy1A mRNA successfully accumulated in the leaf, stem, and sheath of transgenic plants after anthesis. At the same time, the starch and total soluble sugar content in the leaf, stem, and leaf sheath were obviously decreased during the grain-filling period. The photosynthetic rate of transgenic lines was higher than that of the wild types by an average of 4.0 and 9.9%, at 5 and 10 days after flowering, respectively. In addition, the grain-filling rate of transgenic lines was faster than that of the wild types by an average of 26.09%. These results indicate an enhanced transport efficiency of NSCs from source tissues in transgenic rice. Transgenic rice also displayed accelerated leaf senescence, which was hypothesized to contribute to decreased grain weight.

Varietal difference in dynamics of non-structural carbohydrates in nodal segments of stem in two varieties of rice (Oryza sativa L.) at pre- and post-heading stages

ABSTRACT The non-structural carbohydrate (NSC) stored in rice stems (culm plus leaf sheaths) at pre-heading stage is one of the major carbon sources for grain filling. In this study, we conducted field experiments in 2018 and 2019 using two varieties, Momiroman (japonica-dominant) and Teqing (indica), which have different accumulation and remobilization patterns of NSC in the stems. We analyzed NSC dynamics of each of the five nodal segments of internodes and leaf sheaths at pre- and post-heading stages. The dynamics of NSC at pre- and post-heading stages differed among segments. The lower segments of internodes and leaf sheaths accumulated more NSC at pre-heading stage compared to the upper segments in both varieties. The lower internodes in Teqing were morphologically larger than in Momiroman and would be able to store more NSC. However, the upper parts of the stems required biomass for development and formation at the stage of NSC accumulation in stems. Momiroman had longer upper internodes and leaf sheaths and required more biomass than Teqing. The NSC remobilization was later in the upper than the lower internodes for both varieties, which led to the delay of NSC remobilization in the entire culm after heading. These results indicated that ideal morphology of stems, to maximize the potential contribution of stem NSC as the carbon source for grain filling, is large lower internodes and short upper internodes and leaf sheaths.

What happens at night? Physiological mechanisms related to maintaining grain yield under high night temperature in rice

High night temperature (HNT) causes substantial yield loss in rice (Oryza sativa L.). In this study, the physiological processes related to flag leaf dark respiration (Rn) and grain filling under HNT were explored in a multi-parent advanced generation intercross population developed for heat tolerance (MAGICheat ) along with selected high temperature tolerant breeding lines developed with heat-tolerant parents. Within a subset of lines, flag leaf Rn under HNT treatment was related to lower spikelet number per panicle and thus reduced yield. HNT enhanced the nighttime reduction of non-structural carbohydrates (NSC) in stem tissue, but not in leaves, and stem nighttime NSC reduction was negatively correlated with yield. Between heading and harvest, the major difference in NSC concentration was found for starch, but not for soluble sugar. HNT weakened the relationship between NSC remobilization and harvest index at both the phenotypic and genetic level. By using genome-wide association studies, an invertase inhibitor, MADS box transcription factors and a UDP-glycosyltransferase that were identified as candidate genes orchestrating stem NSC remobilization in the control treatment were lost under HNT. With the identification of physiological and genetic components related to rice HNT response, this study offers promising prebreeding materials and trait targets to sustain yield stability under climate change.

Reduced nitrogen application rate with dense planting improves rice grain yield and nitrogen use efficiency: A case study in east China

Dense planting could be a feasible method for reducing nitrogen (N) application rates without compromising rice grain yield in northeast and central China. It is still unclear whether reduced N application with dense planting (RNDP) can achieve higher rice yield and N use efficiency (NUE) in Jiangsu, east China. Three japonica inbred rice (JI) and three indica hybrid rice (IH) cultivars were grown in a field experiment. Their grain yield, NUE, and related traits were compared under two cultivation treatments: conventional high-yielding practice (CHYP) and RNDP. JI showed similar yields under the two treatments, while IH showed lower yield under RNDP than under CHYP, and the partial factor productivity of N and N use efficiency for grain yield increased (P < 0.05) in both JI and IH under RNDP. Compared with CHYP, RNDP reduced spikelets per panicle but increased panicles per m2 and filled-kernel percentage of JI and IH, and JI’s kernel weight was increased (P < 0.05) under RNDP. Shoot biomass weight and nonstructural carbohydrate (NSC) content in the stem at heading and maturity of JI and IH were reduced under RNDP, while harvest index and NSC remobilization reserve were increased (P < 0.05) under RNDP, especially for JI. Our results suggest that RNDP could achieve a higher rice grain yield and NUE, particularly for JI, a dominant rice cultivar type in Jiangsu. For JI, the increased panicles per m2, sink-filling efficiency, harvest index, and NSC remobilization after heading under RNDP contributed to a grain yield similar to that under CHYP.

Low Growth Sensitivity and Fast Replenishment of Non-structural Carbohydrates in a Long-Lived Endangered Conifer After Drought

There is an ongoing debate on whether a drought induced carbohydrate limitation (source limitation) or a direct effect of water shortage (sink limitation) limit growth under drought. In this study, we investigated the effects of the two driest summers recorded in southern Chile in the last seven decades, on the growth and non-structural carbohydrates (NSC) concentrations of the slow-growing conifer Fitzroya cupressoides. Specifically, we studied the seasonal variation of NSC in saplings and adults one and two years after the occurrence of a 2 year-summer drought at two sites of contrasting precipitation and productivity (mesic-productive vs. rainy-less productive). We also evaluated radial growth before, during and after the drought, and predicted that drought could have reduced growth. If drought caused C source limitation, we expected that NSCs will be lower during the first than the second year after drought. Conversely, similar NSC concentrations between years or higher NSC concentrations in the first year would be supportive of sink limitation. Also, due to the lower biomass of saplings compared with adults, we expected that saplings should experience stronger seasonal NSC remobilization than adults. We confirmed this last expectation. Moreover, we found no significant growth reduction during drought in the rainy site and a slightly significant growth reduction at the mesic site for both saplings and adults. Across organs and in both sites and age classes, NSC, starch, and sugar concentrations were generally higher in the first than in the second year following drought, while NSC seasonal remobilization was generally lower. Higher NSC concentrations along with lower seasonal NSC remobilization during the first post-drought year are supportive of sink limitation. However, as these results were found at both sites while growth decreased slightly and just at the mesic site, limited growth only is unlikely to have caused NSC accumulation. Rather, these results suggest that the post-drought dynamics of carbohydrate storage are partly decoupled from the growth dynamics, and that the rebuild of C reserves after drought may be a priority in this species.

Quantifying the effects of short-term heat stress at booting stage on nonstructural carbohydrates remobilization in rice

Extreme heat stress events are becoming more frequent under anticipated climate change, which can have devastating impacts on rice growth and yield. To quantify the effects of short-term heat stress at booting stage on nonstructural carbohydrates (NSC) remobilization in rice, two varieties (Nanjing 41 and Wuyunjing 24) were subjected to 32/22/27 °C (maximum/minimum/mean), 36/26/31 °C, 40/30/35 °C, and 44/34/39 °C for 2, 4 and 6 days in phytotrons at booting stage during 2014 and 2015. Yield and yield components, dry matter partitioning index (DMPI), NSC accumulation and translocation were measured and calculated. The results showed that the increase of high-temperature level and duration significantly reduced grain yield by suppressing spikelet number per panicle, seed-setting rate, and grain weight. Heat stress at booting decreased DMPI in panicles, increased DMPI in stems, but had no significant effect on photosynthetic rate. Stem NSC concentration increased whereas panicles NSC concentration, stem NSC translocation efficiency, and contribution of stem NSC to grain yield decreased. Severe heat stress even transformed the stem into a carbohydrate sink during grain filling. The heat-tolerant Wuyunjing 24 showed a higher NSC transport capacity under heat stress than the heat-sensitive Nanjing 41. Heat degree-days (HDD), which combines the effects of the intensity and duration of heat stress, used for quantifying the impacts of heat stress indicates the threshold HDD for the termination of NSC translocation is 9.82 °C day. Grain yield was negatively correlated with stem NSC concentration and accumulation at maturity, and yield reduction was tightly related to NSC translocation reduction. The results suggest that heat stress at booting inhibits NSC translocation due to sink size reduction. Therefore, genotypes with higher NSC transport capacity under heat stress could be beneficial for rice yield formation.

Agronomic and physiological performance of indica/japonica hybrid rice cultivar under low nitrogen conditions

It is generally believed that indica/japonica hybrid rice (IJHR) cultivars have a higher yield potential under high nitrogen (N) supply, but it is not established whether IJHR could obtain a relatively high yield under low N conditions. In order to fill this gap of knowledge, six rice cultivars were examined in this study, consisting of three IJHR cultivars and three japonica hybrid rice (JHR) cultivars, all of which are prevalent in the lower Yangtze River plain. These cultivars were compared for grain yield and other closely-related agronomic and physiological traits under two N input treatments: one being a low application of N (LN) and the other a normal application of N (NN), in 2016 and 2017 in Hangzhou, Zhejiang Province, China. Compared to JHR, IJHR showed grain yield increases of 15% under NN and 25% under LN. Relative to JHR, there are four main agronomic and physiological traits which are associated with IJHR’s superior yield performance under LN conditions. Firstly, IJHR has less redundant vegetative growth, evidenced by a higher percentage of productive tillers. Secondly, IJHR has the larger sink size, resulting from higher spikelet numbers per panicle and sufficient panicles per m2. Thirdly, IJHR exhibited increased shoot activity during the grain filling period, indicated by an increased accumulation of non-structural carbohydrate (NSC) in the stems at heading time, a higher percentage of NSC remobilization from stem to grains during the ripening period, higher enzyme activity in the grains’ sucrose-to-starch conversion process, and greater photosynthesis production during the ripening period. Finally, IJHR was seen to have improved root morpho-physiological traits, characterized by greater root biomass, deeper soil distribution at heading time, and higher root oxidation activity (ROA) during the ripening period. Our results suggest that IJHR’s improved agronomic and physiological traits will lead to improved yields under low N input conditions.

Influence of Water Management and Nitrogen Application on Rice Root and Shoot Traits

Soil water potential and fertilizer nutrients are the two main factors affecting rice growth and development. A soil‐grown experiment was conducted using mid‐season japonica rice cultivar Xudao 3 with three different nitrogen (N) fertilization rates: (i) none, (ii) moderate nitrogen (240 kg ha–1), and (iii) high nitrogen (360 kg ha–1) and three irrigation regimes: (i) submerged irrigation (0 kPa), (ii) alternate wetting and moderate drying (–20 kPa), and (iii) alternate wetting and severe drying (–40 kPa). In the same N level, root length, root dry weight, root activity (represented by root‐bleeding sap), net photosynthetic rates at main growth stages, and ATPase activity during the grain‐filling stage are higher under the treatment of alternate wetting and moderate drying, when compared with those of submerged irrigation. Meanwhile, non‐structural carbohydrate (NSC) remobilization and shoot dry accumulation are also increased from heading to maturity, which contribute to higher grain yield and higher nitrogen‐use efficiency. In the same irrigation regime, root‐bleeding sap, NSC remobilization, and ATPase are increased significantly under the moderate‐N treatment compared with those of the high‐N treatment, which contribute to higher nitrogen‐use efficiency. However, no significant difference exists in grain yield and crop growth rate. These results indicate that the coordinated relationship between the root and shoot, especially increased root length, enhanced root‐bleeding sap, increased NSC remobilization, enhanced shoot dry accumulation, and ATPase activity during the grain‐filling stage, can promote rice yield and nitrogen‐use efficiency by using the appropriate nitrogen application and alternate wetting and moderate drying.Core Ideas Root and shoot traits were significantly different in response to irrigation regime and nitrogen level treatment. Alternated wetting/moderate drying interacted with moderate N to coordinate the development of root and shoot. Deeper roots increased root‐bleeding sap, NSC remobilization from stems to grain, and activity of grain sink. Greater root length (via root‐shoot relationships) contribute to increased yield and enhanced N‐use efficiency. Alternated wetting/drying irrigation with moderate N promotes grain filling and increased yield and N‐use.

Non-structural Carbohydrates in Dormant Woody Perennials; The Tale of Winter Survival and Spring Arrival

Woody perennials’ reliance on nonstructural carbohydrates (NSC) reserves for the resumption of spring growth necessitates an accumulation of NSC prior to dormancy. It is assumed that during dormancy temperature-regulated biological activities gauge the progression of winter and affect the metabolic rates and physiology of NSC reserves. Thus, changes in temperature signal the arrival of spring and determine the amount of reserves available for growth resumption. As woody perennials are dependent on dispersed storage of NSC during spring, they need an integrated remobilization and redistribution for synchronous and effective development of photosynthetic and reproductive organs. However, it is not known how storage compartments interact at the whole plant level, when NSC reserves are mobilized, or how local and distal storage compartments influence the biology of spring growth resumption. The goal of this mini-review is to shift the focus of winter biology from bud-centric to the whole plant. We discuss winter NSC management in the context of climate change with a special emphasis on how projected mild winters may affect the carbon budget, transport, and allocation during winter. We look at three aspects of NSC regulation underlying dormancy (I) the molecular regulation of dormancy (II) temperature dependent winter NSC metabolism, and (III) spring NSC remobilization and redistribution processes.

Low Nitrogen Application Enhances Starch-Metabolizing Enzyme Activity and Improves Accumulation and Translocation of Non-structural Carbohydrates in Rice Stems.

More than 4 billion inhabitants in Asia depend on rice for 35–60% of the calories consumed in their diets, but new rice cultivars frequently do not reach expected yields because of poor rice grain filling. Here, we quantified the activities of enzymes involved in starch metabolization in rice to investigate the mechanisms regulating the accumulation and translocation of stem non-structural carbohydrates (NSC) under different levels of nitrogen fertilizer application. A pot experiment was conducted using two rice cultivars, Liangyoupeijiu (LYPJ) and Shanyou63 (SY63), under high and low nitrogen applications. Compared with high nitrogen application (HN), low nitrogen application (LN) increased stem NSC concentration before the heading stage and NSC translocation during the grain filling stage; concomitantly, LN significantly shortened the active grain filling period and increased the grain filling rate in superior spikelets. Compared with the LYPJ cultivar, SY63 exhibited a higher grain weight, higher grain filling percentage, and higher stem NSC concentration before heading and greater NSC translocation after heading. During the period between panicle initiation and heading, the activities of adenosine diphosphate-glucose pyrophosphorylase (AGP), starch synthase (StS), and starch branching enzyme (SBE), all enzymes involved in starch synthesis, increased under the LN treatment and positively correlated with increases in stem NSC. During grain filling, the activities of enzymes involved in starch-to-sucrose conversion [α-amylase, β-amylase, and sucrose phosphate synthase (SPS)] increased under the LN treatment and positively correlated with stem NSC remobilization. Overall, the investigated enzymes exhibited higher activities in SY63 than in LYPJ. Our results suggest that low nitrogen increases the activities of AGP, StS, SBE, α-amylase, β-amylase, and SPS, leading to increased accumulation and remobilization of stem starch and NSC in SY63. We conclude that calculated reductions in nitrogen application and the choice of an appropriate cultivar may improve rice grain yields via enhanced stem NSC accumulation and translocation, thereby reducing the costs and increasing the sustainability of rice production.

The effect of alternate wetting and severe drying irrigation on grain yield and water use efficiency of Indica‐japonica hybrid rice (Oryza sativa L.)

AbstractIdentification of a rice cultivar with high yield potential has been heavily sought by researchers in China, and pursuant to this goal, several indica‐japonica hybrid rice (IJHR) cultivars have been studied for over a decade. However, in addition to high yield, it is important that the cultivar also exhibit good water use efficiency (WUE). This study compared the yield performance and WUE of the IJHR cultivars under alternate wetting and severe drying (AWSD) irrigation regimen to the japonica inbred rice (JIR) cultivars. Field experiments were conducted on two representative IJHR cultivars (Chunyou927 and Yongyou538) and two representative JIR cultivars (Xiushui09 and Zhejing99) in 2015 and 2016 with two different irrigation methods: continuous flooding (CF) and AWSD. Irrigation water was 275–349 mm in the AWSD irrigation regimen, which was 49.8%–56.2% of that (552–620 mm) applied to the CF irrigation regimen. Compared to CF, the AWSD irrigation method significantly decreased grain yield in both IJHR and JIR cultivars, with a more significant reduction in JIR cultivars, and WUE was improved in both the IJHR and JIR cultivars, especially in the IJHR cultivars. Compared to the JIR cultivars, the IJHR cultivars were found to have improved agronomic and physiological performances under the AWSD irrigation regimen, such as a larger sink size, higher percentage of productive tillers, higher matter production ability during reproductive and ripening periods, larger root biomass, deeper root distribution and greater nonstructural carbohydrate (NSC) accumulation in the stem at heading, larger NSC remobilization from the stem, and higher root oxidation activity and leaf photosynthetic rates during ripening period. Improved agronomic and physiological traits contributed to an increase in WUE with less yield loss for IJHR cultivars under the AWSD irrigation regimen.

Alternate wetting and moderate drying increases rice yield and reduces methane emission in paddy field with wheat straw residue incorporation

AbstractWheat residue incorporation into the rice paddy field is becoming a popular practice in rice production in China's main rice‐growing area but risks an increased emission of greenhouse gases. This study investigated if an alternate wetting and moderate drying (AWMD) irrigation regime in rice production reduces CH4 emission and increases grain yield when wheat straw residues are incorporated into rice paddy field. One super rice variety was field‐grown in 2012 and 2013 and subjected to four irrigation and straw incorporation treatments: continuously flooded (CF) without straw incorporation (−S), AWMD without straw incorporation (AWMD−S), then CF with straw incorporation (CF + S) and AWMD + S. When compared with the CF, the AWMD regime increased grain yield and water use efficiency (WUE, grain yield over the amount of water used) by 2.7% and 27.6%, respectively, under −S, and by 18.0 and 50.0%, respectively under +S. The AWMD + S treatment also significantly increased nitrogen use efficiency (NUE) compared with the CF + S treatment. The increase in grain yield, WUE and NUE in the AWMD regime, especially under +S, were attributed mainly to a greater root oxidation activity, deeper root distribution and increases in productive tillers, crop growth rate and nonstructural carbohydrate remobilization during grain filling. There was a total of 0.49 kg N2O‐N ha−1 more loss in the AWMD than in the CF regime. However, the AWMD regime substantially decreased seasonal CH4 emissions, global warming potential (GWP, including both CH4 and N2O) and greenhouse gas intensity (grain yield over GWP) by 49.8%, 45.2% and 46.7%, respectively, under −S, and by 57.5, 55.9% and 62.6%, respectively, under +S, when compared with the CF regime. The results demonstrate that the AWMD is an effective practice to increase grain yield and resource‐use efficiency and reduce environmental risks especially, when wheat straw is incorporated into paddy field.