Source-sink Relationships Research Articles

Nitrogen application and soil mulching improve grain yield of rainfed maize by optimizing source-sink relationship and grain filling process on the Loess Plateau of China

The kernel weight of maize (Zea mays L.) is largely regulated by the source-sink relationship during the grain-filling period. The source-sink coordination is the key to high grain yield, which is affected by many management practices, such as nitrogen application and soil mulching. Previous studies have mainly focused on qualitative descriptions of maize source-sink relationships, but the quantitative analysis of maize source-sink relationships under various nitrogen application rates and soil mulching practices have been poorly explored. A three-season (2020–2022) experiment was conducted on rainfed maize on the Loess Plateau of China, with two nitrogen rates (N0, 0 kg N ha–1; N180, 180 kg N ha–1) and three mulching practices (NM, flat cultivation with no mulching; SM, flat cultivation with full straw mulching; RF, ridge-furrow cultivation with transparent film mulching on the ridge). The results showed that compared with N0, N180 increased the maximum leaf area index (LAImax) by 29.6%, leaf area duration (LAD) by 31.4%, maximum 100-kernel weight (HGWmax) by 12.5%, source growth (SG) by 34.2%, sink capacity (SC) by 49.8%, source supply rate (SUR) by 23.4%, sink growth rate (SGR) by 50.7%, and finally increased grain yield by 37.2%. Compared with NM, SM and RF increased LAImax by 8.5% and 25.6%, LAD by 10.6% and 28.0%, HGWmax by 5.5% and 10.3%, SG by 13.6% and 41.6%, SC by 16.4% and by 35.5%, SUR by 8.7% and 35.5%, SGR by 16.3% and 37.1%, and finally increased grain yield by 8.2% and 26.7%, respectively. The structural equation modeling indicated that LAD mainly affected SG, and SG significantly affected source-sink relationships and grain-filling parameters, which mainly affected 100-kernel weight and the number of grains per spike, respectively. The number of grains per spike had a greater impact on the sink capacity than 100-kernel weight. In conclusion, nitrogen application and soil mulching enhanced grain yield of rainfed maize by increasing leaf source size, promoting source growth and grain filling, improving kernel number and optimizing source-sink relationships on the Loess Plateau of China. This study provides a better understanding of source-sink relationships for optimizing maize management practices and identifying key processes in modeling maize yield.

Alteration of Wheat Source-Sink Relation by Nitrogen and Spikelet Removal

The source and sink relationships determine the amount and distribution of biomass in plants. Field and laboratory experiments were conducted to study the effect of nitrogen rate and spikelet removal on seed yield and germination traits of wheat. The field experiment was conducted employing sink manipulation (no spikelet removal and ½ spikelet removal) and source manipulation (nitrogen rate of 0, 75, and 150 kg ha-1). This study was performed as a factorial experiment in a randomized complete block design with three replications. Seeds obtained from the field experiment were subjected to determine the effect of the sink and source manipulation on seed germination traits in the laboratory experiment. Results showed that most traits under study were not affected by source and sink manipulation. Seed yield and seed weight were not affected by spikelet removal and varying nitrogen applications. Although some of the wheat spikelets have been removed, those plants have been able to maintain the number of seeds per spike and the weight of a single seed. The use of nitrogen at the spike emergence stage did not affect the seed yield of the Pishtaz cultivar. Nitrogen needed for the seeds could be compensated by the re-mobilization of nitrogen from various plant organs such as the stem. Nitrogen application of 150 kg ha-1 with the removal of ½ spikelets improved seed germination (%) and vigor comparing control (no spikelet removal with no nitrogen application). Considering that seed yield and seed weight did not change under the influence of source and sink manipulation, it can be concluded that Pishtaz wheat is more sink-limited than source-limited.

Physiological Analysis of Source-Sink Relationship in Rice Genotypes with Contrasting Grain Yields.

Rice is a major staple food, and, hence, doubling its productivity is critical to sustain future food security. Improving photosynthesis, source-sink relationships and grain-filling mechanisms are promising traits for improvement in grain yield. To understand the source-sink relationship and grain yield, a set of contrasting rice genotypes differing in yield and biomass were studied for physiological, biochemical and gene-expression differences. The physiological and yield component traits of selected rice genotypes were analyzed in 2016 and 2017 under field conditions. This led to the categorization of genotypes as high yielding (HY) and high biomass, viz., Dular, Gontra Bidhan 3, Way Rarem, Patchai Perumal, Sahbhagi Dhan, Indira Barani Dhan-1, MTU1010, and Maudamani; while, low yielding (LY) and low biomass, viz. Anjali, Ghanteswari, Parijat, Khao Daw Tai, RKVY-104, Ghati Kamma Nangarhar, BAM4510 and BAM5850. The HY genotypes in general had relatively better values of yield component traits, higher photosynthetic rate (Pn) and chlorophyll (Chl) content. The study revealed that leaf area per plant and whole plant photosynthesis are the key traits contributing to high biomass production. We selected two good-performing (Sahbhagi Dhan and Maudamani) and two poor-performing (Ghanteswari and Parijat) rice genotypes for a detailed expression analysis of selected genes involved in photosynthesis, sucrose synthesis, transport, and starch synthesis in the leaf and starch metabolism in grain. Some of the HY genotypes had a relatively high level of expression of key photosynthesis genes, such as RbcS, RCA, FBPase, and ZEP over LY genotypes. This study suggests that traits, such as leaf area, photosynthesis and grain number, contribute to high grain yield in rice. These good-performing genotypes can be used as a donor in a breeding program aimed at high yields in rice.

Sedimentary infill of Early-Middle Jurassic in the southeastern Tarim Basin and its constraints on the evolution of the Altyn Tagh Fault in the Northeast Tibet Plateau

The Altyn Tagh Fault (ATF) is the boundary between the Tarim Basin and the Tibetan Plateau, which is crucial for the tectonic evolution and uplift of the Tibetan Plateau. However, the Mesozoic tectonic evolution of the ATF remains controversial. This study reconstructed the Early-Middle Jurassic palaeogeographic pattern of the southeast depression of the Tarim Basin (SDTB) and revealed potential source-sink relationships between the SDTB and its adjacent mountains to constrain the Mesozoic tectonic evolution of the ATF based on sedimentology and provenance analyses. The results indicated that the SDTB was infilled with alluvial fan facies during the Early Jurassic and the late Early Jurassic, giving rise to the braided-river delta to lacustrine facies. During the Middle Jurassic, the lacustrine basin expanded with the wide development of lacustrine facies, and the lacustrine basin contracted and was primarily infilled with braided delta facies in the late Middle Jurassic. The Jurassic sedimentary center, the SDTB situated in front of the Altyn Tagh Mountain and East Kunlun Mountain, played a crucial role in the development of three types of hydrocarbon source rocks: charcoal mudstone, coal beds, and dark mudstone. Combined with seismic reflection data interpretations, the Early Jurassic the STDB is a rift basin that underwent a rift-depression transition in the late Early Jurassic, solidifying the characteristics of the depression basin in the Middle Jurassic. The extensional environment in the SDTB resulted from the tectonic effects of slab break-off following the closure of the Tethys Ocean and the spreading of the distal stress field of the Bangonghu–Nujiang Ocean. The analyses of gravel component and heavy mineral indicated that the Jurassic source of the basin was traced back to the ancestral Altyn Mountains, the East Kunlun Mountains, and the internal palaeo-uplift of the basin, which demonstrated that the SDTB and Western Qaidam Basin (WQB) shared a common lacustrine basin during the Jurassic, suggesting that the ATF did not initiate strike-slip movements during this period. This study significantly enhanced our understanding of the Mesozoic tectonic evolution in Northwest China, providing valuable insights into exploring Mesozoic oil-bearing basins in the northern Tibetan Plateau. Furthermore, it served as a useful reference for constraining the timing of the initial slip of similar plate boundary strike-slip faults.

Role of Foliar Growth Retardants on Source Sink Relationship and Photosynthate Partitioning in Pigeonpea (Cajanus cajan L.) Genotypes

Role of Foliar Growth Retardants on Source Sink Relationship and Photosynthate Partitioning in Pigeonpea (Cajanus cajan L.) Genotypes

Fate, risk and sources of antibiotic resistome and its attenuation dynamics in the river water-sediment system: Field and microcosm study

Antibiotic resistance genes (ARGs) in rivers have received widespread attentions. Deciphering the fate and spread mechanisms of ARGs in river system can contribute to the design of effective strategies for reducing resistome risk in the environment. Although some studies have reported the prevalence and distribution of ARGs in rivers worldwide, few have systematically explored their fates, sources and risks in river water-sediment system. Also, the role of natural sunlight on the attenuation and fate of ARGs in river remains to be demonstrated. To fill the gaps, field investigation and microcosm experiment have been conducted in this study to reveal the fate, risk, source-sink relationship and attenuation dynamics of ARGs in an urban river water-sediment system, by utilizing high-throughput sequencing-based metagenomic assembly analysis and machine-learning-based source tracking tool. In all, 527 unique ARGs belonging to 29 antimicrobial classes were identified in the river. Relatively, the level of ARGs in the sediments were significantly higher (p < 0.05) than that in the waters. Variance partitioning analysis indicated the biotic and abiotic factors co-governed the riverine resistome, totally explaining 76% and 83% variations of ARGs in the waters and sediments, respectively. Microcosm experiment under natural light and dark condition showed that light induced the decay of ARGs in the waters and might promote their transfers from waters to sediments, which were also confirmed by the attenuation dynamics of bacteria in the experimental water-sediment system. Notably, the co-occurrences of ARGs with MGEs and VFs on the same contigs suggested resistome risk in the river, and relatively, the risk scores in the sediments were significantly higher (p < 0.05) than those in the waters. Source apportionment with metagenomic resistome signatures showed the Wenyu River was the most dominant contributor of ARGs in the downstream, with average contributions of 44.5% and 40.8% in the waters and sediments, respectively.

The chromatin source-sink hypothesis: a shared mode of chromatin-mediated regulations.

We propose that several chromatin-mediated regulatory processes are dominated by source-sink relationships in which factors operate as 'sources' to produce or provide a resource and compete with each other to occupy separate 'sinks'. In this model, large portions of genomic DNA operate as 'sinks', which are filled by 'sources', such as available histone variants, covalent modifications to histones, the readers of these modifications and non-coding RNAs. Competing occupation for the sinks by different sources leads to distinct states of genomic equilibrium in differentiated cells. During dynamic developmental events, such as sexual reproduction, we propose that dramatic and rapid reconfiguration of source-sink relationships modifies chromatin states. We envision that re-routing of sources could occur by altering the dimensions of the sink, by reconfiguration of existing sink occupation or by varying the size of the source, providing a central mechanism to explain a plethora of epigenetic phenomena, which contribute to phenotypic variegation, zygotic genome activation and nucleolar dominance.

Relative acceleration of orthonormal basis vectors for the geometric conduction blocks of the cardiac electric signal propagation on anisotropic curved surfaces

Geometric conduction blocks stop cardiac electric propagation due to the shape or conductivity properties of the domain. The blocks are considered to cause many abnormal cardiac electric propagations, leading to cardiac electrophysiological pathologies, such as cardiac fibrillation and arrhythmia. Locating such multidimensional conduction blocks is challenging, particularly in a complex domain with a complex shape and strong anisotropy, such as the heart. To address this problem, we propose a novel mathematical model of the geometric conduction block using the relative acceleration adopted from space-time physics. An efficient numerical scheme for the mathematical model is also proposed to predict the unidirectional conduction block effectively, even in a complex domain. The relative acceleration in the cardiac electric propagation corresponds to the sink-source relationship between the excited (after repolarization) and excitable (before depolarization) cardiac cells, representing the geometric growth rate of the volume of metric balls. The trajectory is constructed from the wavefront of diffusion-reaction equations by aligning orthonormal basis vectors along the gradient of the action potential. Relative acceleration is computed along the propagational direction from the connection 1-form of the basis vectors. The proposed mathematical model and numerical scheme are applied to demonstrate geometric conduction blocks in two-dimensional (2D) simple curved domains with strong anisotropy.

Genotype‐by‐environmental interaction effects on earliness, semi‐dwarfism, and yield of rice (Oryza sativa L.) mutants in Tamil Nadu, India

AbstractRice plant architecture improvement helps in the effective and efficient source–sink relationship to enhance yield. The most preferred plant architecture in rice is dwarf type. Improved White Ponni (IWP) is a tall, medium duration, released variety of Tamil Nadu, India, yielding 300 kg more than parental line White Ponni, which is suitable for second season transplanting. To induce variation in plant height to select semi‐dwarf mutants, IWP was subjected to mutagenesis in 2011 using different doses of gamma rays to develop semi‐dwarf and short‐duration mutants. The selection was carried out in segregating populations of M2, and an evaluation of selected better‐performing mutants was done up to 70 selected mutants in M5. Nineteen M5 homozygous, semi‐dwarf, and short‐duration mutants that outperformed the IWP were evaluated in 2015–2016 across five contrasting environments of Tamil Nadu in India. The genotypes were grown in a randomized complete block design with two replications with IWP as a control. In the additive main effects and multiplicative interaction (AMMI) biplot, the analysis revealed that PC1 and PC2 accounted for 49% and 18% of the variation, respectively. Interaction principal component analysis‐1 scores were observed for the mutants, viz., IWP‐15‐5, IWP‐22‐1, and IWP‐30‐5, indicating their superior performance. In the GGE biplot, E1 (Aduthurai), E4 (Coimbatore), and E5 (Thirupathisaram) were the ideal environments for selecting high‐yielding mutants. IWP‐6‐5 and IWP‐16‐2 were the stable mutants for yield (23.59 and 24.51 g, respectively) but with a lower mean than other mutants at favorable environments. Based on the two models, E2 (Killikulam) and E3 (Madurai) were the favorable locations for exploiting high yields; IWP‐30‐5, IWP‐22‐2, and IWP‐22‐3 were stable across environments. These stable, high‐yielding, and early maturing mutants show potential for further advancement and eventual release of new rice varieties.

Late nitrogen fertilization increases biomass of cotton bolls by reinforcing source[sbnd]sink performance

The decrease in reproductive organ biomass is a principal constraint for cotton yield under conditions of limited nitrogen (N). We aimed to alleviate this challenge by reasoning N applications in order to exploit the photosynthetic potential and improve the distribution of photosynthates. Cotton crops were grown in a two-year field experiment (2019–2020) under N-reduced cultivation (23.9 ×104 plants ha−1, 76 cm row spacing, and applied 240 kg N ha−1), N fertigated with five ratios at squaring (SQ): flowering to peak boll (FPB): late peak boll (LPB), i.e., 4:6:0 (N460), 3:6:1 (N361), 2:6:2 (N262, Control), 1:6:3 (N163) and 0:6:4 (N064). Impacts of N treatment (ratio) were investigated for leaf area, chlorophyll content, photosynthetic characteristics, photosynthetic N use efficiency (PNUE), sink capacity characteristics, and biomass accumulation. Correlations between traits were also analyzed. Compared with conventional N262, N064 increased reproduction organs biomass by 10.1–10.3%. Furthermore, during the LPB to boll opening stage, N064 increased fruit branch leaf area by 1.4–26.8%, chlorophyll content by 6.4–27.6%, net photosynthetic rate by 15.1–35.9%, actual photosynthetic efficiency by 14.4–41.6%, photochemical quenching by 18.0–57.7%, PNUE by 15.7–41.0%, and sink capacity by 6.7–10.5%; while it decreased foliage branch leaf area by 13.1–22.4% and chlorophyll a/b by 6.1–10.2%. Overall, late N fertilization was an effective strategy to (1) retain post-flowering photosynthetic capacity by developing more fruit branch leaf area with higher chlorophyll content and lower chlorophyll a/b, (2) optimize sourcesink relationship by increasing boll capacity, and (3) increase biomass in reproductive organs, thus enhancing sustainable and efficient production of cotton under N-reduced cultivation in arid regions.

Selection and Yield Formation Characteristics of Dry Direct Seeding Rice in Northeast China.

Dry direct seeding rice (DSR) is an emerging production system because of increasing labor and water scarcity in rice cultivation. The limited availability of rice cultivars suitable for dry direct seeding hampers the widespread adoption of this cultivation method in Northeast China. This study aimed to investigate grain production and plant characteristics associated with dry direct seeding rice. We conducted a field experiment on 79 japonica rice cultivars in Shenyang City, Liaoning Province, Northeast China, in 2020 and 2021. This study found that the grain yield of the tested rice cultivars ranged from 5.75-11.00 t ha-1, with a growth duration lasting between 144-161 days across the cultivars. These cultivars were then categorized into high yielding (HY), medium yielding (MY), and low yielding (LY) based on daily yield by using Ward's hierarchical clustering method. The higher grain yield for HY compared to MY and LY was attributed to more spikelets per unit area. The HY alleviated the conflict between higher panicle density and larger panicle size by improving the seedling emergence rate and productive stem rate. It also significantly increased shoot biomass at maturity. The HY reduced the period between seeding and beginning of heading (BBCH 51) and the proportion of dry matter partitioned to the leaf at the heading stage. However, it also increased the accumulation of dry matter in the grain and the proportion of dry matter partitioned to the grain at maturity. Furthermore, the HY markedly increased the harvest index and grain-leaf ratio, which are beneficial to coordinate the source-sink relationship. A quadratic function predicted that 98 days is the optimum growth duration before heading (BBCH 51) for achieving maximum yield. In conclusion, for dry direct seeding rice, it is appropriate to select high-yielding japonica inbred rice cultivars with shorter growth duration before heading (about 93-102 day), higher panicle number (about 450-500 × 104 ha-1), more spikelet number per panicle (about 110-130), higher seedling emergence rate (about 70-75%), higher productive stem rate (about 60-70%), and greater harvest index (about 50-55%).

The Sink–Source Relationship Regulated Camellia oleifera Flower Bud Differentiation by Influencing Endogenous Hormones and Photosynthetic Characteristics

To explore the reasons for the differences in flower bud differentiation in Camellia oleifera under different sink–source relationships, different types of new shoots (T1 and T2) were selected to represent different sink–source relationships (new shoots with one fruit borne alongside at the bottom of the new shoots-T1; new shoots without one fruit borne alongside at the bottom of the new shoots-T2), and the flower bud differentiation rate, endogenous hormones and photosynthetic characteristics were determined. With the increase in the sink, the flower differentiation rate decreased significantly and the IAA and GA3 content in the leaves and ABA content in the buds increased significantly, while the GA3 and ZT content in the buds decreased significantly, which were significantly and positively correlated with the flower differentiation rate, with correlation coefficients of 0.777 and 0.817, respectively. Furthermore, an increase in the number of sinks contributed significantly to the increase in soluble sugar and starch content in leaves, while the soluble sugar and starch content in flower buds decreased significantly with the increase in sinks, with maximum differences of 3.45 mg·g−1 (soluble sugar in leaves), 4.09 mg·g−1 (soluble sugar in flower buds), 7.08 mg·g−1 (starch in leaves) and 4.87 mg·g−1 (starch in flower buds), and the high soluble sugar and starch content in flower buds at preflower bud differentiation with correlation coefficients of 0.854 and 0.837, respectively. The chlorophyll content and net photosynthetic rate increased with increasing sinks. In the presence of fruit at the base of the new shoot, more 13C assimilates were allocated to fruit and less to flower buds, resulting in a decrease in the rate of flower bud differentiation. The 13C assimilate allocated to the flower buds of T1 (6.71 mg·g−1) was significantly lower than the 13C assimilate allocated to the flower buds of T2 (10.26 mg·g−1) during late bud differentiation, and the difference between T1 and T2 was greatest during this period. Our work demonstrated that the sink–source relationship regulated Camellia oleifera flower bud differentiation by influencing endogenous hormones and photosynthetic characteristics. To achieve stable production of Camellia oleifera in successive years in the future, the ratio of the number of new shoots of the two types in relation to the different sink–source relationships should be reasonable.

Source-sink response analysis of heavy metals and soil pollution assessment in non-ferrous metal industrial agglomeration areas based on decision unit

Soil heavy metals (HMs) pollution is a worldwide concern. In this study, decision units based on “source-sink relationship” were established using multi-source data. The source-sink response of heavy metals in agricultural soils at the regional scale was analyzed using machine learning methods, receptor models, and geospatial analysis. The comprehensive pollution risk score (CRS) was proposed by integrating a variety of key evaluation indicators to evaluate the pollution degree of each decision unit. We divided the study area into 193 decision units, the proportions of sites with concentrations of Cd, Hg, As, Pb, and Cr exceeding the most stringent risk screening values were 16.4 %, 2.2 %, 4.0 %, 7.6 %, and 0.2 %, respectively. Agricultural activities (livestock manure, fertilizer, sewage irrigation), industrial activities (rare earth ore and tungsten‑molybdenum mining and smelting), and soil parent material are the dominant pollution sources of HMs in the study area. The risk of contamination of each element is ranked from largest to smallest according to the CRS as Cd > Hg > Pb > As > Cr. The western and southwestern water pollution decision units are the areas with the highest risk of soil HMs contamination. This quantitative evaluation framework can provide a relatively accurate decision basis for soil pollution management.

Grain yield trade-offs in spike-branching wheat can be mitigated by elite alleles affecting sink capacity and post-anthesis source activity.

Introducing variations in inflorescence architecture, such as the 'Miracle-Wheat' (Triticum turgidum convar. compositum (L.f.) Filat.) with a branching spike, has relevance for enhancing wheat grain yield. However, in the spike-branching genotypes, the increase in spikelet number is generally not translated into grain yield advantage because of reduced grains per spikelet and grain weight. Here, we investigated if such trade-offs might be a function of source-sink strength by using 385 recombinant inbred lines developed by intercrossing the spike-branching landrace TRI 984 and CIRNO C2008, an elite durum (T. durum L.) cultivar; they were genotyped using the 25K array. Various plant and spike architectural traits, including flag leaf, peduncle, and spike senescence rate, were phenotyped under field conditions for 2 consecutive years. On chromosome 5AL, we found a new modifier QTL for spike branching, branched headt3 (bht-A3), which was epistatic to the previously known bht-A1 locus. Besides, bht-A3 was associated with more grains per spikelet and a delay in flag leaf senescence rate. Importantly, favourable alleles, viz. bht-A3 and grain protein content (gpc-B1) that delayed senescence, are required to improve grain number and grain weight in the spike-branching genotypes. In summary, achieving a balanced source-sink relationship might minimize grain yield trade-offs in Miracle-Wheat.

Comparison of carotenoid, chlorophyll concentrations and their biosynthetic transcript levels in different coloured cauliflower

Carotenoids and chlorophylls are among the most widely distributed pigments in nature that play essential roles in the photosynthetic apparatus and confer diverse colours in plants. Among all vegetables, cauliflower (Brassica oleracea L. ssp. var. botrytis) is rich in phytochemicals and is an important crop grown all over the world. This study investigates carotenoid and chlorophyll concentrations in differently pigmented cultivars and elucidates the role of transcriptional regulation of carotenoid accumulation including lutein and β-carotene. Here, we characterised changes in pigments by UHPLC-DAD-ToF-MS and changes in transcript levels of carotenoid metabolic genes by qRT-PCR in florets and leaves of orange (‘Jaffa’ and ‘Sunset’), purple (‘Di Sicilia Violetto’ and ‘Graffiti’), green (‘Trevi’) and white (‘Clapton’) cultivars. Transcript levels of all carotenoid metabolic genes showed different transcript level patterns in the leaves and florets. Compared to the other cultivars, the orange cultivars had the highest levels of β-carotene in the florets and lutein in the leaves resulting in changes lutein/β-carotene ratios. In the green cultivar, higher transcript levels were also found, especially for phytoene synthase and phytoene desaturase genes of the core biosynthesis pathway. However, no increased carotenoid concentrations were observed, possibly due to a higher carotenoid turnover induced by the carotenoid cleavage dioxygenase 4 in the green cultivar. In the white (‘Clapton’) and purple (‘Di Sicilia Violetto’ and ‘Graffiti’) cultivars the phytoene desaturase transcript levels as well as carotenoid concentrations were low. Chlorophyll concentrations changed in trend comparable to the carotenoid concentrations and were only significantly lower in the leaves of the orange cultivar ‘Jaffa’. Also, the chlorophyll a/b ratio changed in ‘Jaffa’. In florets the highest chlorophylls concentrations were observed for the green cultivar (‘Trevi’) and the purple cultivar (‘Di Sicilia Violetto’). Taken together, the study demonstrates the complex source-sink relationship of carotenoid accumulation in different coloured cauliflower.

Biochar Improves Greenhouse Tomato Yield: Source–Sink Relations under Deficit Irrigation

It is important to evaluate any effects that biochar may have on tomato yield under deficit-irrigation to develop water-saving and yield-increasing best management practices for greenhouse tomato production. For this purpose, greenhouse trials were conducted in 2021 and 2022 with five biochar (B) application rates and three irrigation (W) levels. The B treatments were B0: 0 t ha−1; B1: 15 t ha−1; B2: 30 t ha−1; B3: 45 t ha−1; and B4: 60 t ha−1, and the W levels were W1: 50–70% of field capacity (θf); W2: 60–80% of θf; and W3B0: 70–90% of θf full irrigation without biochar, which was designated as the control. Our objective was to quantify the effects of biochar on the characteristics of tomato sources and sinks to determine, first, the optimal irrigation–biochar combination to achieve high yield tomato production, and, second, evaluate the mechanisms of this effect. At W1 and W2 irrigation levels, the addition of 30–60 t ha−1 and 45–60 t ha−1 biochar could compensate for the adverse effects of deficit-irrigation on the tomato source and sink characteristics. Our results show that in both years the highest tomato yield was obtained with the W2 irrigation level and the B3 biochar application rate, with 52% higher tomato yield compared to the lowest value obtained with the W1 irrigation level and B0 application rate. We conclude that biochar application can improve tomato yield by promoting the filling rather than the building of the sink capacity. The tomato yield was mainly affected by the net photosynthetic rate (Pn), followed by the leaf area, and the leaf chlorophyll content indirectly affected tomato yield through Pn. The W2 irrigation level combined with the B3 biochar application rate resulted in the best water–biochar combination under the experimental conditions.

Coordination of carbon assimilation, allocation, and utilization for systemic improvement of cereal yield.

The growth of yield outputs is dwindling after the first green revolution, which cannot meet the demand for the projected population increase by the mid-century, especially with the constant threat from extreme climates. Cereal yield requires carbon (C) assimilation in the source for subsequent allocation and utilization in the sink. However, whether the source or sink limits yield improvement, a crucial question for strategic orientation in future breeding and cultivation, is still under debate. To narrow the knowledge gap and capture the progress, we focus on maize, rice, and wheat by briefly reviewing recent advances in yield improvement by modulation of i) leaf photosynthesis; ii) primary C allocation, phloem loading, and unloading; iii) C utilization and grain storage; and iv) systemic sugar signals (e.g., trehalose 6-phosphate). We highlight strategies for optimizing C allocation and utilization to coordinate the source-sink relationships and promote yields. Finally, based on the understanding of these physiological mechanisms, we envisage a future scenery of "smart crop" consisting of flexible coordination of plant C economy, with the goal of yield improvement and resilience in the field population of cereals crops.

Relatively high light inhibits reserves degradation in the Coptis chinensis rhizome during the leaf expansion by changing the source-sink relationship.

The early spring is a seasonal high-light "window" for new leaf growth and photosynthetic carbon capture by the shade-tolerant evergreen understory plants. However, it remains unclear how light regulates the source-sink relationship between rhizome (RO), mature leaf (ML), and immature leaf (IL) during Coptis chinensis leaf expansion. Understanding this relationship is essential to reducing RO reserve degradation and ultimately promote RO biomass accumulation. The plants grew in an artificial climate chamber with low (50 μmol m-2 s-1) and relatively high (200 μmol m-2 s-1) light intensity treatments. Leaf fluorescence, foliar phosphorus (P) fractions, soluble sugars, starch, total P, and alkaloid concentrations in ILs, MLs, and RO were measured, and 13C labeling was used to indicate the direction of photosynthetic carbon flow between organs. The plants grown under high light intensity had higher levels of starch in RO and higher RO biomass at the end of the year compared to those grown under low light intensity. The photosystem II (PSII) operating efficiency [Y(II)], relative electron transport rate (rETR), and photochemical quenching (qP), as well as sucrose and glucose, in ILs and MLs under relatively high light, was higher than those under low light. The glucose and starch concentrations in ILs at 35d was significantly higher than that at 15d when plants were under 200 μmol m-2 s-1, while they were not significantly changed and remained low at 50 μmol m-2 s-1. The 13C was detected in the RO when plants were grown at 200 μmol m-2 s-1, regardless of ILs and MLs 13C labeling, while no 13C was detected in the RO when plants were under 50 μmol m-2 s-1. Additionally, the proportion of photosynthetic transport from ILs to MLs was significantly higher than that from MLs to ILs under the 50-μmol m-2 s-1 limit. Total P concentration in ILs was lower under relatively high light, but there was no difference in nucleic acid P concentration in ILs under the two light intensity treatments. The alkaloid concentration in RO was lower under 200 μmol m-2 s-1 than that under 50 μmol m-2 s-1. We propose that relatively high light reduces the need for carbohydrates and P stored in the RO to support IL growth by (1) accelerating the sink-to-source transition in ILs, which inhibits the use of reserves in the RO; (2) using energy from MLs to support IL growth, thereby reducing RO reserve consumption, and (3) reducing the demand for P by investing less in the development of photosynthetic machinery. Furthermore, under low light, MLs serve as a sink and rely on other organs for support, directly or indirectly exacerbating the reserves lost in the RO.

Starch depletion in the xylem and phloem ray parenchyma of grapevine stems under drought.

While nonstructural carbohydrate (NSC) storage can support long-lived woody plants during abiotic stress, the timing and extent of their use are less understood, as are the thresholds for cell mortality as NSCs and water supplies are consumed. Here, we combine physiological and imaging tools to study the response of Vitis riparia to a 6-week experimental drought. We focused on the spatial and temporal dynamics of starch consumption and cell viability in the xylem and phloem of the stem. Starch dynamics were further corroborated with enzymatic starch digestion and X-ray microcomputed tomography imaging. Starch depletion in the stems of droughted plants was detected after 2 weeks and continued over time. We observed distinct differences in starch content and cell viability in the xylem and phloem. By the end of the drought, nearly all the starch was consumed in the phloem ray parenchyma (98 % decrease), and there were almost no metabolically active cells in the phloem. In contrast, less starch was consumed in the xylem ray parenchyma (30 % decrease), and metabolically active cells remained in the ray and vessel-associated parenchyma in the xylem. Our data suggest that the higher proportion of living cells in the phloem and cambium, combined with smaller potential NSC storage area, rapidly depleted starch, which led to cell death. In contrast, the larger cross-sectional area of the xylem ray parenchyma with higher NSC storage and lower metabolically active cell populations depleted starch at a slower pace. Why NSC source-sink relationships between xylem and phloem do not allow for a more uniform depletion of starch in ray parenchyma over time is unclear. Our data help to pinpoint the proximate and ultimate causes of plant death during prolonged drought exposure and highlight the need to consider the influence of within-organ starch dynamics and cell mortality on abiotic stress response.

Triose phosphate utilization in leaves is modulated by whole-plant sink-source ratios and nitrogen budgets in rice.

Triose phosphate utilization (TPU) is a biochemical process indicating carbon sink-source (im)balance within leaves. When TPU limits leaf photosynthesis, photorespiration-associated amino acid exports probably provide an additional carbon outlet and increase leaf CO2 uptake. However, whether TPU is modulated by whole-plant sink-source relations and nitrogen (N) budgets remains unclear. We address this question by model analyses of gas-exchange data measured on leaves at three growth stages of rice plants grown at two N levels. Sink-source ratio was manipulated by panicle pruning, by using yellower-leaf variant genotypes, and by measuring photosynthesis on adaxial and abaxial leaf sides. Across all these treatments, higher leaf N content resulted in the occurrence of TPU limitation at lower intercellular CO2 concentrations. Photorespiration-associated amino acid export was greater in high-N leaves, but was smaller in yellower-leaf genotypes, panicle-pruned plants, and for abaxial measurement. The feedback inhibition of panicle pruning on rates of TPU was not always observed, presumably because panicle pruning blocked N remobilization from leaves to grains and the increased leaf N content masked feedback inhibition. The leaf-level TPU limitation was thus modulated by whole-plant sink-source relations and N budgets during rice grain filling, suggesting a close link between within-leaf and whole-plant sink limitations.