Source-sink Relationships Research Articles

Production Potential of Pigeon Pea [Cajanus cajan (L.) Millsp.] as Influenced by Crop Geometry and Plant Growth Regulators

Background: Pigeonpea being highly branching and indeterminate growth habit responds very well to crop geometry. Hence to achieve potential yields, it is important to maintain optimum plant population which can effectively utilize available moisture, nutrients and solar radiation. The plant growth regulators are also known to enhance the source sink relationship and stimulate the translocation of photo assimilates, thereby increase the productivity. Methods: A field experiment was conducted at experimental farm of Agronomy Department, V.N.M.K.V., Parbhani during kharif season of 2018 and 2019. The experiment was laid out in split plot design with four main plot treatments comprised of four crop geometries as 90 cm x 20 cm, 120 cm x 20 cm 60-120 cm x 20 cm and 75-150 cm x 20 cm and sub plot treatments were five treatments on foliar application of plant growth regulators i.e. NAA @ 40 ppm, Mepiquat chloride @ 50 g a.i. ha-1, Brassinosteroids @ 0.1 ppm, Chlormequat Chloride @ 75 g a.i ha-1 and control. Result: The crop geometry of 120 cm x 20 cm and 75-150 cm x 20 cm recorded higher values of all yield parameters followed by crop geometry of 60-120 cm x 20 cm. While the seed, straw and biological yield of pigeonpea as well as highest net realization of Rs. 72072 ha-1 was obtained with crop geometry of 60-120 cm x 20 cm followed by 90 cm x 20 cm. Among the plant growth regulators foliar application of Brassinosteroids @ 0.1 ppm (G3) tended to recorded higher yield parameters, seed yield and fertility coefficient of pigeonpea as well as highest net realization followed by foliar application of NAA @ 40 ppm.

A fungal powdery mildew pathogen induces extensive local and marginal systemic changes in the Arabidopsis thaliana microbiota.

Powdery mildew is a foliar disease caused by epiphytically growing obligate biotrophic ascomycete fungi. How powdery mildew colonization affects host resident microbial communities locally and systemically remains poorly explored. We performed powdery mildew (Golovinomyces orontii) infection experiments with Arabidopsis thaliana grown in either natural soil or a gnotobiotic system and studied the influence of pathogen invasion into standing natural multi-kingdom or synthetic bacterial communities (SynComs). We found that after infection of soil-grown plants, G. orontii outcompeted numerous resident leaf-associated fungi while fungal community structure in roots remained unaltered. We further detected a significant shift in foliar but not root-associated bacterial communities in this setup. Pre-colonization of germ-free A. thaliana leaves with a bacterial leaf-derived SynCom, followed by G. orontii invasion, induced an overall similar shift in the foliar bacterial microbiota and minor changes in the root-associated bacterial assemblage. However, a standing root-derived SynCom in root samples remained robust against foliar infection with G. orontii. Although pathogen growth was unaffected by the leaf SynCom, fungal infection caused a twofold increase in leaf bacterial load. Our findings indicate that G. orontii infection affects mainly microbial communities in local plant tissue, possibly driven by pathogen-induced changes in source-sink relationships and host immune status.

Ratoon Stunting Disease (Leifsonia xyli subsp. xyli) affects source-sink relationship in sugarcane by decreasing sugar partitioning to tillers

Ratoon Stunting Disease, caused by the bacterium Leifsonia xyli subsp. xyli (Lxx), decreases sugarcane yield by reducing culm growth and tillering, especially in plants with high Lxx titers when the symptoms are more severe. The role of Lxx titers in affecting sugar partitioning and sugarcane growing is still unclear. We hypothesized that high Lxx titers affect source-sink relationship by causing physiological changes in the sugarcane that reduces sugar partitioning to tillers. The study was carried out with susceptible sugarcane genotype CB49260, evaluating physiological traits and biomass production in plants with low (158 ± 28 Lxx cells per 100 ng of plant DNA) and high Lxx titers (2090 ± 385 Lxx cells per 100 ng of plant DNA). Overall, the level of bacterial titers affected sugarcane growth through changes in ethylene level, sugar and biomass partitioning. Plants with high Lxx titers presented a lower number and biomass allocation to tillers than low Lxx titers. Additionally, plants with high Lxx titers had higher biomass allocation to the main culm than low Lxx titers plants due to greater sucrose and starch contents in the main culm caused by the higher number of cell parenchyma, decreased soluble acid invertase activity, and low number of tillers. Changes in sugar and biomass partitioning in plants with high Lxx titers were associated with low release of ethylene in the leaf and culm. Sugarcane with high Lxx titers presented physiological changes that restricted sugar supply for tillering, resulting in a decrease in the number and biomass allocation to the tillers.

Ethephon-Induced Ethylene Enhances Protein Degradation in Source Leaves, but Its High Endogenous Level Inhibits the Development of Regenerative Organs in Brassica napus.

To investigate the regulatory role of ethylene in the source-sink relationship for nitrogen remobilization, short-term effects of treatment with different concentrations (0, 25, 50, and 75 ppm) of ethephon (2-chloroethylphosphonic acid, an ethylene inducing agent) for 10 days (EXP 1) and long-term effects at 20 days (Day 30) after treatment with 100 ppm for 10 days (EXP 2) on protein degradation and amino acid transport in foliar sprayed mature leaves of Brassica napus (cv. Mosa) were determined. In EXP 1, endogenous ethylene concentration gradually increased in response to the treated ethephon concentration, leading to the upregulation of senescence-associated gene 12 (SAG12) expression and downregulation of chlorophyll a/b-binding protein (CAB) expression. Further, the increase in ethylene concentration caused a reduction in protein, Rubisco, and amino acid contents in the mature leaves. However, the activity of protease and expression of amino acid transporter (AAP6), an amino acid transport gene, were not significantly affected or slightly suppressed between the treatments with 50 and 75 ppm. In EXP 2, the enhanced ethylene level reduced photosynthetic pigments, leading to an inhibition of flower development without any pod development. A significant increase in protease activity, confirmed using in-gel staining of protease, was also observed in the ethephon-treated mature leaves. Ethephon application enhanced the expression of four amino acid transporter genes (AAP1, AAP2, AAP4, and AAP6) and the phloem loading of amino acids. Significant correlations between ethylene level, induced by ethephon application, and the descriptive parameters of protein degradation and amino acid transport were revealed. These results indicated that an increase in ethylene upregulated nitrogen remobilization in the mature leaves (source), which was accompanied by an increase in proteolytic activity and amino acid transport, but had no benefit to pod (sink) development.

Cytosolic phosphofructokinases are important for sugar homeostasis in leaves of Arabidopsis thaliana.

ATP-dependent phosphofructokinases (PFKs) catalyse phosphorylation of the carbon-1 position of fructose-6-phosphate, to form fructose-1,6-bisphosphate. In the cytosol, this is considered a key step in channelling carbon into glycolysis. Arabidopsis thaliana has seven genes encoding PFK isoforms, two chloroplastic and five cytosolic. This study focuses on the four major cytosolic isoforms of PFK in vegetative tissues of A. thaliana. We isolated homozygous knockout individual mutants (pfk1, pfk3, pfk6 and pfk7) and two double mutants (pfk1/7 and pfk3/6), and characterized their growth and metabolic phenotypes. In contrast to single mutants and the double mutant pfk3/6 for the hypoxia-responsive isoforms, the double mutant pfk1/7 had reduced PFK activity and showed a clear visual and metabolic phenotype with reduced shoot growth, early flowering and elevated hexose levels. This mutant also has an altered ratio of short/long aliphatic glucosinolates and an altered root-shoot distribution. Surprisingly, this mutant does not show any major changes in short-term carbon flux and in levels of hexose-phosphates. We conclude that the two isoforms PFK1 and PFK7 are important for sugar homeostasis in leaf metabolism and apparently in source-sink relationships in A. thaliana, while PFK3 and PFK6 only play a minor role under normal growth conditions.

Cone-Bearing Branches of Pinus koraiensis Are Not Carbon Autonomous during Cone Development

Cone development in conifer species is crucial to ensure sexual regeneration. A better understanding of carbon (C) source-sink relations at the branch level can guide strategies for improving resource allocation to reproduction. In particular, the evaluation of C relations between vegetative and reproductive branches is helpful to test whether tree branches are carbon autonomous. With this aim, we integrated girdling and defoliation treatments with 13C pulse labeling in situ to evaluate C autonomy in cone-bearing branches of P. koraiensis during the growing season. Girdling significantly reduced branch volumetric development, branch biomass, and non-structural carbohydrates across foliar, twig, and cone tissues; it also arrested cone development. Defoliation effects on these variables were minor, although they tended to increase with defoliation intensity. In addition, 13C increased by 4.5% and 45.4% after 4 h and 24 h of 13C labeling in unlabeled cone-bearing branches, respectively, indicating the C translocation from labeled vegetative branches. These results indicate that the cone-bearing branches are not C autonomous and that the development of female cones relies to a great extent on C import from neighboring branches. However, the amount of C translocated was largely dependent on manipulative alterations of the source-sink balance, thereby denoting extensive plasticity in the degree of branch C autonomy. These results shed light on the reproductive physiology of P. koraiensis.

Density‐ and moisture‐dependent effects of arbuscular mycorrhizal fungus on drought acclimation in wheat

Arbuscular mycorrhizal fungus (AMF) is widely viewed as an ecosystem engineer to help plants adapt to adverse environments. However, a majority of the previous studies regarding AMF's eco-physiological effects are mutually inconsistent. To clarify this fundamental issue, we conducted an experiment focused on wheat (Triticum aestivum L.) plants with or without AMF (Funneliformis mosseae) inoculation. Two water regimes (80% and 40% field water capacity, FWC80 (CK) and FWC40 (drought stress) and four planting densities (6 or 12 plants per pot as low densities, 24 or 48 plants per pot as high densities) were designed. AMF inoculation did not show significant effects on shoot biomass, grain yield, and water use efficiency (WUE) under the low densities, regardless of water regimes. However, under the high densities, AMF inoculation significantly decreased shoot biomass, grain yield and WUE in FWC80, while it significantly increased these parameters in FWC40, showing density and/or moisture-dependent effects of AMF on wheat performance. In FWC40, the relationships between reproductive biomass (y-axis) vs. vegetative biomass (x-axis) (R-V), and between grain biomass (y-axis, sink) vs. leaf biomass (x-axis, source) fell into a typical allometric pattern (α > 1, P < 0.001), and the AMF inoculation significantly increased the values of α. Yet in FWC80, they were in an isometric pattern (α ≈ 1, P < 0.001) and AMF addition had no significant effects on α. Similarly, AMF did not significantly change the isometric relationship between leaf biomass (i.e., metabolic rate) and shoot biomass (body size) in FWC80, while it significantly decreased the α of allometric relationship between both of them in FWC40 (α > 1, P < 0.001). We therefore, sketched a generalized model of R-V and sink-source relationships as affected by AMF, in which AMF inoculation might enhance the capabilities of sink acquisition and utilization under drought stress, while having no significant effect under the well watered conditions. Our findings demonstrate dual density- and moisture-dependent effects of AMF on plant development and provide new insights into current ecological applications of AMF as an ecosystem engineer.

Glucan, Water-Dikinase 1 (GWD1), an ideal biotechnological target for potential improving yield and quality in rice.

SummaryThe source–sink relationship determines the overall agronomic performance of rice. Cloning and characterizing key genes involved in the regulation of source and sink dynamics is imperative for improving rice yield. However, few source genes with potential application in rice have been identified. Glucan, Water‐Dikinase 1 (GWD1) is an essential enzyme that plays a pivotal role in the first step of transitory starch degradation in source tissues. In the present study, we successfully generated gwd1 weak mutants by promoter editing using CRISPR/Cas9 system, and also leaf‐dominant overexpression lines of GWD1 driven by Osl2 promoter. Analysis of the gwd1 plants indicated that promoter editing mediated down‐regulation of GWD1 caused no observable effects on rice growth and development, but only mildly modified its grain transparency and seed germination. However, the transgenic pOsl2::GWD1 overexpression lines showed improvements in multiple key traits, including rice yield, grain shape, rice quality, seed germination and stress tolerance. Therefore, our study shows that GWD1 is not only involved in transitory starch degradation in source tissues, but also plays key roles in the seeds, which is a sink tissue. In conclusion, we find that GWD1 is an ideal biotechnological target with promising potential for the breeding of elite rice cultivars via genetic engineering.

Cytokinin Regulation of Source-Sink Relationships in Plant-Pathogen Interactions.

Cytokinins are plant hormones known for their role in mediating plant growth. First discovered for their ability to promote cell division, this class of hormones is now associated with many other cellular and physiological functions. One of these functions is the regulation of source-sink relationships, a tightly controlled process that is essential for proper plant growth and development. As discovered more recently, cytokinins are also important for the interaction of plants with pathogens, beneficial microbes and insects. Here, we review the importance of cytokinins in source-sink relationships in plants, with relation to both carbohydrates and amino acids, and highlight a possible function for this regulation in the context of plant biotic interactions.

Promotion of potato yield under moderate water deficiency at the seedling stage by modifying sink-source relationship

ABSTRACT Water deficiency is the main bottleneck in potato production in many regions worldwide. The generation of higher tuber yields per unit of water is a key goal for both agronomists and potato growers. In this study, we found that under moderate deficit irrigation (DI; 50% relative water content (RWC)) at the seedling stage of potato growth, the leaf area index (LAI) and dry matter accumulation were lower than control; however, they caught up with and surpassed the control at later developmental stages with a normal water supply, and a higher yield was ultimately achieved. The LAI and total dry weight under severe water stress (35% RWC) also surpassed the control at harvest; however, the final yield remained low, due to the low distribution of dry matter into the tubers. Abscisic acid (ABA) increased under DI conditions at the seedling stage, while gibberellin (GA1 and GA3) levels decreased. Moreover, endogenous ABA increased as plant development proceeded from seedling stage to tuber initiation stage, regardless of water stress. Exogenous ABA application promoted dry matter accumulation and distribution into the tubers. Therefore, it may be that ABA, as a major signaling molecule, mediates water stress to regulate tuber sink capacity at early development period. Through a feedback regulation stronger source capacity was stimulated by sink enhancement mediated by moderate water stress at the seedling stage, reached a higher tuber yield finally by reestablishment of sink-source relationship.

Low‐temperature stress during the flowering period alters the source–sink relationship and grain quality in field‐grown late‐season rice

AbstractLate‐season rice, a major contributor to the production of high‐quality rice in China, often experiences low temperatures during the flowering period. The objective of this study was to determine the effect of low temperature stress on grain quality and to identify related physiological factors in late‐season rice. Sink and source characteristics and grain quality traits of two high‐quality late‐season rice cultivars were compared between a year in which low temperatures occurred during the flowering period (2020) and a normal year (2019) under field conditions. Low temperatures during the flowering period in 2020 resulted in a reduction in spikelet filling and consequent increases in source–sink ratios and grain weight and N content compared to 2019. The head rice rate and protein content of the milled rice were increased in 2020 compared to 2019. Starch gel consistency and peak, trough, breakdown, final, and consistency viscosities were reduced while setback viscosity, paste temperature, and texture properties (hardness, springiness, cohesiveness, resilience, and chewiness) were increased for milled rice (or milled rice flour or cooked milled rice) in 2020 compared to 2019. The glucose production rate and total glucose production from in vitro digestion of cooked milled rice was reduced in 2020 compared to 2019. The results of this study suggest that low temperature stress during the flowering period can improve milling, nutritional, and health qualities but reduce the cooking and eating quality in late‐season rice by altering the source–sink relationship.

减库对大豆叶片碳代谢的影响

<p id="C3">Carbon metabolism is one of the most obvious physiological processes affected by source-sink relationship, which is closely related to plant growth and yield formation. The study of the effect of sink-limiting treatment on carbon metabolism of soybean leaf can provide a theoretical basis for understanding yield reduction mechanism caused by the imbalance of source-sink relationship. Taking early maturing soybean Sudou 13 as materials, pool experiments were carried out at the soybean experimental station of Jiangsu Academy of Agricultural Sciences in 2019 and 2020. The sink-limiting treatments (all pods removal, 1/2 pods removal, and all seed injury) were conducted at R4 stage, and intact (fully podded) plants were used as control. The results showed that sink-limiting treatments delayed leaf senescence and abscission and caused stay-green. Sink-limiting treatments inhibited the net photosynthetic rate (<italic>P</italic>_n) in a short time after treatment, but did not affect the initial carboxylation rate (ɑ), and the decrease of <italic>P</italic>_n was mainly restricted by stomata limitation. With the prolongation of the time after treatment, the inhibition effect on photosynthesis gradually weakened and turned into a promoting effect. At late growth stages, the stay-green syndrome leaves still maintain relatively higher initial carboxylation rate (<italic>a</italic>), sugar phosphate synthase (SPS), sucrose synthase (SuSy), acid invertase (SAI) activity, photosynthetic pigment, soluble sugar, starch, sucrose, and fructose content, which was beneficial to maintaining a relatively high photosynthetic performance. Sink-limiting treatments induced more photosynthetic products to be distributed to vegetative organs, and stimulated stems and leaves to be new sink organs in certain extent, which was beneficial to the output of photosynthetic products and maintained relatively high levels of carbon metabolism of leaves at late growth stages. The effects of removing all pods and seed injury treatments on delaying leaf senescence and abscission, reducing photosynthetic performance and carbon metabolism was significantly higher than those of removing 1/2 pod. In conclusion, sink-limiting under the same source condition could induce stay-green syndrome. The greater the degree of sink-limiting, the more severe the green retention. Sink-limiting treatment significantly affected the carbon metabolism of soybean plant, although it inhibited photosynthetic performance in a short period after treatment. It maintained higher photosynthetic and key enzyme activities of carbon metabolism at late growth stages, which was conducive to the synthesis of more carbohydrates and stimulated the stems, leaves, and petioles to transform into new sink organs to a certain extent.

Potential linkages between juvenile nurseries and exploited populations of Mulloway (Argyrosomus japonicus), explored using otolith chemistry

Many exploited coastal species rely on estuarine nurseries, however, the importance of different estuaries and their contribution to exploited populations can vary. Identification of connectivity between source nurseries and exploited populations is important for effective habitat and fishery management. We present a case study which employs otolith chemistry to investigate source-sink population dynamics across broad spatial scales for an exploited migratory sciaenid, Mulloway (Argyrosomus japonicus). Specifically, we compared the otolith chemical fingerprints of juveniles in putative estuarine nurseries across south-eastern Australia with the sub-yearling chemical fingerprints of post-recruited fish in the exploited component of the stock. Multinomial Logistic Regression (MLR) suggested that two of the eight estuarine nurseries sampled were particularly important sources of Mulloway recruits, and there was strong evidence of stock mixing which exceeded that expected from historic tag-recapture studies. However, there was some uncertainty in the patterns resolved. Variation in otolith signatures between the known-source juveniles and post-recruit fish may be explained by inter-annual variability in these systems, caused by extensive flooding on the central and northern-NSW coast during the study period. These events contributed considerable extrinsic variation to the chemical composition, influencing the lack of overlap between otolith chemistry of putative nurseries and sub-yearling otolith chemistry of exploited fish. The approach presented highlights the importance of considering inter-annual variability when examining source-sink relationships in long-lived species, but the use of otolith fingerprints shows promise for evaluating these questions for both Mulloway and other exploited fish species.

Growth and sink-source relationship of cotton (Gossypium hirsutum L.) under mulched drip irrigation in response to phosphorus fertilization and cultivar

Crop yield highly associates with biomass accumulation and distribution in sink and source organs. Nutrient is critical for the translocation of photo-assimilate to sink and increases crop yield. This study was to evaluate the biomass accumulation and distribution in three cotton cultivars and how it was affected by the phosphorus (P) fertilization rates (0, 75, 150, and 400 kg P2O5 hm−2) under plastic film mulched drip irrigation. Results showed that maximum aboveground dry weight (DW) appeared at 150 days after planting (DAP). There were significant differences between P rates in dry weight of total, and organs, seed cotton yield, yield components and reproductive-vegetative ratio (RVR). The seed cotton yield at optimal P rate (150 kg P2O5 hm−2) was 20.7% higher than at P-free control (0 kg P2O5 hm−2). The boll weight at 150 kg P2O5 hm−2 was significantly higher than those at 0 and 400 kg P2O5 hm−2. The final total DW at 150 kg P2O5 hm−2 was 17.2% higher than 0 kg P2O5 hm−2 treatment. The RVR at flower stage at 150 kg P2O5 hm−2 was 22.4% higher than 0 kg P2O5 hm−2 treatment. A cross all years and P rates, the final total plant DW and seed cotton yield of cultivars XLZ57 was 20.6% and 22.2% higher than other two cultivars, respectively. Significant interactions between cultivars and P rates were found in cotton yield and DW during the growing season. The results would help farmers to optimize cotton managements under plastic film mulched drip irrigation.

Physiological and Expressional Regulation on Photosynthesis, Starch and Sucrose Metabolism Response to Waterlogging Stress in Peanut.

Waterlogging has negative effects on crop yield. Physiological and transcriptome data of two peanut cultivars [Zhongkaihua 1 (ZKH 1) and Huayu 39 (HY 39)] were studied under normal water supply and waterlogging stress for 5 or 10 days at the flowering stage. The results showed that the main stem height, the number of lateral branches, lateral branch length, and the stem diameter increased under waterlogging stress, followed by an increase in dry matter accumulation, which was correlated with the increase in the soil and plant analysis development (SPAD) and net photosynthetic rate (Pn) and the upregulation of genes related to porphyrin and chlorophyll metabolism and photosynthesis. However, the imbalance of the source–sink relationship under waterlogging was the main cause of yield loss, and waterlogging caused an increase in the sucrose and soluble sugar contents and a decrease in the starch content; it also decreased the activities of sucrose synthetase (SS) and sucrose phosphate synthetase (SPS), which may be due to the changes in the expression of genes related to starch and sucrose metabolism. However, the imbalance of the source–sink relationship led to the accumulation of photosynthate in the stems and leaves, which resulted in the decrease of the ratio of pod dry weight to total dry weight (PDW/TDW) and yield. Compared with ZKH 1, the PDW of HY 39 decreased more probably because more photosynthate accumulated in the stem and leaves of HY 39 and could not be effectively transported to the pod.

Alterations in Source-Sink Relations Affect Rice Yield Response to Elevated CO2: A Free-Air CO2 Enrichment Study.

To understand the effects of source-sink relationships on rice yield response to elevated CO2 levels (eCO2), we conducted a field study using a popular japonica cultivar grown in a free-air CO2 enrichment environment in 2017–2018. The source-sink ratio of rice was set artificially via source-sink treatments (SSTs) at the heading stage. Five SSTs were performed in 2017 (EXP1): cutting off the flag leaf (LC1) and the top three functional leaves (LC3), removing one branch in every three branches of a panicle (SR1/3) and one branch in every two branches of a panicle (SR1/2), and the control (CK) without any leaf cutting or spikelet removal. The eCO2 significantly increased grain yield by 15.7% on average over all treatments; it significantly increased grain yield of CK, LC1, LC3, SR1/3, and SR1/2 crops by 13.9, 18.1, 25.3, 12.0, and 10.9%, respectively. The yield response to eCO2 was associated with a significant increase of panicle number and fully-filled grain percentage (FGP), and the response of crops under different SSTs was significantly positively correlated with FGP and the average grain weight of the seeds. Two SSTs (CK and LC3) were performed in 2018 (EXP2), which confirmed that the yield response of LC3 crops (25.1%) to eCO2 was significantly higher than that of CK (15.9%). Among the different grain positions, yield response to eCO2 of grains attached to the lower secondary rachis was greater than that of grains attached to the upper primary rachis. Reducing the source-sink ratio via leaf-cutting enhanced the net photosynthetic rate response of the remaining leaves to eCO2 and increased the grain filling ability. Conversely, spikelet removal increased the non-structural carbohydrate (NSC) content of the stem, causing feedback inhibition and photosynthetic down-regulation. This study suggests that reducing the source-sink ratio by adopting appropriate management measures can increase the response of rice to eCO2.

Spatio-temporal variability in soil CO2 efflux and regulatory physicochemical parameters from the tropical urban natural and anthropogenic land use classes

Urban ecosystems, the heterogeneous and rapidly changing landscape, showed a considerable impact on the global C cycle. However, studies encompassing the spatial differences in urban land uses on soil C dynamics are limited in tropical ecosystems. In this study, seasonal and temporal variability in soil CO2 efflux (SCE) and its regulatory physicochemical variables under five urban land use classes viz., Bare (BAR), Agriculture (AGR), Plantation (PLT), Grassland (GRA) and Lawns (LAW) were assessed from 2014 to 2016. Bare land use was considered as the reference for observing the variation for different land uses. Seasonal measurements of SCE, soil temperature, moisture content, pH, ammonium-N, nitrate-N and microbial biomass C (MBC) were performed whereas soil organic C (SOC), soil N, and soil physical properties were measured annually. Our results showed a significant (P < 0.01) increase in SCE by 89%, 117%, 132% and 166% for land use types from BAR to AGR, PLT, GRA and LAW, respectively. The results revealed a two-fold increase in SCE from anthropogenically managed urban lawns as compared to bare soil. PLT and LAW land use classes showed higher SOC and N contents. SCE was found positively correlated with temperature, moisture, SOC, soil N and MBC whereas negatively correlated with ammonium-N and nitrate-N (at P < 0.05) for the overall dataset. Soil moisture, temperature, SOC, porosity and pH were identified as the major determinant of urban SCE by explaining 63% of the variability in overall SCE. Further, temperature for BAR and LAW; moisture for PLT; ammonium-N for GRA; and nitrate-N for AGR were identified as the major regulators of SCE for different land use classes. The findings revealed that the interaction of soil temperature and moisture with nutrient availability regulates overall and seasonal variability in SCE in an urban ecosystem. Since these variables are highly affected by climate change, thus, the soil C source-sink relationships in tropical urban ecosystems may further change and induce a positive global warming potential from urban ecosystems.

Boll-leaf system gas exchange and its application in the analysis of cotton photosynthetic function.

Estimating the boll development and boll yield from single-leaf photosynthesis is difficult as the source-sink relationship of cotton (Gossypium hirsutum L.) is complicated. As the boll-leaf system (BLS), which includes the main-stem leaf, sympodial leaf, and non-leaf organs, is the basic unit of the cotton source-sink relationship and yield formation, the concept of "BLS photosynthesis" is introduced in this study. We speculate that the characteristics of BLS gas exchange can more accurately reflect the photosynthetic function of the system, thus revealing the law of photosynthesis in the process of boll development. The results showed that the photosynthetic rate of single leaves measured by a BLS chamber was consistent with that measured by a standard single-leaf chamber. BLSs exhibited typical light response curves, and the shape of the curves was similar to those of single leaves. The light compensation point and respiration rate of BLSs were higher than those of single leaves, while the apparent quantum efficiency of BLSs was lower. Compared with single leaves, the duration of the photosynthetic function of BLSs was longer. Increasing plant density decreased the gas exchange rate per unit BLS more significantly under field conditions. There was a better linear correlation between the net CO2 assimilation rate, respiration rate of BLSs and boll biomass. Therefore, we think that the gas exchange of BLSs can better reveal the changes in photosynthetic function of BLSs and boll development. This provides a new basis for analyzing the mechanism and regulation of cotton yield formation.

Single boll weight depends on photosynthetic function of boll-leaf system in field-grown cotton plants under water stress.

Cotton has many leaves and even more bolls, which results in a complicated source-sink relationship. Under water stress, the single boll weight (SBW) of cotton remains relatively stable, while both the leaf area and leaf photosynthetic rate decrease greatly. It is therefore difficult to understand how the formation of SBW is regulated under water stress solely by considering single-leaf photosynthesis. Considering the cotton boll-leaf system (BLS: including the main-stem leaf, sympodial leaves, and non-leaf organs) as the basic unit of the cotton canopy, we speculated that the formation of SBW may depend on photosynthesis in the corresponding BLS under water stress. To verify this hypothesis, five water treatments were set up in the field. The results showed that with increasing water stress, the relative water content (RWC) of the main-stem and sympodial leaves decreased gradually, and the decrease in the sympodial leaves was more obvious. The SBW and the number of BLSs decreased slightly with increasing water stress, while the number of bolls per plant decreased significantly. The area of the BLS decreased gradually with increasing water stress, and the area of sympodial leaves decreased more than that of the main-stem leaves. Gas exchange showed that the photosynthetic rate of the BLS (Pn(BLS)) decreased gradually with increasing water stress. In addition, the single-leaf photosynthesis and carboxylation efficiency (CE) decreased progressively and rapidly with the increase of water stress. Compared with the main-stem leaf, the photosynthetic function of the sympodial leaf decreased more. Further analysis showed that compared with leaf photosynthetic rate, there was a better correlation between Pn(BLS) and SBW. Thus, the formation of SBW mainly depends on Pn(BLS) under water stress, and the increase of BLS to boll is also helpful to maintain SBW to some extent. In BLS, the photosynthesis of the main-stem leaf plays a very important role in maintaining the stability of SBW, while the photosynthetic performance in sympodial leaves may be regulated plastically to influence SBW.

Dissecting Source-Sink Relationship of Subtending Leaf for Yield and Fiber Quality Attributes in Upland Cotton (Gossypium hirsutum L.).

Photosynthesis as a source is a significant contributor to the reproductive sink affecting cotton yield and fiber quality. Moreover, carbon assimilation from subtending leaves adds up a significant proportion to the reproductive sink. Therefore, this study aimed to address the source-sink relationship of boll subtending leaf with fiber quality and yield related traits in upland cotton. A core collection of 355 upland cotton accessions was subjected to subtending leaf removal treatment effects across 2 years. The analysis of variance suggested a significant effect range in the source-sink relationship under subtending leaf removal effects at different growth stages. Further insight into the variation was provided by the correlation analysis and principal component analysis. A significant positive correlation between different traits was observed and the multivariate analysis including hierarchical clustering and principal component analysis (PCA) categorised germplasm accessions into three groups on the basis of four subtending leaf removal treatment effects across 2 years. A set of genotypes with the lowest and highest treatment effects has been identified. Selected accessions and the outcome of the current study may provide a basis for a further study to explore the molecular mechanism of source-sink relationship of boll subtending leaf and utilization of breeding programs focused on cotton improvement.