Source-sink Interactions Research Articles

Simulation of source sink partitioning in wheat under varying nitrogen regimes using DSSAT-CERES-wheat model

Grain yields in wheat can be limited by the assimilate supply (source) or by the carbohydrate demand of the grains (sink). Recently, there have been questions regarding the capability of crop models to simulate the physiology of source-sink interactions in crops; however, crop models scarcely tested with source-sink partitioning. DSSAT_CERES_Wheat model was used with details of field experimental data having treatments of manipulated source (i.e., assimilate supply), sink (i.e., kernel number). The aim of the present study was to assess the impact of different levels of nitrogen and source-sink manipulation on wheat crop and to model source-sink partitioning in wheat under varying N-Regimes and climatic conditions. The experiment was conducted during wheat growing seasons of 2015–16 and 2016–17, at two locations (Islamabad and URF Koont Chakwal), under five different levels of nitrogen and three source sink treatments (Control (100 % RUE), 50 % shading pre-anthesis (50 % RUE), 50 % spike removal i.e. spike halving) using randomized complete block design. Recommended rates of fertilizer were applied with the exception of nitrogen which was 0, 50, 100, 150 and 200 kg ha−1, while each treatment was replicated thrice. CERES-Wheat model was calibrated using 2015–16 observed data while model was evaluated using two-year field collected data of two sites i.e. Islamabad and Chakwal. The model was able to simulate treatments impacts on phenology (R2, RMSE and d-index values of 0.89, 2.80 days and 0.97 respectively at Islamabad while at Chakwal R2 = 0.89, RMSE = 2.65 days and d-index = 0.94), leaf area index (R2 = 0.94, 0.94, RMSE = 0.51, 0.38 and d-index = 0.98 and 0.92 at Islamabad and Chakwal respectively), biomass (R2 = 0.98, 0.96, RMSE = 370, 450 kg ha−1 and d-index = 0.96 and 0.95 at Islamabad and Chakwal respectively), grain yield (R2 = 0.97,0.96, RMSE = 0.17, 0.2 t ha−1, and d-index = 0.95 and 0.93 at Islamabad and Chakwal respectively), harvest index, soil nitrogen, crop nitrogen and grain nitrogen with good accuracy. The observed range for biomass water use efficiency (BM_WUE) was 34.1–14.5 kg ha−1 mm−1 while grain WUE remained in the range of 10.3–3.7 kg ha−1 mm−1. The results depicted that model could reproduce observed effects of shading and halving the spikes. Crop response to modified radiation use efficiency (RUE) was variable among sites which could be critical for studying crop environment interactions, improving WUE, estimating genetically and atmospheric CO2-related increased RUE, analyzing impact of solar dimming and source manipulations under biotic stress.

Weak synaptic connections may facilitate spiral wave formation under source-sink interactions

This study explores the interaction between two distinct sites, termed the source and the sink, to analyze the possibility of spiral wave formation. To this aim, a grid of memristive FitzHugh–Nagumo elements is designed to simulate biological excitable media, such as the myocardium. The source, characterized by high excitation levels with a gradual increase in the recovery variable, is primed to generate an excitatory wavefront. In contrast, the sink remains quiescent in excitation yet elevated in the recovery state, thus tending to absorb excitation as it is temporarily unexcitable but soon recoverable. Existing literature on spiral wave formation primarily focuses on rotor formation under source–sink adjacency. This work, on the other hand, examines the potential for re-entrant behavior under spatial separation between the source and the sink. Within the context of eight-nearest neighbor coupling, the results indicate that the time delay for the excitation wave to reach the refractory state of the sink, due to the increased distance, may still facilitate re-entry if the intensity of connections is sufficiently weak. However, beyond a certain threshold of the source–sink distance under weak connections, wave breakage may occur without resulting in re-entry. For the birth of a spiral wave rotor, the tip of the excitatory wavefront must converge with its refractory back, specifically at the outermost contour in the final stage of refractoriness, referred to as the wavetail. The formation of a spiral rotor cannot arise from a wavefront encountering any site earlier in the stage of refractoriness.

The significance of radiative heat and mass transfer through a vertical sheet with chemical reaction: Designing by artificial approach Levenberg-Marquardt

The present study examines the impact of incorporating soft computing algorithms during neural network training on the evaluation and prediction performance of artificial neural networks. The research centers on a magneto hydrodynamic flow model (RHMT-VSCR) that depicts the movement of rotating fluid along a vertical sheet in a permeable medium. Furthermore, the model considers the impact of heat source-sink interactions, thermal radiation, and reactive species in conjunction with the effects of Hall current on the enhancement of energy and solute profiles. Because the induced magnetic field has a negligible magnetic Reynolds number, it is disregarded. A set of governing nonlinear PDEs is converted to a system of ODEs by applying an appropriate postulate of similarity variables in order to analyze the system. The multilayer perceptron network utilizes a supervised Levenberg–Marquardt Backpropagation algorithm (LMLA-BPNN) to ascertain the ideal quantity of neurons to be included in the hidden layer of artificial neural networks intended for modeling purposes. The bvp4c numerical approach is utilized to establish a continuous neural network mapping, which produces datasets that are utilized for the purposes of authentication, training, and testing. The range i.e., 10−2−10−8 of absolute error of the reference and target data demonstrates the optimal accuracy performance of LMLA-BPNN networks. After acquiring knowledge of neural network mapping, it is applied to approximate solutions for a wide range of scenarios through the manipulation of physical constraints, including suction/injection quantities, magnetic parameter, and porosity parameter, which influence the characteristics of flow, energy, and concentration.To assess the precision of the proposed method, statistical graphs based on regression, mean squared error analysis graphs, and error histogram graphs are employed. The results of the research demonstrate that the Levenberg-Marquardt Backpropagation neural network mappings' derivation, convergence, authentication, and stability were effectively validated.

Source-sink coordinated peanut cultivar increases yield and kernel protein content through enhancing photosynthetic characteristics and regulating carbon and nitrogen metabolisms

The grain yield of crops is determined by the synergistic interaction between source activity and sink capacity. However, source-sink interactions are far from being fully understood of peanut. Therefore, a 2-year field study (2018–2019) was conducted to compare differences in photosynthetic characteristics, carbon and nitrogen metabolism, and yield and quality of different source–sink peanut varieties. Four representative source–sink types were examined: JH5 (source–sink coordination type), SH9 (sufficient source–large sink type), ZH24 (sufficient source–few sink type), and HY36 (large source–few sink type). The results showed that the photosynthetic potential of HY36 was higher than that of the other varieties after flowering because of a large source (leaves), whereas the chlorophyll content and net photosynthetic rate of HY36 were significantly lower than those of JH5 and ZH24. Proportions of dry matter transferred to pods were significantly different among four source–sink peanut varieties. From 50 days after flowering, the dry matter distribution ratio of pods exceeded that of stems and leaves in JH5, significantly earlier than other varieties, which prolong the duration of pod-filling period, followed by SH9 and ZH24. The activities of nitrate reductase, glutamine synthetase, glutamate dehydrogenase, and glutamate synthase in JH5 were the highest among the varieties, and thus, the highest protein content was also in JH5. The activities of sucrose synthase and sucrose phosphate synthase in ZH24 were significantly higher than those in HY36. The highest oil content was also in ZH24. Among pod sink characteristics and yield, SH9 had the longest flowering period and the highest gynophore formation rate but the lowest pod-bearing rate, and the effective proportion and pod fullness were also lower than those of other varieties. The highest pod rate was in ZH24. The effective proportion and pod fullness of JH5 were higher than those of the other varieties, and its yield was also the highest, followed by SH9 and ZH24, with the lowest yield in HY36. The obtained results indicate that the source–sink coordinated variety had high Pn and chlorophyll content in the late growth stage, a long functional period of leaves, and a high proportion of assimilates transported to pods, thus promoting effective proportions and pod fullness to improve peanut yield and protein content, suggesting that different cultivation and management measures should select for different peanut varieties to best coordinate the relationship between the source and sink.

An urban metabolism framework purpose to assess the dynamics of linear alkylbenzenes (LABs) discharge flows and driving forces at the city level in Guangdong province, China

Linear alkylbenzenes (LABs) are a class of molecular markers derived from anthropogenic activities. A comprehensive understanding of the mechanism that determines their entry into anthroposphere, in terms of magnitude and pathway, is the prerequisite to establish effective mitigation measures. This study develops a methodology framework to analyze the source-sink interactions and driving factors of the direct and indirect LAB discharges from production and living activities in Guangdong Province, China from 2004 to 2017. Results indicated that the total LAB discharges of Guangdong into the environment were averaged at 2.9 kt yr−1, of which 61.9% originated from the Pearl River Delta (PRD) urban agglomeration. An average proportion of 76.0% was discharged into water bodies with the remaining released into land bodied. From 2014 to 2017, the LAB discharges increased by seven times, resulting from the steady increase of urban residential sources, while contribution from industrial sources continuously declined during the studied period. Meanwhile, the discharging hotspots expanded from Guangzhou city to other super-cities around it, including Shenzhen and Dongguan. The other cities exhibited a decreasing trend in discharges as a function of distance from these hotspot cities. The multisectoral sources of LABs differed considerably among cities, and the source contribution of each city changed significantly with progressive urbanization. The factor decomposition analysis indicated that LAB discharges in PRD cities primarily contributed by the pollutant concentration and reflected the treatment structure, while peripheral cities of the PRD mainly contributed by the per capita consumption and pollutant discharge per unit of GDP. Overall, our results provide a scientific database and supports for the regional co-remediation of anthropogenic pollution.

Extinction risks and mitigation for a megaherbivore, the giraffe, in a human-influenced landscape under climate change.

Megaherbivores play "outsized" roles in ecosystem functioning but are vulnerable to human impacts such as overhunting, land-use changes, and climate extremes. However, such impacts-and combinations of these impacts-on population dynamics are rarely examined using empirical data. To guide effective conservation actions under increasing global-change pressures, we developed a socially structured individual-based model (IBM) using long-term demographic data from female giraffes (Giraffa camelopardalis) in a human-influenced landscape in northern Tanzania, the Tarangire Ecosystem. This unfenced system includes savanna habitats with a wide gradient of anthropogenic pressures, from national parks, a wildlife ranch and community conservation areas, to unprotected village lands. We then simulated and projected over 50 years how realistic environmental and land-use management changes might affect this metapopulation of female giraffes. Scenarios included: (1) anthropogenic land-use changes including roads and agricultural/urban expansion; (2) reduction or improvement in wildlife law enforcement measures; (3) changes in populations of natural predators and migratory alternative prey; and (4) increases in rainfall as predicted for East Africa. The factor causing the greatest risk of rapid declines in female giraffe abundance in our simulations was a reduction in law enforcement leading to more poaching. Other threats decreased abundances of giraffes, but improving law enforcement in both of the study area's protected areas mitigated these impacts: a 0.01 increase in giraffe survival probability from improved law enforcement mitigated a 25% rise in heavy rainfall events by increasing abundance 19%, and mitigated the expansion of towns and blockage of dispersal movements by increasing abundance 22%. Our IBM enabled us to further quantify fine-scale abundance changes among female giraffe social communities, revealing potential source-sink interactions within the metapopulation. This flexible methodology can be adapted to test additional ecological questions in this landscape, or to model populations of giraffes or other species in different ecosystems.

The Inferior Grain Filling Initiation Promotes the Source Strength of Rice Leaves

Poor grain-filling initiation in inferior spikelets severely impedes rice yield improvement, while photo-assimilates from source leaves can greatly stimulate the initiation of inferior grain-filling (sink). To investigate the underlying mechanism of source-sink interaction, a two-year field experiment was conducted in 2019 and 2020 using two large-panicle rice cultivars (CJ03 and W1844). The treatments included intact panicles and partial spikelet removal. These two cultivars showed no significant difference in the number of spikelets per panicle. However, after removing spikelet, W1844 showed higher promotion on 1000-grain weight and seed-setting rate than CJ03, particularly for inferior spikelets. The reason was that the better sink activity of W1844 led to a more effective initiation of inferior grain-filling compared to CJ03. The inferior grain weight of CJ03 and W1844 did not show a significant increase until 8 days poster anthesis (DPA), which follows a similar pattern to the accumulation of photo-assimilates in leaves. After removing spikelets, the source leaves of W1844 exhibited lower photosynthetic inhibition compared to CJ03, as well as stronger metabolism and transport of photo-assimilates. Although T6P levels remained constant in both cultivars under same conditions, the source leaves of W1844 showed notable downregulation of SnRK1 activity and upregulation of phytohormones (such as abscisic acid, cytokinins, and auxin) after removing spikelets. Hence, the high sink strength of inferior spikelets plays a role in triggering the enhancement of source strength in rice leaves, thereby fulfilling grain-filling initiation demands.

Metabolic modelling revealed source–sink interactions between four segments of Setaria viridis leaves

Metabolic modelling revealed source–sink interactions between four segments of Setaria viridis leaves

Autophagy in maternal tissues contributes to Arabidopsis seed development.

Seeds are an essential food source, providing nutrients for germination and early seedling growth. Degradation events in the seed and the mother plant accompany seed development, including autophagy, which facilitates cellular component breakdown in the lytic organelle. Autophagy influences various aspects of plant physiology, specifically nutrient availability and remobilization, suggesting its involvement in source-sink interactions. During seed development, autophagy affects nutrient remobilization from mother plants and functions in the embryo. However, it is impossible to distinguish between the contribution of autophagy in the source (i.e. the mother plant) and the sink tissue (i.e. the embryo) when using autophagy knockout (atg mutant) plants. To address this, we employed an approach to differentiate between autophagy in source and sink tissues. We investigated how autophagy in the maternal tissue affects seed development by performing reciprocal crosses between wild type and atg mutant Arabidopsis (Arabidopsis thaliana) plants. Although F1 seedlings possessed a functional autophagy mechanism, etiolated F1 plants from maternal atg mutants displayed reduced growth. This was attributed to altered protein but not lipid accumulation in the seeds, suggesting autophagy differentially regulates carbon and nitrogen remobilization. Surprisingly, F1 seeds of maternal atg mutants exhibited faster germination, resulting from altered seed coat development. Our study emphasizes the importance of examining autophagy in a tissue-specific manner, revealing valuable insights into the interplay between different tissues during seed development. It also sheds light on the tissue-specific functions of autophagy, offering potential for research into the underlying mechanisms governing seed development and crop yield.

Contrasting Metabolisms in Green and White Leaf Sectors of Variegated Pelargonium zonale—An Integrative Transcriptomic and Metabolomic Study

The photosynthetically active green leaf (GL) and non-active white leaf (WL) tissues of variegated Pelargonium zonale provide an excellent model system for studying processes associated with photosynthesis and sink-source interactions, enabling the same microenvironmental conditions. By combining differential transcriptomics and metabolomics, we identified the main differences between these two metabolically contrasting tissues. Genes related to photosynthesis and associated pigments, the Calvin-Benson cycle, fermentation, and glycolysis were strongly repressed in WL. On the other hand, genes related to nitrogen and protein metabolism, defence, cytoskeletal components (motor proteins), cell division, DNA replication, repair and recombination, chromatin remodelling, and histone modifications were upregulated in WL. A content of soluble sugars, TCA intermediates, ascorbate, and hydroxybenzoic acids was lower, while the concentration of free amino acids (AAs), hydroxycinnamic acids, and several quercetin and kaempferol glycosides was higher in WL than in GL. Therefore, WL presents a carbon sink and depends on photosynthetic and energy-generating processes in GL. Furthermore, the upregulated nitrogen metabolism in WL compensates for the insufficient energy from carbon metabolism by providing alternative respiratory substrates. At the same time, WL serves as nitrogen storage. Overall, our study provides a new genetic data resource for the use of this excellent model system and for ornamental pelargonium breeding and contributes to uncovering molecular mechanisms underlying variegation and its adaptive ecological value.

TaTPP-7A positively feedback regulates grain filling and wheat grain yield through T6P-SnRK1 signalling pathway and sugar-ABA interaction.

Grain size and filling are two key determinants of grain thousand-kernel weight (TKW) and crop yield, therefore they have undergone strong selection since cereal was domesticated. Genetic dissection of the two traits will improve yield potential in crops. A quantitative trait locus significantly associated with wheat grain TKW was detected on chromosome 7AS flanked by a simple sequence repeat marker of Wmc17 in Chinese wheat 262 mini-core collection by genome-wide association study. Combined with the bulked segregant RNA-sequencing (BSR-seq) analysis of an F2 genetic segregation population with extremely different TKW traits, a candidate trehalose-6-phosphate phosphatase gene located at 135.0 Mb (CS V1.0), designated as TaTPP-7A, was identified. This gene was specifically expressed in developing grains and strongly influenced grain filling and size. Overexpression (OE) of TaTPP-7A in wheat enhanced grain TKW and wheat yield greatly. Detailed analysis revealed that OE of TaTPP-7A significantly increased the expression levels of starch synthesis- and senescence-related genes involved in abscisic acid (ABA) and ethylene pathways. Moreover, most of the sucrose metabolism and starch regulation-related genes were potentially regulated by SnRK1. In addition, TaTPP-7A is a crucial domestication- and breeding-targeted gene and it feedback regulates sucrose lysis, flux, and utilization in the grain endosperm mainly through the T6P-SnRK1 pathway and sugar-ABA interaction. Thus, we confirmed the T6P signalling pathway as the central regulatory system for sucrose allocation and source-sink interactions in wheat grains and propose that the trehalose pathway components have great potential to increase yields in cereal crops.

Physiological implications of SWEETs in plants and their potential applications in improving source-sink relationships for enhanced yield.

The sugars will eventually be exported transporters (SWEET) family of transporters in plants is identified as a novel class of sugar carriers capable of transporting sugars, sugar alcohols and hormones. Functioning in intercellular sugar transport, SWEETs influence a wide range of physiologically important processes. SWEETs regulate the development of sink organs by providing nutritional support from source leaves, responses to abiotic stresses by maintaining intracellular sugar concentrations, and host-pathogen interactions through the modulation of apoplastic sugar levels. Many bacterial and fungal pathogens activate the expression of SWEET genes in species such as rice and Arabidopsis to gain access to the nutrients that support virulence. The genetic manipulation of SWEETs has led to the generation of bacterial blight (BB)-resistant rice varieties. Similarly, while the overexpression of the SWEETs involved in sucrose export from leaves and pathogenesis led to growth retardation and yield penalties, plants overexpressing SWEETs show improved disease resistance. Such findings demonstrate the complex functions of SWEETs in growth and stress tolerance. Here, we review the importance of SWEETs in plant-pathogen and source-sink interactions and abiotic stress resistance. We highlight the possible applications of SWEETs in crop improvement programmes aimed at improving sink and source strengths important for enhancing the sustainability of yield. We discuss how the adverse effects of the overexpression of SWEETs on plant growth may be overcome.

Carbon and Nitrogen Allocation between the Sink and Source Leaf Tissue in Response to the Excess Excitation Energy Conditions.

Plants are inevitably exposed to extreme climatic conditions that lead to a disturbed balance between the amount of absorbed energy and their ability to process it. Variegated leaves with photosynthetically active green leaf tissue (GL) and photosynthetically inactive white leaf tissue (WL) are an excellent model system to study source-sink interactions within the same leaf under the same microenvironmental conditions. We demonstrated that under excess excitation energy (EEE) conditions (high irradiance and lower temperature), regulated metabolic reprogramming in both leaf tissues allowed an increased consumption of reducing equivalents, as evidenced by preserved maximum efficiency of photosystem II (ФPSII) at the end of the experiment. GL of the EEE-treated plants employed two strategies: (i) the accumulation of flavonoid glycosides, especially cyanidin glycosides, as an alternative electron sink, and (ii) cell wall stiffening by cellulose, pectin, and lignin accumulation. On the other hand, WL increased the amount of free amino acids, mainly arginine, asparagine, branched-chain and aromatic amino acids, as well as kaempferol and quercetin glycosides. Thus, WL acts as an important energy escape valve that is required in order to maintain the successful performance of the GL sectors under EEE conditions. Finally, this role could be an adaptive value of variegation, as no consistent conclusions about its ecological benefits have been proposed so far.

Co-Overexpression of Two Key Source Genes, OsBMY4 and OsISA3, Improves Multiple Key Traits of Rice Seeds

Optimized source-sink interactions are determinants of both rice yield and quality. However, most source genes have not been well studied in rice, a major grain crop. In this study, OsBMY4 and OsISA3, the key β-amylase and debranching enzymes that control transient starch degradation in rice leaves, were co-overexpressed in rice in order to accelerate starch degradation efficiency and increase the sugar supply for sink organs. Systematic analyses of the transgenic rice indicated that co-overexpression of OsBMY4 and OsISA3 not only promoted rice yield and quality, but also improved seed germination and stress tolerance. Moreover, since the OsBMY4 gene has not been characterized, we generated osbmy4 mutants using CRIPSR/Cas9 gene editing, which helped to reveal the roles of β-amylase in rice yield and quality. This study demonstrated that specific modulation of the expression of some key source genes improves the source-sink balance and leads to improvements in multiple key traits of rice seeds.

Wood structure explained by complex spatial source-sink interactions

Wood is a remarkable material with great cultural, economic, and biogeochemical importance. However, our understanding of its formation is poor. Key properties that have not been explained include the anatomy of growth rings (with consistent transitions from low-density earlywood to high density latewood), strong temperature-dependence of latewood density (used for historical temperature reconstructions), the regulation of cell size, and overall growth-temperature relationships in conifer and ring-porous tree species. We have developed a theoretical framework based on observations on Pinus sylvestris L. in northern Sweden. The observed anatomical properties emerge from our framework as a consequence of interactions in time and space between the production of new cells, the dynamics of developmental zone widths, and the distribution of carbohydrates across the developing wood. Here we find that the diffusion of carbohydrates is critical to determining final ring anatomy, potentially overturning current understanding of how wood formation responds to environmental variability and transforming our interpretation of tree rings as proxies of past climates.

Centennial Change and Source–Sink Interaction Process of Traditional Agricultural Landscape: Case from Xin’an Traditional Cherry Cultivation System (1920–2020)

In contrast to modern agriculture, long-standing traditional agricultural practices such as agricultural heritage systems (AHS) are important inspirations for promoting harmonious human–land relations. However, some AHS have been in danger as their traditional agricultural landscapes (TALs) were changed by rapid modernization and urbanization. Thus, how do we figure out the change processes? What conservation measures can be taken? Taking the Xin’an Traditional Cherry Cultivation System in the loess hilly areas of Henan Province as a case, this study introduced the source–sink landscape theory to analyze the structure and process of the TAL during 1920–2020. Results show that, during 1920–1950, the traditional rural landscape (TRL) and the agricultural (natural) ecological landscape (ANEL) in the TAL were relatively balanced because they were source and sink to each other. Since 1985, the source expansion and sink resistance of both TRL and ANEL have been greatly hindered by the sink growth of modern village landscapes (MVL). As the core source landscape, TRL needs salvage protection for inheriting local characteristics by effective measures. TAL conservation should highlight rurality preservation through expanding the protection scope of TRL, endowing the MVL with more indigenous cultural features, etc. All these may contribute to rural vitalization and sustainable development.

Accumulation of Secondary Metabolites of Rhodiola semenovii Boriss. In Situ in the Dynamics of Growth and Development.

Rhodiola semenovii Boriss. (Regel and Herder) might be a promising replacement for the well-known but endangered Rhodiola rosea L. In this research, the metabolic profile of R. semenovii, including drug-active and stress-resistant components, was studied in the context of source–sink interactions in situ in the dynamics of growth and development. Gas chromatography with mass spectrometric detection and liquid chromatography methods were used. The data obtained allow for assumptions to be made about which secondary metabolites determine the level of stress resistance in R. semenovii at different stages of ontogeny in situ. For the first time, an expansion in the content of salidroside in the above-ground organs, with its maximum value during the period of seed maturation, and a significant decrease in its content in the root were revealed in the dynamics of vegetation. These results allow us to recommend collecting the ground component of R. semenovii for pharmaceutical purposes throughout the seed development stage without damaging the root system.

PO-639-07 AUTOMATIC UNIPOLAR ELECTROGRAM MORPHOLOGY ANALYSIS USING A CONVOLUTED NEURAL NETWORK CLASSIFIER

Unipolar electrogram (EGM) morphology contains information of near-field cardiac substrate properties and the relative source-sink interactions of the wavefront as it approaches and leaves. S wave unipolar morphology indicates a region of electrical source and may physiologically represent a site of focal activation or the rapid spread of activation from activity leaving a conducting isthmus. An R morphology indicates a region of electrical sink and may physiologically represent wavefronts propagating into an unexcitable obstacle such as an ablation line.

Effects of source-sink alteration by pruning on physiological parameters and fruit production of Rosa roxburghii Tratt. on the Yunnan-Guizhou Plateau in China

The formation of economic yield and fruit quality of Roxburgh rose (Rosa roxburghii Tratt.) depends essentially on its source-sink interaction. Thus, a pruning experiment was conducted to assess the effects of source-sink regulation on photosynthetic physiology and fruit yield of Roxburgh rose, which was of great significance to production. Cutting off vegetative branches reduced physiological fruit loss and malformed fruits but increased single fruit quality and yield. Results revealed that the stomatal characteristics, the composition of mesophyll tissue, and photosynthesis of leaves on reproductive branches were significantly affected by the ratio of the vegetative and reproductive shoots. Our data indicated that the source-sink ratio could reflect the balance between vegetative growth and reproductive growth of the tree during the whole fruit period. Fruit tree pruning had guiding significance for improving the fruit yield of Roxburgh rose.

Exploring optimal stomatal control under alternative hypotheses for the regulation of plant sources and sinks.

Experimental evidence that nonstomatal limitations to photosynthesis (NSLs) correlate with leaf sugar and/or leaf water status suggests the possibility that stomata adjust to maximise photosynthesis through a trade-off between leaf CO2 supply and NSLs, potentially involving source-sink interactions. However, the mechanisms regulating NSLs and sink strength, as well as their implications for stomatal control, remain uncertain. We used an analytically solvable model to explore optimal stomatal control under alternative hypotheses for source and sink regulation. We assumed that either leaf sugar concentration or leaf water potential regulates NSLs, and that either phloem turgor pressure or phloem sugar concentration regulates sink phloem unloading. All hypotheses led to realistic stomatal responses to light, CO2 and air humidity, including conservative behaviour for the intercellular-to-atmospheric CO2 concentration ratio. Sugar-regulated and water-regulated NSLs are distinguished by the presence/absence of a stomatal closure response to changing sink strength. Turgor-regulated and sugar-regulated phloem unloading are distinguished by the presence/absence of stomatal closure under drought and avoidance/occurrence of negative phloem turgor. Results from girdling and drought experiments on Pinus sylvestris, Betula pendula, Populus tremula and Picea abies saplings are consistent with optimal stomatal control under sugar-regulated NSLs and turgor-regulated unloading. Our analytical results provide a simple representation of stomatal responses to above-ground and below-ground environmental factors and sink activity.