Dynamic Source-Sink Regulation and Carbon Allocation in Fruit Crops: Implications for Yield, Quality, and Climate Resilience
Abstract
Carbon allocation and source-sink interactions are fundamental determinants of yield, fruit quality, and climate resilience in perennial fruit crops. Unlike annual species, fruit crops must continuously distribute assimilates among reproductive, vegetative, and storage sinks, balancing current production with future growth. Although photosynthetic carbon supply has traditionally been regarded as the primary driver of productivity, increasing evidence shows that sink demand actively regulates source activity through metabolic and signalling feedback, making crop performance dependent on the coordinated interaction of source capacity, sink strength, phloem transport, and non-structural carbohydrate reserves. This review synthesizes current physiological, biochemical, and modelling knowledge to develop an integrated framework for understanding carbon allocation in major fruit crops, including apple, grapevine, citrus, peach, and mango. It examines the roles of carbohydrate reserves, sink activity, and phloem transport in regulating fruit growth, quality, and seasonal carry-over effects, while highlighting the impacts of drought, heat stress, elevated atmospheric CO₂, and nutrient limitations on source-sink coordination. Emerging approaches for analysing carbon dynamics and key research priorities are also discussed. Optimizing sink activity and reserve dynamics, together with climate-smart orchard management, is essential for sustaining fruit productivity, quality, and resilience under changing climatic conditions.
Keywords
Download Options
Introduction
The productivity and sustainability of perennial fruit crops depend not only on carbon assimilation but also on the efficient allocation of photoassimilates among vegetative, reproductive, and storage sinks. Unlike annual crops, fruit trees and vines must simultaneously support current-season fruit development, maintain perennial structures, and accumulate reserves for future growth. Consequently, carbon allocation is a major determinant of yield stability, fruit quality, and long-term orchard performance (Pallas et al., 2018; White et al., 2016).
Carbon allocation comprises the transport, distribution, storage, remobilization, and utilization of assimilated carbon, whereas carbon partitioning describes its distribution among competing sinks during development (Marcelis & Heuvelink, 2007). Source capacity denotes the ability of photosynthetically active organs to produce and export assimilates, while sink strength reflects the capacity of developing organs to attract and utilize them according to their size and metabolic activity (Marcelis, 1996). In perennial fruit crops, non-structural carbohydrate (NSC) reserves stored in roots, trunks, and branches buffer temporal imbalances between carbon supply and demand and sustain growth during periods of limited photosynthesis (Martínez-Vilalta et al., 2016).
Conclusion
Carbon allocation in fruit crops is a dynamic, integrated process that underpins productivity, fruit quality, and long-term orchard performance. Yield depends not only on photosynthetic carbon supply but also on the coordinated regulation of source capacity, sink strength, phloem transport, and non-structural carbohydrate (NSC) reserves across developmental stages. Evidence indicates that sink activity actively regulates carbon assimilation through metabolic and signalling feedback, while competition among fruits, vegetative organs, and storage tissues, together with reserve accumulation and remobilization, links current carbon allocation with future productivity. Consequently, maintaining functional sink activity and adequate carbohydrate reserves is fundamental for sustaining yield stability and reducing alternate bearing.
Climate change is expected to intensify disruptions in source-sink coordination through drought, heat stress, elevated CO₂, nutrient limitations, and extreme weather events, with sink processes and phloem transport often more vulnerable than photosynthesis. Emerging approaches, including isotopic tracing, high-throughput phenotyping, omics technologies, remote sensing, and functional-structural modelling, provide unprecedented opportunities to quantify and predict carbon dynamics in perennial fruit crops. Their integration with precision orchard management, optimized rootstock-scion combinations, and climate-smart practices will facilitate resilient production systems.
References
[1] Ainsworth EA and Long SP (2021). 30 years of free-air carbon dioxide enrichment (FACE): What have we learned about future crop productivity and its potential for adaptation? Global Change Biology 27(1), 27–49. https://doi.org/10.1111/gcb.15375
[2] Chaves MM, Flexas J and Pinheiro C (2010). Photosynthesis under drought and salt stress: Regulation mechanisms from whole plant to cell. Annals of Botany 103(4), 551–560. https://doi.org/10.1093/aob/mcn125
[3] Chen LQ, Qu XQ, Hou BH, Sosso D, Osorio S, Fernie AR and Frommer WB (2012). Sucrose efflux mediated by SWEET proteins as a key step for phloem transport. Science 335(6065), 207–211. https://doi.org/10.1126/science.1213351
[4] Dar SQ, Dar KR, Sharma MK, Mir SA, Khan FA, Dar MA and Chattoo MA (2021). Seasonal accumulation of total sugars, reducing sugars and non-reducing sugars in the fruits of Malus domestica Borkh. cv. Fuji Zehn Aztec during fruit development. The Pharma Innovation Journal 10(6), 552–555.
[5] De Schepper V, De Swaef T, Bauweraerts I and Steppe K (2013). Phloem transport: A review of mechanisms and controls. Journal of Experimental Botany 64(16), 4839–4850. https://doi.org/10.1093/jxb/ert302
[6] Farquhar GD, Ehleringer JR and Hubick KT (1989). Carbon isotope discrimination and photosynthesis. Annual Review of Plant Physiology and Plant Molecular Biology 40, 503–537. https://doi.org/10.1146/annurev.pp.40.060189.002443
[7] Figueroa CM and Lunn JE (2016). A tale of two sugars: Trehalose 6-phosphate and sucrose. Plant Physiology 172(1), 7–27. https://doi.org/10.1104/pp.16.00417
[8] Fiorani F and Schurr U (2013). Future scenarios for plant phenotyping. Annual Review of Plant Biology 64, 267–291. https://doi.org/10.1146/annurev-arplant-050312-120137
[9] Ghazannfar Ghani, Rather ZA, Nazki IT, Khan FA, Mir SA, Parveen K and Lone RA (2019). Photosynthate partitioning and plant senescence in tulip (Tulipa gesneriana) influenced by foliar application of nutrients under different environmental conditions. Research Journal of Agricultural Sciences 10(3), 547–551.
[10] Goldschmidt EE (2013). The evolution of fruit tree productivity: A review. Economic Botany 67(1), 51–62. https://doi.org/10.1007/s12231-012-9219-6
[11] Hartmann H and Trumbore S (2016). Understanding the roles of non-structural carbohydrates in forest trees—From what we can measure to what we want to know. New Phytologist 211(2), 386–403. https://doi.org/10.1111/nph.13955
[12] Ho LC (1988). Metabolism and compartmentation of imported sugars in sink organs in relation to sink strength. Annual Review of Plant Physiology and Plant Molecular Biology 39, 355–378. https://doi.org/10.1146/annurev.pp.39.060188.002035
[13] Hsiao TC and Xu LK (2000). Sensitivity of growth of roots versus leaves to water stress: Biophysical analysis and relation to water transport. Journal of Experimental Botany 51(350), 1595–1616. https://doi.org/10.1093/jexbot/51.350.1595
[14] IPCC (2023). Climate Change 2023: Synthesis Report. Contribution of Working Groups I, II and III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. Intergovernmental Panel on Climate Change, Geneva, Switzerland.
[15] Kader AA (2008). Flavor quality of fruits and vegetables. Journal of the Science of Food and Agriculture 88(11), 1863–1868. https://doi.org/10.1002/jsfa.3293
[16] Keller M (2020). The Science of Grapevines: Anatomy and Physiology. 3rd edn. Academic Press, London, UK.
[17] Khan FA and Zaidi PH (2000). Malformation-induced changes in carbon and nitrogen metabolism and C/N ratio in mango. Annals of Agricultural Research 21(1), 90–92.
[18] Khan FA, Kumar A, Narayan S, Khan FU and Astha (2023). Watercore and fruit quality of apple cultivars as influenced by harvesting time and calcium sprays. Biotech Today 13(1), 31–40.
[19] Knoblauch M and Oparka K (2012). The structure of the phloem—Still more questions than answers. The Plant Journal 70(1), 147–156. https://doi.org/10.1111/j.1365-313X.2012.04931.x
[20] Lakso AN and Corelli Grappadelli L (1992). Implications of pruning and training practices to carbon partitioning and fruit development in apple. Acta Horticulturae 322, 231–239. https://doi.org/10.17660/ActaHortic.1992.322.28
[21] Li Y, Li Y, Wang H and Xu Y (2022). Sugar signalling networks integrating trehalose-6-phosphate, SnRK1 and TOR in plant growth and stress responses. Plant Physiology and Biochemistry 188, 77–86. https://doi.org/10.1016/j.plaphy.2022.08.018
[22] Loescher WH, McCamant T and Keller JD (1990). Carbohydrate reserves, translocation and storage in woody plant roots. HortScience 25(3), 274–281. https://doi.org/10.21273/HORTSCI.25.3.274
[23] Marcelis LFM (1996). Sink strength as a determinant of dry matter partitioning in the whole plant. Journal of Experimental Botany 47(Special Issue), 1281–1291. https://doi.org/10.1093/jxb/47.Special_Issue.1281
[24] Marcelis LFM and Heuvelink E (2007). Concepts of modelling carbon allocation among plant organs. In: Heuvelink E (Ed.), Tomatoes, pp. 103–111. CABI, Wallingford, UK.
[25] Marschner P (Ed.) (2012). Marschner's Mineral Nutrition of Higher Plants. 3rd edn. Academic Press, London, UK.
[26] Martínez-Vilalta J, Sala A, Asensio D, Galiano L, Hoch G, Palacio S, Piper FI and Lloret F (2016). Dynamics of non-structural carbohydrates in terrestrial plants: A global synthesis. Ecological Monographs 86(4), 495–516. https://doi.org/10.1002/ecm.1231
[27] McAtee P, Karim S, Schaffer R and David K (2013). A dynamic interplay between phytohormones is required for fruit development, maturation and ripening. Frontiers in Plant Science 4, 79. https://doi.org/10.3389/fpls.2013.00079
[28] Mehvish Bashir, Bhat R, Sharma MK, Mir SA, Khan FA, et al. (2023). Effect of fruitlet thinning on apple production and quality under high-density plantation. International Journal of Environment and Climate Change 13(10), 4302–4311.
[29] Osorio S, Ruan YL and Fernie AR (2014). An update on source-to-sink carbon partitioning in tomato. Frontiers in Plant Science 5, 516. https://doi.org/10.3389/fpls.2014.00516
[30] Pallas B, Costes E and Pradal C (2018). Carbon allocation and developmental plasticity in fruit trees: Concepts and modelling approaches. Frontiers in Plant Science 9, 1759. https://doi.org/10.3389/fpls.2018.01759
[31] Palmer JW, Giuliani R and Adams HM (1992). Effect of crop load on fruiting and leaf photosynthesis of 'Braeburn'/M.26 apple trees. Tree Physiology 11(1), 19–33. https://doi.org/10.1093/treephys/11.1.19
[32] Palmer JW, Harker FR, Tustin DS and Johnston J (2013). Fruit dry matter concentration: A new quality metric for apples. Journal of the Science of Food and Agriculture 93(11), 2586–2594. https://doi.org/10.1002/jsfa.6223
[33] Patrick JW (1997). Phloem unloading: Sieve element unloading and post-sieve element transport. Annual Review of Plant Physiology and Plant Molecular Biology 48, 191–222. https://doi.org/10.1146/annurev.arplant.48.1.191
[34] Paul MJ and Foyer CH (2001). Sink regulation of photosynthesis. Journal of Experimental Botany 52(360), 1383–1400. https://doi.org/10.1093/jexbot/52.360.1383
[35] Pawar PMA, Derleth C and Marsh EL (2019). From sink to source: The role of carbohydrate metabolism in perennial plant productivity and resilience. Frontiers in Plant Science 10, 1874. https://doi.org/10.3389/fpls.2019.01874
[36] Ruan YL (2014). Sucrose metabolism: Gateway to diverse carbon use and sugar signaling. Annual Review of Plant Biology 65, 33–67. https://doi.org/10.1146/annurev-arplant-050213-040251
[37] Ruan YL and Patrick JW (1995). The cellular pathway of post-phloem sugar transport in developing tomato fruit. Planta 196(3), 434–444. https://doi.org/10.1007/BF00203641
[38] Sevanto S (2014). Phloem transport and drought. Journal of Experimental Botany 65(7), 1751–1759. https://doi.org/10.1093/jxb/ert467
[39] Sevanto S, McDowell NG, Dickman LT, Pangle R and Pockman WT (2014). How do trees die? A test of the hydraulic failure and carbon starvation hypotheses. Plant, Cell and Environment 37(1), 153–161. https://doi.org/10.1111/pce.12141
[40] Stamp N (2003). Out of the quagmire of plant defense hypotheses. The Quarterly Review of Biology 78(1), 23–55. https://doi.org/10.1086/367580
[41] Sugiura T, Ogawa H, Fukuda N and Moriguchi T (2013). Changes in the taste and textural attributes of apples in response to climate change. Scientific Reports 3, 2418. https://doi.org/10.1038/srep02418
[42] Sukhvibul N, Whiley AW, Vithanage V, Smith MK, Doogan VJ and Hetherington SE (2005). Effect of temperature on fruit set and fruit development in mango (Mangifera indica L.). Scientia Horticulturae 105(4), 467–474. https://doi.org/10.1016/j.scienta.2005.02.005
[43] Terrer C, Jackson RB, Prentice IC, Keenan TF, Kaiser C, Vicca S, Fisher JB, Reich PB, Stocker BD, Hungate BA, Peñuelas J and Franklin O (2020). Nitrogen and phosphorus constrain the CO₂ fertilization of global plant biomass. Nature Climate Change 10(7), 684–689. https://doi.org/10.1038/s41558-020-0740-2
[44] Turgeon R (2010). The role of phloem loading reconsidered. Plant Physiology 152(4), 1817–1823. https://doi.org/10.1104/pp.110.153023
[45] Tworkoski T and Fazio G (2015). Effects of size-controlling apple rootstocks on growth, abscisic acid and hydraulic conductivity of scion of different vigor. International Journal of Fruit Science 15(4), 369–381. https://doi.org/10.1080/15538362.2015.1047586
[46] Urban L, Aarrouf J and Bidel LPR (2017). Heat stress effects on leaf physiology and fruit production in plants. Acta Horticulturae 1153, 113–124. https://doi.org/10.17660/ActaHortic.2017.1153.16
[47] Vos J, Evers JB, Buck-Sorlin GH, Andrieu B, Chelle M and De Visser PHB (2010). Functional-structural plant modelling: A new versatile tool in crop science. Journal of Experimental Botany 61(8), 2101–2115. https://doi.org/10.1093/jxb/erp345
[48] Warschefsky EJ, Klein LL, Frank MH, Chitwood DH, Londo JP, von Wettberg EJB and Miller AJ (2016). Rootstocks: Diversity, domestication and impacts on shoot phenotypes. Trends in Plant Science 21(5), 418–437. https://doi.org/10.1016/j.tplants.2015.11.008
[49] White AC, Rogers A, Rees M and Osborne CP (2016). How can we make plants grow faster? A source–sink perspective on growth rate. Journal of Experimental Botany 67(1), 31–45. https://doi.org/10.1093/jxb/erv447.