Source-Sink Dynamics in Photosynthetic Performance

Plants rely on a finely tuned balance between the production of photosynthates in source leaves and the utilisation of those assimilates by sink organs such as fruits, roots, stems and meristems. This source–sink dynamic governs not only biomass accumulation and crop yield but also responses to environmental fluctuation and resource limitation. Source strength reflects the capacity of photosynthetic tissues to fix carbon and convert it into transportable sugars, while sink strength describes the demand from growing or storage organs. Phloem-mediated translocation connects these compartments, and its capacity is influenced by sink activity, carbohydrate concentrations and hormonal signals. Feedback mechanisms may downregulate photosynthesis under excessive sugar accumulation, whereas enhanced sink demand can upregulate leaf assimilation and enzyme activities. Advances in in vivo imaging and isotope labelling have revealed the spatial and temporal heterogeneity of assimilate partitioning within individual organs. Understanding these processes is crucial for optimising crop management, breeding for yield stability and improving carbon use efficiency in a changing climate.

Research from Nature Portfolio

Studies on fruit‐bearing trees have demonstrated that manipulating crop load profoundly alters the distribution of carbon and nitrogen isotopes between reproductive and vegetative tissues. Reducing fruit number increases allocation of both 13C‐derived carbohydrates and 15N‐derived nitrogen to leaves, branches and roots, thereby enhancing nitrogen use efficiency and improving fruit quality under moderate sink demand. Conversely, high crop loads draw down reserves, limiting assimilate availability to vegetative sinks and constraining overall plant performance. These findings highlight how deliberate adjustment of sink strength can modulate source activity, optimise resource partitioning and inform precision horticultural practices.

Source-Sink Dynamics in Photosynthetic Performance publication trend

The graph below shows the total number of articles in source-sink dynamics in photosynthetic performance across all publications each year (not limited to Nature Index journals).

Technical terms

Assimilate: A carbohydrate product of photosynthesis that is transported to sinks.

Source strength: The capacity of photosynthetic tissues to produce and export assimilates.

Sink strength: The capacity of non‐photosynthetic tissues to import and utilise assimilates.

Phloem translocation: The transport of sugars and nutrients through the phloem from sources to sinks.

Sink limitation: A condition in which sink demand is insufficient to utilise all assimilates produced.

Source limitation: A condition in which assimilate production is insufficient to meet sink demand.

Non-structural carbohydrates (NSC): Soluble sugars and starch stored in tissues and available for metabolic use.

Feedback inhibition of photosynthesis: Downregulation of photosynthetic activity due to accumulation of assimilates in leaves.

References

1. Effects of crop load on distribution and utilization of 13C and 15N and fruit quality for dwarf apple trees. Scientific Reports (2017).
2. Quantifying the source–sink balance and carbohydrate content in three tomato cultivars. Frontiers in Plant Science (2015).
3. Non-invasive 11C-Imaging Revealed the Spatiotemporal Variability in the Translocation of Photosynthates Into Strawberry Fruits in Response to Increasing Daylight Integrals at Leaf Surface. Frontiers in Plant Science (2021).
4. Photosynthetic limitation as a factor influencing yield in highbush blueberries (Vaccinium corymbosum) grown in a northern European environment. Journal of Experimental Botany (2018).