In nature, there exist multiple versions of the CO2 molecule, with slightly different weights. Most of the CO2 we observe in the atmosphere contains 12C, but sometimes we find the heavier version, containing 13C. Scientists can, under controlled conditions, artificially increase atmospheric 13C-CO2 and use it as a molecular marker for photosynthesis. Adding these marked, or labelled, molecules of CO2 to the air allows scientists to track them after being absorbed by plants, and determine their fate within the plant.
This concept is called pulse labelling. Researchers can measure these marked carbohydrates in each plant organ (e.g. leaves, stems and roots) to estimate how much of the marked carbohydrates is allocated to each of the plant organs with isotope ratio mass spectrometry, a technique that can detect differences between CO2 containing 13C or 12C.
Due to climate change, plants will increasingly grow in more challenging conditions, like extended periods of drought. This is especially relevant for cassava, one of Africa’s most important crops in terms of production and food security. Pulse labelling helps to understand carbon resource management of cassava under different environmental stressors, including drought. Plants organize and distribute new carbohydrates according to their needs, but cassava breeders and farmers are most interested in those plants that distribute most of the new carbohydrates to their roots.
Drought can influence this distribution pattern depending on the variety or on management practices. Therefore, knowing how plants organize new carbohydrates under stressed conditions can help select better varieties (that distribute more to root tissue) or improve agronomic practices like fertilizer management (which can influence carbohydrate transport). Since cassava roots are the organ of interest, we want to know how much of the new carbohydrates are transported to the roots.
We found that potassium fertilizer application influences carbohydrate distribution to stems and roots, initially increasing the share of carbohydrates to the roots. This finding, despite its simplicity, can be a step up to better fertilizer management.