Research PaperPotassium fertilizer improves drought stress alleviation potential in cotton by enhancing photosynthesis and carbohydrate metabolism

Under drought, limited photo-assimilates synthesis and their poor partitioning is a main constraint to final yield production in cotton (Gossypium hirsutum L.). To study the potassium (K) role in photo-assimilation and carbohydrate metabolism in cotton under soil drought stress during flowering and boll formation stage, a two-year pot experiment was conducted in 2015 and 2016. Two cotton cultivars namely Simian 3 (low-K tolerant) and Siza 3 (low-K sensitive) were grown under three K rates (0, 150 and 300 kg K2O ha−1). Plants were exposed to well-watered [(75 ± 5%) soil relative water content (SRWC)] and water stress (35-40% SRWC) for 7 days followed by re-watering to SRWC (75 ± 5%). The results showed that water-stressed plants under K0 application exhibited significant decline in net photosynthesis, stomatal conductance, intercellular CO2 concentration and ribulose-1,5-bisphosphate carboxylase (Rubisco) activity and resulting in reduced photo-assimilates synthesis and partitioning towards reproductive organs in both cultivars. Conversely, K application decreased the decline in photosynthesis, Rubisco activity and biomass accumulation and partitioning. The positive effects of K application increased as increasing K rates, and that was more pronounced in Siza 3 than Simian 3. Drought stress decreased starch content but increased sucrose content; whereas, K application maintained higher concentration of sucrose in leaves of water-stressed plants through the regulation of higher sucrose phosphate synthase (SPS), sucrose synthase (SuSy) and lower soluble acid invertase (SAI) activities. The results of the study concluded that K application regulated the photo-assimilation and translocation process along with the related enzymes activities in cotton. The study suggests that K nutrient management strategy has the potential to minimize the impacts of drought stress in cotton.