Interactive effects of low phosphorus and elevated CO2 on root exudation and nutrient uptake in wheat is modified under sulphur nutrition

We investigated the influence of elevated CO2 concentration (e[CO2]) on the interaction of phosphorus (P) and sulphur (S) on nutrient uptake efficiency of wheat. Experiments were conducted on wheat varieties PDW-233 (Triticum durum) and PBW-396 (T. aestivum) under different levels of [CO2] (400 and 700 ppm) with low P (5 µM), low S (10 µM) or low P/S and control (P 500 µM and S 2000 µM). Results revealed an increased biomass accumulation under e[CO2] with low P or S as compared to ambient CO2 concentration (a[CO2]). The root biomass was doubled with higher belowground dry matter partitioning under low nutrient and e[CO2]. Low P and S restricted plant growth directly by reduction in biomass accumulation and limited exudation of total carboxylates from root, however e[CO2] helped to overcome these deficiencies. Interactive effects of e[CO2] and low P or low P/S resulted in increased root length, surface area, volume and number of lateral roots. Under limited P and e[CO2], S provided stability to enzymes involved in root exudation and accelerated mobilization of P and its uptake efficiency. The activity of enzymes viz., phosphoenolpyruvate carboxylase, citrate synthase, malate dehydrogenase and pyruvate kinase, involved in carboxylate synthesis showed significant increase under e[CO2]. Further, the concentration of P and S increased under e[CO2] in shoot and root tissues of both varieties. Under limited P and S supply, e[CO2] helped in modification of root morphology and higher root exudation, which improved nutrient uptake in both varieties.