Critical shoot phosphorus concentrations for changes in root morphology to improve phosphorus uptake in cotton

Background In recent years, the response of cotton (Gossypium hirsutum L.) root morphology and rhizosphere processes to phosphorus (P) deficiency have attracted extensive attention. However, the dynamics of root morphology and physiology to shoot P concentration (SPC) under various P conditions remain unclear. Aim We aimed to determine the changes in root morphology and physiology and their relationships with SPC under different levels of P supply. Method The cotton cultivars XLZ13 and XLZ19 were grown in a hydroponic experiment with seven rates of P supply (0–2.0 mM P L−1) and in a root box experiment with seven P levels (0–400 mg P kg−1). Root morphological and physiological parameters were determined 60 days after planting (hydroponic experiment) and 75 days after transplanting (root box experiment). Results Cotton plant growth, P uptake, and root morphology differed significantly between the two genotypes and among the P levels. Cotton plants had the maximum shoot biomass when the SPC of XLZ13 and XLZ19 were 4.6–5.9 mg g−1 and 3.9‐5.0 mg g−1, respectively. Total and specific root lengths initially increased with increasing SPC and peaked at an SPC of XLZ13 and XLZ19 about 6.0–7.0 mg g−1 and 4.0‐5.0 mg g−1, respectively. Root physiological responses (rhizosphere acidification, acid phosphatase [Apase] activity) decreased as the SPC increased. Conclusions The critical SPC for optimal root morphology were 5–6 mg g−1. P deficiency did not induce rhizosphere acidification but promoted root and rhizosphere APase activity.