Low availability of phosphorus (P) is a major constraint to production of cotton (Gossypium hirsutum L.). The extent to which genotypic variation in root traits exists or contributes to P-acquisition efficiency (PAE) in cotton is unknown. To assess genetic variation in PAE, the biomass and P-acquisition characteristics of 32 cotton genotypes were evaluated in a hydroponic experiment. Significant genotypic variation in biomass and P content was detected among the cotton genotypes in two seasons. We then conducted a 2-year pot experiment to compare P-efficiency traits between three P-efficient and two P-inefficient genotypes under P-deficient and P-sufficient conditions (0 and 75 mg P2O5 kg–1 soil, respectively). We detected significant differences in biomass accumulation and allocation, P accumulation and allocation, root traits and PAE among the five cotton genotypes under P-sufficient and P-deficient conditions. Compared with P-inefficient genotypes, P-efficient genotypes had longer surface fine roots, and greater total root surface area, total root length, surface root length, and P concentration (partitioning index) in bolls. Root morphology, especially surface fine root length and middle root length, played an important role in P uptake under P-deficient conditions.
Limited information is available on accumulation, distribution, and remobilisation of dry matter (DM) and nutrients in cotton (Gossypium hirsutum L.) under the interaction of nutrient management and genotype. We conducted a 2-year field experiment to study the impacts of phosphorus (P) treatments (0, 16.5, 33, 66, 132 and 198 kg P ha–1) on growth and P absorption, allocation and remobilisation in three cotton genotypes. At maturity, the maximum DM and P content allocation to seeds were 20.7% and 62.3%, respectively. Compared with the anthesis stage, leaf DM and P content at maturity significantly decreased by 46.3% and 73.6%, respectively; thus, seed P content was mainly contributed by leaves. Compared with the control (nil P), optimal P fertilisation (33–66 kg P ha–1) increased leaf DM and P content at anthesis by 21.2% and 40.8%, promoted P translocation from leaves to seeds by 43%, and improved lint yield at maturity by 22.8%. At anthesis and maturity, the DM and P content of the entire plant, and lint and seed yields were higher in genotypes XLZ57 and XLZ19 than in XLZ13. Suitable P doses increase DM and P accumulation and yield, and improve source–sink relationships of DM and P in cotton.
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