Effects of Localized Potassium Supply on Root Potassium Uptake in Cotton (Gossypium hirsutum L.)

Cotton (Gossypium hirsutum L. cv. Liaomian 17) seedlings were grown in nutrient solution, and a split-root system with two compartments was used to examine the effect of localized potassium (K) supply on K uptake and seedlings growth. Potassium was supplied at 2.5 and 0.01 mM K in the +K and -K compartments, respectively, with three treatments of +K+K, –K–K and +K–K. Shoot dry weight in +K–K was similar to that in +K+K, but higher than that in –K–K. K concentrations [K] of shoot in +K–K was lower than that in +K+K, but 59.6% higher than that in –K–K. In +K–K treatment, root [K] was 42.1% greater in the +K than in the –K root half, and the similar trend was observed for root dry weight. However, localized K supply (+K–K) did not influence the root length, surface area and volume in root halves because of the short treatment period (5 d). The results of K⁺ uptake kinetic parameters indicated that the maximum influx rate (V_max) in +K+K was lower than that in –K–K. With respect to +K–K treatment, the +K root half showed an increase in V_max compared with +K+K, whereas the –K root half had a decreased V_max compared with –K–K. This suggested that the root-to-shoot or root-to-root signal(s) are originated in the –K root half to transfer the change of K supply, and then the +K root half up-regulates its K uptake ability after receiving signal(s) from shoot or the –K root half. Taken together, the localized K supply enhanced K uptake in +K root half but reduced K uptake in –K root half, probably through transmission of long-distance signals, and the former could compensate the latter to some extent, which was reflected by shoot biomass and shoot [K].