Dynamics of mineral nutrient element concentrations in developing cotton leaves, bracts, and floral buds in relation to position in the canopy

Plant mineral nutrient element status is an important factor influencing co tton (Gossypium hirsutum L.) growth, development, metabolism, and yield. A field study was conducted to determine changes in mineral nutrient element concentrations in leaves, bracts, and floral buds of field-grown cotton pla nts during development of squares (floral bud with three bracts) as affecte d by fruiting position within the plant canopy. During square ontogeny, the nitrogen (N), phosphorous (P) and potassium (K) concentrations of sympodia l leaves and floral bracts decreased, whereas the calcium (Ca) and magnesiu m (Mg) increased, and sulfur (S) concentration exhibited little change (lea ves) or increased (bracts) with increasing square age. The N, P, Ca, and S concentrations in floral buds declined synchronously; K and Mg concentratio ns showed an increasing trend within the first 20 days, peaked at about 25- day square age, and then sharply decreased three to five days before flower ing. During square development, the effect of main-stem node (MSN) and symp odial branch fruiting position in the plant canopy on mineral nutrient elem ent concentrations of bracts was greater than on those of floral buds. Diff erences in the mineral nutrient element concentrations existed among the sy mpodial leaves, bracts, and floral buds. This study provides the patterns o f mineral nutrient element concentrations in these plant tissues during the square development phase in relation to MSNs and branch fruiting positions in the cotton plant canopy.