关键词: 海南省、热带水果、比较优势, 海南省、热带水果、比较优势

Abstract:

In the present study, whole- and split-root experiments were together conducted to study the effects of different nitrogen (N) forms on the concentration and accumulation of nutrient elements in different parts of tomato (Lycopersicon esculentum Mill.) seedlings. Results obtained were as follows. Under both homogeneous and localized supply, the concentration of total N in flower was higher than those in leaf and root and they are all higher than that in stem. In a whole-root system, with the increase of NH4+/NO3- ratio in nutrient solution, the concentration of total N increased both in leaf and stem. The mixed supply of NO3- and NH4+ nutrition at the ratio of 75:25 led to a significant increase in the concentration of phosphorus (P) and potassium (K) in root. In a split-root system, however, when compared to the controle (N|N), localized supply of sole NH4+ (N|A) significantly decreased the concentration of total N both in flower and stem, but increased the concentration of total N in the root which was exposed to sole NH4+, also it decreased the concentration of P and K in both half roots in N|A treatment. Localized supply of either sole NH4+ or the mixture of NO3- and NH4+ at the ratio of 75:25 both decreased the concentration of calcium (Ca) and magnesium (Mg) in all parts of tomato plants but increased the concentration of sulphur (S) in leaves. With the increase of NH4+/NO3- ratio in nutrient solution in a homogeneous supply, the concentration of boron (B) and manganese (Mn) in leaves and Zinc (Zn) and molybdenum（Mo）in leaves and root all increased. Local supply of sole NH4+ in solution significantly increased the concentration of Fe, B, Zn, Cu and Mo in root. In addition, the mixed supply of NH4+/NO3- led to a significant increase in N, P and K accumulation in the plants no matter what culture mode was.