Effects of local nitrogen supply on water uptake of bean plants in a split root system

To study the effects of local nitrogen supply on water and nutrient absorption, French bean (Phaseolus vulgaris L.) plants were grown in a split root system. Five treatments supplied with different nitrogen forms were compared: homogeneous nitrate (NN) and homogenous ammonium (AA) supply, spatially separated supply of nitrate and ammonium (NA), half of the root system supplied with N-free nutrient solution, the other half with either nitrate (N0) or ammonium (A0). The results showed that 10 d after onset of treatments, root dry matter (DM) in the nitrate-supplied vessels treated with NA was more than two times higher than that in the ammonium-supplied vessels. Water uptake from the nitrate-supplied vessels treated with NA was 281% higher than under ammonium supply. In treatments N0 and A0, the local supply of N resulted in clearly higher root DM, and water uptake from the nitrate-supplied vessels was 82% higher than in the -N vessels. However, in A0 plants, water uptake from the -N nutrient solution was 129% higher than from the ammonium-supplied vessels. This indicates a compensatory effect, which resulted in almost identical rates of total water uptake of treatments AA and A0, which had comparable shoot DM and leaf area. Ammonium supply reduced potassium and magnesium absorption. Water uptake was positively correlated with N, Mg and K uptake.