Effects of root-zone temperature and N, P, and K supplies on nutrient uptake of cucumber (Cucumis sativus L.) seedlings in hydroponics

The nutrient uptake and allocation of cucumber (Cucumis sativus L.) seedlings at different root-zone temperatures (RZT) and different concentrations of nitrogen (N), phosphorus (P), and potassium (K) nutrients were examined. Plants were grown in a nutrient solution for 30?d at two root-zone temperatures (a diurnally ?uctuating ambient 10 degrees C-RZT and a constant 20 degrees C-RZT) with the aerial parts of the plants maintained at ambient temperature (10 degrees C30 degrees C). Based on a Hoagland nutrient solution, seven N, P, and K nutrient concentrations were supplied to the plants at each RZT. Results showed that total plant and shoot dry weights under each nutrient treatment were significantly lower at low root-zone temperature (10 degrees C-RZT) than at elevated root-zone temperature (20 degrees C-RZT). But higher root dry weights were obtained at 10 degrees C-RZT than those at 20 degrees C-RZT. Total plant dry weights at both 10 degrees C-RZT and 20 degrees C-RZT were increased with increased solution N concentration, but showed different responses under P and K treatments. All estimated nutrient concentrations (N, P, and K) and uptake by the plant were obviously influenced by RZT. Low root temperature (10 degrees C-RZT) caused a remarkable reduction in total N, P, and K uptake of shoots in all nutrient treatments, and more nutrients were accumulated in roots at 10 degrees C-RZT than those at 20 degrees C-RZT. N, P, and K uptakes and distribution ratios in shoots were both improved at elevated root-zone temperature (20 degrees C-RZT). N supplies were favorable to P and K uptake at both 10 degrees C-RZT and 20 degrees C-RZT, with no significantly positive correlation between N and P, or N and K uptake. In conclusion, higher RZT was more beneficial to increase of plant biomass and mineral nutrient absorption than was increase of nutrient concentration. Among the three element nutrients, increasing N nutrient concentration in solution promoted better tolerance to low RZT in cucumber seedlings than increasing P and K. In addition, appropriately decreased P concentration favors plant growth.