This study was conducted to determine whether using wood vinegar instead of nitric acid to adjust the pH of nutrient solution in hydroponics had any effects on the lettuce. Photosynthesis, mineral elements, water absorption, and the growth of the lettuce were all comparable to those of lettuce in the control group, in which nitric acid was used to adjust the pH. Nitric acid was added to half a unit of Enshi formula to adjust the pH of the control group. The rates of growth, water and mineral element absorption, and photosynthesis were low in lettuce plants grown in nutrient solution with 1 ml L -1 wood vinegar. However, the lettuce grown in solutions with 0.25 ml L -1 wood vinegar showed no significant differences from the control group. Therefore, wood vinegar concentration of 0.25 ml L -1 was found to be sufficient to keep the pH of the nutrient solution within the optimum range for growth.
Hydroponic cultures were conducted to investigate the effects of phosphorus (P), sulfur (S), and silicon (Si) on arsenic (As) accumulation and toxicity to wheat seedlings. The results showed that As concentrations in roots and shoots of wheat seedlings and arsenite [As(III)] in the nutrient solution were significantly decreased with increasing P concentrations. Si had no significant effect on As accumulation in wheat seedlings until the Si concentration was increased to 960 lmol L -1 . In the treatment with 960 lmol L -1 Si, both arsenate [As(V)] uptake and As(III) efflux were significantly decreased compared to the treatment without Si. The application of 480 and 960 lmol L -1 S resulted in a significant decrease in As concentrations in wheat shoots, but an increase in As accumulation in wheat roots. Both total As(III) efflux and the relative As(III) efflux were significantly decreased when the S concentration was 960 lmol L -1 . Different concentrations of P significantly increased the relative root elongation (RRE), total root length (TRL), root surface area (RSA), root volume (RV), and number of root tips (NRT), and decreased root average diameters (RAD). There were no significant effects of S on RRE, TRL, RSA, RV, RAD, and NRT of wheat seedlings under 15 lmol L -1 As(V). Silicon with concentration of 960 lmol L -1 significantly increased TRL and TRS of wheat seedlings when compared with the treatment without Si under 15 lmol L -1 As(V).
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