1.
Effect of substrates and free ammonia on kinetic characteristics of nitritation and nitratation by entrapped nitrifiers.
Li, Z, Zhang, Z, Zhang, Z
Journal of environmental biology. 2014;(4):759-63
Abstract
In the present study, nitrifying bacteria entrapped in waterborne polyurethane gel was used to investigate the kinetic characteristics of nitritation and nitratation in relation to achieve shortcut nitrification. The nitrite accumulation rate was over 80% during the acclimation period. The following kinetic parameters were experimentally obtained: maximum nitrification rate (v(max)), half-saturation coefficient (K(s) and K(o)), and inhibition coefficient (K(IH)). The bacterial populations were also determined by fluorescence in situ hybridization. 73.5% proportion of ammonia oxidizing bacteria (AOB) resulted in a significantly higher ammonia oxidizing rate than nitrite oxidizing rate, which is in agreement with higher V(max) of nitritation (608.5 mgNl(-1)-pellet h(-1)) over nitratation (66.3 mgN l(-1)-pellet h(-1)).
2.
Potassium nitrate application alleviates sodium chloride stress in winter wheat cultivars differing in salt tolerance.
Zheng, Y, Jia, A, Ning, T, Xu, J, Li, Z, Jiang, G
Journal of plant physiology. 2008;(14):1455-65
Abstract
A sand culture experiment was conducted to answer the question whether or not exogenous KNO(3) can alleviate adverse effects of salt stress in winter wheat by monitoring plant growth, K(+)/Na(+) accumulation and the activity of some antioxidant enzymes. Seeds of two wheat cultivars (CVs), DK961 (salt-tolerant) and JN17 (salt-sensitive), were planted in sandboxes and controls germinated and raised with Hoagland nutrient solution (6 mM KNO(3), no NaCl). Experimental seeds were exposed to seven modified Hoagland solutions containing increased levels of KNO(3) (11, 16, 21 mM) or 100 mM NaCl in combination with the four KNO(3) concentrations (6, 11, 16 and 21 mM). Plants were harvested 30 d after imbibition, with controls approximately 22 cm in height. Both CVs showed significant reduction in plant height, root length and dry weight of shoots and roots under KNO(3) or NaCl stress. However, the combination of increased KNO(3) and NaCl alleviated symptoms of the individual salt stresses by improving growth of shoots and roots, reducing electrolyte leakage, malondialdehyde and soluble sugar contents and enhancing the activities of antioxidant enzymes. The salt-tolerant cultivar accumulated more K(+) in both shoots and roots compared with the higher Na(+) accumulation typical for the salt-sensitive cultivar. Soluble sugar content and activities of antioxidant enzymes were found to be more stable in the salt-tolerant cultivar. Our findings suggest that the optimal K(+)/Na(+) ratio of the nutrient solution should be 16:100 for both the salt-tolerant and the salt-sensitive cultivar under the experimental conditions used, and that the alleviation of NaCl stress symptoms through simultaneously applied elevated KNO(3) was more effective in the salt-tolerant than in the salt-sensitive cultivar.