Abstract: 【Objective】The soil nitrate is not only fruit tree’s nitrogen nutrition but also the latent environmental pollution factor. The carbonization straw, a product of incomplete combustion of crop straw, is applied into the soil to improve soil physical and chemical properties. This study focused on the changes of nitric oxide (NO) and nitrate metabolism related enzymes in the roots and the root zone soil of apple tree applied with carbonized corn straw. The purpose was to reveal the regulating effects of carbonized straw on the nitrate metabolism of apple roots and it’s root-zone soil, so as to provide a theoretical basis for the control of soil nitrate transformation and the improvement of orchard soil management.【Method】In the spring, the carbonized corn straw and soil was mixed according to the mass ratio of 0.5%-8.0% (w/w) and loaded to the clay pots, and then the 3-year-old ‘Fuji’ apple trees (rootstock for Malus hupehensis Rehd) in similar growth were transplanted to the pots. After 120-190 d of transplantation, the change of NO formation and the activity of nitrate reductase (NR) in roots and root zone soil was investigated, the activity of nitric oxide synthase (NOS) in roots and activity of hydroxylamine reductase (HyR) and the nitrification intensity in root zone soil were measured regularly.【Result】It was significantly different that the responses of nitric oxide formatiom and nitrate metabolic in roots and root zone soil to the applicationrate of carbonized corn straw to the soil. The rate of NO formation, the activity of NR and NOS in root increased significantly when carbonized straw applied into the soil at 1%-2% (w/w), and they all decreased significantly while the application rate reached 8%. The NR activity in root increased significantly when carbonized straw applied into the soil at 0.5%-2.0% (w/w) and dropped significantly while the application rate at 4.0%-8.0%. It was more significant after 120-170 d of treatment that the effects of carbonized straw on the nitric oxide formation and nitrate reduction in root. The rate of NO formation, the activity of NR and NiR in the soil of root zone all increased significantly when carbonized straw applied into the soil at 1%-2% (w/w). But the rate of NO formation decreased significantly when the carbonized straw applied over 1%; the activity of NR and NiR in root zone soil dropped significantly when the application rate over 2.0%. It was 120-155 d after treatment that the effects of carbonized straw on the nitric oxide formation and nitrate reduction in root were most significant. The application of carbonized straw promoted the nitrification in the soil of root zone. The nitrification strength of root zone soil reached maximum when the dose of carbonized straw applied at 2%, and soil HyR activity increased gradually with the application rate of carbonized straw increased from 0.5% to 8.0%. It was more significant after 120-170 d of treatment that the effects of carbonized straw on the nitrification of root zone soil.【Conclusion】The application of carbonized straw into soil influenced the NO formation in apple roots and the nitrate metabolism in root zone soil significantly. The reduction of nitrate to NO in apple roots and root zone soil is promoted by carbonization straw in the lower application rate of 0.5%-1.0%. The nitrification in the soil of root zone was promoted by carbonization straw in the higher application rate of 2.0%-4.0%. It is most significant that the nitrate reduction promoted by carbonization straw in the soil of root zone when the application rate was 0.5%. The rate of NO formation in roots was the highest when the application rate of carbonization straw was 1.0%. The nitrification strength of root zone soil was the highest when the application rate of carbonization straw was 1.0%.

Key words: carbonized straw, root, root-zone soil, nitric oxide, nitrate metabolism