炭化秸秆对苹果根系一氧化氮生成及根区土壤硝酸盐代谢的影响

Effects of Carbonized Straw on the Nitric Oxide Formation and Nitrate Metabolism in Apple Roots and Its Root Zone Soil

【目的】土壤硝酸盐既是果树的氮素营养来源,也是潜在的环境污染因素;炭化秸秆是作物秸秆不完全燃烧的产物,施入土壤能够改善土壤的理化特性。本研究主要探讨苹果根系和根区土壤一氧化氮(NO)及土壤硝酸盐代谢相关酶在土壤施用炭化玉米秸秆后的变化,旨在揭示炭化秸秆对苹果根系及根区土壤硝酸盐代谢的调控作用,从而为控制土壤硝酸盐转化及改善果园土壤管理提供理论依据。【方法】在春季,将炭化玉米秸秆与土壤按照0.5%—8.0%(w/w)的比例混匀后装入陶盆,然后将生长势相近的3年生‘富士’苹果幼树(砧木为平邑甜茶)移栽到陶盆中,于移栽120—190 d后定期检测苹果根系和根区土壤NO生成速率以及硝酸还原酶(NR)的活性,并分别测定根系一氧化氮合酶(NOS)活性和根区土壤亚硝酸还原酶(NiR)与羟胺还原酶(HyR)活性以及土壤硝化强度的变化等。【结果】苹果根系及其根区土壤NO生成和硝酸盐代谢对炭化秸秆施用量的反应明显不同,根系NO生成速率和一氧化氮合酶活性在炭化秸秆施用量为1.0%—2.0%(w/w)时明显升高,在8.0%时显著下降;根系硝酸还原酶活性在炭化秸秆施用量为0.5%—2.0%(w/w)时明显升高,在4.0%—8.0%时显著下降;在处理后第120—170天,炭化秸秆对根系NO生成和硝酸还原的作用效果更突出。在炭化秸秆施用量为0.5%时,根区土壤NO生成速率、硝酸还原酶活性和亚硝酸还原酶活性均明显升高;在炭化秸秆施用量超过1%后,土壤硝酸还原酶和亚硝酸还原酶活性明显降低;在炭化秸秆施用量超过2%时,土壤NO生成速率则明显降低;在处理后第120—155天,炭化秸秆对根区土壤NO生成和硝酸还原的作用最明显。施用炭化秸秆还明显促进苹果根区土壤的硝化作用,在炭化秸秆施用量为2.0%—4.0%时,土壤硝化强度提高最明显;随着炭化秸秆用量由0.5%增加到8.0%,根区土壤羟胺还原酶活性逐渐升高;在施用后140—170 d,炭化秸秆对根区土壤硝化作用的效果最显著。【结论】土壤施用炭化秸秆明显干扰苹果根系及根区土壤硝酸盐代谢,较低施用量(0.5%—1.0%)的炭化秸秆促进根系和土壤硝酸盐还原形成NO,较高施用量(2.0%—4.0%)的炭化秸秆增强根区土壤的硝化作用,其中,0.5%的炭化秸秆对根区土壤硝酸盐还原的促进作用最突出,1.0%的炭化秸秆对根系NO的生成作用最显著,根区土壤硝化强度在炭化秸秆施用量为2%时达到最大。

【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 application rate 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%.