氮素形态对专用小麦中后期根际土壤微生物和酶活性的影响

Effects of nitrogen forms on rhizosphere microorganisms and soil enzyme activity under cultivation of contrasting wheat cultivars during booting and grain filling period

采用盆栽方法研究了酰胺态氮、铵态氮和硝态氮对强筋小麦(Triticum aestivum L.)"豫麦34"、中筋小麦"豫麦49"和弱筋小麦"豫麦50"生育中后期根际微生物和土壤酶活性的影响。结果表明,专用小麦根际真菌、细菌、放线菌数量和土壤脲酶、蛋白酶、硝酸还原酶活性以及根际pH值对氮素形态的反应不同。"豫麦34"施用硝态氮,对根际土壤真菌、细菌(除成熟期外)和放线菌数量均具有明显的促进作用;"豫麦49"施用铵态氮,根际土壤细菌和放线菌数量最大,根际真菌数量在孕穗期和开花期以酰胺态氮处理最大,而成熟期以硝态氮处理最大;"豫麦50"施用硝态氮,对根际土壤真菌、细菌和放线菌数量均具有明显的促进作用。不同专用小麦品种均表现为在酰胺态氮处理下,根际土壤脲酶活性最高;在铵态氮处理下,根际土壤蛋白酶活性最高;在硝态氮处理下,根际土壤硝酸还原酶活性和pH值最高。

Soil microorganisms and enzymes are main components of soil biochemical properties. They play an important role in nutrient transformation and decomposition of crop residues. Application of different forms of nitrogen is an important measure to regulate nitrogen metabolism of wheat （ Triticum aestivum L. ）. In order to understand the effects of nitrogen forms on rhizosphere microbial populations and soil enzyme activity under cultivation of contrasting wheat cultivars with specialized end-uses from booting stage to grain filling period, pot experiments were carried out on a sandy loam at the Experimental Farm of Henan Agricultural University during 2004 --2006. The soil contained 9.1 g·kg^-1organic matter, 0. 90g·kg^-1 total N, 22.68 mg·kg^-1 olsen-P and 0.23 g·kg^-1 NH4OAc-K. Each pot （30cm in diameter and 40 cm in height） was filled with 20 kg of sieved soil. Cultivars used in the study were： Yumai 34′ （ a strong gluten cultivar）, Yumai 49′（medium gluten） and Yumai 50′ （weak gluten）. Nitrogen forms were CO（ NH2 ）2-N, NH4＋ -N as NH4HCOaand NO3 -N as NaNO3. Nitrification inhibitors dicyandiamide （DCD） was applied to each pot. Prior to sowing, each pot received 3.06 g N, 2.9 g P2O5 and 3.3 gK2O, and additional 2.04 g N was also applied to each pot during the elongation stage. Seven plants from each pot were selected when plants had five leaves. The experiment was arranged in a completely randomized design with ten replications, and all pots were managed in the same way. Rhizosphere soil samples in a depth of 5 -- 20 cm for each treatment were taken at booting, flowering and ripening stage of wheat, respectively. Samples were fully mixed, put into sterile bags and transported to the lab as quickly as possible. Part of soil sample was sieved through a 1 mm screen for analysis of microbial quantity, and part was air-dried for determination of soil enzyme activities, including urease, protease and nitrate reductase with sodium phenoxide colorimetry, ninhydrin colorimetry and 2,4-D restraining, respectively. This study showed that the quantity of microorganisms, activity of enzymes and pH in rhizosphere soils planted with contrasting wheat cultivars for specialized end-uses responded differently to nitrogen forms. The quantitY of fungi, bacteria（ with the exception of ripening stage of wheat）and actinomyces were the highest for wheat cultivar ‘ Yumai 34’ received NO3 -N. while for cultivar ‘ Yumai 49’ , bacteria and actinomyces in rhizosphere soil were promoted greatly by NH4＋^-N, fungi populations were stimulated by CO（ NH2 ）2-N in booting and flowering stages and by NO3--N during grain filling. When NO3-N was applied to wheat cultivar Yumai 50＇, the quantity of fungi, bacteria and actinomyces in rhizosphere soil were increased greatly. The activity of urease, protease and nitrate reductase in rhizosphere soil of all three wheat cultivars were stimulated by CO（NH2） 2-N, NH4^＋-N and NO3^--N, respectively, and pH were the highest in NO3^--N treatments.