Enzyme Activities And Microbial Diversities Of NifH、AmoA、NosZ Genes In The Soil Crust Of Different Sand-fixation Plantations

The purpose of this study was to determine the changes of microbial diversities of functional genes related to nitrogen cycle in the soil crust under age sequences of sand-fixation plantations in Horqin sandy land. Soil crusts under3typical sand-fixation plantations (Caragana microphylla, Hedysarum fruticosum and Artemisia halodendron) were selected as the research objects. The soil nutrient contents, enzyme activities and diversities of nifH, amoA or nosZ genes (PCR-DGGE-clone libraries) in the soil crust of different sand-fixation plantations were studied.The results showed that ages and types of plantations had significant influence on the contents of organic matter, total nitrogen, available nitrogen, total phosphorus and the activities of protease, urease, nitrate reductase and phosphomonoesterase. Under the same type of plantations, all the indicators in the crusts of C. microphylla and A. halodendron platations were increased along with the age, which was opposite to the trend of that of H. fruticosum. There were significant linear regression correlations between the plantatioan age and organic matter, total phosphorus and the enzyme activities (protease, urease, nitrate reductase and phosphomonoesterase), respecitively. Moreover, all the indicators in the soil crust of C. microphylla were significantly higher than those of the soil under crusts at the same age; and these indictors in the crust of A. halodendron plantations were the least among the three types.The diversities of functional genes related to nitrogen cycle were influenced by the age and type of plantations, too. The nifH and amoA genes diversities’trends along with growing ages were the same as soil nutrient contents and enzyme activities in all three soil crusts, while nosZ gene diversity almost remained at a certain level. Among all the28-yr and17-yr plantations, the C. microphylla had highest diversities of nifH and amoA genes, while the diversity of nosZ gene in the H.fruticosum was highier than those in the C. microphylla and A. halodendron. However, among13-yr plantations, the diversities of all three functional genes in the C. microphylla were higher than those in the A. halodendron. The soil crust of C. microphylla had higher nifH and amoA genes diversities than the soil under crusts obviously. The diversities of all three genes under the natural community of C. microphylla were almost same as those under the17-yr (or more) plantations.In general, all the identified nitrogen-fixing bacteria by cloning and sequencing belonged to y-Proteobacterium, Azotobacter chroococcum and Paenibacillus durus. Ammonium-oxidating bacteria within Nitrosospira and Nitrosomonas were widely distributed in all the soil crusts of different sand-fixation plantations and the species of denitrifying bacteria with nosZ genes includes Pseudomonas, Achromobacter and Azospirillum.