Effects Of Intensive Management On Soil CO₂、N₂O Emission And Ammonia-oxidizing Organisms In Phyllostachys Praecoxf.prevelnalis Forest

Heavy winter mulching to increase soil temperature and winter fertilization are widely usedtechniques for intensive management of Lei Bamboo （Phyllostachys praecoxf.prevelnalis）forests to increase bamboo shoot production and economic return. However, the effect of thoseintensive management techniques on CO₂and N₂O emissions and soil ammonia-oxidizingorganisms is poorly understood. We conducted two experiments: a) the first contrast experiment tostudied the effect of different feitiliaers on gas emission and soil ammonia-oxidizing organisms inLei Bamboo （Phyllostachys praecoxf.prevelnalis） forests mulched; b) the second experimentto validated the effect of the first experiment in the field unmulched without plants.The results showed that CO₂and N₂O emissions were2-14times （average=6.8times） and7-47times （average=26.3times）, respectively, higher in the mulched than in the un-mulched plots.The mulched plots released about194ton ha^-1more CO12and38kg ha-more N₂O than theun-mulched plots during the four months experiment period. There was no systematic fertilizertreatment effect on CO₂emission in the second experiment; however, the highest N₂O emissionrates were observed in the urea alone treatment. The redundancy analysis （RDA） indicated that thegreenhouse gas emission rates were negatively related to soil nutrient concentration. In order toreduce greenhouse gas emissions from intensively managed bamboo forests, we recommend thatcompound fertilizers or the combination of urea and KCl fertilizers should be applied andapplying urea along should be avoidedSoil samples were collected on the date one month after fertilization and mulching. Thecomposition and abundance of soil AOB and AOA communities under different treatments wereinvestigated using denaturing gradient gel electrophoresis （DGGE） and real-time polymerasechain reaction （RT-PCR）. It was found that from the first trial that mulching practice improved theactivity of soil AOB but did not alter its community structure significantly. Soil AOB communitystructure was affect by fertilizer treatments at some extent, with three repetitions were firstclustered as one group and the similarity among the repetitions were higher than those betweentreatments. However, the affect did not reached at significant level with all the samples beingclustered at the similarity of0.61. Soil AOB diversity （Shannon index） was improved bycompound fertilizer （Treat1） but deceased by urea （Treat2）, especially by urea and potassium chloride （Treat3）. The abundance of soil AOB characteristic as amoA gene copy number wasenhanced by fertilizer application with the order as Treat2＞Treat3＞Treat1＞Control2（nofertilizer）, the Urea treatments （Treat2and Treat3）was much higher than （p<0.05） CK2,indicating urea greatly stimulated the activity of soil AOB. Soil AOA community and diversity（Shannon index） were not affect by both mulching and fertilization practice with all the samplesbeing clustered at the similarity of0.67. As similar to soil AOB, mulching practice improved theactivity of soil AOA but did not alter its community structure significantly. The abundance of soilAOA characteristic as amoA gene copy number was the highest in Treat3, followed by CK2andTreat2, and the lowest in treat, the significant difference （p<0.05） was observed between thehighest and lowest. Relative lower ratios of AOA to AOB （less than0.5） compared with otherreports were observed, indicating the quite different composition of soil ammonia-oxidizingorganisms induced by intensive management in Lei Bamboo stand.In conclusion, accumulating result would be expected by application of the same fertilizer forlong time although short-term affect was not considerably. Winter mulching and over fertilizationcould result in negative impacts of soil ammonia-oxidizing organisms, combining with the stagecharacteristic of nitrification inhibitors DMPP and diversity characteristic of soilammonia-oxidizing organisms. It was recommended to apply proper rate of N, K and DMPPrather than large amount of single urea.