稻虾共作模式下稻田土壤反硝化作用的变化及其功能微生物的调控机理

Denitrification is one of important components of terrestrial nitrogen cycling, and is also a factor affecting crop nitrogen use efficiency. Rice-crayfish integrated system can intensively use natural resources and increase in rural incomes, which has been developed rapidly in China. Aquatic organisms raised in paddy field can change soil substrate concentration and microbial habitat, hereby affecting soil denitrification. However, the effect of field modification engineering on soil denitrification is relatively discussed. Moreover, relatively less research reveals the relationship between denitrification and related microorganisms in the rice-crayfish system under integrated crop–aquatic organism–soil–microorganism system. Therefore, a field experiment is conducted to study changes in soil nitrogen pools under different rice cropping systems (traditional rice cultivation and rice-crayfish integrated system). Using lab incubation, we will evaluate changes in the intensity, potential and rate of soil denitrification. We will also study changes in the community composition of denitrifying microorganims by terminal-restriction fragment length polymorphism (T–FRLP). Moreover, we will measure nirS and nirK abundances by RT-PCR to quantify denitrifying microorganisms. Furthermore, the study will also reveal the driving mechanism of denitrifying microorganisms to denitrification. Therefore, the study will provide a scientific basis on how to apply nitrogen fertilizers to develop the ecological planting–breeding model.

稻田土壤反硝化作用是陆地氮循环的重要组分，也是影响氮肥利用率的重要途径。稻虾共作作为一种集约利用自然资源，有利于增加农民收入的稻作模式，在我国已得到迅速发展。然而，该系统由于虾的引入，改变了土壤底物浓度与微生物的生境，势必影响着土壤反硝化作用，但是其田间工程改造的影响往往被忽略。此外，较少研究从“作物—水生生物—土壤—微生物”角度探讨稻虾共作下反硝化微生物与硝化作用的内在关系。为此，本项目拟通过大田试验，设置传统稻作和稻虾共作两种模式，研究土壤氮库的动态变化规律；利用室内培养法研究土壤反硝化作用的变化特征；利用T–FRLP技术，研究稻虾共作下功能微生物群落结构；利用定量PCR技术，测定nirS、nirK基因的丰度，研究土壤反硝化微生物的数量特征；结合土壤碳氮变化，探明稻虾共作下反硝化微生物对反硝化作用的影响机理。本项目旨在为发展稻虾共作模式及制定合理氮素管理措施提供理论依据。

稻田土壤反硝化作用是陆地氮循环的重要组分，也是影响氮肥利用率的重要途径。稻虾共作作为一种集约利用自然资源，有利于增加农民收入的稻作模式，在我国已得到迅速发展。然而，该系统由于虾的引入，改变了土壤底物浓度与微生物的生境，势必影响着土壤反硝化作用。本项目通过大田试验，研究了稻虾共作模式对土壤水体氮素动态、土壤有机碳库、土壤水体氧气可利用性、土壤反硝化作用、土壤温室气体排放和土壤反硝化微生物的影响。结果表明：在水稻全生育期，虾稻田的土壤NH4+含量比常规稻田降低了18.5%。与常规稻作模式相比，短期稻虾共作模式下土壤总有机碳和稳定态碳含量并没有显著差异，但是增加了土壤活性有机碳的含量。稻虾共作模式增加了土壤和水体pH含量，提高了土壤Eh，增加了田面水DO，降低了土壤反硝化作用强度、反硝化作用速率和反硝化势，分别降低了稻季、非稻季、全年N2O排放35.54%、50.82%和37.75%。稻虾田土壤细菌微生物群落发生了明显的变化，在水稻种植前，nirK基因拷贝数减少了37.32%，nirK/nirS降低了38.48%。因此，本项目表明，虾稻共作模式下更好的土壤通气性，更低的矿质氮水平、更高的活性有机碳含量，改变了土壤细菌微生物的群落结构，降低了反硝化细菌的丰度，进而抑制了土壤反硝化作用，降低了N2O排放。本研究能够为虾稻共作模式进一步合理氮肥管理，减少温室气体排放提供理论依据。