持续加强的人类活动和剧烈的全球环境变化正在对陆地生态系统产生干扰。如干旱的强度和土壤盐渍化的日益加剧，不仅影响地上生态系统过程，也对地下生态系统过程产生影响。土壤细菌和真菌作为陆地生态系统的重要组成成分和分解者，其群落组成和多样性对上述干扰的响应也会影响地上和地下生态系统功能。秸秆的分解是农业生态系统中重要的生态过程，在土壤生态系统稳定和土壤资源的可持续利用上扮演着重要角色，但目前关于极端干旱对盐渍化农田土壤中微生物群落结构和秸秆分解影响的认识还较为缺乏。本研究通过室内实验，研究极端干旱水分恢复后盐渍化土壤微生物（细菌和真菌）群落组成和多样性变化特征，探究极端干旱及其遗留效应对盐渍化土壤中玉米秸秆分解的影响及机理。得出以下结果：

（1）极端干旱使得水分恢复后第3和21周的细菌OTU低于连续湿润处理，且显著性差异表现在第3周。极端干旱显著降低盐渍土中水分恢复后第3周的细菌Shannon多样性和Simpson多样性。极端干旱降低水分恢复后第3和21周的细菌Chao1指数和ACE指数。水分恢复3周后，极端干旱与连续湿润处理间细菌β多样性有较大的差异，后期差异减小。极端干旱降低与有机物质分解和促进细胞呼吸有关细菌属（Roseiflexus属和Haliangium属）的相对丰度。

（2）盐渍土中极端干旱处理水分恢复后第3和21周的细菌OTU、Shannon指数和Simpson指数显著高于非盐渍土。盐渍土中水分恢复后各时间段的细菌Chao1指数和ACE指数高于非盐渍土。水分恢复前期，极端干旱与连续湿润处理间细菌β多样性有较小的差异，后期差异增大。盐分降低了与有机物质降解和N循环有关的细菌属（Gaiella属和Sphingomonas属）的相对丰度，但增加了与P循环有关的细菌属（Gemmatimonas属）的相对丰度

（3）极端干旱和盐分对水分恢复后不同时间段的土壤真菌OTU、α多样性均没有显著影响。极端干旱使得水分恢复后第3和21周的真菌Shannon指数以及第3周的Chao1指数和ACE指数高于连续湿润处理，但差异性不显著。在连续湿润处理中，盐渍土使得水分恢复后第21周的Shannon、Chao1和ACE指数均高于非盐渍土。水分恢复后第3周，极端干旱与连续湿润处理间真菌β多样性有较大的差异；而水分恢复后第21周，盐渍土与非盐渍土处理间真菌β多样性有较大的差异。极端干旱使得非盐渍土中水分恢复后第15和21周的真菌属（相对丰度>0.5 %）相对丰度低于连续湿润处理；盐渍土使得促进有机质分解类真菌（Chaetomium属和Mortierella属）相对丰度增加。

（4）极端干旱显著地影响玉米秸秆分解率，使得秸秆的分解率显著低于连续湿润处理。极端干旱显著降低盐渍土和非盐渍土中第8、12和30周秸秆N和P的累积释放率。极端干旱显著降低第12和30周秸秆K释放率。极端干旱使得第30周秸秆C释放率低于连续湿润处理，且显著性差异体现在非盐渍土处理。极端干旱使得盐渍土中第8周和12周的剩余秸秆C/N显著低于连续湿润处理，但使得30周的剩余秸秆C/N显著高于连续湿润处理。

（5）第8、12和30周盐渍土中秸秆N释放率高于非盐渍土，且显著性差异表现在第8周的连续湿润处理。盐渍土中第8、12和30周的秸秆P释放率高于非盐渍土，且显著性差异表现在不同时间段和水分处理。盐渍土使得极端干旱处理中第12、30周和连续湿润处理中第30周的秸秆K释放率显著高于非盐渍土。盐渍土使得连续湿润处理中第8、12和30周的剩余秸秆C/N显著高于非盐渍土。

（6）秸秆K和C的释放率与真菌光黑壳属Preussia、细菌鞘氨醇单胞菌属Sphingomonas、细菌组粘菌属Haliangium等与有机质分解功能的属正相关性较强。秸秆N和P的释放率与细菌Shannon指数、细菌Chao1指数、细菌组粘菌属Haliangium和细菌溶杆菌属Gaiella相关性较强。

Human activities and dramatic global environmental changes are disrupting terrestrial ecosystem. Drought events and soil salinization are increasing, which have an impact on  underground ecosystem. Soil bacteria and fungi are important components and decomposers of terrestrial ecosystem, whose community composition and diversity in response to drought and salinization also affect the function of terrestrial ecosystem. Straw decomposition is an important ecological process in agro-ecosystem, which plays a significant role in soil ecosystem stability and sustainable utilization of soil resource. However, the research about the effect of extreme drought events on microbial community and straw decomposition in salinized farmland soil is still lacking. In this study, the community composition and diversity of microorganisms (bacteria and fungi) in salinized soil after extreme drought were studied through mesocosm experiment, and the effects of extreme drought and its legacy effects on the decomposition of maize straw in saline soil were studied. The results are as follows:

(1) In saline soil, extreme drought events significantly decreased bacterial Shannon index and Simpson index in the 3rd week after water recovery. Extreme drought events decreased bacterial Chao1 index and ACE index. At the early stage after moisture recovery, there was a significant difference in bacterial β- diversity between extreme drought treatments and wetting treatments. Extreme drought events reduced the relative abundance of Roseiflexus and Haliangium.

(2) Bacteria OTU, Shannon index and Simpson index in saline soil was significantly higher than that of non-saline soil in the 3rd and 21st weeks after moisture recovery under extreme drought treatments. Bacterial Chao1 index and ACE index in saline soil were higher than that in non-saline soil after moisture recovery. At the later stage after moisture recovery, there was a significant difference in bacterial β- diversity between saline soil treatments and non-saline soil treatments. The relative abundance of Gaiella and Sphingomonas reduced in saline soil treatments, which are associated with organic matter degradation and N cycling. However, the relative abundance of Gemmatimonas increased, which is associated with P cycling.

(3) Extreme drought events and soil salinity had no significant effect on soil Fungal α-diversity and OTU at different stages after moisture recovery. The Shannon index of fungi was higher than that in the wetting treatments at the 3rd and 21st week after moisture restoration , and the Chao1 index and ACE index at the 3rd week were higher than that in the wetting treatments. The Shannon index, Chao1 index and ACE index of saline soil were all higher than those of non-saline soil at the 21st week after moisture recovery in wetting treatments. There were significant differences in fungal β- diversity between extreme drought treatments and wetting treatments at the early stage after moisture recovery, and between saline and non-saline treatments at the later stage after moisture recovery. The total relative abundance of fungi (relative abundance > 0.5 %) in non-saline soil at 15th week and 21st week after moisture recovery was lower than that in wetting treatments due to extreme drought. Saline soil increased the relative abundance of Chaetomium and Mortierella.

(4) Extreme drought events significantly reduced the decomposition rate of maize straw. Extreme drought events significantly reduced the N and P cumulative release rate of straw at the 8th, 12th and 30th weeks in the saline and non-saline soil. Extreme drought events significantly reduced K cumulative release rate of straw at the 12th week and the 30th week. Extreme drought events reduced the C cumulative release rate of straw in the 30th week. In the saline soil, extreme drought events made the C / N of residual straw in the 8th week and 12th week significantly lower than that in the wetting treatments, but made the C/N of residual straw in the 30th week significantly higher than that in the wetting treatments.

(5) The N cumulative release rate of straw at the 8th, 12th and 30th weeks in saline soil was higher than that in non-saline soil. The P cumulative release rate of straw at the 8th, 12th and 30th weeks was higher than that in non-saline soil. The K cumulative release rate of straw at the 12th and 30th weeks was significantly higher in saline soil than in non-saline soil. The residual straw C/N at the 8th, 12th and 30th weeks of wetting treatments was significantly higher in saline soil than in non-saline soil.

(6) The release rate of straw K and C had a positive correlation with the genuses of bacteria and fungi having the function to decompose organic matter such as Preussia, Sphingomonas, Haliangium and so on.