外源-土著菌谱系距离对腐秆菌在土壤中定殖及促腐的影响机制

Cellulose-decomposing bacteria can effectively accelerate decomposition and nutrient release of crop straws, which could help to promote crop seeding growth. The central issue in developing cellulose-decomposing bacteria is improving their colonization in cropland soil, which is determined by traits of alien cellulose-decomposing bacteria and resident native communities. Our previous studies suggested that bacterial phylogenetic distance could be a useful surrogate for the trait relationships of alien and native species. However, we know little about how alien-native phylogenetic distance influences the colonization and function of cellulose-decomposing bacteria in soils. Using soil microcosm and field experiments, we plan to investigate the phylogenetic distance (PD) and functional difference (FD) between inoculated cellulose-decomposing bacteria and resident bacterial communities, and link them to the colonization and function of cellulose-decomposing bacteria, using the 16S rRNA sequencing and BIOLOG ECO approach. Through GFP labeling and Q-PCR detecting methods, we will obtain the dynamics of survival and activities of inoculated soil cellulose-decomposing bacteria. The relationship between cellulose-decomposing bacteria colonization and wheat straw decomposition, and its association with PD will be identified by using solid-state 13C NMR spectroscopy that can identify the chemical structure of the wheat straw. Our findings will provide rationales for the selection of cellulose-decomposing bacteria as well as the theoretical basis for improved decomposition of crop straws.

腐秆菌能促进还田秸秆降解和养分释放，提高播种质量与秸秆养分还田利用率。腐秆菌接入土壤后能否成功定殖是其发挥促腐功效的关键，而这一过程主要受腐秆菌性质和土著菌特征调控。前期研究发现，外源-土著菌谱系距离可将外源菌性质和土著菌特征两影响因素整合在一起，但究其是如何影响腐秆菌在土壤中定殖和促腐的尚不清楚。本项目基于前期基础，采用室内模拟和田间原位试验相结合的方法，利用16S rRNA测序和BIOLOG 微孔板技术，解析外源腐秆菌与土著菌群间谱系距离及功能差异；通过GFP标记和Q-PCR检测技术，追踪腐秆菌接入土壤后的存活数量和活性，阐明外源-土著菌谱系距离对腐秆菌接入土壤后定殖状况的影响；利用固相13C-NMR技术，研究腐秆菌土壤定殖状况与还田麦秸化学结构变化的耦合关系，揭示外源-土著菌谱系距离影响腐秆菌促腐能力的作用机制。项目研究结果可为还田秸秆的促腐细菌筛选及快速腐解提供科学依据。

腐秆菌能促进还田秸秆降解，提高播种质量与秸秆养分利用率。腐秆菌的定殖及对土著菌群的影响均会调控其秸秆促腐，而这些均受腐秆菌性质和土著菌特征的影响。外源-土著菌谱系距离可整合外源菌和土著菌两方面影响，但究其调控菌株定殖和促腐的机制尚不清楚。本项目通过荟萃分析定量分析了外源腐秆菌田间施用的效应及影响因素；利用控制试验探究了外源腐秆菌与土著菌谱系距离对其土壤定殖、影响和促腐的作用及机制；结合田间试验对外源-土著菌谱系距离与腐秆菌促腐间关系做了验证。结果显示：与不施相比，施用腐秆剂总体上可显著促进秸秆降解（0.5614~1.3373），提升土壤氮磷钾含量（TN：0.8656~1.2749，TP：0.5104~1.4675，TK：0.151~0.6184，AN：0.653~1.1747，AP：0.6363~0.9284，AK：0.8253~1.1679）和作物产量（1.1342~1.4484），但当气候、土壤和施肥等不同时腐秆菌的作用强度和方向会改变，这表明外源菌与土著菌间环境适应和资源获取等性状差异会影响其定殖和促腐。外源-土著菌谱系距离可反映物种间生态位差异（SQR9：r=0.73，P=0.02；MC29：r=0.80，P=0.01），但不能反映相对适应性差异；外源腐秆菌的存活量和对土著菌群的影响程度均受谱系距离的调控，但二者的调控方向相反、调控程度也会随菌株种类和接入时间的改变而变化（前期存活，SQR9：r=0.75，P=0.02；后期存活，SQR9：r=0.68，P=0.05；前期影响，SQR9：r=-0.77，P=0.02）；各腐秆菌接种均可显著加速秸秆腐解，但潮土的秸秆促腐表现在前期而其余供试土壤的却在后期显现（P<0.05），腐秆菌接入后期的秸秆腐解率提升效应与其存活及影响均存在显著相关关系（存活，MC29：r=0.73，P=0.02；影响，MC29：r=0.79，P=0.01），从而说明外源-土著菌谱系距离可用于指导秸秆还田促腐时腐秆菌剂的选择和应用。考虑外源-土著菌谱系距离后采用的促腐处理（SFD2）与其他处理（CK、SFD1和SFD3）相比可显著提升沿淮稻田还田麦秸还田初期的降解量（P<0.05），改变土壤微生物量碳氮比（P<0.05）和提升作物产量（P<0.05），由此可知在试验区农田优选功能菌与土著菌群生态位差异较小的腐秆剂施用。