蓝藻结皮群落结构与结皮强度的连接机理

Cyanobacterial crusts are the first stage of biocrust formation, and it is the only feasible pathway that is able to be applied in desertification control at a large scale by now. During the formation process, the crusts that Microcoleus dominated is nearly the global first stage, and then the abundance of Scytonema obviously is enhanced as well, and at the later stage, the surface color of the crusts becomes dark and the cohesion is correspondingly stronger. Therefore, cyanobacterial crusts were obviously divided into two types, namely Microcoleus crusts and Scytonema crusts. .In order to deep revealed the mechanism that cyanobacteria stabilizing sand surface, the project would firstly study on the fine community structure of the crusts dominated respectively by Microcoleus and Scytonema by high-throughput sequencing approach, the natural samples would carefully take from Horqin Sandy Land, Hopq Desert and Gurbantunggut Desert. In order to obtain the driver factors of the community structure, the real-time PCR for main organisms and soil parameters (such as pH, EC, texture, nutrient and ion etc.) would be also considered. Then we would construct the man-made Microcoleus and Scytonema crusts in the field, take typical samples at different stages including the crustal formation and disintegration stages, check their activities of extracellular enzymes (glucosidase, cellulase, hemicellulase, chitinase, N-acetyl glucosamine enzymes, insoluble acid invertase of cell wall) and the contents of extracellular polymers (total amount, capsular part and released part), organic carbon concentrations (total organic carbon, biomass carbon and labile carbon), and main microorganisms and soil parameters, try to link the community structure and crustal strength by structural equation models. At the same time, we would combine metagenomic and metatranscriptomic approach synchronously, insight the functional community structure and metabolism traits, quantify the speed their fixation and degradation in carbon and nitrogen by 13CO2和15N2 approach, and explore the real community structure that participatating in the metabolism by DNA-SIP method. In order to predict the distribution depths of microorganisms possessing potential in degradation of different extracellular polymers, the crustal vertical profiles in light intensity, pH, Rd, N2O, NO and O2 were detected by microelectrodes at micrometer scale. Finally, we would focus on the extracellular enzymes, using their all information from metagenomic, metatranscriptomic and DNA-SIP analysis, insight the mechanism on community structure and crustal strength both from the selectivity on extracellular polymers, metabolism pathways on glycans and microbial composition and abundance.

蓝藻结皮是生物结皮形成的首要阶段，也是生物结皮固沙技术可规模化应用的唯一途径。为揭示其固沙机理，本项目拟以蓝藻结皮群落系统为依托，选择强度不同的微鞘藻结皮和伪枝藻结皮，先通过基于核糖体的高通量测序、核酸定量及环境检测，掌握它们的分类群落结构及关键环境要素。然后原位构建人工结皮，在结皮发育形成和胁迫解体的不同节点，从胞外酶活性与胞外聚合物各部、有机碳各部、主要微生物、及土壤要素的交互变化规律，通过结构方程模型，建立群落结构与结皮强度的生化连接；从宏基因组、宏转录组分析，透视结皮强度与群落功能基因和代谢途径的连接；从同位素标记和DNA-SIP技术，确定代谢强度和功能群落；从结皮剖面微米级理化指标，掌握不同功能菌群的垂直分布和活性大小；最后，聚焦结皮强度维持、及自养和异养微生物物质与能量主要连接的EPSs，从它们利用的偏好性、胞外聚糖代谢和参与微生物的群落结构，解析群落结构与结皮强度的连接机理。

蓝藻结皮是生物结皮形成的首要阶段，也是生物结皮固沙技术目前可应用的唯一途径。为深入揭示其固沙机理，本项目以地衣结皮和藓结皮为参照，选择强度不同的微鞘藻结皮和伪枝藻结皮，先通过基于原核和真核核糖体的高通量测序、核酸定量及环境检测，揭示群落结构及与环境要素的关系，细菌、微真核和古菌的聚集规律和被确定性与随机性影响的机制。然后，利用宏基因组技术，从碳、氮、硫循环特征、关键变量、及结皮稳定性的关系，透视结皮强度与群落功能基因、代谢途径、及元素循环的连接；结合宏转录组、宏蛋白组、同位素标记等技术，发现整个代谢被胞内外高分子降解基因活性比调节，夏季以偶联硫循环的混合营养为主，秋季以偶联氮循环的光自养为主；蓝藻结皮和藓结皮在夏季积累的生物量碳较秋季更多，地衣结皮则在秋季积累更多。在组学初步认识后，以2株蓝藻为材料，研究它们在不同生长阶段细胞表面特性(表面电性、疏水性、官能团)、胞外多糖(EPSs)荚膜和释放部分产量、单糖组分、官能团和水溶性粘度，探究了它们EPSs与结皮稳定速率间的关系，获得优良藻株；再利用优良藻株，在库布齐沙漠流沙上原位构建了人工结皮，在结皮形成不同阶段，检测细胞壁成分相关胞外酶活性、胞外聚合物、有机碳(OC)、微生物、及土壤理化属性，同步进行宏基因组、宏转录组、宏蛋白组分析，利用大数据模型建立群落结构、代谢与结皮强度的连接路径和机理；还对我们团队以往恢复的人工结皮中蓝藻进行测序鉴定，发现即使恢复15年的生物结皮，其中的优势固沙蓝藻仍是初期接入的Microcoleus vaginatus和Scytonema javanicum。总之，结皮富碳储留特征，与强度正相关的EPSs，主要受pH和PO43+影响，通过蓝藻等为主的同化聚群增加OC，受氧化还原电势、C/N、溶解态有机碳、湿度等影响，通过酸杆菌等为主异化菌群降解OC，而合成与分解间的平衡受干旱度和盐度调节。

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