土壤微生物对微量痕量碳源的响应机制研究--触发基质响应

Our preliminary work indicated that trace concentrations of substrates such as glucose, amino acids and root extracts (Trigger Substances) caused the soil microbial biomass to evolve about 2 to 5 times more CO2-C that was contained in the original substrate. Root extract produced the largest trigger substance response, presumably because it contained a large number of different, capable substances, capable of activating a wider range of micro-organisms than simple ones. The true significance of the ‘trigger response’ awaits evaluation. We consider that it may be due to the biomass shifting from a form of dormancy (albeit with high ATP and Adenylate Energy Charge) when it senses an input of substrate, which is first signaled by the (‘Trigger Substances). For example it may increase enzyme production at this stage. Our hypothesis is that the ‘trigger response’ is a previously unknown response of the microbial biomass which gives it an advantage in survival in the substrate poor environment in soil. The aim of this research is to fully investigate the phenomenon. We will use RNA/DNA analyses combined with 13C-labeled stable isotope probing and high-throughput sequencing technologies to investigate the soil total and active microbial communities, and further ascertain the functional microbial groups associated with the ‘Trigger Substance’ response. We will reveal the mechanism of the Trigger Substances Response’, and accept or reject our hypothesis.We believe that, when fully evaluated, the ‘Trigger Substances’ response could well be one of the most intriguing phenomena in soil microbiology to emerge in recent times.

早期的研究表明，微小痕量物料（触发基质）的输入，如葡萄糖、氨基酸、根系提取物等，都会引起土壤微生物释放出2-5倍于物料碳量的CO2。其中，根系提取物导致土壤释放的CO2量最大，这可能与基质本身结构更为复杂，激活微生物种类更多有关。我们提出“触发基质响应”理论，主要指土壤中某类“触发基质”激活休眠状态（尽管具有高的能量）的微生物，释放胞外酶，以充分地利用全部输入底物及其它有机碳源类物质的现象，这也可以解释微生物在贫瘠环境里的生存策略。不过，目前的研究还较为罕见，大多仅是理论的提出且有待验证。本研究通过培养实验验证触发分子响应现象是否普遍存在于不同类型土壤，通过DNA-SIP、高通量测序等技术分析微生物种群结构并获取与触发响应过程有关的功能微生物，揭示这些微生物组群如何驱动触发分子响应过程，结合基质土壤理化特征，深入探究触发基质响应的机制，最终接受或拒绝触发基质响应的假说。

微量的易分解底物（如葡萄糖和植物根系提取物）的添加可以引起土壤在几小时到几天内释放出数倍于添加底物碳量的触发碳，这个现象被定义为触发基质响应。然而迄今有关土壤触发基质响应的研究还十分有限，探究触发基质响应的影响因素，微生物量动态和参与周转的碳库有助于全面理解触发基质响应。本研究通过13C同位素标记技术和高通量测序技术，研究了不同土壤类型、底物浓度、底物类型和土壤深度影响下的土壤微生物触发基质响应，微生物量动态和触发碳碳源，揭示了驱动触发基质响应的关键族群。实验结果表明，触发基质响应是一个短暂的微生物响应过程，主要分为两个阶段，前期（0-24小时）由底物矿化诱导，后期（24-120小时）由微生物生物量碳（MBC）的消耗主导。实验结果为验证土壤微生物的触发基质响应提供科学证据，增进对土壤碳周转过程的理解，为土壤微生物底物周转和全球变暖研究提供理论基础。