土壤含水量驱动土壤病毒和细菌多度及其与土壤异养呼吸关系的变化

土壤微生物是维持陆地生态系统稳定性和功能的重要组成部分。病毒是地球上数量最多的生物实体，也是若干类型生境中微生物数量的重要调节者。因此，了解病毒与微生物的相互作用，对深入认识包括碳循环在内的生态系统过程具有重要意义。在实验室建立土壤微宇宙实验系统，跟踪调查恒定低含水量、恒定高含水量和波动含水量3种水分处理下土壤病毒和细菌多度的变化，以及土壤异养呼吸速率对土壤病毒-细菌相互作用的响应。相较于低水分处理，高水分处理显著增加了病毒多度（P<0.001）和病毒-细菌多度比（P=0.0026），波动水分处理显著增加了病毒多度（P<0.001）。在高水分处理的土壤微宇宙中，细菌和病毒多度呈现出随时间动荡的信号，即细菌多度表现出增加-降低-增加的趋势，而病毒多度则表现出增加-降低的趋势，且其变化滞后于细菌。土壤异养呼吸速率与土壤含水量（P<0.001）、细菌多度（P=0.0045）和病毒多度（P<0.001）都具有显著的正相关关系。这些结果说明：病毒导致的下行控制可能是细菌多度的重要影响因子，在水分增加情形下，病毒有可能通过加速细菌的更新速率进而加速土壤呼吸。因此，病毒与细菌的相互作用可能是碳循环的重要决定因素。

Soil water content drives viral and bacterial abundances and their correlations with soil heterotrophic respiration

Soil microbes are a critical component for maintaining stability and function of terrestrial ecosystems. Viruses, the most abundant biological entities on the earth, can regulate the dynamics of microbial communities in several types of habitats. Therefore, understanding the interactions between viruses and microorganisms is of great significance for further exploring the ecosystem processes including carbon cycle. Here we report a microcosm experiment that addresses the possible link between top-down regulation of bacteria by viruses and soil heterotrophic respiration. Soil microcosms were set up in the laboratory and incubated under three water-content treatments (constant low-water, constant high-water and fluctuating water content). The changes of viral and bacterial abundances responded to above-mentioned soil water content, and their correlation with soil heterotrophic respiration were investigated. Viruses and bacteria were extracted from soil using extraction buffer and enumerated with epifluorescence microscopy direct counting method, and the soil respiration rate was measured by CO₂ concentration analyzer. The results showed that bacterial abundances were higher than viral abundances under the condition of three water treatments, regardless of sampling time. The viral abundances (P<0.001) and virus-to-bacteria ratio (P=0.0026) were significantly increased in the high-water treatment, while only viral abundances (P<0.001) were significantly increased in the fluctuating water treatment compared with the low-water treatment. Signal of oscillation in viral and bacterial abundances was observed in the treatment of high-water content. The bacterial and viral abundances showed a trend of increase-decrease-increase and increase-decrease over time, respectively, but the change of viruses lagged behind bacteria. These are consistent with an expectation that water content increase is akin to resource enrichment to our soil bacteria-viruses system. Soil heterotrophic respiration rate was positively correlated with soil water content (P<0.001), bacterial abundance (P=0.0045) and viral abundance (P<0.001). These results indicated that top-down control by viruses could be a crucial force to regulate soil bacterial abundance particularly under water-replete conditions. Our results imply an alternative explanation for the positive effect of water content on soil respiration:predation of bacteria by viruses that can accelerate the recruitment of the bacterial community was exacerbated by high water treatment. Therefore, the interactions between viruses and bacteria may be an important determinant of the soil carbon cycle. Overall, the present work contributes to expanding the current knowledge about the relationship between soil viruses and bacteria, and provides some empirical evidence supporting related researches on the effect of viruses on microbial community structure in soil.