Resilience of rhizosphere microbial predators and their prey communities after an extreme heat event

Climate change is known to disrupt aboveground food chains when the various trophic layers respond differently to warming. However, little is known about belowground food chains involving microbial preys and their predators. Here, we study how climate warming- induced heat shocks influence resistance (change immediately after a disturbance) and resilience (ability to recover back to pre-disturbance levels) in rhizosphere microbial communities.
We used three species of rhizosphere protists as microbial predators and six different rhizosphere bacterial communities as their prey. Protist species and bacterial communities were extracted from Centaurea stoebe – a range-expanding plant species in the Northern Europe. We then examined the temporal dynamics of protists and bacterial communities after an extreme heat event for several generations with sufficient recovery periods. We hypothesized that bacterial community resistance and resilience after the extreme heat event would be higher particularly when extreme heat effects would negatively affect their predators.
Our results show that prey community biomass was strongly reduced after the extreme heat event and persisted with lower biomass throughout the recovery period. Opposite to what was expected, predators showed negligible changes in their density after the same heat event. However, abundances of the three predators varied markedly in their temporal dynamics independent of the extreme heat event. Extreme heat event further increased the inactive density of one of the predators, whereas another predator showed a decline in its body size owing to extreme heat event. Bacterial community resistance and resilience after the extreme heat event were independent of predators, although species-specific effects of predators on bacterial community resilience were different only in the last week of recovery. Predator resilience (based on active predator density) also varied among the three predators but converged over time.
Our results highlight that extreme heat events can be more detrimental to microbial prey communities than microbial predators when microbial predators can exhibit thermal acclimation (e.g. change in body size or become inactive) to overcome heat stress. Such thermal acclimation may promote predator resilience after extreme heat events.

众所周知，当不同营养层级（trophic layers）对气候变暖产生差异化响应时，气候变化会破坏地上食物链。然而，学界对包含微生物猎物及其捕食者的地下食物链却知之甚少。本研究聚焦气候变暖诱导的热冲击如何影响根际微生物群落（rhizosphere microbial communities）的抵抗力（resistance，即扰动发生后即刻的群落变化情况）与恢复力（resilience，即恢复至扰动前水平的能力）。
我们选取3种根际原生生物（protists）作为微生物捕食者，以及6种不同的根际细菌群落作为其猎物。所有原生生物物种与细菌群落均分离自矢车菊属植物*Centaurea stoebe*——一种在北欧的分布扩张型植物物种。随后，我们在极端热事件发生后设置充足的恢复周期，连续观测多代原生生物与细菌群落的时间动态。我们提出假说：若极端热事件对捕食者产生负面影响，则细菌群落的抵抗力与恢复力会显著提升。
研究结果显示，极端热事件发生后，猎物群落的生物量大幅降低，并在整个恢复周期内维持较低的生物量水平。与预期相反，同一热事件并未使捕食者的种群密度产生显著变化。不过，三种捕食者的丰度在时间动态上存在显著差异，且该差异不受极端热事件的影响。极端热事件进一步提升了其中一种捕食者的非活跃种群密度，而另一种捕食者的个体体型则因极端热事件出现缩小。尽管捕食者对细菌群落恢复力的物种特异性影响仅在恢复周期的最后一周有所体现，但细菌群落的抵抗力与恢复力均与捕食者无关。三种捕食者的恢复力（基于活跃捕食者种群密度计算）同样存在物种间差异，但随时间推移逐渐趋同。
本研究结果表明，当微生物捕食者能够通过热驯化（thermal acclimation，例如调整个体体型或进入非活跃状态）来应对热胁迫时，极端热事件对微生物猎物群落的危害会大于其捕食者。此类热驯化作用或可提升极端热事件后捕食者的恢复力。