Global climate change and grasslands: soil microbial diversity to the rescue!

What will the world look like in the future? Scientists continuously try to model how plants, ecosystems and biodiversity might be impacted by different global changes so policy makers and conservationists can be proactive. These “crystal ball predictions” are usually based on experiments measuring how plants grow under different temperatures, water and soil nutrient contents. Things get a bit more complicated when trying to understand what is happening to the soil microbes as well as the plants and any feedback between these two.  

Dr Gaowen Yang and three colleagues from Freie Universität Berlin and Berlin‐Brandenburg Institute of Advanced Biodiversity Research (BBIB) investigated the growth of four grass, herb and legume species respectively on low, moderate and high soil biodiversity soil mixtures exposed to three global change disturbances (e.g. warming, drought and nitrogen deposition). The researchers found that stresses were more pronounced when the plants were grown on soil mixtures with reduced microbial diversity. Drought and nitrogen (N) deposition disturbances decreased plant diversity but plants were able to recover on moderate and high soil biodiversity. A former study has shown that losing rare soil microbial species that induce systemic resistance also change plant-pest interactions. Dr Yang has previously explored how soil processes and diversity are impacted by an increasing number of environmental changes (e.g. two versus ten) and discussed how soil biota can affect ecosystem stability. 

In the current study, Yang and colleagues collected around 46 kg of soil from Brandenburg and prepared soil mixtures to represent low, moderate and high soil microbial diversity using the dilution-to-extinction approach (e.g. different proportions of fresh soil and sterilised soil). These soil mixtures incubated for two months before any experiments so the microbes could build up. Yang and colleagues set up a microcosm experiment where each pot contained two seedlings of four grass, herb and legume species respectively, 24 in total. The seedling grew on the three different soil mixtures for two and half months and were harvested three times.

The first harvest occurred after 2.5 months after the establishing phase on the different soil mixtures. The scientists measured above-ground biomass of each species. Afterwards, the pots were exposed to three global change effects (e.g. drought, warming, increased N deposition) and plants were harvested after two months. The researchers then allowed the plants to recover for two months and harvested them for the third time. Soil microbial DNA was extracted to measure bacterial and fungal community changes during disturbance and recovery phases.

All stresses were more pronounced when the plants were grown on soil mixtures with reduced microbial diversity. For example, drought decreased legume biomass by 89% at high soil biodiversity mixture but the reduction was 95% on low soil biodiversity.. Warming decreased legume biomass by 31% on high soil biodiversity but 80% on low soil biodiversity. The effects were slightly different for herbs and grasses. 

“The decrease in legume persistence by soil biodiversity loss could be partly attributed to the

absence of soil mutualists, for instance, AM [arbuscular mycorrhizal] fungi,” Yang and colleagues wrote. 

“Following global change disturbances, a full recovery of soil bacterial diversity has been observed in the present study, indicating that soil bacteria are highly resilient to global change disturbances, supporting previous work.”

The biomass of legumes fully recovered after the disturbances on high and moderate soil biodiversity but not under low soil biodiversity. Drought and N deposition disturbances decreased plant diversity. 

“Our study shows that the loss of biodiversity could result in a negative feedback, which can further decrease plant diversity by decreasing legumes.”

This study highlighted the importance of soil microbial diversity for predicting plant responses to three main global change disturbances.