COS 233-2 - Long-term warming disturbs the positive relationship between ecosystem function and microbial diversity

Background/Question/Methods

Soil microbial diversity supports ecosystem function and can mitigate climate change related to stress on ecosystems. Previous works found increased microbial diversity and higher rates of respiration and enzyme activity in soils that had been warmed +5°C above ambient. Together these studies hint that warming might have an overall positive effect on the relationship between microbial diversity and ecosystem function, but the role diversity has in maintaining ecosystem function under stress is not clear.

Using the soil warming plots at Harvard Forest in Petersham, MA, this study investigated how long-term warming impacts the relationship between ecosystem multifunctionality and microbial diversity. We hypothesized warming would result in a stronger positive relationship between microbial diversity and ecosystem multifunctionality due to simultaneous increases in ecosystem function and microbial diversity.

In July and October of 2019, soils from two different experimental sites, two soil horizons, and two warming treatments were sampled. To assess ecosystem multifunctionality, microbial biomass, respiration, N-acetyl glucosaminidase activity, beta glucosidase activity, phenol oxidase activity, total carbon, and total nitrogen were measured. Multifunctionality was calculated using the averaging approach in the multifunc package in R. Additionally, the bacterial community was sequenced using 16S rRNA gene sequencing and processed using the DADA2 pipeline.

Results/Conclusions

Contrary to our predictions, we found that long-term warming decreased ecosystem multifunctionality, and that these effects were stronger in July compared to October (p < 0.005). Of the individual ecosystem functions, total N, respiration, and microbial biomass were the most negatively impacted by warming (all p < 0.01). We found that microbial diversity, calculated using Shannon's H, Simpson's diversity, or Pielou's J (all p > 0.1), and microbial community structure (p > 0.1) were not affected by warming. Overall, the warmed plots had a weaker relationship between ecosystem multifunctionality and bacterial diversity (p < 0.01), contradicting our hypothesis.

Our results highlight the importance that season has in determining ecosystem function. Additionally, results from this study indicate that microbial community diversity itself is resistant to warming, but that the functioning of these communities is adversely impacted by warming. This suggests that the ability of biodiversity to promote high levels of ecosystem function is diminished under increased temperatures.