Microbial carbon cycling in the winter wheat rhizosphere under several climate change scenarios - Insight from an ecotron experiment

Abstract

In the context of climate change, the atmospheric CO2 emissions and extreme events such as drought or flooding are expected to increase in temperate regions. These changes may result in altered plant exudation patterns, which can have implications for the microbial communities. Microorganisms play a crucial role in the carbon cycle, and an increase in their respiration rates could potentially shift the soil from a carbon sink to a carbon source. Numerous studies have explored the individual impacts of these parameters on the carbon cycle. However, only a limited number of studies have taken into consideration multiple environmental parameters simultaneously, leading to uncertain predictions. Therefore, it is essential to conduct multifactorial experiments encompassing possible futuristic scenarios.

To address this, an Ecotron experiment was conducted, simulating three different scenarios with varying concentrations of greenhouse gases expressed in CO2 equivalent: a near-future scenario at 550 ppm, a far-future scenario at 775 ppm, both derived from the Representative Concentration Pathway (RCP) 8.5, and a past scenario at 420 ppm. The aim of this multifactorial experiment was to investigate how the combined effects of increasing CO2 concentrations and extreme events could influence the carbon cycle and interactions between plants and microbial communities in both conventional and organic cultivated soils.

The main findings of this study show that both CO2 levels and the sampling day have significant effects on root exudation. As a result, there were reductions in the abundance of low molecular weight compounds, particularly glucose. However, these changes are primarily positively correlated with rainfall. Additionally, a notable decrease in the abundance of bacterial genes was observed, correlated with variable climatic conditions and the sampling day. Despite these significant changes in microbial characteristics, the fungal to bacterial ratio (F:B ratio) remained stable in the face of climate change, indicating the adaptability of the soil microbial community to warming conditions. Factors such as soil diversity and sampling day also played a crucial role in influencing the F:B ratio. Furthermore, an increase in basal respiration was observed, likely due to reduced soil moisture during dry periods.

In conclusion, this study provides crucial insights into soil microbial dynamics and their responses to environmental changes, with implications for carbon cycling and climate feedback mechanisms. Understanding these complexities is essential for developing mitigation and adaptation strategies to address global environmental challenges. The study lays the groundwork for future research in this field and highlights the need to deepen our understanding of the underlying mechanisms.