Drought Impacts on Plant-Soil Carbon Allocation-Integrating Future Mean Climatic Conditions

Area of Science:

• Soil Science
• Microbiology
• Climate Change Ecology

Background:

• Droughts significantly alter soil microbial communities and plant-soil carbon dynamics.
• Previous climate conditions can modify drought impacts on soil microbiomes.
• Future climate projections indicate warmer and drier conditions, necessitating studies under simulated future climates.

Purpose of the Study:

• To investigate the effects of simulated drought on an agroecosystem pre-conditioned to warmer and drier conditions.
• To trace the allocation of recently assimilated carbon from plants to soil microbes under drought and rewetting.
• To assess the legacy effects of reduced mean precipitation and continuous warming on carbon cycling.

Main Methods:

• Utilized the 'Hohenheim Climate Change' field experiment with 12 years of simulated climate change.
• Applied an 8-week drought followed by rewetting to an arable agroecosystem.
• Used in situ ¹³CO₂ pulse labeling of winter wheat to track carbon allocation dynamics before, during, and after drought.

Main Results:

• Severe drought reduced soil respiration and gram-positive bacteria abundance but did not affect other microbial groups or total microbial biomass carbon.
• Pre-exposure to reduced mean precipitation had a legacy effect, decreasing carbon allocation to microbial biomass by 50%.
• Continuous soil warming increased plant biomass, labile carbon, respiration, and shifted microbial carbon sources towards soil organic matter.

Conclusions:

• Moderate shifts in precipitation patterns can create legacies affecting plant-derived carbon allocation in microbial biomass during drought.
• Soil warming is a dominant factor influencing temperate agroecosystem responses to drought, primarily by increasing temperature.
• Future drought impacts on agroecosystems will likely be dominated by rising temperatures rather than precipitation changes alone.