Forest soils represent the largest terrestrial pool of carbon (C) in the world – they contain more C than the atmosphere and at least twice as much C as the aboveground vegetation. Interactions between plants and soils can have a major impact on the C balance of forests and play a decisive role in determining whether C is stored in the soil or released to the atmosphere.

It is thought that forests will respond to elevated atmospheric CO2 levels by increasing their growth, which also leads to greater inputs of plant C to the soil. Recent work has shown that this can stimulate the microbial decomposition of older, stored soil C, releasing CO2 to the atmosphere through so-called ‘priming effects‘. Consequently, increased plant growth does not necessarily result in greater soil C storage.Bluebells in the plots (Wytham)

Priming effects are a great example of the complexity of plant-soil interactions and their potential importance in ecosystem responses to environmental change. Despite the importance of forest soils for the global C balance, we still know surprisingly little about the actual processes leading to the sequestration or release of soil C.

Investigating changes in soil C dynamics involves studying microbial processes, plant ecology, and biogeochemical cycles. Consequently, we need to combine techniques from different disciplines and harmonise these methods across multiple scales (microscopic to ecosystem). The experimental design of FORESTPRIME aims to integrate results across a wide range of scales by combining the precision and detail of small-scale laboratory studies with large field plots.

The project aims to answer the following research questions:

  • What controls soil carbon release in forest ecosystems?
  • Are there general patterns in soil C release by priming across different forest types?
  • What are the long-term consequences of increased plant growth for soil carbon storage?
  • Can the results of small-scale lab studies by reliably extrapolated to larger scales?

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