Nexus of deadwood moisture, lignin degradation and matter transport in changing forest ecosystems
Deadwood is crucial to forest ecosystems since it is habitat for circa 30% of all forest species and it plays a major role in above- and belowground carbon and nutrient cycling. Essential to all of the above is deadwood moisture, which is at risk of being reduced by longer dry periods and increased evapotranspiration due to changing climate and land-use intensity.
However, the factors that regulate deadwood moisture, especially via lignin degradation, are unknown. Fungal oxidation of lignin produces water and micro-pores in cell walls, thus increasing the water-holding capacity of deadwood. Subsequent water fluxes into and from deadwood can enhance lignin degradation through enrichment of metal cations and increase soil organic carbon through seepage of degraded lignin. Deadwood’s store of water and carbon could thus become relevant to both soil biota and forest ecosystem functioning depending on the extent to which increasing land-use intensity leads to drier conditions.
DeMoLD’s research questions are,
- i) to what extent do fungi regulate deadwood moisture through lignin degradation depending on water availability, and
- ii) how does fluctuating deadwood moisture regulate matter transport to and from soil under changing climate and land-use intensity?
To answer these questions, DeMoLD aims to
- i) quantify the sources of deadwood moisture,
- ii) assess fungal degradation of beech and pine wood and lignin along moisture gradients,
- iii) determine the importance of transport processes to and from soil and thus
- iv) correlate fungal regulation of lignin degradation, transport of the degradation products and contribution to soil organic matter with moisture fluctuations caused by changes in climate and land-use intensity.
- In decreasing order, deadwood water is sourced from soil via capillary rise, atmosphere via precipitation and lignocellulose via enzymatic oxidation.
- When deadwood dries out, fungal enzymes oxidize more lignin in and between cell walls, which increases the proportion of micro-pores.
- Lignin-derived compounds are transported to soil when deadwood is wetter than soil, and metal cations are transported to deadwood when soil is wetter than deadwood.
- Sites with warmer temperatures, less precipitation and more acidic cations have the largest degree of lignin degradation in deadwood and the largest contribution of deadwood to soil organic matter.
- Water-soluble organic matter indicates lignin degradation in deadwood and the potential contribution to soil carbon.
- Isotopically labelled precipitation in laboratory experiments to quantify deadwood water sources.
- Moisture content, lignin degradation, water retention, enzymatic activity and matter transport in the new BEClimWood experiment.
- Cumulative contribution of degraded lignin to individual density fractions and soluble phenols underneath heavily decayed deadwood in the BELongDead experiment.
- Synthesis of the three experiments to identify deadwood-water-soil interactions in changing forest ecosystems
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