Measuring fungal decomposition of lignin in soil.
Studying decomposition of organic components is important to improve our knowledge how climate change will affect carbon cycling in ecosystems. Soil fungi produce large quantities of phenol oxidases and are therefore the primary agents of lignin degradation (Hammel, 1997). Hence, any change in the fungal biomass will affect the production rate of phenol oxidases and the degradation rate of lignin-like compounds. Warmer conditions will, besides increasing soil temperature, probably increase the frequency of wildfires with a resulting net loss of carbon to the atmosphere with a positive feedback to global climate change. However, finding evidence for these climate-induced changes in soil is strongly hampered by the presence of large soil carbon pools and fluxes.
Stable Isotope Solution : 13C plant components
The use of 13C-lignin enables to distinguish between the decomposition processes of interest and the disturbing background processes. Waldrop & Harden (2008) used 13C-lignin (IsoLife BV) to study the effects of wildfires in relation to permafrost in boreal forests containing significant amounts of soil carbon. Fungal biomass, phenol oxidase activity and 13C-lignin decomposition were therefore measured in permafrost and non-permafrost soils from both burned and unburned forests ecosystems.
The results showed a significant relationship between fungal relative abundance and phenol oxidase activity in soil (Figure 1a), and between phenol oxidase activity and lignin decomposition (Figure 1b). The measured 13C-lignin decomposition rate in four soils (Figure 2) was not affected by permafrost conditions, but clearly by effects of wildfire on fungal abundance in the soil.
Figure 1. Relationships between fungal abundance -> phenol oxidase activity (A), and phenol oxidase activity -> lignin decomposition rate (B).
The measured 13C-lignin decomposition in four soils was not affected by permafrost conditions, but clearly by effects of wildfire on fungal abundance in the soil (Figure 2).
Figure 2. Effects of wildfires on lignin decomposition rate in permafrost and non-permafrost soils.
The authors concluded that the measured lignin decomposition rate – as derived from 13CO2respiration after 13C-lignin addition – was not affected by permafrost conditions, but clearly by effects of wildfires on fungal abundance in the soil, with subsequent reductions in phenol oxidase activity. Over the short term, wildfires reduce fungal biomass, enzyme activities, lignin decomposition rate, and the rate of CO2 respiration from soil. Fires apparently affect soil fungi as was also shown byBastias et al (2009) for cellulose decomposers.
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Fungal degradation of lignin. In: Driven by Nature: Plant litter quality and decomposition. Eds. G Cadish and KE Giller), CAB International, Wallingford, UK. pp 33-45.
Waldrop MP, JW Harden. 2008.
Interactive effects of wildfire and permafrost on microbial communities and soil processes in an Alaskan black spruce forest.
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Bastias BA, IA Anderson, J Ignacio-Castro, PI Parkin, JI Prosser, JWG Cairney. 2009.
Influence of repeated prescribed burning on incorporation of 13C from cellulose by forest soil fungi as determined by RNA stable isotope probing.
Soil Biology & Biochemistry 41: 467-472. doi:10.1016/j.soilbio.2008.11.018