Abstract
By storing carbon in the soil, forests contribute to climate change mitigation. Edaphic (soil-related) factors, such as soil pH, as well as tree species affect forest carbon cycles, but are difficult to disentangle. We studied how conversion of deciduous stands to mono-culture spruce plantations affected the soil organic matter (SOM) composition along a lithological gradient in the Mullerthal (Luxembourg) and Gaume (south-east Belgium) regions. Parent materials in these regions range from decalcified sands to calcareous marls. A twin plot setup of adjacent deciduous and coniferous stands on the same parent material was used to evaluate the effect of edaphic factors versus litter input differences on SOM composition and soil organic carbon (SOC) stocks. Lignin and cutin/suberin molecular proxies were identified with thermally assisted hydrolysis and methylation (THM), to distinguish litter sources (coniferous vs deciduous and leaf litter vs roots) in the studied stands. In this study, SOC stocks were influenced more by parent material than by forest type. Lignin yield, composition and degradation state were influenced both by litter input chemistry and edaphic context. There appear to be important interaction effects between the two, as the relative importance of parent material and litter quality was site specific. We therefore advice that carbon stock models include data on both vegetation history as well as edaphic context.
Highlights
The soil is the most important sink of terrestrial carbon, storing at least 1500 Pg of organic carbon as soil organic matter (SOM) (Batjes, 2014)
This is in line with earlier findings by Reich et al (2005), who investigated 14 tree species including the dominant tree species of the present study and found that the effect of a tree species on the soil pH depends on the amount of calcium in the foliage
Lignin yield strongly depends on litter input, differences in lignin yield upon conversion were more pronounced in acid soils compared to soils with a more favourable pH
Summary
The soil is the most important sink of terrestrial carbon, storing at least 1500 Pg of organic carbon as soil organic matter (SOM) (Batjes, 2014). Increasing forest SOM stocks is proposed as important measure to contribute to the mitigation of climate change (Stocker et al, 2013). Naudts et al (2016) found a temperature increase caused by species conversion. This already shows that not all forest conversion contributes to climate change mitigation. There is ample evidence that forest management influences SOM quantity (Jandl et al, 2007), the relationships between tree species, parent material, management decisions and forest SOM quantity are not sufficiently clear to design optimal management, planning and policy plans that are effective in mitigating the consequences of climate change (Naudts et al, 2016)
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