Contrasting Effects of Metal Contaminations and Soil Liming on Cations Exchange Capacity and Global DNA Methylation in Betula papyrifera Populations from a Mining Region

The Greater Sudbury Region in Northern Ontario (Canada) has been one of the most contaminated regions in the world. Soil liming with dolomitic limestone applications has decreased significantly the level of soil acidity resulting in forest regeneration. This reclamation process does not affect the level of soil metal contamination but results in metals availability decrement. The coping mechanisms of birch (Betula papyrifera) to soil metal contamination have been recently characterized. The objective of this study was to assess the effects of soil liming and metal contamination on Cations Exchange Capacity (CEC) and whole DNA methylation in B. papyrifera. Cytosine and adenine methylations were measured using tandem Mass Spectrometry (MS/MS) coupled with LC (LC-MS/MS). The present study confirms that liming increases significantly soil pH even over 30 years after dolomitic applications. There was a decrease of cations exchange capacity and cytosine methylation in metal-contaminated sites compared to uncontaminated sites. CEC was significantly higher (p≤0.05) in limed and reference distal sites compared to unlimed areas. No significant difference in cytosine methylation level was observed between metal-contaminated limed and unlimed areas. This suggests that metal contamination mostly nickel and copper, the main elements found in higher concentrations in contaminated sites might be associated with cytosine methylation.