Differential responses of soil Carbon,Nitrogen and Phosphorus stocks and available pools to conversion from native forest to exotic plant plantation in soils of contrasting origin.

Land use change is a global issue with tremendous social, economic and environmental implications. Currently, many countries display high rates of deforestation and forest conversion from native forest to industrial tree plantations which have a direct impact on soil C and N stocks. Even though, there is a significant number of studies that highlighted the effects of forest substitution on C sequestration, the impact on ecological stoichiometry and biogeochemical cycling has not been well assessed. The soils considered in this study encompass the main forest soil types found in south central Chile representing a range of soil properties and mineralogy (crystalline to amorphous ash derived soils). To reduce confounding factors due to site history, we exclusively selected pair sampling sites (native versus plantation) that shared a similar land-use history and had close to identical soil and geomorphic conditions in which two independent 625m² plots were established at adjacent Native Forests (NF) and Pine Plantations (PL).To determine C:N:P inventories alongside N and P available pools, the plot was divided into four sub-quadrants where bulk soil samples were collected at 6 depth intervals in the central soil pit and in four augers at each quadrant up to a depth of 240 cm. The C and N total pools were significantly different between soil types but not between forest types (p=0.02). The highest average C stock across all soils was found in NF (202.22 ± 82.77 Mg ha^-1) compared to PL (172.55 ± 87.73 Mg ha^-1)^. When comparing each soil type individually, disregarding forest type, the Young Ash soil displayed significantly higher C and N than all the other studied soils. On the contrary, the Recent Ash soil displays changes in the C:N:P stoichiometry_. Available Phosphorus was significantly different among sites, but not for forest types across sites. Overall, native forest exhibits higher stocks of available NO₃^- and we did not find a significant effect of forest type in NH₄⁺ stocks. Our result indicates the differential capacity that contrasting soils have to resist this major soil biogeochemical pools alteration.