Forest floor and Na azide effect on elements in leachate from contrasting New Hampshire and Virginia forest soils

Abstract

As northeastern forests experience increased temperatures and fluctuations in precipitation patterns, montane soils will lose forest floor (Oi, Oe, Oa horizons) formation and their associated ecosystem services. Here, we conducted comparative laboratory soil column experiments to examine the effects of forest floor on sourcing and weathering of macroelements (Al, Si), macronutrients (Ca, Mg, P), and micronutrients (Cu and Zn) from two contrasting soils: a supraglacial-till Inceptisol (Mt. Moosilauke, NH) and colluvium Ultisol (Lesesne State Forest, VA). Forest floor addition caused a significant increase in the leaching of Ca, Mg, and Mn in the two soils. The forest floor only control leachate indicates the two mineral soils were net accumulators of Al, Si, P, Cu, and Zn from the forest floor. Using partition coefficient, Kd, values, leachate Ca and Mg could be sourced directly from the forest floor traversing the soil column. We aimed to assess the biotic influence on element release from soil using a Na azide treatment to suppress microbial activities. Under Na azide treatments, Al, Ca, Mg, Mn, and Cu leachate decreased significantly for both soils, but Na azide also did not affect or increased leachate Si, P, Cu, and Zn for the Lesesne soil. We attribute the effects from Na azide to changes in pH, dissolved organic carbon, and oxidation-reduction potential as opposed to suppression of microbes. Thus, our results suggest that the loss of the forest floor will reduce the storage of nutrients in the mineral soil, even across varying parent materials.