Nutrient availability measurement techniques in arctic tundra soils: in situ ion exchange membranes compared to direct extraction

Abstract

The use of ion exchange membranes (IEMs) as an alternative to direct chemical extractions for measuring soil nutrient availability has many theoretical advantages but was not well-investigated in the arctic. We compared the two methods in a low Arctic tundra ecosystem, and investigated the applicability of IEMs to determine experimental treatment effects on soil fertility and plant nutrient acquisition. We compared IEM incubation and soil sample water-extraction methods to assess the intra-seasonal availabilities of ammonium, nitrate, and phosphate in tundra soils from experimental fertilization treatments. We determined plant species’ foliar nutrient concentrations in those treatments to evaluate the effectiveness of the two methods in predicting plant nutrient acquisition. We also incubated IEMs in summer greenhouse warming and snowfence treatment soils and investigated the corresponding plant community biomass responses. NH4-N accumulations on IEMs across the fertilization treatments were closely correlated to NH4-N pools obtained by soil extraction. However, the IEM method was more sensitive and so was able to detect effects of low level fertilization that corresponded with increases in plant foliar nutrient concentrations. Furthermore, temporal pattern of IEM nutrient fluxes differed from the nutrient pools. The warming treatment enhanced phosphate but not ammonium fluxes, although plant community biomass increased. The snowfence treatment had no effects on either flux, and the overwinter fluxes of both nutrients were extremely low compared to the growing season. We conclude that the IEM method is a relatively sensitive, simple, and effective method for measuring nutrient availability in tundra soils.