Fine root dynamics along a 2,000-m elevation transect in South Ecuadorian mountain rainforests

Abstract

Fine root turnover plays an important role in the cycling of carbon and nutrients in ecosystems. Not much is known about fine root dynamics in tropical montane rainforests, which are characterized by steep temperature gradients over short distances. We applied the minirhizotron technique in five forest stands along an elevational transect between 1,050 and 3,060 m above sea level in a South Ecuadorian montane rainforest in order to test the influence of climate and soil parameters on fine root turnover. Turnover of roots with diameter < 2.0 mm was significantly higher in the lowermost and the uppermost stand (0.9 cm cm−1 year−1) than in the three mid-elevation stands (0.6 cm cm−1 year−1). Root turnover of finest roots (d < 0.5 mm) was higher compared to the root cohort with d < 2.0 mm, and exceeded 1.0 cm cm−1 year−1 at the lower and upper elevations of the transect. We propose that the non linear altitudinal trend of fine root turnover originates from an overlapping of a temperature effect with other environmental gradients (e.g. adverse soil conditions) in the upper part of the transect and that the fast replacement of fine roots is used as an adaptive mechanism by trees to cope with limiting environmental conditions.