Fine root decomposition in two subalpine forests during the freeze–thaw season

Little is known about fine root decomposition during the freeze–thaw season. To characterize fine root decomposition during this time (from October 2006 to April 2007), a field experiment was conducted to examine the decomposition of fine roots (diameters of 0–1 and 1–2 mm) of Minjiang fir ( Abies faxoniana Rehd. & E.H. Wilson) and Asian white birch ( Betula platyphylla Sukaczev) using buried litterbags in their respective habitats in western Sichuan, China. Over one freeze–thaw season, 14%–20% of mass was lost and 12%–31% of C, 6%–36% of N, 15%–25% of P, and 37%–43% of K were released. These losses accounted for about 40%–55% of mass lost and 23%–54% of C, 23%–89% of N, 25%–42% of P, and 48%–58% of K released within the first year of fine root decomposition. The amount of mass loss and bioelements release during the freeze–thaw season correlated closely with initial substrate quality and bioelement traits. Compared with birch fine root, fir fine root decomposition could be influenced more by decomposition processes during the freeze–thaw season. Results suggest that fine root decomposition during the freeze–thaw season can strongly contribute to ecosystem C and nutrient cycling.