Decomposition of spruce litter needles of different quality by Setulipes androsaceus and Thysanophora penicillioides

Abstract

Various biotic and abiotic factors may change the quality of cast spruce needles or induce premature casting, subsequently altering the composition of needle litter. We tested the decomposition efficiency of Setulipes androsaceus, a key litter decomposer in spruce forests, on needles of the Norway spruce (Picea abies) that fell into three different categories of quality. We designed a cultivation experiment to test the decomposition rate of the following needle categories: (1) naturally senesced brown needles, (2) intact, prematurely fallen green needles, and (3) frass pellets produced by caterpillars of the spruce web-spinning sawfly (Cephalcia spp.). Needles from each category were cultivated both independently and in combination. After a 4-month incubation, dry weight loss and the decrease of p-hydroxyacetophenone (p-HAP) and catechin were measured as markers of decomposition. Colonization of green needles by mycelia of S. androsaceus was initially inhibited. However, within the experimental period, those green needles successfully colonized by S. androsaceus lost more mass (22% of dry weight) than the brown needles (18% of dry weight). S. androsaceus also decreased the p-HAP and catechin contents of the green needles. Another fungal decomposer, Thysanophora penicillioides, was introduced only to the treatment that contained all three needle categories, and it induced less weight loss than S. androsaceus, but degraded the two phenolics to a similar extent. Neither the green nor the brown needles exhibited a more rapid rate of decomposition when cultivated in combination with another category of needles. We conclude that the increased proportions of green needles and frass pellets in the litter will be connected with temporarily increased decomposition activity of S. androsaceus.