Soil fauna affects the optical properties in alkaline solutions extracted (humic acid-like) from forest litters during different phenological periods

Abstract

The formation of soil organic matter via humification of plant litter is important for long-term carbon sequestration in forests; however, whether soil fauna affects litter humification is unclear. In this study, we quantified the effects of soil fauna on the optical properties (i.e., ΔlogK and E4/E6) of the alkaline-extracted humic acid-like solutions of four foliar litters by removing soil fauna via litterbags with different mesh sizes in two subtropical evergreen broad-leaved forests. Litterbags were collected at the leaf falling, budding, expanding, maturation, and senescence stages from November 2013 to October 2015 to assess whether the effects of soil fauna on litter humification vary in different plant phenology periods. The results showed that soil fauna significantly reduced the ΔlogK and E4/E6 values in the leaf expanding stage of oak litter and in the leaf falling stage of camphor and fir litters. The richness index of soil fauna explained 21%, 55%, 19%, and 45% of the variations in the E4/E6 values for oak, fir, camphor, and pine litters, respectively. The effects of litter water content on these optical properties were greater than that of temperature. These results indicated that soil fauna plays a key role in litter humification in the leaf expanding and falling stages and are potentially involved in soil carbon sequestration in these subtropical forests.

The Contributions of Soil Fauna to the Accumulation of Humic Substances during Litter Humification in Cold Forests

“…Following our first hypothesis, we verified that the process of humidification promoted by soil fauna differed on species. Except for willow, we found soil fauna significantly promoted the accumulation of humic substances in litters of birch, fir, and cypress (Figure 4), indicating soil fauna could promote the process of humidification depending on species [37,41]. Additionally, we found soil fauna individual density significantly related to humification degree besides cypress (Figure 8), possibly by the presence of high concentration of volatile organic compounds in cypress, which could inhibit the activity of soil decomposer [42].…”

“…All litter materials were air-dried at room temperature (25 • C) for 15 days and then weighted 10 ± 0.05 g for each sample that was placed in a 20 cm × 20 cm litterbag with one type of foliar litter. Litterbags with two mesh sizes were used to exclude and permit the access of soil fauna into the litterbags to determine fauna effects on litter humification [37]. Specifically, there were two types of litterbags, with both types having the bottoms of the litterbags with a mesh size of 0.04 mm, but the tops had two mesh sizes (0.04 mm and 3.00 mm): 0.04 mm for the treatment to exclude the entry of soil fauna (fauna exclusion) and 3.00 mm for the control to permit the entry of macro-, meso-and microfauna [36,38].…”

“…The soil fauna in the litterbags were extracted by the Tullgren funnel method over a period of 48 h at 30 • C, as previously described [37]. All extracted soil fauna were counted and classified under a microscope (Leica MZ 125, Leica Microsystems GmbH, Wetzlar, Germany).…”