*2.4. Chemical Analysis*

Once the samples of five species were transferred to the laboratory, all litter samples were carefully removed from the bags, in which visible roots, mosses and soils were completely removed from the litter samples. One cleaned subsample was oven dried at 105 ◦C (for more than 48 h) to measure the dry mass and water content. The remaining mass was evaluated based on the dry mass as presented elsewhere. Another subsample was used to determine the total humus, humic acid and fulvic acid contents in the foliar litter.

We used the alkali method to extract the humus in the foliar litter. Although this method was recently questioned [7], alkali extraction provides a quantitative measurement of the magnitude of humus accumulation in decomposing litter. Specifically, a 1.00 g airdried subsample was placed in a 150 mL bottle and extracted with a 100 mL mixed solution of 0.1 M NaOH and Na4P2O7 at 80 ◦C for 1 h after shaking for 30 min. The dissolved solution was filtered and stored under anaerobic conditions as the total extractive humus.

Humic acid and fulvic acid were isolated using 0.05 M HCl to pH 2.0 and kept at 80 ◦C for 30 min. Humic acid (not soluble in acid but soluble in alkali) was separated out as floccules and filtered and re-dissolved with 0.05 M NaOH. The isolated humic acid and total extractive humus were filtered through 0.45 μm meshes, and 200 μL solutions were determined using a TOC analyzer (multi N/C 2100, Analytik Jena, Thüringen, Germany).

**Figure 1.** Temperatures and freeze–thaw cycles in the control and reduced snow cover plots. (**a**) Snow depths (±SE, *n* = 18) on each sampling date. Differences between control and reduced snow cover plots were significant (*p* < 0.05) on all sampling dates. (**b**) Daily temperatures (*n* = 6) at the litter surface during the four years of decomposition. Sampling dates were scheduled at approximately the ends of the snow formation, coverage and melt stages, and the growing season. Winter times, with the snow formation, coverage and melt stages, are shaded. The dashed line is drawn at a daily temperature of zero. (**c**) Mean temperatures (±SE, *n* = 6) at individual stages. Times between two adjacent sampling dates were defined as separate stages to better understand the effect of snow reduction at the snow formation, coverage and melt stages. SF: snow form stage, SC: snow cover stage, SM: snowmelt stage, GS: growing season. (**d**) Freeze–thaw cycles (±SE, *n* = 6) at the individual stages. Values were calculated using the quotients of the total number of freeze–thaw cycles and the days of certain stages. \* *p* < 0.05, \*\* *p* < 0.01, \*\*\* *p* < 0.001.

The humus content (including humic acid and fulvic acid) was defined as alkaliextractable substances and calculated as a percentage of the litter mass. The fulvic acid content (FA, % of litter mass) represented the difference between the total extractive humus and humic acid.

$$\text{FA} \ (\%) = \text{Hu} - \text{HA} \tag{1}$$

where Hu and HA are the contents of the total extractive humus and humic acid, respectively.

A 0.5 g air-dried subsample was oven dried at 105 ◦C for 48 h to determine the litter moisture, which was used to adjust the final value of the humus content.
