Soil respiration of two dominant tundra communities under controlled temperatures in Changbai Mountain, Northeast China

Numerous seasonal snowpacks exist on alpine tundra of Changbai Mountain, Northeast China. The structure and species composition are distinct between snowpack and nonsnowpack communities, implying the difference in ecological processes in the subsurface. In order to clarify the relationship between soil respiration with thermal condition in snowpacks, as well as its seasonal variation, the respiration in response to temperature was measured based on simulated experiments. In addition to soil temperature, primary productivity was also investigated by harvesting the current-year aboveground growth. Field sampling was conducted in two community types: Rhododendron aureum community occurred in snowpack and Vaccinium uliginosum var. alpinum community (as reference) in snow-free area. An Li-8100 soil respiration system (Li-COR Co.) was used for measuring CO2 release. Soil organic matter, total nitrogen and available nitrogen were analyzed. Hydrolizable nitrogen in Vaccinium community was 370-585 mg kg−1, total nitrogen was 0.298%-0.468%, and organic matter was 13.5%-17.3%. In Rhododendron community, hydrolizable nitrogen was 445-583 mg kg−1, total nitrogen was 0.465%-0.696%, and organic matter was 15%-22%. Organic matter within 10 cm depth was 4.07 kg m−2 in Vaccinium community, and 5.31 kg m−2 in the other. Temperature-dependent equations indicated that Q10 values in both communities were around 2, with the ranges of 1.81-2.67 in Vaccinium community and 1.67-2.21 in Rhododendron community. The temperature-dependent equation was formed as y = aebx, where y is respiration rate (μmol kg−1 h−1), a and b are coefficients, and x is temperature in Celsius degree. Coefficient a was 52-148 in Vaccinium community and 34-167 in Rhododendron community, with significant variation among samples taken in different years. The daily respiration (g C kg−1 d−1) equation was y = 0.021733e0.084063x for Vaccinium community, and y = 0.023482e0.06x for Rhododendron community, both varied significantly with season. As to yearly respiration rate, it was 8.57-17.96 g C kg−1 a−1 in Vaccinium community, with a peak in May and relatively even in other time. The yearly respiration calculated by an integrated equation fitted with samples taken in all seasons was 10.24 g C kg−1 a−1. By covering Vaccinium community with a quilt in the field during the winter, soil temperature was slightly raised. During the frozen season, the temperature was raised by approximately 1.5 °C. Hence the annual respiration was 544.41 g C m−2, 12 g C m−2 higher than that of the reference. Respiration for Rhododendron community was in the range of 4.57-21.15 g C kg−1 a−1, with its maximum in May. By the integrated equation, it was 10.35 g C kg−1a−1or 537 g C m−2 a−1. The yearly respiration was 441-544  g C m−2 a−1 in Vaccinium community and 449-486 g C m−2 a−1 in Rhododendron community. Taking the form of respiration on the basis of per kg of organic carbon, it was 118 g C (kg C) − 1 a−1 in Vaccinium community and 101 g C (kg C) − 1 a−1 in Rhododendron community. In particular, winter respiration in Vaccinium community was 2.10 g C kg−1, or 20.50% of yearly total, and merely 1.59% in the coldest month. While in Rhododendron community, it was 3.40 g C kg−1, or 32.84% of yearly total, significantly higher than that in Vaccinium community. The respiration in Rhododendron community at elevation 2260 m was 468.21 g C m−2 a−1, and the biomass growth was 400 g C m−2 a−1. In contrast, due to the thinner snow cover, in elevation 2036 m the biomass growth was 225.0 g C m−2 a−1 versus the respiration rate of 486.60 g C m−2 a−1. Leaf area index varied significantly in Rhododendron communities, ranging from 1.48 to 3.14, also owing to the difference in snow depth. As a contrary, in Vacciniumu community, the biomass growth was 120.75 g C m−2 a−1 and the leaf area index was 1.58. In conclusion, snowpacks provide a suitable condition for microbiomes in the winter, and contribute a large proportion of respiration. This also implies the vigorous activity in nitrogen release during the frozen season, which results in the rapid thriving of plants after snowmelt.