Annual soil CO2 efflux in a cold temperate forest in northeastern China: effects of winter snowpack and artificial nitrogen deposition

Abstract

We conducted a snow depth 0 cm (non-snowpack), 10 cm, 20 cm, 30 cm and natural depth) gradient experiment under four quantities of nitrogen addition (control, no added N; low-N, 5 g N m−2 yr−1; medium-N, 10 g N m−2 yr−1; and high-N, 15 g N m−2 yr−1) and took an-entire-year measurements of soil respiration (Rs) in Korean pine forests in northeastern China during 2013–2014. No evidence for effects of N on Rs could be found during the growing season. On the other hand, reduction of snowpack decreased winter soil respiration due to accompanied relatively lower soil temperature. We found that winter temperature sensitivities (Q10) of Rs were significantly higher than the growing season Q10 under all the N addition treatments. Moderate quantities of N addition (low-N and medium-N) significantly increased temperature sensitivities (Q10) of Rs, but excessive (high-N) addition decreased it during winter. The Gamma empirical model predicted that winter Rs under the four N addition treatments contributed 4.8. ± 0.3% (control), 3.6 ± 0.6% (low-N), 4.3 ± 0.4% (medium-N) and 6.4 ± 0.5% (high-N) to the whole year Rs. Our results demonstrate that N deposition will alter Q10 of winter Rs. Moreover, winter Rs may contribute very few to annual Rs budget.

Short Legacy Effects of Growing Season Nitrogen Addition and Reduced Precipitation alter Soil Respiration during Nongrowing Season

“…A previous study showed that N addition generally accelerated nongrowing season N mineralization [16], which could be attributed to an increase in microbial activity and change in microbial communities. Our previous results in the study site also confirmed that N addition affected soil microbial activity and community composition in the nongrowing season [26], which may increase litter decomposition, soil N mineralization, and Rs. Second, the positive response of nongrowing season Rh, Ra, and Rs to N addition can be explained by alleviating the limitation of nongrowing season soil C availability.…”

“…Thus, the winter usually starts in November and ends in late April (base on phenology); October and May in the study area belong to the transitional months of the winter and growing seasons. Each winter (from November to April) was divided into three specified periods, the early winter (November and December), deep winter (January and February), and late winter (March and April) based on the snowpack thickness, soil temperature, and air temperature [26].…”

Nitrogen deposition may enhance soil carbon storage via change of soil respiration dynamic during a spring freeze-thaw cycle period

“…In general, the N addition exerted a negative impact on spring FTC R s and decreased it by 6% (low-N), 39% (medium-N) and 36% (high-N) compared with the control. The predicted annual R s was 974.3 ± 67.1 g C m −2 yr −1 without N addition treatment; the values of R s in winter were 46.8 g C m −2 yr −1 (control), 35.7 g C m −2 yr −1 (low-N), 41.89 g C m −2 yr −1 (medium-N) and 62.35 g C m −2 yr −1 (high-N) 48 . Under different quantities of N addition, the cumulative R s during spring FTC period contributed 37.49% (control), 46.88% (low-N), 25.50% (medium-N) and 18.03% (high-N), respectively, to the winter R s and contributed 1.80% (control), 1.69% (low-N), 1.10% (medium-N) and 1.15% (high-N), respectively, to the annual R s ( Fig.…”

Freeze-thaw processes of active layer regulate soil respiration of alpine meadow in the permafrost region of the Qinghai-Tibet Plateau

“…One possible explanation is that microbes are warm-adapted and more sensitive to Ts when the freezing process is initiated. Furthermore, the process of the diurnal freezing-thawing cycle of surface soil also happened in the earlier ZC substage, and Rs increased rapidly from a very low level over diurnal cycle, indicating that microbes responded rapidly to minor changes in Ts even within several hours (Liu et al, 2016). As the freezing process developed rapidly downwards from the 345 surface soil and upwards from the bottom of the active layer in the ZC substage, the trapped CO2 in the soil pores would be squeezed out and released during the transition of soil moisture from the liquid to solid state, leading to a dramatically fluctuating Rs.…”

“…Although many studies have showed that freeze-thaw events affect soil respiration (Rs) in tundra, boreal, and temperate soils (Liu et al, 2016;Du et al, 2013), the Rs and Q10 values in different freeze-275 thaw stages of the active layer are still rarely reported in permafrost regions on the Qinghai-Tibet Plateau. It can be seen through our observation that the different freeze-thaw stages of active layer strongly regulated the Rs emissions and the Rs emission models and SR (sum soil respiration) among the different freeze-thaw stages were significantly different.…”