To explore how to respond to seasonal freeze–thaw cycles on forest ecosystems in the context of climate change through thinning, we assessed the potential impact of thinning intensity on carbon cycle dynamics. By varying the number of temperature cycles, the effects of various thinning intensities in four seasons. The rate of mass, litter organic carbon, and soil organic carbon (SOC) loss in response to temperature variations was examined in two degrees of decomposition. The unfrozen season had the highest decomposition rate of litter, followed by the frozen season. Semi-decomposed litter had a higher decomposition rate than undecomposed litter. The decomposition rate of litter was the highest when the thinning intensity was 10%, while the litter and SOC were low. Forest litter had a good carbon sequestration impact in the unfrozen and freeze–thaw seasons, while the converse was confirmed in the frozen and thaw seasons. The best carbon sequestration impact was identified in litter, and soil layers under a 20–25% thinning intensity, and the influence of undecomposed litter on SOC was more noticeable than that of semi-decomposed litter. Both litter and soil can store carbon: however, carbon is transported from undecomposed litter to semi-decomposed litter and to the soil over time. In summary, the best thinning intensity being 20–25%.
We investigated the residual rate and mass loss rate of litter, as well as the carbon release dynamics of litter and soil across seasons, to better understand the effects of seasonal fluctuations on carbon dynamics in mixed coniferous forests. The study was carried out in natural mixed coniferous forests in the Xiaoxinganling region of Heilongjiang Province, China, and the number of temperature cycles in the unfrozen season, freeze–thaw season, frozen season, and thaw season was controlled. The goal of the study was to examine how the carbon release dynamics of litter and soil respond to the freeze–thaw process and whether there are differences in carbon release dynamics under different seasons. Repeated-measures analysis of variance was used to analyze the residual mass rate and mass loss rate of litter, litter organic carbon and soil organic carbon during the unfrozen season, freeze-thaw season, frozen season, and thaw season. Litter decomposition was highest in the unfrozen season (15.9%~20.3%), and litter and soil carbon were sequestered throughout this process. Temperature swings above and below 0°C during the freeze–thaw season cause the litter to physically fragment and hasten its decomposition. Decomposition of litter was still feasible during the frozen season, and it was at its lowest during the thaw season (7.2%~7.8%), when its organic carbon was transported to the soil. Carbon migrates from undecomposed litter to semi-decomposed litter and then to soil. The carbon in the environment is fixed in the litter (11.3%~18.2%) and soil (34.4%~36.7%) in the unfrozen season, the carbon-fixing ability of the undecomposed litter in the freeze-thaw season is better, and the carbon in the semi-decomposed litter is mostly transferred to the soil; the carbon-fixing ability of the litter in the frozen season is worse (-3.9%~ -4.3%), and the organic carbon in the litter is gradually transferred to the soil. The carbon-fixing ability of the undecomposed litter in the thaw season is stronger, and the organic carbon in the semi-decomposed litter is mostly transferred to the soil. Both litter and soil can store carbon; however, from the unfrozen season until the thaw season, carbon is transported from undecomposed litter to semi-decomposed litter and to the soil over time.
We are submitting the enclosed manuscript entitled “ Effects of seasonal changes on the carbon dynamics in mixed coniferous forests ” for your consideration as an article in PLOS ONE . We feel that the results will be of general interest to the readership of the journal. We characterized seasonal changes in the residual rate and mass-loss rate of litter, as well as the carbon release dynamics of litter and soil, in mixed coniferous forests in the Xiaoxinganling region by conducting a controlled freeze–thaw experiment. The carbon release rate and mass-loss rate of litter at two levels of decomposition (undecomposed and semi-decomposed) were measured during four seasons: the unfrozen season, freeze–thaw season, frozen season, and thaw season. The temperature was higher, the mass-loss rate was faster, and the overall mass-loss rate of litter was higher in the unfrozen season than in the other three seasons; litter organic carbon increased and soil organic carbon increased due to the strong carbon sequestration capacity of plants. The temperature fluctuated above and below 0°C during the freeze–thaw season, which results in the physical breakage of the undecomposed litter and increases in the mass-loss rate. This leads to increases in the organic carbon of undecomposed litter and decreases in the soil organic carbon of undecomposed litter; the opposite patterns were observed for changes in the organic carbon of semi-decomposed litter and soil organic carbon. There was noticeable mass loss of litter during the frozen season, and the rate of mass loss of litter during the thaw season was the lowest. Litter organic carbon decreased and soil organic carbon increased in both seasons. The organic carbon of undecomposed litter was highest in the thaw season, followed by the freeze–thaw season, frozen season, and unfrozen season. The organic carbon of semi-decomposed litter was highest in the frozen season, followed by the thaw season, freeze–thaw season, unfrozen season to freeze–thaw season, frozen season, thaw season, and unfrozen season. After freeze–thaw treatment, the organic carbon in deadfall soil was highest in the unfrozen season, freeze–thaw season, frozen season, thaw season to unfrozen season, frozen season, thaw season, and freeze–thaw season. The findings of this study provide new insights into the material cycling process under freeze–thawing, as well as information on the effect of seasonal freeze–thaws on the forest carbon cycle.
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