Mineral protection mediates soil carbon temperature sensitivity of nine old-growth temperate forests across the latitude transect.

Temperature sensitivity (Q10) of soil microbial respiration serves as a crucial indicator for assessing the response of soil organic carbon (SOC) to global warming. However, the biogeographic variation in Q10 remains inconsistent. In this study, we examined Q10 and its potential drivers in nine old-growth mixed broad-leaved Korean pine (Pinus koraiensis Sieb. et Zucc.) forests (the climax community of Asian temperate mixed forest) under a wide range of climatic conditions. We found that stand characteristics (arbuscular mycorrhizal tree basal area to ectomycorrhizal tree basal area ratio and root to shoot ratio) contributed to soil C sequestration by facilitating the accumulation of soil recalcitrant C components. Contrary to the C quality-temperature hypothesis, Q10 was not correlated with C quality (soil C to nitrogen ratio and recalcitrant C to labile C ratio). Soil mineral protection parameters (Fe/Al oxides) had negative effect on Q10 because they inhibited microbial activities by decreasing substrate accessibility. Additionally, soils with high microbial biomass C and microbial biomass C to soil organic C ratio had high Q10. Overall, understanding the complex relationships among Q10, mineral protection, and microbial attributes on a spatial scale is essential for accurately predicting soil C cycling in forest ecosystems.

[Pyrolysis and gas emissions characteristics of six tree species in Heilongjiang Province, China]. / 黑龙江省6种乔木叶片热解特性及气体释放特征.

Forest fuels are the basis of fire occurrences, while ground dead fuels are an important part of forest fuels. Undestanding the pyrolysis characteristics and gas emissions of forest fuels is of great significance to explore the effects of forest fire on atmospheric environment and carbon balance, as well as to prevent and combat forest fire. In this study, the thermogravimetric analysis and gas emission analysis were conducted on leaf litter of six tree species (Pinus sylvestris var. mongolica, Picea koraiensis, Fraxinus mandshurica, Juglans mandshurica, Quercus mongolica, Betula platyphylla) in Heilongjiang Province to explore the pyrolysis process and combustibility of forest fuels, to analyze their pyrolysis characteristics, pyrolysis kinetics characteristics, gas emission characteristics. A four-dimensional evaluation of their combustibility was conducted based on pyrolysis parameters. The results showed that the pyrolysis temperature of holocellulose in the leaves of those six tree species ranged in 143.31-180.48 ℃ at the beginning and 345.04-394.38 ℃ at the end, lignin pyrolysis temperature ranged in 345.04-394.38 ℃ at the beginning and 582.85-609.31 ℃ at the end. The pyrolysis of the six kinds of arbor blades during the pyrolysis process affected fuel ash content, quality and temperature of the total pyrolysis. The activation energies of two main pyrolysis stages of leaves of six tree species were 18.88-27.08 kJ·mol-1 and 13.25-27.54 kJ·mol-1, respectively, and the pre-exponential factors were 3.13-26.28 min-1 and 1.30-22.55 min-1. The holocellulose activation energy and pre-exponential factor of the pyrolysis stage for P. koraiensis, F. mandshurica, Q. mongolica, and B. platyphylla were greater than that of the lignin pyrolysis stage, while the opposite was true for P. sylvestris var. mongolica and J. mandshurica. The release amounts of CO and CO2 at the pyrolysis stage of the holocellulose was 535.16-880.11 mg·m-3 and 7004.97-10302.05 mg·m-3, and that at the pyrolysis stage of lignin was 240.31-1104.67 mg·m-3 and 20425.60-33946.68 mg·m-3, respectively. The release of CO and CO2 at the pyrolysis stage of healdellulose was less, but mass loss was greater than that at the pyrolysis stage of lignin. In the four-dimensional combustibility ranking of the six tree species leaves, B. platyphylla was the best ignitable, P. koraiensis was the most combustible, and P. sylvestris var. mongolica was the most sustainable and consumable. The ignitability was significantly positively correlated with pyrolysis kinetics parameters of the holocellulose, while the sustainability was negatively correlated with that of lignin.