Pedosphere最新文献

The formation and growth of segregation ice dominate the frost heave during soil freezing, which is closely related to water migration. To analyze segregation ice during soil freezing for different soils, a freezing-thawing experiment was conducted with Lanzhou loess (LZL) and Qinghai-Tibet Plateau silty clay (QSC) using a novel layered nuclear magnetic resonance approach. During LZL freezing, the unfrozen water content first increased and then decreased with decreasing temperature near the freezing front, but decreased with decreasing temperature in other layers, whereas during the freezing of QSC, the unfrozen water content in different layers (including the freezing front) decreased with decreased temperature. Notably, the increased liquid water near the freezing front during LZL freezing was primarily adsorbed water. In addition to the temperature gradient, the squeezing action during soil freezing was another important factor affecting water migration, especially at the early stage of soil freezing. However, which of the two factors, squeezing action and temperature gradient, was the dominant one causing water migration depended on soil structure. At the early stage of soil freezing, the squeezing action had a significant effect on the water migration of LZL, but no significant effect on that of QSC. Furthermore, water accumulation of LZL near the freezing front due to squeezing action at the early stage of freezing limited the formation and growth of segregation ice. This study provided an improved understanding for ice segregation and water migration during soil freezing.

Globally, soil is the largest terrestrial carbon (C) reservoir. Robust quantification of soil organic C (SOC) stocks in existing global observation-based estimates avails accurate predictions in carbon-climate feedbacks and future climate trends. We investigated the magnitudes and distributions of global and regional SOC estimates (i.e., density and stocks) based on five widely used global gridded SOC datasets, a regional permafrost dataset developed in 2021 (UM2021), and a global-scale soil profile database (World Soil Information Service) reporting measurements of a series of physical and chemical edaphic attributes. The five global gridded SOC datasets were the Harmonized World Soil Database (HWSD), World Inventory of Soil Emission Potentials at 30 arc-second resolution (WISE30sec), Global Soil Dataset for Earth System Models (GSDE), Global Gridded Soil Information at 250-m resolution (SoilGrids250m), and Global Soil Organic Carbon Map (GSOCmap). Our analyses showed that the magnitude and distribution of SOC varied widely among datasets, with certain datasets showing region-specific robustness. At the global scale, SOC stocks at the top 30 and 100 cm were estimated to be 828 (range: 577–1 171) and 1 873 (range: 1 086–2 678) Pg C, respectively. The estimates from GSDE, GSOCmap, and WISE30sec were comparable, and those of SoilGrids250m and HWSD were at the upper and lower ends. The spatial SOC distribution varied greatly among datasets, especially in the northern circumpolar and Tibetan Plateau permafrost regions. Regionally, UM2021 and WISE30sec performed well in the northern circumpolar permafrost regions, and GSDE performed well in China. The estimates of SOC by different datasets also showed large variabilities across different soil layers and biomes. The discrepancies were generally smaller for the 0–30 cm soil than the 0–100 cm soil. The datasets demonstrated relatively higher agreement in grasslands, croplands, and shrublands/savannas than in other biomes (e.g., wetlands). The users should be mindful of the gaps between regions and biomes while choosing the most appropriate SOC dataset for specific uses. Large uncertainties in existing global gridded SOC estimates were generally derived from soil sampling density, different sources, and various mapping methods for soil datasets. We call for future efforts for standardizing soil sampling efforts, cross-dataset comparison, proper validation, and overall global collaboration to improve SOC estimates.

Priming effect (PE) on soil organic carbon (SOC) decomposition caused by the addition of organic carbon (C) is an important ecological process in regulating soil C cycle. Additionally, most priming studies are confined to laboratory trials, while the assessment of soil PE under field conditions with variable weather conditions is scarce. This study assessed the direct effects of glucose addition and in-situ warming on the extent of PE under field conditions in a temperate forest. We evaluated soil PE using ¹³C-glucose labelling, a simple and novel technique, based on the Keeling plot method. Glucose addition significantly enhanced native SOC decomposition and induced strong PE. However, the effect of in-situ warming on the extent of PE was not significant. This study confirms the importance of PE in regulating SOC turnover under field conditions.

Straw return can effectively improve farmland soil microenvironment and fertility. However, excessive straw in the topsoil adversely affects seed germination and crop growth. At present, the characteristics and key driving factors of straw decomposition in dry farmlands are unclear. Based on the interactions between tillage practices including zero tillage (ZT), chisel tillage (CT), and plow tillage (PT) and nitrogen (N) fertilization, i.e., low N (N1, 180 kg ha^-1), normal N (N2, 240 kg ha^-1), and high N (N3, 300 kg ha^-1), quantitative polymerase chain reaction technology and an enzymatic detection kit were used to investigate the effects of key straw C-degrading enzyme activities and microbial abundance in soil on maize straw decomposition during the growth period of winter wheat in the winter wheat/summer maize double cropping system in a dry farmland of the Loess Plateau, China. Between 2018 and 2020, ZT and CT significantly increased winter wheat yield (by 10.94% and 12.79%, respectively) and straw decomposition velocity (by 20% and 26.67%, respectively), compared with PT. Compared to N1 and N3, N2 significantly increased wheat yield (by 4.65% and 5.31%, respectively) and straw decomposition velocity (by 26.33% and 13.21%, respectively). The partial least squares pathway modelling showed significant positive direct effects of soil moisture, NO₃^-, NH₄⁺, total N, bacteria, and cellulase, laccase, and xylanase activities on straw decomposition, while soil pH, fungi, and Actinomycetes had significant negative direct effects. Overall, conservation tillage (ZT and CT) combined with N2 was beneficial for straw decomposition in the drylands of the Loess Plateau and improved straw resource utilization and basic soil fertility. The results of the study clarified the key drivers of straw decomposition in dry farmlands and provided new ideas for developing updated soil management practices and adaptive N application strategies to promote the resource utilization of straw and achieve the goals of carbon peaking and carbon neutrality.