In order to explore the effects of different forest types on active soil carbon pool, the amounts and density of soil organic carbon (SOC) were studied at different soil horizons under typical coniferous and broad-leaved forests in the mountainous area of Beijing. The results showed that the amount of total SOC, readily oxidizable carbon and particulate organic carbon decreased with increasing depths of soil horizons and the amounts at depths of 0-10 cm and 10-20 cm in broad-leaved forest was clearly higher than that in coniferous forests. The trend of a decrease in SOC density with increasing depth of the soil horizon was similar to that of the amount of SOC. However, no regular trend was found for SOC density at different depths between coniferous forest and broad-leaved forests. The ratio of readily oxidizable carbon to total amount of SOC ranged from 0.36-0.45 and the ratio of particulate organic carbon to total amount of SOC from 0.28-0.73; the ratios decreased with increasing depths of soil horizons. Active SOC was significantly correlated with total SOC; the relationship between readily oxidizable carbon and particulate organic carbon was significant. A broad-leaved forest may produce more SOC than a coniferous forest.
Clematis fruticosa Turcz. is a dominant native shrub with the potential for spontaneous vegetation succession for restoration of the ecologically fragile and arid Daqing Mountains of Inner Mongolia, which represent an important ecological transition zone in northern China. However, knowledge regarding the interactions between native species and their root-associated arbuscular mycorrhizal (AM) fungi across different seasons and elevation gradients remains obscure. High AM fungal spore density, root colonization and arbuscular richness suggested that C. fruticosa could establish intimate symbiotic associations with AM fungi. A total of 174 AM fungal virtual taxa were identified from rhizosphere soil samples, and Glomus was dominant. The most distinct AM fungal community composition and the greatest richness and diversity were observed in the spring and at the highest elevation. Seasons • elevation interactions significantly affected Simpson diversity but not AM fungal community composition, observed richness and Shannon index. Seasons had a significant direct on AM fungal observed richness and Shannon index, and elevation had a significant direct on AM fungal observed richness. Soil available phosphorus was the most important driving factor in AM fungal richness and diversity, followed by seasons and soil moisture content. These results provied new insights suggesting that there are active and diverse "functional ingredients", for example root-associated AM fungi during the growing season, particularly with an earlier onset in the spring. They are potentially major contributors to the re-vegetation of degraded lands and the maintenance of soil structure in arid and semiarid ecosystems, which is attributable to seasonal variation in host physiology in stressful environments. Highlights• We studied the effects of seasons and elevation on AM fungal richness, diversity and community in ecologically fragile mountain areas. • Distinct community composition and greater richness and diversity of AM fungi were detected in the spring and at the highest elevation. • AM fungal richness and diversity depended on certain soil variation related to seasons and elevation.
The variation of soil organic carbon (SOC) spatial distribution is dependent on the relative contributions of different environmental factors, and the dominant factors change according to study scales. Here, geostatistical and remote sensing techniques were used to gain deep knowledge about SOC spatial distribution patterns and their dominant determinants at different study scales; specifically, the structure of the spatial variability of SOC content at the county, regional, and watershed scales in Aohan, China were analyzed. The results show that altitude and normalized difference vegetation index (NDVI) are the key predictors explaining 49.6% of the SOC variability at the county scale; NDVI and slope are the key predictors explaining 36.2% of the SOC variability at the regional scale; and terrain factors are the most significant factors at the watershed scale. These three scales have a moderate spatial correlation in terms of SOC content. As the study scale widens, the spatial variability attributable to the random factors increases gradually, whereas the variability attributable to the structural factors gradually weakens. Soil type and land use type are the key factors influencing the SOC content at these three scales. At all scales, the SOC contents of the different land use types differ significantly in the order forestland > shrubland > grassland. Conservation of regional soil and water and prevention of soil desertification are effective measures for improving SOC content.
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