[Effects of Cunninghamia lanceolata stand types on the changes of aggregate-related organic carbon and nutrients in surface soil]

Exploring the microscopic characterization of organic carbon and nutrients in surface soil of different Chinese fir stands at aggregate scale can lay a theoretical foundation for promoting the sustainable use of soil resources with implications for improving soil health and fertility. We mea-sured the concentrations of soil organic C (OC), total nitrogen (TN), alkali-hydrolyzed nitrogen (AN), Olsen-P (AP), and available K (AK) in aggregate fractions collected from 0-10 cm and 10-20 cm soil layers in three different stands, mixed plantation of Cunninghamia lanceolata and Michelia macclurei (Ⅰ), C. lanceolata and Mytilaria laosensis (Ⅱ) and pure plantation of C. lanceolata (Ⅲ) respectively. Soil aggregates were classified into >2, 0.25-2, and <0.25 mm fractions by a dry-sieving procedure. The organic carbon and nutrient contents of soil aggregates in different stands increased with the decreases of particle size while the contribution rate of aggregates with different particle sizes to soil organic carbon and nutrient storage in 0-10 cm soil layer mainly was (>2 mm)>(0.25-2 mm)>(<0.25 mm), which was (>2 mm)>(<0.25 mm)>(0.25-2 mm) in 10-20 cm soil layer. The average weight diameter (MWD), the contents and stocks of OC, TN, AN and AP in surface soil aggregates of different stands ranked as Ⅰ>Ⅱ>Ⅲ (except the AP in 10-20 cm soil layer), while the contents and stocks of AK ranked as Ⅲ>Ⅰ>Ⅱ. Compared with pure plantation, aggregate structure of surface soil of mixed plantations was more stable, and Ⅰ was better than Ⅱ, because Ⅰ was artificially disturbed but Ⅱwas not. Therefore, the mixed plantation of C. lanceolata and M. macclurei could effectively promote the formation and stability of soil aggregates, and alleviate decomposition of soil organic matter and nutrient loss in plantations.