Distribution of organic carbon and nutrients in soil aggregates under different Cunninghamia lanceolata stand types in southern Guangxi of China

Abstract Background: By microscopically characterizing soil organic carbon (Corg) and nutrients pertaining to different Cunninghamia lanceolata stands at aggregate scale. A theoretical foundation can be laid to more sustainably employ soil resources in Cunninghamia lanceolata plantations, thus improving soil health and fertility.Methods: Soil Corg, total nitrogen (Ntot), available phosphorus (Pava) and exchangeable cations (including calcium (Ca2+), magnesium (Mg2+), potassium (K+) and sodium (Na+)) received the analysis within aggregate fractions acquired from 0-10 cm and 10-20 cm depth in three different stands, mixed stand of Cunninghamia lanceolata and Michelia macclurei (stand A), Cunninghamia lanceolata and Mytilaria laosensis (stand B) and pure stand of Cunninghamia lanceolata (stand C), respectively. The soil aggregates were classified into macro-aggregates (>2 mm), meso-aggregates (2-0.25 mm) and micro-aggregates (<0.25 mm) fractions by one dry-sieving process.Results: The two mixed stands displayed a relationship with the higher stable characteristic pertaining to soil aggregates than the pure stand, especially stand A. Meanwhile, micro-aggregates acted as the main fractions that carried soil Corg, Ntot, and Pava, and both micro- and macro-aggregates referred to the main fractions that carried exchangeable cations. As for the soil nutrient stocks, only the exchangeable K+ cation stock of the pure stand dominated among the Corg and nutrients stocks, in addition, the rest of the other nutrients stocks of the mixed forests (stand A and B) took an advantage over the pure stand. Moreover, the Corg and nutrients stocks in stand A and B were reflected in the macro-aggregates, differently, those of stand C were mainly reflected in the micro-aggregates.Conclusions: Thus, selecting suitable broadleaf tree species mixed with Cunninghamia lanceolata can alleviate the problems of pure stand soil aggregate stability reduction and soil Corg and nutrient loss for promoting soil resources to be sustainably utilized and protecting the health and quality of soil in the hilly area in southern Guangxi, China.