[Fractionation of dissolved organic carbon along soil profiles during the leaching process].

Two distinct soil types in mid-subtropical China were selected for soil sampling at the depth of 0-10, 10-20, 20-40, 40-60, 60-80, 80-100 cm for soil cores preparation. Dissolved organic carbon (DOC) extracted from recently fallen litters of Castanopsis carlesii with ultrapure water was leached through such soil cores to investigate the fractionation and retention pattern when migrating along the soil layers. The results showed the leachates out of deeper soil cores had lower concentrations and were chemically simpler, the hydrophobic pools contributed to the majority of the retention, but the proportion of retained hydrophilic materials gradually increased with the increasing soil depth. The infrared spectrum suggested that the hydrophobic materials containing aromatic rings could be easily absorbed by soils, but alkanes and simple carbohydrates would transport into subsoils with soil solution. Proportional decrease in the highly sorptive DOC restricted C sorption by subsoils, and thus the adsorption occurred mainly in 0-40 cm soil layers, suggesting that the chemical nature of DOC had a greater influence on sorption capacity of the soils than soil physicochemical properties. The retention amounts of DOC by different soil types differed significantly, which were significantly positively correlated with the contents of clay, iron and aluminum oxides.

[Decomposition dynamics of leaf litter in logging residue of a secondary Castanopsis carlesii plantation and its chemical composition changes].

A field experiment was conducted to understand the decomposition rates and chemical composition changes of leaf litter in logging residues of a 35-year-old secondary Castanopsis carlesii plantation over a period of one year. Mass loss rate of leaf litter showed an exponential decrease with time from May 2012 to April 2013, with a total 80% loss of initial dry mass. Net potassium (K) release was observed during this period, with only 5% of initial K remained. Nitrogen ( N) featured a pattern of accumulation at the early stage and release later, while phosphorus (P) exhibited a sequence of release, accumulation, and release. The remaining of N and P were 19% and 16% of their initial mass, respectively. The release rate was highest for K and the lowest for N. Decomposition of lignin indicated a trend of release-accumulation-release from May 2012 to October 2012, with no further significant change from November 2012 to the end of the experiment. The concentration of cellulose nearly unchanged during the experiment. The N/P rate increased with decomposition, ranging from 18.6 to 21.1. The lignin/N rate fluctuated greatly at the early stage and then almost stabilized thereafter.

[Comparison on concentrations and quality of dissolved organic matter in throughfall and stemflow in a secondary forest of Castanopsis carlesii and Cunninghamia lanceolata plantation].

In this paper, monthly variation of dissolved organic matter (DOM) concentrations as well as humification and aromaticity indices in throughfall and stemflow from secondary broadleaved Castanopsis carlesii (BF) forest and Cunninghamia lanceolata plantation (CP) were measured. The DOC concentrations in throughfall were significantly higher with greater variation in BF than in CP. The concentrations of DOC in throughfall were averagely 7.2 and 3.2 times of those in rainfall in BF and CP forests, respectively. The DOC concentrations of stemflow in CP were averagely 2.5 times as much as those in BF, and the DOC concentrations in stemflow tended to be greater in dry season than in rain season for the two forests. A significantly negative relationship was' found between the DOC concentrations in stemflow and the amounts of stemflow for both BF and CP. Moreover, the humification and aromaticity indices of DOM in throughfall in BF was significantly greater than in CP. In contrast, the humification and aromaticity indices of DOM from stemflow of CP were significantly greater than those of BF. This result indicated that the structure of DOM from throughfall was more complex in BF than in CP, and the structure of DOM from stemflow was vice versa. These results indicated that DOM in stemflow and throughfall showed significant variations in quantity and quality between BF and CP and may greatly impact the accumulation of soil organic carbon.