ABSTRACT
Investigating the relationship of soil aggregate stability with the organic carbon in the aggregate and its response to land use change is conducive to the estimation of soil carbon sink potential, improvement of rocky desertification, and rational land use in karst areas of Southwest China. In order to explore the effects of land use change on the composition and stability of soil aggregate stability as well as the content of aggregate organic carbon, the soil (0-30 cm) of five land use types (secondary forest, pomelo forest, paddy field, pepper forest, and dry land) was selected as the research object. The characteristics and correlation of soil aggregate components and organic carbon under different land use patterns were obtained, and the contribution of soil aggregates to the change in organic carbon after land use change was calculated. The results showed that the macroaggregates in the surface soil (0-15 cm) of the secondary forest, pomelo forest, and paddy field were 63.32%, 52.38%, and 47.77%, respectively, which were significantly higher than that of dry land (23.70%), as was also seen in the lower layer (15-30 cm). The geometric mean diameter (GMD) and mean weight diameter (MWD) of soil aggregates in the secondary forest, pomelo forest, and paddy field were significantly higher than those in dry land. In the surface soil, the organic carbon of the secondary forest and paddy field was significantly higher than that of other land use patterns. By contrast, in the lower soil layer, only the organic carbon of the paddy field was significantly higher than that of the others. Under different land use patterns, the organic carbon content of aggregates followed the same order of macroaggregates > microaggregates > silt and clay, indicating that macroaggregates allowed soil organic carbon to accumulate, whereas silt and clay did the opposite. According to correlation analysis, the content of soil macroaggregates was significantly positively correlated with GMD, MWD, and soil aggregate organic carbon, suggesting that the increase in soil macroaggregates could improve the stability of soil aggregates and store more soil organic carbon. Further, as land use change may have significantly affected the soil aggregate, moderate development of forestry and paddy cultivation is suggested to improve the soil carbon sequestration potential in the karst area of Southwest China.
ABSTRACT
The composition of soil organic carbon and its stability mechanism are the key to understanding the terrestrial carbon sink capacity. The stability of soil organic carbon in a karst ecosystem greatly affects the soil carbon fixation capacity. In order to understand the impact of human activities on the stability of soil organic carbon in karst areas, the karst valley area of Zhongliang Mountain in Chongqing was selected as an example, and soil samples of four typical land use modes (mixed forest, bamboo forest, grassland, and cultivated land) were collected in layers to analyze the total organic carbon (TOC) and heavy fraction organic carbon (HFOC). The distribution characteristics of light fraction organic carbon (LFOC), labile organic carbon (LOC), and recalcitrant organic carbon (ROC) were analyzed quantitatively by using a structural equation model to provide basic data for soil carbon sink assessment and soil quality protection in karst areas. The results showed that the organic carbon components under different land use patterns in karst areas had obvious surface accumulation, and the content of organic carbon components in the surface layer was 1.2 times that in the bottom layer. Except for LFOC, the content of other organic carbon components was the highest in the mixed forest, followed by that in the bamboo forest and wasteland, with the lowest in cultivated land. Mixed forest ω(TOC) content was the highest, 42.5 g·kg-1, followed by that of bamboo forest (36.6 g·kg-1) and grassland (18.7 g·kg-1), and cultivated land content was the lowest, 13.4 g·kg-1. The soil organic carbon content of cultivated land was 68.5%, 63.5%, and 28.3% lower than that of mixed forest, bamboo forest, and grassland, respectively. Mixed forest had the highest content of ω(HFOC), 21 g·kg-1, followed by those of bamboo forest (20.9 g·kg-1), grassland (18.2 g·kg-1), and cultivated land (13.5 g·kg-1). The mixed forest ω(LOC) content was the highest, 16.3 g·kg-1, followed by those of bamboo forest (14.9 g·kg-1), grassland (11.5 g·kg-1), and cultivated land (5.3 g·kg-1). Mixed forest ω (ROC) content was the highest, 25.7 g·kg-1, followed by those of bamboo forest (21.6 g·kg-1), grassland (15.9 g·kg-1), and cultivated land (10.3 g·kg-1). The bamboo forest land ω(LFOC) content was 15.9 g·kg-1, followed by those of mixed forest (13.9 g·kg-1), grassland (7.3 g·kg-1), and cultivated land (4.9 g·kg-1). The recalcitrant organic carbon index (ROCI) was used to indicate the stability of soil organic carbon. The variation range of ROCI was 33.9%-64.5%, of which the highest was mixed forest (64.5%-66.3%), and the lowest was cultivated land (33.8%-39.6%). The ROCI of mixed forest, bamboo forest, and grassland were 1.8 times, 1.6 times, and 1.4 times that of cultivated land, respectively. Karst area ω (inert organic carbon) content and ROCI showed that human agricultural activities caused the reduction in soil organic carbon content and the destruction of soil physical structure, resulting in the accelerated decomposition and turnover rate of soil organic matter. The most important factor affecting soil stability in karst areas was soil pH. Tillage activities caused soil pH to rise, reduced soil microbial activity, and were not conducive to the accumulation of the inert organic carbon and soil organic carbon pool in the soil.
ABSTRACT
Recently, the indoor air pollution, especially the volatile organic compounds (VOCs) is attracting more and more attention. The determination of indoor air organic gases becomes the key issue. In the present paper, a simultaneous quantitative measuring method of indoor air multi-component VOCs was established based on FTIR combined with chemometrics. The 3 200-2 600 cm(-1) and 1 100-600 cm(-1) bands of IR spectrum were used to establish validation model, and excellent coefficients were obtained (r(2) =0. 970, 0. 955 and 0. 946 for benzene, toluene and dimethylbenzene, respectively). The root mean standard error of calibration for benzene, toluene and dimethylbenzene is 0. 074 2, 0. 081 9 and 0. 087 7, respectively. The root mean standard error of prediction is 0. 132, 0. 134 and 0. 033 3, respectively. The error of unknown sample prediction is acceptable. The IR method is effective for simultaneous analysis of indoor air multi-component VOCs. The model established by partial least squares (PLS) is better than that by principal components analysis (PCR).
