通过湿筛法得到不同造林地(桤木林、杜仲林、刺槐林、滇柏林和未造林地)不同土层(0—10,10—20,20—30 cm)土壤大团聚体(>2 mm)、中间团聚体(0.25～2 mm)、微团聚体(53 μm～0.25 mm)以及粉+黏团聚体(<53 μm)和土壤微生物量及微生物碳代谢活性。结果 表明:造林对土壤团聚体稳定性有显著的影响,造林地会导致大团聚体的破碎化,未造林地>0.25 mm的大团聚体含量均小于林地。在0—30 cm的土层深度内,在土壤的各粒径团聚体中,桤木林、杜仲林以>0.25 mm的大团聚体为主,占粒径总组成的20%以上; 刺槐林、滇柏林以中间团聚体和粉+黏团聚体为主; 而未利用林地则以粉+黏团聚体为主,约占粒径总组成的40%。在0—30 cm土层深度的各土层上,桤木林、杜仲林团聚体MWD和GMD值均明显高于其他林地,而在20—30 cm土层,这种差异变小,说明人类活动对土壤团聚体稳定的影响主要集中在0—10 cm的土壤表层。不同林地土壤微生物对不同种类碳源的利用强度存在较大差异,碳水化合物和羧酸类碳源是土壤微生物的主要碳源,其次为氨基酸类、酚酸类和聚合物类,胺类碳源的利用率最小。相关性分析表明:造林过程中,土壤氨基酸类、碳水化合物类、羧酸类与大团聚体、中团聚体、MWD和GMD呈显著正相关(p<0.05); 微生物量碳、微生物量氮、微生物代谢熵与微团聚体和粉微团聚体呈显著正相关(p<0.05)。总体上看,喀斯特地区造林后土壤结构趋于改善,并且微生物碳代谢活性增强。
Soil aggregates play an important role in soil fertility, quality and sustainable utilization.(0—10, 10—20, 20—30 cm)large soil aggregate(>2 mm), intermediate aggregate(0.25～2 mm), micro aggregate(53 μm～0.25 mm)and glue powder+aggregate(<53 μm)mass fraction in different soil layers of different planting areas(Alnus cremastogyne, Eucommia ulmoides, Robinia pseudoacacia, Cipressus duclouxiana forest and not planting area, CK)were obtained by wet sieving method, and soil microbial biomass and microbial activity of carbon metabolism were measured. The results showed that afforestation had a significant impact on the stability of soil aggregates, and the fragmentation of large aggregates was caused by afforestation, and the contents of >0.25 mm large aggregates in unforested areas were lower than those in forested areas, indicating that the soil structure tended to be improved after afforestation; in the soil depth of 0—30 cm, >0.25 mm large aggregates in the Alnus cremastogyne forest and Eucommia ulmoides forest are dominated and accounted for more than 20% of the total aggregates; intermediate aggregates and powder+sticky aggregates in Eucommia ulmoides and Cipressus duclouxiana were main components of the aggreates; however, the powder+cohesive aggregates in unused woodlands were of dominant, accounting for about 40% of the aggregates; in the depth of 0—30 cm, the MWD and GMD values of aggregates in Alnus cremastogyne and Eucommia ulmoides forest were significantly higher than those of other woodlands, while in the depth of 20—30 cm, the differences were smaller, indicating that the influence of human activities on the stability of soil aggregates mainly concentrated in the surface layer of 0—10 cm; the utilization intensities of different types of carbon sources by soil microorganisms in different woodlands were quite different; carbon sources of carbohydrates and carboxylic acids were the main carbon sources of soil microorganisms, followed by amino acids, phenolic acids and polymers, and amine carbon sources had the lowest utilization rate. Correlation analysis showed that amino acids, carbohydrates and carboxylic acids were significantly positively correlated with macroaggregates, mesocarbons, MWD and GMD during afforestation (p<0.05). Microbial biomass carbon, microbial biomass nitrogen and microbial metabolic entropy were positively correlated with microaggregates and powder microaggregates (p<0.05). In summary, soil structure tended to be improved after afforestation in karst areas, and the activity of microbial carbon metabolism was enhanced.
