关键词: 喀斯特地区, 天然次生林, 自然演替, 碳氮, 含量与储量

Abstract:

Objective: This study is aimed to investigate the variation characteristics of soil carbon and nitrogen storage of typical communities in the process of vegetation natural restoration succession, and provide data support for vegetation restoration and reconstruction in southwest karst area. Method: By using the space-for-time substitution method, the natural restoration succession stages of abandoned cropland (abandoned cropland for half a year), grassland (5-10 a), shrub (15-25 a), shrub-forest (30-40 a) and forest (50-60 a) in karst trough valley of Zhongliang Mountain in Chongqing were selected as the research objects, permanent plots were established in each succession stages; the contents of soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), total potassium (TK), ammonium nitrogen (NH₄⁺-N), nitrate nitrogen (NO₃^?-N), soil carbon-nitrogen ratio (C/N) and soil pH in 0-10, 10-30, 30-50, 50-70 cm were measured to estimate the soil carbon and nitrogen storage in each succession stage, and analyze the soil carbon and nitrogen content and storage characteristics in different stages of natural restoration succession. Result: The natural vegetation restoration and succession significantly increased SOC and TN contents and storage (P < 0.001), and the highest SOC and TN contents and storage were found in shrub-forest, with contents of 57.75 g·kg ^?1 and 6.31 g·kg^?1 and storage of 87.71 t·hm^?2 and 10.06 t·hm^?2, respectively, which increased by 51.88% and 30.31% compared with the abandoned farmland stage. The SOC storage in 0-30 cm soil layer accounted for 64.02%-73.68% of the 0-70 cm soil layer, and the soil TN storage accounted for 64.73%-78.55%. The soil C/N in 0-70 cm soil layer increased first and then decreased during the natural vegetation restoration succession, and the soil C/N in shrubland stage was the highest, which was 9.56. The C/N ratio of forest stage in 0-30 cm soil layer was the highest, which was 9.98, and the C/N ratio of 30-70 cm soil layer was relatively low. Soil NH₄⁺-N storage of shrub-forest stage was the highest (0.103 t·hm^?2), soil NO₃^?-N storage of abandoned farmland stage was the highest (0.076 t·hm^?2), followed by shrub-forest stage (0.038 t·hm^?2). The SOC and TN storage were significantly positively correlated with soil NH₄⁺-N, NO₃^?-N and TP contents (P < 0.05), in addition, the SOC storage was also significantly positively correlated with soil TN and TK contents ( P < 0.05), and the soil TN storage was also significantly positively correlated with SOC contents ( P < 0.05). Soil C/N was positively correlated with SOC, TN, and NH ₄⁺-N contents (P < 0.01), positively correlated with TP contents ( P < 0.05), and negatively correlated with TK contents ( P < 0.01). Conclusion: The succession of natural vegetation restoration in the karst area can significantly improve soil carbon and nitrogen content and storage (P < 0.001), and the effects on carbon and nitrogen content and storage and C/N in the 0-30 cm soil layer were more obvious than those in the 30-70 cm soil layer. There is a certain correlation between carbon and nitrogen storage and nutrient cycling. From the natural restoration succession of vegetation to the shrub-forest stage, soil carbon and nitrogen storage have been significantly increased to the peak ( P < 0.001); and the natural restoration of vegetation has a significant influence on the improvement of soil quality ( P < 0.001).

Key words: karst area, natural secondary forest, natural succession, carbon and nitrogen, content and storage