The relationship between plant functional traits is a powerful indicator of the tradeoff between resource acquisition and resource conservation strategies. Karst is one of the most vulnerable terrestrial ecosystems in the world, where vegetation has been stressed for a long time by drought and was highly sensitive to extreme weather and extreme precipitation. Under the background of extreme rainfall, the changes of plant ecological strategies in karst areas are still unknown. Therefore, in this study, herbaceous plants in the early succession stage of karst abandoned farmland community in southwest China were selected as the research object. Under the condition that annual precipitation remained unchanged, four treatment groups were set up by artificially controlling the size and frequency of single precipitation. Natural rainfall was used as the control group (CK), and three treatment groups were set up: moderate rain frequency enhancement group (T10), heavy rain frequency enhancement group (T25), and rainstorm frequency enhancement group (T50). We simulated the treatment of rainfall extreme in order to study the relationship between the response characteristics of functional traits of plant roots, leaves, stems and the the relationship between economic spectrum. The main results are as follows: (1) the responses of functional traits of roots, leaves, stems to rainfall extremes were different. The theoretical hydraulic conductivity of roots increased with rainfall extremes, while the theoretical hydraulic conductivity of stems and leaves increased only in heavy rain frequency enhancement group. Stems were the most sensitive organ in plants to rainfall extremes. (2) Each organ of roots, stems, and leaves had its own stable "fast-slow" economic spectrum. In the rainfall extreme treatment, only the ecological strategies of plants in rainstorm frequency enhancement group changed, that is, plants would choose a stable economic spectrum between resource acquisition and resource conservation strategies. (3) Roots, stems, and leaves showed similar and stable economic spectrum. The extreme rainfall increased the correlation coefficient between stem and root economic spectrum in all three treatment groups, while the correlation coefficient between leaf and root economic spectrum increased only in the heavy rain frequency enhancement treatment group, and the correlation coefficient between leaf and stem economic spectrum increased only in the moderate rain frequency enhancement treatment group. In conclusion, roots and leaves of herbaceous plants in the initial stage of succession of abandoned farmland had their own stable economic patterns, and the extreme rainfall led to the decoupling of above-ground and below-ground resource conservation and acquisition strategies reflected by roots and leaves economic patterns. The study has improved the understanding of the relationship between functional traits of different plant organs and the correlation between above-ground and subsurface parts of plants, revealed the "fast-slow" plant economic spectrum of different plant organs, the differences in plant adaptive ability and the diversity of functional strategies reflected therefrom, and promoted the in-depth understanding of plant resource acquisition and environmental response strategies. The study provides new insights for predicting the adaptation trend and response strategies of herbaceous plants in karst abandoned farmland under the background of future climate change.