Soil organic acids released by plants are important for improving soil nutrient availability. To clarify the relationships between soil organic acids and the concentrations and ratios of nutrients at different stages of vegetation restoration in a karst ecosystem, we measured the concentrations of oxalic acid, malic acid, acetic acid, organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), nitrogen (AN) and phosphorus availability (AP), and microbial biomass carbon (MBC) in rhizosphere soils and bulk soils of six plant species (three for shrubland and three for primary forest) in dry and wet seasons. Our results showed that the oxalic acid concentrations of rhizosphere soils in primary forest were higher than those in shrubland in both seasons, whereas the concentrations of malic acid and acetic acid showed an opposite trend. Moreover, the concentrations of oxalic acid in rhizosphere soils in both vegetations were higher than those of bulk soils in both seasons. The concentrations of oxalic acid of rhizosphere and bulk soils were higher in the wet season than that in the dry season, whereas those of malic acid and acetic acid were lower. Furthermore, the oxalic acid concentrations were significantly positively correlated with SOC, TN, TP, AN, and N∶P ratios, and significantly negatively correlated with C∶N ratios. Soil AN and AP concentrations were significantly positively correlated with oxalic acid concentrations and MBC. Our results suggest that seasonal changes in organic acid exudate may be related to soil nutrient status and plant nutrition requirements, and that the interactions between organic acids and soil microorganisms may enhance nitrogen and phosphorus availability. Therefore, seasonal changes in organic acid concentrations of rhizosphere soils may be an important mechanism for plant adaption to soil nutrient limitations in karst ecosystems.