An assessment of bioactive compound profiles and biological activities in selected Bulbine species under short-term exposure to concurrent elevated carbon dioxide and temperatures

Abstract

South Africa has been identified as a climate change hotspot by the Intergovernmental Panel on Climate Change (IPCC), primarily due to rising temperatures over the past four decades. Anthropogenic activities, particularly industrialization, have contributed significantly to the increase in greenhouse gases, notably atmospheric carbon dioxide (CO2). These changes pose a potential threat to plant life by altering physiological and metabolic processes. Medicinal plants, in particular, may be highly sensitive to such environmental shifts, which can affect their phytochemical composition and therapeutic potential. While most studies have examined the effects of individual abiotic factors on medicinal plants, natural ecosystems subject plants to simultaneous environmental stresses. This study aimed to evaluate the effects of concurrent elevated CO2 and temperature on the phytochemical content and biological activities of Bulbine abyssinica, Bulbine frutescens, and Bulbine natalensis. Mature potted plants were subjected to elevated CO2 (600 and 800 ppm) and high day/night temperatures (40/30 °C and 45/35 °C) for eight days in a controlled climate simulation chamber. Plant organs, including leaves, roots, and underground stems, were harvested at intervals (48, 96, 144, and 192 hours) for analysis. Control plants were maintained at ambient CO2 (400 ppm) and temperatures (27/25 °C). Methanol extracts of plant parts were screened for ten phytochemical groups and quantitatively assessed for total phenolic, flavonoid, tannin, and proanthocyanidin content using UV-Vis spectrophotometry. Antioxidant activity was evaluated using DPPH, hydrogen peroxide, and metal chelation assays. Antimicrobial potential was investigated via agar diffusion and minimum inhibitory concentration (MIC) assays against several Gram-positive and Gram negative bacteria and yeasts. Results showed that leaf extracts generally exhibited a greater diversity of phytochemical groups than underground organs. Notably, the underground stem of B. abyssinica and B. natalensis accumulated higher tannin content under stress conditions, while B. frutescens leaves showed enhanced proanthocyanidin levels. Elevated CO2 and temperature increased the accumulation of bioactive compounds across species relative to controls. Enhanced antioxidant activity was observed, especially for H2O2 scavenging and iron chelation, with underground organs often outperforming leaves. Antibacterial activity under elevated CO2 and temperature was moderate (10–19 mm inhibition zones) overall, with enhanced MIC responses observed at higher stress levels (800 ppm CO2 and 45/35 °C). Among the tested microbes, Enterococcus faecalis showed consistent inhibition across all species. In conclusion, short-term exposure to concurrent elevated CO2 and temperature significantly influences the synthesis of phytochemicals and enhances certain biological activities in Bulbine species. These findings highlight species-specific and organ-specific responses that may inform future conservation and pharmaceutical utilization strategies under climate change scenarios.