Physiological Alteration in Sunflower Plants (Helianthus annuus L.) Exposed to High CO2 and Arbuscular Mycorrhizal Fungi

Abstract

Sunflower plants (Helianthus annuus L.) in a CO₂-enriched atmosphere (eCO₂) were used herein to examine the developmental and physiological effects of biofertilization with mycorrhizae (Rhizophagus irregularis). The eCO₂ environment stimulated colonization using R. irregularis mycorrhizal fungi, as compared to plants grown under ambient CO₂ conditions (aCO₂). This colonization promotes plant growth due to an increased nutrient content (P, K, Mg, and B), which favors a greater synthesis of photosynthetic pigments. Biofertilized plants (M) under eCO₂ conditions have a higher concentration of carbon compounds in their leaves, as compared to non-biofertilized eCO₂ plants (NM). The biofertilization (M) of sunflowers with R. irregularis decreased the C/N ratio, as compared to the NM plants, decreasing the hydrogen peroxide content and increasing the antioxidant enzyme activity (catalase and APX). These results suggest that sunflower symbiosis with R. irregularis improves the absorption of N, while also decreasing the plant's oxidative stress. It may be concluded that biofertilization with mycorrhizae (R. irregularis) may potentially replace the chemical fertilization of sunflower plants (H. annuus L.), resulting in more environmentally friendly agricultural practices. This information is essential to our understanding of the mechanisms influencing the C and N dynamic in future climate change scenarios, in which high CO₂ levels are expected.

Keywords: C/N ratio; biofertilization; nutrients; oxidative stress; photosynthetic pigments.

Figure 1

H₂O₂ content (A), catalase (B) and APX (C) activities in leaves of sunflower inoculated (M) or not inoculated (NM) with R. irregularis and ambient (aCO₂) and elevated CO₂ treatments (eCO₂). Data are means ± SE. Different letters show significant difference among the treatments according to Tukey’s test (p 0.05). ** p < 0.01, * p < 0.05, NS = not significant.