Impact of elevated CO₂ and Temperature on Nodulation and Crop Weed Competition in Groundnut (Arachis hypogaea L.)

Rising atmospheric CO₂ and temperature due to climate change pose significant threats to agricultural productivity, particularly in semi-arid tropics. These changes can alter weed distribution, population dynamics and crop-weed interactions. Assessing groundnut’s adaptability to changing climates, weed competition and herbicide efficacy is crucial for developing resilient cultivars and effective herbicide management systems to mitigate yield and quality losses, thereby enhancing global food security.

A two-year (2022-23 and 2023–24) experiment was conducted in a Carbon Dioxide and Temperature Gradient Chamber (CTGC) at the Central Research Institute for Dryland Agriculture, Hyderabad. The study evaluated groundnut under four climate variables: ambient CO₂ + ambient temperature (aCO₂ + aT) (396-405 ppm), elevated CO₂ (eCO₂, 550±50 ppm), elevated temperature (eT₂ +2°C) and combined eCO₂ + eT (550±50 ppm and +2°C) , three crop-weed combinations (groundnut + C₃ weeds, groundnut + C₄ weeds, groundnut + C₃ + C₄ weeds) and four herbicide rates (0X, 1X, 1.5X, 2X) using a completely randomized design. Growth parameters, soil rhizobium population and nodulation were assessed at 60 days after sowing (DAS).

Pooled data revealed that eCO₂ significantly enhanced groundnut growth and nodulation, with increases in plant height (25%), leaf area (26%), chlorophyll content (12%), Rhizobium population (22%), nodulation (58%) and dry matter production (22%) compared to ambient conditions. Combination of elevated CO₂ and temperature also showed positive effects, though less pronounced, while eT alone reduced all parameters. Herbicide application at various rates showed suppressive effect on Rhizobium population, nodulation and chlorophyll content compared to no application. However, plant height, leaf area and dry matter production were significantly higher at 1.5 X rate over no application under eCO₂ conditions in contrast to 1.0X rate under aCO₂ + aT, eCO₂ + eT and eT conditions. Groundnut exhibited better competitiveness against C₄ weeds compared to C₃ weeds or their combination. The findings revealed that groundnut growth and nodulation were significantly enhanced in treatments eCO₂ and eCO₂ + eT but reduced under eT. Herbicide efficacy declined under eCO₂, suggesting the need for higher application rate under future climate scenarios. These findings highlight the importance of adaptive strategies to sustain groundnut productivity under climate change scenario.