Adapting fodder oats to climate change: Enhancing growth, yield, and microbial dynamics under elevated CO2 and temperature

The effects of elevated atmospheric carbon dioxide concentration (e[CO₂]) and temperature (e°T) on various traits of oat (Avena sativa L.) varieties using open-top chambers (OTC) were investigated. A simulated environment was created for the experiment i.e., ambient temperature and CO₂ (a°T + a[CO₂]); elevated temperature (3 °C > ambient temperature) (e°T); elevated CO₂ (550 ± 50 ppm) (e[CO₂]); and a combination of ambient temperature with elevated CO₂ (a°T + e[CO₂]), for accessing the effect of e°T and e[CO₂] on oats. a°T + e[CO₂] increased plant height to 121 cm compared to 114 cm in a°T + a[CO₂] and 111 cm in e°T + e[CO₂]. Seed weight was highest in a°T + e[CO₂] (3.09 g) compared to 2.53 g in a°T + a[CO₂] and 2.60 g in e°T + e[CO₂]. Leaf number and tillers were significantly higher in a°T + e[CO₂] (61.4 leaves, 10 tillers) than in a°T + a[CO₂] (27.6 leaves, 5.6 tillers) and e°T + e[CO₂] (44.3 leaves, 6.93 tillers). Chlorophyll content was highest in a°T + e[CO₂] (5.13 mg/g) compared to 3.61 mg/g in a°T + a[CO₂] and 1.47 mg/g in e°T + e[CO₂]. In contrast, germination rate was best in a°T + a[CO₂] (81.6 %) compared to e°T + e[CO₂] (60.3 %) and a°T + e[CO₂] (63.1 %). Malondialdehyde (MDA), a stress marker, was significantly higher in e°T + e[CO₂] (1.35 nmol/g) compared to a°T + a[CO₂] (0.299 nmol/g). Membrane stability index (MSI) was lowest in e°T + e[CO2] (13.2) compared to 20.9 in a°T + a[CO₂], indicating greater stress under e°T + e[CO₂]. Starch content in a°T + e[CO₂] (14.6 %) was more than double that of a°T + a[CO₂] (7.09 %). Microbial activity also showed significant differences. Dehydrogenase was highest in e°T + e[CO₂] (13.86 µg/g/day) compared to a°T + a[CO₂] (8.80) and a°T + e[CO₂] (12.62). Total bacterial count (TBC) increased in e°T + e[CO₂] (72) compared to a°T + a[CO₂] (61). Similarly, phosphate-solubilizing bacteria (PSB) and fungi (PSF) were highest in e°T + e[CO₂] (PSB: 104.5, PSF: 8.5) compared to a°T + a[CO₂] (PSB: 75.0, PSF: 4.0). Rhizobium and Azotobacter counts were elevated in a°T + e[CO₂] (95 and 94) compared to a°T + a[CO₂] (72.5 and 42.0), showing a strong positive impact of e[CO₂] on microbial populations. Specific oat varieties such as JHO-2000–4 and JHO-99–2 performed best under these conditions, showing higher yields and better stress tolerance. While e[CO₂] offers substantial benefits to oat plant growth and soil microbial activity, the additional stress from e°T complicates these benefits.