EFFECTS OF ARBUSCULAR MYCORRHIZAL FUNGI AND <em>RHIZOBIUM</em> ON PHOTOSYNTHETIC ACTIVITY AND GROWTH RESPONSE IN <em>ACACIA</em> <em>AURICULIFORMIS</em> SEEDLINGS UNDER ELEVATED CO₂

Abstract

Effects of different levels of elevated carbon dioxide (CO₂) on the activity of microbial symbionts (arbuscular mycorrhizal (AM) fungi and Rhizobium sp.) in Acacia auriculiformis seedlings were studied to understand the relationship between A. auriculiformis, Rhizobium sp. and CO₂. Seedlings of A. auriculiformis were inoculated with AM fungi and Rhizobium sp. and placed in open top chambers fitted with elevated CO₂ supplying facilities. These seedlings were maintained in the open top chambers for 180 days under different levels of elevated CO₂ (ambient control, 600 and 900 ppm). After 180 days, nodule numbers, seedling growth and photosynthesis of A. auriculiformis seedlings inoculated with microbial symbionts significantly improved under 600 and 900 ppm of CO₂. The net photosynthetic rate was higher in 900 ppm CO₂ than 600 ppm and ambient control due to inoculation of AM fungi and Rhizobium sp. The uninoculated seedlings showed very poor performance under 900 ppm elevated CO₂. This study showed that the microbial symbionts can improve growth and photosynthesis of A. auriculiformis seedlings under the elevated CO₂ level conditions (600 and 900 ppm).