Alfalfa yield under elevated CO 2 and temperature depends on the Sinorhizobium strain and growth season

Abstract

The aim of the present study was to analyse the effect of elevated CO 2 at different temperature, inoculation with three Sinorhizobium meliloti strains and growth in two seasons (summer and autumn) on plant growth, photosynthesis and N 2 fixation (estimated as apparent nitrogenase activity, ANA). One of the objectives was to demonstrate that most efficient N 2-fixing strains could improve alfalfa forage production. The second objective was to test if S. meliloti strains alter their efficiency under climate change conditions. The third objective was to show if seasonal changes may modify alfalfa productivity. Interaction of CO 2 and temperature enhanced alfalfa dry matter in both seasons; however, plants produced more dry matter in autumn than in summer, due to the negative effect of elevated summer temperature on N 2-fixation. Higher yield in summer corresponded to plants in symbiosis with 102F78 strain being not related to enhanced nodule dry matter or apparent nitrogenase activity but to putative lower carbon consumption for N 2 fixing process. Contrariwise, in autumn the highest yield was obtained by 102F34 as a consequence of increased nodule dry matter induced under elevated CO 2 and temperature. © 2011 Elsevier B.V.