Growth and reproductive responses to elevated CO2 in wild cereals of the northern Negev of Israel

How might wild relatives of modern cereals have responded to past, and how might they respond to future, atmospheric CO2 enrichment under competitive situations in a dry, low-nutrient environment? In order to test this, Aegil ops and Hordeum species, common in semiarid annual grasslands of the Middle East, were grown in nine model ecosystems (400 kg each) with a natural mat rix of highly diverse Negev vegetation established on native soil shipped t o Basel, Switzerland. In a simulated, seasonally variable climate of the no rthern Negev, communities experienced a full life-cycle in 280 (preindustri al), 440 (immediate future) and 600 ppm of CO2 (end of the next century). N either Aegilops (A. kotschyi and A. peregrina), nor Hordeum spontaneum show ed a significant biomass response to CO2 concentrations exceeding 280 ppm. The reproductive output remained unaffected or even declined (A. peregrina) under elevated CO2. Non-structural carbohydrates in leaf tissues increased and N concentration decreased with increasing CO2 concentration. N concent ration, germination success and seedling development of newly formed grains were either unchanged or reduced in response to high CO2 treatment of pare nt plants. In a separate fertilizer x CO2 trial with A. kotschyi nested in smaller model communities, we found no effect of P addition, but a 2-3-fold biomass increase by NPK addition compared to the unfertilized control. A s ignificant stimulation of biomass by CO2 enrichment (+ 44% between 280 and 600 ppm) was obtained only in the NPK treatment. These data suggest that in creased CO2 concentration had little direct effect on growth and reproducti on in these 'wild cereals' in the recent past, and the same seems to hold f or their future, except if N-rich fertilizer is added.