Growth and reproductive responses to elevated CO sub(2) 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 CO sub(2) enrichment under competitive situations in a dry, low-nutrient environment? In order to test this, Aegilops and Hordeum species, common in semiarid annual grasslands of the Middle East, were grown in nine model ecosystems (400 kg each) with a natural matrix of highly diverse Negev vegetation established on native soil shipped to Basel, Switzerland. In a simulated, seasonally variable climate of the northern Negev, communities experienced a full life-cycle in 280 (preindustrial), 440 (immediate future) and 600 ppm of CO sub(2) (end of the next century). Neither Aegilops (A. kotschyi and A. peregrina), nor Hordeum spontaneum showed a significant biomass response to CO sub(2) concentrations exceeding 280 ppm The reproductive output remained unaffected or even declined (A. peregrina) under elevated CO sub(2). Non-structural carbohydrates in leaf tissues increased and N concentration decreased with increasing CO sub(2) concentration. N concentration, germination success and seedling development of newly formed grains were either unchanged or reduced in response to high CO sub(2) treatment of parent plants. In a separate fertilizer x CO sub(2) 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 significant stimulation of biomass by CO sub(2) enrichment (+ 44% between 280 and 600 ppm) was obtained only in the NPK treatment. These data suggest that increased CO sub(2) concentration had little direct effect on growth and reproduction in these 'wild cereals' in the recent past, and the same seems to hold for their future, except if N-rich fertilizer is added.