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, 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 CO₂ (end of the next century). Neither Aegilops (A. kotschyi and A. peregrina), nor Hordeum spontaneum showed 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 concentration, germination success and seedling development of newly formed grains were either unchanged or reduced in response to high CO₂ treatment of parent 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 significant stimulation of biomass by CO₂ enrichment (+44% between 280 and 600 ppm) was obtained only in the NPK treatment. These data suggest that increased CO₂ 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.