Effects of CO and nutrient enrichment on tissue quality of two California annuals.

The effects of CO enrichment and soil nutrient status on tissue quality were investigated and related to the potential effect on growth and decomposition. Two California annuals, Avena fatua and Plantago erecta, were grown at ambient and ambient plus 35 Pa atmospheric CO in nutrient unamended and amended serpentine soil. Elevated CO led to significantly increased Avena shoot nitrogen concentrations in the nutrient amended treatment. It also led to decreased lignin concentrations in Avena roots in both nutrient treatments, and in Plantago shoots and roots with nutrient addition. Concentrations of total nonstructural carbohydrate (TNC) and carbon did not change with elevated CO in either species. As a consequence of increased biomass accumulation, increased CO led to larger total pools of TNC, lignin, total carbon, and total nitrogen in Avena with nutrient additions. Doubling CO had no significant effect on Plantago. Given the limited changes in the compounds related to decomposibility and plant growth, effects of increased atmospheric CO mediated through tissue composition on Avena and Plantago are likely to be minor and depend on site fertility. This study suggests that other factors such as litter moisture, whether or not litter is on the ground, and biomass allocation among roots and shoots, are likely to be more important in this California grassland ecosystem. CO could influence those directly as well as indirectly.