Interactive effects of elevated CO(2) and mineral nutrition on growth and CO(2) exchange of sweet chestnut seedlings (Castanea sativa).

The effects of elevated atmospheric CO(2) (700 micro mol mol(-1)) and fertilization were investigated on 2-year-old sweet chestnut (Castanea sativa Mill.) seedlings grown outdoors in pots in constantly ventilated open-sided chambers. Plants were divided into four groups: fertilized controls (+F/-CO(2)), unfertilized controls (-F/-CO(2)), fertilized + CO(2)-treated plants (+F/+CO(2)) and unfertilized + CO(2)-treated plants (-F/+CO(2)). Dry matter accumulation and allocation were measured after one growing season and CO(2) exchange of whole shoots was measured throughout the growing season. Shoot growth and total leaf area of unfertilized plants were not affected by elevated CO(2), whereas both parameters were enhanced by elevated CO(2) in fertilized plants. Elevated CO(2) increased total biomass by about 20% in both fertilized and unfertilized plants; however, biomass partitioning differed. In unfertilized plants, elevated CO(2) caused an increase in root growth, whereas in fertilized plants, it stimulated aboveground growth. At the whole-shoot and leaf levels, photosynthetic activity of both fertilized and unfertilized plants increased in response to elevated CO(2), but the seasonal pattern of this enhancement varied with nutrient treatment. In unfertilized plants, a downward acclimation of photosynthesis was observed early in the season (June), and was related to reductions in nitrogen and chlorophyll content and to starch accumulation. The decrease in the slope of the A/C(i) curve suggested a decrease in Rubisco activity. In both fertilized and unfertilized plants, shoot respiration decreased during the night in response to elevated CO(2) until mid-July. The decrease was not related to changes in sugar concentration.