Impact of elevated CO2 on root traits of a sapling community of three birches and an oak : a free-air-CO2 enrichment (FACE) in northern Japan

We evaluated the root response to elevated CO2 fumigation of 3 birches (Betula sp.) and 1 deciduous oak (Quercus sp.) grown in immature volcanic ash soil (VA) or brown forest soil (BF). VA is a nutrient-poor, phosphorus-impoverished soil, broadly distributed in northern Japan. Each species had been exposed to either ambient (375-395 mu mol mol(-1)) (aCO(2)) or elevated (500 mu mol mol(-1)) (eCO(2)) CO2 during the daytime (more than 70 mu mol m(-2) s(-1)) over 4 growing seasons. The results suggest that eCO(2) did not cause an increase in total root production when the community had grown in fertile BF soil, however, it did cause a large increase when the community was grown in infertile VA soil. Yet, carbon allocation to plant roots was not affected by eCO(2) in either the BF or VA soils. Rhizo-morphogenesis appeared to occur to a greater extent under eCO(2). It seems that the saplings developed a massive amount of fine roots under the VA and eCO(2) conditions. Unexpectedly, eCO(2) resulted in a larger total root mass when the community was grown in VA soil than when grown in BF soil (eCO(2) x VA vs. eCO(2) x BF). These results may hint to a site-specific potential of communities to sequester future atmospheric carbon. The growing substance of plants is an important factor which root response to eCO(2) depends on, however, further studies are needed for a better understanding