Increases in mycorrhizal colonization and seedling growth in <i>Pinus</i><i>echinata</i> and <i>Quercus</i><i>alba</i> in an enriched CO₂ atmosphere

Abstract

Forest tree biomass is hypothesized to increase in a CO 2 -enriched atmosphere if mechanisms exist to ensure acquisition of limiting nutrients in forest soils. Investment of additional photosynthate produced at elevated CO 2 into mycorrhizal proliferation and root growth may provide one such mechanism. To test this hypothesis, mycorrhizal density and seedling biomass were measured in shortleaf pine (Pinusechinata Mill.) and white oak (Quercusalba L.) grown in unfertilized forest soil in controlled-environment chambers at 360 μL L −1 and 700 μL L −1 CO 2 . Mycorrhizal density was greater at elevated CO 2 in both species after 6 weeks of exposure; in white oak, the increased density persisted for 24 weeks. Root dry weight was increased 76% in P. echinata and 91% in Q. alba at 700 μL L −1 CO 2 ; total seedling dry weight was increased by 66 and 56%, respectively. It is hypothesized that increased photosynthesis at elevated CO 2 offsets the carbon requirement for mycorrhizal establishment on shortleaf pine. Greater mycorrhizal density and enhanced 1st-year root growth in both species may facilitate future nutrient acquisition, supporting further biomass increases in an enriched CO 2 atmosphere.