The effects of elevated CO2concentrations on the root growth of Lolium perenne and Trifolium repens grown in a FACE* system

Abstract

AbstractLolium perenneandTrifolium repenswere grown in a Free Air CO2Enrichment (FACE) system at elevated (600 μimol mol‐1) and ambient (340 μmol mol‐1) carbon dioxide concentrations during a whole growing season. Using a root ingrowth bag technique the extent to which CO2enrichment influenced the growth ofL, perenneandT. repensroots under two contrasting nutrient regimes was examined. Root ingrowth bags were inserted for a fixed time into the soil in order to trap roots. It was also possible to follow the mortality of roots in bags inserted for different time intervals. Root ingrowth of bothL. perenneandT. repensincreased under elevated CO2conditions. InL. perenne, root ingrowth decreased with increasing nutrient fertilizer level, but forT. repensthe root ingrowth was not affected by the nutrient application rate. Besides biomass measurements, root length estimates were made forT, repens.These showed an increase under elevated CO2concentrations. Root decomposition appeared to decrease under elevated CO2concentrations. A possible explanation for this effect is the observed changes in tissue composition, such as the increase in the carbon: nitrogen ratio in roots ofL. perenneat elevated CO2concentrations.