The physiological and genetic basis of productivity and water use in Poplar in current and future climates

This thesis presents data from field and glasshouse experiments to determine the physiological traits associated with high yield. Data is also presented from CO2 enrichment experiments carried out in open top chambers and FACE facilities to investigate root growth and water use including preliminary data which may be useful in eventually identifying the genetic control of physiological traits in poplar.A field trial at two contrasting sites in the UK using five poplar genotypes with contrasting physiological traits showed that large leaf size and rapid leaf expansion were good indicators of high yield while rate of leaf production was not. A glass house study using rhizotrons to observe root growth showed high yielding genotypes to have correspondingly high rates of root elongation and density.Root measurements made on an F2 population of poplar grown under elevated CO2 in open top chambers provided data that will form the basis of future QTL mapping projects in collaboration with research groups in the USA.Data presented from a study of sap flow and water use in poplars grown in a Free Air CO2 Enrichment facility in Italy showed that elevated CO2 effects on water use in poplar are likely to vary throughout the growing season. Water use was increased at the start of the growing season under elevated CO2 , but was reduced towards the end of the growing season compared to ambient conditions.The implications of these findings are discussed in relation to the economic viability of poplar as a biomass crop for renewable energy and the possible consequences of global climate change for the future of poplar cultivation are explored.