Relationships between growth, specific leaf area and water use in six populations of Eucalyptus microtheca seedlings from two climates grown in controlled conditions

Abstract

Summary To gain a better understanding of those parameters that control growth and productivity of Eucalyptus microtheca populations from seasonally dry to semi-arid sites in Australia we measured their total plant biomass, allocation of dry matter to roots and shoots, specific leaf area (SLA) and water use. For this purpose the seedlings were raised up to five months under three different pot moisture conditions applied by cyclical watering regimes. Young seedlings of six provenances of Eucalyptus microtheca fell generally into two groups, the Rockhampton, Walgett and Maree provenances which evolved in evenly distributed, though erratic, rainfall conditions at semi-arid sites, and the Pilbara, West Kimberleys and Camooweal provenances which evolved in seasonally dry sites with a reliable monsoon. The former group had the greater leaf area and total plant biomass. Specific leaf area correlated positively with leaf area and total plant biomass at various times across the experimental period. However, as only minor differences in the average plant water use and carbon discrimination were detected among the populations, greater biomass production in semi-arid populations appears to stem from their capacity to produce a large total leaf area with thin leaves, which thus contributes to the total plant photosynthesis. The root: shoot ratio was consistently higher in seedlings from seasonally dry sites compared to those from semi-arid sites. A higher ratio in seasonally dry sites is likely to be beneficial as it allows an adequate water supply for longer during the dry period. A greater allocation to roots apparently reduces the amount of leaf area produced, decreasing growth potential.