E. K. Sadanandan Nambiar

PubMedDate not supplied

Elongation of Eucalyptus roots during day and night.

Root elongation was measured in mature Eucalyptus pauciflora Sieber ex Sprengel subsp. pauciflora trees in a high-elevation stand, and in seedlings of E. pauciflora and E. nitens (Deane & Maiden) grown in a glasshouse. Elongation of non-mycorrhizal roots (>10 mm long) was measured at 0600 and 1800 h on several consecutive days. Root elongation of seedlings of both species in the glasshouse was greater than that of mature E. pauciflora trees in the forest. For seedlings of comparable size, roots of E. nitens elongated faster than roots of E. pauciflora. Root elongation was always greater during the night than during the day in both species, in both the glasshouse and forest environment. Both water and osmotic potentials of root tips of E. pauciflora seedlings were lower during the night than during the day. The derived turgor pressure value of root tips was greater during the night than during the day and there was no difference in turgor pressure above the yield threshold.

Journal Article↗

PubMedDate not supplied

Nutrient retranslocation in temperate conifers.

Controversy exists about the relationship between retranslocation from leaves and uptake from soil in the mineral nutrition of trees. Evidence is presented to show that uncertainty has arisen partly because the significance of retranslocation from young leaves has been overlooked. Retranslocated nutrients are important for the production of new tissues at all stages of development from the seedling to the mature tree. Retranslocation is not, as has been thought, primarily associated with senescence and late stages in stand development. The key variables that determine the amount and rate of retranslocation in trees are the rates of nutrient uptake and growth. The amount and rate of retranslocation increase as tree growth rate increases, indicating that soil and environmental factors that promote growth also promote nutrient retranslocation. Retranslocation efficiency is increased by high soil fertility and rapid nutrient uptake and growth. Knowledge of the relationships between nutrient uptake and nutrient retranslocation should facilitate the development of simple models of whole-tree growth. Because nutrient retranslocation is driven by shoot growth rather than by nutrient supply in the soil, there is continual competition among shoots for internal nutrient reserves. This has implications for models describing shoot growth and crown development. Research on gas exchange processes in the crown should pay greater attention to the highly dynamic nature of nutrients in foliage.

Journal Article↗