Almost a third of the Earth’s surface, more than four billion hectares, is covered by various kinds of forests. In future, intensive forestry and farming could produce the required amount of energy, food and raw material with far smaller acreage.
“In 2010, FAO estimated the value of agriculture and forestry to be about $3.2 trillion. This figure could be significantly increased with the help of knowledge about the hormonal regulation of the development and growth of trees to advance forest growth,” says Juha Immanen, who defended his doctoral dissertation at the Faculty of Biological and Environmental Sciences at the University of Helsinki.
“The areas of intensified production could be located near the consumers of forest products, which would mean that natural forests could be left alone and biodiversity would remain almost intact,” continues Immanen.
In his doctoral dissertation on tree growth, Immanen focuses on cambial cells close to the tree bark. The vascular cambium is a thin growth layer extending around the tree trunk that produces xylem cells on the inside and phloem cells on the outside of the trunk. Xylem is responsible for conducting water and providing structural support, while phloem transports nutrients from the leaves to the roots.
Cambial development, in other words the radial growth of trees and its rate, is regulated by hormones. Plant hormones, like animal hormones, function in a delicate balance.
“Cytokinins are important growth regulators in trees, but by far not the only ones. Cytokinins and auxins together clearly regulate cambial development and radial growth rate in trees,” states Immanen.
Cytokinin and auxin display slightly different distribution profiles across the cambium. The greatest concentration of cytokinins is in the developing phloem, while auxin is most concentrated in the developing xylem. Both hormones are of high amplitude in the cambium.
“By manipulating the cytokinin concentration in the cambial zone, we have been able to increase and decrease cambial cell division activity. The radial growth of the hybrid aspen (Populus tremula x tremuloides) used in the study increased dramatically under greenhouse conditions when we genetically increased the concentration of cytokinins in the cambium. At the same time, the trunk biomass grew,” Immanen concludes.
The trees that grew thicker due to the increased concentration of cytokinins were slightly shorter than non-manipulated trees. Their internodes were shorter, and they had more leaves and branches than normal trees. Their wood was denser, but microscopic images revealed that structurally it looked very similar to wood in normal trees.