Belowground microbial processes underpin forest productivity

Nitrogen-fixing bacteria associated with mycorrhizal fungi and mycorrhizas can be demonstrated with microaerophilic procedures. The chemical substrate s in mycorrhizal fungi or mycorrhizas often stimulate the growth and nitrog enase activity of the associated N-2 fixers. In addition, the associated N- 2 fixers are producers of plant-growth-promoting substances and B-group vit amins. Combined inoculation of mycorrhizal fungi with N-2 fixers enhances m ycorrhiza formation. Other microbes in the mycorrhizosphere have capacities to breakdown primary minerals, thereby releasing nutrients available for u ptake by plants. Thus, land restoration can be achieved by planting trees w ith nitrogen-fixing and rock weathering capacities, such as alders and some pines. The treatment can enhance nutrient availability and increase soil o rganic matter that provides organic substrate for nutrient release, maintai n soil structure and enhance water-holding capacity. Also changes in tree s pecies compositions on the site are likely to alter belowground processes t hrough changes in functional processes of organisms that constitute ecosyst ems.