ABSTRACT
When Pseudotsuga menziesii (Douglas fir) is planted into upland parts of the South Island of New Zealand, the trees can become chlorotic and stunted. The cause of this problem has been attributed to nutritional problems, lime-induced chlorosis linked to iron and magnesium deficiency, manganese induced iron deficiency, herbicide damage, or a lack of effective ectomycorrhizal fungi.
When large numbers of containerised Douglas fir destined for runout pastures became chlorotic in a large newly-built greenhouse, a research programme was instigated in order to define the problem and then rectify it. A large survey of green and chlorotic trees in the field and in the greenhouse found a lack of mycorrhizas on chlorotic trees, whereas green healthy trees in the field were consistently mycorrhizal. Experiments determined that suspensions of Rhizopogon parksii spores could be used to establish mycorrhizas on Douglas fir but the rate of nutrients normally applied in the greenhouse supressed mycorrhizal formation. A commercial method of establishing R. parksii mycorrhizas on Douglas fir was devised and almost 100 million mycorrhizal Douglas firs trees were produced over the following decade.
The methods devised in the resolution of this problem with Douglas fir could benefit others who have assumed that chlorosis in the production of plantation forestry trees is a simple nutritional one that can be fixed by applying nutrients, in particular nitrogen and phosphorus.
