Modulation by frankia increases growth of casuarinaceae in a New Zealand horticultural soil

Abstract

Casuarina cunninghamiana and C. glauca are widely used for shelterbelts in New Zealand and have other utilitarian potential. Their nitrogen (N)-fixing Frankia symbiont does not occur naturally in New Zealand soils. Plants nodulated after artificial inoculation with Frankia culture HFPCcl3 were planted on a horticultural-quality Manawatu silt loam soil near Palmerston North. After 6-8 years, trees nodulated at planting were significantly larger in stem diameter and height (equivalent to 16-61% additional volume) over trees not nodulated at planting. Nodulated trees were also rated higher for vigour. Excavation of root systems revealed that nodules were confined to the residual zone of potting media around the original seedling root systems and there was no evidence of Frankia spreading through the soil to infect nearby roots. More widespread availability of Frankia inoculum in the soil being explored by feeder roots might have increased nodulation and subsequent tree growth, but New Zealand soil temperatures are suboptimal for Casuarinaceae nodulation and N fixation. © 1994 The Royal Society of New Zealand.