Mycorrhizae and Microbial Communities in Organic Production
For several years, we have studied the soil microbial communities in organic production of tomatoes in California. This abstract from Cavagnaro et al. (2006) describes one of the field studies that set the background for our current research:
'Effects of arbuscular mycorrhzal fungi (AMF) on plant growth and nutrition are well known, however their effects on the wider soil biota are less clear. This is in part due to difficulties associated with establishing appropriate non-mycorrhizal controls in the field. Here we present results of a field experiment using a new approach to overcome this problem. A previously well-characterized mycorrhizal defective tomato mutant (rmc) and its mycorrhizal wildtype progenitor were grown at an organic fresh market tomato farm (Yolo County, CA). At the time of planting, root ingrowth cores amended with different levels of N and P, were installed between experimental plants to study localized effects of mycorrhizal and non-mycorrhizal tomato roots on soil ecology. Whilst fruit yield and vegetative production of the two genotypes were very similar at harvest, there were large positive effects of AMF on plant nutrient contents, especially P and Zn. The presence of roots colonized by AMF also resulted in improved aggregate stability by increasing the fraction of small macro aggregates, but only when N was added. Effects on the wider soil community including nematodes, fungal biomass as indicated by ergosterol, microbial biomass C, and phospholipid fatty acid (PLFA) profiles were less pronounced. Taken together, these data show that AMF provide important ecosystem services in terms of plant nutrition and aggregate stability, but that a change in this one functional group had only a small effect on the wider soil biota. This indicates a high degree of stability and resilience in soil communities of this organic farm.'
Cavagnaro, T.R., L.E. Jackson, K.M. Scow, and K.R. Hristova. 2007. Effects of
arbuscular mycorrhizas on ammonia oxidizing bacteria in an organic farm soil.
Microbial Ecology 54:618-626. Cavagnaro Jackson Skow Hristova 07
Cavagnaro, T., L.E. Jackson, J. Six, H. Ferris, S. Goyal, D. Asami, K.M. Scow. 2006.
Arbuscular mycorrhizas, microbial communities, nutrient availability, and soil
aggregates in organic tomato production. Plant and Soil 282:209-225. Cavagnaro et al 2006