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Mycorrhizal Inoculum Potential as an Indicator of Ecosystem Disturbance in the Mountain Tropics of Southern Mexico

talk/poster
Mycorrhizae in Stressed Ecosystems
Asbjornsen, H1, A. Cayetano2, M. Valdés2, S. Palacios-Mayorga3 & K. Vogt1
1Yale University, School of Forestry and Environmental Studies. New Haven, CT 06511
2National School of Biological Sciences, Polytecnic Institute. 11340 México DF
3Institute of Geology, National Autonomous University, México D. F
ICOM1 Abstract
Among the legacies observed within disturbed oak forest ecosystems in the mountains of the state of Oaxaca, Mexico are the clearings (patches). These clearings were used for cultivating various subsistence crops, and many were abandoned within the last 20-30 years. The dominant trees (oak and pine) are strongly ectomycorrhizal (EM). We hypothesize that the mycorrhizal status of the soils may serve as an indicator for the degree of disturbance. We evaluated the mycorrhizal potential (MIP) of the soil for two ecosystems with different degrees of disturbance. Within each ecosystem, MIP was determined for three microsites (forest, edge and open). The method used was the Most Probable Number technique, and the trap plants were Alnus acuminata and Pinus oaxacana. The greatest degree of variation in the ecto-MIP was observed in the most disturbed ecosystem (200-2500 propagules/g soil). For the least disturbed ecosystem the lowest ecto-MIP was observed in open microsites (1000 propagules/g soil) We also observed strong differences in the percentage of EM feeder roots of pine seedlings between the different microsites within each ecosystem. The greatest degree of variation in the number of propagules was observed in the most disturbed ecosystem. MIP of arbuscular propagules was the same in all microsites including the forest sites, but percent of colonization was higher in the forest of the most disturbed ecosystem (73%) compared to the other microsites (30-60%). Only arbuscules were found in the roots from the the forest sites, and vesicules in addition of arbuscules were observed in roots from the clearings.