Mycorrhizal ecology in a Sierran mixed-conifer forest: Effects on seedling establishment (California).

摘要

Ectomycorrhizal fungi (EMF) may colonize new seedlings either by vegetative growth of hyphae from established mycelia in the soil or by spore. Seedlings that are colonized by hyphal spread from an established mycelium become immediately linked to a network of hyphae in the soil and potentially linked to other host plants. By enabling translocation of water, nutrients, or carbon, these hyphal networks may increase the supply of critical resources to seedlings. For tree seedlings regenerating in the resource-limited environment of a forest understory, connections to mycorrhizal networks may confer benefits that translate into increased growth and survival for the seedlings.; Seedlings that were allowed to form hyphal connections consistently had a better chance of surviving and grew larger than seedlings that were prevented from forming hyphal connections. This increase in performance was of a magnitude that is ecologically significant for seedlings regenerating in forest gaps.; We then assessed the effects of the different colonization regimes on EMF communities found on Ps. menziesii roots in our study. There is evidence that EMF species that dominate the spore bank differ from those that largely spread through mycelial expansion. We quantified the EMF community on Ps. menziesii seedlings and compared the EMF taxa found on seedlings that were open to hyphal colonization to those found on seedlings that were colonized by spore. We found extremely high overall mycorrhizal species richness (137 species) and the majority of these species were rare, each accounting for less than 2% of the overall abundance.; We found that there was no decline in EMF species richness after the first year on seedlings when hyphal connections were prevented. Yet, after two years, species richness dramatically declined on seedlings where hyphal access was prevented.; In the final part of the research, we link EMF colonization dynamics with host plant autecology with regards to forest management. We examine mycorrhizal colonization on two conifer species planted across a gradient from forest to cut within group selection cuts. The ability of seedlings to be colonized by hyphal spread decreases with increasing distance away from the intact forest into the cut. I looked at mycorrhizal colonization dynamics and seedling performance in both an early-successional conifer, Pinus ponderosa, and a mid-successional conifer, Pseudotsuga menziesii. This research showed that the symbionts of different plant species respond to disturbance in highly individualized ways that reflect the life history strategies of their host plants. While the symbionts of the mid-successional conifer were not able to colonize seedlings farther than several meters away from the intact forest, colonization by symbionts of the early-successional P. ponderosa were as likely to colonize seedlings toward the center of the clearcut as those on the edge of the intact forest. The fact that the fungal symbionts of P. ponderosa are capable of long-distance dispersal may give this species a significant dispersal advantage following large disturbance events. (Abstract shortened by UMI.)