Impacts of Heat on the Spore Bank Community Structure in Mixed Conifer Forest Soil Using Pinus jeffreyi Seedlings as a Host Species Megan Canright Abstract The effect of temperature on the presence and community composition of ectomycorrhizal fungi associated with Pinus jeffreyi seedlings was investigated in this study We followed the colonization of ectomycorrhizal fungi in 8 month old Pinus jeffreyi seedlings whose soil had been subjected to one of four treatments no heat 40 C heating 55 C heating and 70 C heating Ectomycorrhizas were harvested by hand under dissecting microscope from 8 month old seedlings and subjected to PCR RFLP analysis of the ITS region of the ribosomal DNA for identification to the species or genus level Significant difference in species richness was analyzed using Wilcoxon s rank sum test Species diversity was measured using the ShannonWeaver index and tested for significant difference among treatments using t tests Species richness was significantly higher in heated treatments as compared to non heated treatments however no significant difference in species richness was found between seedlings heated at different temperatures Species diversity was also significantly different between heated and nonheated treatments but was not different across heated treatments Preliminary results indicate that species composition experiences a shift across treatments Results may show that dominant species include Rhizopogon subcaerulescens in non heat treated seedlings Russula amoenolens in 40 C seedlings Suillus brevipes in 55 C seedlings and Cenoccocum geophilium and Tomentella sublilicina in 70 C treatments Thelephoraceae sp may be seen equally across all treatments If preliminary results reflect actual results species seen in heat treatments may be either the most heat resistant ectomycorrhizae or are stimulated by heat and may play a role in the re establishment of forest ecosystems directly following fire as other less heat resistant mycorrhizae rebuild their communities In short the overall effect of increased temperature seems to be increased species richness and diversity accompanied by a shift in species composition from basidiomycetes to ascomycetes Introduction Historically fire has been a common disturbance in California pine stands especially before the onset of modern fire prevention techniques Biswell 1989 Studies of historical and pre historical forest fire regimes have shown that moderate intensity fires typically afflicted pine stands every 3 to 11 years Brown et al 2001 Prescribed fire has been utilized in pine stands as a management technique for over 50 years in an attempt to encourage the success of the pine Biswell 1989 Fire reduces tree density and prevents succession by more shade tolerant species such as white fir and protects against disease pest infestation and stand replacing wildfire Choromanska et al 2001 Fule et al 1997 Moderate intensity prescribed burning has proven to be a useful management tool in Pinus jeffreyi Jeffrey pine stands for the prevention of bark beetle infestation In addition Pinus jeffreyi responds well to prescribed fire in terms of overall stand health stand health and density of P jeffreyi have been shown to increase with prescribed fire treatments Roy Vankat 1999 Mycorrhizae commonly associate symbiotically with various Pineaceae species including Pinus jeffreyi Walker and Kane 1997 found that after 6 months mycorrhizal Jeffrey pine seedlings had greater root dry weight increased shoot dimensions and overall weight Mycorrhizal hyphae penetrate soils branching into fine thread like extensions called hyphae which are much finer than root hairs The hyphae are very absorptive and are more efficient than plant roots in taking up nutrients Mycorrhizae associate with pine roots helping the tree to take up minerals namely nitrogen and nutrients in exchange for sugars produced by the pine during photosynthesis The increased nitrogen nutrition due to mycorrhizae allows mycorrhizal plants to grow much more quickly than non mycorrhizal plants Varma and Hock 1999 The role of mycorrhizal fungi in the re establishment of pine forests following fire disturbance is unknown Some research has been conducted looking at the affect of fire on mycorrhizal numbers and biomass Stendell et al 1999 found that one year following prescribed fire ectomycorrhizal biomass was not significantly reduced in comparison to pre burn quantities indicating that mycorrhizae are not adversely affected by fire Vazquez et al 1993 found that hyphal length post fire exceeded pre burn values However little research has attempted to tackle the question of how mycorrhizal species composition is altered in response to fire The goal of this study is to take the first step towards this understanding by addressing the relationship between mycorrhizal community structure and soil temperature A mixed conifer ecosystem with a historically naturally occurring fire regime was chosen to conduct this experiment because it can be assumed that organisms in this type of environment will respond to temperature disturbance due to the natural fire regime Three main questions will be addressed by this study in the forest system What does the spore bank look like for the soil taken from the site Does temperature have a significant effect on the species composition of mycorrhizae in this soil If so which species are more resistant to heat disturbance or which species may be stimulated by heat The study was conducted using Jeffrey pine seedlings set up in bioassays as a host which mycorrhizae were expected to infect Jeffrey pine was used because pine species are the dominant post fire regeneration species and thus would be colonized more readily by mycorrhizae following temperature disturbance Thus Jeffrey pine gives a more accurate picture of the post heat spore bank community as these species are more likely to colonize the dominant post fire tree species The seeds were planted in treated soil taken from the site Analysis of these bioassays without heat treatment is expected to give a picture of the soil spore bank in Teakettle the Sierran mixed conifer forest where the soil was collected This information can be used to determine which species are out competed in fire disturbed settings If species changes do occur with temperature treatments dominant species found can be looked at and studied in order to reach further understanding of their roles in the re establishment of
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