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Ectomycorrhizal (ECM) fungi contribute significantly to ecosystem respiration, but little research has addressed the effect of temperature on ECM fungal respiration. Some plants have the ability to acclimate to temperature such that long-term exposure to warmer conditions slows respiration at a given measurement temperature and long-term exposure to cooler conditions increases respiration at a given measurement temperature. We examined acclimation to temperature and temperature sensitivity (Q 10 ) of respiration by ECM fungi by incubating them for a week at one of three temperatures and measuring respiration over a range of temperatures. Among the 12 ECM fungal isolates that were tested, Suillus intermedius, Cenococcum geophilum, and Lactarius cf. pubescens exhibited significant acclimation to temperature, exhibiting an average reduction in respiration of 20-45% when incubated at 23 1C compared with when incubated at 11 or 17 1C. The isolates differed significantly in their Q 10 values, which ranged from 1.67 to 2.56. We also found that half of the isolates significantly increased Q 10 with an increase in incubator temperature by an average of 15%. We conclude that substantial variation exists among ECM fungal isolates in their ability to acclimate to temperature and in their sensitivity to temperature. As soil temperatures increase, ECM fungi that acclimate may require less carbon from their host plants than fungi that do not acclimate. The ability of some ECM fungi to acclimate may partially ameliorate the anticipated positive feedback between soil respiration and temperature.

Robertson, S. J., Rutherford, P. M., López-Gutiérrez, J. C. and Massicotte, H. B. 2012. Biochar enhances seedling growth and alters root symbioses and properties of sub-boreal forest soils. Can. J. Soil Sci. 92: 329–340. Biochar application may enhance soil properties, improve plant productivity, and increase long-term carbon storage, but impacts of biochar on plant-microbe symbioses mediating plant nutrient uptake in temperate or boreal soils are not well known. We planted lodgepole pine (Pinus contorta var. latifolia) or sitka alder (Alnus viridis ssp. sinuata) seeds in pots containing field-collected forest soils (from central British Columbia) amended with 0, 5, or 10% (dry mass basis) biochar with and without urea fertilizer (150 mg N kg−1). Pine seedlings were harvested at 4 mo and roots were assessed for abundance and diversity of ectomycorrhizal (ECM) morphotypes using light microscopy and DNA sequencing. Biochar raised soil pH, exchangeable cations and cation exchange capacity in some treatments in both soils. Pine had greater biomass in biochar+fertilizer treatments compared to control and fertilizer-only treatments; this corresponded in part to an increase in abundance of some ECMs. Alder seedlings were harvested at 2, 3 and 4 mo to measure N fixation in root nodules using acetylene reductase assay (ARA). Alder seedlings had greater shoot biomass when grown in biochar-amended soils compared with unamended control. Although mean ARA rates (at 4 mo) were greater in biochar-amended soils compared with controls, the data showed great variation and differences were not statistically significant (P>0.05). This study showed that biochar addition can enhance soil properties and the early growth of pine and alder in some sub-boreal forest soils; small changes in ECM abundances may be expected.

Although the level of diversity of root-associated fungi can be quite high, the effect of plant distribution and soil environment on root-associated fungal communities at fine spatial scales has received little attention. Here, we examine how soil environment and plant distribution affect the occurrence, diversity, and community structure of root-associated fungi at local patch scales within a mature forest. We used terminal restriction fragment length polymorphism and sequence analysis to detect 63 fungal species representing 28 different genera colonizing tree root tips. At least 32 species matched previously identified mycorrhizal fungi, with the remaining fungi including both saprotrophic and parasitic species. Root fungal communities were significantly different between June and September, suggesting a rapid temporal change in root fungal communities. Plant distribution affected root fungal communities, with some root fungi positively correlated with tree diameter and herbaceous-plant coverage. Some aspects of the soil environment were correlated with root fungal community structure, with the abundance of some root fungi positively correlated with soil pH and moisture content in June and with soil phosphorous (P) in September. Fungal distribution and community structure may be governed by plant-soil interactions at fine spatial scales within a mature forest. Soil P may play a role in structuring root fungal communities at certain times of the year.In temperate forests, most trees form relationships with ectomycorrhizal (ECM) fungi, and the diversity of this fungal group alone can approach 100 species within a forest stand (17,20,60). The ECM mutualism may be necessary for the success of some native plant species, as approximately 90% of roots of some tree species are colonized by ECM fungi (65). Nevertheless, we still know surprisingly little about what controls the community structure and distribution of root-associated fungi in forest systems (44,46). The occurrence of root-associated fungi may broadly reflect soil environmental conditions and the presence of preferred plant hosts (28, 61), but how these factors interact to influence the diversity, distribution, and community structure of these fungi within forest habitat patches at a local scale is uncertain.The distribution of root-associated fungi may be primarily a species response to local soil environmental conditions. For example, both the quality (i.e., nutrient content) and the quantity of soil organic matter are known to influence the diversity of ECM communities (18,20,32). ECM fungi also vary in drought tolerance (14, 36), resistance to fire (61, 65), and tolerance to soil acidity (19) and temperature (56). Changes in soil chemistry, especially as they relate to pH and the availability of nitrogen (N) and phosphorous (P), might favor selection of fungi most capable of tolerating environmental extremes (2,28,29).Plant distribution and identity may, however, play the strongest role in structuring the below-ground diversity of rootassociated fung...