Field-growing silver birch (Betula pendula Roth) clones (clone 4 and 80) were exposed to elevated CO 2 and O 3 in open-top chambers for three consecutive growing seasons (1999)(2000)(2001). At the beginning of the OTC experiment, all trees were 7 years old. We studied the single and interaction effects of CO 2 and O 3 on silver birch below-ground carbon pools (i.e. effects on fine roots and mycorrhizas, soil microbial communities and sporocarp production) and also assessed whether there are any clonal differences in these belowground CO 2 and O 3 responses. The total mycorrhizal infection level of both clones was stimulated by elevated CO 2 alone and elevated O 3 alone, but not when elevated CO 2 was used in fumigation in combination with elevated O 3 . In both clones, elevated CO 2 affected negatively light brown/orange mycorrhizas, while its effect on other mycorrhizal morphotypes was negligible. Elevated O 3 , instead, clearly decreased the proportions of black and liver-brown mycorrhizas and increased that of light brown/ orange mycorrhizas. Elevated O 3 had a tendency to decrease standing fine root mass and sporocarp production as well, both of these O 3 effects mainly manifesting in clone 4 trees. CO 2 and O 3 treatment effects on soil microbial community composition (PLFA, 2-and 3-OH-FA profiles) were negligible, but quantitative PLFA data showed that in 2001 the PLFA fungi : bacteria-ratio of clone 80 trees was marginally increased because of elevated CO 2 treatments. This study shows that O 3 effects were most clearly visible at the mycorrhizal root level and that some clonal differences in CO 2 and O 3 responses were observable in the below-ground carbon pools. In conclusion, the present data suggests that CO 2 effects were minor, whereas increasing tropospheric O 3 levels can be an important stress factor in northern birch forests, as they might alter mycorrhizal morphotype assemblages, mycorrhizal infection rates and sporocarp production.
Aims: The microbiota at industrial full‐scale composting plants has earlier been fragmentarily studied with molecular methods. Here, fungal communities from different stages of a full‐scale and a pilot‐scale composting reactors were studied before and after wood ash amendment.
Methods and Result: The portion of fungal biomass, determined using phospholipid fatty acid analysis, varied between 6·3% and 38·5% in different composting phases. The fungal internal transcribed spacer (ITS) area was cloned and sequenced from 19 samples representing different stages of the composting processes. Altogether 2986 sequenced clones were grouped into 166 phylotypes from which 35% had a close match in the sequence databases. The fungal communities of the samples were related with the measured environmental variables in order to identify phylotypes typical of certain composting conditions. The fungal phylotypes could be grouped into those that dominated the mesophilic low pH initial phases (sequences similar to genera Candida, Pichia and Dipodascaceae) and those found mostly or exclusively in the thermophilic phase (sequences clustering to Thermomyces, Candida and Rhizomucor), but a few were also present throughout the whole process.
Conclusions: The community composition was found to vary between suboptimally and optimally operating processes. In addition, there were differences in fungal communities between processes of industrial and pilot scale.
Significance and Impact of the Study: The results of this study reveal the fungal diversity with molecular methods in industrial composting process. This is also one of the first studies conducted with samples from an industrial biowaste composting process.
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