Here we describe a quantitative PCR-based approach to estimating the relative abundances of major taxonomic groups of bacteria and fungi in soil. Primers were thoroughly tested for specificity, and the method was applied to three distinct soils. The technique provides a rapid and robust index of microbial community structure.

Fungi are an important and diverse component of soil communities, but these communities have proven difficult to study in conventional biotic surveys. We evaluated soil fungal diversity at two sites in a temperate forest using direct isolation of small-subunit and internal transcribed spacer (ITS) rRNA genes by PCR and high-throughput sequencing of cloned fragments. We identified 412 sequence types from 863 fungal ITS sequences, as well as 112 ITS sequences from other eukaryotic microorganisms. Equal proportions of Basidiomycota and Ascomycota sequences were present in both the ITS and small-subunit libraries, while members of other fungal phyla were recovered at much lower frequencies. Many sequences closely matched sequences from mycorrhizal, plant-pathogenic, and saprophytic fungi. Compositional differences were observed among samples from different soil depths, with mycorrhizal species predominating deeper in the soil profile and saprophytic species predominating in the litter layer. Richness was consistently lowest in the deepest soil horizon samples. Comparable levels of fungal richness have been observed following traditional specimenbased collecting and culturing surveys, but only after much more extensive sampling. The high rate at which new sequence types were recovered even after sampling 863 fungal ITS sequences and the dominance of fungi in our libraries relative to other eukaryotes suggest that the abundance and diversity of fungi in forest soils may be much higher than previously hypothesized.

Longleaf pine (Pinus palustris Mill.) restoration in the southeastern United States offers opportunities for carbon (C) sequestration. Ecosystem C stocks are not well understood in longleaf pine forests, which are typically of low density and maintained by prescribed fire. The objectives of this research were to develop allometric equations for above-and below-ground biomass and quantify ecosystem C stocks in five longleaf pine forests ranging in age from 5 to 87 years and in basal area from 0.4 to 22.6 m 2 ·ha −1 . Live aboveground C (woody plant + ground cover) and live root C (longleaf pine below stump + plot level coarse roots + plot level fine roots) ranged from 1.4 and 2.9 Mg C·ha −1 , respectively, in the 5-year-old stand to 78.4 and 19.2 Mg C·ha −1 , respectively, in the 87-year-old stand. Total ecosystem C (live plant + dead organic matter + mineral soil) values were 71.6, 110.1, 124.6, 141.4, and 185.4 Mg C·ha −1 in the 5-, 12-, 21-, 64-, and 87-year-old stands, respectively, and dominated by tree C and soil C. In the 5-year-old stand, ground cover C and residual taproot C were significant C stocks. This unique, in-depth assessment of aboveand below-ground C across a series of longleaf pine stands will improve estimates of C in longleaf pine ecosystems and contribute to development of general biomass models that account for variation in climate, site, and management history in an important but understudied ecosystem.Résumé : La restauration du pin des marais (Pinus palustris Mill.) dans le sud-est des États-Unis offre une opportunité de stocker du carbone (C). Les stocks de C de l'écosystème ne sont pas bien connus dans les forêts de pin des marais qui ont typiquement une faible densité et se maintiennent grâce au brûlage dirigée. Les objectifs de ces travaux de recherche consistaient à élaborer des équations allométriques pour la biomasse aérienne et souterraine et à quantifier les stocks de C de l'écosystème dans cinq forêts de pin des marais dont l'âge allait de 5 à 87 ans et dont la surface terrière variait de 0,4 à 22,6 m 2 ·ha -1 . Le C aérien vert (plantes ligneuses + couverture végétale) et le C des racines vivantes (souches de pin des marais + grosses racines et racines fines présentes dans les placettes) variaient respectivement de 1,4 et 2,9 Mg C·ha -1 dans le peuplement âgé de 5 ans à 78,4 et 19,2 Mg C·ha -1 dans le peuplement âgé de 87 ans. Le C total de l'écosystème (plantes vivantes + matière organique morte + sol minéral) atteignait respectivement 71,6, 110,1, 124,6, 141,4 et 185,4 Mg C·ha -1 dans les peuplements âgés de 5, 12, 21, 64 et 87 ans et était dominé par le C des arbres et du sol. Dans le peuplement âgé de 5 ans, le C contenu dans la couverture végétale et les racines pivotantes résiduelles constituait un stock important de C. Cette évaluation unique et approfondie du C aérien et souterrain dans une série de peuplements de pin des marais améliorera les estimations du C dans les écosystèmes dominés par cette essence et contribuera au développement de modèles généraux de biomass...

No abstract