Afforestation alters community structure of soil fungi.

Relatively little is known about the effect of afforestation on soil fungal communities. This study demonstrated that afforestation altered fungal community structure and that changes were correlated to pools of soil C. Pasture at three locations on the same soil type was afforested with Eucalyptus globulus or Pinus pinaster. The structure of fungal communities under the three land uses was measured after 13y using automated ribosomal intergenic spacer analysis (ARISA). Afforestation significantly altered the structure of fungal communities. The effect of location on the structure of fungal communities was limited to pasture soils; although these contained the same plant species, the relative composition of each species varied between locations. Differences in the structure of fungal communities between pasture, E. globulus and P. pinaster were significantly correlated with changes in the amount of total organic C and microbial biomass-C in soil. Afforestation of patches of agricultural land may contribute to conserving soil fungi in agricultural landscapes by supporting fungal communities with different composition to agricultural soils.

Low pore connectivity increases bacterial diversity in soil.

One of soil microbiology's most intriguing puzzles is how so many different bacterial species can coexist in small volumes of soil when competition theory predicts that less competitive species should decline and eventually disappear. We provide evidence supporting the theory that low pore connectivity caused by low water potential (and therefore low water content) increases the diversity of a complex bacterial community in soil. We altered the pore connectivity of a soil by decreasing water potential and increasing the content of silt- and clay-sized particles. Two textures were created, without altering the chemical properties or mineral composition of the soil, by adding silt- and clay-sized particles of quartz to a quartz-based sandy soil at rates of 0% (sand) or 10% (silt+clay). Both textures were incubated at several water potentials, and the effect on the active bacterial communities was measured using terminal restriction fragment length polymorphism (TRFLP) of bacterial 16S rRNA. Bacterial richness and diversity increased as water potential decreased and soil became drier (P < 0.012), but they were not affected by texture (P > 0.553). Bacterial diversity increased at water potentials of

Minerals in soil select distinct bacterial communities in their microhabitats.

We tested the hypothesis that different minerals in soil select distinct bacterial communities in their microhabitats. Mica (M), basalt (B) and rock phosphate (RP) were incubated separately in soil planted with Trifolium subterraneum, Lolium rigidum or left unplanted. After 70 days, the mineral and soil fractions were separated by sieving. Automated ribosomal intergenic spacer analysis was used to determine whether the bacterial community structure was affected by the mineral, fraction and plant treatments. Principal coordinate plots showed clustering of bacterial communities from different fraction and mineral treatments, but not from different plant treatments. Permutational multivariate anova (permanova) showed that the microhabitats of M, B and RP selected bacterial communities different from each other in unplanted and L. rigidum, and in T. subterraneum, bacterial communities from M and B differed (P<0.046). permanova also showed that each mineral fraction selected bacterial communities different from the surrounding soil fraction (P<0.05). This study shows that the structure of bacterial communities in soil is influenced by the mineral substrates in their microhabitat and that minerals in soil play a greater role in bacterial ecology than simply providing an inert matrix for bacterial growth. This study suggests that mineral heterogeneity in soil contributes to the spatial variation in bacterial communities.

Altering the mineral composition of soil causes a shift in microbial community structure.

This study tests the hypothesis that altering the mineral composition of soil influences microbial community structure in a nutrient-deficient soil. Microcosms were established by adding mica (M), basalt (B) and rock phosphate (P) to soil separately, and in combination (MBP), and by planting with Lolium rigidum, Trifolium subterraneum or by leaving unplanted. The effects of mineral and plant treatments on microbial community structure were assessed using automated ribosomal intergenic spacer analysis. Bacterial community structure was significantly affected by both mineral (global R=0.73 and P<0.001) and plant (global R=0.71 and P<0.001) treatments, as was the fungal community structure: mineral (global R=0.65 and P<0.001) and plant (global R=0.65 and P<0.001) treatments. All pairwise comparisons of bacterial and fungal communities between different mineral treatments and between different plant treatments were significantly different (P<0.05). This study has shown that mineral addition to soil microcosms resulted in substantial changes in both bacterial and fungal community structure, dependent on the type of mineral added and the plant species present. These results suggest that the mineral composition of soil may be an important factor influencing the microbial community structure in soil.