Pedobiologia最新文献

Faunal-mediated nutrient cycling, especially N mineralization, has the potential to make a significant contribution to nutrient supply to crop plants in production systems involving e.g. green manure cover crops. We investigated the effects of enchytraeids on N mineralization from mung bean residues in microcosm experiments using an organically-farmed soil with an inherently large population of enchytraeids. Enchytraeids promoted N mineralization by 23% after a distinct lag of between four and 12 weeks, concomitant with a substantial increase in population size followed by an almost complete collapse. Nitrogen release from the necromass would have contributed a small but significant fraction of the N mineralized, and the result suggested the presence of other mechanisms. Enchytraeids suppressed nematode populations, while did not affect the mean weight diameter (MWD) of soil aggregates, although mung bean residues increased MWD. We conclude that enchytraeids have potential to play significant roles in mediating N supply to crops but matching supply-and-demand periods may be challenging.

Arbuscular mycorrhizal (AM) fungi contribute to soil structure, but little is known about the effect of individual fungal species on soil aggregation. In this study, the influence of 3 AM fungi species on soil aggregation in a Vitric Andosol was determined using physical, micromorphological, and imaging analyses. We used a pipe of polyvinyl chloride (PVC) with a six-way connector, which was filled with soil plus AM fungal inoculum (Funneliformis mosseae, Rhizophagus intraradices, Gigaspora gigantea or non-inoculated -control-). Then lateral pipe connectors (experimental units) were covered with mesh systems (0.5, 0.25, and 0.034 mm), and PVC tubes filled with sterile soil were connected laterally using a clamp. The greenhouse experiment consisted of four treatments each with 32 experimental units. Four experimental units of each treatment were separated and collected at different times during the year: three were used to determine water-stable aggregates (disturbed soils), and one was preserved (undisturbed soil) to elaborate soil thin sections. Thematic micro-maps were constructed with image mosaics from a whole soil thin section, and micromorphological analyses were conducted using spatial operators. Our results showed that AM fungi affect soil aggregation forming micro-aggregates and macro-aggregates of different sizes. The most significant effects were observed with F. mosseae > R. intraradices > Gi. gigantea > control. Aggregation hierarchy was observed in micromorphological analysis, where F. mosseae and R. intraradices start binding organo-mineral particles and microaggregates to form macroaggregates, modifying soil structure from intergrain (apedal= without peds) to crumb aggregates (pedal= with peds). Gigaspora gigantea only promoted macroaggregation, by associating with pumice particles. The two AM fungi from Glomeraceae possess similar morphology compared to that isolate belonging to Gigasporaceae, which explain in part, their differential contribution traits on soil aggregation, as highlighted by using together physical and micromorphological analyses of soil thin sections based on high-resolution image mosaics.

Microbial inoculants are recognized as environmentally friendly methods to promote plant growth and improve soil properties. However, the effects of inoculation on the rhizosphere and rhizoplane community structure of plants remain poorly documented and need further investigation. Rhodopseudomonas palustris (R. palustris) strain has nitrogen fixing ability and Bacillus subtilis (B. subtilis) strain is a plant growth-promoting rhizobacterium (PGPR). In this study, we investigated the effects of single and co-inoculation with R. palustris and B. subtilis on the increase of rice yield as well as on the microbial communities in the rhizosphere and rhizoplane of rice through potting experiments, respectively. The results showed that inoculation significantly increased rice yield and seed setting rate, with co-inoculation raising the yield by up to 13.7%. Inoculation influenced both rhizosphere and rhizoplane community structures and functions, amplifying the differences between them. The most significant changes were brought about by the combined inoculation treatment. Co-inoculation with R. palustris and B. subtilis had a synergistic effect. The profound alterations of rhizoplane bacterial community structures and functions were proved to be positively correlated with rice yield and seed setting rate (r = 0.59–0.76, p < 0.05). These results provide new ideas for the investigation of the potential microbiological mechanisms of microbial co-inoculation in practical agricultural applications.

The Atlantic Forest is the most threatened Brazilian biome, with less than 10% of its original surface cover remaining. Thus, several programs of payment for ecosystem services have been developed in this biome focusing on revegetation of degraded areas. Forest regeneration promotes the development of soil invertebrate communities that play an important role in soil processes, delivering a wide range of ecosystem services. We studied the changes in macrofauna communities in three forests under different regeneration stages and the relationship between these invertebrates and soil chemical and physical properties. Macrofauna and soil chemical and physical properties were sampled until 30 cm depth in three forest fragments of the Brazilian Atlantic Forest under different regeneration stages: young regenerating forest (∼8 years old), secondary forest in intermediate regeneration stage (∼20 years old) and native secondary forest fragment. No significant differences in saturated hydraulic conductivity (K_s) were observed among sites, however, the old native forest showed reduction in K_s in deeper layers compared to young regenerating forests. Several macrofauna taxa were positively correlated with K_s and soil carbon. The stage of regeneration modified the abundance and diversity of these invertebrates in general (except for earthworms), and the old native forest showed high abundance of most taxa. In conclusion, our study highlights the potential of macrofauna communities as robust indicators of soil functions re-establishment in regenerating forests within the Atlantic Forest biome. The observed positive correlations between macrofauna abundance and diversity with soil water infiltration and organic carbon content emphasize the key role of these invertebrates to essential ecosystem functions.

Scattered throughout the Namib Desert of Namibia are populations of Welwitschia mirabilis, a unique, low-lying, and slow-growing gymnosperm plant. We studied soils under Welwitschia plants and in adjacent interplant areas along a 400-km range to examine the potential of these plants as resource islands supporting nematode communities. We found significant differences in nematode density and community structure among the sites that were correlated to differences in climate, edaphic factors, and plant size and density. Soils from the Torra Conservancy site, which receives the most precipitation and had the highest density of Welwitschia plants, contained the highest organic matter and the most diverse nematode communities, with the broadest representation of nematode trophic groups. The largest and likely oldest Welwitschia plants occurred in the Messum Crater, the site with the least rainfall, which hosted the densest nematode communities (mean = 14,683 kg⁻¹ soil). These communities consisted almost entirely of the bacterial-feeding nematode Panagrolaimus sp. Two other sites, Welwitschia Plain, a well-known tourist destination, and Hope Mine, the southernmost known population, contained the fewest nematodes with moderate levels of diversity. Differences in nematode abundance between Welwitschia soils and interplant soils were not discernable at three of the four field sites, suggesting the resource island effect is not very strong. Interplant spaces also support diverse and abundant nematode communities, perhaps due to the growth of cryptobiotic crusts or ephemeral rainfall-induced vegetation.