Yuji Jiang Bo Sun Chen Jin Feng Wang. Soil aggregate stratification of nematodes and microbial communities affects the metabolic quotient in an acid soil . Soil Biology and Biochemistry 2013http://dx.doi.org-10.1016-j.soilbio.2013.01.006.

Abstract

The addition of fresh organic matter is known to modify both soil aggregation and soil biotic community composition. We hypothesized that fertilization alters the composition of soil nematode and microbial communities in soil aggregates and the interaction between nematodes and microbes can stimulate or inhibit microbial activity. We used a field experiment with 9 years of manure application to investigate changes in nematodes and microbial communities among aggregate size fractions in an acid soil planted with maize in subtropical China. Nematodes microbial communities and metabolic quotient (qCO₂) were examined within three aggregate size fractions from soils under four fertilization regimes. Three aggregate fractions include large macroaggregates (>2000 μm; LA) small macroaggregates (250–2000 μm; SA) and inter-aggregate soil and space (<250 μm; IA). Four manure treatments include no manure (M₀) low-rate manure with 150 kg N ha⁻¹ y⁻¹ (M₁) high-rate manure with 600 kg N ha⁻¹ y⁻¹ (M₂) and high-rate manure with 600 kg N ha⁻¹ y⁻¹ and lime at 3000 kg Ca(OH)₂ ha⁻¹ 3 y⁻¹ (M₃). Fertilization influenced the proportion of the aggregate size fractions. The proportion of the LA fraction significantly increased under M₂ and M₃ treatments compared to M₀ and M₁ treatments while the SA fraction significantly decreased. Aggregate fractions significantly affected the total number of nematodes and the abundance of bacterivorous nematodes (dominant genus Protorhabditis) and plant parasitic nematodes (dominant genus Pratylenchus) with values following the trend of LA > SA > IA. A high value for the nematode structure index (SI) in the LA fraction suggested a complex community structure with many linkages in the food web. Aggregate fractions also influenced microbial biomass and diversity. PLFA signature analysis revealed that microbial biomass and diversity (Shannon index) increased with decreasing aggregate size. However the SA fraction had a significantly higher soil metabolic quotient (qCO₂) than the IA fraction. Only fertilization had a significant effect on the compositions of nematode groups whil