The effects of soil structure on protozoa in a clay‐loam soil

Abstract

Physical disruption of a clay-loam soil by slaking, grinding and compaction was used to determinc the specific effects of soil structure on soil protozoa. Individual air-dry aggregates (1 -2 cm diameter) were wetted slowly, or had their structure disrupted by slaking or grinding. They were then moistened with nutrient solution and incubated, at a matric potential of -10 kPa. The nutrient solution had to supply at least 400 pg C g-' dry soil before protozoan populations increased measurably. Numbers of ciliate protozoa were enhanced by grinding, regardless of the amount of nutrient added. The moisture content and, therefore, the final nutrient concentration of the disrupted aggregates, changed markedly and could account for the observed increase in protozoan biomass from slowly wet to slaked to ground aggregates. There were no differences in protozoan biomass when the applied nutrient concentration was adjusted so that all treatments contained the same amount of nutrient. Soil cores were prepared from sieved (2-4 mm diameter), ground and ground/compacted soil. Thin sections revealed that the pore space accessible to protozoa decreased in these three treatments from 24% to 13% to 9%, respectively. Protozoan biomass was unaffected by grinding but showed a greater than 30-fold decrease following compaction that could not be accounted for solely by the reduced pore space. Grinding and compacting could have favoured anaerobic conditions in the core which would have reduced protozoan activity. Soil structure had no measurable direct effect on protozoan populations, but it had a much greater indirect effect through its influence on moisture content and aeration status.

Impact of Protists on the Activity and Structure of the Bacterial Community in a Rice Field Soil

“…1 and 2). Altogether, this indicates that protists have a stimulating effect on carbon and nitrogen mineralization in water-saturated soils, as found previously for upland soils (1,14,22,27,53).…”

Physical disturbance to ecological niches created by soil structure alters community composition of methanotrophs

“…Numerous endogenous and exogenous factors are known to affect soil aggregation and subsequently soil structure (Lal, 1991). For example, it was suggested that intense drying of the top soil, followed by sudden rewetting, could lead to soil aggregate disintegration, which could subsequently cause changes in the soil structure (Griffiths and Young, 1994). Soil fauna are reported to influence soil structure to varying degrees.…”

A study of population numbers and ecological interactions of soil and forest floor microfauna

“…The large increase in the late summer could be explained by concentrations of microfauna over spatially discrete and hetererogeneously organic substrates, or "hotspots" with microbial and microfaunal migration from the soil to the litter (Alphei, 1998 andYoung, 1994). The other invertebrate taxa recorded during the study are also known to graze on fungi and bacteria and the microfauna may, therefore, be indirectly contributing to the decomposition of the litter.…”

“…These correlations suggest that the invertebrates present were feeding in the rhizosphere, and might have been characterised by very limited movement elsewhere because of low moisture and an impervious soil structure. The ANOVA test for protozoa indicated some differences between the sites (see table 1), which may be due to aggregations in hotspots of decomposition in the soil where bacteria may have accumulated on invertebrate faecal pellets (Alphei, 1998 andYoung, 1994).…”