Contributions by fungi and bacteria to aggregate stability of cultivated soils

Abstract

Stability changes during ageing (sterile) or incubation (non-sterile) of both natural field aggregates and remoulded aggregates from five soils were studied for periods up to 30 days. Growth of fungal hyphae, estimated by ergosterol measurement, corresponded to temporary stability increases in both types of aggregates during the first 15 days. Thereafter, fungal hyphae disappeared and were replaced by actinomycetes and bacteria. Increased stability due to entanglement by hyphae was comparable to that due to thixotropy in remoulded aggregates. Bacterial growth accompanied the fall in stability associated with fungal decline, but had little direct effect in stabilizing soil aggregates. Destruction of polysaccharides by periodate oxidation greatly diminished aggregate stability. The role of bacterial polysaccharides in soil aggregate stability is discussed.

Bioremediation of Crude Oil Contaminated Soil by Petroleum-Degrading Active Bacteria

“…After 12 days of bioremediation, the TPH concentration of the sample having the strain SY 43 declined to 213.3mg·kg -1 and the RE of TPH was 81.1%; while the TPH removal efficiency of the sample containing the strain SY 23 and in the blank sample were 60.3% and 25.6%, respectively. After 18 days of inoculation, the removal efficiency in the three samples climbed up to 88.4%, 73.4%, and 37%, respectively.…”

“…These observations indicate that the contaminated samples inoculated with petroleum-degrading active bacteria had higher oil removal efficiency than in the blank sample. The average degradation rates of TPH by SY 43 and SY 23 was 0.044 g·kg -1 ·d -1 , 0.034 g·kg -1 ·d -1 respectively; while the corresponding average degradation rate of the cells was 2.14×10 -6 mg· cell -1 ·d -1 and 1.64×10 -6 mg· cell -1 ·d -1 respectively. Figure 6 shows that the petroleum removal ability of SY 43 is higher than that of SY 23 .…”

“…The soil samples inoculated with SY 21 , SY 22 , SY 23, and SY 44 strains showed higher oil removal efficiencies. The removal efficiency of TPH reached up to 50% after 2 days of inoculation.…”

Rainfall effects on erosion of earthworm casts and phosphorus transfers by water runoff

“…For our study conditions, which included a gentle slope and weak runoff during the 2-month period, we suggest that during rainfall events, most of the cast material moved over a few centimetres and/or mixed with the soil surface matrix, but did not reach the water collectors. During dry periods, we observed the stabilization of many casts by fungi or only moss colonization, as was observed by Tisdall and Oades (1982) and Molope et al (1987). These stabilized casts were potential sources of phosphorus which may be reallocated with time.…”

Movimentação de partículas de calcário no perfil de um Cambissolo em plantio direto

“…A não-mobilização do solo e o aumento da matéria orgânica determinam, ao longo do tempo, um ambiente propício para a atividade de minhocas, larvas de insetos e de outros organismos e o aumento da atividade microbiana. Esses processos contribuem para a formação e estabilização dos agregados do solo, melhorando também a sua estrutura (Molope et al, 1987). Quando essas propriedades físicas são preservadas, as taxas de infiltração instantânea de água no sistema plantio direto e em pastagem nativa são maiores do que no preparo de solo com revolvimento convencional Petrere & Anghinoni, 2001).…”