SOIL FAUNA AND SOIL STRUCTURE

被引:335
作者
LEE, KE
FOSTER, RC
机构
[1] Division of Soils, CSiRO, Glen Osmond, SA, 5064
来源
AUSTRALIAN JOURNAL OF SOIL RESEARCH | 1991年 / 29卷 / 06期
关键词
D O I
10.1071/SR9910745
中图分类号
S15 [土壤学];
学科分类号
0903 ; 090301 ;
摘要
Significant effects of soil fauna on soil structure are achieved mainly by a few groups among the larger soil invertebrates that are widely distributed and generally present in large numbers. Of these groups the most important are earthworms, termites and ants. The review deals mainly with earthworms, which are distributed throughout all but the coldest and the driest regions of the world. The effects of termites and ants on soil structure are also discussed. These groups of soil animals are also widely distributed, but are most common and most effective in influencing soil structure in tropical and warm temperate regions. A brief section deals with the influence of microarthropods, which are commonly found in large numbers, but because of their small size are unable to make large burrows in the mineral soil horizons, and are largely confined to pre-existing voids in litter and surface soil horizons. Their faecal pellets are granular and largely organic, with little included mineral soil material, and they sometimes make up the major proportion of forest litter layers. Quantitative assessment of the influence of earthworms on soil structure is available, but information on other groups is largely qualitative. The burrows of earthworms contribute to macroporosity and so influence water infiltration and aeration. Anecic species, that live in semi-permanent burrows opening to the soil surface and feed at the surface, provide more or less vertical channels for water infiltration and gas exchange. Endogeic species, that burrow continuously in search of food within the soil, provide more horizontally oriented, frequently extensive and intersecting networks of macropores that promote water movement and gas diffusion. Burrows that penetrate soil surface crusts are particularly important for water entry to the soil. Water movement through pores of the dimensions of earthworm burrows is important only when rainfall or irrigation supplies water at rates that exceed the capacity of the soil surface for capillary uptake. The combination of increase in surface area available for capillary uptake through the burrow walls and of hydraulic pressure resulting from the column of water in a water-filled burrow increases infiltration. Occupied burrows of anecic species may be sealed with soil or plant litter by the resident earthworm when water is ponded on the soil surface, or blocked by the earthworm's body, so as to be ineffective for water infiltration. When burrows are air-filled they provide surfaces that penetrate below ground and facilitate gas exchange. The casts of earthworms frequently make up the majority of structural aggregates in the upper 10-20 cm of soil profiles. Tests of aggregate stability show that casts are frequently more stable, sometimes less stable than other soil aggregates. Their stability may result from clay-organic matter complexes that act as adhesives. The presence of casts deposited on the surface enhances water infiltration, but this may sometimes be offset by the increased loss of fine material from casts in surface runoff. Termites and ants are social insects. Important effects on soil structure are generally concentrated in small areas around nests, and so do not affect soils on the scale of the effects of the non-social, dispersed populations of earthworms. Burrows of most species, apart from those in nests, are 'highways', generally used over considerable periods of time, that provide access to concentrated food sources. There are exceptional cases where large termite mounds that have associated extensive underground gallery systems transform the hydrology and pedological processes over large areas. Soil particles that are used for nest construction are stuck together with excreta or salivary secretions, frequently forming massive cemented layers that reduce water infiltration. Burrows opened to the surface for foraging or flight of alates by species of termites that live below ground are usually sealed when not in use, so probably have little effect on water infiltration or aeration. Ground-dwelling ants have burrows for access to their nests that are often permanently open to the surface. These may be effective in promoting water entry and aeration. Information on the effects of termites and ants on soil structure is mainly qualitative and there is a need for a more quantitative approach.
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页码:745 / 775
页数:31
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