Role of Arthropods in Soil Fertility
Arthropods which are divided into macro, meso and microbial, can’t be seen with naked eye but play a key role in soil fertility, soil structure and soil texture by their activity. Ants and termites enhance the soil abilities to ensure water holding capacity, water filtration, nutrient availability and their flow. Soil also provide a barrier against excessive leaching of nutrients, with the help of these arthropods. Nitrogen fixation, nutrient recycling and formation of pores are also performed by the arthropods.
Arthropods represents the 85% of soil fauna .Macro fauna improves the structure of soil. They compete with soil organisms and the biological equilibrium is maintained in soil. Meso-fauna are pathogens of plants in nature. Micro fauna are predators of algae and bacteria, so their population is regulated in soil.
Arthropods are ecosystem engineers, their burrows contain a wide range of tunnels and nests of termites and ants. These tunnels improve the soil aeration, root penetrating and porosity. Feces of the arthropods make the aggregate of soil which improves the nutrient holding capacity of the soil .They are also responsible for the soil formation and nutrient cycling.
Soil is composed by the weathering process of the Rocky Mountains. A good soil comprises of some living organisms, water, air, minerals and nutrients. Soil supports the soil because it’s the fundamental part of the earth .The interaction of parent material, topography, climatic conditions, micro-organisms and time form the soil properties.
Classification of soil biodiversity
Soil organisms are classified into 3 groups
Nematodes, mites and springtails are biological regulators through their predation of plants by regulating their space and dynamics
Termites, ants and earthworms are eco engineers. They modify and regulate the habitat and availability of resources for the microorganisms.
Bacteria, fungi and protozoans are the chemical engineers. They are responsible for the decomposition of the organic matter into nutrients, which are beneficial for the animals and plants.
This includes the species of Acarine taxa and collembola. Large number of micro arthropods are found in the under cultivated soil surface. These organisms are dominant in equatorial to Polar Regions. Also found from temperate to tropical forests, grasslands to the cold and hot desserts.
The members of acari feed on the dead plants. The members of prostigmata and mesostigmata feed on the mesofauna and micro fauna. In the forests and grassland soils, acari’s most dominant group is oribatids, which play a key role decomposition. With higher density in coniferous soils than deciduous, 105-106 individual’s m-2 population of oribatids have been recorded.
. While the population of oribatids in desert ecosystem is too much reduced and they have no significant role in turnover of organic matter. A reasonable moisture content hinders the distribution of the oribatids. Oribatids are considered successful soil arthropods because more than 9000 species of 172 families are lived in soil. Due to low nutritional diet the species show prolonged lifecycles, slow development and growth, low reproduction rate and influence in parts. Some of their families show parthenogenesis. Life time is reduced in cold environment while prolonged in temperate environment. Oribatids are divided into four groups on the basis of their different feeding habits; macrophytophages feed onfungi and bacteria, macrophytophages; feed on decaying material of plants and somehow on fungi . Panphytophages; feeding habit is expanded, on plant matter and fungi, corpophages; mainly feed on feces. Most of the oribatids are fungi ores.
They are hexapods and commonly classified as wingless insects. Bearing ventral tube and fercula. Now they are considered closely related to insect on tribe basis but still differ from insect. There are 6500 species,18 families have been discovered. As like oribatids, they are also abundantly found in the soil and their density is high in coniferous forests. Agricultural soils are enriched in collembolan. A few off springs are reproduced in the reproductive period in euedaphic species. Fecundity ranges from 50-100 eggs/female. 1-4 generations are expected when the climate is favorable. Lifespan ranges from 2-12 months. Mainly collembolan feed on other collembolan (living/died), algae, fungal hyphae, bacteria and stored products. Most of their species are fungivorous.
These area whitish colored, long body, sized up to 1cm. blind in nature. Abdomen is divided into ten segmented, ending with a paired cerci. Coxa, bladder and styli are present on the ventral side of 1-7 segments. Diplura contains both, predatory and detritivorous kinds.
Protura are also creamy white in color, blind length range from .5mm-1.5mm.Don’t have antennae & body is 12 segmented. 1-3 segments bear rudimentary legs. They are absent in heavy soils, rich diversity found in forest soil, grasslands and also plantation soils . Mostly found in the root zone of plants and feed on mycorrhizal fungi.
Symphyla do not contain eyes and antennae. These are small arthropods having whitish colored, cylinder like body and 12 segmented abdomen, which contains a pair of cerci at the end of abdomen. They are highly hygrotactic, live in 100% R.H, mostly found in forest and grassland soils. There are 208 species, 13 genera and 2 families have been discovered. They are widely spread through soil profile. Attack on vegetable matter on early stage of decomposition.
Millipedes and centipedes
Millipedes have great variations in their morphology. Their body length varies from a few mm – 20cm, pairs of legs varies from 9-200. They have thousands of legs for their wave like motion which represent their name, millipedes. There are12000 species and 2947 genera have been described. Naturally widely distributed, abundantly found in calcareous soils. In some species their life span is upto11 years prolonged, about 2000 eggs a single female lays. They feed on mycelium, hyphae and dead plants, known as decomposers as well as accelerators in nutritional availability and flow.
Centipedes are active in night time. They have a large number of legs but less than millipedes. They have predatory nature and have poisonous claws by which they control and paralyze their prey. They cannot dig up, so they tend to use earth cracks as shelter. They are moist loving, are abundantly found in the grasslands.
Termites are social insects, live in soil and wood by making their colonies. Have labor division, workers make the colonies. They feed on the wood mostly. There are 2600 species and 281 genera have been discovered up till now. They feed on cellulosic food, gathered by workers from leaf debris, grasses and fungi.
- Maintenance of soil fertility by Arthropods
Basically, soil fertility is a term that represents the ability or level of soil by which it can fulfill the nutritional requirements of plants for their growth. Ecosystem engineers and Litter transformers are two groups of arthropods, work for the soil fertility. Ecosystem engineers alter the habitats and make sure the availability of nutrients for other species, that’s why the hydrology of soil is altered. Ants and termites are most important members of this profession. Litter transformers is a wider group of arthropods which humidify the plant debris, enhance its ability for being decomposed, also for increasing the arthropods population.
Arthropods in Nutrient Cycling
Up to 90% production that enters the food web, decomposed and recycled there, is primarily terrestrial. Its huge part is produced in the leaves and woody material that falls in the soil. Roots lead all the above and below-ground inputs, by providing nitrogen 2.3 times more. Plant litter consists of sugar and starch, which is easily digestible to the soil organisms while it also have cellulose and tannins which make resistance against breakdown. Physical and biological processes in combined form make sure the decomposition of the material. For further division into small particles by the action of micro-flora and fauna, the litter should be properly weathered. The soil micro arthropods perform well in humid environment, so the litter decomposition is greatest in the tropics which are highly humid. Hence, the activity of arthropods regarding decomposition is negligible in tropical area.
Mineralization of nutrients
Nutrients must be available to soil in the form of inorganic that’s why these are easily taken by roots. Mineralization is the process based on catabolism process in which the conversion takes
place by decomposing organisms, by which the organic material is converted into inorganic form, breakdown of amino acids into NH4+ and NO3–. The action of soil arthropods on plant litter may be directly or indirectly effective or resistant in decomposition, but in real it makes the nutrients more concentrated in the soil. The nutrients are mostly concentrated and suspended in the micro-arthropods, which is secreted out in feces or mortality.
Collembolan species grazing initiates the growth and respiration of fungus. Hence proved that, by grazing of arthropods the mineralizing process of nutrients is speeded up. When collembolan grazes on fungi, then N and Ca are mineralized. Termites play an important role in mineralization of soil by during the process of colony building. Soil with nutrients. Their foraging behavior and turning back to the colony also play role in nutrient mobilization.
Ants have their own role, their colony site have higher amount of nutrients in it rather than the other soil. Secretions from body and decomposing process on it, strengthen the nutrient amount in the soil. On barren land there is lack of microbial activity and nutrients, ants make sure the nutrient availability in soil by animal tissues. When a colony dies, the colony site play an important role in plant colonization, with the passage of time, grazing land is converted into a wood land.
Effect of arthropods on soil structure
Arthropods contribute in soil structure an aggregate by different ways. A reasonable soil structure ensure the deep root penetration, low erosion, water holding capacity, nutrient availability and microbial activity.
Formation of pores and voids
Termites, collembola and the oribatid mites play an important role in forming pores in the soil, they form small galleries in the soil. Although they use the soil cracks for shelter. These small galleries and ants nests ensure the water infiltration, aeration and water storage. The bulk of old colony material infilters the water 27 times more than the surrounding soil. Subterranean termites reduces the water filtration and increases the flow of sand and soil particles.
Soil aggregate formation
Soil structure is made up of soil aggregates, aggregates are formed by the microbial activity. Invertebrates contribute in aggregate formation by the combination of feces and minerals with undigested part of food. Soil aggregate stabilizes the nutrients, hinders the leaching too.
Phosphorus is the basic component available in soil for plants but in the form of in bounded form. Plants cannot consume it completely. So, with the activity of fungi and bacteria, this bounded form is revealed. Other products, citric acid, oxalic acid are produced by these organisms. On the roots of some plants fungi is wrapped on naturally, there is mutualism in between root and the fungus.
Malik Abubakar, Muhammad Yahya, Muhammad Shajar, Sheikh Muhammad Aqeel, Mujahid Tanvir
University college of Agriculture, University of Sargodha