Mesoflora and methane bacteria. Most of soil bacteria

Mesoflora and macroflora because occur above the surface of soil (land-surface), therefore are ex­cluded from this discussion:

1. Microfauna:

It includes animals with body size within the range of 20 µ to 200µ. It includes all Protozoa and small-sized mites, nematodes, rotifers, tradigrades and copepode Crustacea. Soil inhabiting protozoans like amoeba, ciliates, zoomastigine flagellates occur near the surface soils, while the testate forms like Thecamoeba, Euglypha and Difflugia, have a wider vertical distribu­tion.

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The common terrestrial polyclad is Bipalium. The nematodes such as Rhabditis, Diplogaster, Tylenchus, Heterodera, Aphelen- choides, Mononchus, Pratylenchus, Xiphinema and Criconemoides, abound by as much as 1-3 million in raw humus soils to 20 million /m2 in grassland soils.

2. Micro flora:

The micro flora of soil includes bacteria, soil fungi, soil actinomycetes, blue green algae and algae in soil, micro flora bacteria from about 90 per cent of the total population. Fungi and algae together represent one per cent and actinomycetes cover only 9 per cent.

Soil bacteria grow fairly well in the neutral soils richly supplied with organic nutrients. Soil inhabitant bacteria fall into two cate­gories namely—autotrophic bacteria and heterotrophic bacteria. The autotrophic bacteria derive their energy from the oxidation of simple carbon compounds or from inorganic substances and their carbon from the atmospheric.

The common autotrophic bac­teria of soil are nitrifying bacteria, hydrogen bacteria, sulphur bac­teria, iron bacteria, manganese bacteria, carbon monoxide bacteria and methane bacteria. Most of soil bacteria are heterotrophic bacteria depending upon the organic matter of soil for their energy source and are primarily concerned with the decomposition of cellulose, and other carbohydrates, proteins, fats and waxes.

They bring about mineralization of organic matter of soil and release considerable amount of nitrogen, phosphorus and other nutrients for plants. The common nitrogen-fixing bacteria of soil are Rhizobium (occurs in root nodules of leguminous plants); Azobacter and Clostridium pasteurianum (the latter two are free occurring in soil).

Majority of soil fungi are found in acidic soils. They may be parasitic, saprophytic and symbiotic. Parasitic fungi of soil infect roots of plants and cause plant diseases such as cotton root rot and many kinds of wilts, rusts, blights and smuts.

Certain wilt-forming fungi produce toxins which are harmful, for example, Fusarium lini, which causes wilt of flax (Alsi) and secrets HCN and Fusarium dum, a fungus causing wilt of pigeon pea (Arhar) secretes fusaric acid in the roots of host plants.

However, certain parasitic fungi produce growth stimulating substances for host plant. Fusarium sp., for example, have been found to secrete Gibberellin and Gibberellic acid (C19H22O6). Symbiotic fungi of soil live on the roots of certain plants and both fungus and plants are benefitted.

Saprophytic fungi depend on dead organic matter of soil and derive the energy from decomposition of the latter. They break down cellulose, lignin, gum, sugars, starch, protein, etc., into simple gradients to be utilized by higher plants as nutrients.

Actinomycete fungi prefer saline soils and bring about the de­composition of organic matter such as cellulose. They produce a variety of antibiotics of great economic significance for man. The most important blue green algae of soil are those which fix nitrogen in soil. Anabaena, Nostoc, Microcystis, Tolypothrix, Oscillatoria, etc., are important nitrogen fixing blue green algae of soil. They also make soil aggregates because of having mucilage.

3. Mesofauna:

Mesofauna include animals with body size with­in the range 200 mews to 1 cm. The micro-arthropods Acarina (mites) and Collembola (spring tails) are important members of this group which also includes the larger nematodes, rotifers, and tardigrades, together with most of the isopods, Arachnida (spiders), Chelognathi (pseudoscorpions), Opiliones (harvestmen), Enchytraeidae (pot- worms) insect larvae and small millipedes (Diplopoda), isopods and molluscs.

Among annelids the microscopic enchytraeids are represented by Enchytraeus fridericia and Achaeta lumbricellus, which are more abundant in organic soils and forests than in grass land. Oniscus, Porcellio, and Armadillidum are the most common isopods (crustacean) of the tropics in the humid zone. Among the soil arachnids, mites are the most predominant. Mites flourish in moist organic soils and certain mites such as Galumna, Cepheus, and Hemo- robates occur in lichens and mosses.

Certain mites, such as, Schelorbates and Brachychthornus live in humus the mites are saprophagous, predatory and phytophagous and are involved in the process of organic decomposition and its resultant processes. Certain arachnids like scorpions, Thelyphonus, Galeodes, and some spiders are crepuscular, hiding under rocks or in crevices in soil and in loose litter, and has no ecological significance in decompo­sition like other arachnids. Many opiliones or harvestmen occur in forest litter, frequently preying upon soil organisms.

Besides mites, only the pseudoscorpions or chelognathi occur in surface soils and most decaying vegetations. Of the xerophit litter inhabitants are Stenatemnus indicus, Dhanus indicus, Fealla indica and the hygrophil inhabitants living in the litter and under stones are—Comsaditha indica, Tyrannochthonius madrasensis, Tyrannochithonius chelatus and Hygrochelifer indicus (Mu-thy, 1964), feeding on Collembola. enchytraeids etc.

The common millipedes or diplopodes of forest soil which are chief decomposers of soils are Spirostreptus, Thyropygus, Glomeris, Arthrosphaera, Polydesmus, lulis, etc. Tardigrades or bear animal­cules occur in surface layer of moist soils in grassland and being represented by the Macrobiotus and Hypsibius.

Among insects, apterygote Collembola form numerically the most important groups of soil insects. Others like Dermaptera, Psocoptera, Dictyoptera, Isoptera, Coleoptera, a few Hymenoptera and some Diptera also occur in soil, sometimes as juveniles. The termites such as Reticulotermes and Odontotermes are important soil-dwellers of tropics and play an important role in the breakup of organic materials and their mixing up with mineral soils.

Among the Hymenoptera, ants are the most important soil dwelling forms. Among Collembola, Onchuridae, Isotomidae, Poduridae and Entomobrydae are richly represented in the soil both in num­ber and species composition. Large-sized Collumbola such as Tomocerus, Entomobrya and Orchesella occur in surface layer, while the smaller Onychurus, Tullbergia, etc., and occur in deeper layers of soils.

Among Diplura Insecta, Anajapyx, Japyx and Campodea are often found in small numbers in moist soils under stones and in humus. Proturans are more abundant than Diplura and very common in moist forest and grassland soils which abound in species of Eosentomon, Acerentomon and Acerentulus.

Recently, Singh and Mukharji (1971, 1973) studied quantitative and qualitative composition of soil arthropods in five fields (viz., Rose (Rosa indica), sugarcane (Saccharum officinarum), Falsa (Grewia asiatica), Botanical garden (Canna indica) and uncultivated field) situated within the campus of Banaras Hindu University, Varanasi, India and have reported following species:

(i) Acarina (Arachnida):

(a) Mesostigmata:

Asca sp., Dermanyssus sp., Gamasiphis bengalensis, Gamasellodes sp., Hypoaspis vacua, Kleemannia sp., Macrocheles coprophila, Pachylaelaps dor- salis, Parasitus consanguines, Proctolaelaps curtipilis, Typhlodromus sp., and Urosternella sp.

(b) Prostigmata:

Allothrombium australiense, Coccotydeus sp., Coccorhagidia sp., Cunaxa setirostris, Imparipes sp., Microtro- mbidium hystricinum, pronematus sp. and Tydeus sp.

(c) Astigmata:

Tyrophagus sp.

(d) Cryptostigmata:

Cryptostigmata sp., Epilohmannia cyli- ndrica, Epilohmannia pallida pacifica, Fosseremus quadripertitus, ‘ Galumna sp., Gehypochthonius sp., Leptogalumna sp„ Lohmannia sp., Oppia sp., Peloribates sp., Protoribates sp., Rhysotritia ardua and Scheloripates sp.

(ii) Insecta:

(a) Collembola:

Cyphodcrus sp., DrepanuJa sp., Entomobrya santsris, Entomobrya sp., Folsomia fimetaria, Fotfo­nt ides parvulus, Hypogastrura sp., Isotoma viridis, Isotoma pinn a fasciata, Isotomurus, palustria, Isotomina thermophila, Isotomides sp., Isotoma (Desoria) sp., Isotomurus punctiferus, Isotomina pontica, Nea- nura muscorum, Onychiurus armatus, Proisotoma sp., Pseudachorutes, Sminthurus virdis annulatus, Salina indica, Seira biformis, Seira indica, Tullbergia sp., Xenylla sp.

(b) Diplura:

Anajapyx sp., Campodea sp., Heterojapyx sp., Japyx sp., Projapyx sp.

(iii) Arachnida:

(a) Pseudoscorpionida: Clielifer sp., Ntobi- sium muscorum.

(b) Palpigradi: Koenenia sp.

(c) Uropygi: Thelyphonus sp.

(iv) Symphyla: Scutigerella sp., Scolopendrella sp.

(v) Pauropoda: Eurypauropus sp., Decapauropus sp., Pauro- pus sp.

(vi) Schizomida: Nyctalops sp., Trithyreus sp.

4. Macroflora of soil:

Warming (1909) have recognised follow­ing five ecological classes of plants on the basis of soil characteri­stics on which they grow: 1. Oxylophytes: Plants usually found on acid soils, e.g., Rhododendron, Rumex sp. 2. Halopbytes: Plants usually found on saline soils, e.g., Salsola foetida, Salicoraia and Suaeda fruticosa. 3. Psammopbytes: These plants grow on sand 4. Lifhophytes: Plants which grow on rock surfaces. 5. Chasmo- phytes: Plants which grow in rock crevices.

Soil supports a variety of plants like herbs, shrubs, trees and thalloid plants, all of which have specific adaptations for their particular soil types. For instance, in areas of thick soil, roots may be thick and deep; in areas of thin soil cover, roots may be broad and flat, in areas with water logged swampy soils, roots may be swollen buttresses (Clapham Jr., 1973).

5. Macrofauna of soil:

Macrofauna of soil includes those animals whose body size is greater than 1 cm. Here belong the majority of Lumbricidae, the Mollusca, the large-sized chilopods, arachnids and insects and the soil-dwelling or fossorial vertebrates.

Earthworms usually occur in abundance in alkaline and moist soils and sparse in acid soils. They have been proverbial for their influence on the process of breaking up litter fragments, decom­position of organic materials and mixing them thoroughly with mineral soils resulting in the formation of organic soils. Some of the common Indian annelidan species of soil are Megascolex, Phere- tima, Octochaetus, Drawida and Moniligaster.

Among chilopods the carnivorous Scolopendra and Lithobius are common in moist soils feeding on leaf litter inhabitants. Land snails are abundant in soils rich in lime. Among insects, Gryllotalpa and Forficula are adapted for fossorial life in soil.

Among soil vertebrates following animals are well adapted for fossorial or burrowing life in soils: Ichthyophis, Cacopus systema, Breviceps (Amphibia); Sphenodon, Uromastix, limbless lizards, snakes (Rcptilia); burrowing owl (Aves) and monotrcmcs, kangaroo-rats, moles (Talpa), prairie dogs, hedgehog, haies, ground squirrels, otter, badgers and rodents (Mammalia).

Adaptations of soil animals:

Animals which are adapted for digging the burrows and for subterranean mode of life are called fossorial animals. These animals may dig either for their food or simply for retreat. Zoologically they are primitive, defenseless and unambitious animals.

They have following adapt­ations: 1. The body contour is either cylindrical (e.g., Ichihyophis, limbless lizards, snakes, earthworms, Scolopendra, etc.), or spindle- shaped or fusiform (e.g., Talpa, Echidna, etc.) as to offer least resi­stance to subterranean passage. 2. The head tapers interiorly to form a sort of snout for burrowing. 3. The tail is short or vestigial. 4. The eyes tend to become vestigial as they are of no use in dark habitat. 5. The external ears also tend to disappear since they would be obstructing in burrowing. 6. For digging, many struc­tures may be found in different fossorial animals. For example, hands are well adapted for digging. In the insect Grylloialpa, the fore-leg’s are modified for digging purpose.

The ground-dwelling animals which may be cursorial (runn­ing), like ostrich, rhea ungulates, wolves, cats, bears, hyaenas, etc ; salutatory (jumping) like rodents, rabbits, wallabies, kangaroos, etc., or graviportal (heavy) like turtles, armadillos, elephants, hippopotami, etc., exhibit different kinds of adaptations for diffe­rent kinds of soils.

For example, if the soil is firm and hard, the large animals inhabiting the ecosystem tend to have small hooves or paws; if the soil is wet and spongy, they tend to have broad hooves or paws.