SOIL ACARINA AND COLLEMBOLA IN FOREST AND CULTIVATED LAND OF KHASI HILLS, MEGHALA YA

During the last decade considerable work has been done on the Indian soil fauna, and quite a number of reports exist on the soil fauna of North-East India with particular reference to Meghalaya (Reddy & Alfred 1977, 1978a, 1978b; Vatsauliya and Alfred 1980 ; Darlong & Alfred, 1982 ; Hattar & Alfred 1986 ; Paul & Alfred 1986). Most of these studies are confined to jhum cultivation and pine forest soils of Khasi Hills, Meghalaya, and as such there is hardly any work done on cultivated system from this region. The study was undertaken to compare the distribution and diversity of mesofauna with particular reference to Collembola and Acarina of pine forest soil and an adjacent cultivated land, for one annual cycle at four different soil depths.


INTRODUCTION
During the last decade considerable work has been done on the Indian soil fauna, and quite a number of reports exist on the soil fauna of North-East India with particular reference to Meghalaya (Reddy & Alfred 1977, 1978a, 1978b;Vatsauliya and Alfred 1980 ;Darlong & Alfred, 1982 ;Hattar & Alfred 1986 ;Paul & Alfred 1986).Most of these studies are confined to jhum cultivation and pine forest soils of Khasi Hills, Meghalaya, and as such there is hardly any work done on cultivated system from this region.The study was undertaken to compare the distribution and diversity of mesofauna with particular reference to Collembola and Acarina of pine forest soil and an adjacent cultivated land, for one annual cycle at four different soil depths.

MATERIALS AND METHODS
The study sites were located in Shillong at an altitude of 1500 m.The sites studied comprised of a pine forest (Pinu,8 kesiya Royle) and an adjacent plot of cultivated land belonging to vegetable research station, Government of Meghalaya, Shillong.Seasonal vegetables were grown in the vegetable land.The usual type of tillage followed in the hills of North-East India was carried out ~nd a rotational method of agronomic practices were followed.Both the sites have an area of 2.5 hat of flat and undulating slopes.Although soil samples were taken out fortnightly intervals from September, 1981 to August, 1982, the results are presented as monthly averages.'In both the systems soil samples consisted of 5 cm.sq. in surface area to a depth of 40 ems.divided into four depths of 10 cm.each.Five random cores of each soil layer from each system were collected by a rectangular iron cover (5XSx LO em.) and extraction of soil fauna was done using modified Tullgren funnels (Macfadyen, 1953;Southwood, 1966).The period of extraction was 7•10 days at constant 40°C depending on the moisture content of soil samples.Similarly soil samples were also collected for analysing the physico-chemical parameters.The method of ~7 alkey and and Black (1934) was followed for the analysis of the chemical factors of soil.The fauna were statistically analysed for their C. V., species diversity (Shannon Weiner) and species similarity (QS).The soils of the Ecosystems studied were (a) pine forest-sandy loam in texture and brown in colour (b) cultivated land-sandy loam in texture and light brown in colour.Different factors were analysed by taking samples from four soil depths.The minimum and maximum values of soil factors analysed are given in Table 1.The contents of organic carbon, soil conductivity, phosphate and potassium were found to vary seasonally in both systems.The temperature, pH and moisture content was found to vary significantly.The humidity recorded was quite high.

Vertical Distribution pattern of OoZlembola :
The mean seasonal density of Collembola in pine forest and cultivated land as given in Fig.I for one annual cycle from September 1981 to August, 1982 reveals that in the upper 0-10 cm.soil depth in pine forest (Fig. IA) the Collembola were recorded maximum in November and minimum in December, and in the cultivated land maximum in February and minimum in October.
In the 10-20 cm.soil depth in pine forest (Fig. IB) they were maximum in.January and minimum in August, and in cultivated land maximum in April and minimum in December.
In the 20-30 cm. and 30-40 cm. (Figs.Ie & 10) soil depths their numbers were significantly low in both the systems but their numbers fluctuated in different months.
[sotoma (Desoria) trispinata, Megalothorax minimu8 J Sphaerdea cf.cornuta and Onyckiuru8 spp.were common to both the systems as against 11 and 6 species in pine forest and cultivated land respectively.The species I sotoma (Desoria) tripinata was dominant in both the systems and its density being two times higher in the cultivated land in the 0-10 em soil depth and reverse in the case of 10-20 cm soil layer.
In the 20-30 cm soil layer the no. of species sharply reduced to six in pine forest with marked reduction in their density and was found to be constant at six species in cultivated land.Out of the two species viz.Megalothorax minimU8 and Sphaeridea of cornuta being common to both the systems the latter species was dominant in both the systems.In the 30-40 cm soil layer in pine forest the no. of species further reduced to four as well as in cultivated land.In this layer two species viz.Sphaeridea cf.cornuta and Onychiurus spp.were common to both the systems, the former being domiuant in pine forest and Xenylla spp. in cultivated land.As seen in Table 2 for C. V. values (%) cultivation seems to have very little impact on Collembola as compared to the forest.
In the upper 0-10 cm and 10-20 cm soil depth 2 species of Acarina viz.Sckelaribates albialatus and Parasitus divortus were common to both the systems as against 8 and 5 species in pine forest ~nd cultivated land respectively-The species Scheloribates albia-latu8 was found to be dominant in both the systems.
In the 20-30 cm and 30-40 cm soil depths only one species namely Parasitus divortu8 was common to both the systems while Scheloribates huancayensis was dominant in 20-30 cm soil depth and Epilohmannia spp. in 30-40 cm soil depth in pine forest.In cultivated land Para8itus divortus was dominant in both these depths.As seen in Table 3 for C. V. values (%) for Acarina the values were always higher in the cultivated land than in pine forest indicating the disturbed nature of the former system.

Parameters affecting M e80jaunal Distribution and Diversity :
Soil temperature throughout the sampling period varied slightly depending on vegetative cover and soil depth.Generally higher relative humidity and vegetative cover increased the moisture content of the soil especially near the surface exposing the mesofauna to greater temperature and moisture fluctuations.Changes in soil depth coincide with similar changes in moisture, temperature, organic matter, quality and quantity, pore space and soil temperature (Wallwork, 1970 ;Mitchell, 1979).Fluctuation in these factors tended to decrease with depth as the physical environment became more stable.Within the soil environment various layers are produced which provide various micro-habitats able to support different species of Collembola and Acarina.The numbers of Collembola and Acarina greatly decreased with depth due to similar-drops in organic matter and pore space volume in pine forest but in cultivated land the reduction was less as compared to pine forest.It is the combination of many soil factors which might have contributed to the overall mesofaunal composition of both cultivated land and pine forest.In view of the present study it could be inferred that the collective influence of all the factors in controlling the population and vertical distribution of soil mesofauna especially Collembola and Acarina was more pronounced in both the systems studied.
In general the soil fauna of arable land is less abundant and diversified than the fauna of forested ecosystems (Edwards & Lofty 1969 ; Ghilarov, 1975).This is evident from data of cultivated land as compared with pine forest and the number of species recorded in each system.Similar sampling and extraction techniques were used in both the ecosystems; the difference between them being due to litter accumulation in pine forest which have a great impact on the abundance of many species of Acarina.An experiment performed by Karg (1967) showed the importance of litter layer that when it is removed from the forest site, the abundance and species number were reduced by more than 50% and the species composition became similar to that in the cultivated land, as is evident in our present study.The abundances reported in this paper are high for Acarina in pine forest as compared to cultivated land.The ColIembola being in the reverse (cf. Hate, 1967).The Collembola seem to be less affected by cultivation than Acarina (Christiansen, 1964).
In the present investigation it was seen that interestingly enough the pine forest possessing higher number of species reveal their possible occupation of most ecological niches in a rather stabilised ecosystem where fluctuations of abiotic factors are most extreme.The reverse is in cultivated land where number of species decreased because of the catastrophes imposed on the system by ploughing, harrowing, manure, insecticides, application of fertilizers, cultivation and harvesting etc. Ploughing and harrowing generally decrease the abundance of soil aninlals (Tischler 1955 ;Sheals 1956 ;Ghilarov 1975 ;Edwards 1977).The direct negative effects of ploughing are partly due to abrasive damage to the animals and partly due to trapping of animals in the soil when it is inverted and the existing system of cracks and pores is destroyed.Since the cultivated land studied was subject to intensive ploughing and harrowing it could have possibly affected the mesofauna!composition as compared to pine forest.Secondary affects, e.g., drying of the uppermost part of the soil and removal of litter from the surface probably could affect the mesofaunal composition in cultivated land as compared to pine forest.Thus cultivated land harboured a depleted soil fauna because of frequency and type of cultivation and degree of plant cover and intensity of soil cultivation and the species diversity of Collemboia and Acarina reduced as  compared to the forest system.The investigation also revealed that the abundance of soil mesofauna in cultivated land was higher in comparision to number of species as compared to pine forest.
However, eveness is indicative of phenomena in the reverse in that cultivated land reversal means more eveness than in the pine forest which could be attributed to cumulative influence of minor fluctuations in various abiotic factors which probably contribute a factorial complex thereby nullifying the effect of individual components.

TABLE 2 .
TABI.JE 1. l\1inimum a.nd l\Iaximum Values of Soil Factors in Four Different Soil Depths in Pine Forest & Cultivated Land.l\Iean population densities of Collembola species and their co-effioient of Valianoe in pine forest & cultivated land.