Studies on the biology of soil-dwelling nematodes of tussock grassland

摘要

Tussock grassland is the indigenous grassland of New Zealand. It covers one-fifth of the land area and is related to the "steppes" of the northern hemisphere (Zotov, 1939; Allan, 1946). Two types of grassland exist; tall tussock grassland which is dominated by plants of Chionochloa species, and low tussock grassland which is dominated by bunch grasses of Festuca and Poa species (Barker, 1953). The low tussock grasslands occur mainly in the South Island, covering almost five million hectares (Cockayne and Levy, 1956). During the early period of European settlement and agricultural development, montane tussock grasslands represented one of the few natural resources that maintained agricultural production without modification (Cockayne, 1915); but continued mismanagement by burning and overgrazing led to changes in species composition, and to deterioration and erosion in many areas (Cockayne A., 1910,1915; Cockayne, 1919a, 1919b; Zotov, 1938; Cumberland, 1945; Raeside and Gibbs, 1945). With a steady decline in the relative value of production from the high country grasslands, and a growing realization of the importance of soil and water conservation, interest in the ecology of tussock grasslands intensified through the 1950's, culminating in the formation of the Tussock Grasslands and Mountain Lands Institute in 1960. The ecological problems of tussock grassland management are well documented (see Hercus, 1956; Drummond and Leatham, 1959; McCaskill, 1963; O'Connor, 1966; Tussock Grasslands and Mountain Lands Institute Review, 1961-1970). However apart from entomological considerations (Dick, 1940; Kelsey, 1957), studies on the soil fauna and micro-flora were neglected until Thornton (1958a) introduced a co-ordinated effort by a group of workers on the biology of tussock grasslands soils. The programme included investigations on distribution and population dynamics of fungi (Thornton, 1958b), yeasts (Di Menna, 1958), bacteria (Stout, 1958a; Ross, 1958), protozoa (Stout, 1958b), streptomycetes (Vernon, 1958), algae (Flint, 1958) and earthworms (Lee, 1958), with respect to three tussock grassland soils. This was followed by a parallel study of fungi (Thornton, 1960b), yeasts (Di Menna, 1960), bacteria (Stout, 1960a; Ross, 1960) and protozoa (stout, 1960b) in cultivated and uncultivated tussock grassland soils (Thornton, 1960a). Subsequent work on the bacterial flora was carried out by Robinson (1962) and Robinson and MacDonald (1964). More recently, attention has been drawn to the problems involved in the establishment of legumes and nodule-forming bacteria in tussock soils (e.g. Blair, 1967; Adams and Lowther, 1970). Knowledge of several groups of organisms in high country soils is lacking (Hayward, 1967), nematodes included. Nematodes constitute an important part of the soil fauna... “being more numerous than any other animal of comparable size. Obviously they must be considered in any comprehensive study of soil biology,” (Christie, 1959). The present project was initiated with the support of the Miss E. L. Hellaby Indigenous Grasslands Research Trust, to investigate the biology of nematodes in a tussock grassland soil. From an agriculturist's viewpoint, ecological research is essential to the understanding of nematodes as factors in the biology of the soil, and to the interpretation of plant-nematode interactions in the aetiology of plant disease. Despite the significance of such studies and the increasing interest in soil biology, there are many gaps in current knowledge. As might be expected, the economically important plant parasitic nematodes have received most attention (e.g. Dropkin, 1955; Christie, 1959; Jones, 1959, 1965; Seinhorst, 1961; Thorne, 1961; Oostenbrink, 1966; Jenkins and Taylor, 1967; Paramonov, 1968); for more general reviews see Nielsen, (1949,1967), Winslow (1960), and Wallace (1963). Although there is a considerable volume of literature on various aspects of nematode ecology there have been few attempts to interpret pattern and process in a nematode population as a whole. Too often, ecological discussion is restricted to consideration of physico-chemical factors on populations without due regard to the ecology of the species involved and their interactions with the various components of the soil fauna and flora. In view of the lack of information on nematodes in tussock grassland soils in New Zealand, and the lack of understanding of many aspects of nematode ecology in general, studies were undertaken, with the following objectives: i)to consider the interrelationships between nematodes and the soil fauna and flora under laboratory conditions, and to study the biology of species representing a range of ecological niches in the soil; ii)to investigate nematodes in the field situation by considering the distribution and annual variation of the populations with regard to changes in biotic and abiotic factors of the environment and the biology of the species involved; iii)to investigate the significance of plant parasitic nematodes in causing damage to tussock grassland plants.