63

Presidential Address delivered at the Eleventh Annual General Meeting. SOME ASPECTS OF

K. E. LEE Soil Bureau, US.1.H., LOwer Hilli.

It is well known that in most vast special importance for the effective use of soils numbers and great variety of living organisms and economic plants. Earlier ideas of a trophic may be found. They range in complexity pyramid~ with herbivores feeding on grass and from the simplest of single-celled animals themselves being fed on by carnivores are plants and bacteria, through to burrowing oversimplified. Most of the energy available mammals and higher plants, and include in the system is actually falling to the unseen representatives of almost every major group decomposers beneath the soil surface. of organisms. Photosynthesis by the green plants that grow on the soil surface is the Apart from a few large animals, such as source of energy upon which the whole popula- earthworms, which are able to make burrows, tion ultimately depends, and most of the soil organisms live in the naturally occurring organisms are decomposers of plant tissue. spaces between soil aggregates~ and to a large Macfadyen (in press) has recently con- extent on the surfaces of the aggregates. The structed a balance sheet for the total annual feeding roots of higher plants share these flow of energy through a meadow exploited ecological niches with the microfauna and by means of grazing cattle. Of the total energy microflora, and the environment that prevails captured by plant photosynthesis, less than in these minute spaces is of fundamental one seventh is respired by the plants, about two importance not only to plant growth, but as sevenths are consumed by herbivores, and a reflection of the general physical, chemical about four sevenths are exploited by organisms and biological conditions in the soil that are engaged in the decomposition of plant material the basic concern of soil scientists. If we~ for after it is dead. Macfadyen has further instance, plot the numbers of dominant groups developed this line of investigation and has of soil animals in a series of soils~ we find ana lysed the proportion of the total energy peak populations of one group or another at handled bv the soil animals engaged in what different stages in the series. If we continue he calls the "decomposer industry" into four this process further, say to individual species components~ due respectively to the herbivores~ of mites, or Coli em bola, we find peak popula- carnivores (predators)~ large decomposers tions under particular plant species, in soils (those which have a mechanical effect on the with certain textures or structure, moisture soil) and small decomposers. characteristics, and so on. If we knew enough about the ecological preferences of some com- Some of the material exploited by the decom- mon soil animals, their food requirements, posers is returned to the soil in a form that limiting temperatures and moisture, reaction can be used again by higher plants, and this to acidity, pattern of nitrogen excretion, we is the basis of organic cycJes~ which are a could predict much of importance to the soil fundamental concern of . However, scientist, and also to the growth of plants, from from the point of view of the farmer and a study of population figures. This mav sound agriculturist~ it is most important that, dis- rather impracticable, but Ghilarov (t956a) has counting the cne seventh of energy respired successfully used what he calls "soil inverte- by pasture plants~ two thirds of the energy brate complexes" as diagnostic criteria for available from grass growth is lost to the Russian soils whose affinities were in dispute. "decomposer industry" and never becomes In New Zealand~ profile characteristics due to available to the grazing animal. Study of the soil animals, especially earthworms~ may be ecology of individual species and groups of soil used to distinguish yellow-grey carths from organisms~ especially of their distribution~ brown-grey earths, and may prove to be the numbers, population dynamics, food prefer- most useful character for field recognition of ences and energy consumption, acquires a some yellow-grey earths. 64 PRESIDENTIAL ADDRESS

I should like now to discuss some trends men!. Using measurements of the respiratory in the study of soil organisms that have rate of litter decomposing organisms, made at developed during the last few years and their monthly intervals for a year, he has attempted implications both in the furtherance of the to work out a balance sheet of the carbon study of ecology and the better understanding cycle, with encouraging results. He intends of the properties of soils and soil forming now to study the colonisation of dead leaves processes. by soil organisms, and relate population In New Zealand, as a continuing changes to the rate and process of decay, and study began with the formation of a biology make a study of the contribution of individual section in the Soil Bureau, in 1946. It arose groups of organisms to the processes of decom- initially as an offshoot of soil surveys. position. This is an example of the kind of Pedologists in Ihe field felt the need to get work that is occupying an increasingly impor- some better understanding of the influence of tant place in soil biology work in New Zea- living organisms on profile development and land. We are trying to get down to quantitative the processes of soil formation. The first assessment of the contribution of individual studies were largely qualitative, and were species and groups of organisms to the turn- aimed at finding out what kinds of organisms over of organic material in the soil, and hence were present, - how the species composition to their contribution to the processes that varied from one soil to another, and whether control soil formation and fertility. differences could be correlated in some logical Mycological work has recently been concen- manner with soil maps, vegetation, climate and trated on the fungi that live in close proximity various soil properties such as moisture content, to grass roots. Among these fungi are some, texture, structure and chemical information. known as endophytic mycorrhizae, which grow The lack of basic information concerning partly within plant roots and also have hyphal the constitution of soil populations is so great systems ramifying through the surrounding that this qualitative approach has continued soil. The pathways by which minerals become right through 10 the present, and will need to available to plants are not well understood. continue for many years to come. In New This is particularly true, for instance, of the Zealand soils there are many groups, particu~ transference of nitrogen, originally fixed by larly of animals, of which we know virtually nodule bacteria of legumes, through the soil nothing, and there is an open field for taxo~ to become available to grasses. It may well nomic and ecological work. So far, we have be that endophytic mycorrhizae provide the accumulated information on some bacteria, pathway, and a study of these fungi may prove yeasts, fungi, algae, protozoa, and earthworms~ most rewarding. and on a number of minor groups in the fauna, On the other hand, it is known that about and have had some success in relating their half the nitrogen excreted by earthworms is distribution to pedological infonnation. excreted in the fonn of ammonia. It has been Comparative studies have been made of soil calculated by Satchell (pers. comm.) in Eng- organisms under particular vegetation types in land that a population of eartbwonns, various parts of New Zealand, e.g., a compre- Lumbricus terrestris, in a woodland soil, turns hensive study of soils under grazed pastures over approximately 100 kg/ha. of nitrogen and native tussock, and of changes induced by per year. This figure is approximately equal the destruction of native vegetation and its to the amount of nitrogen available from the replacement by pasture. litter fall. Since earthworms in New Zealand Qualitative studies have given soil biologists pastures feed mainly on dead roots of pasture a background against which detailed quantita" plants (Waters t955), it is possible that they tive and physiological studies can be planned are major contributors to the mineralisation and interpreted, and in the last few years an of nitrogen and its cycling through the soil. increasing proportion of the Soil Bureau's An attempt to assess the amount of nitrogen biological work has been quantitative and cycled by earthworms is being planned. physiological. A great deal of work in is at Dr Stout has worked on the ecology of the present in progress in Britain and Europe. At animal and microbial populations of the litter Liverpool, Prof. Burges and his school have layer of a soil under beech forest, relating made a detailed study of microbial ecology in numbers to physical features of the environ- an iron-humus under pines. They have LEE: SOIL ECOLOGY 65 used direct microscopic examination of plastic small changes in physical and chemical impregnated sections of soil and litter horizons characteristics of the soil evironment. A wide to measure the quantity of fungal hyphae variety of techniques for the extraction of and the species involved in successive stages animals from soil samples has been developed. of decomposition of plant debris; and have Many have evolved from the classical Berlese extended their studies to measurements of funnel, which has been refined to a high degree oxygen uptake by soil and litter samples, and of efficiency. Notable in the development of the use of this data as a measure of microbial extraction methods have been Murphy and activity. Their work has contributed much to Macfadyen in Britain. A recently published an understanding of the processes and rate of volume on research methods in soil zoology breakdown of , and at the (Murphy 1963) discusses extraction methods same time it is important for its illustration of in detail. Now that efficient methods of extrac- succession in microbial communities and tion are available, soil animals are a fruitful relationships between the fauna and microflora and readily accessible field for students of of the soil. animal populations, and for establishing basic principles in the study of mechanisms of Direct examination of soil sections as a competition between species, reaction to method of studying the ecology of soil organ- environmental change, control of animal popu- isms is a relatively new technique, and one lations, and many other fundamental aspects of capable of providing much information, animal ecology. especially concerning micro-organisms. The preparation of satisfactory sections requires For measuring oxygen uptake and carbon the spaces in the soil to be impregnated with dioxide production, much use has been made a matrix that will bind the soil particles of the Warburg apparatus. Respiratory mea- together without causing significant shrinkage surements done in the Soil Bureau have been of organic material, and without excessive carried out with a Warburg apparatus. This damage to soil organisms in the soil spaces. records reduction in pressure in a sealed Impregnation techniques have been developed chamber as oxygen is used up and carbon largely in England and Europe. Haarlov in dioxide is produced and absorbed. Its useful- Denmark used agar and Minderman in ness is limited by the small volume of air con- Holland used gelatine, but these materials are tained in the system, and consequently the suitable mainly for and soils with high relatively short period for which experiments organic matter content. Kubiena, in Germany, can be continued. Macfadyen has developed has developed a technique using plastic resins an ingenious and very accurate respirometer for impregnation, and this technique, combined which can be run continuously for long periods, with freeze drying of samples to minimise and which automatically records the amount shrinkage, has been developed in Europe and of oxygen used and the rate at which it is used. England to become a most useful tool in soil The apparatus was designed originally for use ecology and also in the study of . with small soil arthropods, but undoubtedly has a much wider application in physiological Much of the work on soil animals done in und ecological research. England and Europe has consisted of detailed studies of populations at specific sites, rather Ghilarov 0949, 1956 a & b, t958) bas put than the broad coverage of a range of soils forward the hypothesis that terrestrial inverte- that has been characteristic of New Zealand brates evolved from aquatic ancestors by way soil biology. Soil animals are very numerous. of the soil as an intermediate habitat. He Up 10 2.3 million arthropods per square points out that in the spaces between soil metre have been found in forests in Sweden particles there is an environment in which (Forsslund t948), up to 20 million nematodes many invertebrate groups of aquatic origin per square metre in the top few centimetres could live and obtain oxygen without danger of Danish pasture soils (Overgaard Nielsen of desiccation. The fact that the soil fauna t949), up to about 200,000 Enchytraeidae does include a wide variety of invertebrates, (Oligochaeta) per square metre (Overgaard ranging from most delicate aquatic animals, Nielsen 1955) and about t250 lumbricid earth- such as protozoa, ostracods and copepods, worms per square metre (Waters 1955). Most through intermediate forms, to thoroughly soil animals exhibit violent fluctuations in waterproofed and highly successful terrestrial numbers, both seasonally and in response to animals such as spiders and some insects,. giye~ 66 PRESIDENTIAL ADDRESS

some credibility to his hypothesis. Whether his REFERENCES theory is accepted or not, a close study of the FORSSLUND, K. H., 1958. Nagot om insamJingsmetodiken physiology, ecology and morphology of soil- vid marksfaunaundersokninger. Medd. Skogsforskn. 1nst. Stockh., 37 (7), 1-22. inha biting animals could provide much GHILAROV, M. S., 1949. The peculiarities of the soil animals might have adapted themselves to life as an environment and its significance in the in a terrestrial environment. evolution of insects. Moscow & Leningrad, (in Russian). I have not mentioned a wide range of work GHII..AROV,M. S., 1956(a). Significance of the soil that is in progress in the fields of physiology, fauna studies for the soil diagnostics. Proc. 6th feeding behaviour, pest control, biochemical Congo Int. Soc. Soil Sci., Paris, 3: 23. studies of humus formation and decomposition, GHILAROV,M. S., 1956(b). Soil as the environment of the invertebrate transition from the aquatic to the and many other aspects of soil biology. I hope terrestrial life. Proc. 6th Congo Int. Soc. Soil Sci., I have left with you the impression that the Paris, 3: 307-13. study of the ecology of soil organisms is an GHILAROV,M. S., 1958. Proc. 15th Int. Congo Zool., expanding and vigorous branch of biology. It London, 354--7. MACFADYEN,A. (in press). Energy flow in ecosystems is only a short time since soil science was the and its exploitation by grazing in Symposium on exclusive province of geologists, chemists and Grazing ed. Crisp, D. J. British Ecological Sec. physicists. Biologists have now been accepted Oxford. as essential contributors to soil studies and I MURPHY, P. W. (Ed.), 1963. Progress in soil zoology. Butterworths Scientific Publications, London. believe that especially those with an ecological OVERGAARD, NIELSON, C., 1949. Studies on the soil outlook and a willingness to use a variety of microfauna. II. Nat. Jutland. 2: 1-131. techniques and to collaborate with physicists, OVERGAARD, NIELSON, C., 1955. In Soil Zoology ed. D. chemists and pedologists, can make a major K. McE. Kevan, Butterworths Scientific Publica. tions, London. contribution to soil science, and at the same WATERS,R. A. S., 1955. Numbers and weights of earth- time add much to the understanding of funda- wonns under a highly productive pasture. N.Z. J. mental biological problems. ScL Tech. A36: 516-25.