Denizens of the Soil: Small, but Critical by Andy Moldenke, Research Entomologist, Oregon State University, Corvallis, Oregon

Very few people really understand how soils work. Id like to give soil all of the bacteria and fungi that normally lived in that soil. three illustrative examples of how soil arthropods, soil microbes • The only thing missing were all the little arthropods. Those fungi and roots work together as a combined system in the real world. and bacteria release a certain amount of nitrogen, (x). Now, in The first example is of onion production. Basically, the plant is another pot he put the same litter with the fungi and bacteria that incapable of taking up any phosphorus at all from the soil unless normally are there and put in an oak seedling. What did he find? it has mycorrhizae on the roots. With mycorrhizae, the roots pick He found exactly the same amount of nutrients (x) because the oak up lots of phosphorous. The growth of the onion plant depends tree seedling didnt do anything. Then, he took another pot and added upon the number ofarthropods called springtails living in the soil. a millipede. What happened? The amount of nutrient recycling went Springtails function by eating the tips of the mycorrhizae which up ninefold. Then he ran the experiment a fourth time, with both a stimulates the mycorrhizae to grow, dissolve more of the soil millipede and an oak seedling There was no extra nutrient building around it, and feed it to the plant. As you increase the number of (x), but the growth ofthe seedling oak tree was four times what it was springtails in the soil, the plant grows faster until there are so when there werent any arthropods present. The activity of those many springtails that they eat all arthropods affected the rates of de- the mycorrhizae. Then growth composition, and all of that extra drops to zero again. nitrogen went directly into the growth of the plant. The second example is from oak forests in Europe. When oak trees Anderson has taken many many soil live on sandy soil they grow very types and many different kinds of slowly. They dont make many vertebrates in that experiment. What leaves so theres not much litter at hes found is that the rate of nutrient the end of the year. But the litter turnover is dependent upon the soil that does come down year after year type, but within any given kind of piles up very thick. Most of the soil type, its really independent of nutrients are in the litter layer, un- how many bacteria and fungi you used, not part of the biological have in that system. Its actually growth of that ecosystem. On the Penknife oriband mite independent of the kind of arthropod other hand, oak trees that grow on clay soil grow very fast and have or invertebrate you put in there. Its only dependent on how many lots of leaves. But when the leaves hit the ground they decompose of them are there. They can be tiny little oribatid mites or great very rapidly and make a very thin litter layer. In fact, all of those big oribatid mites, it doesnt make any difference. nutrients in that ecosystem are bound up into the tree growth itself Soil invertebrates are system catalysts. They dont do much of An oak tree puts lots of chemicals in its leaves called phenols that anything chemically in the processing that takes place in the soil, prevent caterpillars from destroying the trees. Whenthe leaves die and but they regulate the rate of decomposition and the rate of nutrient enter the litter on the ground, all those chemicals are still in the leaf recycling. They do that by crushing up the resources and the When a millipede or an earthworm conies along and starts to eat that living microbes that are in the soil, by mixing the organic and the leaf the pH changes and the phenols polymerize and form a great big inorganic components of the soil, and by driving the complex plastic rubbery mass killing the millipede. However, on clay soil, a processes of microbial succession. They feed on the current little springtail lives in the soil. At night, before it comes up to feed microbial crop, and by their own feces they provide for a new and on the litter, it fills itsbelly with inorganic claypatticles. Then it comes different type of microbial succession to take place. up to eat fungi and leaves and litter. The inorganic clay particles in the gut prevent the polymerization from taking place and the Now whats the punch line of the story here? The punch line is springtail lives and grows happily. As a result, the nutrients in that dirt isnt dirty, soil isnt soiled, litter isnt garbage. Theres that ecosystem cycle; they dont pile up on the ground. The moral something missing in the way we use those words; its the living of the story is that the productivity of that entire forest ecosystem component thats missing. The upper layers of soil, which are the is basically the result of one little arthropod in that soil. only ones that are important in growing plants and trees and everything else, are alive. Litter and topsoil are, in fact, biologi- The last example is another one from oak forests in England. Joe cally the most diverse part of any terrestrial ecosystem. They are Anderson went out in oak forests in England and brought all the also the most chemically diverse part of any ecosystem. In our different soils back to the lab. He sterilized those soils killing the forest soils in the Blue Mountains there are literally hundreds of bacteria, fungi, arthropods, worms, etc. Then he added back to the Continued on page 4

Natural Resource News - Edition - August 1993 Denizens cont. crush it and crack it open with shears and The point that I want to make is that all the Continued from page 3 then jab them into its mouth like you would upper layers of the soil are biogenic. The spaghetti. Another species feeds by insert- microstructure of the soil is fashioned by species ofarthropods in every square meter ing the whole feeding aparatus into the arthropods and worms, and therefore the of soil. There are literally hundreds of breathing pores on the pine needles. When major chemical and physical properties are thousands of individual arthropods per they feel a fungal hypha, they grab it. As directly under biocontrol. Every chemical square meter of soil. These are all things they pull one chelicera, the other one goes and physical property of soils is basically you can see walking around in your hand; in and it all works hydrostatically. There driven by the surface:volume ratio of the theyve got eyes theyve got legs, they get are also some oribatids that suck bacteria particles that make it up. The upper layers hungry, they get tired, they lust after their through straws. Huge muscles that work of soil are composed of the living bodies of mates, they do little mating dances, they the suction cup inside the mouth attach to countless invertebrates, fungi, and bacte- have behavior. These are not bacteria, the back of its head. ria, and the skeletons of all the dead ones as they are not amoebae, these are rather well. highly complicated organisms. The other major group of soil dwellers are springtails. There are about 100,000 per Oregon State University is actually the first You can find a variety of these critters any square meter out in the forest. Theyre place in the U.S. where researchers have time you go out and take a shovelful ofdirt. called springtails because they have this actually made slides of soil and looked at The most common things in the soil are tail at the end of the body that normally is them. We found that even deep down in the oribatid mites; and the variation among held underneath under very high blood soil all of it is made up of invertebrate feces. mites is amazing. The biggest one is the pressure. When attacked, they have a little Most things eat the manure or feces of the size of a period on a printed page; the clamp which releases and catapults the other things The total nutrient content of smallest one is 1/250th of an inch in springtail way up into the air. A springtail the soil is actually of secondary impor- length. There is a long-legged oribatid that may be 1/12th of an inch long can tance. Also of secondary importance is mite. There is a flat-backed, aircraft- jump maybe a yard away. Avery effective whether the nutrients are immobilized in carrier oribatid mite. There are oribatid device. Another springtail is all covered the organic debris or whether theyre im- mites that have great big ostrich plume with scales like the wings of a butterfly. mobilized in the inorganic phase down in feathers all over their bodies. the mineral soil. The critical parameter is Now springtails and oribatid mites are just how dynamic soil-converting processes are. There are about 250,000 oribatid mites in two things in the soil. Any meter of soil In other words, how many dung beetles do every square meter of soil. One is called a has lots and lots of things that live in it. you have in the system, and how many pen-knife oribatid mite. When its at- Bright, red bdellid mites are not only in the species do you have in that system? Now, tacked, it folds up like a turtle. One is what soil. They are used in biological control in when I occasionally teach a lecture to forest I call a stegasaurus oribatid mite. The many parts of the world. In Oregon we use groups in ecology at OSU, the first thing I mite itself is very small and has big, move- them heavily in the pear industry down in do when I come in to the board is I write able flat plates covering the body. Some of Ashland and Medford. There are "BPGT." I write those on the board at the them have basically bombay doors: flex- pseudoscorpions, skunk spiders, centi- beginning of a lecture and I tell everyone at ible wings that they can retract their legs pedes, and snail-feeding beetle. the beginning that they are supposed to be into. One even has a special trap door that able to tell me what that means. Ill tell you comes up and protects the en- what it is and make a long tire bottom of the face, all the story short: "Bug Poop little appendages for eating. Grows Trees." There is another oribatid mite that has a cannon on the side of I want to finish up by giv- the body. It shoots a sticky goo ing you three facts for your when attacked. There is one consideration, because that hides by covering the whole youve probably never top of the body with mud that it thought like a root before. cements on top. I want you to think like a root. The first fact is that Oribatid mites are fungal feed- plant roots are only pas- ers. They eat fungal hypha with sive sponges. They can do great lobster-like claws. A fun- nothing themselves. They gal hypha is like a piece of can do no decomposition; spaghetti with a skeleton on the outside. So the mite has to Continued on page 5 Stilt-legged mite with shed larval skins on back 4 Natural Resource News - Special Edition - August 1993 Denizens. cont. The second solution to that problem is an Nitrogen-fixing bacteria, do something Continued from page 4 incomplete solution: a mycorrhizae. A unique, something that cant be substi- mycorrhizae is a symbiosis between a fun- tuted for. Another example of that is the they can effect no process of nutrient solu- gus and a plant root. The fungus makes an cyanide-producing millipede that is so bility; they can make no chemical change attachment to the plant root and grows out common in western Oregon. All the in the soil. The second point is that soil into the soil. As it grows out into the soil, nutrient transfers take place in the soil chemical transformations—the decompo- the plant pumps fuel into the mychorrhiza itself, from one fecal particle to another sition, the mineralization, and the recy- (sugars fixed in photosynthesis), the my- fecal particle and pass it down that chain cling—are actually caused by the extra- corrhiza dissolves its surroundings, and of succession. But how do you get from a cellular digestion of the secreted enzymes what it doesnt want it sends to the plant dead leaf on the ground to a fecal particle? of bacteria and fungi in the soil. There are root. Well, thats the role of the cyanide-feed- some abiotic changes that take place in the ing millipede in our forest. Theres really soil, freezing and thawing and drying, but There are several living species that live in only one common millipede in that whole those generally take place at times when the soil, each one responding to its own set forest system from southern Alaska all the theyre not terribly useful to the plants. of environmental variables, its own unique way to northern California. Basically The third point is that absorption of nutri- web. We can use that information as every single leaf, both deciduous and co-- ents is directly dependent upon the cells indicator species. If you bring me back a niferous, that falls on the ground, actually surface area In all soils, anywhere you are vial full of soil from an area Ive studied, goes through the gut of that one species of in the world, the surface area of soil mi- I can tell you the time ofyear you took that millipede before it even enters the soil crobes is millions, billions, zillions times sample. I can tell you the stage of forest ecosystem. So there you have one species that of plant roots. Plant roots are at a succession. I can tell you the altitude you that does something that cant really be competitive handicap to get those nutri- took it from. I can tell you the overstory substituted for by anything else. Its a ents. canopy. I can probably tell you something keystone. about the understory canopy. I can tell you So in the real world, how does it work? whether it was from a north-facing slope, There are a few morals Id like you to get. How do plants grow? On the one hand in east-facing slope, etc. If you took it from the real world, you have a plant thats got Sisters and the Ponderosa Pine forest there, First, soils are alive. They are biogenic. a lot of energy from photosynthesis but it I could tell you how far it was from the All the upper layers are in fact nothing but needs nutrients to grow. On the other hand nearest tree trunk, whether that tree trunk living critters or the feces of living crit- you have a soil microbe thats got lots of was alive or dead, or whether it was a ters. nutrients but it needs energy to grow. juniper or a Ponderosa Pine. I can tell you that because of the species composition of Second, soil arthropods are the regulators Now therere two solutions to the problem. that soil community. in most soil processes. They are the sys- The first solution is soil critters—anything tem catalysts that drive the microbial pro- from protozoa to the two-foot long Oregon So the structure of the actual community cesses of chemical excitement. All of earthworm. Nutrients are either pooled in can give useful information if you take the those processes would stop if we didnt dead plant cells in the soil or in the tissue time to decipher. For instance, if you ask have the critters here feeding upon them. of the living microbes themselves. Each what happens if we fumigate stumps to time one of those invertebrates feeds, it control the root rot? What does it do to the Third, soils are by far the most biologi- alters the physical state of those nutrients whole ecosystem? How far does it go out cally diverse part ofany terrestrial ecosys- usually by crunching it up with its jaw. It away from that stump and does it last for tem. exposes those nutrients to new kinds of weeks, months, years, or for decades? What microbes in its own gut. It extracts its own about broadcast burning? Do the effects Fourth, by monitoring the types of diver- little percentage as tax. The invertebrate last for two or three years, five or ten years, sity that are there you can learn how an grows and then it defecates, and for a few twenty years, fiftyyears, one hundred yens? ecosystem is functioning. We can gener- seconds or at most a few minutes there are You can answer those questions with this ate useful information on different time soluble nutrients available to the commu- kind of information. scales and spatial scales that is different nity at large. As soon as theyre grabbed up from what you can learn by looking at soil they are immobilized again. Now remem- The second useful thing I think we can do cores or tree rings. ber everybody in the soil is eating every- is to look at the notion of a keystone body elses pre-packaged resources. This species. Of all the hundreds of species out Last, we need to start to use our eyes and process is going on all the time. Sooner or there, are there some that play a crucial examine the world we live in. We will see later some ofthose nutrients are going to be role in an important ecological pathway? what a really neat world we live in and just released close enough to a root that the root One species that cant be substituted for by maybe we will stop treating soil as if it can grab it. any other? were dirt.

Natural Resource News - Special Edition - August 1993