Biodiversity Laboratory Measuring Impacts on Soil Biodiversity in Agroecosystems Objectives: 1) To compare processes occurring in natural ecosystems with those of agroecosystems; 2) To become familiar with some important agronomic plants; 3) To become familiar with methods of ecological sampling; 4) To compare soil invertebrate and soil seed bank diversity among different agricultural land uses. Introduction Whether or not farmers realize it, crops and agricultural soils are subject to the same ecological principles that operate in nature. To understand the impact of agriculture on biodiversity, we will consider ecological processes occurring in a forest setting relatively undisturbed by humans, and compare them to similar processes occurring in three different agroecosystems. We will also discuss various characteristics of plants involved in agroecosystems. In nature plants grow by intercepting the energy of sunlight, using it to convert carbon dioxide and water to plant biomass. The amount of biomass produced represents the net primary production of the ecosystem. A portion of this biomass is transformed as it passes through subsequent trophic levels of the ecosystems, first into herbivores (animals (or pathogens) that kill and eat plants), and then into carnivores (animals that kill and eat other animals). Furthermore, at each step in the food chain, scavengers and detritivores (animals, such as earthworms, and microorganisms that eat dead organic matter) may shunt some of the biomass into their bodies and ultimately back to the atmosphere in the form of carbon dioxide and water through the process of decomposition. The following table compares the amount of biomass produced in a typical forest ecosystem to a few different agroecosystems: Table 1: Typical Above-ground Annual Biomass Production Occurring in Northeastern U.S. Dry Matter (tons/acres/year) Ecosystem Deciduous forest ~ 2.0 Potatoes* 1.7 2.8* Grass hay 3.6 4.2 Alfalfa hay 5.4 6.3 Silage corn 6.0 8.8 * corresponds to biomass of tubers It is clear from Table 1 that agroecosystems are capable of producing comparable or higher biomass yields than typical forest ecosystems of the same region. Agroecosystems are able to attain such high levels of primary production through careful management of the mineral nutrients provided to crop plants. There are four sources of mineral nutrients in natural ecosystems, 1) weathering of rock, 2) atmospheric deposition of dust, 3) fixation of atmospheric nitrogen by soil microbes, and 4) decomposition of the remains of plants, animals, and microorganisms in the soil. By far the largest source of minerals on an annual basis in natural ecosystems comes from decomposition. Thus, in natural ecosystems, recycling of minerals previously used by organisms is the most important source of nutrition for subsequent plant growth. In agroecosystems, conventional farmers supplement the natural sources of mineral nutrients with the addition of chemical fertilizers and, to a lesser extent, manure, if available. This is necessary because harvesting the crop removes large amounts of minerals from the agroecosystem. Organic farmers, in contrast, do not use chemical fertilizers, but work to conserve the natural sources of minerals, which they enhance through the addition of organic wastes and rock powders, and through the use of crop rotations that maximize atmospheric nitrogen fixation. In addition, organic farmers maintain high levels of organic matter in the soil, which prevents loss of minerals by the leaching action of rainfall and irrigation water that percolates through the soil. Soil Biodiversity Study Page 1
Major Themes Covered During Our Field Walk Evolutionary Innovation: C4 Photosynthesis and the Prominence of Maize Stages of Ecological Succession Nutrient Cycles and Resource Flows Evolutionary Innovation: Woody vs. Herbaceous Stems Evolutionary Innovation: Insect Pollination vs. Wind Pollination Plants as Indicators of Soil Conditions Herbaceous Plant Lifecycles: Annuals, Biennials, and Perennials Types of Herbaceous Root Systems: Taproot vs. Fibrous Importance of Legumes in Agroecosystems All Flesh Is Grass and Importance of the Rumen in Agriculture Importance of Cover Crops Allelopathy in Oats Taxonomic Under-representation of Crop Plants Native vs. Introduced Species Soil Biodiversity Study Page 2
Species Lists Table 2: Characteristics of Cover Crops and Weeds Common Name Scientific Name Plant Lifecycle Native or Introduced Alfalfa Medicago sativa perennial introduced Comments Aster Aster spp. perennial native Canada fleabane Erigeron canadensis annual native Canada thistle Cirsium spp. perennial native Clover, red Trifolium pratense perennial introduced Clover, white Trifolium repens perennial introduced Crabgrass Digitaria spp. annual introduced Dandelion Taraxacum officinale perennial introduced Evening primrose Oenothera biennis biennial native Foxtail Setaria spp. annual introduced Goldenrod Solidago spp. perennial native Hairy vetch Vicia villosa perennial introduced Horsetail Equisetum spp. perennial native Lambsquarters Chenopodium album annual native Oats Avena fatua annual introduced Quackgrass Agropyron spp. perennial introduced Ragweed Ambrosia spp. annual native Timothy-grass Phleum pratense perennial introduced Wild carrot Daucus carota biennial introduced Wild parsnip Pastinaca sativa biennial introduced Witchgrass Panicum spp. annual native Soil Biodiversity Study Page 3
Table 3: Families of Garden Plants (Note that all are annuals, and all have been introduced to North America except for maize and sunflower, which are natives) Common Name Scientific Name Plant Family Comments Beet Beta vulgaris Lambsquarter Broccoli Brassica oleracea Brassica Cabbage Brassica oleracea Brassica Cauliflower Brassica oleracea Brassica Cucumber Cucumis sativus Cucurbit Endive Cichorium spp. Composite Kale Brassica oleracea Brassica Lettuce Lactuca sativa Composite Maize, popcorn Zea mays Grass Maize, sweet corn Zea mays Grass Mustard Brassica spp. Brassica Onion Allium spp. Onion Pepper Capsicum annuum Nightshade Potato Solanum tuberosum Nightshade Pumpkin Cucurbita spp. Cucurbit Radish Raphanus sativus Brassica Snap bean Phaseolus vulgaris Legume Soy bean Glycine max Legume Squash, winter Cucurbita spp. Cucurbit Sunflower Helianthus annuus Composite Swiss chard Beta vulgaris Lambsquarter Tomato Solanum lycopersicum Nightshade Soil Biodiversity Study Page 4
Overview: Sampling for Soil Invertebrates and the Soil Seed Bank Field biologists measure biodiversity using a variety of methods to identify areas of richer or poorer diversity. In this study, we will use the Berlese-Tullgren method of sampling tiny invertebrate soil-inhabiting animals, such as earthworms and centipedes. These soil invertebrates are extremely important to the decomposition processes that take place in the soil. Once we have separated the invertebrates from the soil (this will take about three weeks), we will measure the soil seed bank, which is the number of viable seeds contained in the soil. We will quantify the soil seed bank after incubating the soil under conditions favorable for the germination of the seeds it contains. We will use data gathered from our soil samples to quantitatively compare soil biodiversity among the different agricultural cropping systems. Sampling methods will be employed in a manner that ensures an unbiased random sample that is representative of the true diversity of the area studied. It is also important to replicate the sampling process in order to assess how thorough our sampling has been. Soil Sampling We will obtain soil samples from the following natural ecosystem and three agroecosystems: 1) a climax forest dominated by white ash, hop hornbeam, and sugar maple; 2) an organically managed mixed-crop vegetable garden; 3) an organically managed permanent pasture hay field dominated by timothy-grass, red clover, and wild carrot; and 4) a monoculture stand of silage corn grown with the use of herbicides. The class will divide into four teams, one for each ecosystem type. Each team will obtain four replicate samples collected at random at their ecosystem type. Each replicate sample will consist of a composite of three (3) soil cores taken at random for the respective sampling site. Members of other teams will assist their colleagues in obtaining the soil cores for the composite samples. We will use a bulb planter rotated into the soil to its full capacity (roughly 10cm long x 6cm diameter) for removing soil cores. To collect a sample, a sampling orb is randomly tossed over the shoulder into the sampling area to mark the location of the sample. A soil core is removed from that point, and placed in a labeled plastic bag. Cores are taken by two other helpers to obtain a total of three cores, all of which are placed in an appropriately labeled plastic bag. The following table illustrates the sampling regime and indicates how to label samples for one of the ecosystem types: Table 4: Sampling Regime for Soil Biodiversity Study. Ecosystem Type Label for Replicate Samples CF 1 Cores Required/Replicate CLIMAX FOREST SAMPLES CF 2 CF 3 CF 4 Use the following label abbreviations for the agroecosystem types: Vegetable garden: VG Permanent pasture: PP Monoculture corn: MC Soil Biodiversity Study Page 5
Setting Up a Berlese Funnel to Obtain Soil Invertebrates 1) We will use one Berlese-Tullgren funnel per replicate sample. To fill, temporarily place the funnel in a large beaker, which will serve to catch any soil falling through the funnel. 2) Place the soil sample carefully into the funnel so as to minimize the amount of soil that falls through the screen. Transfer the funnel to the stand, placing the large beaker underneath the stand, to capture any soil that may continue to fall out during the set-up procedure. 3) Make up two labels, both of which include your name and the sample name. One label will go on the Berlese funnel, and other label will go on a collection vial. 4) Fit a labeled collection vial filled 3/4ths full with preservative to the bottom opening of the funnel, and secure it with tape. Once the sample vial is in place, you need to take great care that as little soil as possible falls into the vial. If a lot of soil ends up in the vial, it will make your life miserable when we sort through the assortment of animals collected in the vial!! 5) Return to the funnel any soil that has fallen into the beaker during the set-up procedure, taking care to handle the funnel as gently as possible. 6) Lastly, fit the funnel with a lamp, securing the lamp to funnel with two metal clamps. WORK GENTLY!! Over the following three weeks the heat from the lamp will gradually dry out the soil in the funnel from top to bottom. As the soil animals move downward to escape the drying conditions, they will eventually fall into the preservative vial attached below the funnel. Soil Seed Bank Sample Preparation When the above drying process has finished, we will transfer the soil in the Berlese funnel to a plastic tray that will be placed in the greenhouse under conditions that will encourage the germination of seeds present in the soil samples. 1) Remove the label with your name and sample name from the Berlese funnel, and place it on a green plastic growing tray. 2) Empty the soil from the funnel into the labeled green tray. 3) We will incubate the seeds for two weeks, and then collect data on the seedlings that develop. Soil Biodiversity Study Page 6