Biodiversity Laboratory Agroecosystems and Agricultural Biodiversity Objectives: 1) To compare processes occurring in natural ecosystems with those of agroecosystems; 2) To become familiar with some important agronomic plants; 3) To assemble a collection of specimens to illustrate principles discussed. 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 Ecosystem (tons/acres/year) 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.
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Major Themes Covered During Our Field Walk Principles of Ecological Succession Applied to Agroecosystems
Nutrient Cycles and Resource Flows: Natural vs. Agricultural Ecosystems
Evolutionary Innovation: Woody vs. Herbaceous Stems
Evolutionary Innovation: C4 Photosynthesis and the Prominence of Maize
Evolutionary Innovation: Insect Pollination vs. Wind Pollination
Plants as Indicators of Soil Conditions
Herbaceous Plant Lifecycles: Annuals vs. Biennials vs. Perennials
Types of Herbaceous Root Systems: Taproot vs. Fibrous vs. Prop
Importance of Legumes in Agroecosystems
“All Flesh Is Grass” and Importance of the Rumen in Agriculture
Importance of Cover Crops in Agroecosystems
Types of Weed Control: herbicide (glyphosate) vs. tillage vs. permanent mulch
Taxonomic Under-representation of Crop Plants
Differences Between Straw and Hay for Making Compost
Native vs. Introduced Species
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Species Lists Table 2: Characteristics of Cover Crops and Weeds Common Name
Scientific Name
Plant Family
Plant Lifecycle
Native or Introduced
Alfalfa
Medicago sativa
Legume
perennial
introduced
Aster
Aster spp.
Composite
perennial
native
Canada
Erigeron canadensis
Composite
annual
native
Canada thistle
Cirsium spp.
Composite
perennial
native
Clover,
Trifolium pratense
Legume
perennial
introduced
Trifolium repens
Legume
perennial
introduced
Crabgrass
Digitaria spp.
Grass
annual
introduced
Dandelion
Taraxacum officinale
Composite
perennial
introduced
Evening
Oenothera biennis
Evening
biennial
native
Comments
fleabane
red Clover, white
primrose
primrose
Foxtail
Setaria spp.
Grass
annual
introduced
Goldenrod
Solidago spp.
Composite
perennial
native
Hairy vetch
Vicia villosa
Legume
perennial
introduced
Lambsquarters
Chenopodium album
Lambs-
annual
native
quarters Oats
Avena fatua
Grass
annual
introduced
Quackgrass
Agropyron spp.
Grass
perennial
introduced
Ragweed
Ambrosia spp.
Composite
annual
native
Timothy-grass
Phleum pratense
Grass
perennial
introduced
Wild
Daucus carota
Carrot
biennial
introduced
Wild parsnip
Pastinaca sativa
Carrot
biennial
introduced
Witchgrass
Panicum spp.
Grass
annual
native
carrot
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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
Beet
Beta vulgaris
Lambsquarter
Broccoli
Brassica oleracea
Brassica
Cabbage
Brassica oleracea
Brassica
Carrot
Daucus carota
Carrot
Cauliflower
Brassica oleracea
Brassica
Celery
Apium graveolens
Carrot
Cucumber
Cucumis sativus
Cucurbit
Endive
Cichorium spp.
Composite
Kale
Brassica oleracea
Brassica
Lettuce
Lactuca sativa
Composite
Maize, dent
Zea mays
Grass
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
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Agroecosystem Field Trip Activities
1. Assemble collection of leaves of members of the Brassica family to illustrate its diversity. 2. Use potato fork to lift some tubers without damaging them. 3. Use digging fork to open up compost pile to show different stages of decomposition within it. 4. Use a spade to dig a simple soil pit to demonstrate layering of soil. 5. Use digging fork to lift storage roots, leaving storage root intact. 6. Collect specimens to demonstrate different types of root systems. 7. Assemble collection of plants of Legume family to illustrate its diversity, and use digging fork to lift roots to show example of nitrogen-fixing root nodules. 8. Assemble collection of fruits and seeds of Legume family to illustrate its diversity. 9. Assemble collection of different types of fruits of Nightshade family to illustrate its diversity. 10. Assemble collection of different types of fruits of Cucurbit family to illustrate its diversity. 11. Assemble plant collection of different members of Lambsquarters family to illustrate its diversity. 12. Assemble plant collection of different members of Grass family to illustrate its diversity 13. Assemble collection of biennials to show difference between first-year plants and second-year plants. 14. Assemble a plant collection showing differences between an herbaceous perennial and a woody perennial. 15. Assemble a collection to show differences between wind-pollinated flowers and insect-pollinated flowers. 16. Show the class the difference between straw and hay with respect to making compost.
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STUDY QUESTIONS 1) What is one reason why agroecosystems are capable of attaining higher levels of net primary production than found in natural forest ecosystems? 2) What physiological mechanism of the maize plant is responsible for it ascending to such an important prominence in American agriculture? Please explain. 3) Which stages of ecological succession are represented in most agroecosystems? 4) How are nutrient cycles and resource flows in agroecosystems similar to those in natural ecosystems? How are they different? 5) How do nutrient cycles and resource flows in conventional agroecosystems differ from those in organic agroecosystems? 6) Why does the ability of a plant to produce a woody stem represent an evolutionary innovation? What is the advantage of producing a woody stem compared to producing an herbaceous stem? 7) Why does the ability of a plant to attract insect pollinators represent an evolutionary innovation? What is the advantage of employing insect pollinators compared to employing wind pollination? 8) What are the differences among the following plants: annuals, biennials, and perennials? 9) Is it possible to have a woody annual or woody biennial? Please explain. 10) What are the differences among taproot, fibrous, and prop root systems? 11) Why are legumes important to agroecosystems, particularly organic agroecosystems? 12) What is meant by the phrase “All flesh is grass?” 13) How and why are cover crops used in agroecosystems, particularly organic agroecosystems? 14) What are advantages and disadvantages of controlling weeds using herbicide? Using tillage? Using permanent mulch? 15) Is the diversity of crop plant families representative of the diversity of the Plant Kingdom in general? Please explain. 16) How well are native plants represented in most agroecosystems? Please explain.
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