PRODUCERS

1. PRODUCERS READINGS: FREEMAN, 2005 Chapter 54 Pages 1229-124

2. Producers are autotrophs. • Autrotrophs are organisms that can make their own food - complex organic molecules - from CO2. • Such organisms include green plants and cyanobacteria (blue-green algae). • These organisms use the energy of the sun to produce their own food from CO2 and H2O. • Ecologists call these organisms producers.

3. Producers and Photosynthesis • The carbon (C) in organic molecules is found at very low concentrations in the atmosphere. • The process by which producers use CO2 to make organic molecules is called photosynthesis.

4. An Overview of Photosynthesis SUNLIGHT (H20)12 • Beginning in the 1770s experiments showed that the green parts of plants in the presence of sunlight, water, and carbon dioxide could release oxygen. • By the 1840’s it was known that carbohydrates (sugars) were produced and a rough formula for photosynthesis could be written. (CO2) 6 C6H1206 (H20)6 (O2)6

5. Conversion of Light Energy into Chemical Bond Energy • Photosynthesis concerts light energy into chemical bond energy by adding carbon, oxygen and hydrogen atoms to existing 5 carbon compounds • This process increases plant mass, as measured by dry weight (biomass). • Many other biomolecules and mineral elements are required for biomass production.

6. Photosynthesis Takes Place in Chloroplasts • At the plant level, photosynthesis takes place primarily in the leaf. • Each leaf contains millions of chloroplasts. • The chloroplast is the site of photosynthesis.

7. Summary of Photosynthesis • Green plants use light energy to convert carbon dioxide and water into sugar and oxygen. • Sugars produced in photosynthesis are converted into biomolecules that make up the dry weight (biomass) of a plant. • In short, plants are able to make themselves (organic molecules) from inorganic molecules (carbon dioxide and water).

8. Atoms, Biomass and Nutrients • C,H,O,N are the major atomic building blocks of living things. Their rank order of mass is: 0 > C >> H > N >> 50 or so others • A comparison of biomass with the make-up of the earth leads to the conclusion that life forms concentrate certain atoms.

9. ATOMIC COMPOSITION OF VASCULAR PLANTS • Recalling that biomass refers to dry weight, around 90% of plant biomass comes from carbon dioxide (CO2) in the air. • H from water is the most abundant atom, but it is only 6% of plant dry weight (biomass).

10. ESSENTIAL PLANT NUTRIENTS • Macronutrients (those that make up 0.1% or more of biomass and, thus, required in relatively large quantities): O, C, H, N, K, Ca, Mg, P, S, (SI) • Micronutrients (those that make up 0.01% or less of biomass and, thus, required in small quantities): CI, Fe, Mn, Zn, B, Cu, Mo, Ni, (Na), Co?, (Se)? See Table 37.1 on page 854 In Freeman (2005) for a more complete description of essential nutrients

11. Phosphorus Deficiency in Corn • Phosphorous in the form of phosphate is a major ingredient in plant fertilizers. • P deficient plants may remain greener than normal and develop a purple discoloration on leaves. • Phosphate is an important constituent of DNA, RNA, ATP, and NADP.

12. Nitrogen Deficiency in Corn • Nitrogen deficiency results in young plants that are stunted in growth and pale green to yellow. • N deficiency that occurs later results in a yellowing of the lower leaves. • N is an important element in amino acids (proteins) and nucleic acids (DNA. RNA, ATP, NADP).

13. Nitrogen (N) is the 4th major contributor to biomass. • The element nitrogen (N) makes up about 6% of plant dry weight. • Nitrogen (N2) is approximately 80% by volume of the atmosphere. Yet, plants can not take in and utilize N2 by way of leaves. • Only bacteria are able to fix and convert atmospheric nitrogen (N2) into forms that plants can use - ammonia (NH3) or nitrate (NO3) .

14. SOIL • Soil is the environment that provides the mineral nutrients for plant growth and development. • It is a complex of inorganic particles, organic materials and living and dead organisms. • During the process of soil development, the residues of plants, microbes and animals return more than the green plants take away.

15. Soil Testing for Plant Nutrients • Soil testing for macronutrients is a common practice among gardeners and agriculturists. • Simple soil test kits give crude determination of N, P and K. The major ingredients of fertilizers.

16. SOIL NITROGEN • Stores of soil nitrogen can be quite high. Total N can reach 760 gN/m 2 in a tallgrass prairie. Rich forest soils can be as high as 550 gN/m 2 . • Two sources of nitrogen are lightning and nitrogen-fixing bacteria.

17. NITROGEN FIXATION AND LEGUMES • Nitrogen fixation occurs when certain bacteria convert dinitrogen (N2) into ammonium (NH4+) . • Legumes are a large family of plants that form a mutualism with nitrogen fixing bacteria.

18. Plant biomass increases as N increases and then levels off. • Plants of Old Field Goldenrod were grown in pots that contained total soil N that varied from150 to 1650 mg N / kg of dry soil. • Higher soil nitrogen yielded greater plant biomass up to about 1000 mg N / kg of soil and then biomass remained more or less constant.

19. Intraspecific Competition for Nitrogen • Since nitrogen is an important nutrient resource, one might expect that individuals compete for N. • These experimental results confirm this prediction. • Note that high density plants remain small at all N levels. Why?

20. Interspecific Competition for Nitrogen • The same experimenters examined two more species: stiff golden rod (top) and little bluestem. • Of the three, stiff golden reached maximum size at lowest N concentration; little bluestem at highest. • What would you predict concerning the outcome of interspecific competition between stiff golden rod and little bluestem?

21. MAJOR FACTORS THAT INFLUENCE PRODUCTION • As we have seen, nutrient availability can influence production as measured by biomass or seed set. • Given the importance of water in photosynthesis, it is also a major factor in influencing production. • Lastly temperature, particularly associated with day length and seasonality, influences production.

22. PRECIPITATION AND PRODUCTION • The effect of precipitation (water) is seen as one travels from east to west through the NA grassland biome. • The tallgrass prairies of Illinois (top) receive about 36 inches per year. • Those of western Kansas only about 15 inches.

23. BIOMASS AS A MEASURE OF PRODUCTION • Biomass is a universal measure of production. • The change in weight of a cactus plant over a year can be used as a measure of production. • Also, the change in weight of vegetation in a square meter of a desert from one year to the next can be used as a measure of production.

24. NET PRODUCTION • All plants not only increase in mass through photosynthesis, but like other living things they use some of that stored energy for respiration. • That which goes unused is called net production.

25. NET PRODUCTION, GROSS PRODUCTION & RESPIRATION • Plants accumulate matter (and energy) through photosynthesis (gross production). • Plants use matter (and energy) during respiration (respiration). • Net production = Gross production - Respiration • Production (Gross or Net) is either expressed in units of mass (g /m2 /year) or energy (kcal /m2 /year).

26. MEASURING NET PRODUCTION • Field measurement of net production entails random plot assignment, clipping and sorting vegetation, drying and weighing plant material. • Data is often reported as grams of biomass per square meter per year.

27. Net production can be used to answer a variety of experimental questions. • Question: Does fall burning decrease net production in a prairie community? • Null Hypothesis: No difference between burned and unburned plots. • Method: Burn a random sample of plots; do not burn a random sample. • Conclusion: Reject null hypothesis. Results suggest that burning actually increases net production. Why?

28. NET PRODUCTION IN SOME MAJOR BIOMES Net Production / Unit Area (grams/meter 2 /year)

29. PRODUCERS READINGS: FREEMAN, 2005 Pages 1229-1242