Higher Plants Review C3 Vs C4 Pathways of Photosynthesis In
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Photosynthetic autotrphs (cont.) Higher plants Review C3 vs C4 pathways of photosynthesis in Figure 6.5 C4 plants are found in warm environments where there is moisture available in summer (monsoonal climates). Quantum yield (QY) – CO2 fixed per photon absorbed changes as a function of temperature in C3 but not C4. At current [CO2]atm, QY of C3 photosynthesis is higher than C4 below 25°C, QY of C4 is higher than C3 above about 25°C. In great plains of N. America, average daily growing season temperature of 25C equates to about 41°N latitude (Ft. Collins, CO). This is crossover point for C3 / C4 dominance in grasses!!! Biochemstry scales to ecosystems!!! This knowledge helps us determine what plant materiels are suitable for revegetation in different habitats and how climate change might affect grassland processes (thru shifts in dominance by C3 vs C4 grasses) CAM (Fig 6.6) – CAM - Separates carboxylation and carbon reduction in time, not space, by storing C4 acid in vacuole (Figure 6.6 in book is misleading!). PEP carboxylase fixes CO2 at night and C4 acid is stored. Next day decarboxylation produces CO2 for Rubisco (normal C3 fixation pathway). Pretty damn cool, right!!! This is an alternative photosynthetic pathway for water conservation. Water-use efficiency is very high because of carboxylation at night (little transpiration!!) Nutrients and plants Some 30 to 40 elements are required by organisms in general. Plants require 16. Macronutrients: C, O, H, N, P, K Micronutrients: S, Ca, Mg, Fe, Mn, Zn, Cu, Mo, B, Cl Next to H2O, nitrogen and phosphorus are soil nutrients that are most limiting to plant growth. Generally plants take up these nutrients from soil solution at root surfaces, either passively in water stream, or actively thru ATP-driven channels. Some plants have very unique ways to get these nutrients: Nitrogen fixing bacteria associated with special structures called nodules on roots of legumes. Mesquite Mycorrhizal associations are effective at extracting phosphorus. (Fungus/root interaction) Carnivorus plants - pitcher plants, sun dew, fly traps... Other Insect harboring leaves of Dischidia major - Borneo, Tresseder et al. 1995, About 40% of plant carbon is from ant respiration, and 30% Nitrogen from decomposition of detritus brought to leaf by ants. Using Organic Molecules for energy needs (Heterotrophs) Herbivores Carnivores Omnivores Detritivores (Monday) Herbivores All organisms that consume plant material; subsist on diets high in cellulose. Getting enough fiber is not a problem for herbivores; getting enough protein is. Most carbohydrates in plant material are locked in indigestible cellulose, and proteins are locked in chemical compounds. Herbivores do not have the enzymes necessary to digest cellulose, so they depend on bacteria and protozoa for these and to synthesize fatty acids, proteins, and vitamins. Most vertebrates carry these bacteria and protozoans in their foregut or hindgut where anaerobic fermentation takes place. Several strategies have evolved to attain required nutrients. Ruminants such as cattle and deer, have specialized anatomically to digest cellulose; specifically, a 4-chambered stomach (rumen, reticulum, omasum, and abomasum). The rumen and reticulum (= foregut) contain bacteria and protozoans and function as fermentation vats; this is where most digestion occurs. Once reduced, the bolus (or cud) is regurgitated, chewed, and passes to the omasum and abomasum (= hindgut). Non-ruminants, such as horses and rabbits, are much less efficient; most digestion takes place in the hindgut. Non-ruminants have simple stomachs and gain some efficiency by having long intestinal tracts that slow the passage of food. Some non-ruminants, such as lagomorphs (rabbits and hares), employ coprophagy to increase the amount of nutrients they can extract from food. They eject two types of pellets (soft and hard), of which soft pellets are higher in protein, and are reingested. Carnivores Organisms that consume muscle (first-level carnivores or second- level consumers consume herbivores). First-level carnivores provide energy for second-level carnivores. As the feeding level of carnivores increases, their numbers decrease and their fierceness, agility, and size tend to increase. The major concern for carnivores is to obtain sufficient food. Their food is similar to their own flesh and is easily assimilated. Omnivores Consume energy from more than one trophic level. Detritivores (next time).