BIOL 4120: Principles of Ecology Lecture 20: Nutrient Regeneration in Terrestrial and Aquatic Ecosystems

1. BIOL 4120: Principles of Ecology Lecture 20: Nutrient Regeneration in Terrestrial and Aquatic Ecosystems Dafeng Hui Office: Harned Hall 320 Phone: 963-5777 Email: dhui@tnstate.edu Bread grow mold Grandma and wolf Bread grow mold Grandma and wolf

2. 20.3 Rates of Decomposition and influencing factors Rate at which nutrients are made available to primary producers is determined largely by rate of decomposition. influenced by: temperature, moisture, chemical compositions of leaves Decomposers

3. Spartina was introduced in China (sediments purpose) and become an invasive species now.Spartina was introduced in China (sediments purpose) and become an invasive species now.

4. Figure 21.8Figure 21.8

5. Figure 21.9Figure 21.9

6. 20.4 Nutrient regeneration can follow many paths As we have seen, organic detritus is consumed by many types of organisms in soil, including invertebrates, bacteria, saprotrophic fungi, and mycorrhizal fungi. Various micro­organisms and plants compete for the inorganic nutrients released by decomposition. As a result, the pathways of nutrient cycling can be extremely complex ( Figure 24.9). The first step in decomposition is the breakdown of large organic polymers such as structural carbohydrates, lignin, proteins, and DNA into their monomeric subunits, including amino acids and nucleic acids. As we have seen, microorganisms secrete enzymes and other reactive sub­stances to accomplish this goal. Ecologists consider depo­lymerization to be the rate- limiting step in the decomposi­tion of detritus and, consequently, the limit on the overall productivity of terrestrial ecosystems. Microorganisms can degrade the organic monomers produced by depolymerization to inorganic forms when their intake of nutrients exceeds their requirements. When microorganisms incorporate inorganic nutrients into their own organic structures, those nutrients are removed from the available pool in the soil— a process known as immobilization— until the microorganisms die and are decomposed or are eaten by other consumers and digested. As we have seen, organic detritus is consumed by many types of organisms in soil, including invertebrates, bacteria, saprotrophic fungi, and mycorrhizal fungi. Various micro­organisms and plants compete for the inorganic nutrients released by decomposition. As a result, the pathways of nutrient cycling can be extremely complex ( Figure 24.9). The first step in decomposition is the breakdown of large organic polymers such as structural carbohydrates, lignin, proteins, and DNA into their monomeric subunits, including amino acids and nucleic acids. As we have seen, microorganisms secrete enzymes and other reactive sub­stances to accomplish this goal. Ecologists consider depo­lymerization to be the rate- limiting step in the decomposi­tion of detritus and, consequently, the limit on the overall productivity of terrestrial ecosystems. Microorganisms can degrade the organic monomers produced by depolymerization to inorganic forms when their intake of nutrients exceeds their requirements. When microorganisms incorporate inorganic nutrients into their own organic structures, those nutrients are removed from the available pool in the soil— a process known as immobilization— until the microorganisms die and are decomposed or are eaten by other consumers and digested.

7. Mineralization, immobilization and net mineralization rate Mineralization: a process that microbial decomposers –bacterial and fungi- transform nitrogen and other elements contained in organic matter compounds into inorganic (or mineral) forms. Organic N? ammonia (waste product of microbial metabolism) Immobilization: uptake and assimilation of mineral nitrogen by microbial decomposer. N used by microbes to grow Net mineralization rate: different between the rate of mineralization and immobilization

8. Pathways of decomposition in soils shift depending on the relative availability of inorganic nutrients. For example, in nitrogen- poor soils, both microorganisms and plants tend to use amino acids as a nitrogen source. Because nitrogen is in short supply, microorganisms do not pro­duce much ammonium or nitrate as a waste product of their metabolism. In soils with higher concentrations of nitrogen, microorganisms produce more ammonium and nitrate in microsites with high nitrogen availability, but plants and microorganisms in low- nitrogen micro­sites nearby compete intensely for this resource. At even higher levels of nitrogen availability, nitrogen ceases to limit growth, and microorganisms metabolize much of the organic nitrogen in amino acids to nitrate, which can be taken up directly by plants. Thus, with increasing levels of nitrogen in the soil, the primary source of nitrogen for plants shifts from amino acids and other small organic compounds to ammonium and, finally, to nitrate. In addi­tion to shifting the system between nutrient cycling path­ways, nutrient addition ( fertilization) often increases the overall rate of decomposition of organic matter because fertilization supports the growth of populations of bacteria and fungi. Pathways of decomposition in soils shift depending on the relative availability of inorganic nutrients. For example, in nitrogen- poor soils, both microorganisms and plants tend to use amino acids as a nitrogen source. Because nitrogen is in short supply, microorganisms do not pro­duce much ammonium or nitrate as a waste product of their metabolism. In soils with higher concentrations of nitrogen, microorganisms produce more ammonium and nitrate in microsites with high nitrogen availability, but plants and microorganisms in low- nitrogen micro­sites nearby compete intensely for this resource. At even higher levels of nitrogen availability, nitrogen ceases to limit growth, and microorganisms metabolize much of the organic nitrogen in amino acids to nitrate, which can be taken up directly by plants. Thus, with increasing levels of nitrogen in the soil, the primary source of nitrogen for plants shifts from amino acids and other small organic compounds to ammonium and, finally, to nitrate. In addi­tion to shifting the system between nutrient cycling path­ways, nutrient addition ( fertilization) often increases the overall rate of decomposition of organic matter because fertilization supports the growth of populations of bacteria and fungi.

9. Chemical compositions of leaves in response to nutrients C:N ratio low C:N ratio – high protein level High C:N ratio – low in proteins, high in lignin and secondary metabolites Leaf C:N ratio is influenced by nutrients availability in the environment Leaf C:N ratio influences decomposition rate and interactions with herbivores Nutrient requirements for compensatory growth Need to mention herbivores or not? Grazer can sense the quality of leaf (C:N ratio).Need to mention herbivores or not? Grazer can sense the quality of leaf (C:N ratio).

10. Figure 21.12. when leaf N content is high, N mineralization rate is high. If the rate is higher than immobilization rate, then no net N accumulation observed.Figure 21.12. when leaf N content is high, N mineralization rate is high. If the rate is higher than immobilization rate, then no net N accumulation observed.

11. Na: Mike Kasper (OU): litter decomposition inlfuenced by NaCL, tropic, PNAS 2009, latest issue Na: Mike Kasper (OU): litter decomposition inlfuenced by NaCL, tropic, PNAS 2009, latest issue

12. Some kinds of fungi grow on the surfaces of, or inside, the roots of plants. This symbiotic association of fungus and root is called a mycorrhiza ( plural, mycorrhizae; liter­ally, “ fungus root”). Mycorrhizae enhance a plant’s ability to extract less soluble nutrients, such as phosphorus, from soil and may greatly increase primary production, espe­cially on poor soils. Two principal forms of mycorrhizae are recognized: arbuscular mycorrhizae ( AM) and ectomychor­rhizae ( EcM). AM fungi penetrate cell walls in root tis­sue and form vesicles or branched structures in intimate contact with root cell membranes. The name arbuscular, meaning “ treelike,” refers to the branched structures pen­etrating the root. AM are formed only by fungi in the taxonomic division Glomeromycota and are typically associated with the roots of herbaceous species, including many crop plants. EcM fungi are commonly associated with woody plants. They form a dense sheath around the outsides of small roots and penetrate the spaces between the cells of the root cortical layer ( Figure 24.7). Most EcM fungi belong to the divisions Basidiomycota ( typical mush­rooms) and Ascomycota ( morels and truffles, for exam­ple). Other specialized forms of non- AM fungi associated with orchids penetrate the walls of root cells, but do not form sheaths. Mycorrhizae occur everywhere, but they promote plant growth most strongly in soils that are relatively depleted of nutrients ( Figure 24.8). Mycorrhizae increase a plant’s uptake of minerals by penetrating a greater volume of soil than the roots could accomplish alone and by increasing the total surface area available for nutrient assimilation. In addition, because the fungi secrete enzymes and acid ( hydrogen ions) into the surrounding soil, mycorrhizae are more effective than plant roots alone at extracting certain inorganic nutrients from the soil. Mycorrhizae, especially EcM forms, may also protect plant roots from disease by physically excluding pathogens or by producing anti­biotics ( antibacterial toxins). The main advantage of this association for the fungi appears to be that they gain a reliable source of organic carbon in the form of simple sugars transported from the leaves to the roots of their host plants. Some kinds of fungi grow on the surfaces of, or inside, the roots of plants. This symbiotic association of fungus and root is called a mycorrhiza ( plural, mycorrhizae; liter­ally, “ fungus root”). Mycorrhizae enhance a plant’s ability to extract less soluble nutrients, such as phosphorus, from soil and may greatly increase primary production, espe­cially on poor soils. Two principal forms of mycorrhizae are recognized: arbuscular mycorrhizae ( AM) and ectomychor­rhizae ( EcM). AM fungi penetrate cell walls in root tis­sue and form vesicles or branched structures in intimate contact with root cell membranes. The name arbuscular, meaning “ treelike,” refers to the branched structures pen­etrating the root. AM are formed only by fungi in the taxonomic division Glomeromycota and are typically associated with the roots of herbaceous species, including many crop plants. EcM fungi are commonly associated with woody plants. They form a dense sheath around the outsides of small roots and penetrate the spaces between the cells of the root cortical layer ( Figure 24.7). Most EcM fungi belong to the divisions Basidiomycota ( typical mush­rooms) and Ascomycota ( morels and truffles, for exam­ple). Other specialized forms of non- AM fungi associated with orchids penetrate the walls of root cells, but do not form sheaths. Mycorrhizae occur everywhere, but they promote plant growth most strongly in soils that are relatively depleted of nutrients ( Figure 24.8). Mycorrhizae increase a plant’s uptake of minerals by penetrating a greater volume of soil than the roots could accomplish alone and by increasing the total surface area available for nutrient assimilation. In addition, because the fungi secrete enzymes and acid ( hydrogen ions) into the surrounding soil, mycorrhizae are more effective than plant roots alone at extracting certain inorganic nutrients from the soil. Mycorrhizae, especially EcM forms, may also protect plant roots from disease by physically excluding pathogens or by producing anti­biotics ( antibacterial toxins). The main advantage of this association for the fungi appears to be that they gain a reliable source of organic carbon in the form of simple sugars transported from the leaves to the roots of their host plants.

13. Plant roots and mycorrhizal fungi Fungi assist the plant with the uptake of nutrient from the soil (extended water and nutrients absorption) Plant provides the fungi with carbon, a source of energy. Another mutualism formed with plant root and fungi Another mutualism formed with plant root and fungi

15. 20.6 Key ecosystem processes influence the rate of nutrient cycling Primary productivity determines rate of nutrient transform from inorganic form to organic form (nutrient uptake) Decomposition determines the rate of transformation of organic to inorganic form (N mineralization) Rates of these two determine the internal cycling At Ecosystem level, nutrient cycling is determined by two key ecosystem processes.At Ecosystem level, nutrient cycling is determined by two key ecosystem processes.

16. Tropic forest? Tropic forest?