Readings

1. Readings • Chapter 13 textbook • Van Breeman, N., and Finzi, A. 1998. Plant-soil interactions: ecological aspects and evolutionary implications. Biogeochemistry 42:1-19. (online journal, UNR library website) • Beisner, B., D. Haydon, and K. Cuddington. 2003. Alternative Stable States in Ecology. Frontiers in Ecology and the Environment 2003 1(7): 376-382. (on reserve in FA library)

2. Changes to schedule • Today: Nutrient cycling and plant-soil interactions • Lab tomorrow • Return exams, discuss. • Lecture – disturbance and succession • Lecture and discussion – state and transition models

3. Exam stats • Exams are graded; I would like to check them over one more time. Return tomorrow. • Range: 51% to 93% • Average 70.4% • Additional assignment for those who are not happy with their grade: reduce midterm value to 15% final grade, new assignment 15%.

4. Outline • Plant nutrition, macro- and micro-nutrients • Nutrient availability: soil chemistry, biotic effects, and litter decomposition • Nutrient cycling and plant-soil interactions • Transfer of nutrients among ecosystems • Example of nutrient transfer: marine derived nitrogen and phosphorus in forest ecosystems • Ecosystem stability

5. Plant nutrition • Mineral nutrients (elements) divided into groups based on amounts required: Text p. 335. • Macronutrients (C, O, H, N, K, Ca, P, Mg, Su) • Micronutrients (Fe, Cl, Cu, Mn, Zn, Mo, B, trace Na and Co) • Macronutrients major components of important structural/metabolic molecules, or stomatal control (K) • Micronutrients used in less common molecules or for coenzymes (catalysts) • Adaptations for low nutrient habitats: carnivory, symbioses, nutrient “banking”, sclerophylly, efficient use, efficient resorption

6. Nutrient availability • Most plant mineral nutrition from soil • Some absorption/dry deposition from atmosphere • Nutrient pools: states of nutrients in soils • Organic • Exchangeable • Sorbed (adhered to soil particles) • Locked in minerals • Flux of nutrients in nutrient pools affected by chemical and biological processes

7. Abiotic processes • Weathering: process by which exposed geological substrates are converted to soils. • Rate of weathering, nutrients released, and type of minerals formed affect nutrient pools and availability (different soil structure and chemistry formed by different weathering patterns) • e.g. serpentine soils: nutrients not readily available, uptake difficult; plants become nutrient limited. • E.g. high Fe and Al soils – phosphate adsorbed and less available. • Fire: volatalization, nutrient release as soluble ash, change in pH and wettability, potential for leaching

8. Abiotic processes cont. • Fire: volatalization, nutrient release as soluble ash, change in pH and wettability, potential for leaching • Leaching: movement of nutrients dissolved in water. • Can come from leaves to soil (increasing concentrations) • Can come from shallow soil to deep (decreasing concentrations) • Atmospheric deposition: trace gasses and atmospheric aerosols trapped in clouds, deposited in precipitation or as dry deposition. Can be substantial nutrient input. • Precip may become acid and cause plant damage.

9. Biological processes • Plants alter soil chemistry and change nutrient availability. • Three main mechanisms: • Increased root mass and changes in physiology (increases rhizosphere) • Altering root’s environment with root exudates (increases nutrient concentrations, trees can act as “pumps”, also change pH and make nutrients more available) • Symbioses: mycorrhizae and N-fixing microbes

10. Biological processes • Litter deposition: senesced plant material deposited on soil • Litter quality (ratio of C to N) affects decomposition • Plant resorption of nutrients before parts dropped affects plant nutrient use efficiency and litter quality • Litterfall can cause nutrient pulses: e.g. temperate deciduous forest • Difference in litter characteristics between woody and herbaceous species (for eg) can affect rates of cycling. Cause positive feedbacks and possible thresholds?

11. Biological processes • Decomposition: by soil microbes (bacteria and fungus) • Rate determined largely by carbon content and type. • Lignin (recalcitrant fraction) hard to break down; nutrient release slows as cellulose fraction disappears.

12. Nutrient cycles • Movement of materials essential to organisms. EG Carbon cycle, nitrogen cycle, hydrologic cycle. • Two types: • gaseous (e.g. nitrogen). Reservoir is atmosphere. • Sedimentary (no gaseous phase, e.g. phosphorus) Reservoir is earth’s crust • Phosphorus: net loss of P from land to ocean via leaching • Nitrogen: net increase in N deposition because of human activities (especially near urban centers)

13. Nutrient movement • Nutrients move between ecosystems. Both natural and anthropogenic inputs/transfer. • leaching P from terrestrial to aquatic systems • Addition of N from exhaust emissions • Long-distance movement of N and other materials in high atmosphere. • Formation of stable compounds in atmosphere over urban centers • Long-distance transport to “pristine” ecosystems • Deposition in precipitation • e.g. smog effects from LA and LV in Mojave

14. Nutrient movement between ecosystems: example • Marine-derived Nitrogen (and other nutrients) in boreal forest ecosystems • Salmon are a major nutrient input to northern riparian forest (e.g. Moore 1998) • Stable isotope analyses (marine N has more heavier isotopes) shows substantial input of marine nitrogen to riparian forest and this travels up food chain • Bears transport carcasses long distances from river: marine N input affects upland forest • Question: Salmon used to run as far inland as Missoula MT. Has there been an impact on forest productivity?

15. Ecosystem stability • For community ecology – refers to species composition and diversity (more tomorrow) • For ecosystems ecology – refers to nutrient retention and cycling (eg Sparrow et al). • Definitions: • Resilience – ability to return to pre-disturbance conditions • Resistance – ability to resist change with disturbance • Involves nutrient pools and movement over several temporal scales.

16. Ecosystem stability: factors • Resorption: ability to move nutrients from a plant part before abscission. • Nutrient Use Efficiency: productivity per unit nutrient. • Storage: ability to store nutrients in ecosystem (e.g. standing crop of biomass – trees) • Immobilization: biological uptake of nutrients How would these factors affect stability (resistance and resilliance) and does type of disturbance matter?