Readings 1.Chapter 13 textbook 2.Van Breeman, N., and Finzi, A Plant-soil interactions: ecological aspects and evolutionary implications. Biogeochemistry 42: (online journal, UNR library website) 3.Beisner, B., D. Haydon, and K. Cuddington Alternative Stable States in Ecology. Frontiers in Ecology and the Environment (7): (on reserve in FA library)

Changes to schedule 1.Today: Nutrient cycling and plant-soil interactions 2.Lab tomorrow 1.Return exams, discuss. 2.Lecture – disturbance and succession 3.Lecture and discussion – state and transition models

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%.

Outline 1.Plant nutrition, macro- and micro-nutrients 2.Nutrient availability: soil chemistry, biotic effects, and litter decomposition 3.Nutrient cycling and plant-soil interactions 4.Transfer of nutrients among ecosystems 5.Example of nutrient transfer: marine derived nitrogen and phosphorus in forest ecosystems 6.Ecosystem stability

Plant nutrition Mineral nutrients (elements) divided into groups based on amounts required: Text p –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

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

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

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.

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

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?

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.

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)

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

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?

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.

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?