I. Basic ConceptsPlant productionDecompositionEEMB/ES 171OutlineI. Basic ConceptsEcosystem “physiology” Ties together “biological ecology” with physical sciences ThermodynamicsEnergy is lost to heatMass is conservedThus: Elements cycle; energy spiralsScalesTime- things look different at different time scalesSpace- questions and key controls change with spatial scaleLinking of scales- balance of integrative and reductionist approaches Aggregation- species, functional groups, biomesSystem behaviorConnectivityFeedbackPositiveNegativeStability-Resistance- how much does a system respond to a disturbanceResilience- how fast does a system recover from disturbanceWhether a system is resistant or resilient may differ based on different aspects of the systemStability vs. diversity- does diversity provide functional stability?Approaches to studying ecosystems:BudgetaryMeasure the processes; descriptiveMechanistic Understand the component processes- integrate through modelingII. Ecosystem StructureWhat is an ecosystem?Physical boundsElement cycling is dominated by internal recycling, rather than external inputsJenny’s ClORPT(H) equationClimate:TemperatureAvailable moisture- AET vs. PETSeasonality and extremesDisturbance regimeOrganisms:The organisms with access to a siteRelief:Slope- rates of movement of material Aspect- energy inputsConcave vs. convex landscape positions- do water and soil accumulate or get diffused?Parent Material:Bedrock typeTime:Old soils become depleted in mineral elements (P, Ca, K etc.)SoilSoil horizons and formationTexture- sand, silt, clayStructureClay- any mineral particle smaller than 2 MAluminosilicates:LayeredHigh surface area, particularly 2:1 claysElectrically chargedCation Exchange Capacity (CEC)Iron and Aluminum hydrous oxides Variable charge and CEC. Soil Organic MatterBehaves similarly to clays in many functional ways-StructureWater holding capacityCECIII. C CyclePlant productionPhotosynthesis vs. Net Primary Productivity (NPP)NPP = Photosynthesis – plant respirationGPP = Total ecosystem photosynthesisNEE = GPP – soil respirationNEP = GPP – soil respiration – leaching and harvest lossesLiebig’s Law of the minimum: growth limited by a single limiting factorSpecies can adapt to adjust allocation to reduce demand, increase supply- may be co-limitedCommunities: species adapted to low nutrients have low maximum growth rates, may not be limited by nutrients, even at low nutrient supply. Fertilization will increase total communityproduction through species replacement.Resource Use EfficiencyWater use efficiency (WUE) = g production / g water usedNitrogen use efficiency (NUE) = g production / g N used Measured by N content of senesced materialAllocationSource sink relationships- Root growth:Resource patch encourages growth for exploitationOverall resource availability encourages a shift to aboveground growthStructural vs. metabolic materialHigh rates of metabolism require nutrient rich bioactive moleculesProtein, lipids, nucleic acidsPhysical structure requires large, long, strong polymersCellulose- linear glucose polymersLignin- complex 3-d phenolic based polymer. Makes wood woody.Mutualists (“microbial mercenaries”)MycorrhizaeArbuscular (endo): many plants. Primarily supply P.Ecto: on conifers, some deciduous trees. Many rolesN fixers- plant supplies C, bacteria supplies NLegume-rhizobium associationActinorhizal association on alder, ceanothus, others.Defense chemicals (outgrow herbivory or defend against it)Tannins- C rich chemicalsProduced when C is available and N is limitingBind to proteins and make them undigestableAlkaloids- N rich chemicalsResource availabilityWater potentialComponentsMatric potential- from interactions with surfaces and capillary poresSolute potential- from interactions with dissolved solutesGravitational potentialPressure potentialWater potential vs. contentFine textured soils will have a higher water content at a given water potentialFine textured soils will have a lower water potential at a given water content. Field capacity: water content/potential after drainage- ca. –0.01 MPaPermanent wilt point: point where plants wilt and die. Commonly defined as –1.5 MPaAvailable water = F.C. – PWPPlants may be out of equilibrium with their environment and act as a conduit for water fromMoist soil to dry atmosphereMicrobes must be in equilibrium with their environmentDecompositionWho is responsibleMicro and Meso Fauna- break material down physicallyMicroorganisms (bacteria and fungi) break material down chemicallyRate- often expressed as exponential decay: dX/dt = -k X Litter contains multiple components, each of which has a different k value.Controls Temperature- exponential responseMoisture- At low water content, water availability limits decomposersAt high water content, soils saturate and oxygen limits decompositionWater filled pore space integrates these effects, optimum at 60%Litter Quality- fundamental chemical decomposability State Factors of Litter Quality:SizeLarge molecules can not be taken up and must be processed extra-cellularlyTypes of bondsAromatic rings are hard, some kinds of bonds are easyRegularityRegular structures can be processed by a single specialized enzymeRandom structures (e.g. lignin) are hard to break down- “shotgun” reactionsNutrient availabilityN, P, etc. are required for microbial growthIn fresh litter, most N is in proteins- easy to break downIn old material, N may be in complex structures- hard to break downSecondary chemicalsTannins- complex substrates and enzymesIndices of quality:C/N ratio, Lignin content, Lignin/N ratioOrganisms:Specific organisms may be required to break particular chemicalsSome evidence exists that different decomposers may act at different ratesNutrient Release: MineralizationMicrobes use all the C they can, N will be released when it is in excess relative to C.If N is limiting, microbes may immobilize nutrients from the soilCalculations:Account for biomass production based on substrate use efficiency (SUE)Calculate how much N is needed to produce that amount of biomassCalculate the extent of mineralization/immobilizationTime course of decompositionStage 1. Leaching of soluble materialStage 2. Decomposition of free cellulose – net immobilizationStage 3. Decomposition of lignin-cellulse complex- net mineralizationSoil Organic MatterWhat is it?Complex mix of plant debris, microbial products, humic material (fulvic, humic, humin)Humic acid: Complex