Presentation on theme: "NUTRIENT CYCLING AND RETENTION"— Presentation transcript:
1 NUTRIENT CYCLING AND RETENTION Chapter 19Molles: Ecology 2nd Ed.
2 Disturbance increases ecosystem nutrient loss Chapter ConceptsDecomposition rate influenced by temperature, moisture, and chemical composition of litter and environmentPlants and animals modify distribution and cycling of nutrients in ecosystemsDisturbance increases ecosystem nutrient lossMolles: Ecology 2nd Ed.
3 Global phosphorus cycle doesn’t include substantial atmospheric pool Largest quantities of P are in mineral deposits and marine sedimentsMuch of this not directly available to plantsSlowly released in terrestrial and aquatic ecosystems – weathering of rocksMolles: Ecology 2nd Ed.
5 Includes major atmospheric pool – N2 Nitrogen CycleIncludes major atmospheric pool – N2Only nitrogen fixers can use atmospheric supply directlyBlue-green algae, soil bacteria, bacteria of legume roots, some fungi= energy-demanding processN2 reduced to ammonia (NH3)Molles: Ecology 2nd Ed.
6 Nitrogen fixers fix nitrogen = anaerobic (stinks) Once N fixed – available to organismsUpon death of organism, N can be released by fungi and bacteria during decompositionMolles: Ecology 2nd Ed.
8 Carbon CycleMoves between organisms and atmosphere due to photosynthesis and respirationIn aquatic ecosystems, CO2 dissolves into water – then used by primary producersAlthough some C cycles rapidly, some remains stored in unavailable forms for long timeMolles: Ecology 2nd Ed.
10 Occurs primarily during decomposition Decomposition RatesRate at which nutrients are made available to primary producers is determined largely by rate of mineralizationOccurs primarily during decompositionRate in terrestrial systems influenced by temperature, moisture, and chemical compositionsMolles: Ecology 2nd Ed.
11 Decomposition in Temperate Forest Ecosystems Melillo et.al. (1982)Litter bags to study decomposition in temperate forests:Leaves with higher lignin:nitrogen ratios lost less mass= higher N availability in soil might have contributed to higher decomposition ratesMolles: Ecology 2nd Ed.
13 Decomposition in Aquatic Ecosystems Gessner and Chauvet (1994)Stream in French PyreneesLeaves with more lignin decomposed slowerHigher lignin inhibits fungi colonization of leavesMolles: Ecology 2nd Ed.
14 Suberkropp and Chauvet Tulip tree leaves degraded faster in Alabama streams with higher nitrate concentrationsMolles: Ecology 2nd Ed.
15 Nutrient Cycling in Streams Webster (1975) – nutrients in streams are subject to downstream transportLittle nutrient cycling in one placeNutrient SpiralingFig 19.13Molles: Ecology 2nd Ed.
16 Webster (1975)Spiraling Length = length of stream required for a nutrient atom to complete a cycleRelated to rate of nutrient cycling and velocity of downstream nutrient movementFig 19.13Molles: Ecology 2nd Ed.
17 Nutrient Cycling in Streams Spiraling Length:S = VTS = Spiraling LengthV = Average velocity of nutrient atomT = Average time to complete cycleShort lengths = high nutrient retentivenessLong lengths = low nutrient retentivenessFig 19.13Molles: Ecology 2nd Ed.
18 Stream Invertebrates and Spiraling Length Grimm (1988):Sycamore Creek, AZCollector-gatherer insect larvaeMayflies + chironomidsAquatic invertebrates increase rate of N cyclingMolles: Ecology 2nd Ed.
19 How much N do invert’s contribute to nutrient dynamics of stream? Rapid recycling of N by macroinvertebrates increases primary productionExcreted and recycled 15-70% of nitrogen pool as ammoniaMolles: Ecology 2nd Ed.
21 Animals and Nutrient Cycling in Terrestrial Ecosystems Huntley and Inouye (1988)Pocket gophers alter N cycle by bringing N-poor subsoil to surfaceMolles: Ecology 2nd Ed.
22 MacNaughton et al. (1988)Positive relationship between grazing intensity and rate of turnover in plant biomass in Serengeti PlainWithout grazing, nutrient cycling occurs more slowly through decomposition and feeding of small herbivoresMolles: Ecology 2nd Ed.
24 Plants and Ecosystem Nutrient Dynamics Fynbos is a South African temperate shrub/woodland known for high plant diversity and low soil fertilityTwo species of Acacia introduced to stabilize shifting sand dunesMolles: Ecology 2nd Ed.
25 Witkowski (1991)Compared nutrient dynamics under canopy of native shrub and introduced AcaciaAmount of litter similar, but nutrient content was significantly differentAcacia – N fixerMolles: Ecology 2nd Ed.
26 Introduced Tree and Hawaiian Ecosystem Native flora = 1,200 species> 90% endemic~ 4,600 new species introduced to HawaiiFiretreeMyrica fayaMolles: Ecology 2nd Ed.
27 Nitrogen fixation by Myrica large N input Vitousek and Walker (1989)Invading N-fixing tree Myrica faya is altering N dynamics of Hawaiian ecosystemsIntroduced in late 1800’s as ornamental or medicinal plant – later used for watershed reclamationNitrogen fixation by Myrica large N inputLeaves contain high N contentHigh decomposition rateMolles: Ecology 2nd Ed.
29 Disturbance and Nutrient Loss From the Hubbard Brook Forest Vitousek et al.19 forests around N. America11 deciduous, 8 coniferousAcidic to neutral soilsEffects of disturbance and environmental conditions on N lossMolles: Ecology 2nd Ed.
30 Dig trenches around them, line w/plastic Vitousek studies:Square meter plotsDig trenches around them, line w/plasticTrenching increased concentrations of nitrate in soil water up to 1,000XNitrate losses higher at sites with rapid decompositionUptake by vegetation most important in ecosystems with fertile soils and warm, moist conditionsMolles: Ecology 2nd Ed.
31 Similar study on disturbance by forest clearcutting: Fig 19.21Molles: Ecology 2nd Ed.
32 Flooding and Nutrient Export by Streams Meyer and Likens found P exports were highly episodic and associated with periods of high flowAnnual peak in P input associated with spring snowmeltMost export was irregular because it was driven by flooding caused by intense periodic stormsMolles: Ecology 2nd Ed.
33 Disturbance increases ecosystem nutrient loss SummaryDecomposition rate influenced by temperature, moisture, and chemical composition of litter and environmentPlants and animals modify distribution and cycling of nutrients in ecosystemsDisturbance increases ecosystem nutrient lossMolles: Ecology 2nd Ed.