Lecture 5: Nutrient Cycles PDF

1/20/25 Biol 3290 Lecture 5: NUTRIENT CYCLES cont’d Jan 20 2025 Outline: Nutrient Use Efficiency (NUE) Major plant nutrients The Nitrogen cycle The phosphorus cycle Factors that affe...

1/20/25 Biol 3290 Lecture 5: NUTRIENT CYCLES cont’d Jan 20 2025 Outline: Nutrient Use Efficiency (NUE) Major plant nutrients The Nitrogen cycle The phosphorus cycle Factors that affect cycling Abiotic Fire Volcanism Biotic microbial decomposition herbivores 1 Announcements This week in the lab: – Approx 30 minutes – Measure ethylene (7d) with your group – Go directly to the greenhouse (not 106 LUM) at: 2:30 pm – groups 1 and 2 3:00 pm – groups 3 and 4 3:30 pm – groups 5 and 6 4:00 pm – group 7 Reminder: choose an article for your presentation – Published in a peer-reviewed journal, in the year of your birth, on a plant ecology topic (see course outline) – Signup sheet will be posted later this week 2 1  1/20/25 3 Which of the following is NOT considered a macronutrient for plants? a) K b) Fe c) N d) P e) Ca f) S 4 2  1/20/25 5 Recall: Bioelements = elements that cycle through living organisms. Nutrients move from one “compartment” to another within ecosystems. Biogeochemical cycles involve nutrient exchanges between biological and non-biological compartments Cycles are closed when viewed on a global scale; open when viewed on a local scale 6 3  1/20/25 Recall: Compartments are arbitrarily defined – e.g. all plants, or one species, or the leaves of one species each contain a quantity (pool) of nutrients exchange nutrients with other compartments – flux = rate of movement into / out of a compartment 7 A protein in soil humus is broken down by microbes, releasing ammonium (NH4+) into the soil. This is an example of a) immobilization b) mobilization c) nitrogen becoming available to plants for growth d) a) and c) e) b) and c) 8 4  1/20/25 Recall: Plants take up essential elements in mineral (inorganic) form C: CO2 O: H2O or O2 H: H2O Macronutrients Micronutrients Essential to some plants N: NO3-, NH4+ Cl: Cl- Na: Na+ K: K+ 3+ Fe: Fe , Fe 2+ Co: Co2+ Ca: Ca+ Mn: Mn2+ Si: SiO3- Mg: Mg2+ B: B(OH)3, B(OH)4- P: H2PO4-, HPO4- Zn: Zn2+ S: SO42- Cu: Cu2+ Ni: Ni2+ Mo: MoO42- Principal forms in which mineral elements are absorbed 9 Recall: Definitions Immobilization: – Uptake of mineral nutrients from soil solution by microbes or plants --> conversion into organic form e.g. NH4+ --> uptake by plant root --> conversion to amino acids – Makes nutrient unavailable to (other) plants Mineralization: – Release into soil solution of mineral nutrients from organic molecules by respiration/decomposition E.g. amino acids --> decomposition --> NH4+ – makes nutrient available for use by plants 10 5  1/20/25 Nutrient Use Efficiency (NUE) Eutrophic soils – High in nutrients – E.g. soils derived from recent glacial till Large areas of northern hemisphere – E.g volcanic soils 11 Nutrient Use Efficiency (NUE) Oligotrophic soils – Old, weathered, infertile – Former Gondwana continents – Vegetation adapted Efficient recycling within plant Leaf fall and reabsorption 12 6  1/20/25 Plants in oligotrophic soils follow different strategies E.g.: Australian soils very low in P – Eucalyptus trees contain only 20-50% as much P as N. hemisphere trees – Other nutrients similar in concentration But - other oligotrophic plants often contain relatively high nutrient conc. compared with eutrophic More efficient uptake / storage 13 Nutrient Use Efficiency (NUE) Nutrient Use Efficiency (N.U.E.) = A / L where – A = nutrient productivity (dry weight produced / unit nutrient in plant) – L = nutrient requirement for maintenance of one unit plant biomass Nitrogen NUE ~0.7 Nitrogen NUE ~0.4 14 7  1/20/25 Nutrient Use Efficiency (NUE) Retention Time in a plant = 1/Ln – Ln = relative nutrient requirement for maintenance of same nutrient – E.g. if 0.1g N needed to maintain 1g of N in tissues for 1 yr, then Ln = 0.1g/g/yr or 0.1/yr  Therefore, R.T. = 10 years – Note: RT is inversely related to turnover rate (see lect 4) 15 Three different models of nutrient use efficiency. Which describes a plant in which NUE is unaffected by resource (nutrient) availability? a) b) c) 16 8  1/20/25 17 NUE in tropical and temperate forests 18 9  1/20/25 Oligotrophic forests have dense layer of fine roots in upper humus that maintains high NUE, productivity If forest is cleared for agriculture and the humus/root layer removed, soils become unproductive. In eutrophic soils, productivity is maintained even if the humus/root layer is removed 19 THE NITROGEN CYCLE Fluxes (italic numbers) in 1012g/yr; pools (bold numbers) as indicated (g) 20 10  1/20/25 Human addition of N to the global N cycle has resulted in: – Increase in N-based trace gases in the atmosphere, eg NO, NO2 – Increase in atmospheric NH3 (mostly from fertilizers) – Increased deposition of N on land / in oceans from fertilizers (usually coupled with P additions) – Eutrophication of soils, lakes, coastal areas – In Sweden: forest production is 30% higher now than in 1950s 21 Critical load = amt N that can be added and absorbed by plants – If exceeded, excess N goes into groundwater or back to atmosphere – Nitrate ions (highly soluble) remove calcium, magnesium, potassium ions from solution (less soluble salts) – Excess nitrate can therefore lead to limitation of growth by other nutrients 22 11  1/20/25 Effect of N addition on species richness in three Minnesota grasslands. From Krebs, 2001. 23 Netherlands have the highest rate of N deposition in world Due to intensive livestock operations Species-rich heathlands have been converted to species-poor grassland/forest Plant (and animal) species adapted to sandy, infertile soils are being lost because of N enrichment 24 12  1/20/25 The phosphorus cycle Fluxes (italic numbers) in 1012g /yr and pools (bold numbers) in 1012g 25 The hydrologic (water) cycle Fluxes (italic numbers) in 1000s km3/yr and pools (bold numbers) in 1000s km3 26 13  1/20/25 The hydrologic cycle affects nutrient cycling P=E+T+R+I Precipitation (P) carries nutrients in solution into an ecosystem. Runoff (R), infiltration (I): remove nutrients from a system or move them down a soil column Evapotranspiration (E, T): concentrates / conserves nutrients In Europe, N. America: human activity elevates concentrations of Ca, K, Mg, N, Na, and S in precipitation 27 Rainfall is often acidic Combines with carbon dioxide to produce carbonic acid, H2CO3 pH of “pure” water in equilibrium with atmosphere: 5.65 “acid” rain has pH lower than this hydrogen ions in acid rain displace Ca2+, Mg2+, and K+ in soil --> nutrient deficiency 28 14  1/20/25 Calculating evapotranspiration Impermeable bedrock (e.g. Hubbard Brook): E+T=P-R Permeable substrate: estimated using lysimeter 29 Fire Occurs in most terrestrial ecosystems Canada: destroys ~2 million ha (0.6%) of coniferous forest/yr ¯ pptn, ­ wind --> ­ fire risk 30 15  1/20/25 Fire ignition sources i. Natural fires: lightning – ­ frequency with ¯ latitude Ignition probability – ­ with ¯ precipitation, humidity – ­ with ­ temperature, wind Eastern US: moist conditions all year Southwestern US: dry conditions in late winter, early spring – Most fires in May/June (even though more thunderstorms in July/August) ii. Inhabited areas: humans – > 2/3 of worldwide fires – Canada: ~65% 31 Fire Fire alters nutrient availability Release from dead vegetation – Non-volatile nutrients (e.g. P) mobilized for plant use – N availability may increase or decrease some is lost as volatile NOx after burning Clears leaf litter Allows light to reach soil --> shade intolerant plants can regenerate 32 16  1/20/25 Role of fire In Boreal forest: – low temperature, pH --> slow decomposition – acid soil Burning raises soil pH --> increases growth of N-fixing bacteria Azotobacter, Rhizobium 33 Fire – boreal forests Typical pattern of succession following fire in N.W. Canada/Alaska 2-5 yrs: plants with – Small seeds – Suckers / lignotubers – Seeds requiring scarification 30 yrs: large shrubs, tree saplings 50 yrs: deciduous trees dominant 100 yrs: spruce dominant 200 yrs: moss covers ground; deciduous trees disappear 34 17  1/20/25 Role of fire In Tallgrass prairie: – litter accumulation traps nutrients, shades soil Burning eliminates litter – sunlight can reach soil – makes non-volatile nutrients available (e.g. P, K) – …but N may be reduced through volatization Effect similar to grazing – Defoliation-tolerant grasses maintained while trees, shrubs eliminated 35 In Chaparral a.k.a. Mediterranean shrubland Occurs around coast of California – Also: Mediterranean coast, S.E. coasts of Africa, Australia, S. America, Summers warm, winters mild (little fluctuation) – 15-20C Normal pptn: 30-100cm/yr – Almost all in fall/winter/spring Soils highly weathered, low nutrients Fire and drought common in summer “Crown fire” regime: fire burns everything  ashen landscape. 36 36 18  1/20/25 Fires in California chaparral are unusual at this time of year Current fires around Los Angeles are due to severe drought conditions – Rainy season normally begins in October – Since May 5 2024, no rainfall event of more than 2.5 mm  Rapid evaporation; no soil absorption 37 37 Santa Ana winds are exacerbating the fires Common in fall/winter High pressure buildup over Nevada desert  winds blow westward though the Sierra Nevada mountains, losing moisture over dry ground Mountains act as wind tunnel  hurricane force 38 38 19  1/20/25 Physiognomy of chaparral Open woodlands, scrub, grassland 40-50% are annuals – Survive summer as seeds Perennials mostly woody & evergreen – Few herbs Some spp. drought deciduous Sclerophyllous leaves – litter resists decomposition Burning accelerates N release – breaks down litter – removes microbial inhibitors – e.g. tannins in leaves – improves “wettability” of soil 39 39 Adaptations of chaparral plants Dimorphism in some plants – Leaves large in winter, small in summer Root systems – Drought deciduous / dormant Shallow --> capture rainfall – Evergreen --> both deep and Black sage, Salvia mellifera shallow roots A drought-deciduous shrub of California chaparral Fire resistance: thick bark, epicormic sprouts, serotinous cones all common 40 40 20  1/20/25 Fire - adaptations 1. Fire-resistant bark – Protects living (cambium) layer – Depends on thickness 0.6 cm: protects against 500°C for 1 minute 2.6 cm: for 20 minutes – Fir, larch pine in western North America: > 10cm thick Bark of cork oak, Quercus suber. Grows in fire-prone western Mediterranean chaparral 41 Fire - adaptations 2. Deep root systems E.g. Surface fire – Above soil: 600°C – Soil surface: 80°C – 10cm below: 33°C Deep root system of a pine tree 42 21  1/20/25 Fire - adaptations 3. Epicormic sprouts – From latent buds beneath bark – “fire column” grows from trunk – E.g. pines, redwoods, oaks, eucalyptus Pitch pine Pinus rigida 43 Fire - adaptations 4. Lignotubers – Swellings @ root/shoot interface – Contain buds, food reserves – Underground --> protected – Moderate heating stimulates bud development Eucalyptus sp. 44 22  1/20/25 Fire - adaptations 5. Suckers – Allow regrowth from roots 45 Fire - adaptations 6. Seeds requiring scarification = heating from fire – Seedlings grow in post-fire conditions (high light, nutrients) – Serotinous cones remain closed until heated Serotinous cones (above) on Jack pine, Pinus banksiana. Sealing resin melts at 60°C. Can remain viable up to 75 yrs on a tree. Most trees also produce regular cones (left) 46 23  1/20/25 Land use practices have decreased fire frequency in N. America Texas, midwestern plains: fire-resistant grasslands being replaced with shrubland, woodland Fire suppression --> fuel buildup If fires occur, will be more intense 47 Fire - beneficial effects Solution: prescribed burns Prescribed burn in High Park 48 24  1/20/25 Fire - beneficial effects - prescribed burns Usually safe and effective Have occasionally gotten out of control Prescribed burn went awry in Los Alamos, NM, in 2000; caused severe damage 49 25