Net Radiation Incident at the Surface

Transcription

1 EO 01 Terrestrial Ecosystem Processes Terrestrial Ecosystem Processes Energy Balance Net Radiation Incident at the Surface R n = K ( 1 α) + ( εl εσt s ) K αk L εσt s Soil Heat Flux () Upward and downward conduction of sensible heat Driven by vertical temperature gradient in soil Modulated by soil thermal properties Direction of gradient changes as surface temperature changes Averages near zero over 2-hour period K αk L εσt s Veg Layer Soil ( 1 α)k εl ( 1 α)k εl 1

2 Biomass Heat Storage (J) ain and loss of sensible heat by vegetation Observed as heating of biomass during the day and cooling at night Affected by vegetation density, leaf area, stem diameter and number, net radiation, air temperature, etc. Averages near zero over 2-hour period K αk L εσt s Photosynthesis (P) Some of solar radiation absorbed by canopy is used for photosynthesis, storing that energy in the form of chemical compounds enerally, P is small enough to be ignored for energy balance purposes P of C grasses (e.g. sugarcane) can be significant K αk L εσt s ( 1 α)k εl J ( 1 α)k εl J P K Surface Energy Balance Sensible energy (H) and latent energy (λe) are major components of the energy balance The partitioning between H and λe is determined by surface characteristics, especially vegetation type and moisture availability αk L εσt s H λe Surface Energy Balance R n = K ( 1 α) + ( εl εσt s ) = H + λe + + J + P Radiative Exchange K L αk εσt s Storage Turbulent Flux H λe ( 1 α)k εl J P ( 1 α)k εl J P 2

3 Surface Energy Balance Photosynthesis can generally be ignored. R n = H + λe + + J Surface Energy Balance For 2-hour or multi-day periods, other storage terms ( and J) can be ignored. This allows the energy balance equation to be simplified: R n = H + λe Radiative Exchange K αk L εσt s Storage Turbulent Flux H λe Radiative Exchange K L αk εσt s Storage Turbulent Flux H λe ( 1 α)k εl J X P ( 1 α)k εl X J X P X Surface Energy Balance R n = H + λe λe Surface Energy Balance 700 Brazil: Bare Soil Kd 900 Thailand: 25-yr Secondary Vegetation Kd Rn E H :00 :00 8:00 12:00 16:00 20:00 0:00 R n Energy Partitioning H 00 Rn H E :00 :00 8:00 12:00 16:00 20:00 0:00 3

4 Diurnal Cycles Regional Energy Balance Surface Energy Balance Mean energy fluxes. Site Rn day all day all E day all H day all Thailand (l) Harvested barley (m) Fallow rice paddy (n) Irrigated bare soil (o) 2-yr Secondary veg (p) 3-yr Secondary veg (q) 8-yr Secondary veg (r) 25-yr Secondary veg Day refers to 12-hour period 6:00-18:00

5 Ecosystem Processes Controlling Ecosystem Water Balance Evapotranspiration (link to energy cycling) Transpiration Rainfall interception - Wet canopy evaporation - Throughfall - Stemflow Cloud water interception Influences on soil hydraulic properties CWI RF Irr ΔSM ET - Transpiration - Wet canopy evaporation - Soil evaporation RO WR Stoma Leaf stomata (stoma) are important in controlling fluxes of water, energy, and carbon dioxide Stoma Pea Leaf Stoma, Vicea sp. (SEM x3,520). This image is copyright Dennis Kunkel at 5

6 Stomata Ohm s Law Analogy for Heat Water and CO2 Exchanges by Leaves Bonan (2008, Figure 16.2) Latent Heat of Vaporization λ = 2.5 x 106 J kg-1 at 20ºC Typical summer evap. rate: 5 mm per day Water density: 1000 kg m-3 5 mm = 5 kg per square meter 5 kg 1 day J W = 12 m2day 8600 s kg m2 Latent Heat of Vaporization λ = 2.5 x 106 J kg-1 at 20ºC Another way of stating the latent heat of vaporization: The amount of latent heat flux per mm/day of evap: λ = W m-2 per mm day-1 Examples: (a) 5 mm per day: λe = 5 mm day-1 x W m-2 per mm day-1 = 11.8 W m-2 (b) λe = 110 W m-2 : E = 110 W m-2 / W m-2 per mm day-1 = 3.88 mm day-1 6

7 Rainfall Interception Measuring Throughfall 7

8 Measuring Throughfall Measuring Stemflow Cloud Water Interception Terrestrial Ecosystem Adapted from a lecture by Dr. Creighton M. Litton Department of Natural Resources and Environmental Management University of Hawai i at Mānoa Carbon Input (PP) Autotrophic respiration (R) Net primary production (NPP) Net ecosystem production (NEP) Net biome production (NBP) Belowground C flux (TBCA) C allocation & global patterns 31 8

9 Terrestrial Ecosystem Terrestrial Metabolism Why should we care about C cycling? C is the energy currency of all ecosystems Plant (autotrophic) production is the base of almost all food/energy pyramids Central to all ecosystem goods & services Plant C cycling, to a large extent, controls atmospheric CO 2 concentrations Forests account for 80% of global terrestrial biomass and 75% of global terrestrial productivity Plant-derived C fundamental to soil processes Belowground resources are a primary control over ecosystem processes The breathing of Earth Photosynthesis ross Primary Production C enters via photosynthesis ross Primary Production (PP) Net photosynthesis (ross photo - foliage dark R during the day) 1. Accumulates in ecosystems (C sequestration) as: (a) plant biomass; (b) SOM & microbial biomass; or (c) animal biomass 2. Returned to the atmosphere via (a) respiration (R; autotrophic or heterotrophic); (b) VOC emissions; or (c) disturbance 3. Transferred laterally to another ecosystem How do you measure PP? Measure photosynthesis of every leaf in the canopy? Measure a few leaves and scale to the canopy? 9

10 ross Primary Production How do you measure PP? Modeling studies LAI estimates from remote sensing or field studies APAR or FPAR Leaf Area Index Absorbed PAR LUE from existing studies Plug it all into a TEM or DVM ross Primary Production How do you measure PP? Eddy flux / covariance CO 2 sensor above the canopy Vertical flux of CO 2 is a function of the covariance of wind velocity and gas concentration Really measure Net Ecosystem Exchange (NEE) NEE = PP - R ecosystem Light Use Efficiency Terrestrial Ecosystem Model Dynamic lobal Vegetation Model 38 ross Primary Production ross Primary Production How do you measure PP? Sum of individual components Need measurements of all the individual components Only ~30 studies worldwide What controls PP? Within a given set of biotic & environmental conditions: Leaf area LAI (leaf area / unit ground area; m 2 m -2 ) rowing season length N availability Temperature, light, & CO 2 Litton et al. (2007) 10

11 lobal Terrestrial PP Distribution Net Primary Production How is PP distributed globally across biomes? Biomes PP Net primary production (NPP) Net annual C gain (or loss) by plants NPP = PP R plant ANPP, ANPP wood, ANPP foliage, BNPP, TNPP, etc. Net Primary Production What controls NPP globally? lobal Distribution of Net Primary Production How is NPP distributed globally across biomes? Biomes NPP Running et al. (200) 11

12 lobal Distribution of Net Primary Production Respiration How is NPP distributed globally across biomes? lobal distribution of terrestrial biomes and their total carbon in plant biomass a. Area (10 6 km 2) Total C pool (Pg C) Total NPP (Pg C yr -1 ) Biome Tropical forests Temperate forests Boreal forests Mediterranean shrublands Tropical savannas and grasslands 1.9 Temperate grasslands Deserts Arctic tundra Crops Ice 15.5 Total a Data from [Roy, 2001 #3858]. Biomass is expressed in units of carbon, assuming that plant biomass is 50% carbon. Tropical forests are ~12% of land area, but account for ½ of global biomass and 1/3 of NPP R plant = R growth + R maint + R ion What respires? All living biomass, all the time Why does living biomass respire? Provides energy for essential metabolic processes Mitochondrial oxidation of CHO s to make ATP Not wasted C Respiration R growth (growth/construction) C in new biomass + C used to generate that biomass = total C cost Similar across species Varies widely by compound Function of concentration & cost Protein rich (leaves), structural (wood), and defense How do you measure R growth? ~25% x NPP Total C cost = ~1.23g CHOs per 1 g of biomass produced R maint (maintenance of existing biomass) Repair of non-growing tissues Protein turnover (~85%) Membrane lipids Respiration + R ion (transport across membranes) ½ of R total How do you measure R maint? Strongly correlated with temperature and N content 12

13 Respiration Ecosystem Carbon Balance R maint R m = R 0 (Q 10 ) (T/10) R m = x N content NPP = PP - R plant Typically measured on annual time scales Units of biomass or C / unit area / unit time g C m -2 yr -1 How do you measure NPP? T w ( C) Remember that we typically get PP by measuring all the components, including NPP Ryan et al. (200) Curtis et al. (2005) Ecosystem Carbon Balance Net Ecosystem Production Measuring NPP NPP = ΔBiomass Biomass from allometric equations Need to account for biomass increment and loss because plant tissue is continually shed NPP = (ΔLeaf Bio. + Leaf Litter) + (ΔWood Bio. + Wood Litter) + (ΔRoot Bio. + Root Litter) Litterfall quantified with littertraps Metrosideros polymorpha Litton & Kauffman (2008) Net ecosystem production (NPP) Net annual C gain (or loss) by an ecosystem NEP = PP R ecosystem NEP = NPP R hetero Same as NEE??? What are we missing? 13

14 Net Biome Production Carbon Allocation Net biome production (NBP) Net ecosystem C gain (or loss) by large regions over long time scales NBP = NEP ± F lateral - F disturb - F leach - F emissions Information most useful for C sequestration estimates Both natural & anthropogenic disturbances TBCA (Total Belowground Carbon Allocation) Measuring BNPP and R below is exceedingly difficult Would also miss a lot of C that goes to other components TBCA is the total amount of C that plants allocate belowground Root production + root respiration + C to symbionts + rhizodeposition Based on conservation of mass Direct measurements of all inputs & outputs of C except the one you can t measure and you want to solve for TBCA = F S + F E - F A + ΔC S + ΔC R + ΔC L See: Carbon Allocation Carbon Allocation TBCA (Total Belowground Carbon Allocation) TBCA is as easy as taking a bath High LAI is needed to maximize PP (or NPP), yet LAI is largely constrained by aboveground and belowground resource availability How do plants deal with this dilemma? Alter allocation in response to resource availability Allocate growth and biomass to aboveground to maximize C gain Allocate growth and biomass to belowground to maximize belowground resource capture iardina & Ryan (2002) 1

15 Carbon Allocation Carbon Allocation Liebig s Law of the Minimum Plants allocate growth to tissues that maximize capture of the single most limiting resource Allocate to roots when substrate is dry or nutrient poor Allocate to stem (&/or leaves) when light is limiting (a) more biomass, (b) more efficient, and/or (c) longer retention Plants constantly adjust allocation Prevents overwhelming limitation by one resource Tends to result in plants being limited by multiple resources Do global patterns exist for C allocation? Litton et al. (2007) examined a diverse global dataset of forest stand C budgets Divided allocation into 3 separate components: Biomass (the amount of organic material present) Flux (the flow of carbon to a given component per unit time) Partitioning (the fraction of PP used by a given component) Carbon Allocation Terrestrial Ecosystem Carbon Exchange lobal forest C allocation patterns Biomass flux or partitioning Why? Does C storage = C sequestration? C storage C sequestration!!!!!!!! lobal forest C allocation patterns R uses a ~constant fraction of PP Litton et al. (2007) Litton et al. (2007) 15

16 Terrestrial Ecosystem Carbon Exchange lobal forest C allocation patterns As resources (PP) increase, partitioning shifts from belowto aboveground Partitioning to foliage is ~constant An increase in resources increases partitioning to wood Terrestrial Ecosystem Carbon Exchange Disturbance & succession are major causes of variation in C storage and C sequestration rates Barnes et al. (1998) or Wardle et al. (200) Litton et al. (2007) 16