Lesson 11. Energy fixation by plants and Primary Production

Transcription

1 Lesson 11. Energy fixation by plants and Primary Production

2 ENERGY LAWS First Thermodynamic Law: energy cannot be created or destroyed, it can be only transformed. Second Thermodynamic Law: the whole processes related to energy transformation can only occur with a degradation of energy.it means that in a close thermodynamic system any process related to a transformation of energy leads to a global increase of entropy.

3 BIOLOGICAL SYSTEMS : ORGANISMS, ECOSYSTEMS and BIOSPHERE All biological systems, ecosystems and biosphere are open thermodynamic systems, hence they possess dissipative structures that export entropy. (Prigogine et al. 1972). Sun

4 Raymond Lindeman ( ) was the first to understand the processes of energy flow in ecosystems Lindeman (1942). The trophic-dynamic aspect of ecology. Ecology, 23:

5 METABOLIC DIVERSITY IN ORGANISMS Autotrophic organisms: Photoautotrophic Chemioautotrophic

6 SOLAR EMISSION: black body with 6000ºK

7 RELATIVE ABSORBANCE OF CHLOROPHYLL a and b (isolated) and PLANT LEAVES. Chlorophyll has to absorbance peaks at approximately 430 (blue) and 680 nm (red). Leaves have different absorbance spectrum.

8 What does it occur when the molecule of chlorophyll is excited by light? Photochemical path: The energy might be transferred to other chlorophyll molecules and reach reaction centres. Heat: The excited chlorophyll molecules might reach basal state only transferring energy as heat. Fluorescence: Chlorophyll might emit a photon with a higher wave length. This process is called fluorescence. Chl* hλ Chl

9 C 3 Photosynthesis To fix carbon, plants must open stomata to let in CO2. Water gradient may allow water to escape.

10 C 4 Photosynthesis

11 CAM Photosynthesis

12 Photosynthetic Capacities C4 Grasses umol/m 2 s Sun leaves (deciduous trees) Shade leaves (deciduous trees) Conifers Grassland crops CAM 5-12

13 THE ROLE OF PLANT STRUCTURE AND TRANSPOR SYSTEM Schematic comparison between an aquatic and a forest ecosystem in relation to the patterns of light and nutrients fluxes.

14 Primary production: Fixation of energy by autotrophs in an ecosystem. Rate of primary production: Amount of energy fixed over a given period of time. Gross primary production: Total amount of energy fixed by autotrophs. Net primary production: Amount of energy leftover after autotrophs have met their metabolic needs.

15 Energy dissipation through the leaf nm IR, amarillo Verde,... 50% % Indice de Area Foliar IAF % PPB PPB Absorbida por el aparato fotosintético pero no fijada en materia orgánica. PPN

16 Light efficiency is very low in natural ecosystems Which is the percentage of PAR that is really transformed in Primary Production? Conifers: 1-3% Semideciduous forests: 0,5-1% Deserts: 0,01-0,2% Crops with auxiliary energy: 3-10%

17 Energy balance of a corn field (Transeau, 1920) Total-available energy x 10 6 kcal Used in photosynthesis.. 33 x 10 6 kcal Transpiration x 10 6 kcal Total-used energy x 10 6 kcal Non-used energy x 10 6 kcal Energy dispersed as heat in respiration... 8 x 10 6 kcal Photosynthesis efficiency... 1,6% Efficiency for PAR light... 8,0%

18 Endosomatic and Exosomatic energy Endosomatic or internal energy: it is the amount of energy that flows in trophic chains through primary production. Exosomatic or external energy: it is the external energy that flows outside trophic chains, but it might have an important role in primary production. Natural systems: Rain, wind, tides, stream currents, etc. Human systems: Irrigation, plough, nutrient fertilizer, etc

19 Primary Production in Terrestrialecosystems.

20 Which are the factors limiting Primary Production? Internal factors: chlorophyll, nitrogen. Physical factors: PAR radiation, temperature, water. Biological factors: successional stage, structure, herbivory.

21 Water Temperature

22 Actual Evapotranspiration and Terrestrial Primary Production Rosenzweig estimated influence of moisture and temperature on rates of primary production by plotting relationship between annual net primary production and annual actual evapotranspiration (AET). AET: Annual amount of water that evaporates and transpires off a landscape. Cold dry ecosystems tend to have low AET.

23 Evapotranspiration and Terrestrial Primary Production

24 Primary Production is correlated with the length oh Photosynthetic period.

25 At global scale climate is the main factor controlling Primary Production in terrestrial ecosystems P (t/ha año) B (t/ha) R =PAR (kcal/m 2 año)

26 Soil Fertility and Terrestrial Primary Production Significant variation in terrestrial primary production can be explained by differences in soil fertility. Shaver and Chapin found arctic net primary production was twice as high on fertilized plots as unfertilized plots. Bowman suggested N is main nutrient limiting net primary production in a dry tundra meadow, and N and P jointly limit production in a wet meadow.

27 Herbivory Positive effects: Nutrient mobilization. Vegetative growth increase. Compensatory effects: Reduces self.shading. Mobilization of stored sugars.. Redistribution of photosynthetic products.. Defense mechanisms. Negative effects: Meristems grazing.. Bark lost. Grazing of photosynthetic biomass.

28 Net Ecosystem Production Net Ecosystem production (NEP) is the difference between NPP and heterotrophic respiration (animals and decopomsers). This index is measuring the amount of C that can be accumulated in the ecosystem.

29 Odum s models of temporal changes of gross primary production, respiration, net primary production and biomass in two types of ecosystems.

30 metros sobre nivel del mar Monte Blanco Monte Intermedio Monte Negro Nivel freático invierno Nivel freático verano Metros Real Iniciales Maduras Esperada Iniciales Maduras MB g/m 2 año rango MN g/m 2 año rango

31 Relationship P/B Producción Primaria Neta P/B rates Forests: 0,042. Terrestrial ecosystems: 0,29. Aquatic ecosystems: 17.

32 How do we measure Primary Production? O 2 CO 2 H 2 O H 2 O and nutrients Sugars

33 Infra-Red Gas Analyser (IRGA) The chamber

34 Aire de referencia CIRCUITOSIMPLIFICADO DE UN IRGA Cámara análisis Mezcla Medida Referencia

35 Agricultural production and external energy Clasificación de Odum Sistemas naturales sin subsidio kcal/m 2 año. Sistemas naturales con subsidio kcal/m 2 año Sist. accionados por energía solar con subsidio humano kcal/m 2 año Industrial urbano, con combustibles kcal/m 2 año

36 Relationship between external energy and agricultural production

37 Which will be the future?