UCSB EEMB 171 - Lecture 9-11 2015 (1) (120 pages)

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Lecture 9-11 2015 (1)



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Lecture 9-11 2015 (1)

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Pages:
120
School:
University of California, Santa Barbara
Course:
Eemb 171 - ECOSYSTEM PROCESSES
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what regulates C gain or loss across scales How do we account for these effects Are there integrating variables that scale up canopy processes increase range of light intensities over which light use efficiency LUE is constant leaf nitrogen N controls photosynthetic capacity what regulates C gain or loss across scales these variables are all correlated with each other net photosynthesis leaf N specific leaf area leaf lifespan Why photosynthesis a chemical overview net photosynthesis balance between Cfixed respired leaf N concentration N is necessary for making chlorophyll specific leaf area surface area mass leaf lifespan fast or slow turnover what are the biological tradeoffs high N high photosynthesis capacity big surface area mass quick turnover low N low photosynthesis capacity small surface area mass slow turnover image source http www wallpapers247 com wallpaper Big Green Leaf http www pitzer edu offices arboretum scott lawn sage asp leaf lifespan months net photosynthesis nmol g1 sec 1 leaf lifespan months leaf N mg g 1 specific leaf area cm 2 g 1 leaf N mg g 1 leaf N mg g 1 specific leaf area cm 2 g 1 what regulates C gain or loss across scales NPP is about half of GPP what regulates C gain or loss across scales GPP ecosystem respiration both positively correlated with greenness NDVI these relationships make ecosystem C cycling modeling possible source Vourlitis et al 2003 Spatial variation in regional CO 2 exchange for the Kuparuk River Basin Alaska over the summer growing season large spatial scale modeling of GPP leaf area index leaf area per unit ground area can be measured by satellite remote sensing to produce NDVI greenness index live green plants appear relatively dark in the PAR relatively bright in the near infrared N content physiological activity how much chlorophyll large spatial scale modeling of GPP Maximum NDVI bimonthly average Air temperature average daily Solar radiation average daily measured NDVI for the Kuparuk watershed northern Alaska 1994 1995 source Vourlitis et al 2003 Spatial variation in regional CO 2 exchange for the Kuparuk River Basin Alaska over the summer growing season modeled ecosystem respiration for the Kuparuk watershed northern Alaska 1994 1995 high rate is 5 g C m 2 d 1 source Vourlitis et al 2003 Spatial variation in regional CO 2 exchange for the Kuparuk River Basin Alaska over the summer growing season modeled GPP for the Kuparuk watershed northern Alaska 1994 1995 high rate is 4 g C m 2 d 1 source Vourlitis et al 2003 Spatial variation in regional CO 2 exchange for the Kuparuk River Basin Alaska over the summer growing season modeled NEE for the Kuparuk watershed northern Alaska 1994 1995 high rate is 2 g C m 2 d 1 source Vourlitis et al 2003 Spatial variation in regional CO 2 exchange for the Kuparuk River Basin Alaska over the summer growing season caveats To model NPP and NEE you must model plant respiration Not trivial respiration results from multiple processes with different rates in different tissues roots cannot be remotely sensed method requires lots of measurements LAI N What regulates productivity at an ecosystem scale What controls leaf area N etc LIMITING RESOURCE Liebig s Law of the Minimum Plant growth is limited by a single resource at any one time Another resource becomes limiting only when the supply of the first resource is increased above the point of limitation Chapin et al pg 383 By the deficiency or absence of one necessary constituent all others being present the soil is rendered barren for all those crops to the life of which that one constituent is indispensible Translated from Liebig 1855 Liebig s Law of the Minimum It is indisputable that when a plant needs 12 substances to develop it will not grow if any one of those is missing and it will always grow poorly when one of those is not available in a sufficiently large amount as required by the nature of the plant Translated from Sprengel 1928 Liebig s Law of the Minimum Implications 1 If you add more of the limiting resource production will increase 2 If you add anything else production will be unaffected This probably applies to crop plants but does it apply to ecosystems Production Growth testing Liebig s Law of the Minimum Threshold Limited by resource Limited by either A Another resource B Genetic limit to growth Resource Supply e g N CO2 etc testing Liebig s Law of the Minimum Production Growth testing Liebig s Law of the Minimum Add N Resource Supply e g N CO2 etc Production Growth testing Liebig s Law of the Minimum Add P Add N Resource Supply e g N CO2 etc Production Growth testing Liebig s Law of the Minimum Add Ca Add N Resource Supply e g N CO2 etc Production Growth testing Liebig s Law of the Minimum Add micronutrients Fe Mg Add N Resource Supply e g N CO2 etc Maximum possible growth rate testing Liebig s Law of the Minimum issues 1 it isn t absolute lowest quantity that matters but relative lowest quantity Supply Demand Demand varies among species 2 plants can shift allocation to control demand e g produce low nutrient foliage CAM photosynthesis 3 plants can control resource supply e g shift allocation to resource acquisition systems root shoot ratio testing Liebig s Law of the Minimum imagine P is limiting N is not What does a plant do produce low P high N foliage increase allocation to P acquisition now P is less limiting N is relatively more limiting Both N P become somewhat limiting balance point where multiple resources are somewhat limiting may be better that where one is very limiting testing Liebig s Law of the Minimum Plants evolve to tolerate low resource conditions low growth rates Production Growth If you increase resource availability these plants may be outcompeted by faster growing plants Crop species adapted to high resource availability Species adapted to low resource availability Resource Supply e g N CO2 etc Production Growth community level response to increasing resources including species replacement Resource Supply e g N CO2 etc ecosystems and nutrient limitation Low nutrient systems Plant adapted to low nutrients Low maximum growth rates Not nutrient limited Very high nutrient systems Not nutrient limited Moderate nutrient systems Plants have a high capacity to use nutrients High maximum growth rates Nutrient limited which biome degree of nutrient limitation ecosystems and nutrient limitation Add nutrients increase growth Add nutrients replace community Add nutrients no response nutrient availability


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