Lecture 30 Decomposition2009 forWeb

Lecture 30 Decomposition2009 forWeb - Decomposition Outline...

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1 Decomposition Decomposition This week: This week: Chp Chp . 21 (today & Fri.) (today & Fri.) 2 Outline Why care about decomposition? What is decomposing? Who is doing the decomposition? How does decomposition occur? Decomp. processes How fast? Decomposition rates and controls CO 2 3 Decomposition Def.: The physical & chemical breakdown of dead organic matter (dead plants, animals, microbes, etc.) CH 2 O + O 2 CO 2 + H 2 O Focus here: aerobic decomposition photosynthesis Decomp. 4 Why Care About Decomposition? • Provides energy for detrivores Forms the base of the soil food chain • Releases CO 2 to atmosphere Will global warming accelerate? • Produces complex soil organic matter Stores carbon in ecosystems; affects soil fertility • Recycles nutrients Decomp. rate can limit nutrient supply to plants 5 Global C Pools (Pg C) Souce: Sabine et al. 2004 (Atmosphere, Vegetation), Davidson & Janssens 2006. (Soil) Boxes are to scale Atmosphere 750 Vegetation 650 650 Litter 200 Litter 200 Upland Soil Upland Soil (to 3 m depth) (to 3 m depth) 2300 2300 6 0 200 400 600 800 1000 1200 Tropical forest Temp. forest Boreal forest S h r u b la n d T ropical savanna Te m p . g a s land Desert s c ru Tu dra Dun e , o ck, ice Cultivated W tla NPP (kg C m -2 yr -1 ) NPP and Soil C by Ecosystem Type 0 5 10 15 20 25 Tr ical forest mp . fo st Bo eal forest bland ica l sava Tem g rassland Desert scr ub Tundr ock, ice Cultivate etlands Soil Carbon (kg C m 68 Schlesinger 1977
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7 Soil carbon stocks represent the balance of plant C inputs and losses to decomposition . Forest Floor Inputs : plant litter (dead leaves, wood, and roots) • dead critters (fungi, bacteria, chipmunks, etc.) Outputs : CO 2 , and CH 4 from decomposition Output : Dissolved organic carbon (DOC) Mineral Soil and Humus 8 What’s decomposing? Mostly, dead plant parts: •S t a r c h , ~2-8% •P r o t e i n s • Cellulose & Hemicellulose, 25-65% •F a t s & W a x e s • Phenolics •Tannins •Lignin Increasingly difficult to decompose 9 Cellulose – VERY long chains of simple sugar molecules (2000-15,000) Bonds between sugars flipped from starch structure – Large fraction of leaves, wood – Main constituent of cell walls Cellulose fibers used to make paper – Cannot be used for plant (or human) respiration; moderate quality for microbial breakdown 10 Tannins – Small polymers made from phenolic acids 6-C ring structures – Difficult to break down
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This note was uploaded on 01/10/2010 for the course BIOEE 2610 at Cornell University (Engineering School).

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Lecture 30 Decomposition2009 forWeb - Decomposition Outline...

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