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PK13:Trophic interactions among soil organisms in contrasting land‐use systems in Kenya, studied with stable‐isotope technique
PK13:Trophic interactions among soil organisms in contrasting land‐use systems in Kenya, studied with stable‐isotope technique
PK13:Trophic interactions among soil organisms in contrasting land‐use systems in Kenya, studied with stable‐isotope technique
PK13:Trophic interactions among soil organisms in contrasting land‐use systems in Kenya, studied with stable‐isotope technique
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PK13:Trophic interactions among soil organisms in contrasting land‐use systems in Kenya, studied with stable‐isotope technique

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A presentation by Dr. Jan lagerlöf

A presentation by Dr. Jan lagerlöf

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  • 1. 5/27/2010 Trophic interactions among soil organisms in contrasting  land‐use systems in Kenya, studied with stable‐isotope  Project facts technique • Research grants from Formas (Swedish Research Council for  Environment, Agricultural Sciences and Spatial Planning) in co‐operation  with Sida Jan Lagerlöf1, Mary Gikungu2, Crispus Maribie3, Jamleck Muturi John4, and Peter Okoth5 • Special call for Swedish scientists’ work at CGIAR Institutes: Five months  1 Swedish University of Agricultural Sciences (SLU), Dept. of  work during two consecutive years + technical assistance, travelling,  work during two consecutive years + technical assistance travelling Ecology, P.O.Box 7044, SE‐750 07 Uppsala, Sweden some equipment, etc 2National Museum of Kenya, P.O.Box 30197‐00100, Nairobi, Kenya • Two periods: 2008‐2009 + 2010‐2011 3 School of Biological Sciences, University of Nairobi, P.O.Box 30197‐00100, Nairobi, Kenya Encurrage 4 Dept. of Zoological Sciences, Kenyatta University, P.O.box 43844‐ Swedish scientists to 00100, Nairobi, Kenya work with 5 TSBF‐CIAT, c/o ICRAF, Gigiri, P.O.Box 30677‐00100, Nairobi tropical agriculture and environment in CGIAR 1 institutions 2 How to study food webs and feeding relationships 1. Gut content analyses: – Microscope observations – Immunological methods, ELISA – Biochemical methods, e.g. DNA analysis Collembola, Folsomia fimetaria gut content Photo J. Lagerlöf 3 4 FAO web page How to study food webs and feeding relationships How to study food webs and feeding relationships 2. Observation of feeding behaviour 3. Attractiveness of different food sources 5. Trace food sources to the next trophic level by 4. Growth and reproduction on different food sources – Radioactive isotopes (e.g. 14C) – Stable isotopes (e.g. 13C, 15N) Fungivorous nematodes (Aphelenchus avenae) feeding on Amoeba (Testacea) feeding hyphae of the plant parasitic fungus on nematod Verticillium dahliae Photo SLU Photo J. Lagerlöf 5 6 1
  • 2. 5/27/2010 How to study food webs and feeding relationships Types of studies that can be done with stable isotopes Stable isotopes – can be analysed with  mass spectrometer • Ratios of natural abundances of stable isotopes in different parts of  • Isotope ratios (e.g. 13C/12C=R) are compared relative to a standard. The  a food web – for studies of trophic levels deviation (δ) of the ratio relative to the standard is expressed per  thousand (“per mil” or ‰) Study 1 in BGBD Kenya: Natural isotope ratios of soil organisms in  • δX = [(R sample/R standard)‐1)]*1000 soil with different disturbance regimes • X is either N or C • Enrichment of food items and follow the enrichment though the  food web – for studies of feeding relations:  • Organism tissues are more enriched in both the heavy isotopes of  plant material → grazers → predators → top predators nitrogen 15N and carbon 13C than their food source Study 2 in BGBD Kenya: Enrichment of the growing crop with 13C  • → Increase of δN with approximately 3.4‰ per trophic level  in field experiment ‐ following of 13C in the food web. • → Increase of δC with approximately 1‰ per trophic level 7 8 Study 1 in BGBD Kenya: Natural isotope ratios in of soil organisms in soil  Study 1 in BGBD Kenya: Natural isotope ratios in of soil  with different disturbance regimes organisms in soil with different disturbance regimes Procedure: • Sampling microarthopods in the field Oct ‐ Nov 2008 • Extraction of microarthropods • Sorting into taxonomic groups (family or genera for  collembola and mites, higher l l f ll b l d i hi h level for others) h ) • Drying freezing Natural Forest Napier (fodder grass) • Weighing into tin capsuls, 0.02‐0.2 mg dw per sample • Hypothesis: Disturbed systems have shorter food chains and each species group  • Analysis of δ13C and δ 15N signatures (‰) by mass  will have broader feeding niche than in less disturbed systems. • Activity: Sampling of microarthropods in Natural Forest and Napier (fodder  spectrometry, in Sweden Lund University grass), BGBD sites in Embu. Sorting into lower taxa. Determination of 13C/12C and  15N/14N ratios.  Start September – November 2008 9 10 Photo J. Lagerlöf Study 2 in BGBD Kenya: Enrichment of the growing crop with 13C in field  experiment ‐ following of 13C in the food web Study 2: Food webs in agricultural fields studied with 13C labelling (control without labelling) four replicates Start April 2009 Field experiment: Organic matter Field experiment, • Hypothesis:  KARI Research Station Embu, 4 ‐ Certain soil animals and other organisms are linked to the growing crop  replicates in blocks (grazer food chain) as their primary food source, directly or indirectly.  ‐ Others are linked to dead organic matter (decomposer food chain).  ‐ This will vary with degree of organic matter amendment and  Studied treatments: Maize Manure, 4 tons/ha/y disturbance. disturbance Bare soil Manure, 4 tons/ha/y • Questions asked:   Maize NPK, 120 kg/y ‐ To what extent do taxonomic and functional groups of soil animals  Bare soil NPK, 120 kg/y derive their nourishment from the growing crop, directly of indirectly? ‐ To what extent do they use the dead organic matter as their basic food  source?  Labelling: of growing maize crop (manure and ‐ How will this vary with organic matter amendment? NPK fertilized) with 13CO2, 27-28 April 2009 11 12 2
  • 3. 5/27/2010 13CO2 labelling of maize Embu April 2009 450,0 340,0 C 2 c n e tra ninc a b r p m 430,0 hme p 320,0 300,0 410,0 280,0 260,0 390,0 240,0 O o c n tio 220,0 370,0 200,0 180,0 350,0 160,0 140,0 330,0 -5 5 15 25 35 45 55 0 5 10 15 20 25 30 35 40 Time minutes CO2 upptake in maize with CO2 emission from bare soil NPK fertilization with NPK fertilization 300,0 570,0 Labelling of maize 250,0 with 13CO2 (above) 520,0 200,0 470,0 150,0 Monitoring of CO2 420,0 100,0 concentration in the 50,0 370,0 atmosphere of the 0,0 perpex box (left) 0 5 10 15 20 25 30 35 320,0 -50,0 0 5 10 15 20 25 30 35 40 CO2 upptake in maize with CO2 emission from bare soil 13 manure fertilzation with manure fertilization 14 Preliminary results study 1 Study 2: Sampling: Soil, plants, roots and soil organisms (mesofauna, and Natural abundanceδ13C and δ15N signatures (‰) of Soil Arthropods microorganisms) 2, 4 and 6 weeks after labelling from Natural Forest Embu, Kenya  (each symbol representing one Analyses: isotope ratios in animals, plantmaterial and soil - Mass observation) spectrometer 35 In microorganisms – fatty acid analysis (PLFA) followed by mass 30 Coll spectrometer analysis Oribat 25 Gamasina 20 δ15N‰ Uropodina 15 Trombid 10 Pseudoscorp Chilopoda 5 Diplopod 0 Symphyla ‐30 ‐25 ‐20 ‐15 ‐10 ‐5 0 Ant δ13C‰ 15 16 Natural abundances of δ13C and δ15N signatures (‰) of Oribatid mite families 10 9 Brachyphy δ 8 Carabodidae Natural 1 Natural abundance δ13C and δ15N signatures (‰)  5 7 Damfielidae forest 6 Eupthacaridae of Soil Arthropods from  Napier Field, Embu, Kenya   N 5 ‰ Galumnaeidae (each symbol representing one measurement ) 4 Hermannidae 3 Northridiidae 60 2 Oppiidae 1 Otocephidae 50 0 Ptacaridae ‐30 ‐25 ‐20 ‐15 ‐10 ‐5 0 δ 40 Coll δ13C‰ 1 Oribat 5 30 60 Gamasina N ‰ 20 Chilopoda Napier δ 50 Ant 1 10 Trombid 5 40 Hermannidae N 0 ‰ 30 Oppiidae ‐25 ‐20 ‐15 ‐10 ‐5 0 Otocepheidae 20 δ13C‰ 10 0 ‐25 ‐20 ‐15 ‐10 ‐5 0 17 δ13C‰ 18 3
  • 4. 5/27/2010 Natural abundances of δ13C and δ15N signatures (‰) of Natural abundances of δ13C and δ15N signatures (‰) of predatory mite Gamasina families Collembola families 30 25 Brachystom δ 20 Entom 10 Natural 1 Hypogastr 9 forest 5 15 8 Gamasina spp, Isotomid N ‰ Neanurid Natural 7 Laelapidae 10 δ Odontellid forest 1 6 Liacaridae 5 Macrochelidae 5 Onychiur 5 Sminth N 4 Oligogamasidae 0 ‰ 3 Parasitidae ‐30 30 ‐25 25 ‐20 20 ‐15 15 ‐10 10 ‐5 5 0 2 Polyaspidae δ13C‰ 1 Rhodacaridae 18 0 δ 16 ‐30 ‐25 ‐20 ‐15 ‐10 ‐5 0 Napier 1 14 δ13C‰ 5 12 N ‰ 10 Poduridae 8 6 4 2 0 ‐15 ‐14.8 ‐14.6 ‐14.4 ‐14.2 ‐14 δ13C‰ 19 20 Preliminary conclusions: Discussion and comments -The technique functions -There are differences in feeding among taxonomic groups (family, genera) of mite and collembola – shown as different natural • We are grateful for comments and  abundance δ13C and δ15N signatures suggestions. Continuation of the work: • There is place for people to join in and study  -Continuation of analysis of δ13C and δ15N signatures i C ti ti f l i f d i t in other organisms or questions in these  other organisms or questions in these soil, microorganisms and microarthropods in study 1 and 2 ongoing or planned experiment. - Collecton of more data on natural δ13C and δ15N for microarthropods and other soil organism groups; • Suggestions for follow‐up studies and new  earthworms, enchytraieds, nematodes applications for funding. -Extended labelling experiment with sampling of larger number of organism groups 21 22 Thank you for your attention 23 Photo: H. Friberg J. Lagerlöf & N.N. 4

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