Role of mycorrhizal fungi in belowground C and N cycling Doc. Jussi Heinonsalo Department of Forest Sciences, University of Helsinki Finnish Meteorological Institute Finland
The aim and learning goals of this lecture To undestand the link between plant photosynthesis and soil organic matter (SOM) decomposition To undertand why this is important from climate change perspective
Role of mycorrhizal fungi in belowground C and N cycling Why this is important to study and understand? Reason1: Increase in CO 2 -levels Temperature increase in northern latitudes Northern boreal forest zone Source: IPCC Climate Change 2014 Synthesis Report Summary for Policymakers
Role of mycorrhizal fungi in belowground C and N cycling Why this is important to study and understand? Reason 2: Northern boreal forests soilscontain a lot of nitrogen (N), but the forest growth is still limited by N. Plant N uptake n. 20-30 kg! Tot al N in soil approx. 2000 kg! Why plant s do not take up N? Korhonen ym. 2013 Biogeosciences, 10, 1083 1095
The formation and decomposition of SOM Photosynthesis forms organic material that ends up in soil The more the forest grows the more organic matter enters soil and the soil C stock increases? Bacteria and fungi are responsible for SOM decomposition The higher temperature, the faster SOM decomposes? Soil CO 2 flux increases due to higher decomposition rate? Kuva:ht t p:/ / sciencewit hmrsb.weeb ly.com/microorganisms.html
The effect of soil temperature on photosynthesis and soil respiration The increasing temperature increase both photosynthesis and soil respiration Cold = 7-12 C Medium = 12-15 C Warm = 16-22 C Faster carbon turnover ( C flow through soil ) Not clear if the C remaining in the ecosystem is changing Pumpanen, Heinonsalo, Rasilo, Villemot, Ilvesniemi (2012) Tree Physiology
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Transport of photosynthetically assimilated C to soil Rhizosphere means the soil associated with roots and mycorrhizosphere soil associated with roots and mycorrhizal fungi Carbon allocated to soil by plants increase microbial activity in rhizosphere and mycorrhizosphere Microbial communities are different than in soil NOT associated with roots or fungal hyphae Root Kuva: Sari Timonen Mycorrhizal fungi Fungal hyphae
Mycorrhizal symbiosis Variety of different mycorrhizal associations (ecto-, ericoid-, arbuscular etc. See in Finnish: Timonen ja Valkonen, Sienten Biologia 2013) Forest trees in Boreal region form ectomycorrhizal plant-fungal symbiosis Association in almost every individual root tip Fungi receives carbohydrates from host plant, fungi delivers nutrients for the plant
C- allocation within rhizosphere and mycorrhizosphere EM= fungal mycelium R= rhizosphere M1/M2= mycorrhizosphere Source: Heinonsalo et al. 2004 Plant and Soil
Who are there in the soil? Fungal community structure analysed seasonally and vertically Santalahti et al. 2016 FEMS Microbiology Ecology
Bacteria on roots and soils of different plant species Soil under different plant differ from each other Some specific, some common bacteria Timonen et al. 2016 Microbial Ecology
Fungal hyphae and decomposition processes The enzymes exuded by fungal hyphae are important in SOM decomposition Auto- and heterotrophic organisms different strategies In the Figure, the enzymatic decomposition machinery of a brown-rot fungi Mycorrhizal, root-associated symbiotic fungi have similar activities Figure: T. Lundell in Timonen ja Valkonen (Eds.), Sienten Biologia, 2013 s. 270
Priming i.e. increase (or decrease) of SOM decomposition due to additional labile C input Plants allocate photosynthetically assimilated C compounds to soil that support microbial activity In forest soil, plants need N that is mostly bound to SOM and not easily available to plants Plant aims to obtain N with help of mycorrhizal fungi SOM decomposition induced Yellow hyphae: Piloderma olivaceum, mycorrhizal fungi -producese.g. β-glucosidase, protease, phosphatase, peroxidase and laccase enzymes -all important in SOM decomposition Priming Kuzyakov et al. 2000, SBB
Experiment to show Piloderma s role in plant organic N uptake Laboratory scale Protease production by ectomycorrhizl fungal strain Piloderma sp. Axenic growth experiment of Scots pine with Piloderma sp. for organic (amino acids or BSA protein) N uptake Field scale Monthly soil sampling from March to October Using 454 sequencing, abundance of Piloderma genus Morphotyping Piloderma in root tips Measurements of protease activities in root tips
Piloderma s role in plant organic N uptake Spring Summer Autumn Main results: Scots pine can access BSA protein only with help of Piloderma fungi The abundance of Piloderma correlates significantly with photosynthesis (GPP) photosynthesis and N uptake linked? Heinonsalo, Sun, Santalahti, Bäcklund, Hari, Pumpanen (2015) PLOS One
The role of Scots pine in priming Treatment 1 SOM Growth in standardized soil T and light conditions Treatment 2 SOM + glucose Treatment 3 seedling Treatment 4 seedling + glucose C4-glucose addition during 1 month + incubation afterwards Natural isotope measurements; 14 C-AMS, 13 C, 15 N Nutrient measurements (ICP, C/N) Soil fauna nematodes, bacteria, mycorrhiza Enzyme activity Photosynthesis measurements (Pmax)
The role of Scots pine in priming Main results: In planted microcosms, older CO 2 in soil respiration older SOM decomposed stabile SOM pool affected Plants induced priming effect Lindén, Heinonsalo, Buchmann, Oinonen, Sonninen, Hilasvuori, Pumpanen (2014) Plant and Soil
By which mechanisms plant induce priming? Greenhouse experiment with 2-year old Scots pine Within one month, following enzymes were added to planted or non-planted pots in liquid form Proteases (Pr) Laccase, manganese peroxidase and proteases (LMPr) BSA protein as control
By which mechanisms plant induce priming? Main results: Total N quantities in soil decrease if Both oxidative and protease enzymes were added in non-planted soil OR Plant was present Presence of plant had an effect on Dissolved N (less if plant) NH 4 (less if plant) Total amino acids (more if plant) SOM content (less if plant) SOM decomposition by enzymes the critical step Plants induce the production of these enzymes? Kieloaho, Pihlatie, Dominguez Carrasco, Kanerva, Parshintsev, Riekkola, Pumpanen, Heinonsalo (2016) SBB
Photosynthesis and decomposition of soil organic material consequences Modelling Current models do not take into account priming The model development needs further work to improve accuray of the predictions in the future Soil C is lost here! Estimated changes in soil C stock until 2050 (Crowther ym. Quantifying soil carbon losses in response to warming 2016 Nature). RED COLOUR= PREDICTED LOSS
Summary Increase in plant photosynthesis increase both biomass production (more C) and decomposition (C lost) The activity of decomposer microbes increase with higher temperature and increased litter production Plant-associated microbial communities diverse Plants have a dynamic effect on SOM decomposition through rootassociated microbes: priming! Does the soil C stocks increase or decrease in the future boreal forests? Research on this topic goes actively on all over the world
Literature Mycorrhizal types, fungal role in decompostion etc. Timonen ja Valkonen (Eds.). 2013. Sienten Biologia. Priming-phenomen, principles, research methods etc. Kuzyakov ym. 2000. Review of mechanisms and quantification of priming effects. Soil Biology and Biochemistry 32:1485-1498. Changes in soil C stocks and modelling Crowther ym. 2016. Quantifying soil carbon losses in response to warming Nature 540:104-111. Sulman ym. 2014. Microbe-driven turnover offsets mineral-mediated storage of soil carbon under elevated CO 2. Nature Climate Change 4: 1099-1102. Own papers, e.g. Heinonsalo et al. 2004 Plant and Soil Heinonsalo et al. 2010 SBB Linden et al. 2014 Plant and Soil