Interaction between tannins and fungal necromass stabilizes fungal residues in boreal forest soils

See also the Commentary on this article by Hattenschwiler et al., 223: 5-7.Peer reviewe

Lannoitetypen huuhtoutumisen kinetiikasta ja määristä ruokohelvellä ja nurmella

Maatalous aiheuttaa noin 50 % Suomen vesistöjen typpikuormituksesta. Huuhtoumaan vaikuttaa mm. kasvilaji. Monivuotisten energiakasvien typpihuuhtoumia ei tunneta hyvin. Tässä työssä verrattiin Ruokohelven (Phalaris arundinaceae) ja nurmen typen huuhtoumia kivennäismaalla. Nurmiviljelyn tiedetään vähentävän typpihuuhtoumaa. Ruokohelpi on bioenergiakasvina osoittautunut tehokkaaksi hiilinieluksi eloperäisillä mailla, ja sen dityppioksidipäästöt eloperäisiltä mailta ovat olleet alhaiset. Tutkimuksessa sovellettiin isotooppitekniikoita antamalla typpilannoitus typpi-15 rikastetulla (10 AT-%) ammoniumnitraattina (15NH415NO3). Työssä määritettiin mikä on lannoitetypen huuhtouman osuus kokonaistyppihuuhtoumasta..Ruokohelpi- ja nurmikoealat lannoitettiin noudattaen kasvikohtaisia käytäntöjä (ruokohelpi 80 kg N ha-1, nurmi 2 * kertaan 100 kg N ha-1). Vesinäytteet kerättiin typpianalyyseihin maaperään 0,8 m syvyyteen esiasennetuista keraamisista imuputkista. Näytteistä määritettiin mineraalitypen (NH4 ja NO3) pitoisuudet sekä niiden typpi-isotooppikoostumukset. Näytteenottomenetelmä ei sallinut huuhtouman määrällistä arviointia, vaan enemmänkin laadullisen (15N/14N). Tutkimus toteutettiin Maaningalla kesäkuusta 2011 kesäkuuhun 2012 koealoilla, jotka oli perustettu keväällä 2009.Kummallakin kasvilla nitraattityppipitoisuudet 0,8 m syvyydellä olivat keskimäärin 7 mg NO3-N l-1 heinäkuun loppuun asti, jonka jälkeen NO3-N-pitoisuudet lähtivät laskuun, ruokohelvellä nopeammin. Lokakuun 2011 lopussa ruokohelpiviljelmän NO3-N pitoisuus jäi alle 1 mg l-1 kun se nurmella oli 3,5 mg l-1.Ensimmäisen lannoituksen jälkeen lannoitetypen prosentuaalinen osuus 0,8 m syvyyden nitraattitypestä oli kummallakin kasvilla alle 1 %. Ruokohelvellä lannoiteperäinen huuhtouma ei juuri muuttunut kasvukauden edetessä. Nurmelle annettu toinen lannoitus nosti lannoiteperäisen typen huuhtouman 34,5±19,2 %:iin. Suuri huuhtouma liittyi todennäköisesti toisen lannoituksen jälkeen tulleeseen rankkasateeseen, mikä huuhtoi pintamaahan kertynyttä lannoitetyppeä syvemmälle maaprofiiliin. Kohonnutta lannoitetypen huuhtoumaa ei kuitenkaan seurannut kohonnut NO3-N kokonaispitoisuus.Nurmelta huuhtoutuvan nitraattitypen kokonaispitoisuus ei poikennut merkittävästi ruokohelven vastaavasta, vaikka nurmea lannoitettiin enemmän. Sen sijaan toista lannoitusta seurannut lannoitetypen huuhtouma nurmelta oli huomattavan korkea

Inferring Phytoplankton, Terrestrial Plant and Bacteria Bulk delta C-13 Values from Compound Specific Analyses of Lipids and Fatty Acids

Stable isotope mixing models in aquatic ecology require delta C-13 values for food web end members such as phytoplankton and bacteria, however it is rarely possible to measure these directly. Hence there is a critical need for improved methods for estimating the delta C-13 ratios of phytoplankton, bacteria and terrestrial detritus from within mixed seston. We determined the delta C-13 values of lipids, phospholipids and biomarker fatty acids and used these to calculate isotopic differences compared to the whole-cell delta C-13 values for eight phytoplankton classes, five bacterial taxa, and three types of terrestrial organic matter (two trees and one grass). The lipid content was higher amongst the phytoplankton (9.5 +/- 4.0%) than bacteria (7.3 +/- 0.8%) or terrestrial matter (3.9 +/- 1.7%). Our measurements revealed that the delta C-13 values of lipids followed phylogenetic classification among phytoplankton (78.2% of variance was explained by class), bacteria and terrestrial matter, and there was a strong correlation between the delta C-13 values of total lipids, phospholipids and individual fatty acids. Amongst the phytoplankton, the isotopic difference between biomarker fatty acids and bulk biomass averaged -10.7 +/- 1.1 parts per thousand for Chlorophyceae and Cyanophyceae, and -6.1 +/- 1.7 parts per thousand for Cryptophyceae, Chrysophyceae and Diatomophyceae. For heterotrophic bacteria and for type I and type II methane-oxidizing bacteria our results showed a -1.3 +/- 1.3 parts per thousand, -8.0 +/- 4.4 parts per thousand, and -3.4 +/- 1.4 parts per thousand delta C-13 difference, respectively, between biomarker fatty acids and bulk biomass. For terrestrial matter the isotopic difference averaged -6.6 +/- 1.2 parts per thousand. Based on these results, the delta C-13 values of total lipids and biomarker fatty acids can be used to determine the delta C-13 values of bulk phytoplankton, bacteria or terrestrial matter with +/- 1.4 parts per thousand uncertainty (i.e., the pooled SD of the isotopic difference for all samples). We conclude that when compound-specific stable isotope analyses become more widely available, the determination of delta C-13 values for selected biomarker fatty acids coupled with established isotopic differences, offers a promising way to determine taxa-specific bulk delta C-13 values for the phytoplankton, bacteria, and terrestrial detritus embedded within mixed seston.Peer reviewe

Much more than carbon: Element stocks in ice-rich permafrost of the Yedoma domain

Soils of the permafrost zone store globally relevant reservoirs of frozen matter, such as organic matter, mineral elements as well as other biogeochemical relevant compounds like contaminants. Besides the well-studied organic carbon (OC), other compounds can become available in active biological and hydrological element cycling as global climate change is warming northern permafrost regions nearly four times faster than the global average. Current heating in Siberia is unprecedented during the past seven millennia, triggering widespread permafrost degradation and collapse. This is especially relevant for our study region, the Yedoma domain. In this region, a large amount of belowground ice is present and the ground can become unstable with warming, allowing the mobilisation of previously frozen sediments with their geochemical element contents. With this presentation, we synthesise recent studies, which have improved the understanding of various frozen stocks. Here, we estimated that the Yedoma domain contains 41.2 Gt of nitrogen (N), which increases the previous estimate for the circumpolar permafrost zone by ~46 %. The highest element stock within the Yedoma domain is estimated for Si (2739 Gt), followed by Al, Fe, K, Ca, Ti, Mn, Zr, Sr, and Zn. The stocks of Al and Fe (598 and 288 Gt, respectively) are in the same order of magnitude as OC (327-466 Gt). Concerning contaminants, we focused on mercury. Using the ratio of mercury to OC (R(HgC), value based on own measurements: 2.57 μg Hg g C−1) and the OC levels from various studies for a first rough estimation of the Hg reservoir, we estimate the Yedoma mercury pool to be ~542,000 tons. In conclusion, we find that deep thaw of the Yedoma permafrost domain and its degradation will bear the potential to change the availability of various elements in active biogeochemical and hydrological cycles in northern regions, which will have the potential to change crucial ecosystem variables and services

More than carbon: Frozen element inventories in ice-rich Yedoma permafrost

Soils of the permafrost zone store globally relevant reservoirs of frozen matter, such as organic matter, mineral elements as well as other biogeochemical relevant compounds like contaminants. Besides well-studied organic carbon (OC), other compounds can become available in active biological and hydrological element cycling as global climate change is warming northern permafrost regions nearly four times faster than the global average. Current heating in Siberia is unprecedented during the past seven millennia, triggering widespread permafrost degradation and collapse. This is especially relevant for our study region, the Yedoma domain. In this region, a large amount of belowground ice is present and the ground can become unstable with warming, allowing the mobilisation of previously frozen sediments with their geochemical element contents. With this presentation, we want to synthesise recent studies, which have improved the understanding of various frozen stocks. Here, we estimated that the Yedoma domain contains 41.2 Gt of nitrogen, which increases the previous estimate for the circumpolar permafrost zone by ~46%. The highest element stock within the Yedoma domain is estimated for r Si (2739 Gt), followed by Al, Fe, K, Ca, Ti, Mn, Zr, Sr, and Zn. The stocks of Al and Fe (598 and 288 Gt) are in the same order of magnitude as OC (327–466 Gt). Concerning contaminants, we focused on mercury. Using the ratio of mercury to OC (RHgC, our found value: 2.57 μg Hg g C−1) and the OC levels from various studies for a first rough estimation of the Hg reservoir, we estimate the Yedoma mercury pool to be ~542000 tons. In conclusion, we find that deep thaw of the Yedoma permafrost domain and its degradation will bear the potential to change the availability of various elements in active biogeochemical and hydrological cycles, which will have the potential to change crucial ecosystem variables and services

Áhrif hækkaðs jarðvegshita á myndun koldíoxíðs (CO2 ), metans (CH4 ), hláturgass (N2 O), nituroxíðs (NO) og nitraðrar sýru (HONO) í skógarjarðvegi á Suðurlandi.

Geothermal areas can be local sources of greenhouse gases, both directly from the geothermal system or because of soil warming effects on biological sources. In this study we repeated field measurements methane (CH4) and nitrous oxide (N2O) fluxes along the soil temperature (Ts) gradient in a Sitka spruce (Picea sitchensis) stand at the ForHot study site in southern Iceland, where geothermal soil warming had started eight years earlier. We complemented these results with in situ measurements of carbon dioxide (CO2) and topsoil sampled in the same plots to study the production rates of those gases at 20 °C in the laboratory, as well as nitric oxide (NO) and nitrous acid (HONO). We showed that the eight year long exposure to elevated Ts had changed the topsoil, including its microbial properties and the production potentials of these gases. However, the production rates of CO2, CH4 and N2O measured in laboratory conditions did not clearly follow the in situ fluxes. We discuss both adaptation of microbes and origin of greenhouse gases (depth patterns and microbial vs. geothermal sources) as possible reasons for these discrepancies.Jarðhitasvæði geta verið uppsprettur ýmissa gróðurhúsalofttegunda, annað hvort beint upp úr jarðhitakerfinu eða vegna áhrifa aukins jarðvegshita á ýmsa lífræna ferla. Í þessari rannsókn endurtókum við mælingar á flæði metans (CH4) og hláturgass (N2O) með auknum jarðvegshita (Ts) í foldu í sitkagreniskógi (Picea sitchensis) á ForHot rannsóknasvæðinu á Suðurlandi, þar sem jarðhitasvæði hafði færst undir átta árum áður. Við bættum einnig við mælingum á losun koldíoxíðs (CO2) í foldu og bárum - niðurstöðurnar saman við losun þessara sömu gastegunda og nituroxíðs (NO) og nitraðrar sýru (HONO) úr jarðvegskjörnum úr sömu reitum sem mældir voru við 20 °C á rannsóknastofu. Niðurstöðurnar sýndu að átta ára jarðvegshlýnun hafði bæði breytt efnasamsetningu og örveruflóru reitanna og þar með getu til að framleiða áðurnefndar lofttegundir. Hinsvegar breyttist framleiðslugeta CO2, CH4 og N2O við 20 °C ekki reglulega með auknum Ts í foldu. Við ræðum bæði aðlögun örvera að auknum hita og hvernig uppruni gróðurhúsalofttegunda (úr mismunandi dýpi í jarðvegi og hvort hann er líffræðilegur eða jarðfræðilegur) getur mögulega útskýrt þær niðurstöður sem við fengum.The project was funded by the Academy of Finland (no. 297735 and no. 132045). This work also contributes to the ForHot-Forest (Project No.163272-051 of the Icelandic Research Council), as well as to the Nordic CAR-ES project and the ClimMani COST Action (ES1308) and the International Program CryoCARB and COUP. The Kuopio Naturalists’ Society is thanked for a travel grant. Jaana Rissanen is thanked for assisting in the laboratory at the University of Eastern Finland. We also want to acknowledge the staff at the Reykir campus of the Agricultural University of Iceland for great logistic support.Peer Reviewe

Forest fires in Canadian permafrost region : the combined effects of fire and permafrost dynamics on soil organic matter quality

Wildfires burn approximately 1% of boreal forest yearly, being one of the most significant factors affecting soil organic matter (SOM) pools. Boreal forests are largely situated in the permafrost zone, which contains half of global soil carbon (C). Wildfires advance thawing of permafrost by burning the insulating organic layer and decreasing surface albedo, thus increasing soil temperatures. Fires also affect SOM quality through chemical and physical changes, such as the formation of resistant C compounds. The long-term post-fire effects on SOM quality, degradability and isotopic composition are not well known in permafrost forests. We studied the effect of forest fires on the proportional sizes of SOM pools with chemical fractionation (extracting with water, ethanol and acid) of soil samples (5, 30 and 50cm depths) collected from a fire chronosequence in the upland mineral soils of the Canadian permafrost zone. We also determined the C-13 and N-15 isotopic composition of soil after fire. In the topsoil horizon (5cm) recent fire areas contained a smaller fraction of labile SOM and were slightly more enriched with N-15 and C-13 than older fire areas. The SOM fraction ratios reverted towards pre-fire status with succession. Changes in SOM were less apparent deeper in the soil. Best predictors for the size of recalcitrant SOM fraction were active layer depth, vegetation biomass and soil C/N ratio, whereas microbial biomass was best predicted by the size of the recalcitrant SOM fraction. Results indicated that SOM in upland mineral soils at the permafrost surface could be mainly recalcitrant and its decomposition not particularly sensitive to changes resulting from fire.Peer reviewe