Drivers of CO2 fluxes in the tundra and within four tundra vegetation types

Ilmaston lämmetessä arktisten ekosysteemien olosuhteissa ja kasvillisuuden koostumuksessa ennakoidaan tapahtuvan muutoksia, jotka vaikuttavat yksittäisten ympäristöjen ja koko arktisen alueen hiilen kiertoon. Kasvillisuuden koostumuksessa tapahtuvat muutokset vaikuttavat ekosysteemien kykyyn sitoa hiiltä, mutta pensastumisen kaltaisilla kasvillisuuden määrän ja koostumuksen muutoksilla voi olla myös maaperän hiileen liittyviä takaisinkytkentöjä. Tundraympäristöjen hiilenkierrossa tapahtuvien muutosten ennakoimiseksi on ymmärrettävä, miten eri tekijät säätelevät hiilidioksidivoita olosuhteiltaan ja kasvillisuuden koostumukseltaan heterogeenisen tundran eri osissa. Nivaatioiden muodostamilla ympäristögradienteilla kerätystä aineistosta tutkittiin, miten vuot vaihtelevat, ja mitkä eri mikroilmasto-, kasvillisuus- ja maaperämuuttujat ovat yhteydessä hiilidioksidivoihin tundralla ja sen kasvillisuustyypeissä kasvukauden aikana. Ekosysteemirespiraation (ER) vaihtelu oli perustuotantoa (GPP) pienempää, ja nettoekosysteemivaihto (NEE) kasvoi (hiilidioksidin nettonielu) GPP:n kasvaessa. Hiilidioksidin nettosidonta oli suurinta pystyvarvikossa muita kasvillisuustyyppejä suuremmasta ER:stä huolimatta, ja pienintä pienen kasvipeitteen karukoissa, jotka olivat pienestä GPP:stä huolimatta pääosin hiilidioksidin nettonieluja. Kasvillisuuden määrä oli tärkeä GPP:n ja NEE:n vaihtelua selittänyt tekijä koko aineistossa ja kasvillisuustyypeissä. Kasvillisuuden määrä selitti ilmalämpötilan ja maaperän kosteuden ohella myös ER:n vaihtelua koko aineistossa ja eri kosteus- sekä lämpöolosuhteet kasvillisuuden määrän ohella kasvillisuustyypeissä. Mikroilmasto-olosuhteet auttoivat selittämään NEE:n vaihtelua koko aineistossa, karukossa ja maanmyötäisessä varvikossa ilmalämpöolosuhteiden ollessa kosteutta ja maaperän lämpötilaa tärkeämpiä NEE:tä selittäviä tekijöitä karukkoa lukuun ottamatta. Ilmalämpötila oli muita kasvillisuustyyppejä voimakkaammin yhteydessä suurempaan GPP:hen ja ER:ään pystyvarvikoissa, ja ilmalämpötila oli pystyvarvikoissa kasvillisuuden määrää tärkeämpi ER:n vaihtelua selittävä tekijä. Maaperän lämpötila ei ollut koko aineistossa tai varvikkotyypeissä yhteydessä suurempaan ER:ään. Karukoissa maaperän lämpötilan ER:ää ja hiilidioksidin nettolähdettä lisäävä vaikutus kasvoi kosteuden kasvaessa. Orgaanisen kerroksen paksuus oli heikossa yhteydessä suurempaan hiilidioksidin nettolähteeseen niittyjä lukuun ottamatta ja maaperän pH selitti voiden vaihtelua osin kasvillisuuden määrän kautta. Hiilidioksidivoita vaikuttaa säätelevän tundralla ja sen kasvillisuustyypeissä ensisijaisesti kasvillisuuden määrä ja toissijaisena mikroilmasto-olosuhteet, joista erityisesti ilmalämpötila ja kosteusolosuhteet vaikuttavat olevan yhteydessä ER:ään. Maaperän lämpötilan hajotustoimintaa lisäävä vaikutus on voinut olla pieni suhteessa autotrofiseen respiraatioon, eikä ole siksi ollut havaittavissa positiivisena vasteena ER:n ja maaperän lämpötilan välillä koko aineistossa ja varvikkotyypeissä. Kuivuus ja varjostuksen takia alhainen maaperän lämpötila varvikkotyypeissä ovat voineet hidastaa hajotustoimintaa, heikentää sen lämpötilariippuvuutta ja pienentää heterotrofisen respiraation osuutta ER:stä. Tulokset viittaavat lisääntyvän kasvillisuuden määrän ja kasvillisuuden korkeuskasvun voimistavan hiilen sidontaa tundraekosysteemeissä riippumatta kasvillisuustyypistä. Varpukasvillisuuden lisääntymisen maaperän lämpötilaa laskeva vaikutus ja mahdollinen kuivuuden lisääntyminen esimerkiksi kasvukauden pidentymisen seurauksena voivat hidastaa hajotustoimintaa ja vahvistaa tundran hiilidioksidin nettonielua kasvukauden aikana. Kasvillisuuden määrän, mikroilmaston ja maaperän ominaisuuksien vaihteleva kyky selittää voiden vaihtelua eri kasvillisuustyypeissä voi viitata eri kasvillisuustyyppien hiilidioksidivoiden olevan herkkiä eri ympäristötekijöiden muutoksille. Tulokset korostavat siten kasvillisuustyypin ja kasvillisuuden koostumuksen huomioinnin merkitystä tundran hiilidioksidivoissa tapahtuvia muutoksia ennakoitaessa. Myös hajotustoimintaa rajoittavien tekijöiden merkitys tundran hiilidioksidivoiden muutoksissa voi olla keskeinen. Hajotustoimintaa rajoittavat tekijät voivat määrittää sitä, missä ympäristöissä kasvillisuuden tuottoisuuden kasvu kasvattaa hiilidioksidin nettonielua, ja missä hiilidioksidin nettonielu pienenee tai ympäristö muuttuu hiilidioksidin nettolähteeksi.As the climate warms tundra ecosystems will face changes that have an impact on their carbon cycle. Arctic tundra is already experiencing changes in plant species composition and distribution, and vegetation height expected to increase. Vegetation shifts such as shrubification can increase carbon uptake from the atmosphere to the tundra ecosystems but changes in soil microclimate and plant-microbe interactions related to vegetation shifts can also create feedbacks that increase carbon losses from the ecosystems to the atmosphere. To better understand changes in tundra carbon dioxide (CO2) fluxes related to climate change and vegetation shifts, it’s crucial to understand the factors controlling CO2 fluxes in the tundra in general and in the tundra environments that differ in their vegetation composition. We used environmental gradients created by late-lying snowbanks to collect the data and we used modelling to understand the factors controlling CO2 fluxes in the tundra and within four different vegetation types during the growing season. The vegetation types included in the study were barrens, meadow-like environments, prostrate shrub tundra (heat) and erect shrub tundra (shrub). Gross primary production (GPP) and ecosystem respiration (ER) were the highest in shrub plots, smaller in the heat and in meadow-like environments and the smallest in barrens. Net CO2 sink increased with vegetation cover and GPP, but also barrens with little vegetation were still mostly net CO2 sinks during the growing season due to low ER. The amount of vegetation measured in vegetation height and cover well explained the variation in GPP and net ecosystem exchange (NEE) in the whole data and within vegetation types. ER was also related to the amount of vegetation but was more affected by microclimate, mainly air temperature and soil moisture, than GPP and NEE. In shrub plots, variation in ER was explained by air temperature more than by vegetation cover or height. Microclimate variables were not important in explaining variation in GPP in the whole data or within vegetation types but air temperature in heath and in the whole data and soil temperature and soil moisture in barrens helped to explain variation in NEE. In the whole data, heat and shrub plots soil temperature was not related to higher ER. Depth of organic layer explained some variation in NEE and ER in the whole data and some variation in NEE in some of the vegetation types. Soil pH was not an important factor explaining CO2 fluxes, but it was related to vegetation type and vegetation distribution especially in the whole data. The main factor controlling CO2 fluxes in the tundra and within different vegetation types seemed to be the amount of vegetation. Air temperature and soil moisture help to explain the variation especially in ER. The ability of vegetation parameters to explain variation in ER may be partly because of a relatively small amount of heterotrophic respiration compared to autotrophic respiration in the system or because of a positive link between the amount of vegetation and the amount of decomposition. Drought during the field campaigns may have limited decomposition and decreased temperature sensitivity of decomposition which may partly explain the insensitivity of ER to soil temperature. In heat and in shrub plots the shading effect of vegetation lowered soil temperature and may have slowed decomposition. As the ability of vegetation, microclimate and soil variables to explain variation in CO2 fluxes differed between vegetation types, CO2 fluxes of different vegetation types may respond to changes in the tundra environment differently. The results imply that the effect of vegetation composition should be considered when estimating how tundra ecosystem CO2 fluxes will respond to climate change. Similarly, the role of factors controlling decomposition, such as drought and shading effect of shrub vegetation, may be important in determining the future carbon balance of the tundra

Geomorphological processes shape plant community traits in the Arctic

Aim Geomorphological processes profoundly affect plant establishment and distributions, but their influence on functional traits is insufficiently understood. Here, we unveil trait-geomorphology relationships in Arctic plant communities. Location High-Arctic Svalbard, low-Arctic Greenland and sub-Arctic Fennoscandia. Time period 2011-2018. Major taxa studied Vascular plants. Methods We collected field-quantified data on vegetation, geomorphological processes, microclimate and soil properties from 5,280 plots and 200 species across the three Arctic regions. We combined these data with database trait records to relate local plant community trait composition to dominant geomorphological processes of the Arctic, namely cryoturbation, deflation, fluvial processes and solifluction. We investigated the relationship between plant functional traits and geomorphological processes using hierarchical generalized additive modelling. Results Our results demonstrate that community-level traits are related to geomorphological processes, with cryoturbation most strongly influencing both structural and leaf economic traits. These results were consistent across regions, suggesting a coherent biome-level trait response to geomorphological processes. Main conclusions The results indicate that geomorphological processes shape plant community traits in the Arctic. We provide empirical evidence for the existence of generalizable relationships between plant functional traits and geomorphological processes. The results indicate that the relationships are consistent across these three distinct tundra regions and that geomorphological processes should be considered in future investigations of functional traits.Peer reviewe

Geomorphological processes shape plant community traits in the Arctic

Aim Geomorphological processes profoundly affect plant establishment and distributions, but their influence on functional traits is insufficiently understood. Here, we unveil trait-geomorphology relationships in Arctic plant communities. Location High-Arctic Svalbard, low-Arctic Greenland and sub-Arctic Fennoscandia. Time period 2011-2018. Major taxa studied Vascular plants. Methods We collected field-quantified data on vegetation, geomorphological processes, microclimate and soil properties from 5,280 plots and 200 species across the three Arctic regions. We combined these data with database trait records to relate local plant community trait composition to dominant geomorphological processes of the Arctic, namely cryoturbation, deflation, fluvial processes and solifluction. We investigated the relationship between plant functional traits and geomorphological processes using hierarchical generalized additive modelling. Results Our results demonstrate that community-level traits are related to geomorphological processes, with cryoturbation most strongly influencing both structural and leaf economic traits. These results were consistent across regions, suggesting a coherent biome-level trait response to geomorphological processes. Main conclusions The results indicate that geomorphological processes shape plant community traits in the Arctic. We provide empirical evidence for the existence of generalizable relationships between plant functional traits and geomorphological processes. The results indicate that the relationships are consistent across these three distinct tundra regions and that geomorphological processes should be considered in future investigations of functional traits.Peer reviewe

Geomorphological processes shape plant community traits in the Arctic

AIM : Geomorphological processes profoundly affect plant establishment and distributions, but their influence on functional traits is insufficiently understood. Here, we unveil trait–geomorphology relationships in Arctic plant communities. LOCATION : High-Arctic Svalbard, low-Arctic Greenland and sub-Arctic Fennoscandia. TIME PERIOD : 2011–2018. MAJOR TAXA STUDIED : Vascular plants. METHODS : We collected field-quantified data on vegetation, geomorphological processes, microclimate and soil properties from 5,280 plots and 200 species across the three Arctic regions. We combined these data with database trait records to relate local plant community trait composition to dominant geomorphological processes of the Arctic, namely cryoturbation, deflation, fluvial processes and solifluction. We investigated the relationship between plant functional traits and geomorphological processes using hierarchical generalized additive modelling. RESULTS : Our results demonstrate that community-level traits are related to geomorphological processes, with cryoturbation most strongly influencing both structural and leaf economic traits. These results were consistent across regions, suggesting a coherent biome-level trait response to geomorphological processes. MAIN CONCLUSIONS : The results indicate that geomorphological processes shape plant community traits in the Arctic. We provide empirical evidence for the existence of generalizable relationships between plant functional traits and geomorphological processes. The results indicate that the relationships are consistent across these three distinct tundra regions and that geomorphological processes should be considered in future investigations of functional traits.DATA AVAILABILITY STATEMENT: Data and code are openly available (Kemppinen et al., 2022; https://doi.org/10.5281/zenodo.6410638).Arctic Interactions at the University of Oulu and Academy of Finland.Nessling foundation and the Kone Foundation.Carl Tryggers Stiftelse.Academy of Finland Flagship fundingAcademy of FinlandFinnish Cultural FoundationArctic Interactions at the University of Oulu; Academy of Finland; Nessling Foundation; the Kone Foundation; Carl Tryggers Stiftelse and Finnish Cultural Foundation.http://www.wileyonlinelibrary.com/journal/gebPlant Production and Soil Scienc

Set-up and instrumentation of the greenhouse gas measurements on experimental sites of continuous cover forestry

A set of experimental study sites was established to monitor greenhouse gas (GHG) emissions from drained peatland forests under different harvesting regimes in Finland. The purpose of these experimental sites is to study the effects of continuous cover forestry (CCF) and clear-cutting (CC) on ecosystem processes including GHG emissions and stand development on drained peatland forests. The sites represent fertile Norway spruce dominated peatland forests, where soil GHG emissions are high due to drainage that has exposed peat to decomposition in aerobic conditions. Two “flagship” sites for greenhouse gas (GHG) monitoring have been established and instrumented by the Natural Resources Institute Finland (Luke), University of Helsinki (UH) and the Finnish Meteorological Institute (FMI). The sites host continuous GHG monitoring with Eddy Covariance (EC) towers and with automatic chambers. In addition, greenhouse gas (CO2, CH4, and N2O) emissions are monitored with manually operated chambers at four sites, where effects of selection (CCF) harvests are studied with replicated treatments. These data will be used to calculate the ecosystem and soil GHG balances of the sites by using methodologies standardized earlier and compatible with the IPCC guidelines. On all experimental sites, ground water table (WT), tree growth and regeneration are monitored in different management trials. These data will form the basic data needed for designing and demonstrating optimal harvesting cycles and evaluating and generalizing the climate impacts. The results including the biological drainage capacity (evapotranspiration) of different-sized tree stands as well as the soil GHG balance of different tree stand – WT combinations will be incorporated into existing models that can be used to estimate the mitigation obtained with different management options and in different site and climatic conditions. The study sites are actively used for training and demonstration of alternative peatland management practices by host projects and by multiple stakeholders. The host projects and organizations also promote further extensions for the measurements and all complementary research activities are welcome to these study sites

Consistent trait-environment relationships within and across tundra plant communities

A fundamental assumption in trait-based ecology is that relationships between traits and environmental conditions are globally consistent. We use field-quantified microclimate and soil data to explore if trait–environment relationships are generalizable across plant communities and spatial scales. We collected data from 6,720 plots and 217 species across four distinct tundra regions from both hemispheres. We combined these data with over 76,000 database trait records to relate local plant community trait composition to broad gradients of key environmental drivers: soil moisture, soil temperature, soil pH and potential solar radiation. Results revealed strong, consistent trait–environment relationships across Arctic and Antarctic regions. This indicates that the detected relationships are transferable between tundra plant communities also when fine-scale environmental heterogeneity is accounted for, and that variation in local conditions heavily influences both structural and leaf economic traits. Our results strengthen the biological and mechanistic basis for climate change impact predictions of vulnerable high-latitude ecosystems

Soil microbial functional diversity changes under contrasting N2O emission events

editorial reviewedDenitrification, the reduction of nitrogen oxides (NO3-and NO2-) to NO, N2O and, ultimately, to N2 gas in soils, is classified as a microbiologically ‘broad process’ which can be conducted by a wide array of microbes belonging to remote phylogenetic groups. Further, understanding how environmental and management factors drive denitrification is challenging because they are scale-dependent, with large scale drivers affecting denitrification fluxes both directly and through drivers working at detailed small scales.  Despite of this, we hypothesized that denitrification processes, although highly complexes due to the multiple processes and environmental conditions involved, they could present a functional convergence at the microbial community level explained by a short list of microbial groups or functions.   On the other hand, different methodological approaches to assess soil microbial diversity are currently used; among them are multiple substrate-induced respiration by MicroResp™, enzymes activities and functional genes abundance and structure by GeoChip 5S microarray. We applied all those methods to study functional diversity in 5 different soils from 5 countries: Finland, Belgium; France, Switzerland and Italy. Studied soils have a wide range of soil pH, organic Carbon and Nitrogen content, and texture. Soils were sampled at Hot Moment and Low flux emission of N2O.    The main objective of this study was to explore possible convergences in terms of functional microbial diversity in contrasting N2O emission events (low emission versus hot moments).   Result showed that MicroResp™ , enzyme activities and GeoChip 5S microarray were reliable ecological indicator to evaluate soil microbial functionality diversity. Results stressed the importance to study soil microbiome at different magnitude of N2O emission with the aim to gain a deeper knowledge of nitrifiers community. Reciprocal relationship of those methodologies, soil proprieties and magnitude of flux emission of N2O are discussed.  

Observations of climate impacts of cutover peatland afforestation, and peatland forest restoration, in Finland

Non peer reviewe