Maximizing the information obtained from chamber-based greenhouse gas exchange measurements in remote areas

Measurements of greenhouse gas (GHG) fluxes, particularly methane (CH4) and nitrous oxide (N2O) in mountain ecosystems are scarce due to the complexity and unpredictable behavior of these gases, in addition to the remoteness of these ecosystems. In this context, we measured CO2, CH4, and N2O fluxes in four semi-natural pastures in the Pyrenees to investigate their magnitude and range of variability. Our interest was to study GHG phenomena at the patch-level, therefore we chose to measure the gas-exchange using a combination of a gas analyzer and manual chambers. The analyzer used is a photoacoustic field gas-monitor that allows multi-gas instantaneous measurements. After implementing quality control and corrections, data was of variable quality. We tackled this by categorizing data as to providing quantitative or only qualitative information:•50% and 59% of all CH4 and N2O data, respectively, provided quantitative information above the detection limit.•We chose not to discard data providing only qualitative information, because they identify highest- and lowest-flux peak periods and indicate the variability of the fluxes, along different altitudes and under different climatic conditions.•We chose not to give fluxes below detection limit a quantitative value but to acknowledge them as values identifying periods with low fluxes.Measurements of greenhouse gas (GHG) fluxes, particularly methane (CH4) and nitrous oxide (N2O) in mountain ecosystems are scarce due to the complexity and unpredictable behavior of these gases, in addition to the remoteness of these ecosystems. In this context, we measured CO2, CH4, and N2O fluxes in four semi-natural pastures in the Pyrenees to investigate their magnitude and range of variability. Our interest was to study GHG phenomena at the patch-level, therefore we chose to measure the gas-exchange using a combination of a gas analyzer and manual chambers. The analyzer used is a photoacoustic field gas-monitor that allows multi-gas instantaneous measurements. After implementing quality control and corrections, data was of variable quality. We tackled this by categorizing data as to providing quantitative or only qualitative information:•50% and 59% of all CH4 and N2O data, respectively, provided quantitative information above the detection limit.•We chose not to discard data providing only qualitative information, because they identify highest- and lowest-flux peak periods and indicate the variability of the fluxes, along different altitudes and under different climatic conditions.•We chose not to give fluxes below detection limit a quantitative value but to acknowledge them as values identifying periods with low fluxes.Measurements of greenhouse gas (GHG) fluxes, particularly methane (CH4) and nitrous oxide (N2O) in mountain ecosystems are scarce due to the complexity and unpredictable behavior of these gases, in addition to the remoteness of these ecosystems. In this context, we measured CO2, CH4, and N2O fluxes in four semi-natural pastures in the Pyrenees to investigate their magnitude and range of variability. Our interest was to study GHG phenomena at the patch-level, therefore we chose to measure the gas-exchange using a combination of a gas analyzer and manual chambers. The analyzer used is a photoacoustic field gas-monitor that allows multi-gas instantaneous measurements. After implementing quality control and corrections, data was of variable quality. We tackled this by categorizing data as to providing quantitative or only qualitative information:•50% and 59% of all CH4 and N2O data, respectively, provided quantitative information above the detection limit.•We chose not to discard data providing only qualitative information, because they identify highest- and lowest-flux peak periods and indicate the variability of the fluxes, along different altitudes and under different climatic conditions.•We chose not to give fluxes below detection limit a quantitative value but to acknowledge them as values identifying periods with low fluxes.Peer reviewe

Plant Functional Diversity, Climate and Grazer Type Regulate Soil Activity in Natural Grasslands

Global change modifies vegetation composition in grasslands with shifts in plant functional types (PFT). Although changes in plant community composition imply changes in soil function, this relationship is not well understood. We investigated the relative importance of environmental (climatic, management and soil) variables and plant functional diversity (PFT composition and interactions) on soil activity and fertility along a climatic gradient. We collected samples of soil and PFT biomass (grasses, legumes, and non-legume forbs) in six extensively managed grasslands along a climatic gradient in the Northern Iberian Peninsula. Variation Partitioning Analysis showed that abiotic and management variables explained most of the global variability (96.5%) in soil activity and fertility; soil moisture and grazer type being the best predictors. PFT diversity accounted for 27% of the total variability, mostly in interaction with environmental factors. Diversity-Interaction models applied on each response variable revealed that PFT-evenness and pairwise interactions affected particularly the nitrogen cycle, enhancing microbial biomass nitrogen, dissolved organic nitrogen, total nitrogen, urease, phosphatase, and nitrification potential. Thus, soil activity and fertility were not only regulated by environmental variables, but also enhanced by PFT diversity. We underline that climate change-induced shifts in vegetation composition can alter greenhouse gas—related soil processes and eventually the feedback of the soil to the atmosphere.This work was funded by the Spanish Science Foundation (FECYT) through the projects CAPAS (CGL2010-22378-C03-01), BIOGEI (CGL2013-49142-C2-1-R) and IMAGINE (CGL2017-85490-R). H. Debouk was supported by a FPI fellowship from the Spanish Ministry of Economy and Competitiveness (BES-2011-047009). L. San Emeterio was funded by a Talent Recruitment grant from Obra Social La Caixa—Fundación CAN

Assessing the effect of global change on plant functional structure, greenhouse gases, and soil functions in grasslands

L'objectiu d'aquesta tesi és investigar el paper dels grups funcionals de plantes (GFP) en relació a l’estabilitat de la comunitat vegetal, els fluxos de GEH i les funcions del sòl, i com aquestes interaccions es regulen pel clima. La composició de GFP va influenciar els GEH i les funcions del sòl però les variables ambientals van regular aquest efecte. L’escalfament va afavorir la dominància d’espècies oportunistes i de creixement ràpid en detriment d’espècies més conservatives, causant una reducció en la diversitat específica. La composició i l’estructura funcional van tenir una major influencia en la productivitat i l’estabilitat de la comunitat que la diversitat específica. Els GEH es van reduir amb l’altitud, i incrementar durant l’estiu. La interacció entre GFP va afavorir l’assimilació de CH4 i N2O en comparació a la dominància d’un sòl GFP. Les interaccions entre GFP van també afavorir les funcions de sòl relacionades amb el cicle del N.El objetivo principal de esta tesis fue investigar el efecto de los grupos funcionales de plantas sobre la estabilidad de la vegetación, los flujos de GEI y las funciones del suelo, y cómo las condiciones climáticas regulan sus interacciones. La estructura funcional de las plantas en pastos influyó la estabilidad de la vegetación, los flujos de GEI, la actividad y fertilidad del suelo, y ese efecto está regulado por el clima. El calentamiento causó la dominancia de especies oportunistas sobre las más conservadoras; reduciendo así la riqueza específica. Los rasgos funcionales tuvieron una mayor influencia en la productividad y estabilidad de las comunidades frente al efecto de la diversidad. Los flujos de GEI aumentaron en verano y disminuyeron con la altitud. La interacción entre grupos funcionales incrementó la absorción de CH4 y N2O respecto a grupos individuales. Las interacciones entre grupos funcionales favorecieron también las funciones de suelo relacionadas con el ciclo de N.The main objective of this thesis is to investigate how plant functional types (PFT) affect vegetation stability, greenhouse gas (GHG) fluxes and soil functions, and how these interactions are regulated by climatic conditions. We found that plant functional structure strongly influences vegetation stability, GHG fluxes, and soil activity and fertility in grassland, but this relationship is regulated by climate. Warming lead to the dominance of acquisitive fast growing species over conservative species; thus reducing species richness. The functional traits structure in grasslands had greater influence on the productivity and stability of the community under warming, compared to diversity effects. GHG fluxes decreased with altitude- the colder the grassland site the lower the fluxes-, and increased during summer. The interaction between PFTs enhanced CH4 and N2O uptake compared to single PFTs. Also, PFT evenness and pairwise interactions between PFTs enhanced soil functions related to the N cycle

Functional Trait Changes, Productivity Shifts and Vegetation Stability in Mountain Grasslands during a Short-Term Warming.

Plant functional traits underlie vegetation responses to environmental changes such as global warming, and consequently influence ecosystem processes. While most of the existing studies focus on the effect of warming only on species diversity and productivity, we further investigated (i) how the structure of community plant functional traits in temperate grasslands respond to experimental warming, and (ii) whether species and functional diversity contribute to a greater stability of grasslands, in terms of vegetation composition and productivity. Intact vegetation turves were extracted from temperate subalpine grassland (highland) in the Eastern Pyrenees and transplanted into a warm continental, experimental site in Lleida, in Western Catalonia (lowland). The impacts of simulated warming on plant production and diversity, functional trait structure, and vegetation compositional stability were assessed. We observed an increase in biomass and a reduction in species and functional diversity under short-term warming. The functional structure of the grassland communities changed significantly, in terms of functional diversity and community-weighted means (CWM) for several traits. Acquisitive and fast-growing species with higher SLA, early flowering, erect growth habit, and rhizomatous strategy became dominant in the lowland. Productivity was significantly positively related to species, and to a lower extent, functional diversity, but productivity and stability after warming were more dependent on trait composition (CWM) than on diversity. The turves with more acquisitive species before warming changed less in composition after warming. Results suggest that (i) the short-term warming can lead to the dominance of acquisitive fast growing species over conservative species, thus reducing species richness, and (ii) the functional traits structure in grassland communities had a greater influence on the productivity and stability of the community under short-term warming, compared to diversity effects. In summary, short-term climate warming can greatly alter vegetation functional structure and its relation to productivity

Functional Trait Changes, Productivity Shifts and Vegetation Stability in Mountain Grasslands during a Short-Term Warming

Plant functional traits underlie vegetation responses to environmental changes such as global warming, and consequently influence ecosystem processes. While most of the existing studies focus on the effect of warming only on species diversity and productivity, we further investigated (i) how the structure of community plant functional traits in temperate grasslands respond to experimental warming, and (ii) whether species and functional diversity contribute to a greater stability of grasslands, in terms of vegetation composition and productivity. Intact vegetation turves were extracted from temperate subalpine grassland (highland) in the Eastern Pyrenees and transplanted into a warm continental, experimental site in Lleida, in Western Catalonia (lowland). The impacts of simulated warming on plant production and diversity, functional trait structure, and vegetation compositional stability were assessed. We observed an increase in biomass and a reduction in species and functional diversity under short-term warming. The functional structure of the grassland communities changed significantly, in terms of functional diversity and community-weighted means (CWM) for several traits. Acquisitive and fast-growing species with higher SLA, early flowering, erect growth habit, and rhizomatous strategy became dominant in the lowland. Productivity was significantly positively related to species, and to a lower extent, functional diversity, but productivity and stability after warming were more dependent on trait composition (CWM) than on diversity. The turves with more acquisitive species before warming changed less in composition after warming. Results suggest that (i) the short-term warming can lead to the dominance of acquisitive fast growing species over conservative species, thus reducing species richness, and (ii) the functional traits structure in grassland communities had a greater influence on the productivity and stability of the community under short-term warming, compared to diversity effects. In summary, short-term climate warming can greatly alter vegetation functional structure and its relation to productivity

Results of multiple regression models to assess the effect of the plant functional traits (SLA, LDMC, height, start of first flowering, % prostrate, % rhizomes) on above-ground biomass, with transplant (highland and lowland) and site (p1 and p2 sites in the highland).

<p>^a***P < 0.001</p><p>^bP-values in bold indicate significant relationships (P-values < 0.05)</p><p>Results of multiple regression models to assess the effect of the plant functional traits (SLA, LDMC, height, start of first flowering, % prostrate, % rhizomes) on above-ground biomass, with transplant (highland and lowland) and site (p1 and p2 sites in the highland).</p

Effect of the transplant on the diversity indices.

<p>Effect of the transplant experiment on diversity indices: Species richness (left), Simpson’s reciprocal diversity index with equivalent numbers (centre), and Functional diversity’s index Rao with equivalent numbers (left) along time. The black points correspond to the lowland, and the white points correspond to the highland. The whiskers refer to standard deviation. See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0141899#pone.0141899.g001" target="_blank">Fig 1</a> for more information on sampling dates and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0141899#pone.0141899.t001" target="_blank">Table 1</a> for the corresponding statistical tests.</p

Effect of the transplant experiment on the CWM of traits.

<p>Effect of the transplant experiment on the Community weighted means (CWM) of SLA (upper left), % of rhizomatous species (upper right), start of first flowering (lower left), and % of prostrate plants (lower right) along time. The black points correspond to the lowland, and the white points correspond to the highland. The whiskers refer to standard deviation. The x axis indicates the dates of the repeated samplings (frequency) within each turf. The first sampling was done in mid May and the last one in the lowland at the beginning of September. For the corresponding statistical tests see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0141899#pone.0141899.t001" target="_blank">Table 1</a>.</p

Relationship between the initial CWM SLA and the change in vegetation composition.

<p>Relationship between the initial CWM SLA and the change in vegetation composition (Bray-Curtis dissimilarity) between beginning and end of experiment, in both the highland and the lowland. The black points correspond to the lowland, and the white points correspond to the highland. Solid linear regression line reflects significant relationship (p < 0.05) in the lowland; and no line represents no significance.</p