BUSCADOR RECOLECTA

Incluye material complementario, Grasslands are one of the major sinks of terrestrial soil organic carbon (SOC). Understanding how environmental and management factors drive SOC is challenging because they are scale-dependent, with large-scale drivers affecting SOC both directly and through drivers working at small scales. Here we addressed how regional, landscape and grazing management, soil properties and nutrients, and herbage quality factors affect 20 cm depth SOC stocks in mountain grasslands in the Pyrenees. Taking advantage of the high variety of environmental heterogeneity in the Pyrenees, we built a dataset (n = 128) that comprises a wide range of environmental and management conditions. This was used to understand the relationship between SOC stocks and their drivers considering multiple environments. We found that temperature seasonality (difference between mean summer temperature and mean annual temperature; TSIS) was the most important geophysical driver of SOC in our study, depending on topography and management. TSIS effects on SOC increased in exposed hillsides, slopy areas, and relatively intensively grazed grasslands. Increased TSIS probably favours plant biomass production, particularly at high altitudes, but landscape and grazing management factors regulate the accumulation of this biomass into SOC. Concerning biochemical SOC drivers, we found unexpected interactive effects between grazer type, soil nutrients and herbage quality. Soil N was a crucial SOC driver as expected but modulated by livestock species and neutral detergent fibre contenting plant biomass; herbage recalcitrance effects varied depending on grazer species. These results highlight the gaps in knowledge about SOC drivers in grasslands under different environmental and management conditions. They may also serve to generate testable hypotheses in later/future studies directed to climate change mitigation policies., Research in this paper is based on the PAS-TUS Database, which was compiled from different funding sources over time, the most relevant being the EU Interreg III-A Programme (I3A-4-147-E) and the POCTEFA Programme/Interreg IV-A (FLUXPYR, EFA 34/08); the Spanish Science Foundation FECYT-MICINN (CARBOPAS: REN2002-04300-C02-01; CAR-BOAGROPAS: CGL2006-13555-C03-03 and CAPAS: CGL2010-22378-C03-01); and the Foundation Catalunya-La Pedrera and the Spanish Institute of Agronomical Research INIA (CARBO-CLUS: SUM2006-00029-C02-0). Leticia San Emeterio was funded through a Talent Recruitment grant from Obra Social La Caixa- Fundación CAN. The ARAID Foundation provided support to Juan José Jiménez. This work was funded by the Spanish Science Foundation FECYT-MINECO (projects BIOGEI: GL2013-49142-C2-1-R and IMAGINE: CGL2017-85490-R) and the University of Lleida (PhD Fellowship to Antonio Rodríguez).

Soil is the largest terrestrial carbon pool, making it crucial for climate change mitigation. Soil organic carbon (SOC) is suggested to depend on biodiversity components, but much evidence comes from diversity-function experiments. To disentangle the relationships of plant guild diversity with SOC storage (kg m−2) at broad spatial scales, we applied diversity-interaction models to a regional grassland database (n = 96) including wide environmental conditions and management regimes. The questions were: (1) Are the effects of plant guilds on SOC stocks in natural grasslands consistent with those found in experimental systems? (2) Are plant guild effects on SOC stocks independent of each other or do they show interactive—synergistic or antagonistic—effects? (3) Do environmental variables, including abiotic and management, modify guild effects on SOC stocks? Among our most novel results we found, legume effects on grassland SOC vary depending on legume proportion consistently across broad spatial scales. SOC increased with legume proportion up to 7–17%, then decreased. Additionally, these effects were strengthened when grasses and forbs were codominant. Grazing intensity modulated grass proportion effects on SOC, being maximum at relatively high intensities. Interpreting our results in terms of existing contrasted ecological theories, we confirmed at broad spatial scales and under wide-ranging environmental conditions the positive effects of plant guild diversity on SOC, and we showed how legumes exert a keystone effect on SOC in natural grasslands, probably related to their ability to fix inorganic N. Niche complementarity effects were illustrated when codominance of forbs and grasses at optimum legume proportions boosted SOC storage, whereas grass dominance increased SOC stocks at medium–high grazing intensities. These findings can facilitate the preparation of regional and local strategies to ameliorate the soil capacity to absorb carbon., Research in this paper is based on the PASTUS database, compiled from different funding sources over time, the most relevant being: the EU Interreg III- A Programme (I3A- 4- 147- E) and the POCTEFA Programme/Interreg IV- A (FLUXPYR, EFA 34/08); the Spanish Science Foundation FECYT- MICINN (CARBOPAS: REN2002- 04300- C02- 01; CARBOAGROPAS: CGL2006- 13555- C03- 03 and CAPAS: CGL2010- 22378- C03- 01); the Foundation Catalunya- La Pedrera; and the Spanish Institute of Agronomical Research INIA (CARBOCLUS: SUM2006- 00029- C02- 0). This work was funded by the Spanish Science Foundation FECYT- MINECO (BIOGEI: CGL2013-49142-C2-1-R and IMAGINE: CGL2017-85490-R) and the University of Lleida (PhD Fellowship to AR). This research article has received a grant for its linguistic revision from the Language Institute of the University of Lleida (2021 call).

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 a_ected 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.

1. Grassland diversity can support sustainable intensification of grassland production through increased yields, reduced inputs and limited weed invasion. We report the effects of diversity on weed suppression from 3 years of a 31-site continental-scale field experiment. 2. At each site, 15 grassland communities comprising four monocultures and 11 four-species mixtures based on a wide range of species' proportions were sown at two densities and managed by cutting. Forage species were selected according to two crossed functional traits, "method of nitrogen acquisition" and "pattern of temporal development". 3. Across sites, years and sown densities, annual weed biomass in mixtures and monocultures was 0.5 and 2.0 t DM ha−1 (7% and 33% of total biomass respectively). Over 95% of mixtures had weed biomass lower than the average of monocultures, and in two-thirds of cases, lower than in the most suppressive monoculture (transgressive suppression). Suppression was significantly transgressive for 58% of site-years. Transgressive suppression by mixtures was maintained across years, independent of site productivity. 4. Based on models, average weed biomass in mixture over the whole experiment was 52% less (95% confidence interval: 30%-75%) than in the most suppressive monoculture. Transgressive suppression of weed biomass was significant at each year across all mixtures and for each mixture. 5. Weed biomass was consistently low across all mixtures and years and was in some cases significantly but not largely different from that in the equiproportional mixture. The average variability (standard deviation) of annual weed biomass within a site was much lower for mixtures (0.42) than for monocultures (1.77). 6. Synthesis and applications. Weed invasion can be diminished through a combination of forage species selected for complementarity and persistence traits in systems designed to reduce reliance on fertiliser nitrogen. In this study, effects of diversity on weed suppression were consistently strong across mixtures varying widely in species' proportions and over time. The level of weed biomass did not vary greatly across mixtures varying widely in proportions of sown species. These diversity benefits in intensively managed grasslands are relevant for the sustainable intensification of agriculture and, importantly, are achievable through practical farm-scale actions.

With the aim to improve mixture design, particularly in regions vulnerable to climate change, we tested several forage communities following the biodiversity-ecosystem function (BEF) framework. We sowed monocultures and 4-species mixtures from a pool of 7 forage species in a sub-Mediterranean region (Eastern Pyrenees) and assessed the diversity effects on yield and resistance to weed invasion. The tested species included two grasses and five legumes with contrasting temporal patterns and different climatic amplitudes. The communities differed in their specific composition (mixture types) and the relative abundance of the components, following a simplex design, which allowed us to estimate separately the two components of the diversity effect: the individual species effects and that due to species interactions. Whereas monocultures performed in a highly variable way within and across harvests, both in relation to yield and weed suppression, mixture variability was narrower. Both functions increased in mixtures(with significant interaction effects between 24% and 57% for yield and 13% and 96% for weed suppression), especially in those mixtures including Mediterranean species, which showed the highest diversity effects that persisted over the three experimental years. Extreme climatic events during the experimental period might have affected not only the species' individual performances but also the strength of species interactions. Both components of diversity, identities and interactions, were key in maintaining high performances. We conclude that, under the current climate change scenario, it is important to include species in mixtures that increase resistance or resilience not only at the species level but also at the community level, through enhanced interaction effects.

Biochar applications have been proposed for mitigating some soil greenhouse gas (GHG) emissions. However, results can range from mitigation to no effects. To explain these differences, mechanisms have been proposed but their reliability depends on biochar type, soil and climatic conditions. Furthermore, it is found that the mitigation capacity is dependent on how the biochar is aging under field conditions. The effects on N2O, CH4 and CO2 emission rates of a gasification pine biochar (applied as 0, 5, and 30 t ha−1) were studied between 8 and 21 months of the application in an alkaline soil cropped to barley under Mediterranean climate. Together with GHG, soil chemical and biological properties were assessed, namely, changes in labile organic matter content and nutrient status, and pH, as well as microbial abundance, activity, and functional composition. During the 2 years of the application, significant changes were observed at the highest rate of biochar application such as higher contents of water, K+, Mg2+, SO42−, higher basal respiration, and with non-significant changes in microbial community, though with some temporal effects. Regarding GHG, N2O decreases coupled with CH4 increases in the summer sampling were measured, although only for the highest application rate scenario. Such effects were unrelated to pH, bioavailable nitrogen status, or bulk soil microbial community shifts. We hypothesized that the key is the porous structure of our wood biochar, which is able to provide more and diversified microbial microhabitats in comparison to bulk soil. At higher temperatures in summer, biologically-induced anoxic conditions in biochar pores acting as microsites may be promoted, where total denitrification to N2 occurs which leads to N2O uptake, while CH4 production is promoted.

Increasing numbers of fungal species have been described recently from semi-natural grassland soils, raising the conservation interest of these species-rich habitats. Here, we characterize the soil fungal community inhabiting six fairy rings in a montane grassland of the Eastern Pre-Pyrenees through fungal DNA metabarcoding of ITS2 amplicons. Distinct soil fungal communities were observed outside of the rings compared to inside the ring areas. Higher abundances of fungi belonging to Pleosporales and Eurotiales were observed outside fairy rings, whereas zones belonging to the fairy rings showed higher abundances of Agaricales. Fungal diversity was higher inside the rings than outside. We found diverse saprotrophic or putative saprotrophic taxa associated with the studied rings, including the genera Clavaria, Psathyrella, Tricholoma, Amanita and Lycoperdon. These findings highlight the importance of particular keystone taxa in the structuring of fungal communities and their effect on the overall grassland fungal community., This study was developed within the projects BIOGEI (CGL 2013-49142-C2-1-R) and CAPAS (CGL 2010-22378-C03-01) funded by the Spanish Science Foundation (FECYT) jointly with the FPU programme (FPU12/05849) run by the Spanish Ministry of Education. Funding from the project IMAGINE (CGL 2017-85490-R) allowed the completion of this work.

© 2022 The Authors. European Journal of Soil Science published by John Wiley & Sons Ltd on behalf of British Society of Soil Science. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited., Fairy rings promoting circular greening belts in the vegetation can shape soil microbial communities by altering soil conditions. Knowledge about soil variables involved in this process is incomplete. We characterised the soil microbial communities of six fairy rings in a montane grassland using phospholipid fatty acid (PLFA) profiling, and studied if changes in soil properties corresponded to changes in soil microbial PLFA patterns. Exchangeable potassium (K) decreased inside the current rings, while soil moisture increased in the zones where the greening belts were two years before sampling (R2015). Fairy ring associated changes in PLFA composition were highly related to soil K. Gram-negative bacteria were associated with the zones outside the ring with the highest K content, whereas Gram-positive bacteria proportions increased inside the ring-affected zones. An environmental stress indicator, the iso to anteiso ratio of PLFA 17:0, decreased in the R2015 zones, coinciding with the highest soil moisture contents. Our findings highlight the unreported importance of soil K in fairy ring dynamics affecting microbial communities. This common omission could lead to incorrect conclusions. Hence, the effects of fairy rings on soil should be further tested. Highlights Exchangeable potassium (K) decreased inside the current fairy rings. Fairy ring associated changes in PLFA microbial composition were present related to soil K. Soil moisture increased in the zones where the rings were 2 years before sampling. An environmental stress indicator decreased in those areas., COST Action ES1406; Universitat de Lleida; Spanish Science Foundation FECYT-MINECO, Grant/Award Numbers: IMAGINE, BIOGEI, CGL201785490-R, GL2013-49142-C2-1-R, Peer reviewed

Iberian holm oak meadows are savannah-like ecosystems that result from traditional silvo-pastoral practices. However, such traditional uses are declining, driving changes in the typical tree—open grassland structure of these systems. Yet, there are no studies integrating the whole ecosystem—including the arboreal and the herbaceous layer—as drivers of greenhouse gas (GHG: CO2, CH4 and N2O) dynamics. Here, we aimed at integrating the influence of tree canopies and interactions among plant functional types (PFT: grasses, forbs, and legumes) of the herbaceous layer as GHG exchange drivers. For that purpose, we performed chamber-based GHG surveys in plots dominated by representative canopy types of Iberian holm oak meadows, including Quercus species and Pinus pinea stands, the last a common tree plantation replacing traditional stands, and unraveled GHG drivers through a diversity-interaction model approach. Our results show the tree–open grassland structure, especially drove CO2 and N2O fluxes, with higher emissions under the canopy than in the open grassland. Emissions under P. pinea canopies are higher than those under Quercus species. In addition, the inclusion of diversity and compositional terms of the herbaceous layer improve the explained variability, with legumes enhancing CO2 uptake and N2O emissions. Changes in the tree cover and tree species composition, in combination with changes in the structure and composition of the herbaceous layer, will imply deep changes in the GHG exchange of Iberian holm oak meadows. These results may provide some guidelines to perform better management strategies of this vast but vulnerable ecosystem., This work was funded by the Spanish Science Foundation FECYT-MINECO: BIOGEI (GL2013-49142-C2-1-R) and IMAGINE (CGL2017-85490-R) projects and supported by a FPI fellowship to Mercedes Ibañez (BES-2014-069243).

1. Grassland diversity can support sustainable intensification of grassland production through increased yields, reduced inputs and limited weed invasion. We report the effects of diversity on weed suppression from 3 years of a 31-site continental-scale field experiment. 2. At each site, 15 grassland communities comprising four monocultures and 11 fourspecies mixtures based on a wide range of species' proportions were sown at two densities and managed by cutting. Forage species were selected according to two crossed functional traits, 'method of nitrogen acquisition' and 'pattern of temporal development'. 3. Across sites, years and sown densities, annual weed biomass in mixtures and monocultures was 0.5 and 2.0 t DM ha−1 (7% and 33% of total biomass respectively). Over 95% of mixtures had weed biomass lower than the average of monocultures, and in twothirds of cases, lower than in the most suppressive monoculture (transgressive suppression). Suppression was significantly transgressive for 58% of site-years. Transgressive suppression by mixtures was maintained across years, independent of site productivity. 4. Based on models, average weed biomass in mixture over the whole experiment was 52% less (95% confidence interval: 30%-75%) than in the most suppressive monoculture. Transgressive suppression of weed biomass was significant at each year across all mixtures and for each mixture. 5. Weed biomass was consistently low across all mixtures and years and was in some cases significantly but not largely different from that in the equiproportional mixture. The average variability (standard deviation) of annual weed biomass within a site was much lower for mixtures (0.42) than for monocultures (1.77). 6. Synthesis and applications. Weed invasion can be diminished through a combination of forage species selected for complementarity and persistence traits in systems designed to reduce reliance on fertiliser nitrogen. In this study, effects of diversity on weed suppression were consistently strong across mixtures varying widely in species' proportions and over time. The level of weed biomass did not vary greatly across mixtures varying widely in proportions of sown species. These diversity benefits in intensively managed grasslands are relevant for the sustainable intensification of agriculture and, importantly, are achievable through practical farm-scale actions. Dades primàries associades a l'article http://hdl.handle.net/10459.1/60559, Co-ordination of this project was supported by the EU Commission through COST Action 852 ‘Quality legume-based forage systems for contrasting environments’. M.T.S., R.L. and A.R. were supported by the Spanish Ministry of the Economy and Competitiveness through projects CARBOAGROPAS (CGL2006-13555-C03-01/BOS) and BIOGEI (CGL2013-49142-C2-1-R) and the Ministry of the Environment through OPS (209/PC08/3-08.2). L.K. was supported by an award from Science Foundation Ireland (09/RFP/EOB2546). A.L., J.A.F., J.C. and M.S. were partly supported by the EU FP7 project ‘AnimalChange’ under grant agreement no. 266018.

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.

Grasslands are one of the major sinks of terrestrial soil organic carbon (SOC). Understanding how environmental and management factors drive SOC is challenging because they are scale-dependent, with large-scale drivers affecting SOC both directly and through drivers working at small scales. Here we addressed how regional, landscape and grazing management, soil properties and nutrients, and herbage quality factors affect 20 cm depth SOC stocks in mountain grasslands in the Pyrenees. Taking advantage of the high variety of environmental heterogeneity in the Pyrenees, we built a dataset (n=128) that comprises a wide range of environmental and management conditions. This was used to understand the relationship between SOC stocks and their drivers considering multiple environments. We found that temperature seasonality (difference between mean summer temperature and mean annual temperature; TSIS) was the most important geophysical driver of SOC in our study, depending on topography and management. TSIS effects on SOC increased in exposed hillsides, slopy areas, and relatively intensively grazed grasslands. Increased TSIS probably favours plant biomass production, particularly at high altitudes, but landscape and grazing management factors regulate the accumulation of this biomass into SOC. Concerning biochemical SOC drivers, we found unexpected interactive effects between grazer type, soil nutrients and herbage quality. Soil N was a crucial SOC driver as expected but modulated by livestock species and neutral detergent fibre contenting plant biomass; herbage recalcitrance effects varied depending on grazer species. These results highlight the gaps in knowledge about SOC drivers in grasslands under different environmental and management conditions. They may also serve to generate testable hypotheses in later/future studies directed to climate change mitigation policies., Research in this paper is based on the PASTUS Database, which was compiled from different funding sources over time, the most relevant being the EU Interreg III-A Programme (I3A-4-147-E) and the POCTEFA Programme/Interreg IV-A (FLUXPYR, EFA 34/08); the Spanish Science Foundation FECYT-MICINN (CARBOPAS: REN2002-04300-C02-01; CARBOAGROPAS: CGL2006-13555-C03-03 and CAPAS: CGL2010-22378-C03-01); and the Foundation Catalunya-La Pedrera and the Spanish Institute of Agronomical Research INIA (CARBOCLUS: SUM2006-00029-C02-0). Leticia San Emeterio was funded through a Talent Recruitment grant from Obra Social La Caixa – Fundación CAN. The ARAID Foundation provided support to Juan José Jiménez. This work was funded by the Spanish Science Foundation FECYT-MINECO (projects BIOGEI: GL2013-49142-C2-1-R and IMAGINE: CGL2017-85490-R) and the University of Lleida (PhD Fellowship to Antonio Rodríguez).

Forage systems are the major land use, and provide essential resources for animal feeding. Assessing the influence of forage species on net ecosystem CO2 exchange (NEE) is key to develop management strategies that can help to mitigate climate change, while optimizing productivity of these systems. However, little is known about the effect of forage species on CO2 exchange fluxes and net biome production (NBP), considering: species ecophysiological responses; growth and fallow periods separately; and the management associated with the particular sown species. Our study assesses the influence of cereal monocultures vs. cereal legume mixtures on (1) ecosystem scale CO2 fluxes, for the whole crop season and separately for the two periods of growth and fallow; (2) potential sensitivities of CO2 exchange related to short-term variations in light, temperature and soil water content; and (3) NBP during the growth period; this being the first long term (seven years) ecosystem scale CO2 fluxes dataset of an intensively managed forage system in the Pyrenees region. Our results provide strong evidence that cereal-legume mixtures lead to higher net CO2 uptake than cereal monocultures, as a result of higher gross CO2 uptake, while respiratory fluxes did not significantly increase. Also, management associated with cereal legume mixtures favoured vegetation voluntary regrowth during the fallow period, which was decisive for the cumulative net CO2 uptake of the entire crop season. All cereal legume mixtures and some cereal monocultures had a negative NBP (net gain of C) during the growth period, indicating C input to the system, besides the yield. Overall, cereal legume mixtures enhanced net CO2 sink capacity of the forage system, while ensuring productivity and forage quality., We would like to thank F. Gouriveau, E. Ceschia and J. Elbers for their critical contribution to the installation of the eddy covariance tower and to data analysis, and D. Estany and H. Sarri for field assistance. The flux tower was installed during the FLUXPYR project (EFA34/08, INTERREG IV-A POCTEFA, financed by EU-ERDF, Generalitat de Catalunya and Conseil Régional Midi-Pyrénées). The following additional projects also contributed with funding to this work: CAPACITI (FP7/2007-2013 grant agreement n° 275855), AGEC 2012 (Generalitat de Catalunya), CAPAS (Spanish Science Foundation, CGL2010-22378-C03-01), BIOGEI (Spanish Science Foundation, CGL2013-49142-C2-1-R, supported by a FPI fellowship for Mercedes Ibañez, BES-2014-069243) and IMAGINE (Spanish Science Foundation, CGL2017-85490-R). We would like to acknowledge the Forest Science and Technology Centre of Catalonia (CTFC) for support with study site maintenance.

Unmanned aerial systems (UAS) are cost-effective, flexible and offer a wide range of applications. If equipped with optical sensors, orthophotos with very high spatial resolution can be retrieved using photogrammetric processing. The use of these images in multi-temporal analysis and the combination with spatial data imposes high demands on their spatial accuracy. This georeferencing accuracy of UAS orthomosaics is generally expressed as the checkpoint error. However, the checkpoint error alone gives no information about the reproducibility of the photogrammetrical compilation of orthomosaics. This study optimizes the geolocation of UAS orthomosaics time series and evaluates their reproducibility. A correlation analysis of repeatedly computed orthomosaics with identical parameters revealed a reproducibility of 99% in a grassland and 75% in a forest area. Between time steps, the corresponding positional errors of digitized objects lie between 0.07 m in the grassland and 0.3 m in the forest canopy. The novel methods were integrated into a processing workflow to enhance the traceability and increase the quality of UAS remote sensing., This research was funded by the Hessian State Ministry for Higher Education, Research and the Arts, Germany, as part of the LOEWE priority project Nature 4.0—Sensing Biodiversity. The grassland study was funded by the Spanish Science Foundation FECYT-MINECO through the BIOGEI (GL2013- 49142-C2-1-R) and IMAGINE (CGL2017-85490-R) projects, and by the University of Lleida; and supported by a FI Fellowship to C.M.R. (2019 FI_B 01167) by the Catalan Government.

Fairy rings promoting circular greening belts in the vegetation can shape soil microbial communities by altering soil conditions. Knowledge about soil variables involved in this process is incomplete. We characterised the soil microbial communities of six fairy rings in a montane grassland using phospholipid fatty acid (PLFA) profiling, and studied if changes in soil properties corresponded to changes in soil microbial PLFA patterns. Exchangeable potassium (K) decreased inside the current rings, while soil moisture increased in the zones where the greening belts were two years before sampling (R2015). Fairy ring associated changes in PLFA composition were highly related to soil K. Gram-negative bacteria were associated with the zones outside the ring with the highest K content, whereas Gram-positive bacteria proportions increased inside the ring-affected zones. An environmental stress indicator, the iso to anteiso ratio of PLFA 17:0, decreased in the R2015 zones, coinciding with the highest soil moisture contents. Our findings highlight the unreported importance of soil K in fairy ring dynamics affecting microbial communities. This common omission could lead to incorrect conclusions. Hence, the effects of fairy rings on soil should be further tested. Highlights Exchangeable potassium (K) decreased inside the current fairy rings. Fairy ring associated changes in PLFA microbial composition were present related to soil K. Soil moisture increased in the zones where the rings were 2 years before sampling. An environmental stress indicator decreased in those areas., COST Action ES1406; Universitat de Lleida; Spanish Science Foundation FECYT-MINECO, Grant/Award Numbers: IMAGINE, BIOGEI, CGL201785490-R, GL2013-49142-C2-1-R

Understanding the mechanisms underlying net ecosystem CO2 exchange (NEE) in mountain grasslands is important to quantify their relevance in the global carbon budget. However, complex interactions between environmental variables and vegetation on NEE remain unclear; and there is a lack of empirical data, especially from the high elevations and the Mediterranean region. A chamber-based survey of CO2 exchange measurements was carried out in two climatically contrasted grasslands (montane v. subalpine) of the Pyrenees; assessing the relative contribution of phenology and environmental variables on CO2 exchange at the seasonal scale, and the influence of plant functional type dominance (grasses, forbs and legumes) on the NEE light response. Results show that phenology plays a crucial role as a CO2 exchange driver, suggesting a differential behaviour of the vegetation community depending on the environment. The subalpine grassland had a more delayed phenology compared to the montane, being more temperature than water constrained. However, temperature increased net CO2 uptake at a higher rate in the subalpine than in the montane grassland. During the peak biomass, productivity (+74%) and net CO2 uptake (NEE +48%) were higher in the subalpine grassland than in the montane grassland. The delayed phenology at the subalpine grassland reduced vegetation's sensitivity to summer dryness, and CO2 exchange fluxes were less constrained by low soil water content. The NEE light response suggested that legume dominated plots had higher net CO2 uptake per unit of biomass than grasses. Detailed information on phenology and vegetation composition is essential to understand elevation and climatic differences in CO2 exchange., The current study was developed within the project CAPACITI supported by a Marie Curie Intra European Fellowship within the 7th European Community Framework for Nuria Altimir (PIEF-GA-2010-275855) and the project BIOGEI (CGL2013-49142-C21-R) supported by a FPI fellowship for Mercedes Ibáñez (BES-2014-069243) funded by the Spanish Science Foundation (FECYT).

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., Spanish Science Foundation funded the
project CAPAS (CGL2010-22378-C03-01), http://
www.fecyt.es/: MTS. Spanish Science Foundation funded the project BIOGEI (CGL2013-49142-C2-1-
R), http://www.fecyt.es/: MTS. Spanish Ministry of
Economy and Competitiveness funded the FPI shortterm visit to the Czech Academy of Sciences (BES-2011-047009): HD.

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., We would like to thank Helena Sarri and Mercedes Ibañez, for their assistance during field work. We would also like to thank Mari Pihlatie from the University of Helsinki for fruitful discussions and suggestions. This work was funded by the Spanish Science Foundation (FECYT) through the projects CAPAS (CGL2010-22378-C03-01) and BIOGEI (CGL2013-49142-C2-1-R). The project was also developed within the project CAPACITI supported by a Marie Curie Intra European Fellowship within the 7th European Community Framework to NA (PIEF-GA-2010-275855), HD was supported by a FPI fellowship from the Spanish Ministry of Economy and Competitiveness (BES-2011-047009). Funding through the project “Potential for capture or emission of greenhouse gases in agro-pastoral systems” (2012-AGEC-00080) by the Catalan Government is also acknowledged. We are particularly grateful to two anonymous reviewers for improving the paper, through their useful comments and suggestions.