Open Access
Disruption of traditional grazing and fire regimes shape the fungal endophyte assemblages of the tall-grass Brachypodium rupestre
(Frontiers Media, 2021) Durán Lázaro, María; San Emeterio Garciandía, Leticia; Múgica Azpilicueta, Leire; Zabalgogeazcoa, Iñigo; Vázquez de Aldana, Beatriz R.; Canals Tresserras, Rosa María; Agronomia, Bioteknologia eta Elikadura; Institute on Innovation and Sustainable Development in Food Chain - ISFOOD; Agronomía, Biotecnología y Alimentación; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
The plant microbiome is likely to play a key role in the resilience of communities to the global climate change. This research analyses the culturable fungal mycobiota of Brachypodium rupestre across a sharp gradient of disturbance caused by an intense, anthropogenic fire regime. This factor has dramatic consequences for the community composition and diversity of high-altitude grasslands in the Pyrenees. Plants were sampled at six sites, and the fungal assemblages of shoots, rhizomes, and roots were characterized by culture-dependent techniques. Compared to other co-occurring grasses, B. rupestre hosted a poorer mycobiome which consisted of many rare species and a few core species that differed between aerial and belowground tissues. Recurrent burnings did not affect the diversity of the endophyte assemblages, but the percentages of infection of two core species -Omnidemptus graminis and Lachnum sp. -increased significantly. The patterns observed might be explained by (1) the capacity to survive in belowground tissues during winter and rapidly spread to the shoots when the grass starts its spring growth (O. graminis), and (2) the location in belowground tissues and its resistance to stress (Lachnum sp.). Future work should address whether the enhanced taxa have a role in the expansive success of B. rupestre in these anthropized environments.
Open Access
Pyric herbivory decreases soil denitrification despite increased nitrate availability in a temperate grassland
(Elsevier, 2024-07-04) Múgica Azpilicueta, Leire; Le Roux, Xavier; San Emeterio Garciandía, Leticia; Cantarel, Amélie; Durán Lázaro, María; Gervaix, Jonathan; Creuzé des Châtelliers, Charline; Canals Tresserras, Rosa María; Agronomía, Biotecnología y Alimentación; Agronomia, Bioteknologia eta Elikadura; Institute on Innovation and Sustainable Development in Food Chain - ISFOOD
Pyric herbivory, the combination of controlled burning and targeted grazing, is an effective strategy for restoring abandoned, shrub-encroached rangelands to open ecosystems. This practice may impact soil nitrogen pools by altering soil nitrification and denitrification rates, and may lead to an increase of nitrogen losses through nitrate leaching and N-gas emissions. This research, located in the south-western Pyrenees, investigated the effects of pyric herbivory on soil nitrification and denitrification potentials and mineral nitrogen content in a gorse-encroached temperate rangeland six months after the burning was implemented. The study included three treatments: high-severity burning plus grazing, low-severity burning plus grazing, and unburned and ungrazed areas (control). We measured soil nitrification and denitrification potentials (net and gross), the limitation of denitrifiers by nitrogen or organic carbon, and the abundance of nitrite- and nitrous oxide-reducing bacteria. Additional soil and vegetation data complemented these measurements. Results showed that pyric herbivory did not significantly affect nitrification potential, which was low and highly variable. However, it decreased gross denitrification potential and nitrous oxide reduction to dinitrogen in high-severely burned areas compared to the control. Denitrification rates directly correlated with microbial biomass nitrogen, soil organic carbon, soil water content and abundance of nirS-harbouring bacteria. Contrary to the expected, soil nitrate availability did not directly influence denitrification despite being highest in burned areas. Overall, the study suggests that pyric herbivory does not significantly affect mid-term nitrification rates in temperate open ecosystems, but may decrease denitrification rates in intensely burned areas. These findings highlight the importance of assessing the potential impacts of land management practices, such as pyric herbivory, on soil nutrient cycling and ecosystem functioning.
Open Access
Relating the spatial distribution of a tall-grass to fertility islands in a temperate mountain grassland
(Elsevier, 2021) San Emeterio Garciandía, Leticia; Durán Lázaro, María; Múgica Azpilicueta, Leire; Jiménez, Juan José; Canals Tresserras, Rosa María; Agronomia, Bioteknologia eta Elikadura; Institute on Innovation and Sustainable Development in Food Chain - ISFOOD; Agronomía, Biotecnología y Alimentación; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Plant-soil feedback mechanisms influence the abundance and rarity of plant species and can favour invasive processes, including those of native species. To explore these mechanisms, we analysed correlations between spatial distributions of plant biomass and soil properties in two neighbouring grasslands at different phases of expansion of the native Eurasian tall-grass Brachypodium rupestre (Host) Roem & Schult (B. rupestre cover: >75 and 25–50%). For this, we applied spatially explicit sampling, geostatistical analysis and structural equation models (SEM) to probe causal relationships among measured variables involved in nutrient accumulation. We hypothesized that if litter accumulates as a result of reduced grazing, ‘fertility islands’ (spots of high SOM and nutrient contents) will form under B. rupestre clumps because the increase in resource inputs from litter will trigger SOM build-up and promote microbial growth. Our results show that ‘fertility islands’ of P and amino acids occurred under the patchy clumps of B. rupestre in the less invaded grassland. In addition, the SEMs indicated that nutrient accumulation was partially due to mineralization of the SOM and modulated by the soil microbial biomass. However, there was no correlation between spatial patterns of B. rupestre biomass, SOM and microbial biomass. Moreover, the SEMs explained small amounts of variance in them (SOM r2 = 0.22 and microbial biomass r2 = 0.08), suggesting that factors other than B. rupestre biomass were responsible for the high fertility below the patches. Our spatially explicit approach demonstrated that litter inputs in dense temperate grassland communities can generate ‘fertility islands’ that may favour the stability and expansion of a tall-grass invader and suggest that herbivory may enhance or inhibit this phenomenon.
Open Access
Restorative pyric herbivory practices in shrub-encroached grasslands enhance nutrient resource availability and spatial heterogeneity
(Elsevier, 2024-05-31) Canals Tresserras, Rosa María; Múgica Azpilicueta, Leire; Durán Lázaro, María; San Emeterio Garciandía, Leticia; Agronomía, Biotecnología y Alimentación; Agronomia, Bioteknologia eta Elikadura; Institute on Innovation and Sustainable Development in Food Chain - ISFOOD
Pyric herbivory (PH), the combination of prescribed burnings and targeted herbivory, is a promising tool for landscape restoration that emulates historical disturbance regimes. Nitrogen (N) and phosphorus (P) are crucial nutrients for plant growth and although several studies have analysed the single effects of fire or grazers in their availability, the combined effect of both disturbances in the soil nutrient budgets have been rarely considered. This research was planned to analyse the 2-year impact of PH restoration practices on the availability of N and P in two Ulex gallii-encroached grasslands in the Pyrenees. We monitored available forms of N and P for two years using periodic replacements of ion exchange resins to test the hypothesis that mid-term effect of targeted grazing was more relevant than short-term effect of burning. Additionally, we investigated the role of temperature and precipitation on nutrients accumulation and compared its significance to management factors. Burning transformed vegetation and litter into a spatially heterogeneous layer of ash and charred material, which resulted in a variable availability of N and P at the rhizosphere level. After two periods of PH, nutrient availability was higher in soils from grazed plots compared to ungrazed, and the impacts of early burns were scarcely discernible. Nitrate was found to be the most rainfall-dependent nutrient, and grazing also affected its spatial distribution. Our results suggest that the heterogeneous nutrient enrichment enhanced by PH is important for promoting the establishment of a diverse pool of plant species, including both N2-fixing and non-fixing species. In these rainy areas, the use of burnings alone, without grazing, may perpetuate the dynamics of N2-fixing shrub encroachment.
Open Access
Soil C/N ratios cause opposing effects in forests compared to grasslands on decomposition rates and stabilization factors in southern European ecosystems
(Elsevier, 2023) Blanco Vaca, Juan Antonio; Durán Lázaro, María; Luquin, Josu; San Emeterio Garciandía, Leticia; Yeste Yeste, Antonio; Canals Tresserras, Rosa María; Agronomía, Biotecnología y Alimentación; Agronomia, Bioteknologia eta Elikadura; Ciencias; Zientziak; Institute for Multidisciplinary Research in Applied Biology - IMAB; Institute on Innovation and Sustainable Development in Food Chain - ISFOOD; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Soils store an important amount of carbon (C), mostly in the form of organic matter in different decomposing stages. Hence, understanding the factors that rule the rates at which decomposed organic matter is incorporated into the soil is paramount to better understand how C stocks will vary under changing atmospheric and land use conditions. We studied the interactions between vegetation cover, climate and soil factors using the Tea Bag Index in 16 different ecosystems (eight forests, eight grasslands) along two contrasting gradients in the Spanish province of Navarre (SW Europe). Such arrangement encompassed a range of four climate types, elevations from 80 to 1420 m.a.s.l., and precipitation (P) from 427 to 1881 mm year–1. After incubating tea bags during the spring of 2017, we identified strong interactions between vegetation cover type, soil C/N and precipitation affecting decomposition rates and stabilization factors. In both forests and grasslands, increasing precipitation increased decomposition rates (k) but also the litter stabilization factor (S). In forests, however, increasing the soil C/N ratio raised decomposition rates and the litter stabilization factor, while in grasslands higher C/N ratios caused the opposite effects. In addition, soil pH and N also affected decomposition rates positively, but for these factors no differences between ecosystem types were found. Our results demonstrate that soil C flows are altered by complex site-dependent and site-independent environmental factors, and that increased ecosystem lignification will significantly change C flows, likely increasing decomposition rates in the short term but also increasing the inhibiting factors that stabilize labile litter compounds.
Open Access
Comparison of culturing and metabarcoding methods to describe the fungal endophytic assemblage of brachypodium rupestre growing in a range of anthropized disturbance regimes
(MDPI, 2021) Durán Lázaro, María; San Emeterio Garciandía, Leticia; Canals Tresserras, Rosa María; Agronomia, Bioteknologia eta Elikadura; Institute on Innovation and Sustainable Development in Food Chain - ISFOOD; Agronomía, Biotecnología y Alimentación; Gobierno de Navarra / Nafarroako Gobernua, CENEDUCA18; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Fungal endophytes develop inside plants without visible external signs, and they may confer adaptive advantages to their hosts. Culturing methods have been traditionally used to recognize the fungal endophytic assemblage, but novel metabarcoding techniques are being increasingly applied. This study aims to characterize the fungal endophytic assemblage in shoots, rhizomes and roots of the tall grass Brachypodium rupestre growing in a large area of natural grasslands with a continuum of anthropized disturbance regimes. Seven out of 88 taxa identified via metabarcoding accounted for 81.2% of the reads (Helotiaceae, Lachnum sp. A, Albotricha sp. A, Helotiales A, Agaricales A, Mycena sp. and Mollisiaceae C), revealing a small group of abundant endophytes and a large group of rare species. Although both methods detected the same trends in richness and fungal diversity among the tissues (root > rhizome > shoot) and grasslands (low-diversity >high-diversity grasslands), the metabarcoding tool identified 5.8 times more taxa than the traditional culturing method (15 taxa) but, surprisingly, failed to sequence the most isolated endophyte on plates, Omnidemptus graminis. Since both methods are still subject to important constraints, both are required to obtain a complete characterization of the fungal endophytic assemblage of the plant species.
Open Access
Decoupling of traditional burnings and grazing regimes alters plant diversity and dominant species competition in high-mountain grasslands
(Elsevier, 2021) Múgica Azpilicueta, Leire; Canals Tresserras, Rosa María; San Emeterio Garciandía, Leticia; Peralta de Andrés, Francisco Javier; Agronomia, Bioteknologia eta Elikadura; Zientziak; Institute on Innovation and Sustainable Development in Food Chain - ISFOOD; Agronomía, Biotecnología y Alimentación; Ciencias; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Over millennia, the combination of controlled burnings and extensive grazing has maintained mosaic landscapes and preserved mountain grasslands in southern Europe. In the last century, deep socio-economic changes have led to an abandonment of traditional uses, to a general decline of the domestic herbivory and to a misuse of burning practices. This study aims to quantify how the decoupling of burning and grazing regimes affects in the long-term the structure, diversity and dynamics of high-mountain, shrub-encroached grasslands. In spring 2012, four treatments (burned-grazed, burned-ungrazed, unburned-grazed and unburned-ungrazed) were set up at three sites in the Special Area of Conservation Roncesvalles-Selva de Irati, in southwest Pyrenees. During seven years, we monitored floristic composition and the height of the native tall-grass Brachypodium rupestre in four plots at each site. In the burned plots, we surveyed the resprout of the dominant shrub Ulex gallii and the dynamics of recovering of the herbaceous vegetation. Plant communities evolved differently in grazed and ungrazed plots. Extensive grazing, despite being lower than in previous decades, maintained plant diversity and limited shrub encroachment. The total absence of grazing fostered the encroachment of U. gallii at two sites and the expansion of B. rupestre at the other site. When B. rupestre cover was >60%, the encroachment of U. gallii was reduced. This research highlights the competition that occurs between shrubs and tall-grasses in the absence of grazing, and the modulating effect exerted by the burnings and the site-specific features. Understanding local plant dynamics is the first step to design the most appropriate practices that help to preserve diversity at the landscape and the community level in high-mountain grasslands of south Europe.
Open Access
Pyric herbivory increases soil microbial diversity but has a site-dependent effect on soil mesofauna in the mid-term
(Elsevier, 2023) San Emeterio Garciandía, Leticia; Baquero, Enrique; Antón Sobejano, Rodrigo; Jordana, Rafael; Múgica Azpilicueta, Leire; Sáez, José L.; Virto Quecedo, Íñigo; Canals Tresserras, Rosa María; Agronomía, Biotecnología y Alimentación; Agronomia, Bioteknologia eta Elikadura; Ciencias; Zientziak; Institute on Innovation and Sustainable Development in Food Chain - ISFOOD; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Woody plant encroachment threatens grassland biomes at a global scale. Pyric herbivory combines prescribed burnings and targeted grazing to restore open habitats and has proved to be successful in promoting landscape and plant community diversity. However, less is known on the effects of pyric herbivory practices on belowground biodiversity. We evaluated the midterm effect on mesofauna, bacteria and fungi of prescribed burns and targeted horse grazing regimes implemented to restore a grassland encroached by gorse (Ulex gallii Planch.). We hypothesized that 1) low-intensity shrub-to shrub burnings had no effect or had a transient effect of low magnitude on soil microbial diversity, and that 2) targeted horse grazing after burning increased soil mesofauna and microbial diversity in the midterm. We established an experiment in two shrub-encroached grasslands in western Pyrenees with three treatments (no burning and no grazing as control, burning but no grazing, and burning and grazing). We measured soil properties and soil diversity of fungi and bacteria (DNA-metabarcoding) just after fire, and vegetation structure, soil properties and soil diversity of fungi, bacteria and mesofauna after two periods of targeted grazing (a year and a half after the burning). The response to pyric herbivory differed among soil organisms. Fungi were more sensitive to burning than bacteria, but both recovered a year and a half after burning –fungi only recovered in the presence of grazing–. Grazing increased soil fungi and bacteria diversity indexes (~20 % and ~5 % increase, respectively) at the two sites. A year and a half after burning, burned and ungrazed areas had a 30 % more mesofauna diversity than control areas whereas grazing of the burned areas decreased mesofauna diversity by 30 % at one of the sites compared to the control. Since the responses to pyric herbivory vary among soil organisms, a wide range of management intensities across space and time are recommended for maximizing soil biodiversity.