Decoupling of traditional burnings and grazing regimes alters plant diversity and dominant species competition in high-mountain grasslands

Pyric herbivory decreases soil denitrification despite increased nitrate availability in a temperate grassland

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.

What is a fire resilient landscape? Towards an integrated definition

The concept of fire resilience has become increasingly relevant as society looks to understand and respond to recent wildfire events. In particular, the idea of a 'fire resilient landscape' is one which has been utilised to explore how society can coexist with wildfires. However, the concept of fire resilient landscapes has often been approached in silos, either from an environmental or social perspective; no integrated definition exists. Based on a synthesis of literature and a survey of scientists and practitioners, we propose to define a fire resilient landscape as 'a socio-ecological system that accepts the presence of fire, whilst preventing significant losses through landscape management, community engagement and effective recovery.' This common definition could help guide policy surrounding fire resilient landscapes, and exemplify how such landscapes could be initiated in practice. We explore the applicability of the proposed definition in both Mediterranean and temperate Europe.

Fire does not transform shrublands of Echinospartum horridum (Vahl) Rothm. into grasslands in the Pyrenees: Development of community structure and nutritive value after single prescribed burns

Prescribed fire has been extensively used in recent years to control woody encroachment into mountain and other grassland-dominated landscapes. In the Aragon Pyrenees, prescribed burns have been mainly used to remove the native thorny shrub Echinospartum horridum (Vahl) Rothm., whose populations are spreading to the detriment of grasslands. To study the effectiveness of the burning of E. horridum to preserve grasslands for livestock grazing, the vegetation of six sites burned 0.5, 2, 3, 6, 15 and 35 years ago was sampled and compared with that of nearby unburned shrubland (control) and grassland (reference). In addition, the nutritional quality of E. horridum was examined and compared to that of the reference grassland to evaluate to what extent shrub growth can be controlled by herbivores after burning. Initial shrub cover recovered as early as 15 years after fire, with E. horridum being dominant. Plant diversity was greatest at intermediate number of years after fire. Initial floristic composition and life-form spectrum were restored 15-35 years after burning. Echinospartum horridum exhibited early lignification that restricts its availability as a palatable forage for the first two years after burning and makes it unlikely to be consumed thereafter, highlighting the difficulty in controlling the expansion of this species by livestock herbivory. The analysis of the nutrient levels suggested an increased shortage of limiting elements, such as phosphorus or sulfur, in the mid-term after burning due to substantial nutrient losses and exports during and after the burn. Our results question the suitability and sustainability of a single prescribed burn as management tool alone to control the expansion of E. horridum and call for caution in its application for fighting shrub encroachment in the Central Pyrenees.

Biodiversity and Ecosystem Function under Simulated Gradient Warming and Grazing

Biodiversity and ecosystem functions and their relationship with environmental response constitute a major topic of ecological research. However, the changes in and impact mechanisms of multi-dimensional biodiversity and ecosystem functions in continuously changing environmental gradients and anthropogenic activities remain poorly understood. Here, we analyze the effects of multi-gradient warming and grazing on relationships between the biodiversity of plant and soil microbial with productivity/community stability through a field experiment simulating multi-gradient warming and grazing in alpine grasslands on the Tibetan Plateau. We show the following results: (i) Plant biodiversity, soil microbial diversity and community productivity in alpine grasslands show fluctuating trends with temperature gradients, and a temperature increase below approximately 1 °C is beneficial to alpine grasslands; moderate grazing only increases the fungal diversity of the soil surface layer. (ii) The warming shifted plant biomass underground in alpine grasslands to obtain more water in response to the decrease in soil moisture caused by the temperature rise. Community stability was not affected by warming or grazing. (iii) Community stability was not significantly correlated with productivity, and environmental factors, rather than biodiversity, influenced community stability and productivity.

Comparison of Culturing and Metabarcoding Methods to Describe the Fungal Endophytic Assemblage of Brachypodium rupestre Growing in a Range of Anthropized Disturbance Regimes

Simple Summary

The richness (number of species) of the fungi kingdom is estimated at 1.5 million species, but the vast majority remains unknown. Many of them inhabit plants—the so-called fungal endophytes—and may establish different types of interactions with their host plant. Fungal endophytes have been traditionally studied by letting them grow in appropriate culturing media in petri dishes, but novel massive DNA sequencing techniques which do not require a cultivation step (metabarcoding) are gaining ground. Both techniques were applied and compared to characterize the mycobiome of plants of a tall grass (Brachypodium rupestre) growing in high-mountain grasslands with different plant diversity (low and high). The two methods showed similar trends comparing endophyte richness between plant tissue types (root > rhizome > shoot) and between grasslands (low-diversity > high-diversity). However, the metabarcoding identified almost six times more endophyte species than the culturing although the most isolated fungal species via culturing, Omnidemptus graminis, was not recognized via metabarcoding. We conclude that the complementation of both techniques is still the best option to obtain a complete characterization of the fungal endophytic assemblage of the plant species.

Abstract

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.

The Influence of Climate Warming and Humidity on Plant Diversity and Soil Bacteria and Fungi Diversity in Desert Grassland

Our study, which was conducted in the desert grassland of Ningxia in China (E 107.285, N 37.763), involved an experiment with five levels of annual precipitation 33% (R33), 66% (R66), 100% (CK), 133% (R133), 166% (R166) and two temperature levels (inside Open-Top Chamber (OTC) and outside OTC). Our objective was to determine how plant, soil bacteria, and fungi diversity respond to climate change. Our study suggested that plant α-diversity in CK and TCK were significantly higher than that of other treatments. Increased precipitation promoted root biomass (RB) growth more than aboveground living biomass (ALB). R166 promoted the biomass of Agropyron mongolicum the most. In the fungi communities, temperature and precipitation interaction promoted α-diversity. In the fungi communities, the combination of increased temperature and natural precipitation (TCK) promoted β-diversity the most, whose distance was determined to be 25,124 according to PCA. In the bacteria communities, β-diversity in CK was significantly higher than in other treatments, and the distance was determined to be 3010 according to PCA. Soil bacteria and fungi α- and β-diversity, and ALB promoted plant diversity the most. The interactive effects of temperature and precipitation on C, N, and P contents of plants were larger than their independent effects.