Juvenile Plant-Microbe Interactions Modulate the Adaptation and Response of Forest Seedlings to Rapid Climate Change.

The negative impacts of climate change on native forest ecosystems have created challenging conditions for the sustainability of natural forest regeneration. These challenges arise primarily from abiotic stresses that affect the early stages of forest tree development. While there is extensive evidence on the diversity of juvenile microbial symbioses in agricultural and fruit crops, there is a notable lack of reports on native forest plants. This review aims to summarize the critical studies conducted on the diversity of juvenile plant-microbe interactions in forest plants and to highlight the main benefits of beneficial microorganisms in overcoming environmental stresses such as drought, high and low temperatures, metal(loid) toxicity, nutrient deficiency, and salinity. The reviewed studies have consistently demonstrated the positive effects of juvenile plant-microbiota interactions and have highlighted the potential beneficial attributes to improve plantlet development. In addition, this review discusses the beneficial attributes of managing juvenile plant-microbiota symbiosis in the context of native forest restoration, including its impact on plant responses to phytopathogens, promotion of nutrient uptake, facilitation of seedling adaptation, resource exchange through shared hyphal networks, stimulation of native soil microbial communities, and modulation of gene and protein expression to enhance adaptation to adverse environmental conditions.

The N-fixing legume Periandra mediterranea constrains the invasion of an exotic grass (Melinis minutiflora P. Beauv) by altering soil N cycling.

Melinis minutiflora is an invasive species that threatens the biodiversity of the endemic vegetation of the campo rupestre biome in Brazil, displacing the native vegetation and favouring fire spread. As M. minutiflora invasion has been associated with a high nitrogen (N) demand, we assessed changes in N cycle under four treatments: two treatments with contrasting invasion levels (above and below 50%) and two un-invaded control treatments with native vegetation, in the presence or absence of the leguminous species Periandra mediterranea. This latter species was considered to be the main N source in this site due to its ability to fix N2 in association with Bradyrhizobia species. Soil proteolytic activity was high in treatments with P. mediterranea and in those severely invaded, but not in the first steps of invasion. While ammonium was the N-chemical species dominant in plots with native species, including P.mediterranea, soil nitrate prevailed only in fully invaded plots due to the stimulation of the nitrifying bacterial (AOB) and archaeal (AOA) populations carrying the amoA gene. However, in the presence of P. mediterranea, either in the beginning of the invasion or in uninvaded plots, we observed an inhibition of the nitrifying microbial populations and nitrate formation, suggesting that this is a biotic resistance strategy elicited by P. mediterranea to compete with M. minutiflora. Therefore, the inhibition of proteolytic activity and the nitrification process were the strategies elicited by P.mediterranea to constrain M.munitiflora invasion.

Invasion of the Brazilian campo rupestre by the exotic grass Melinis minutiflora is driven by the high soil N availability and changes in the N cycle.

The Serra do Rola Moça State Park (PESRM) in Minas Gerais State, Brazil is a preserved site representative of the campo rupestre biome over an ironstone outcrop that has a high level of plant diversity. Almost 60% of this grassy field has been invaded by the exotic molasses grass (Melinis minutiflora), which constitutes a severe threat to the biodiversity and survival of this biome, particularly due to the impacts of annual fires and inappropriate restoration interventions. Many invasive species exhibit a high demand for nitrogen (N). Hence, this work aimed to study the N cycle alterations promoted by M. minutiflora in a site of the campo rupestre, where the leguminous species Mimosa pogocephala was prevalent. The biome's soils exhibited a high natural N fertility and low C:N ratio. The main N source in this biome resulted from the biological N fixation performed by M. pogocephala associated with Burkholderia nodosa, as evidenced by the total leaf N content, leaf δ15N signature, nodule occupation and bacterial molecular identification analyses. The displacement of native species by molasses grass was associated with changes in the soil N forms, namely the nitrate increased as the ammonium decreased. The latter was the dominant N form in the native species plots, as observed in the soil analysis of total N, ammonium and nitrate contents. The dominant ammonium form was changed to the nitric form by the stimulation of ammonia-oxidising bacteria populations due to the invasive species. Therefore, the key mechanism behind the invasiveness of the exotic grass and the concomitant displacement of the native species may be associated with changes in the soil N chemical species. Based on this finding and on the high N-based soil fertility found in the campo rupestre N fertilisation procedures for restoration of invaded areas should be strictly avoided in this biome.

Paenibacillus periandrae sp. nov., isolated from nodules of Periandra mediterranea.

A bacterial strain designated PM10T was isolated from root nodules of Periandra mediterranea in Brazil. Phylogenetic analyses based on 16S rRNA gene sequences placed the isolate in the genus Paenibacillus with its closest relatives being Paenibacillus vulneris CCUG 53270T and Paenibacillus yunnanensis YN2T with 95.6 and 95.9% 16S rRNA gene sequence similarity, respectively. The isolate was a Gram-stain-variable, motile, sporulating rod that was catalase-negative and oxidase-positive. Caseinase was positive, amylase was weakly positive and gelatinase was negative. Growth was supported by many carbohydrates and organic acids as carbon sources. MK-7 was the only menaquinone detected and anteiso-C15 : 0 was the major fatty acid. Major polar lipids were diphosphatidylglycerol, phosphatidylmonomethylethanolamine, phosphatidylethanolamine, phosphatidylglycerol and two unidentified lipids. meso-Diaminopimelic acid was detected in the peptidoglycan. The DNA G+C content was 52.9 mol%. Phylogenetic, chemotaxonomic and phenotypic analyses showed that strain PM10T should be considered representative of a novel species of the genus Paenibacillus, for which the name Paenibacillus periandrae sp. nov. is proposed. The type strain is PM10T (=LMG 28691T=CECT 8827T).