Arbuscular mycorrhizal fungi activity in the rhizosphere of tree seedlings subjected to residual herbicides

Trees occurring on the margins of agricultural areas can mitigate damage from residual herbicides. Rhizospheric microbial activity associated with trees is one of the main remedial capacity indicators. The objective of this study was to evaluate the rhizospheric microbiological activity in tree species subjected to the herbicides atrazine and sulfentrazone via the rhizosphere. The experiment was designed in four blocks and a 6 × 3 factorial scheme. The first factor consisted of six tree species from Brazil and the second of atrazine, sulfentrazone, and water solutions. Four herbicide applications were performed via irrigation. The total dry mass of the plants, mycorrhizal colonization, number of spores, basal respiration of the rhizospheric soil, and survival rate of bioindicator plants after phytoremediation were determined. Trichilia hirta had higher biomass when treated with atrazine and sulfentrazone. Herbicides decreased the microbial activity in Triplaris americana and did not affect the microbiological indicators of Myrsine gardneriana, Schizolobium parahyba, and Toona ciliata. Fewer bioindicator plants survived in soil with Triplaris americana and sulfentrazone. Microbiological indicators were influenced in different ways between species by the presence of herbicides in the rhizosphere.

Multi-Omics of Pine Wood Nematode Pathogenicity Associated With Culturable Associated Microbiota Through an Artificial Assembly Approach

Pinewood nematode (PWN), the causal agent of pine wilt disease (PWD), causes massive global losses of Pinus species each year. Bacteria and fungi existing in symbiosis with PWN are closely linked with the pathogenesis of PWD, but the relationship between PWN pathogenicity and the associated microbiota is still ambiguous. This study explored the relationship between microbes and the pathogenicity of PWN by establishing a PWN-associated microbe library, and used this library to generate five artificial PWN–microbe symbiont (APMS) assemblies with gnotobiotic PWNs. The fungal and bacterial communities of different APMSs (the microbiome) were explored by next-generation sequencing. Furthermore, different APMSs were used to inoculate the same Masson pine (Pinus massoniana) cultivar, and multi-omics (metabolome, phenomics, and transcriptome) data were obtained to represent the pathogenicity of different APMSs at 14 days post-inoculation (dpi). Significant positive correlations were observed between microbiome and transcriptome or metabolome data, but microbiome data were negatively correlated with the reactive oxygen species (ROS) level in the host. Five response genes, four fungal genera, four bacterial genera, and nineteen induced metabolites were positively correlated with the ROS level, while seven induced metabolites were negatively correlated. To further explore the function of PWN-associated microbes, single genera of functional microbes (Mb1–Mb8) were reloaded onto gnotobiotic PWNs and used to inoculate pine tree seedlings. Three of the genera (Cladophialophora, Ochroconis, and Flavobacterium) decreased the ROS level of the host pine trees, while only one genus (Penicillium) significantly increased the ROS level of the host pine tree seedlings. These results demonstrate a clear relationship between associated microbes and the pathogenicity of PWN, and expand the knowledge on the interaction between PWD-induced forest decline and the PWN-associated microbiome.

Flooding tolerance of four tropical peatland tree species in a nursery trial

In order to facilitate hydrological restoration efforts, initiatives have been conducted to promote tree growth in degraded and rewetted peatlands in Indonesia. For this initiatives to be successful, tree seedlings need to be able to survive flooding episodes, with or without shade. We investigated the survival of different shading and water levels under controlled conditions in a nursery, with artificial rainwater and with peat soils as the medium. The research focused on the fllowing questions (i) whether trees can grow on flooded peat soils; and (ii) which plant traits allow plants to cope with inundation, with or without shade. The four tree species compared ( Shorea balangeran, Cratoxylum arborescens, Nephelium lappaceum, and Durio zibethinus ) include two natural poineer and two farmer-preferred fruit trees. The experiment used as a split-split plot design with 48 treatment combinations and at least 13 tree-level replicates. The study found that S. balangeran and C. arborescens developed adventitious roots to adapt to the inundated conditions. D. zibethinus, S. balangeran and N. lappaceum grew best under moderate (30%) shading levels, while C. arborescens grew best in full sunlight.

Absence of Consistent Pattern Between Seasons or Among Species in Effects of Leaf Size on Insect Herbivory

Insect herbivory on plant leaves is a major determinant of plant fitness, especially the growth and survival of tree seedlings in forests. Leaf size is believed to significantly affect the intensity of herbivory. Studies often assume the relationship between leaf size and herbivory to be monotonic; however, it is influenced by many factors—the magnitude and direction of whose effects are different—indicating a complex non-monotonic pattern. In this study, we investigated the herbivory of 5754 leaves of 422 seedlings belonging to 43 subtropical tree species over two seasons in southwest China. The effects of leaf size on herbivory differed among seasons; a hump-shaped pattern was detected in December, while a pattern of monotonic increase was detected in September. A variety of patterns including complex non-monotonic patterns presenting U-shaped and hump-shaped patterns, as well as patterns indicating monotonic decrease and increase existed, although most species displayed a leaf-size-independent pattern. The relationship between leaf size and insect herbivory does not follow a constant rule, but differs across species and seasons, indicating that the effects of leaf size on the foraging preferences of insect herbivores may be contingent on both external (e.g., temperature) and intrinsic (e.g., other leaf traits) factors. Therefore, a one-off survey focusing a few species may provide misleading understanding on the overall pattern of the effect of leaf size on herbivory. Similar variations may also exist in other ecological processes, which should be given due consideration in future studies on biotic interactions.

Post-fire early successional vegetation buffers surface microclimate and increases survival of planted conifer seedlings in the Southwestern United States

Climate change and fire-exclusion have increased the flammability of western United States forests, leading to forest cover loss when wildfires occur under severe weather conditions. Increasingly large high-severity burn patches limit natural regeneration because of dispersal distance, increasing the chance of conversion to non-forest. Post-fire planting can overcome dispersal limitations, yet warmer and drier post-fire conditions can still reduce survival. We examined how two shrub species with different structures affect below-shrub microclimate and survival rates of planted tree seedlings (Pinus ponderosa, P. edulis, P. strobiformis, Pseudotsuga menziesii) following a high-severity fire in northern New Mexico. We expected that Gambel oak (Querus gambelii), with its denser canopy, would buffer below-shrub climate causing higher survival rates of planted seedlings more than the lower canopy density New Mexico locust (Robinia neomexicana). Seedlings planted under Gambel oak had survival rates 10% to 35% greater than those planted under New Mexico locust. Higher light availability beneath New Mexico locust corresponded to higher temperatures, lower humidity, and higher vapor pressure deficit, impacting the mortality of planted tree seedlings. These results indicate that by waiting for post-fire shrub establishment, selective use of shrubs can buffer microclimate and increase post-fire planting success in the southwestern United States.

Characterizing the Utility of the Root-to-Shoot Ratio in Douglas-Fir Seedling Production

Nursery-grown tree seedlings are a vital component of successful restoration and reforestation programs, useful when calls for increased planting for industrial forest management are made, and a tool for climate change mitigation. One of the most extensively planted and studied trees in Western North America is Douglas-fir. Building on that body of work, this review was conducted to identify if the root-to-shoot ratio (root:shoot, R:S), a commonly referred-to metric in reforestation planning, yields meaningful guidance for producing seedlings that are better able to establish across a variety of field conditions. The results indicated that there is wide variability in R:S of nursery-grown seedlings. The relationship between R:S and subsequent root growth and seedling survival varies depending on Douglas-fir variety, seedling stocktypes, and site conditions. The biological and physiological basis for using R:S remains, and likely could be used to enhance seedling quality; however, there is an ongoing need for planning and collaboration between researchers and practitioners to identify how to best deploy this evaluation tool.