STUDIES ON THE STIMULATION OF CATALPA BIGNONIOIDES WALT. SEED GERMINATION

Catalpa is a tree with an attractive ornamental value and compact shape. Catalpa bignonioides Walt., is a tree with heights of up to 35 meters and a large trunk. It is an exotic species in North America areal. It grows well in a warm and humid climate, on alluvial, fertile, deep, temperate soils. It has a light temperament, withstands winter frosts well, but is sensitive to late frosts. The degree of germination varies both between species and within them. Within batches of seeds of the same species varies depending on the origin, year of harvest and individual trees. There are different methods and techniques for overcoming drowsiness depending on the seeds. Various pre-treatments are used such as scarification and hot and cold aeration to stimulate the embryo. The paper presents the stimulation of seed germination at catalpa, using different concentrations of Nitragin: 0.1%, 0.3%, 0.5%, 0.7%, 0.9% and following the seed germination interval.

BIOCHAR IN TEMPERATE SOILS: OPPORTUNITIES AND CHALLENGES

Biochar, a carbon-rich material produced by the pyrolysis of organic residues, is frequently used as a soil amendment to enhance soil fertility and improve soil properties in tropical climates. However, in temperate agriculture, the impact of biochar on soil and plant productivity remains uncertain. The objective of this review is to give an overview of the challenges and opportunities of using biochar as an amendment in temperate soils. Among the various challenges, the type of feedstock and the conditions during pyrolysis produces biochars with different chemical and physical properties, resulting in contrasting effects on soils and crops. Furthermore, biochar aging, biochar application rates and its co-application with mineral fertilizer and/or organic amendments add further complexity to our understanding of the soil-amendment-plant continuum. Although its benefits on crop yield are not yet well demonstrated under field studies, other agronomic benefits of biochar in temperate agriculture have been documented. In this review, we proposed a broader view of biochar as a temperate soil amendment, moving beyond our current focus on crop productivity, and instead target its capacity to improve soil properties. We explored biochar’s benefits in remediating low productive agricultural lands, and its environmental benefits through long-term carbon sequestration and reduced nutrient leaching while curtailing our reliance on fertilizer input. We also discussed the persistence of beneficial impacts of biochar in temperate field conditions. We concluded biochar displays great prospective to improve soil health and its productivity, enhance plant stress resilience, mitigate greenhouse gas emissions and restore degraded soils in temperate agriculture.

Soil organic matter dominates the magnitude of porosity and bulk density in temperate soils, with important implications for land surface models

<p>Soil porosity controls the flow of mass and energy through soil, and thus plays a fundamental role in regulating hydrological and biochemical cycling at the land surface. Global land surface and earth system models commonly derive porosity from soil texture using pedotransfer functions. This does not allow for response to change in environment or management, or potentially important climate feedbacks. Furthermore, the approach does not fully represent the baseline spatial variation in this important soil property. Here we show that porosity, and bulk density (BD), depend on SOM in temperate soils, using two comprehensive national data sets, covering the full range of soil organic matter (SOM) (n=1385 & n=2570). Our novel use of analytical models with machine learning (ML) algorithms opens up new physical insight into controls on porosity and BD, while generalized additive mixed models (GAMMs) provide further insights and opportunities for prediction. Our models allow us to consider influence of management on soil compaction and recent observations that soil porosity responds to climate change. The dependence of soil porosity on SOM, more so than texture, indicates the need for a paradigm shift in the conceptualization and modelling of these soil physical properties. Broad habitat was also an important control, and explained some of the variance in the relationship between SOM and porosity. This highlights that changes in soil porosity may occur due to land use or climate change, and will create feedbacks to hydrological and biogeochemical cycling which should be represented in Global land surface models. This will also be important for other pedotransfer functions, e.g. the use of BD to determine carbon stock from concentration.  In addition, we found opportunities for improved representation of the spatial pattern of porosity, even in the absence of measured data on SOM, based on climate and earth observation data.</p>

Metagenomic characterization of soil microbial communities in the Luquillo experimental forest (Puerto Rico) and implications for nitrogen cycling

The phylogenetic and functional diversity of microbial communities in tropical rainforests, and how these differ from temperate communities remain poorly described but are directly related to the increased fluxes of greenhouse gases such as nitrous oxide (N2O) from the tropics. Towards closing these knowledge gaps, we analyzed replicated shotgun metagenomes representing distinct life zones and an elevation gradient from four locations in the Luquillo Experimental Forest (LEF), Puerto Rico. These soils had a distinct microbial community composition and lower species diversity when compared to temperate grasslands or agricultural soils. In contrast to the overall distinct community composition, the relative abundances and nucleotide sequences of N2O reductases (nosZ) were highly similar between tropical forest and temperate soils. However, respiratory NO reductase (norB) was 2-fold more abundant in the tropical soils, which might be relatable to their greater N2O emissions. Nitrogen fixation (nifH) also showed higher relative abundance in rainforest compared to temperate soils, i.e., 20% vs. 0.1-0.3% of bacterial genomes in each soil type harbored the gene, respectively. Finally, unlike temperate soils, LEF soils showed little stratification with depth in the first 0-30cm, with ∼45% of community composition differences explained solely by location. Collectively, these results advance our understanding of spatial diversity and metabolic repertoire of tropical rainforest soil communities, and should facilitate future ecological studies of these ecosystems. Importance: Tropical rainforests are the largest terrestrial sinks of atmospheric CO2 and the largest natural source of N2O emissions, two critical greenhouse gases for the climate. The microbial communities of rainforest soils that directly or indirectly, through affecting plant growth, contribute to these fluxes remain poorly described by cultured-independent methods. To close this knowledge gap, the present study applied shotgun metagenomics to samples selected from three distinct life zones within the Puerto Rico rainforest. The results advance our understanding of microbial community diversity in rainforest soils and should facilitate future studies of natural or manipulated perturbations of these critical ecosystems.

Agriculture increases the bioavailability of silicon, a beneficial element for crop, in temperate soils

Crops may take benefits from silicon (Si) uptake in soil. Plant available Si (PAS) can be affected by natural weathering processes or by anthropogenic forces such as agriculture. The soil parameters that control the pool of PAS are still poorly documented, particularly in temperate climates. In this study, we documented PAS in France, based on statistical analysis of Si extracted by CaCl2 (SiCaCl2) and topsoil characteristics from an extensive dataset. We showed that cultivation increased SiCaCl2 for soils developed on sediments, that cover 73% of France. This increase is due to liming for non-carbonated soils on sediments that are slightly acidic to acidic when non-cultivated. The analysis performed on non-cultivated soils confirmed that SiCaCl2 increased with the < 2 µm fraction and pH but only for soils with a < 2 µm fraction ranging from 50 to 325 g kg−1. This increase may be explained by the < 2 µm fraction mineralogy, i.e. nature of the clay minerals and iron oxide content. Finally, we suggest that 4% of French soils used for wheat cultivation could be deficient in SiCaCl2.

Acidobacteria are active and abundant members of diverse atmospheric H2-oxidizing communities detected in temperate soils

Significant rates of atmospheric dihydrogen (H2) consumption have been observed in temperate soils due to the activity of high-affinity enzymes, such as the group 1h [NiFe]-hydrogenase. We designed broadly inclusive primers targeting the large subunit gene (hhyL) of group 1h [NiFe]-hydrogenases for long-read sequencing to explore its taxonomic distribution across soils. This approach revealed a diverse collection of microorganisms harboring hhyL, including previously unknown groups and taxonomically not assignable sequences. Acidobacterial group 1h [NiFe]-hydrogenase genes were abundant and expressed in temperate soils. To support the participation of acidobacteria in H2 consumption, we studied two representative mesophilic soil acidobacteria, which expressed group 1h [NiFe]-hydrogenases and consumed atmospheric H2 during carbon starvation. This is the first time mesophilic acidobacteria, which are abundant in ubiquitous temperate soils, have been shown to oxidize H2 down to below atmospheric concentrations. As this physiology allows bacteria to survive periods of carbon starvation, it could explain the success of soil acidobacteria. With our long-read sequencing approach of group 1h [NiFe]-hydrogenase genes, we show that the ability to oxidize atmospheric levels of H2 is more widely distributed among soil bacteria than previously recognized and could represent a common mechanism enabling bacteria to persist during periods of carbon deprivation.