This study analyzes the abundance, diversity, trophic structure, ecological indices, and functional traits of nematode communities along a continentality gradient within the Moroccan Argan Forest Biosphere Reserve. A total of 130 soil samples were collected from three distinct bioclimatic zones: insular, coastal, and semi-continental.
Bacterivorous nematodes are the most abundant trophic group in all zones, followed by herbivores, fungivores, omnivores, and predators. At the trophic group level, the insular zone stands out due to a greater representation of four groups (bacterivores, herbivores, fungivores, and omnivores-predators), whose proportions are higher there than in the coastal and semi-continental zones—indicating a more diverse functional composition, which should not be confused with evenness among taxa, which follows an opposite trend (see below).
Total abundance and taxonomic richness of nematodes are significantly higher in the insular zone. In contrast, Shannon's diversity index (a measure of environmental biodiversity) and Simpson's index (a measure of dominance) show no significant differences between zones. This result suggests that the increase in richness in the insular zone is offset by a less even distribution of abundances among taxa: while the overall quantity and number of taxa decrease with continentality, the overall diversity structure remains relatively stable, whereas the relative distribution of species varies significantly.
This compensation is confirmed by Pielou's evenness index, which is significantly lower in the insular zone (0.71) than in the coastal (0.81) and semi-continental (0.77; $F = 18.73, p < 0.001$) zones. In other words, while the insular zone harbors more trophic groups and taxa, these taxa are dominated by a few highly abundant species—unlike the coastal and semi-continental zones, where the less rich communities are more evenly distributed among species.
Non-metric multidimensional scaling (NMDS) analysis reveals a significant geographical structure of trophic communities along the continentality gradient, with a clear differentiation of the coastal zone, which is characterized by high inter-site variability and a high proportion of fungivores, predators, and omnivores. The insular and semi-continental zones exhibit structures that are more similar to each other. Principal component analysis (PCA) confirms these trends: fungivores and predators contribute the most to differentiation between zones, while bacterivores, dominant everywhere, are relatively homogeneously distributed.
Community-Weighted Mean (CWM) values for body weight, which indicate the size structure of the communities, are systematically higher in the insular zone across all trophic groups; the coastal and semi-continental zones show lower and similar values. A comparable trend is observed for carbon use efficiency (CUE), which is higher in the insular zone for most groups, except for herbivores, where no significant difference is observed. Nevertheless, these CUE values remain generally low (less than 0.5) across all zones, suggesting a significant allocation of energy to respiration rather than growth—a potential sign of environmental stress, particularly thermal, or metabolic strategies adapted to local conditions.
The analysis of environmental responses indicates that nematode biomass and productivity progressively decrease with increasing continentality. The metabolic activity of the main trophic groups is highest in the insular zone, intermediate in the coastal zone, and lowest in the semi-continental zone. Temperature range emerges as a major stress factor, showing a negative correlation between temperature fluctuations and metabolic activity: herbivores are the most sensitive to this, followed by bacterivores, fungivores, and then predators.
Finally, analyses linking soil properties to nematode communities show that their abundance is favored by warm conditions and high soil moisture, as well as adequate levels of pH, nitrogen, and calcium carbonate. Conversely, high heavy metal concentrations (copper, zinc, manganese) are associated with a decrease in their abundance. A negative relationship is also observed with altitude and precipitation—a seemingly counterintuitive result given the positive link with soil moisture, which could be explained by indirect effects such as nutrient leaching at higher altitudes or hypoxic conditions caused by excess water. In contrast, community diversity and carbon use efficiency appear to be little influenced by these soil parameters.
Overall, these results confirm that increasing continentality is accompanied by a decrease in nematode abundance and richness, as well as modifications in the functional structure and ecological balances within communities—without major alteration of global diversity indices, but with a clear shift toward greater dominance of certain taxa in the insular zone.
Réf. Braimin A., Benjlil H., Filali Alaoui I. et al., 2026 - Soil Nematode-Mediated Carbon and Energy Fluxes Along a Continental Gradient in Arid Ecosystems. Soil Syst. 2026, 10, 73 - https://doi.org/10.3390/soilsystems10070073
Posted by Jean-Paul Peltier.
This synthesis summarizes current knowledge about the microorganisms (bacteria, fungi, and yeasts) living in association with the argan tree and highlights their key roles in the tree’s health and its environment, both in natural settings and nurseries.
The Players in the Argan Tree Microbiome
Bacteria: Some, known as PGPR (Plant Growth-Promoting Rhizobacteria), are dominated by the genus Streptomyces. They help the argan tree absorb phosphorus (an essential nutrient) from the soil, regulate its hormones for better growth, combat diseases (biocontrol), and produce useful compounds for industry, such as eco-friendly alternatives to plastics (polyhydroxybutyrate).
Fungal Communities: Dominated by arbuscular mycorrhizal fungi (symbiotic fungi associated with roots), which improve phosphorus absorption and help the tree resist drought. They also include endophytic Ascomycetes, a source of bioactive compounds (antioxidants, antifungals), and entomopathogenic fungi that protect the argan tree from harmful insects (biocontrol).
Yeasts: Although less documented, they may possess unexplored metabolic traits with applications in agro-food processes (texturizers, emulsifiers, flavors) and biotechnology.
The study also emphasizes that the perception of microbial diversity is strongly influenced by both the isolation environment and identification methods, ranging from culture-based techniques to high-throughput sequencing and metagenomics.
It concludes that understanding the argan tree microbiome offers major prospects for the sustainable restoration of argan forests, the development of climate-resilient agriculture, and biotechnological innovation.
Réf. Taqarort N., Sadik S., Bouharroud R. & Qessaoui R. 2026 - Microbial diversity associated with the argan tree and its functional and biotechnological potential. Discover Plants (2026) 3:89 https://doi.org/10.1007/s44372-026-00571-7
Posted by Jean-Paul Peltier.
The chloroplast genome (plastome) of Euphorbia resinifera was sequenced using DNA extracted from 5–10 stipular spines (corresponding to approximately 20 mg of frozen tissue) from its tetragonal (rarely trigonal) stems, in order to avoid damaging the spurges by cutting the stems.
DNA libraries, prepared with the NEBNext Ultra II FS DNA Library Prep Kit (New England Biolabs), were sequenced on an Illumina NovaSeq 6000 platform (S2 flow cell). Following raw sequence trimming via Trimmomatic (v0.39) and quality control by FastQC (v0.12.1), the plastome was assembled de novo using the NOVOPlasty (v4.3.5) software, with the rbcL gene of Euphorbia ampliphylla as a seed. This assembly was comparatively validated using GetOrganelle (v1.7.7.0). Genome annotation and analysis were performed via GeSeq (v2.03) and CPGAVAS2, while OGDRAW was used to generate the standardized circular genome map.
The complete plastome of Euphorbia resinifera is a circular DNA molecule of 163,065 base pairs (bp) with a guanine-cytosine (GC) content of 35.11% and 96 SSR (Simple Sequence Repeat) loci. It exhibits the typical quadripartite structure of Angiosperms, consisting of a Large Single-Copy (LSC) region of 91,462 bp (32.06% GC), a Small Single-Copy (SSC) region of 18,285 bp (29.13% GC), and two Inverted Repeats (IR) of 26,659 bp each (42.39% GC). The analysis also details the number, nature of motifs, and distribution of these SSRs, which are key markers of genetic diversity.
The genome features a total of 132 annotated genes, including 87 protein-coding genes, 37 tRNA genes, and 8 rRNA genes, distributed as follows: 82 genes in the LSC region, 12 in the SSC, and 19 in each IR region.
This study provides the first sequenced chloroplast genome among the three cactiform spurge species endemic to Morocco.
Réf. Taha A., Rabeh K., Lamara M., et al., 2026 - Complete chloroplast genome of Euphorbia resinifera: overcoming biogeographical bias in phylogenetic inference and establishing a conservation genomics framework for threatened North-West African cactiform species. Front. Plant Sci. 17:1785579. doi: 10.3389/fpls.2026.1785579
Posted by Jean-Paul Peltier.
Argan orchards (aged 2 to 10 years) managed under extensive systems in the Arganeraie Biosphere Reserve were studied to assess carbon stocks in the main ecosystem components (aboveground argan tree biomass, leaf litter, herbaceous vegetation, and soil). The study, conducted across six sites between 2021 and 2023, combined morpho-physiological and dendrometric measurements with structural equation modeling to analyze interactions among compartments. Carbon stocks were estimated according to IPCC guidelines (2006, revised in 2019).
The results show an increase in carbon stock in argan tree biomass with age (from 0.003 to 1.938 t C ha⁻¹ between 2 and 10 years). Contributions from litter (0.36–8.51 kg C ha⁻¹) and herbaceous biomass (0–0.56 t C ha⁻¹) remain limited. Soil constitutes the main carbon reservoir, with stocks ranging from 10.12 to 80.5 t C ha⁻¹ (0–30 cm) and from 8.49 to 75.94 t C ha⁻¹ (30–60 cm).
These results highlight the dominant role of soil in carbon sequestration and emphasize the potential of extensive arganiculture for ecosystem restoration and climate change mitigation. They also confirm the relevance of integrating these systems into national climate strategies and carbon valuation mechanisms, particularly in arid regions.
Ref. Oumasst A., Tiouidji F. E., Chabbi N., et al. 2026 - Evaluating the dynamics of carbon accumulation in extensive argan orchard ecosystems in arid regions. Ecological Processes (2026) 15:6 - https://doi.org/10.1186/s13717-025-00666-1
Posted by Jean-Paul Peltier.
The study aims to map, using very high spatial resolution satellite imagery, the argan tree formation located in the upper valley of Oued Grou. This stand corresponds to a disjunct population located about 400 km north of the main distribution range of the argan tree. It is considered a site of biological and ecological interest and has been identified as a priority for the implementation of conservation and enhancement measures.
The study area is characterized by a semi-arid bioclimate with mild winters, with annual precipitation estimated between 400 and 450 mm.
Overall, the argan grove appears as a degraded matorral resulting from the combined effects of wood cutting and overgrazing. It includes approximately 775 argan trees scattered over a 1,200 ha area with a silvo-pastoral vocation, located between 200 and 600 m above sea level.
Most of the argan trees grow on very steep slopes exposed to the south or southwest, on Paleozoic schist substrates characterized by poorly developed soils. In these areas, argan trees are mainly associated with five-leaved sumac (Rhus pentaphylla).
A few individuals are also observed on north-facing slopes. However, on these slopes, where soils are generally deeper and better developed, the dominant vegetation formation corresponds to woodlands of thuya (Tetraclinis articulata), wild olive (Olea europaea subsp. europaea), and mastic tree (Pistacia lentiscus).
To date, this site has never been subject to a management plan. This absence of management measures partly explains the degree of degradation observed, with nearly 68% of the area currently occupied by bare soils.
It should be recalled that the presence of the argan tree in the Oued Grou valley was first reported by Emberger in 1924. Furthermore, the study of the chloroplast genome of the argan tree has shown that these stands likely result from a relatively recent dispersal, probably of anthropogenic origin (El Mousadik & Petit, 1996).
Ref. Sahel Y., Dellahi Y. & Chahhou D., 2022 - Mapping the Site of Biological and Ecological Interest of Rganat-Bouchkal (Tsili) Argan forest (Moroccan Central Plateau) using remote sensing. IOP Conf. Ser.: Earth Environ. Sci. 1090 012001
Posted by Jean-Paul Peltier.
Last modified on Thursday, July 16, 2026 at 15h16.