Mucoromycotina fine root endophytes (M-FRE), although commonly present in cultivated crops, represent a largely overlooked symbiosis, and their diversity and ecological functions under field conditions remain poorly understood. The co-occurrence of M-FRE and Glomeromycotina arbuscular mycorrhizal fungi (G-AMF) was assessed in field-grown durum wheat (Triticum turgidum subsp. durum), testing the effects of combined water and nitrogen stress on root colonization and fungal community diversity in roots, rhizosphere, and extra-radical hyphae. The M-FRE colonization was reduced under combined stress but was unaffected by wheat genotype. In contrast, G-AMF colonization varied among genotypes and was insensitive to this combined stress. While G-AMF colonization correlated with root traits, M-FRE abundance was rather determined by soil properties and the applied stress. Colonization by M-FRE but not by G-AMF correlated with nitrogen and phosphorus uptake in plant shoots. Partial 18 S metabarcoding detected 74 G-AMF taxa and 12 M-FRE taxa, some shared across compartments, revealing active growth of M-FRE extra-radical hyphae. Stress had contrasting effects on diversity: G-AMF alpha diversity remained stable, whereas M-FRE diversity declined, with stress driving distinct community structures for both groups. Collectively, our results suggest that M-FRE and G-AMF are structured by distinct ecological drivers, supporting functional differentiation between these morphologically similar symbioses.

Tree roots have the potential to release carbon into deep soil layers, where this carbon is generally considered to exhibit greater stability. However, field studies that investigate the drivers of the soil organic carbon (SOC) balance in the rhizosphere of trees across soil depths and that upscale this balance to the whole soil profile are lacking. This study presents an innovative approach integrating normalized rhizosphere sampling and root density mapping to a depth of 1.5 m under trees from Mediterranean agroforestry and a tree plantation. The estimated SOC balance in the rhizosphere of the Robinia pseudoacacia trees varied from-38 kg C ha-1 to +53 kg C ha-1 at the different soil horizons, with a neutral balance at 0-0.3 m, a negative balance at 0.3-0.5 m and a positive balance at 0.5-1.0 m and 1.0-1.5 m of soil depth. When scaled up to the whole profile, the value was +50.6 kg C ha-1 for the tree plantation and +72.4 kg C ha-1 for the tree row for the agroforestry system, with no significant difference between these two estimates. The balance between hydrolytic and oxidative enzyme activities and between fungal guilds indicated increasing nutritional constraints for microbial saprotrophs at depth. In the subsoil, these nutritional constraints were locally attenuated in the rhizosphere, inducing a substantial increase in microbial abundance and triggering a pronounced shift from oligotrophic to copiotrophic communities, which in turn supported SOC enrichment. In the topsoil, the lower chemical complexity of substrates available to microorganisms increases susceptibility to saprotrophic activity, which likely underlies the observed neutral or negative SOC balances in the rhizosphere. This field study presents a scalable approach for quantifying the rhizosphere SOC balance in deep soil horizons and disentangling its biogeochemical drivers.

We need to adapt crop species and agricultural practices to produce high quantities of quality food for a growing world population, while also reducing the negative impact of agriculture on the environment to meet the targets of the Paris Agreement. It is increasingly recognised that healthy soils are at the heart of this endeavour, sustaining global geochemical cycles and the productivity of most terrestrial ecosystems. This ability of soils to support essential ecosystem services like nutrient cycling arises from diverse communities of soil organisms. Many ecosystem services are a function of how these soil organisms interact with each other, with the aboveground plant species and with the physio-chemical soil matrix. Here, we argue that multiple ecosystem processes and climate change resilience rely on diverse plant and soil communities with complex interactions among various actors carrying out complementary functions, rather than on individual indicator species on their own. We highlight areas of research which could be expanded to advance our understanding from single-species studies to the functional complexity of soil food webs and its integration into land management strategies with the aim to improve the resilience and sustainability of essential terrestrial ecosystems and the services they provide to the human population.

Excessive phosphorus (P) fertilization has resulted in elevated soil P concentrations in some regions in the EU. Legacy soil P imposes a risk for soil functioning and may lead to P losses into the aquatic environment. Recent proposed EU policies aim to optimize P inputs and mitigate excessive soil P concentrations. We present a framework to estimate how much and where P inputs in EU agricultural (cropland and grassland) soils can be optimized. The framework, with assumptions on optimal soil P concentrations and modelled soil P balances, allows calculating how much of the EU agricultural area experiences a build-up or maintenance of soil P concentrations despite having high soil P concentrations. Next, we calculated how much P inputs can be reduced to reach maintenance situation (inputs equal outputs) or to reach optimal soil P concentrations. Assuming optimal soil P concentrations (Olsen) being 20-40 mg kg-1, we calculated that current P inputs across the EU can be reduced by 21 % without adverse impacts on crop production, in line with EU policy objectives. The most appropriate strategy strongly depended on the farming system properties and varied across the European regions. The results are discussed in view of current or desired policies limiting P application rates. The framework, with suggested future improvements on uncertainties in data and models, can guide policy makers and land managers to set targets on P application rates, thereby reconciling agronomic and environmental objectives.

High-input agriculture involves low within-field crop genetic diversity, while plant diversity in natural ecosystems was shown to promote ecosystem functioning. Increasing intra-specific diversity in agroecosystems is a promising strategy to stabilize crop productivity and promote the associated diversity of soil biota. We investigated the effect of within-field diversity of bread wheat varieties on arbuscular mycorrhizal fungi (AMF) and two enzymatic activities involved in organic nitrogen and phosphorus mineralization. We set up a field experiment to test whether varietal or functional diversity modulate the abundance and diversity of AMF and the activity of leucine aminopeptidases and phosphatases in the root zone, considering the influence of root morphology. We used sixteen wheat varieties clustered into four groups according to previously measured traits. The abundance of AMF in roots was measured by qPCR, community composition was analyzed by Illumina metabarcoding on two AMF markers (SSU, LSU), and enzymatic activities were quantified by biochemical assays. Soil properties were the primary drivers of all response variables. Varietal diversity affected nitrogen-related soil enzymatic activities but not those related to phosphorus, with a significant increase of leucine-aminopeptidase activities with increasing varietal diversity. Wheat varietal and functional diversity marginally impacted the abundance of AMF, and functional diversity negatively affected AMF diversity on the SSU marker. Mean root traits modulated enzymatic activities, but not AMF communities. Increasing intra-specific crop diversity affects essential soil microbial processes, providing valuable insights for studying the relationship between plant diversity and soil microbiota in agroecosystems.

Abstract High-input agriculture has been associated with a drastic reduction of within-field crop genetic diversity, while plant (mostly functional) diversity in natural ecosystems has been shown to promote ecosystem functioning. Increasing intra-specific diversity in agroecosystems is a promising strategy to stabilize crop productivity and promote the associated diversity of fauna and microbiota. We investigated the effect of the within-field diversity of bread wheat varieties on arbuscular mycorrhizal fungi (AMF) and two enzymatic activities involved in organic nitrogen and phosphorus mineralization. A field experiment was designed to test whether the number of mixed wheat varieties in a plot, or their functional diversity (previously assessed), influence the abundance and diversity of AMF and the activity of leucine aminopeptidases and phosphatases in the root zone. The AMF abundance was measured by quantitative polymerase chain reaction, community composition was analyzed by Illumina metabarcoding on two AMF specific markers, and potential microbial activities were quantified by biochemical assays. Wheat traits related to root morphology and susceptibility to fungal diseases previously quantified for each variety were also used. Number of varieties significantly increased AMF abundance in roots, whereas functional cluster number did not, with no impact of root morphology. Functional cluster number influenced AMF diversity, though weakly and not linearly, responding most to binary mixtures. Both wheat variety and functional group number increased the potential leucine amino-peptidase activities in the root zone, while no effect was observed for phosphatase activities. Our results highlight that increasing crop intra-specific diversity triggered changes in key processes involved in nutrient acquisition.

• Better manage French soils for the agroecological transition. • Reduce our footprint on soils and close the biogeochemical cycles . • Manage French soils to adapt to- and mitigate climate change. • Control soil sealing, land-take and soil contamination in French soils. • Raising soil awareness and develop transfer of technology to help decision making.

Background and aims The positive effects of cereal-legume intercropping can occur through complementarity and facilitation for the acquisition of soil nitrogen (N) and phosphorus (P). However, the magnitude of the benefits depends on the availability of such resources. To improve our understanding and design best-performing systems, we evaluated the performance and underlying mechanisms of a cereal-legume mixture on two crossed gradients of N and P. Methods In a pot experiment, wheat (Triticum aestivum L.) and white lupin (Lupinus albus L.) were grown separately or together on four levels of N combined with four levels of P. We compared biomass, N content, P content, shoot-to-root biomass ratios and white lupin production of cluster roots and nodules of sole crops with those of intercrops. We used the relative interaction intensity index to determine how the nature of the interaction between the two species changed along the two resource gradients. Results Regardless of N and P supply, combined biomass and N content of intercropped wheat and white lupin were 29% and 23% greater than those of sole crops, respectively. Intercropping increased P content by 34%, on average, particularly at the lowest P supply. While wheat benefited from intercropping in all treatments, white lupin's performances decreased with increasing N and P supply, resulting in a shift from mutualism to competition along the two gradients and compensation mechanisms between the two species. Conclusion Nutrient availability negatively influenced the nature and mechanisms of wheat-lupin interaction. However, we only observed mutualistic interactions under low resource supply, which led to the lowest production, while competition was associated with the most productive situations.

Cereal-legume mixture is a well-known successful intercrop model for an efficient use of soil nutrients [1,2]. Effects of mineral N gradient on the acquisition of major nutrients: potassium (K), calcium (Ca), magnesium (Mg) and sulfur (S) is presented. A greenhouse pot experiment was conducted with wheat (Triticum aestivum L. cv. Lennox) and white lupin (Lupinus albus L. cv. Feodora) grown as sole crops and intercropped along a soil mineral N gradient obtained by 15N addition. Plants were harvested at flowering stage and dry weights of shoots and roots were measured. Potassium, calcium, magnesium and sulfur concentrations in shoots and roots were determined by Inductively Coupled Plasma Mass Spectrometry (ICP-MS).

Alley cropping agroforestry systems are complex agroecosystems highlighted for their positive effects on soil quality. However, the potential spatial heterogeneity of soil quality created by tree rows at the plot scale has seldom been studied. The aim of this study was to evaluate soil quality at the plot scale, under tree rows and along transects perpendicular to the tree row and to compare alley cropping systems with monocropping systems. This study was performed on an alley cropping system that combined hybrid walnut trees (21 years old) and peas. Topsoil was sampled at tree rows between 1 and 2, 2 and 4 and 4 and 6.5 m from the tree row in the alley cropping system, as well as in a neighbouring monocropping plot. Physical, chemical and microbiological indicators of soil quality were measured. Tree row implantation induced spatial heterogeneity in the chemical indicators, microbial biomass, activities and community structure at the alley cropping plot scale. Alley cropping not only improved microbiological soil quality indicators within the tree rows but also in the interrows when compared to a monocropping system. These indicators were then integrated into one soil quality index (SQI) built through a statistical approach. The soil quality index was calculated for the monocropping plot and for each position within the alley cropping plot. After 21 years of agroforestry practice, tree rows and permanent grass cover improved the SQI until 2 m in the interrow. Weighted SQIs were calculated relative to the surface area of each location for the entire alley cropping plot (i.e., tree row + interrow positions) and for the entire alley cropping interrow (i.e., removing the tree row surface area). The weighted SQI of the entire alley cropping plot significantly increased compared with that of the monocropping plot.