Background: The growth of alfalfa (Medicago sativa L.) is significantly hampered by drought and nutrient deficiencies. The identification of root architectural and anatomical characteristics holds paramount importance for the development of alfalfa genotypes with enhanced adaptation to adverse environmental conditions. In this study, we employed a visual rhizobox system to investigate the variability in root system architecture (including root depth, root length, root tips number, etc.), anatomical features (such as cortical traits, total stele area, number and area of vessel, etc.), as well as nitrogen and phosphorus uptake across 53 alfalfa genotypes during the seedling stage. Results: Out of the 42 traits measured, 21 root traits, along with nitrogen (N) and phosphorus (P) uptake, displayed higher coefficients of variation (CVs ≥ 0.25) among the tested genotypes. Local root morphological and anatomical traits exhibited more significant variation than global root traits. Twenty-three traits with CVs ≥ 0.25 constituted to six principal components (eigenvalues > 1), collectively accounting for 88.0% of the overall genotypic variation. Traits such as total root length, number of root tips, maximal root depth, and others exhibited positive correlations with shoot dry mass and root dry mass. Additionally, total stele area and xylem vessel area showed positive correlations with N and P uptake. Conclusions: These root traits, which have demonstrated associations with biomass and nutrient uptake, may be considered for the breeding of alfalfa genotypes that possess efficient resource absorption and increased adaptability to abiotic stress, following validation during the entire growth period in the field.

Vegetation restoration enhances soil erosion resistance by enhancing soil aggregates, but the function of these aggregates and their relationship with soil nutrients and microbes remain unclear. In this study, two land cover types that induce different aggregate ratios were selected to determine the soil aggregate ratio, aggregate ability, nutrients, and microbes. The results showed that high vegetation cover induced a higher macroaggregate ratio and soil water content; stronger soil shear strength; higher mean weight and geometric mean diameters; and lower soil bulk density. Macroaggregates had a lower soil organic matter (SOM) content compared with small macroaggregates. The aggregates and SOM influenced soil microbial diversity, especially microbial species and functions, and the large and small macroaggregate soils contained more microbes involved in SOM degradation, which accelerated the degradation and induced macroaggregate fragmentation. Total phosphorus (TP) had a direct impact on macroaggregates, and TP and macroaggregates showed the same correlation with the main microbial abundance. Taken together, we conclude that in the environment studied, SOM influenced soil microbes and the microbial function in SOM degradation affecting soil aggregates. TP contributed more to soil aggregate variations, especially in large macroaggregate formation.

Introduction: The mechanisms underlying adaptations of root system architecture (RSA) and root anatomy to phosphorus (P) deficiency and drought stress remain unclear in alfalfa ( Medicago sativa L.). This study investigated the root response strategies of two alfalfa cultivars (WL354HQ: WL354; Longdong: LD) with contrasting RSA under P deficiency and drought, and the relationship between root traits and shoot P uptake. Methods: Root morphology and anatomy were assessed under varying P (0, 5, 20 mg P kg ^-1 soil) and water (80 ± 5% and 40 ± 5% field capacity) conditions using visual rhizoboxes, with two years field validation. Results: Under low P and drought stress within the rhizoboxes, WL354 increased fine roots in soil layers below 60 cm, maintained xylem vessel area (XVA) in lateral roots below 90 cm, enlarged cortical cell size (CCS) in taproots and 2 ^nd lateral roots across several soil layers, and reduced cortical cell files (CCF) in both taproots and lateral roots throughout all soil layers. Conversely, LD merely maintained CCS in taproots and 2 ^nd lateral roots across several soil layers, and reduced CCF in taproots across all soil layers and in 1 ^st lateral roots above 90 cm. Simple linear correlation analysis revealed that shoot P uptake was positively correlated with total root surface area in the rhizobox experiment and with xylem vessel area of the taproot in the field experiment. Discussion: Under P deficiency and drought, WL354 implemented a resource acquisition strategy by increasing resource capture and transport in deep soil, and uptake efficiency. In contrast, LD exhibited a relatively conservative strategy focused on uptake efficiency. An increase in total root surface area and xylem vessel area of the taproot may help promote shoot P uptake. These findings offer insight into root trait-based strategies for improving alfalfa productivity in low-P and drought regions.

Background and aims Alfalfa (Medicago sativa. L) growth is largely restricted by abiotic stress such as drought and nutrient deficiency. Identifying root architectural and anatomical characteristics is of great significance for breeding alfalfa genotypes with improved adaptation to adverse environments. Methods Using nutrient solution sand culture method and visual rhizobox cultivation system, we explored the variability in root system architecture (RSA) and anatomy of 53 alfalfa genotypes at the seedling stage. Results Among 44 measured traits, 23 root traits, nitrogen (N) and phosphorus (P) uptake exhibited larger coefficients of variation (CVs ≥ 0.25) across tested genotypes. The variation degrees of local root traits and root anatomical traits were larger than global root traits. Twenty-five traits with CVs ≥ 0.25 constituted 6 principal components (eigenvalues > 1) accounting for 88.9% of the total genotypic variation. Total root length, root length in diameter thin, root tips number, maximal root depth, root length and root tips number in different soil layers were positively correlated with shoot dry mass and root dry mass (P ≤ 0.05). Total stele area (P ≤ 0.05) and xylem vessel area (P ≤ 0.001) were positively correlated with N and P uptake. Conclusion The tested alfalfa genotypes showed larger variation in local root morphological and anatomical traits at the seedling stage. Some important root traits, including root length, root length in diameter thin, root tips number, maximal root depth, total stele area and xylem vessel area have potential function on breeding alfalfa genotypes with improved adaption to abiotic stress.