Leguminous Shrub Research Articles

The ‘fertilizer island effect’ cannot eliminate competition between leguminous shrubs and symbiotic herbs in desert ecosystems

The ‘fertilizer island effect’ — a phenomenon engendered by shrubs — promotes the growth of symbiotic herbs and the stabilization of community structures in scrublands. Specifically, leguminous shrubs contribute significantly to the nitrogen input in desert ecosystems. However, the impact of these inputs on the nutrient balance in symbiotic herbs has seldom been explored. To enhance our understanding of the nutrient balance between nitrogen-fixing legume shrubs and symbiotic non-legume herbaceous plants in desert ecosystems, we focused on a typical legume shrub (Eremosparton songoricum) that grows in the Gurbantunggut Desert of northern China. Subsequently, we examined the biomass, ecological stoichiometry, and rhizosphere soil properties of two plant species (annual plant: Ceratocarpus arenarius; and ephemeral plant: Centaurea pulchella) growing across four horizontal distance ranges from E. songoricum. The results indicated that the closer a herbaceous plant was to the leguminous shrubs, the lower was its biomass and nutrient content. In contrast, herbaceous plants growing further away from the shrubs exhibited better growth conditions. The total biomass of Cer. arenarius and Cen. pulchella was greatest at a distance of D4 (90–100 cm), being 3.07, 2.15, and 1.23 times higher for Cer. arenarius and 2.05, 1.18, and 1.26 times higher for Cen. pulchella compared to distances of D1 (0–10 cm), D2 (30–40 cm), and D3 (60–70 cm), respectively. Meanwhile, the physicochemical properties of the rhizosphere root varied inversely with distance, with nutrient levels decreasing horizontally from D1 to D4 and vertically from 0–5 cm > 5–10 cm > 10–20 cm, showcasing a distinct ‘fertilizer island effect’. As the distance increased, the above-ground and below-ground parts of the symbiotic non-leguminous plants started to rely on different types of soil nutrients from different depths to maximize nutrient acquisition. According to the structural equation model, although soil fertility was higher closer to the central leguminous plants, the biomass of nearby herbaceous plants was lower. In summary, in desert ecosystems, the competitive dynamics exerted by leguminous shrubs significantly overshadowed the nutrient provisioning role of the ‘fertilizer island effect’. Furthermore, the utilization of nutrients by symbiotic non-leguminous plants did not exhibit species-specific patterns, and the dominant shrub continued to play a pivotal role. The evidence from this study promotes a deeper understanding of species coexistence mechanisms and ecological stability in desert environments.

Plant Formations Found in Xerophytic (Arid) Sparse Forests in the Azerbaijan Territory and Their Protection

Based on the ecological and geobotanical studies conducted in xerophytic (arid) sparse forests in the territory of Azerbaijan and the study of the relevant literature, a classification scheme was developed taking into account xerophytic tree species that form such groups as Caragana grandiflora DC. and Astragalus microcephalus Willd. In the course of the study, based on phytocoenological principles, a xerophytic (arid) sparse forest type of vegetation was noted in the Turyanchay Reserve, in the mountainous part of the Lankaran-Yardymli district, in Nakhchivan and the Gabala district located on the southern slope of the Greater Caucasus. It was established that this type of vegetation consists of 1 formation class, 2 formation groups and 2 associations. A geobotanical description and species composition of the formations was carried out and it was established that the sparse forests of Caraganeta-Pistacetum-Juniperosum, found in the leguminous shrubs, need protection from the negative impact of anthropogenic factors. And this, in turn, creates the basis for the conservation of plant formations found in the forest ecosystems of Azerbaijan.

Divergent responses of above‐ and belowground ecosystem functioning to shrub encroachment in the Tibetan semi‐arid alpine steppes

AbstractSemi‐arid alpine ecosystems on the Tibetan Plateau are experiencing rapid climate change and extensive anthropogenic activity, concomitant with the encroachment of shrubs. Shrub encroachment will lead to changes in both the ecosystem structure and functioning of the semi‐arid alpine steppes. Yet, the encroaching impacts of shrubs on the above‐ and belowground ecosystem functioning of the semi‐arid alpine steppes remain uncertain. To quantify shrub encroachment impacts on ecosystem functioning of the semi‐arid alpine steppes, two alpine steppe sites encroached by shrub species are investigated, with one site encroached by leguminous shrub species (Caragana spinifera) and another site encroached by non‐leguminous shrub species (Dasiphora fruticosa). Results shows that the individual ecosystem functions and the ecosystem multifunctionality (EMF) of alpine steppes are significantly enhanced following both leguminous and non‐leguminous shrubs encroachment. We conclude that shrub encroachment tends to facilitate the belowground EMF (BEMF) but has neutral effects on the aboveground EMF (AEMF) in alpine steppes. Our findings also highlight that soil nutrients play critical roles in driving ecosystem functioning responses to shrubs encroachment. These findings further our understanding of shrub encroachment impacts on the ecosystem functioning of the semi‐arid alpine steppes.

Regulation of soil nitrogen cycling by shrubs in grasslands

Globally, grasslands are experiencing shrub expansion, but the effects of such plant community shifts on soil N cycling are seldom investigated. We explored the spatial heterogeneity of total soil N content by grid sampling down to a soil depth of 1.2 m, and analyzed net ammonification and nitrification rates in the top 0.2 m, during the growing season, in response to the patchiness of grasses and four shrub species in a grazed meadow on the Tibetan Plateau. The δ15N analyses of plant, soil, and mineral N (NH4+ and NO3−) revealed differences in N absorption strategies between shrubs and grasses. Heterogeneity in the total soil N distribution was common to at least a depth of 1.2 m. The lower δ15N values of the 1.2 m soil profile under shrubs were consistent with the lower δ15N values of leaves, aboveground litter, and roots of shrubs compared to grasses, reflecting the imprint of long-term N cycling in the soil as affected by shrubs. Increases in total soil N stock in the entire 1.2 m profile by 28%–32% under non-leguminous shrubs relative to grasses were ascribed to N accumulation in the lower 0.8 m. Consequently, deep sampling is essential for accurate estimation of soil N storage in shrubby meadows. The total N stock in soil under the leguminous shrub species was similar to that under grasses, which showed that the effect of shrubification on soil N storage depends on the shrub species. Nitrification rates in the topsoil under all shrubs were greater than under grasses, producing higher 15N-depleted NO3− contents under shrubs. Therefore, the lower δ15N signatures of shrub tissues compared to grasses reflected a preferential or adaptive uptake of NO3− by shrubs. The expansion of shrubs in grasslands creates high heterogeneity in N cycling and storage down to a considerable soil depth.

Kaistella yananensis sp. nov., a Novel Indoleacetic Acid-Producing Bacterium Isolated from the Root Nodules of Sophora davidii (Franch.) Skeels.

A novel endophytic bacterium, designated strain BT6-1-3T, was isolated from the root nodules of a leguminous shrub named Sophora davidii (Franch.) Skeels, found growing wild in Yan'an, Shaanxi Province, China. Cells were Gram-staining-negative, non-motile, catalase-positive, oxidase-positive, and did not produce H2S. Strain BT6-1-3T grew at 15-40°C (optimum 30°C), at pH 6.0-10.0 (optimum pH 9.0), and with 0-1% (w/v) NaCl (optimum 0.5%). The quinone system was menaquinone 6. The major fatty acids present in BT6-1-3T were iso-C11:0, iso-C15:0, and C16:0. The G+C content of genomic DNA was 39.4mol% by whole genome sequencing. According to the analysis of 16S rRNA gene sequence, the closest relative was Kaistella montana WG4 (nucleotide identity was 97.6%). The genome of strain BT6-1-3T was sequenced, and the genome similarity was calculated using average nucleotide identity and genome-to-genome distance analysis with the genomes of other strains of Kaistella. Both strongly supported that the strain BT6-1-3T belonged to the genus Kaistella as a representative of a new species. Based on phylogenetic analysis, chemotaxonomic data, and physiological and biochemical characteristics, strain BT6-1-3T represents a new species of the genus Kaistella and is named as Kaistella yananensis sp. nov. Type strain is BT6-1-3T (= NBRC 115452T = CGMCC 1.60032T).

Positive effects of leguminous shrub encroachment on multiple ecosystem functions of alpine meadows and steppes greatly depended on increasing soil nutrient

Shrub encroachment in grassland ecosystems is projected to intensify worldwide because of rapid climate change and anthropogenic activity, amplifying the encroachment of woody shrubs and strongly altering the ecosystem function. The effects of leguminous shrub encroachment on multiple dimensions of ecosystem functioning, however, remains poorly understood. This study experimentally quantified the effects of leguminous shrub encroachment (primarily Caragana spinifera Kom.) on various ecosystem functionality relevant to plant diversity, productivity, and storage of soil carbon (C) and nitrogen (N) in alpine meadows and steppes. Further, the study assessed the potential influences of shrub encroachment on ecosystem multifunctionality (EMF, EMF-diversity, EMF-productivity, EMF-C, and EMF-N). Our findings suggest that leguminous shrub encroachment enhanced ecosystem multifunctionality in alpine meadows and steppes. Plant diversity and aboveground biomass of herbaceous species increased after leguminous shrub encroachment. Additionally, the impacts of leguminous shrub encroachment on belowground biomass differed with grassland types, increasing in alpine steppes but decreasing in alpine meadows. The shrub encroachment resulted in significant increases in soil nitrogen and overall nutrient contents in both forms of alpine grasslands. Our findings highlight that shrub encroachment’s increasing of ecosystem multifunctionality was closely related to the promotion of plant diversity, biomass of herbaceous plants, and soil nutrients. Overall, our study demonstrates that the encroachment of leguminous shrubs can promote ecosystem multifunctionality in both alpine meadows and alpine steppes. These findings expand our understanding of the ecosystem functioning in leguminous shrub‐encroached alpine meadows and steppes.

Interplanting leguminous shrubs boosts the trophic interactions of soil micro-food web in a karst grassland

Nitrogen (N) is an essential nutrient for ecosystem productivity, restoration and succession processes. Biological N fixation and chemical N addition are both important strategies for accessing N nutrients in soil ecosystem. However, it is unclear which N supplement strategies is more effective in restoring ecosystem stability, particularly in soil micro-food web component, which plays a crucial role in nutrient cycling. Here, an in-situ study was conducted in a natural grassland to investigate the effects of N supply on soil microbial and nematode communities by three legume species: Amorpha fruticose (AF), Derris fordii (DF), and Indigofera atropurpurea (IA) at two interplanting densities (1: low density, 1.5 × 2 m; and 2: high density, 1 × 1 m), and by two N fertilization rates (N5: 5 g N m−2 y−1 and N10: 10 g N m−2 y−1). Results showed the microbial biomass of total-PLFA, bacteria, fungi, actinomycetes and chlorophyta increased by DF1 and IA2, and the biomasses of total nematodes, herbivores and omnivores were promoted by AF1, AF2 and DF1, but the biomass of most components was inhibited by N fertilizers. The interactions of soil micro-food web were complicated by DF1 and DF2, but simplified by N5 and N10. Furthermore, different N supplement strategies showed distinct energy flow patterns, such as the bacterial channel was promoted exclusively in AF2, the plant channel was enhanced in AF1 and AF2, and the fungal channel was boosted in DF1 and DF2 but declined in N5 and N10. These results demonstrated that the structure and energy flow of the soil micro-food web might be benefited by legume interplanting but impaired by N fertilizers. In particular, interplanting with D. fordii granted a more sustainable way of N supplementation for promoting the complexity and stability of the soil micro-food web, compared to interplanting with other legume species. Our findings provide better understanding of the interactions between legumes and soil biota and have important implications for sustainable restoration of degraded karst grasslands.

Genetic Divergence Studies among Indigenous Accessions of Cassia auriculata (L.) Roxb., through Screening and Utilization for Chambal Ravine Rehabilitation

Background: Cassia auriculata, L., is an imperative medicinal and traditional neutral colour leaf hair dye yielding in India. This is a multipurpose and indigenous, perennial leguminous shrub and widely used as traditional medicine to cure diabetics by the rural peoples. Tanner’s cassia is also used as neutral henna and its yields natural golden blonde colouring to hair through the dried leaf powder. Young buds are used for yellow colour dye extraction by textile industries. Screening of high tolerance and best performing genotypes is highly essential in this imperative woody legume shrub to rehabilitate the mass erosion prone gullied and ravine lands for productive purpose of the wasteland and degraded lands. Methods: Thirty different accessions of Cassia auriculata were assembled and numbered from CA-1 to CA-30 from arid and semi-arid regions of Rajasthan (India). The experimental trial was conducted at ICAR-IISWC, Research Centre, Kota-Rajasthan, India during 2019-2022. After evaluation, CA-4 genotype was selected as an elite genotype. The elite genotype was used for high density plantation development with resource conservation for green cover development in non-arable ravine lands. Result: Genetic variation studies of Cassia auriculata indicated that considerable and significant variability, abundant morphometric variations in assembled genotype progenies. Further, genetic divergence analysis was also revealed that nine clusters segregated from 30 genotypes. Thirty genotypes were grouped into nine clusters according overall performance with geographical identity. Finally, C. auriculata (CA-4) genotype was identified and selected as an elite genotype based on its overall superiority in terms of plant growth, higher green biomass, leaf litter biomass, more number branching behaviour and plant coppicing ability which are directly relevant and imperative in soil erosion control, resource conservation and potential rehabilitation effect in resource poor dry regions of non-arable lands.

Collection, distribution, characterization and utilization of Indigofera oblongifolia Forssk.: an important underutilized multi-use leguminous shrub of Indian hot arid region

AbstractIndigofera oblongifolia Forssk. locally known as ‘Goilia or Jhil’, is an important underutilized leguminous browse shrub for small ruminants in hot arid region of India and traditionally utilized for its medicinal value. Its irregular patchy distribution was observed in depression of rocky areas, bunds of farmer fields and along the depression on the road sides in Jaisalmer and Pali district during collection. Soil samples collected from Pali district have high level of pH and electrical conductivity as compared to Jaisalmer which indicates its suitability to saline areas. It exhibited good plant growth under Jodhpur conditions with respect to plant height (171.5 cm), number of branches (47.9) and canopy diameter (100–210 and 115–180 cm in north-south and east-west direction, respectively) after 12 months of planting in fields under protected condition. Morphological characterization showed the presence of high coefficient of variation (%) in the number of raceme per branch (27.3) followed by raceme length (22.9), pod length (21.0) and least in pod width (8.1). Phytochemical results revealed that leaves of I. oblongifolia contained considerable amounts of total phenols (31.44 mg g−1), flavonoids (29.73 mg g−1) and antioxidant capacity (6.26 FRU g−1) which make its suitability as a browse species to ruminants in rangelands. Along with these finding, its traditional knowledge and utilization are detailed in this paper as to hasten further research on its various aspects for its sustainable utilization in rangelands or in alternate land use systems in the Indian hot arid region.

Productivity and Nutritional Quality of Nitrogen-Fixing and Non-Fixing Shrub Species for Ruminant Production

Fodder shrubs are important dry season feed sources for livestock in semi-arid environments. It has been proposed that a mixture of leguminous with non-leguminous shrubs may increase rates of N cycling and improve biomass and fodder quality. The objective of the present study was to assess the biomass productivity and fodder quality of leguminous shrubs growing a mixture with non-leguminous shrubs. Three shrub species—the legume Leucaena leucocephala (Lam.) and the non-legumes Guazuma ulmifolia (Lam.) and Moringa oleifera (Lam.)—were grown as legume/non-legume mixtures and as monocultures. Total fodder production and quality were estimated over five harvests at three-month intervals. The Leucaena–Guazuma mixture had the largest fodder production (9045 kg ha−1 year−1), followed by the Leucaena monocrop (7750 kg ha−1 year−1). Total nitrogen accumulation in the foliage was also high in the Leucaena–Guazuma mixture, reaching 282 kg ha−1 year−1; the Leucaena monocrop accumulated 244 kg N, while the Moringa monocrop took up only 46 kg N ha−1. The concentration of polyphenols was high in Leucaena and Guazuma, while Moringa had the lowest value. The high survival and excellent growth rates, as well as the high foliage production observed in Leucaena and Guazuma, suggest that they have the potential to provide high-quality fodder for livestock.

Shrub encroachment alters plant trait response to nitrogen addition in a semi-arid grassland.

Encroachment of shrubs over large regions of arid and semi-arid grassland can affect grassland traits and growth under a background of increasing nitrogen (N) deposition. However, the effects of N input rates on species traits and the growth of shrubs on grasslands remain unclear. We examined the effects of six different N addition rates on the traits of Leymus chinensis in an Inner Mongolia grassland encroached by the leguminous shrub, Caragana microphylla. We randomly selected 20 healthy L. chinensis tillers within shrubs and 20 tillers between shrubs in each plot, measuring the plant height, number of leaves, leaf area, leaf N concentration per unit mass (LNCmass), and aboveground biomass. Our results showed that N addition significantly enhanced the LNCmass of L. chinensis. The aboveground biomass, heights, LNCmass, leaf area, and leaf number of plants within the shrubs were higher than those between shrubs. For L. chinensis growing between shrubs, the LNCmass and leaf area increased with N addition rates, leaf number and plant height had binomial linear relationships to N addition rates. However, the number of leaves, leaf areas and heights of plants within shrubs did not vary under various N addition rates. Structural Equation Modelling revealed N addition had an indirect effect on the leaf dry mass through the accumulation of LNCmass. These results indicate that the response of dominant species to N addition could be regulated by shrub encroachment and provide new insights into management of shrub encroached grassland in the context of N deposition.

Effect of drip irrigation on seed yield, seed quality and water use efficiency of Hedysarum fruticosum in the arid region of Northwest China

Shortage of high-quality seeds of native species, particularly for xerophyte shrubs, have severely limited grassland restoration in the arid region of China. However, little attention has been devoted to improving seed yield and quality in the xerophyte shrub. We conducted a three-year field experiment from 2019 to 2020 to investigate the effects of four irrigation treatments (i.e., W0: non-irrigated control; W1: irrigation at winter; W2: irrigation at winter and regreening; W3: irrigation at winter, regreening, and peak flowering) via subsurface drip irrigation on the seed yield and quality of Hedysarum fruticosum, a dominant leguminous shrub in the desert areas of China. The results showed that seed yield increased as irrigation frequency increased regardless of growth season. The yearly average seed yields were 98.0, 107.7, 179.3, and 265.5 kg hm−2 for W0, W1, W2, and W3 irrigation, respectively. Seed yield decreased in each subsequent growth year in all irrigation treatments, and the variation in seed yield each year was the highest in W0 and lowest in W3 irrigation. Compared to 2019, the seed yield of W0 decreased by 47 % and 66 %, but yields of the W3 irrigation treatment decreased by 8 % and 19 % in 2020 and 2021, respectively. Meanwhile, irrigation significantly affected seed yield components; the number of florets and pods per stem under the W3 irrigation treatment was two to three times that of W0 irrigation for three years. The structural equation model revealed that pods per stem had the largest direct positive effect on seed yield (path factor p = 0.44), followed by seeds per pod (path factor p = 0.36). Irrigation treatments affected seed germination percentage and seed size, which increased as irrigations times increased. A similar water use efficiency was achieved in W0 and W3 in three years, and W1 treatment had the lowest water use efficiency. In conclusion, we recommend W3 treatment to increase seed yield and quality, especially in arid regions. Future breeding objectives and agronomic practice for H.fruticosum should pay more attention to increasing pods per stem. Our study can be used as a reference for taking appropriate agronomic measures to improve the seed yield of H.fruticosum and similar shrubs.

Shrub-mediated effects on soil nitrogen determines shrub-herbaceous interactions in drylands of the Tibetan Plateau.

Shrub promotes the survival, growth and reproduction of understory species by buffering the environmental extremes and improving limited resources (i.e., facilitation effect) in arid and semiarid regions. However, the importance of soil water and nutrient availability on shrub facilitation, and its trend along a drought gradient have been relatively less addressed in water-limited systems. We investigated species richness, plant size, soil total nitrogen and dominant grass leaf δ13C within and outside the dominant leguminous cushion-like shrub Caragana versicolor along a water deficit gradient in drylands of Tibetan Plateau. We found that C. versicolor increased grass species richness but had a negative effect on annual and perennial forbs. Along the water deficit gradient, plant interaction assessed by species richness (RIIspecies) showed a unimodal pattern with shift from increase to decrease, while plant interaction assessed by plant size (RIIsize) did not vary significantly. The effect of C. versicolor on soil nitrogen, rather than water availability, determined its overall effect on understory species richness. Neither the effect of C. versicolor on soil nitrogen nor water availability affected plant size. Our study suggests that the drying tendency in association with the recent warming trends observed in drylands of Tibetan Plateau, will likely hinder the facilitation effect of nurse leguminous shrub on understories if moisture availability crosses a critical minimum threshold.

Plants for Fitness Enhancement of a Coffee Leaf Miner Parasitoid

The enhancement of pest control through the conservation of natural enemies in agricultural fields is called conservation biological control. One of the strategies used on this system is to introduce or manage plants that can provide food for natural enemies. We assessed the effect of feeding resources on the fitness of a coffee leaf miner parasitoid, Proacrias coffeae Ihering (Hymenoptera: Eulophidae), by evaluating the effect of different nectar resources on the survival of P. coffeae. To do so we used three flowering plants: Bidens pilosa, Galinsoga parviflora, and Varronia curassavica, and the leguminous shrub, Senna cernua Balb. H.S. Irwin & Barneby which produces extrafloral nectar. When feeding on the floral nectar of V. curassavica and on the extrafloral nectar of S. cernua the parasitoids increased their survival, however, no significant differences were found when feeding on B. pilosa and G. parviflora. We evaluated the effect of extrafloral nectar of S. cernua on the egg load of P. coffeae and found an increase in their egg load when exposed to the extrafloral nectar and with increasing age. Our results show the potential of V. curassavica and S. cernua as nutritional resources to enhance the fitness of the parasitoid P. coffeae, by increasing their survival. Based on the research study, it is evident that the introduction of feeding resources for P. coffeae in the coffee agroecosystem will increase their fitness as a potential biocontrol agent by enhancing their survival and reproductive potential.

Evaluation of the productivity and feed value of Wondergraze and Redlands leucaena cultivars under grazing

Context Leucaena leucocephala (leucaena) is a leguminous shrub used for beef grazing in low-rainfall regions (<600–700 mm). Newer cultivars have the potential to extend adoption of the species to higher rainfall (>600–700 mm), frost-free areas of Australia. Aim We compared productivity, nutritional value and animal performance of two leucaena cultivars, new psyllid-resistant Redlands and the 2010-released Wondergraze, under continuous grazing management in a higher rainfall environment. Methods Growing steers were allocated to replicated established stands of Wondergraze or Redlands with inter-row mixed grass–legume pasture from January to July 2021. Pasture and leucaena were characterised for biomass and nutritive characteristics. Botanical composition was measured. Liveweight gain, rumen fermentation, and leucaena mimosine breakdown products were measured in grazing steers. Key results At the beginning of the study, leucaena edible biomass was similar for both cultivars (P > 0.05), but at subsequent samplings, biomass of Redlands was lower than of Wondergraze (P < 0.01). Biomass of both cultivars declined rapidly over the grazing period. Pasture biomass increased between February and July and was significantly higher in Wondergraze paddocks (P < 0.05). Animal performance was not significantly different between cultivar treatments, averaging 0.8 kg/day, but declined over time. Patterns of mimosine conversion to DHP isomers and their conjugation were similar for the two cultivars, suggesting that effectiveness of detoxification did not differ between them. Conclusion The results demonstrate that leucaena can sustain high levels of animal performance when included in tropical grass pastures in a higher rainfall environment if present in a sufficient quantity (>2 t leucaena edible dry matter/ha established leucaena). Implications Grazing leucaena–grass pastures is an effective means of increasing animal productivity in parts of subtropical Australia. However, managing grass and/or leucaena growth to match animal requirements can be challenging.

High-Throughput Absolute Quantification Sequencing Reveals that a Combination of Leguminous Shrubs Is Effective in Driving Soil Bacterial Diversity During the Process of Desertification Reversal

Desertification leads to the extreme fragility of ecosystems and seriously threatens ecosystem functioning in desert areas. The planting of xerophytes, especially leguminous shrubs, is an effective and common means to reverse desertification. Soil microorganisms play a crucial role in nutrient cycling and energy flow in ecosystems. However, the effects of introducing leguminous shrubs on soil microbial diversity and the relevant mechanisms are not clear. Here, we employed the high-throughput absolute quantification 16S rRNA sequencing method to analyze the diversity of soil bacteria in sand-fixing areas of mixed shrublands with three combinations of shrubs, i.e., C. korshinskii × Corethrodendron scoparium (CaKCoS), C. korshinskii × Calligonum mongolicum (CaKCaM), and C. scoparium × C. mongolicum (CoSCaM), in the south of the Mu Us Sandy Land, China. This area suffered from moving dunes 20 years ago, but after introducing these shrubs to fix the dunes, the ecosystem was restored. Additionally, the effects of soil physicochemical properties on soil bacterial composition and diversity were analyzed with redundancy analysis (RDA) and structural equation modeling (SEM). It was found that the Shannon index of soil bacteria in CaKCoS was significantly higher than that in CaKCaM and CoSCaM, and the abundance of the dominant phyla, including Actinobacteria, Proteobacteria, Acidobacteria, Chloroflexi, Planctomycetes, Thaumarchaeota, Armatimonadetes, candidate_division_WPS-1, and Nitrospirae, increased significantly in CaKCoS and CaKCaM compared to that in CoSCaM. RDA showed that the majority of soil properties, such as total nitrogen (TN), available potassium (AK), N:P ratio, soil moisture (SM), and available phosphorus (AP), were important soil environmental factors affecting the abundance of the dominant phyla, and RDA1 and RDA2 accounted for 56.66% and 2.35% of the total variation, respectively. SEM showed that the soil bacterial α-diversity was positively affected by the soil organic carbon (SOC), N:P ratio, and total phosphorus (TP). Moreover, CaKCoS had higher SM, total carbon (TC), total potassium (TK), and AP than CaKCaM and CoSCaM. Collectively, these results highlight a conceptual framework in which the combination of leguminous shrubs can effectively drive soil bacterial diversity by improving soil physicochemical properties and maintaining ecosystem functioning during desertification reversal.Graphical

Alhagi sparsifolia acclimatizes to saline stress by regulating its osmotic, antioxidant, and nitrogen assimilation potential

BackgroundAlhagi sparsifolia (Camelthorn) is a leguminous shrub species that dominates the Taklimakan desert’s salty, hyperarid, and infertile landscapes in northwest China. Although this plant can colonize and spread in very saline soils, how it adapts to saline stress in the seedling stage remains unclear so a pot-based experiment was carried out to evaluate the effects of four different saline stress levels (0, 50, 150, and 300 mM) on the morphological and physio-biochemical responses in A. sparsifolia seedlings.ResultsOur results revealed that N-fixing A. sparsifolia has a variety of physio-biochemical anti-saline stress acclimations, including osmotic adjustments, enzymatic mechanisms, and the allocation of metabolic resources. Shoot–root growth and chlorophyll pigments significantly decreased under intermediate and high saline stress. Additionally, increasing levels of saline stress significantly increased Na+ but decreased K+ concentrations in roots and leaves, resulting in a decreased K+/Na+ ratio and leaves accumulated more Na + and K + ions than roots, highlighting their ability to increase cellular osmolarity, favouring water fluxes from soil to leaves. Salt-induced higher lipid peroxidation significantly triggered antioxidant enzymes, both for mass-scavenging (catalase) and cytosolic fine-regulation (superoxide dismutase and peroxidase) of H2O2. Nitrate reductase and glutamine synthetase/glutamate synthase also increased at low and intermediate saline stress levels but decreased under higher stress levels. Soluble proteins and proline rose at all salt levels, whereas soluble sugars increased only at low and medium stress. The results show that when under low-to-intermediate saline stress, seedlings invest more energy in osmotic adjustments but shift their investment towards antioxidant defense mechanisms under high levels of saline stress.ConclusionsOverall, our results suggest that A. sparsifolia seedlings tolerate low, intermediate, and high salt stress by promoting high antioxidant mechanisms, osmolytes accumulations, and the maintenance of mineral N assimilation. However, a gradual decline in growth with increasing salt levels could be attributed to the diversion of energy from growth to maintain salinity homeostasis and anti-stress oxidative mechanisms.

Soil sampling depth matters in assessing the impact of shrubification on soil organic carbon storage in grazed alpine meadows

The distribution of shrubs is expanding in grasslands of the Qinghai–Tibetan Plateau, but research is rare on the effects of this expansion on the storage of soil organic carbon (SOC). We explored the spatial heterogeneity of SOC by grid sampling in the upper 1.2 m soil profile in a grazed alpine shrubby meadow, in response to patchy distribution of shrub species (leguminous Caragana brevifolia and non-leguminous Potentilla fruticose, Spiraea alpina and Salix oritrepha). The SOC content in the top 0.4 m increased with the size (height and crown diameter) of shrubs, but the soil bulk density decreased with the size of the shrubs. As a result, the SOC stock in the top 0.4 m soil was generally similar among shrub and grass patches across the meadow. The increase in the SOC stock in the entire 1.2 m profile by 35 % under non-leguminous shrubs P. fruticosa, S. alpina and S. oritrepha (39.8–40.5 kg m−2) compared with grasses (29.7 kg m−2) was mainly due to the SOC accumulation at the lower 0.4–1.2 m. The leguminous shrub C. brevifolia did not affect the SOC stock in the 1.2 m soil (32.3 kg m−2) compared with the grasses. Consistent patterns of changes in the natural δ13C signature between plants and SOC across different types of vegetation patches provided robust evidence that the heterogeneity of SOC across the field was a result of the patchy distribution of vegetation. We emphasize the importance of soil sampling depth in assessing the impact of shrubification on SOC storage. The influence depth of shrubification on SOC storage is at least 1.2 m in the profile in grazed Qinghai–Tibetan grasslands.

Fluoroacetate distribution, response to fluoridation, and synthesis in juvenile Gastrolobium bilobum plants

Like angiosperms from several other families, the leguminous shrub Gastrolobium bilobum R.Br. produces and accumulates fluoroacetate, indicating that it performs the difficult chemistry needed to make a C–F bond. Bioinformatic analyses indicate that plants lack homologs of the only enzymes known to make a C–F bond, i.e., the Actinomycete flurorinases that form 5′-fluoro-5′-deoxyadenosine from S-adenosylmethionine and fluoride ion. To probe the origin of fluoroacetate in G. bilobum we first showed that fluoroacetate accumulates to millimolar levels in young leaves but not older leaves, stems or roots, that leaf fluoroacetate levels vary >20-fold between individual plants and are not markedly raised by sodium fluoride treatment. Young leaves were fed adenosine-13C-ribose, 13C-serine, or 13C-acetate to test plausible biosynthetic routes to fluoroacetate from S-adenosylmethionine, a C3-pyridoxal phosphate complex, or acetyl-CoA, respectively. Incorporation of 13C into expected metabolites confirmed that all three precursors were taken up and metabolized. Consistent with the bioinformatic evidence against an Actinomycete-type pathway, no adenosine-13C-ribose was converted to 13C-fluoroacetate; nor was the characteristic 4-fluorothreonine product of the Actinomycete pathway detected. Similarly, no 13C from acetate or serine was incorporated into fluoroacetate. While not fully excluding the hypothetical pathways that were tested, these negative labeling data imply that G. bilobum creates the C–F bond by an unprecedented biochemical reaction. Enzyme(s) that mediate such a reaction could be of great value in pharmaceutical and agrochemical manufacturing.

Environmental filtering drives the establishment of the distinctive rhizosphere, bulk, and root nodule bacterial communities of Sophora davidii in hilly and gully regions of the Loess Plateau of China

In addition to the rhizobia, other non-rhizobial endophytes (NREs) have been simultaneously isolated from the root nodules. The existence of NREs in leguminous root nodules is a universal phenomenon, and they have the potential to enhance legume survival, especially under conditions of environmental stress. However, the diversity and biogeographic patterns of microbial communities inhabiting root nodules are not well studied or understood. Here, we explored and characterized the diversity of NRE bacteria by using 16S rRNA gene high-throughput amplicon sequencing. Additionally, we compared the biogeography and co-occurrence patterns in review of the bacterial microbiota inhabiting the rhizosphere, the bulk soil and the root nodule bacterial communities associated with Sophora davidii, a native N-fixing wild leguminous shrub in hilly and gully regions of the Loess Plateau of China. The results showed the presence of a large diversity of bacteria belonging to 81 phyla, 154 classes, 333 orders, 463 families, and 732 genera inside the nodules. Proteobacteria were dominant in the nodule and rhizosphere soil samples, and Actinomycetes were dominant in the bulk soil samples. Mesorhizobium was the dominant genus in the nodules, accounting for between 60.15 and 83.74% of the bacteria. The microbial community composition of the NRE in the root nodules differed from that in the rhizosphere soil and the bulk soil of S. davidii. Moreover, we found that the biogeographic patterns and assembly process of the rhizobia and non-rhizobia communities differed in the root nodule, the rhizosphere soil and the bulk soil. Furthermore, the correlation analysis between the soil’s physical and chemical properties and the bacteria showed that available phosphorus was the predominant factor affecting the bacterial diversity within the rhizosphere soil. Finally, our results revealed that the microbial network diagram of co-occurrence patterns showed more complexes in the soil than in the root nodules. This indicates that only specific microorganisms could colonize and thrive in the rhizosphere through the selection and filtering effects of roots. In conclusion, there are significant differences in bacterial community composition in the nodules, rhizosphere and bulk soil in the hilly and gully region of the Loess Plateau, which is the result of environmental filtration. Our study improves the understanding of the biogeographic patterns and diversity of bacterial microbiota inhabiting root nodules and can help quantify and define the root nodule assemblage process of S. davidii.