Alfalfa Growth Research Articles

Coastal Ecosystems as Sources of Biofertilizers in Agriculture: From Genomics to Application in an Urban Orchard

Pantoea agglomerans RSO7, a rhizobacterium previously isolated from Spartina maritima grown on metal polluted saltmarshes, had demonstrated good plant growth promoting activity for its host halophyte, but was never tested in crops. The aims of this study were: (1) testing PGP activity on a model plant (alfalfa) in vitro; (2) testing a bacterial consortium including RSO7 as biofertilizer in a pilot experiment in urban orchard; and (3) identifying the traits related to PGP activities. RSO7 was able to enhance alfalfa growth in vitro, particularly the root system, besides improving plant survival and protecting plants against fungal contamination. In addition, in a pilot experiment in urban orchard, a consortium of three bacteria including RSO7 was able to foster the growth and yield of several winter crops between 1.5 and 10 fold, depending on species. Moreover, the analysis of chlorophyll fluorescence revealed that photosynthesis was highly ameliorated. Genome analysis of RSO7 depicted the robustness of this bacterial strain which showed resilience to multiple stresses (heat, cold, UV radiation, several xenobiotics). Together with wide metabolic versatility, genes conferring resistance to oxidative stress were identified. Many genes involved in metal resistance (As, Cu, Ni, Co, Zn, Se, Te) and in tolerance toward high osmolality (production of a battery of osmoprotectans) were also found. Regarding plant growth promoting properties, traits for phosphate solubilization, synthesis of a battery of siderophores and production of IAA were detected. In addition, the bacterium has genes related to key processes in the rhizosphere including flagellar motility, chemotaxis, quorum sensing, biofilm formation, plant-bacteria dialog, and high competitiveness in the rhizosphere. Our results suggest the high potential of this bacterium as bioinoculant for an array of crops. However, the classification in biosecurity group 2 prevents its use according to current European regulation. Alternative formulations for the application of the bioinoculant are discussed.

Melatonin Enhances Seed Germination and Seedling Growth of Medicago sativa Under Salinity via a Putative Melatonin Receptor MsPMTR1.

Alfalfa (Medicago sativa L.) is an important forage crop, and salt stress is a major limiting factor in its yield. Melatonin (MT) is a multi-regulatory molecule in plants. We showed that basal MT content was positively correlated with the salt tolerance degree of different alfalfa varieties. MT and its precursor 5-HT fully recovered seed germination while partially ameliorated seedling growth of salt-stressed alfalfa. The 5-HT showed some divergent effects from MT with regards to growth amelioration under salinity. Salt stress caused stunted plant growth in soil culture, while MT ameliorated it by elevating plant height, fresh weight, branching number, and chlorophyll content. Silencing of a putative MT receptor, MsPMTR1, which was shown to be membrane-localized, abolished the ameliorative effects of MT on salt-stressed alfalfa seedling growth, while overexpression of MsPMTR1 improved plant growth under salt stress. The RNA sequencing analysis showed that nine pathway genes were specifically induced by MT treatment compared with salt stress. These MT-responsive differentially expressed genes include basal metabolic pathway genes, such as “ribosome, elongation factor,” “sugar and lipid metabolism,” and “photosynthesis” and stress-related genes encoding “membrane integrity” related proteins, heat shock protein, peroxidase/oxidoreductase, and protease. Several abiotic stress response-related genes, such as DRE, ARF, HD-ZF, MYB, and REM were repressed by NaCl treatment while induced by MT treatment. In summary, we demonstrated the importance of MsPMTR1 in MT-mediated salt tolerance in alfalfa, and we also analyzed the regulatory mechanism of MT during alfalfa seed germination under salt stress.

Potassium and Phosphorus Fertilizer Impacts on Alfalfa Taproot Carbon and Nitrogen Reserve Accumulation and Use During Fall Acclimation and Initial Growth in Spring.

Phosphorus (P) and potassium (K) impact alfalfa (Medicago sativa L.) performance, but how these nutrients alter taproot physiology during fall acclimation and subsequent growth in spring is unclear. Our objectives were to: (1) determine seasonal patterns for taproot P and K concentrations during fall acclimation and during initial shoot growth in spring; (2) determine how P and K nutrition impacts accumulation of taproot C and N reserves during fall and their subsequent use when shoot growth resumes in spring; and (3) assess how addition of P and K fertilizer impacts survival and shoot growth in spring. Two P (0 and 75 kg ha−1) and two K (0 and 400 kg ha−1) treatments were applied and taproots were sampled between September and December, and again from March to May over 2 years. Concentrations of taproot sugar, starch, buffer-soluble protein, amino-N, and RNA pools were determined. While P and K fertilizer application increased taproot P and K concentrations two- to three-fold, concentrations of P and K in taproots over time did not change markedly during cold acclimation in fall, however, taproot P declined in spring as plant growth resumed. Compared to the 0K-0P treatment, taproots of plants fertilized with 400K-75P had higher starch, protein, amino-N, and RNA, but reduced sugar concentrations in fall. Concentrations of all these pools, except starch, declined during the initial 2 weeks of sampling beginning in late March as shoot growth resumed in spring. Herbage yield in May was highest for the 400K-75P treatment and least for the 0K-0P treatment, differences that were associated with variation in mass shoot−1 and not shoots m−2. High yield of the 400K-75P plants in May was consistently associated with greater concentrations and use of amino-N, soluble protein, and RNA pools in taproots, and not with accumulation and use of starch and sugar pools. Understanding factors leading to the accumulation of taproot N reserves and RNA during cold acclimation in fall and their use during the initial growth in spring should enhance efforts to improve alfalfa growth and herbage yield in spring.

Shoot-soil ecological stoichiometry of alfalfa under nitrogen and phosphorus fertilization in the Loess Plateau

Plants and soil interactions greatly affect ecosystems processes and properties. Ecological stoichiometry is an effective means to explore the C, N, P correlation between plants and soil and the relationship between plant growth and nutrient supply. Serious soil erosion on China’s Loess Plateau has further barrenness the soil. Fertilization solves the problem of ecosystem degradation by improving soil fertility and regulating the ecological stoichiometric between soil and plants. No fertilization (CK), nitrogen fertilization (N), phosphorus fertilization (P) and N and P combined fertilization (NP) treatments were set in an alfalfa grassland. Organic carbon (C), nitrogen (N) and phosphorus (P) nutrients and their stoichiometry were measured in shoot and soil. P and NP fertilization increased shoot C concentration (3.12%, 0.91%), and all fertilization decreased shoot N concentration (6.96%). The variation of shoot C and N concentrations resulted in a greater increase in shoot C:N under the fertilization treatment than that under CK (8.24%). Most fertilization treatments increased shoot P concentration (4.63%) at each cut, which induced a decrease of shoot C:P. Shoot N:P of most treatments were greater than 23, but it was lower under N and NP fertilization than that under CK. Fertilization only increased soil C in 2014, but had no effect on soil N. Soil P content was significantly higher under P fertilization in 2014 (34.53%), and all fertilization in the second cut of 2015 (124.32%). Shoot and soil C:P and N:P having the opposite changes to shoot and soil P, respectively. Our results suggest that the change of P after fertilization largely drove the changes of stoichiometric. The growth of alfalfa in the Loess Plateau was severely restricted by P. It is an effective method to increase the biomass of alfalfa by increasing the addition of N or NP fertilizer to alleviate P limitation.

Growth and physiological impairments in Fe-starved alfalfa are associated with the downregulation of Fe and S transporters along with redox imbalance

BackgroundIron (Fe) is an essential plant nutrient. Its deficiency is a major constraint in crop production systems, affecting crop yield and quality. It is therefore important to elucidate the responses and adaptive mechanisms underlying Fe-deficiency symptoms in alfalfa.Materials and methodsThe experiment was carried out on 12-day-old alfalfa plants grown in hydroponics under Fe-sufficient and Fe-deficient conditions.ResultsThe Fe-starved alfalfa showed decreased plant biomass, chlorophyll score, PSII efficiency, and photosynthesis performance index in young leaves under low Fe. Further, Fe shortage reduced the Fe, Zn, S and Ca concentration in root and shoot of alfalfa accompanied by the marked decrease of MsIRT1, MsZIP, MsSULTR1;1, MsSULTR1;2 and MsSULTR1;3 transcripts in root and shoot. It indicates that retardation caused by Fe-deficiency was also associated with the status of other elements, especially the reduced Fe and S may be coordinately attributed to the photosynthetic damages in Fe-deficient alfalfa. The ferric chelate reductase activity accompanied by the expression of MsFRO1 in roots showed no substantial changes, indicating the possible involvement of this Strategy I response in Fe-deficient alfalfa. However, the proton extrusion and expression of MsHAI1 were significantly induced following Fe-deficiency. In silico analysis further suggested their subcellular localization in the plasma membrane. Also, the interactome map suggested the partnership of MsFRO1 with plasma membrane H+-ATPase, transcription factor bHLH47, and nitrate reductase genes, while MsHAI1 partners include ferric reductase-like transmembrane component, plasma membrane ATPase, vacuolar-type H-pyrophosphatase, and general regulatory factor 2. In this study, SOD and APX enzymes showed a substantial increase in roots but unable to restore the oxidative damages in Fe-starved alfalfa.ConclusionThese findings promote further studies for the improvement of Fe-starved alfalfa or legumes through breeding or transgenic approaches.Graphic

Effects of salt stress levels on nutritional quality and microorganisms of alfalfa-influenced soil.

BackgroundGlobally, there is a large amount of salinized land. These soils have varying degrees of salt stress, causing ionic toxicity and osmotic stress on plants. However, it is not clear how different degrees of salt stress affect plant nutrients and microbial communities. Thus, a comprehensive understanding of plant major nutrients and microbial communities response to salt stress is desirable.ResultsWe analyzed the main nutrients of the salt-tolerant ZhongMu No. 3 alfalfa variety planted in a salt stress environment. In mild and moderate group, the protein content and fatty acid content of alfalfa were the highest, indicating the best nutritional value. The severe group of salt stress affected the growth and development of alfalfa, as manifested by a decrease in the nutritional quality of alfalfa. Pseudomonas and Sphingobacterium that from alfalfa stem and leaf endophytes also increased with an increase in salt stress. In contrast, Sphingomonas, Methylobacterium, and Rhizobium decrease with increasing salt stress. Methylobacterium and Rhizobium have extremely significant differences in response to salt stress, and Exiquobacterium also shows significant differences.ConclusionsSoil salinity would be an important factor beyond which alfalfa nutrient quality and microbial community structure change. This study identified key levels of salt stress that may affect the nutrient quality and microbial community structure. These findings enhance our understanding of the effects of salt stress on the nutritional quality of alfalfa and provide a reference for the sustainable use of salinized soil in the future.

Allelopathic effects of proso millet (Panicum miliaceum L) extracts on seed germination and seedling growth of alfalfa and vetch.

Allelopathic effects of proso millet (Panicum miliaceum L) extracts on seed germination and seedling growth of alfalfa and vetch.

Effects of Melatonin on Morphological Characteristics, Mineral Nutrition, Nitrogen Metabolism, and Energy Status in Alfalfa Under High-Nitrate Stress

Melatonin is an indoleamine small molecular substance that has been shown to play an important role in the growth, development, and stress response of plants. The effects of melatonin on the morphological characteristics, mineral nutrition, nitrogen metabolism, and energy status in alfalfa (Medicago sativa L.) under high-nitrate stress were studied. The alfalfa plants were treated with water (CK), 200 mmol L−1 nitrates (HN), or 200 mmol L−1 nitrates + 0.1 mmol L−1 melatonin (HN+MT), and then were sampled for measurements on days 0 and 10, respectively. The results showed that the HN treatment resulted in a decrease in the morphological characteristics (such as shoot height, leaf length, leaf width, leaf area, and biomass), phosphorus, soluble protein (SP), nitrogen-related enzymes activities and gene relative expression, adenosine triphosphate (ATP), and energy charge (EC). It also caused an increase in nitrogen, sodium, potassium, calcium, nitrate-nitrogen (-N), ammonium-nitrogen (-N), adenosine diphosphate (ADP), and adenosine monophosphate (AMP). However, these parameters were conversely changed in the HN+MT treatment. Besides, these parameters were closely related to each other, and were divided into two principal components. It reveals that melatonin plays an important role in modulating the morphology, mineral nutrition, nitrogen metabolism and energy status, thereby alleviating the adverse effects of high-nitrate stress and improving the growth of alfalfa.

Creating a Field-Wide Forage Canopy Model Using UAVs and Photogrammetry Processing

Alfalfa canopy structure reveals useful information for managing this forage crop, but manual measurements are impractical at field-scale. Photogrammetry processing with images from Unmanned Aerial Vehicles (UAVs) can create a field-wide three-dimensional model of the crop canopy. The goal of this study was to determine the appropriate flight parameters for the UAV that would enable reliable generation of canopy models at all stages of alfalfa growth. Flights were conducted over two separate fields on four different dates using three different flight parameters. This provided a total of 24 flights. The flight parameters considered were the following: 30 m altitude with 90° camera gimbal angle, 50 m altitude with 90° camera gimbal angle, and 50 m altitude with 75° camera gimbal angle. A total of 32 three-dimensional canopy models were created using photogrammetry. Images from each of the 24 flights were used to create 24 separate models and images from multiple flights were combined to create an additional eight models. The models were analyzed based on Model Ground Sampling Distance (GSD), Model Root Mean Square Error (RMSE), and camera calibration difference. Of the 32 attempted models, 30 or 94% were judged acceptable. The models were then used to estimate alfalfa yield and the best yield estimates occurred with flights at a 50 m altitude with a 75° camera gimbal angle; therefore, these flight parameters are suggested for the most consistent results.

Effect of Three Microbial Fertilizer Carriers on Water Infiltration and Evaporation, Microbial Community and Alfalfa Growth in Saline-alkaline Soil

ABSTRACT Previously, studies of microbial fertilizer were mainly focused on isolation of the functional strains; the comparison among carriers of the fertilizer was seldom studied. In the current paper, we aimed to evaluate the effect of three carriers of microbial fertilizer in saline-alkaline soil. Two Bacillus strains and three carriers, namely activated carbon, spent mushroom substrate and peat, were used to produce microbial fertilizer. Water infiltration and evaporation, microbial community and alfalfa growth were determined. The results showed that the carrier activated carbon accelerated the water infiltration. The microbial communities of the activated carbon and peat carrier treatments were similar. Conversely, the spent mushroom substrate carrier treatment contained a relatively higher abundance of Bacillus and Ilumatobacter and a relatively lower abundance of Arthrobacter, JG30-KF-CM45 and Actinomycetales when compared to the other two treatments. Furthermore, pot experiments demonstrated that the microbial fertilizer with the activated carbon carrier promoted alfalfa growth better than the other two treatments. Overall, the microbial community analysis indicated that the more abundant Bacillus did not promote plant growth in the saline-alkaline soil; instead, the role of activated carbon in saline-alkaline soil remediation was highlighted. This study provides a methodology for microbial fertilizer application in saline-alkaline soil.

Land use alters the abundance of herbivore and predatory insects on crops: the case of alfalfa

We assess the effects of changing land use and crop management on alfalfa insect abundance by comparing it in 50 alfalfa fields when they were inserted in landscapes with different proportions of arable crops and orchards. Land use in a buffer of 500 m was assessed, and alfalfa insect abundance was estimated with sticky yellow traps. The number of catches of several herbivores and predators was related to the proportion of landscape components and several field variables. Results indicated that the proportion of orchards in the buffer negatively affected the abundance of predators on alfalfa, likely because orchards treated with pesticides are a sink for predators moving in the landscape, among other possible causes. Other landscape variables such as noncrop habitats, winter cereals, and landscape diversity analysed by the Shannon index had a minor influence. Among field variables, field size influenced positively the abundance of insects on alfalfa, whereas alfalfa growth stage and age affected positively or negatively the different herbivores and predators. Of course, abundance of predators and prey was affected by the abundance of prey and predators, respectively. These findings suggest that a high proportion of intensively managed crops (orchards) in the landscape interferes with the role of alfalfa as a reservoir of predatory insects for adjacent crops and that the responses to local and landscape structures are temporal and species-specific as previously concluded for maize. Consequently, landscape and field management strategies to improve pest control must consider both types of variables as well as their changing influence when we modify them.

Effects of a compound microbial agent and plants on soil properties, enzyme activities, and bacterial composition of Pisha sandstone.

The objective of this study was to investigate the effects of the microbial agent on the improvement of Pisha sandstone soil and find out an effective measure for the control of soil erosion in the Pisha sandstone area. Pisha sandstone containing the microbial agent composed of Bacillus halotolerans P75, Sinorhizobium meliloti D10, Bacillus megaterium H3, Bacillus subtilis HB01, and organic substrate was utilized to be the soil matrix for pot experiment, and then alfalfa, ryegrass, and caragana were planted, respectively. Effects of the microbial agent plus plants on the soil properties of Pisha sandstone were evaluated, and the results showed that the microbial agent plus plants significantly increased the organic matter content, alkali hydrolyzed nitrogen content, available phosphorus content, available potassium content, invertase activity, and urease activity. Meanwhile, inoculation with the microbial agent significantly promoted the growth of alfalfa, ryegrass, and caragana and also influenced the number of soil bacteria and the relative abundance of Proteobacteria, Bacteroidetes, Actinobacteria, and others. However, the effects of the microbial agent plus different plants on the soil properties and bacterial composition of Pisha sandstone were different, while the growth of different plants showed differences, suggesting that there was a different interaction between microbes and different plants in Pisha sandstone soil. In conclusion, the microbial agent plus plants could improve Pisha sandstone soil which could provide some theoretical and experimental references for soil erosion control in the Pisha sandstone area.

Phosphate-Solubilizing Enterobacter ludwigii AFFR02 and Bacillus megaterium Mj1212 Rescues Alfalfa’s Growth under Post-Drought Stress

Drought stress is a prevalent environmental stress that adversely affects agricultural industries worldwide. In this study, bacterial isolates, AFFR02 and Mj1212, showed tolerance to polyethylene glycol-induced (PEG) drought stress (approximately 15%) and possess strong phosphate-solubilizing capacity. Moreover, we investigated the plant growth attributes, chlorophyll content, and ion uptake in alfalfa plants (Medicago sativa L) inoculated with isolates AFFR02 and Mj1212 under drought stress. We observed that drought stress drastically affects alfalfa’s growth attributes: shoot length: SL (24.88%), root length: RL (29.62%), shoot fresh weight: SFW (49.62%), root fresh weight: RFW (45.09%), stalk diameter: SD (52.84%), and chlorophyll content: CC (19.2%). However, in bacterial-inoculated alfalfa plants, the growth attributes significantly recovered were SL (12.42%), RL (21.30%), SFW (50.74%), RFW (46.42%), SD (76.72%), and CC (17.98%). In drought-stressed alfalfa plants, we observed a significant decrease in the relative water content (7.45%), whereas there was an increase in electrical conductivity (68.87%) and abscisic acid contents (164.42%). Antioxidant analysis showed a significant increase in total phenolic content (46.08%), DPPH-scavenging activity (39.66%), total flavonoid (13.68%), and superoxide dismutase (28.51%) in alfalfa treated with drought stress and bacterial isolates AFFR02 and Mj1212 simultaneously. Moreover, an increase in inductively coupled plasma (ICP) analysis of potassium (17.98%), phosphorous (11.14%), calcium (3.07%), and magnesium (6.71%) was recorded for bacteria-inoculated alfalfa plants under drought stress. In conclusion, bacterial isolates AFFR02 and Mj1212 enhance alfalfa growth under drought stress. Therefore, the isolates could be used as potential candidates in smart-climate agricultural practices in drought-stricken areas worldwide.

Root growth, distribution, and physiological characteristics of alfalfa in a poplar/alfalfa silvopastoral system compared to sole-cropping in northwest Xinjiang, China

Root growth, distribution, and physiological characteristics of alfalfa in a poplar/alfalfa silvopastoral system compared to sole-cropping in northwest Xinjiang, China

Impact of bio-fertilizers on germination and early seedling growth of Alfalfa (Medicago sativa L.) under salt stress

Impact of bio-fertilizers on germination and early seedling growth of Alfalfa (Medicago sativa L.) under salt stress

Effects of exogenous ascorbic acid on seed germination and seedling salt-tolerance of alfalfa.

Alfalfa (Medicago sativa L.) is an important legume crop for forage, agriculture, and environment in the world. Ascorbic acid (AsA) plays positive roles in plants. However, its effects on germination and salt-tolerance of alfalfa are unknown. The effects of AsA applications on seed germination and seedling salt-tolerance of alfalfa were investigated. The results revealed that 0.1 and 1 mmol L-1 of exogenous AsA increased germination, amylase, and protease, as well as seedling length, fresh weight (FW), dry weight (DW), and endogenous AsA both in the shoots and roots, except that 1 mmol L-1 AsA reduced the activities of α-amylase, β-amylase and protease on day 3. However, 10 and 100 mmol L-1 AsA inhibited these parameters and even caused serious rot. It indicates that 0.1 mmol L-1 AsA has the optimal effects, whereas 100 mmol L-1 AsA has the worst impacts. Another part of the results showed that 0.1 mmol L-1 AsA not only enhanced stem elongation, FW and DW, but also increased chlorophyll and carotenoids both under non-stress and 150 mmol L-1 NaCl stress. Furthermore, 0.1 mmol L-1 AsA mitigated the damages of membrane permeability, malondialdehyde, and excessive reactive oxygen species (ROS) and ions both in the shoots and roots under 150 mmol L-1 NaCl stress. Hence, 0.1 mmol L-1 AsA improves growth and induces salt-tolerance by inhibiting excessive ROS, down-regulating the ion toxicity and up-regulating the antioxidant system. The principal component analysis included two main components both in the shoots and roots, and it explained the results well. In summary, the optimum concentration of 0.1 mmol L-1 AsA can be implemented to improve the seed germination and seedling growth of alfalfa under salt stress.

Contents and yields of copper, iron, manganese and zinc would be affected by lucerne age and cut.

BackgroundLucerne is a perennial legume forage, which can produce multiple cuts in 1 year. Microelements play fundamental roles in the function, maintenance and adaptation to the environment for lucerne growth. However, the role of the accumulation of copper (Cu), iron (Fe), manganese (Mn) and Zinc (Zn), which vary with lucerne ages or cuts, has not been previously determined. Therefore, a hypothesis on the Cu, Fe, Mn and Zn in lucerne varying with age and cut was tested.MethodsA total of 11, 8, 5, 4 and 1 year old lucerne (Medicago sativa Longdong) were selected as the material (until 2012 year), and samples were taken as three cuts at the cutting periods (early flowering stage) in 2012. Then, the contents and yields of Cu, Fe, Mn and Zn in lucerne were measured and calculated.ResultsThe highest contents of Cu, Fe, Mn and Zn in lucerne were found in the 1 year old among the five ages, at the 3rd cut compared to the other two cuts, and in the leaf among the three organs. The highest yields of Cu, Fe, Mn and Zn were found in the older ages (11 and 8 years old), at the 3rd cut, and in the root among the three organs. The most positive correlations were found between contents, yields and biomass.ConclusionsThe hypothesis was supported by the results. And the contents and yields of lucerne Cu, Fe, Mn and Zn were affected by the age, cut and organ. Furthermore, the yields of lucerne Cu, Fe, Mn and Zn were determined by their contents and lucerne biomass.

Synergistic effect of Pseudomonas alkylphenolica PF9 and Sinorhizobium meliloti Rm41 on Moroccan alfalfa population grown under limited phosphorus availability.

This study looked at the synergistic effect of Pseudomonas alkylphenolica PF9 and Sinorhizobium meliloti Rm41 on the Moroccan alfalfa population (Oued Lmaleh) grown under symbiotic nitrogen fixation and limited phosphorus (P) availability. The experiment was conducted in a growth chamber and after two weeks of sowing, the young seedlings were inoculated with Sinorhizobium meliloti Rm41 alone or combined with a suspension of Pseudomonas alkylphenolica PF9. Then, the seedlings were submitted to limited available P (insoluble P using Ca3HPO4) versus a soluble P form (KH2PO4) at a final concentration of 250 μmol P·plant−1·week−1. After two months of P stress, the experiment was evaluated through some agro-physiological and biochemical parameters. The results indicated that the inoculation of alfalfa plants with Sinorhizobium strain alone or combined with Pseudomonas strain significantly (p < 0.001) improved the plant growth, the physiological and the biochemical traits focused in comparison to the uninoculated and P-stressed plants. For most sets of parameters, the improvement was more obvious in plants co-inoculated with both strains than in those inoculated with Sinorhizobium meliloti Rm41 alone. In fact, under limited P-availability, the co-inoculation with two strains significantly (p < 0.01) enhanced the growth of alfalfa plants evaluated by fresh and dry biomasses, plant height and leaf area. The results indicated also that the enhancement noted in plant growth was positively correlated with the shoot and root P contents. Furthermore, the incensement in plant P contents in response to bacterial inoculation improved cell membrane stability, reflected by low malonyldialdehyde (MDA) and electrolyte leakage (EL) contents, and photosynthetic-related parameters such as chlorophyll contents, the maximum quantum yield of PS II (Fv/Fm) and stomatal conductance (gs). Our findings suggest that Pseudomonas alkylphenolica PF9 can act synergistically with Sinorhizobium meliloti Rm41 in promoting alfalfa growth under low-P availability.

Long-Term Growth of Alfalfa Increased Soil Organic Matter Accumulation and Nutrient Mineralization in a Semi-Arid Environment

Land use patterns and vegetation coverage in semi-arid areas of the Loess Plateau have undergone great changes due to the implementation of the “Grain for Green” project. The introduction of legume pasture species, such as alfalfa (Medicago sativa L.) and sweet clover (Melilotus officinalis L.), is one of the most efficient methods of vegetation restoration and reconstruction in this region. However, there is a need for an effective assessment of the root system distribution and its interaction with soil after long-term introduction. An experiment involving the introduction of alfalfa and sweet clover on abandoned farmlands was initiated in 2003 to assess the long-term effects. After 17 years, root and soil samples at depths of 0–20 and 20–60 cm were collected to characterize the root biomass, root carbon (C), nitrogen (N), and phosphorus (P), soil microbial biomass carbon (MBC) and nitrogen (MBN), soil organic carbon (SOC), and soil N and P. The results showed that the root biomass density of alfalfa in the 0–20 and 20–60 cm layers (63.72 and 12.27 kg m–3, respectively) were significantly higher than for sweet clover (37.43 and 8.97 kg m–3, respectively) and under natural abandonment (38.92 and 9.73 kg m–3, respectively). The SOC, total nitrogen (TN), total phosphorus (TP), available phosphorus (AP), nitrate-nitrogen (NO3–-N), MBC and MBN in the 0–20 and 20–60 cm layers were higher after alfalfa introduction compared with sweet clover introduction and natural abandonment, although the ammonia-nitrogen (NH4+-N) concentration in the 0–20 cm layer was lower. There were significantly positive correlations between root biomass density and both soil nutrients and microbial biomass, while there was a negative correlation between the soil NH4+-N and root biomass density. These results indicate that alfalfa root growth improved soil organic matter accumulation and nutrient mineralization. The accumulation and mineralization of soil nutrients also guaranteed root and microorganism growth. Therefore, it was concluded that alfalfa introduction will promote soil nutrients immobilization and mineralization and may enable sustainable land use in the semi-arid region of the Loess Plateau, China.

Graphene ameliorates saline-alkaline stress-induced damage and improves growth and tolerance in alfalfa (Medicago sativa L.)

Nanoscience is leading to the production of nanotech applications to enhance growth and environmental stress tolerance of plants. However, there are few studies on the morphological and physiological regulative mechanism of coupling effects between graphene (Nano-C) and pH in alfalfa, especially both in promotion and phytotoxicity effect by Nano-C under abiotic stress. The coupling effects of Nano-C and pH on plant growth, photosynthetic parameters and enzymes of the antioxidant defence system on leaves and roots were investigated at graphene concentrations of 0, 5, 10, and 20 g kg−1 in pots trials. The result showed a significantly promoted the plant growth at treatment of 5 g kg−1 Nano-C, whereas 10-20 g kg−1 Nano-C harmed the physiological and morphological characterizations. Under salt and alkali stresses, the dry weight, fresh weight, seedling length and antioxidant enzymes activities were increased significantly at 5 g kg−1 Nano-C treatment. These findings revealed that 5 g kg−1 Nano-C enhanced alfalfa tolerance by modulating various morphological and physiological characteristics. Meanwhile, through models analyses, the equivalent coupling effects of Nano-C and pH were located at rectangular area defined by 5.43–7.80 Nano-C combining 8.59–8.96 pH value, and the final optimal application of Nano-C was at 6.57 g kg−1 when high exposure dose of Nano-C indeed resulted in phytotoxicity to the plant. Results of the model analyses also showed significant synergistic effects on the photosynthesis and antioxidant system. Overall, our findings suggested fundamental insights into carbon nanomaterials-mediated physiological adaptation in plants.