Whole-genome sequencing of allotetraploid bermudagrass reveals the origin of Cynodon and candidate genes for salt tolerance.

Bermudagrass (Cynodon dactylon) is a globally distributed, extensively used warm-season turf and forage grass with high tolerance to salinity and drought stress in alkaline environments. However, the origin of the species and genetic mechanisms for salinity tolerance in the species are basically unknown. Accordingly, we set out to study evolution divergence events in the Cynodon genome and to identify genes for salinity tolerance. We developed a 604.0 Mb chromosome-level polyploid genome sequence for bermudagrass 'A12359' (n = 18). The C. dactylon genome comprises 2 complete sets of homoeologous chromosomes, each with approximately 30 000 genes, and most genes are conserved as syntenic pairs. Phylogenetic study showed that the initial Cynodon species diverged from Oropetium thomaeum approximately 19.7-25.4 million years ago (Mya), the A and B subgenomes of C. dactylon diverged approximately 6.3-9.1 Mya, and the bermudagrass polyploidization event occurred 1.5 Mya on the African continent. Moreover, we identified 82 candidate genes associated with seven agronomic traits using a genome-wide association study, and three single-nucleotide polymorphisms were strongly associated with three salt resistance genes: RAP2-2, CNG channels, and F14D7.1. These genes may be associated with enhanced bermudagrass salt tolerance. These bermudagrass genomic resources, when integrated, may provide fundamental insights into evolution of diploid and tetraploid genomes and enhance the efficacy of comparative genomics in studying salt tolerance in Cynodon.

H2O2 promotes trimming-induced tillering by regulating energy supply and redox status in bermudagrass.

Tillering/branching pattern plays a significant role in determining the structure and diversity of grass, and trimming has been found to induce tillering in turfgrass. Recently, it has been reported that hydrogen peroxide (H2O2) regulates axillary bud development. However, the role of H2O2 in trimming-induced tillering in bermudagrass, a kind of turfgrass, remains unclear. Our study unveils the significant impact of trimming on promoting the sprouting and growth of tiller buds in stolon nodes, along with an increase in the number of tillers in the main stem. This effect is accompanied by spatial-temporal changes in cytokinin and sucrose content, as well as relevant gene expression in axillary buds. In addition, the partial trimming of new-born tillers results in an increase in sucrose and starch reserves in their leaves, which can be attributed to the enhanced photosynthesis capacity. Importantly, trimming promotes a rapid H2O2 burst in the leaves of new-born tillers and axillary stolon buds. Furthermore, exogenous application of H2O2 significantly increases the number of tillers after trimming by affecting the expression of cytokinin-related genes, bolstering photosynthesis potential, energy reserves and antioxidant enzyme activity. Taken together, these results indicate that both endogenous production and exogenous addition of H2O2 enhance the inductive effects of trimming on the tillering process in bermudagrass, thus helping boost energy supply and maintain the redox state in newly formed tillers.

Identification and evolution analysis of YUCCA genes of Medicago sativa and Medicago truncatula and their expression profiles under abiotic stress.

The YUCCAs (YUC) are functionally identified flavin-containing monooxidases (FMOs) in plants that act as an important rate-limiting enzyme functioning in the auxin synthesis IPA (indole-3-pyruvic acid) pathway. In this study, 12 MsYUCs and 15 MtYUCs containing characteristic conserved motifs were identified in M. sativa (Medicago sativa L.) and M. truncatula (Medicago truncatula Gaertn.), respectively. Phylogenetic analysis revealed that YUC proteins underwent an evolutionary divergence. Both tandem and segmental duplication events were presented in MsYUC and MtYUC genes. Comparative syntenic maps of M. sativa with M. truncatula, Arabidopsis (Arabidopsis thaliana), or rice (Oryza sativa L.) were constructed to illustrate the evolution relationship of the YUC gene family. A large number of cis-acting elements related to stress response and hormone regulation were revealed in the promoter sequences of MsYUCs. Expression analysis showed that MsYUCs had a tissue-specific, genotype-differential expression and a differential abiotic stress response pattern based on transcriptome data analysis of M. sativa online. In addition, RT-qPCR confirmed that salt stress significantly induced the expression of MsYUC1/MsYUC10 but significantly inhibited MsYUC2/MsYUC3 expression and the expression of MsYUC10/MsYUC11/MsYUC12 was significantly induced by cold treatment. These results could provide valuable information for functional analysis of YUC genes via gene engineering of the auxin synthetic IPA pathway in Medicago.

CdWRKY2 transcription factor modulates salt oversensitivity in bermudagrass [Cynodon dactylon (L.) Pers.].

Common bermudagrass [Cynodon dactylon (L.) Pers.] has higher utilization potential on saline soil due to its high yield potential and excellent stress tolerance. However, key functional genes have not been well studied partly due to its hard transformation. Here, bermudagrass "Wrangler" successfully overexpressing CdWRKY2 exhibited significantly enhanced salt and ABA sensitivity with severe inhibition of shoot and root growth compared to the transgenic negative line. The reduced auxin accumulation and higher ABA sensitivity of the lateral roots (LR) under salt stress were observed in CdWRKY2 overexpression Arabidopsis lines. IAA application could rescue or partially rescue the salt hypersensitivity of root growth inhibition in CdWRKY2-overexpressing Arabidopsis and bermudagrass, respectively. Subsequent experiments in Arabidopsis indicated that CdWRKY2 could directly bind to the promoter region of AtWRKY46 and downregulated its expression to further upregulate the expression of ABA and auxin pathway-related genes. Moreover, CdWRKY2 overexpression in mapk3 background Arabidopsis could partly rescue the salt-inhibited LR growth caused by CdWRKY2 overexpression. These results indicated that CdWRKY2 could negatively regulate LR growth under salt stress via the regulation of ABA signaling and auxin homeostasis, which partly rely on AtMAPK3 function. CdWRKY2 and its homologue genes could also be useful targets for genetic engineering of salinity-tolerance plants.

Diversity analysis of agronomic and nutritional traits of hybrid offspring of forage bermudagrass.

Because of its excellent stress resistance and forage quality, the forage bermudagrass hybrid population had attracted the attention of scientific researchers in recent years. Studying its diversity could promote the breeding of desirable varieties. The variability in agronomic traits including fresh weight, dry weight, ash content, crude protein content, crude fat, phosphorus content, and relative feed value for 56 bermudagrass was investigated using Wrangler as an experimental reference. Grey correlation analysis and cluster analysis were employed to screen bermudagrass with high yield and superior quality. WCF-34 had the highest 2-year fresh weight (109,773.3 kg/ha), WCF-37 had the highest 2-year dry weight (31,951.6 kg/ha), WCF-24 had the lowest Ash content (7.46%), WCF-26 had the highest crude protein content (16.27%), WCF-27 had the highest curde fat content (3.58%), WCF-13 had the highest P content (0.45%), and WCF-42 had the highest relative feed value (95.32). Combining the results of grey relational analysis and cluster analysis, WCF-42, WCF-34, WCF-38, WCF-37, and WCF-40 were selected as high-quality bermudagrass. Through comprehensive analysis of the agronomic characters of bermudagrass, five bermudagrass were selected, the outcomes of this study would provide a theoretical basis for the breeding and genetic enhancement of bermudagrass.

Involvement of cell cycle and ion transferring in the salt stress responses of alfalfa varieties at different development stages.

BACKGROUND: Alfalfa (Medicago sativa) is the worldwide major feed crop for livestock. However, forage quality and productivity are reduced by salt stress, which is a common issue in alfalfa-growing regions. The relative salt tolerance is changed during plant life cycle. This research aimed to investigate the relative salt tolerance and the underlying mechanisms of two alfalfa varieties at different developmental stages. RESULTS: Two alfalfa varieties, "Zhongmu No.1 (ZM1)" and "D4V", with varying salt tolerance, were subjected to salt stress (0, 100, 150 mM NaCl). When the germinated seeds were exposed to salt stress, D4V exhibited enhanced primary root growth compared to ZM1 due to the maintenance of meristem size, sustained or increased expression of cell cycle-related genes, greater activity of antioxidant enzymes and higher level of IAA. These findings indicated that D4V was more tolerant than ZM1 at early developmental stage. However, when young seedlings were exposed to salt stress, ZM1 displayed a lighter wilted phenotype and leaf cell death, higher biomass and nutritional quality, lower relative electrolytic leakage (EL) and malondialdehyde (MDA) concentration. In addition, ZM1 obtained a greater antioxidant capacity in leaves, indicated by less accumulation of hydrogen peroxide (H2O2) and higher activity of antioxidant enzymes. Further ionic tissue-distribution analysis identified that ZM1 accumulated less Na+ and more K+ in leaves and stems, resulting in lower Na+/K+ ratio, because of possessing higher expression of ion transporters and sensitivity of stomata closure. Therefore, the relative salt tolerance of ZM1 and D4V was reversed at young seedling stages, with the young seedlings of the former being more salt-tolerant. CONCLUSION: Our data revealed the changes of relative order of salt tolerance between alfalfa varieties as they develop. Meristem activity in primary root tips and ion transferring at young seedling stages were underlying mechanisms that resulted in differences in salt tolerance at different developmental stages.

Aspergillus aculeatus enhances nutrient uptake and forage quality in bermudagrass by increasing phosphorus and potassium availability.

Introduction: Potassium and phosphorus are essential macronutrients for plant growth and development. However, most P and K exist in insoluble forms, which are difficult for plants to directly absorb and utilize, thereby resulting in growth retardation of plants under P or K deficiency stress. The Aspergillus aculeatus fungus has growth-promoting characteristics and the ability to dissolve P and K. Methods: Here, to investigate the physiological effects of A. aculeatus on bermudagrass under P or K deficiency, A. aculeatus and bermudagrass were used as experimental materials. Results and discussion: The results showed that A. aculeatus could promote tolerance to P or K deficiency stress in bermudagrass, decrease the rate of leaf death, and increase the contents of crude fat as well as crude protein. In addition, A. aculeatus significantly enhanced the chlorophyll a+b and carotenoid contents. Moreover, under P or K deficiency stress, bermudagrass inoculated with A. aculeatus showed higher N, P, and K contents than non-inoculated plants. Furthermore, exogenous A. aculeatus markedly decreased the H2O2 level and CAT and POD activities. Based on our results, A. aculeatus could effectively improve the forage quality of bermudagrass and alleviate the negative effects of P or K deficiency stress, thereby playing a positive economic role in the forage industry.

Changes in soil properties and the phoD-harboring bacteria of the alfalfa field in response to phosphite treatment.

Phosphite, a reduced form of orthophosphate, is characterized by high solubility, and transportation efficiency and can be used as potential phosphorus fertilizer, plant biostimulant and supplemental fertilizer in agriculture. However, the effects of phosphite fertilizer on soil properties and microorganisms are poorly understood. This study evaluated the effects of phosphate and phosphite fertilizers on the different forms of phosphorus, alkaline phosphatase (ALP) activity, and phoD-harboring bacterial community in the alfalfa (Medicago sativa) field. The study used four concentrations (30, 60, 90, and 120 mg P2O5 kg-1 soil) of phosphate (KH2PO4) and phosphite (KH2PO3) fertilizers for the alfalfa field treatment. The results showed that both phosphite and phosphate fertilizers increased the total phosphorus (TP) and available phosphorus (AP) contents in the soil. The phosphorus content of the phosphite-treated soil was lower than that of the phosphate-treated one. TP, inorganic phosphate (Pi), and AP negatively regulated ALP activity, which decreased with increasing phosphate and phosphite fertilizers concentrations. Furthermore, high-throughput sequencing analysis identified 6 phyla and 29 families, which were classified from the altered operational taxonomic units (OTUs) of the soil samples. The redundancy analysis (RDA) revealed that pH, TP, AP and Pi were significantly related to the phoD-harboring bacterial community constructure. The different fertilizer treatments altered the key families, contributing to soil ALP activities. Frankiaceae, Sphingomonadaceae, and Rhizobiaceae positively correlated with ALP activity in phosphite-treated soil. Moreover, the structural equation model (SEM) revealed that ALP activity was affected by the phoD-harboring bacterial community through altered organic phosphorus (Po), AP, total nitrogen (TN), soil organic carbon (SOC), and pH levels under phosphate fertilizer treatment. However, the effect was achieved through positive regulation of pH and AP under phosphite fertilizer. Thus, the changes in soil properties and phoD-harboring bacteria in response to phosphate and phosphite treatments differed in the alfalfa field. This study is the first to report the effects of phosphite on the soil properties of an alfalfa field and provides a strong basis for phosphite utilization in the future. Highlights: - Phosphite and phosphate increase the total phosphorus and available phosphorus.- The pH was the dominant factor influencing the phoD-harboring bacterial community under phosphite fertilizer.- The response of soil properties and phoD-harboring bacterial community to phosphate and phosphite fertilizers differed in the alfalfa field.

The extended day length promotes earlier flowering of bermudagrass.

Day length is a very critical environmental factor affecting plant growth and development. The extension of light application time has been shown to promote flowering in the long-day plant and to shorten breeding time in some crops. However, previous research on the regulation of bermudagrass flowering by light application time is scarce. Therefore, this study investigated the effect of day length on the growth and flowering of bermudagrass by prolonging the light application time in a controlled greenhouse. Three different light application times were set up in the experiment: 22/2 h (22 hours light/2 hours dark), 18/6 h (18 hours light/6 hours dark), 14/10 h (14 hours light/10 hours dark). Results showed that extending the light application time not only promoted the growth of bermudagrass (plant height, fresh weight, dry weight) but also its nutrient uptake (nitrogen (N) and phosphorous (P) content). In addition, daily light integrals were different when flowering under different light application times. Most importantly, under the 22/2 h condition, flowering time was successfully reduced to 44 days for common bermudagrass (Cynodon dactylon [L.] pers) genotype A12359 and 36 days for African bermudagrass (Cynodon transvaalensis Burtt-Davy) genotype ABD11. This study demonstrated a successful method of bermudagrass flowering earlier than usual time by manipulating light application time which may provide useful insights for bermudagrass breeding.

Mitigation of salt stress on low temperature in bermudagrass: resistance and forage quality.

Climate change causes plants encountering several abiotic stresses simultaneously. Responses of plants to a single stress has been comprehensively studied, but it is hard to speculated infer the effects of stress combination based on these researches. Here, the response mechanism of bermudagrass to low temperature and salt treatment was investigated in this study. The results showed that low temperature (LT) treatment decreased the relative growth rate, chlorophyll fluorescence transient curve, biomass, and crude fat content of bermudagrass, whereas low temperature + salt (LT+S) treatment greatly undermined these declines. Furthermore, at 6 h and 17 d, the expression levels of glyoxalase I (GLYI), Cu-Zn/superoxide dismutase (Cu-Zn/SOD), peroxidase 2 (POD2), and oxidative enzyme 1(CAT1) in roots were considerably higher in the low temperature + salt treatment than in the low temperature treatment. Low temperature stress is more detrimental to bermudagrass, but mild salt addition can mitigate the damage by enhancing photosynthesis and improving the expression of antioxidant system genes (Cu-Zn/SOD, POD2 and CAT1) and glyoxalase system GLYI gene in roots. This study summarized the probable interaction mechanism of low temperature and salt stress on bermudagrass, which can provide beneficial reference for the growth of fodder in cold regions.

Transcriptome analysis of perennial ryegrass reveals the regulatory role of Aspergillus aculeatus under salt stress.

Perennial ryegrass (Lolium perenne) is an important turf grass and forage grass with moderately tolerant to salinity stress. Aspergillus aculeatus has been documented to involved in salt stress response of perennial ryegrass, while the A. aculeatus-mediated molecular mechanisms are unclear. Therefore, to investigate the molecular mechanisms underlying A. aculeatus-mediated salt tolerance, the comprehensive transcriptome analysis of the perennial ryegrass roots was performed. Twelve cDNA libraries from roots were constructed after 12 h of plant-fungus cocultivation under 300 mM salt stress concentrations. A total of 21,915 differentially expressed genes (DEGs) were identified through pairwise comparisons. Enrichment analysis revealed that potentially important A. aculeatus-induced salt responsive genes belonging to specific categories, such as hormonal metabolism (auxin and salicylic acid metabolism related genes), secondary metabolism (flavonoid's metabolism related genes) and transcription factors (MYB, HSF and AP2/EREBP family). In addition, weighted gene co-expression network analysis (WGCNA) showed that blue and black modules were significantly positively correlated with the peroxidase activity and proline content, then the hub genes within these two modules were further identified. Taken together, we found the categories of A. aculeatus-induced salt responsive genes, revealing underlying fungus-induced molecular mechanisms of salt stress response in perennial ryegrass roots. Besides, fungus-induced salt-tolerant hub genes represent a foundation for further exploring the molecular mechanisms.

Different photosynthetic adaptation of Zoysia spp. under shading: shade avoidance and shade tolerance response.

Reduction of ambient solar radiation is an important external challenge for plants, which affects photosynthesis and morphogenesis in agroforestry or gardening. As bottomed sessile organisms, turfgrasses have a set of sophisticated photosynthetic strategies to survive and deal with this abiotic stress. Zoysiagrass (Zoysia spp. Willd.) is an important warm-season, perennial turfgrass that tolerates adversity, wear, trampling and extensive management. However, whole photosynthetic characteristics reaction of the zoysiagrass to shade stress have not been described because our knowledge in this area is very limited. In this study, 85% shade treatment was applied to nineteen zoysiagrass genotypes, and morphological observations and extensive determinations on plant heights, photosynthetic pigments, fluorescence dynamic curves among other parameters were made. The results showed that vegetal and photosynthetic responses of zoysiagrass were affected by shade treatment to varying degrees. Further analysis based on the principal component, subordinate function analysis and clustering methodology revealed that different shading response strategies were adopted by zoysia under shade surroundings. They were divided into four categories. The strongest shade-avoidant response strategy was adopted by 'ZG48' and 'WZG59', which had the largest comprehensive evaluation (D) values, and the stabilized shade-tolerant response was taken on by 'ZG-3' and 'ZG64', which had the lowest D values. Other varieties applied a medium strategy but with a certain tendency. These findings provide new insights into different shading response tactics of turfgrass: shade avoidance and shade tolerance response, which could be selected for further elucidation of the molecular mechanism of plant adaptation to shade environments.

Photosystem II photochemical adjustment of tall fescue against heat stress after melatonin priming.

High temperature is the key factor restricting the survival of tall fescue. Extreme summer hot events arise from global warming further increases this risk. As a candidate chemical priming agent previously reported, melatonin offers innovative solution to improve heat resistance of plants. However, the mechanistic insight remains ill-defined, especially in PSII photochemical reactions. In this study, we investigated the effect of melatonin priming on photosynthetic electron transport of PS II against heat stress in tall fescue. Results showed that melatonin weakened the electron transfer efficiency of PS II per light reaction center (RC) at donor-side and receptor-side, while increased the number of RC per unit cross-sectional area. The quenching analysis further revealed that the proportion of photochemical quenching, Y(II), increased by melatonin. Considering the enriched chl a and nonevent oxidative damage, we argued that inefficient but more abundant RC introduced by melatonin protected the PSII from oxidative damage under heat stress. Notably, these effects were dependent on melatonin concentration but not temperature, an optimal application concentration (50 µmol/L) was uncovered. Besides, melatonin decreased NPQ and encouraged reverse reaction of the xanthophyll cycle. We proposed that melatonin prevents the production of excessive excitation energy. In brief, melatonin plays a distinctive role in regulating photoelectric conversion of PSII of tall fescue under heat stress, increased its survival rate after heat shock.

Comparative genomics reveals the molecular mechanism of salt adaptation for zoysiagrasses.

BACKGROUND: Zoysiagrass (Zoysia spp.) is a warm-season turfgrass. It is widely used as turfgrasses throughout the world, offers good turf qualities, including salt tolerance, resistance to drought and heat. However, the underlying genetic mechanism of zoysiagrass responsive to salt stress remains largely unexplored. RESULTS: In present study, we performed a whole-genome comparative analysis for ten plant genomes. Evolutionary analysis revealed that Chloridoideae diverged from Panicoideae approximately 33.7 million years ago (Mya), and the phylogenetic relationship among three zoysiagrasses species suggested that Zoysia matrella may represent an interspecific hybrid between Zoysia japonica and Zoysia pacifica. Genomic synteny indicated that Zoysia underwent a genus-specific whole-genome duplication (WGD) event approximately 20.8 Mya. The expression bais of homologous genes between the two subgenomes suggested that the B subgenome of Z. japonica contributes to salt tolerance. In additon, comparative genomic analyses revealed that the salt adaptation of Zoysia is likely attributable to the expanded cytochrome P450 and ABA biosynthetic gene families. Furthermore, we further found that many duplicated genes from the extra WGD event exhibited distinct functional divergence in response to salt stress using transcriptomic analysis, suggesting that this WGD event contributed to strong resistance to salt stress. CONCLUSIONS: Here, our results revealed that expanded cytochrome P450 and ABA biosynthetic gene families, and many of those duplicated genes from recent zoysia-specific WGD event contributed to salt adaptation of zoysiagrass, which provided insight into the genetic underpinning of salt adaptation and valuable information for further studies on salt stress-related traits in Zoysia.

Moderately Reducing Nitrogen Application Ameliorates Salt-Induced Growth and Physiological Damage on Forage Bermudagrass.

Nitrogen (N) application is one of the most effective methods to alleviate salt-induced damage on plants. Forage bermudagrass has higher utilization potential on saline soil, but whether its N requirement changed under high salt stress has not been studied. Through examining plant growth-related traits, salt-stress-responsive physiological traits, photosynthesis, N metabolism, and forage quality supplied with different N concentrations under high salt stress (200 mM NaCl), we noticed that the optimum N requirement of forage bermudagrass reduced. When supplied with 10 mM N under higher salt stress, plants had a similar biomass, turf color, and chlorophyll content with plants supplied with 15 mM N, accompanied by a lower firing rate and Na+ content of leaves. The N content, crude protein, crude fat content, the expression of AMTs (ammonium transporters), NR (nitrate reductase), GS (glutamine synthetase), and GOGAT (glutamate synthetase), the chlorophyll fluorescence curve, and parameters of leaves (e.g., PIABS; PICS; ABS/RC; TRo/RC; ETo/RC) all peaked under 10 mM N under high salt stress instead of 15 mM N. Through exploring the proper N application under higher salt stress and its alleviation mechanisms, our results indicated that moderate reduction in N application under high salt level had a maximum promotion effect on the salt tolerance of forage bermudagrass without growth or forage quality inhibition. These response mechanisms obtained can provide a useful reference for N application in moderation rather than in excess on forage bermudagrass, especially in higher salinity areas.

Genetic manipulation of bermudagrass photosynthetic biosynthesis using Agrobacterium-mediated transformation.

Bermudagrass is one of the most extensively used warm-season grasses. It is widely used in landscaping, stadium construction and soil remediation due to its excellent regeneration, trampling and stress tolerances. However, studies on its regulatory mechanism and variety improvement by genetic engineering are still at a standstill, owing to its genetic variability and intrinsic limits linked with some resistance to Agrobacterium infection. In this study, we established a higher efficient Agrobacterium-mediated transformation via screening for vital embryogenic callus and improving infection efficiency. The superior callus was light yellow, hard granular and compact, determined with a differentiation rate of more than 95%. The optimized infestation courses by gentle shaking, vacuuming and sonicating were used. The infested calluses were co-cultured for 3 days, followed by desiccation treatments for 1 day to get higher infection efficiency. Then the CdHEMA1 gene, essential for chlorophyll biosynthesis, was cloned and transferred into bermudagrass to validate the aforementioned optimization procedures integrally. Molecular-level analyses indicated that the CdHEMA1 gene had successfully integrated and was greatly increased in transgenic seedlings. Results of the photosynthetic capacity assessment showed that CdHEMA1 overexpression may considerably enhance the contents of photosynthetic pigments, OJIP curve and reaction center density (RC/CSo) to absorb (ABS/CSo, ABS/CSM) and capture (TRo/CSo) more light energy, hence improve the performance indices PIABS and PICS compared to the wild type. The successful completion of this project would provide a solid platform for further gene function study and molecular breeding of bermudagrass.

Physiological integration between Bermudagrass ramets improves overall salt resistance under heterogeneous salt stress.

Connected ramets of colonal plants often suffer from different environmental conditions such as light, nutrient, and stress. Colonal Bermudagrass (Cynodon dactylon [L.] Pers.) can form interconnected ramets and this connection facilitates the tolerance to abiotic stress, which is a kind of physiological integration. However, how bermudagrass responds to heterogeneously distributed salt stress needs to be further elucidated. Here, we demonstrated that severance of stolons aggravated the damage of salt-stressed ramets, displaying higher relative electrolytic leakage (EL), lower content of chlorophyll, higher accumulation of Na+ , and serious oxidative damages. This finding implied the positive effects of the physiological integration of bermudagrass on salt tolerance. The unstressed ramets connected with the stressed one were mildly injured, implying the supporting and sacrifice function of the unstressed ramets. Physiological integration did not mediate the translocation of Na+ among ramets, but induced a higher expression of salt overly sensitive (SOS) genes in the stressed ramets, consequently reducing the accumulation of Na+ in leaves and roots. In addition, physiological integration upregulated the genes expression and enzymes activity of catalase (CAT) and peroxidase (POD) in both stressed and unstressed ramets. This granted a stronger antioxidant ability of the whole clonal plants under salt stress. Enhanced Na+ transfer and increased reactive oxygen species (ROS) scavenging are mechanisms that likely contribute to the physiological integration leading to the salt tolerance of bermudagrass.

Aspergillus aculeatus enhances potassium uptake and photosynthetic characteristics in perennial ryegrass by increasing potassium availability.

AIM: Potassium (K) is a key determinant for plant development and productivity. However, more than 90% of K in the soil exists in an insoluble form. K-solubilizing microbes play an important role in the transformation of insoluble K. Thus, the objective of this study was to evaluate K-dissolving ability of Aspergillus aculeatus (F) and growth-promoting properties in perennial ryegrass. METHODS AND RESULTS: Perennial ryegrass inoculated with A. aculeatus exhibited enhanced soluble K accompanied with higher growth rate and turf quality, compared with the noninoculated regimen. In addition, A. aculeatus also played a primary role in increasing chlorophyll content and photosynthetic capacity of the plant exposed to LK+F (K-feldspar plus A. aculeatus) treatment, compared with the CK (control, no K-feldspar and A. aculeatus), F (only A. aculeatus) and LK (only K-feldspar) groups. Furthermore, the antioxidase activities (CAT and POD) were significantly increased while the oxidative damage (EL and MDA) was dramatically decreased in the LK+F group compared to the LK (K-feldspar) group. Finally, in perennial ryegrass leaves, the genes expression levels of HAK8, HAK12 and HKT18 were obviously elevated in the LK+F group, compared to the CK, F and LK groups. CONCLUSION: We concluded that A. aculeatus could solubilize K from bound form and be considered as K-solubilizing biofertilizer through supplementing K in soil. SIGNIFICANCE AND IMPACT OF THE STUDY: Aspergillusaculeatus has the potential to be used as a biofertilizer in sustainable agriculture.

Comprehensive analysis of grazing intensity impacts alpine grasslands across the Qinghai-Tibetan Plateau: A meta-analysis.

Livestock grazing is a dominant practice in alpine grasslands and plays a crucial role in the ecosystem service of the Qinghai-Tibetan Plateau. The effects of grazing on alpine grasslands highly depends on grazing intensity. Up to now, we still lack comprehensive understanding of the general responses of alpine grasslands to different grazing intensities over broad geographic scales across the Qinghai-Tibetan Plateau. Here, we conducted a meta-analysis to explore the responses of plant characteristics and soil properties to grazing intensity in alpine grasslands of the Qinghai-Tibetan Plateau based on 52 peer-reviewed literatures. The results showed that grazing did not change the belowground biomass, while significantly increased the ratio of root to shoot (P< 0.05). Light grazing exhibited no significant effects on the plant richness, Shannon-Wiener diversity, soil water content, soil bulk density, nutrients, microbial biomass carbon, and microbial biomass nitrogen (P > 0.05). Moderate grazing significantly increased the plant richness and Shannon-Wiener diversity, while significantly decreased the soil organic carbon and total nitrogen (P< 0.05). Heavy grazing significantly decreased the plant richness, Shannon-Wiener diversity, water content, soil organic carbon, total nitrogen, microbial biomass carbon, and microbial biomass nitrogen, and significantly increased the soil bulk density (P< 0.05). These findings suggest that overgrazing is closely associated with grassland degradation, and moderate grazing is a sustainable practice to provide animal production and simultaneously maintain ecological functions for alpine grasslands on the Qinghai-Tibetan Plateau.