Warm-season Turfgrass Research Articles

Transcriptome Analysis Revealed a Positive Role of Ethephon on Chlorophyll Metabolism of Zoysia japonica under Cold Stress.

Zoysia japonica is a warm-season turfgrass with a good tolerance and minimal maintenance requirements. However, its use in Northern China is limited due to massive chlorophyll loss in early fall, which is the main factor affecting its distribution and utilization. Although ethephon treatment at specific concentrations has reportedly improved stress tolerance and extended the green period in turfgrass, the potential mechanisms underlying this effect are not clear. In this study, we evaluated and analyzed chlorophyll changes in the physiology and transcriptome of Z. japonica plants in response to cold stress (4 °C) with and without ethephon pretreatment. Based on the transcriptome and chlorophyll content analysis, ethephon pretreatment increased the leaf chlorophyll content under cold stress by affecting two processes: the stimulation of chlorophyll synthesis by upregulating ZjMgCH2 and ZjMgCH3 expression; and the suppression of chlorophyll degradation by downregulating ZjPAO, ZjRCCR, and ZjSGR expression. Furthermore, ethephon pretreatment increased the ratio of chlorophyll a to chlorophyll b in the leaves under cold stress, most likely by suppressing the conversion of chlorophyll a to chlorophyll b due to decreased chlorophyll b synthesis via downregulation of ZjCAO. Additionally, the inhibition of chlorophyll b synthesis may result in energy redistribution between photosystem II and photosystem I.

A Survey of Enhanced Cold Tolerance and Low-Temperature-Induced Anthocyanin Accumulation in a Novel Zoysia japonica Biotype.

Zoysia japonica is a warm-season turfgrass that is extensively used in landscaping, sports fields, and golf courses worldwide. Uncovering the low-temperature response mechanism of Z. japonica can help to accelerate the development of new cold-tolerant cultivars, which could be used to prolong the ornamental and usage duration of turf. A novel Z. japonica biotype, YueNong-9 (YN-9), was collected from northeastern China for this study. Phenotypic measurements, cold-tolerance investigation, and whole-transcriptome surveys were performed on YN-9 and LanYin-3 (LY-3), the most popular Z. japonica cultivar in Southern China. The results indicated the following: YN-9 has longer second and third leaves than LY-3; when exposed to the natural low temperature during winter in Guangzhou, YN-9 accumulated 4.74 times more anthocyanin than LY-3; after cold acclimation and freezing treatment, 83.25 ± 9.55% of YN-9 survived while all LY-3 leaves died, and the dark green color index (DGCI) value of YN-9 was 1.78 times that of LY-3; in YN-9, there was a unique up-regulation of Phenylalanine ammonia-lyase (PAL), Homeobox-leucine Zipper IV (HD-ZIP), and ATP-Binding Cassette transporter B8 (ABCB8) expressions, as well as a unique down-regulation of zinc-regulated transporters and iron-regulated transporter-like proteins (ZIPs) expression, which may promote anthocyanin biosynthesis, transport, and accumulation. In conclusion, YN-9 exhibited enhanced cold tolerance and is thus an excellent candidate for breeding cold-tolerant Z. japonica variety, and its unique low-temperature-induced anthocyanin accumulation and gene responses provide ideas and candidate genes for the study of low-temperature tolerance mechanisms and genetic engineering breeding.

Establishing three warm-season turfgrasses with tailored water: II. Root development, nitrate accumulation in plant tissue and soil, and relationship with leaching.

Greenhouse experiments were conducted in 2015 and 2017 to assess the feasibility of establishing three warm-season grasses-buffalograss [Buchloe dactyloides (Natt.) Eng.] 'SWI 2000', inland saltgrass (Distichlis spicata L.), and bermudagrass (Cynodon dactylon L.) 'Princess77'-with tailored water (tertiary treated effluent with 15mg L-1 of NO3 -N) and to examine the impact on nitrate accumulation in soils and plant tissue and on root development. Grasses were established from seed in a loamy sand and irrigated with either tailored or potable water plus granular Ca(NO3 )2 fertilizer. Leachate collected at 10- and 30-cm depths was analyzed for NO3 -N and electrical conductivity. Root samples were collected to measure root length density (RLD) and root surface area (RSA). Weekly clippings were collected to determine total clipping yield and measure N content. Generally, there was no difference in establishment, RLD, or RSA between the two irrigation treatments. Highest RLD values were reported for bermudagrass, followed by buffalograss and inland saltgrass. Correlation analyses suggest that nitrate levels in leachate were lower in faster-growing grasses and in grasses with more extensive root systems, compared with slower-growing grasses with less roots, regardless of fertilization treatment. Total N in clippings was highest in inland saltgrass and lower in buffalograss and bermudagrass, indicating that N was limiting for faster-growing grasses. More research is needed to determine optimal N rates for establishing grasses that both optimize growth and minimize nitrate leaching.

Cultivar blends: A strategy for creating more resilient warm season turfgrass lawns

Cultivar blends: A strategy for creating more resilient warm season turfgrass lawns

Fungicide Sensitivity of Gaeumannomyces Species Associated with Take-All Root Rot of St. Augustinegrass in Texas

Gaeumannomyces species are soilborne fungi associated with take-all root rot (TARR) of St. Augustinegrass ( Stenotaphrum secundatum) and other warm-season turfgrasses. Penetrant fungicides, such as demethylation inhibitors (DMIs) and quinone outside inhibitors (QoIs), have been labeled and used for TARR management. Reports of turfgrass pathogens resistant to these fungicide groups are increasing. However, there is no fungicide sensitivity information for Gaeumannomyces species in turfgrass. In this study, sensitivities to QoI fungicide azoxystrobin and DMI fungicide tebuconazole were determined for Gaeumannomyces species ( G. graminicola, G. arxii, and G. floridanus) isolated from St. Augustinegrass in Texas. A discriminatory concentration of 0.1 µg a.i. ml−1 was deemed suitable for rapid screening and accurate prediction of the effective concentration of a fungicide that inhibits fungal growth by 50% (EC50) for tebuconazole and azoxystrobin. The EC50 values of Gaeumannomyces species ranged from 0.021 to 0.1 µg ml−1 for tebuconazole (with the exception of one isolate having an EC50 value = 0.296 µg ml−1) and from 0.014 to 0.399 µg ml−1 for azoxystrobin. To our knowledge, this is the first study to investigate fungicide sensitivities of Gaeumannomyces species associated with TARR in St. Augustinegrass to fungicides in the DMI and QoI chemical groups. Most isolates tested in this study can be considered sensitive to tebuconazole and azoxystrobin. This indicates that the fungicide resistance of Gaeumannomyces species from St. Augustinegrass in Texas lawns might not be prevalent at the moment. Future field validation needs to confirm in vitro sensitivities and field efficacy of tebuconazole and azoxystrobin.

Heritability estimates for seed yield and its components in <i>Cynodon dactylon</i> var. <i>dactylon</i> (L.) Pers.

Bermudagrass [<italic>Cynodon dactylon</italic> var. <italic>dactylon</italic> (L.) Pers.] is a major warm-season turf and forage grass in the world. Seed yield is an important trait targeted for improvement in bermudagrass breeding programs because of the increased interest in seed-propagated cultivars. Understanding the nature of genetic variation for seed yield and its components in bermudagrass would aid the development of seed-propagated cultivars. The objective of this study was to estimate the genetic variation and narrow-sense heritability for seed yield and its two major components, inflorescences prolificacy and seed set percentage in bermudagrass. Twenty-five half-sib families and their respective clonal parents were evaluated at two Oklahoma locations, Perkins and Stillwater in two years. Half-sib families were different for seed yield, inflorescences prolificacy and seed set percentage, indicating the expression of additive genes in controlling these traits. Family × location effects were observed for seed set percentage and seed yield. All three traits showed family × year interaction effects. There was a significant family × location × year interaction in inflorescences prolificacy and seed set percentage. Narrow-sense heritability estimates for seed yield was 0.18 based on variance component analysis among half-sib families and ranged from 0.26 to 0.68 based on parent-offspring regressions, indicating genetic complexity of seed yield. Heritability estimates were moderate (0.30−0.55) for inflorescences prolificacy and moderate to relatively high (0.41−0.78) for seed set percentage. The results indicate that sufficient magnitudes of additive genetic variation for seed set percentage and inflorescence prolificacy permit positive response to selection and conventional progeny-based genotypic evaluation is necessary for seed yield improvement.

Simulation of Nitrous Oxide Emissions in Zoysia Turfgrass Using DAYCENT and DNDC Ecosystem Models

Nitrous oxide (N2O) is an important greenhouse gas (GHG) implicated in global climate change. Process-based ecosystem models, such as DAYCENT and DNDC, have been widely used to predict GHG fluxes in agricultural systems. However, neither model has yet been applied to warm-season turfgrasses such as zoysiagrass. This study parameterized, calibrated, and validated the DAYCENT and DNDC models for N2O emissions from Meyer zoysiagrass (Zoysia japonica Steud.) using Bayes’ theorem and field data from Braun and Bremer (2018a, 2019) and Lewis and Bremer (2013). Results indicated DAYCENT, but not DNDC, reasonably simulated the impacts of irrigation and N-fertilization practices on biweekly and annual N2O emissions in zoysia turfgrass. When assuming no further climate change, the validated DAYCENT model predicted that typical recommendations for N-fertilization and irrigation in zoysiagrass (a low-input turfgrass) would reduce its cumulative global warming potential (GWP) for the first 45 years after establishment by encouraging soil carbon sequestration. Thereafter, soils would become saturated with carbon and hence, reductions of N inputs would be beneficial for mitigating further increases in N2O emissions and GWP.

Functional Characterization of the Pheophytinase Gene, ZjPPH, From Zoysia japonica in Regulating Chlorophyll Degradation and Photosynthesis.

Pheophytinase (PPH), the phytol hydrolase, plays important roles in chlorophyll degradation. Nevertheless, little attention has been paid to the PPHs in warm-season grass species; neither its detailed function in photosynthesis has been systematically explored to date. In this study, we isolated ZjPPH from Zoysia japonica, an excellent warm-season turfgrass species. Quantitative real-time PCR analysis and promoter activity characterization revealed that the expression of ZjPPH could be induced by senescence, ABA, and dark induction. Subcellular localization observation proved that ZjPPH was localized in the chloroplasts. Overexpression of ZjPPH accelerated the chlorophyll degradation and rescued the stay-green phenotype of the Arabidopsis pph mutant. Moreover, ZjPPH promoted senescence with the accumulation of ABA and soluble sugar contents, as well as the increased transcriptional level of SAG12 and SAG14. Transmission electron microscopy investigation revealed that ZjPPH caused the decomposition of chloroplasts ultrastructure in stable transformed Arabidopsis. Furthermore, chlorophyll a fluorescence transient measurement analysis suggested that ZjPPH suppressed photosynthesis efficiency by mainly suppressing both photosystem II (PSII) and photosystem I (PSI). In conclusion, ZjPPH plays an important role in chlorophyll degradation and senescence. It could be a valuable target for genetic editing to cultivate new germplasms with stay-green performance and improved photosynthetic efficiency.

Influence of Abiotic Factors on Walking Behavior of Hunting Billbugs (Coleoptera: Curculionidae).

The hunting billbug, Sphenophorus venatus vestitus Chittenden, is an important insect pest of warm-season turfgrass. Larvae and adult S. venatus vestitus feed on turfgrass and affect normal grass growth and development. In sod farms and golf courses, management sprays are typically confined to affected areas because of the high insecticide and application costs. Understanding the walking behavior of S. venatus vestitus adults would help us to refine management tactics. Thus, the objective of this study was to determine the influence of abiotic factors on the walking behavior of adult S. venatus vestitus. A series of laboratory, semifield, and field assays were conducted in 2019 and 2020. For the laboratory assays, field-collected S. venatus vestitus adults were acclimated at 15, 18, 21, 28, and 32°C for 24 h, and the distances walked by these pre-acclimated adults were measured on sand and filter paper substrates using Noldus EthoVision XT software. For the semifield assays, the total and net distances walked by pre-acclimated adults were measured on a paved indoor surface. Sphenophorus venatus vestitus males and females moved farther when the temperature increased from 15 to 28°C in the laboratory and semifield assays. For the field assays, field-collected S. venatus vestitus adults were not acclimated. The total and net distances walked by the adults were documented on a paved surface. Increases in temperature and relative humidity did not affect the distance moved by adults, but an increase in wind speed reduced the distance moved.

The Urban Double-Crop: Can Fall Vegetables and a Warm-Season Lawn Co-Exist?

A gardening methodology using double-cropped cool-season vegetables and warm-season turfgrass, thereby capitalizing on the ideal growing season for each, was developed in field trials and tested in volunteers’ landscapes. Broccoli (Brassica oleracea), lettuce (Lactuca sativa), and Swiss chard (Beta vulgaris subsp. Cicla) were planted into an established hybrid bermudagrass lawn (Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt-Davy ‘Tifsport’) in September. The vegetables were planted into tilled strips, 5 cm × 10 cm holes and 10 cm × 10 cm holes in the turf. All treatments produced harvestable yield, though the yield of vegetables planted in the tilled treatments and larger holes was greater than in smaller holes. Efforts to reduce turfgrass competition with vegetables by the application of glyphosate or the use of the Veggie Lawn Pod (an easily installed plastic cover on the lawn) did not increase yield. Tilled treatments left depressions that discouraged spring turfgrass recovery. The double-crop was tested by seven volunteers on their lawns. Though lawn-planted vegetables did not produce as much yield as those planted in the volunteers’ gardens, the volunteers were enthusiastic about this methodology. The volunteers reported that lawn vegetables were more difficult to plant but not more difficult to maintain, and they were easier to harvest than vegetables in their gardens. All volunteers reported satisfactory recovery of their lawns in the spring.

Identification of bHLH genes through genome-wide association study and antisense expression of ZjbHLH076/ZjICE1 influence tolerance to low temperature and salinity in Zoysia japonica

Abiotic stress greatly affects plant growth and developmental processes, resulting in poor productivity. A variety of basic helix-loop-helix (bHLH) transcription factors (TFs) that play important roles in plant abiotic stress response pathways have been identified. However, bHLH proteins of Zoysia japonica, one of the warm-season turfgrasses, have not been widely studied. In this study, 141 bHLH genes (ZjbHLHs) were identified and classified into 22 subfamilies. The ZjbHLHs were mapped on 19 chromosomes except for Chr17 and one pair of the tandemly arrayed genes was identified on Chr06. Also, the co-linearity of ZjbHLHs was found to have been driven mostly by segmental duplication events. The subfamily IIIb genes of our present interest, possessed various stress responsive cis-elements in their promoters. ZjbHLH076/ZjICE1, a MYC-type bHLH TF in subfamily IIIb was analyzed by overexpression and its loss-of-function via overexpressing a short ZjbHLH076/ZjICE1 fragment in the antisense direction. The overexpression of ZjbHLH076/ZjICE1 enhanced the tolerance to cold and salinity stress in the transgenic Z. japonica plants. However, the anti-sense expression of ZjbHLH076/ZjICE1 showed sensitive to these abiotic stresses. These results suggest that ZjbHLH076/ZjICE1 would be a promising candidate for the molecular breeding program to improve the abiotic stress tolerance of Z. japonica.

Long-term Performance of Warm-season Turfgrass Species under Municipal Irrigation Frequency Restrictions

Landscape irrigation frequency restrictions are commonly imposed by water purveyors and municipalities to curtail domestic water use and to ensure adequate water supplies for growing populations during times of drought. Currently, published data are lacking concerning irrigation frequency requirements necessary for sustaining acceptable levels of turfgrass quality of commonly used warm-season turfgrass species. The objective of this 3-year field study was to determine comparative turfgrass quality of drought-resistant cultivars of four warm-season lawn species in the south–central United States under irrigation frequency regimes of 0, 1, 2, 4, and 8× monthly. Turfgrasses used in the study were based on previously reported drought resistance and included ‘Riley’s Super Sport’ (Celebration®) bermudagrass [Cynodon dactylon (L.) Pers.], ‘Palisades’ zoysiagrass (Zoysia japonica Steud.), ‘Floratam’ st. augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze], and ‘SeaStar’ seashore paspalum (Paspalum vaginatum Swartz). During each growing season, slightly reduced irrigation volumes and bypassed events resulted from the 8× monthly treatment (34.95 cm, 38.13 cm, and 27.33 cm) compared with the 4× monthly treatment (35.36 cm, 40.84 cm, and 28.70 cm) in years 1, 2, and 3, respectively. For the once weekly treatment, the average fraction of reference evapotranspiration (ETo) supplied by effective rainfall and irrigation during the summer months was 1.22, 0.67, and 0.83 in years 1, 2, and 3, respectively, and was generally adequate to support acceptable turfgrass quality of all warm-season turfgrasses evaluated. Under the less than weekly irrigation frequency, st. augustinegrass and seashore paspalum generally fell to below acceptable quality levels because the average fraction of ETo supplied by effective rainfall and irrigation during the summer months of years 2 and 3 was 0.51, 0.39, and 0.26 for the 2× monthly, 1× monthly, and unirrigated treatments, respectively. Bermudagrass generally outperformed all other species under the most restrictive irrigation frequencies and also did not differ statistically from zoysiagrass. These results show that as irrigation frequency is restricted to less than once per week, species selection becomes an important consideration.

Genome-Wide Analysis of the HSP20 Gene Family and Expression Patterns of HSP20 Genes in Response to Abiotic Stresses in Cynodon transvaalensis.

African bermudagrass (Cynodon transvaalensis Burtt–Davy) is an important warm-season turfgrass and forage grass species. Heat shock protein 20 (HSP20) is a diverse, ancient, and important protein family. To date, HSP20 genes have not been characterized genome-widely in African bermudagrass. Here, we confirmed 41 HSP20 genes in African bermudagrass genome. On the basis of the phylogenetic tree and cellular locations, the HSP20 proteins were classified into 12 subfamilies. Motif composition was consistent with the phylogeny. Moreover, we identified 15 pairs of paralogs containing nine pairs of tandem duplicates and six pairs of WGD/segmental duplicates of HSP20 genes. Unsurprisingly, the syntenic genes revealed that African bermudagrass had a closer evolutionary relationship with monocots (maize and rice) than dicots (Arabidopsis and soybean). The expression patterns of HSP20 genes were identified with the transcriptome data under abiotic stresses. According to the expression profiles, HSP20 genes could be clustered into three groups (Groups I, II, and III). Group I was the largest, and these genes were up-regulated in response to heat stress as expected. In Group II, one monocot-specific HSP20, CtHSP20-14 maintained higher expression levels under optimum temperature and low temperature, but not high temperature. Moreover, a pair of WGD/segmental duplicates CtHSP20-9 and CtHSP20-10 were among the most conserved HSP20s across different plant species, and they seemed to be positively selected in response to extreme temperatures during evolution. A total of 938 cis-elements were captured in the putative promoters of HSP20 genes. Almost half of the cis-elements were stress responsive, indicating that the expression pattern of HSP20 genes under abiotic stresses might be largely regulated by the cis-elements. Additionally, three-dimensional structure simulations and protein–protein interaction networks were incorporated to resolve the function mechanism of HSP20 proteins. In summary, the findings fulfilled the HSP20 family analysis and could provide useful information for further functional investigations of the specific HSP20s (e.g., CtHSP20-9, CtHSP20-10, and CtHSP20-14) in African bermudagrass.

Relationship between the Phenylpropanoid Pathway and Dwarfism of Paspalum seashore Based on RNA-Seq and iTRAQ.

Seashore paspalum is a major warm-season turfgrass requiring frequent mowing. The use of dwarf cultivars with slow growth is a promising method to decrease mowing frequency. The present study was conducted to provide an in-depth understanding of the molecular mechanism of T51 dwarfing in the phenylpropane pathway and to screen the key genes related to dwarfing. For this purpose, we obtained transcriptomic information based on RNA-Seq and proteomic information based on iTRAQ for the dwarf mutant T51 of seashore paspalum. The combined results of transcriptomic and proteomic analysis were used to identify the differential expression pattern of genes at the translational and transcriptional levels. A total of 8311 DEGs were detected at the transcription level, of which 2540 were upregulated and 5771 were downregulated. Based on the transcripts, 2910 proteins were identified using iTRAQ, of which 392 (155 upregulated and 237 downregulated) were DEPs. The phenylpropane pathway was found to be significantly enriched at both the transcriptional and translational levels. Combined with the decrease in lignin content and the increase in flavonoid content in T51, we found that the dwarf phenotype of T51 is closely related to the abnormal synthesis of lignin and flavonoids in the phenylpropane pathway. CCR and HCT may be the key genes for T51 dwarf. This study provides the basis for further study on the dwarfing mechanism of seashore paspalum. The screening of key genes lays a foundation for further studies on the molecular mechanism of seashore paspalum dwarfing.

A high-quality chromosome-scale assembly of the centipedegrass [Eremochloa ophiuroides (Munro) Hack.] genome provides insights into chromosomal structural evolution and prostrate growth habit

Centipedegrass [Eremochloa ophiuroides (Munro) Hack.], a member of the Panicoideae subfamily, is one of the most important warm-season turfgrasses originating from China. This grass has an extremely developed prostrate growth habit and has been widely used in transitional and warm climatic regions. To better understand the genetic basis of important biological characteristics, such as prostrate growth and seed yield, in warm-season turfgrasses, we present a high-quality reference genome for centipedegrass and use PacBio, BioNano, and Hi-C technologies to anchor the 867.43 Mb genome assembly into nine pseudochromosomes, with a scaffold N50 of 86.05 Mb and 36,572 annotated genes. Centipedegrass was most closely related to sorghum and diverged from their common ancestor ~16.8 Mya. We detected a novel chromosome reshuffling event in centipedegrass, namely, the nest chromosome fusion event in which fusion of chromosomes 8 and 10 of sorghum into chromosome 3 of centipedegrass likely occurred after the divergence of centipedegrass from sorghum. The typical prostrate growth trait in centipedegrass may be linked to the expansion of candidate PROSTRATE GROWTH 1 (PROG1) genes on chromosome 2. Two orthologous genes of OsPROG1, EoPROG1, and EoPROG2, were confirmed to increase the stem number and decrease the stem angle in Arabidopsis. Collectively, our assembled reference genome of centipedegrass offers new knowledge and resources to dissect the genome evolution of Panicoideae and accelerate genome-assisted breeding and improvement of plant architecture in turf plants.

Effects of overseeding times on different warm-season turfgrasses: Visual turf quality and some related characteristics

The sustainability of warm-season turfgrass species in winter dormancy is a major concern in Mediterranean ecology. The concept of overseed a lawn has been still new for many developing countries such as Turkey as part of a regular maintenance. Therefore, a 2-year study was conducted at the experimental fields of Ege University, Izmir/Turkey during 2014-2016 years to compare the effects of four different overseeding times (September 15, September 30, October 15 and October 30) on four warm season turfgrass species (Cynodon dactylon cv. SR9554, Cynodon dactylon × Cynodon transvaalensis cv. Tifway-419, Paspalum vaginatum cv. Sea Spray and Zoysia japonica cv. Zenith) by measuring visual turf quality (1-9 score) and some related characteristics as texture (mm), cover (1-9 score), weed infestation (1-9 score) and colour (1-9 score). ‘50% cv. Troya+50% cv. Esquire’ perennial ryegrass (Lolium perenne L.) mixture was used for overseeding in trial. According to results, visual turf quality performance of 6.0 scores and above were obtained from all treatments. We concluded that October 15 should be most suitable time for overseeding applications. Additionally, L. perenne L. can be practiced successfully in Mediterranean region in order to eliminate the concerns of warm-season turfgrasses in the winter dormancy period observed in cold temperatures. Highlights - No gaps were formed in plots and high coverage degrees were maintained during overseeding periods in all treatments. - Homogeneous spring transition was occurred from Lolium perenne L. to warm-season turfgrass species in all overseeding times. - Visual turf quality performance of 6.0 scores and above which is acceptable level were obtained from all overseeding times. - Better results were obtained from overseeding applications on Paspalum vaginatum and Cynodon dactylon × Cynodon transvaalensis. - The different results among the warm-season turfgrass species can provide effective information for future research studies.

Characteristics of annual N2O and NO fluxes from Chinese urban turfgrasses

Urban turfgrass ecosystems are expected to increase at unprecedented rates in upcoming decades, due to the increasing population density and urban sprawl worldwide. However, so far urban turfgrasses are among the least understood of all terrestrial ecosystems concerning their impact on biogeochemical N cycling and associated nitrous oxide (N2O) and nitric oxide (NO) fluxes. In this study, we aimed to characterize and quantify annual N2O and NO fluxes from urban turfgrasses dominated by either C4, warm-season species or C3, cool-season and shade-enduring species, based on year-round field measurements in Beijing, China. Our results showed that soil N2O and NO fluxes varied substantially within the studied year, characterizing by higher emissions during the growing season and lower fluxes during the non-growing season. The regression model fitted by soil temperature and soil water content explained approximately 50%–70% and 31%–38% of the variance in N2O and NO fluxes, respectively. Annual cumulative emissions for all urban turfgrasses ranged from 0.75 to 1.27 kg N ha−1 yr−1 for N2O and from 0.30 to 0.46 kg N ha−1 yr−1 for NO, both are generally higher than those of Chinese natural grasslands. Non-growing season fluxes contributed 17%–37% and 23%–30% to the annual budgets of N2O and NO, respectively. Our results also showed that compared to the cool-season turfgrass, annual N2O and NO emissions were greatly reduced by the warm-season turfgrass, with the high root system limiting the availability of inorganic N substrates to soil microbial processes of nitrification and denitrification. This study indicates the importance of enhanced N retention of urban turfgrasses through the management of effective species for alleviating the potential environmental impacts of these rapidly expanding ecosystems.

Functional characterization of the chlorophyll b reductase gene NYC1 associated with chlorophyll degradation and photosynthesis in Zoysia japonica

Chlorophyll plays essential roles in photosynthesis and its degradation should be regulated precisely. Chlorophyll b reductase encoded by the gene NYC1 is responsible for catalyzing chlorophyll b degradation and maintaining the stability of photosystems. Although NYC1s have been characterized in many plants, their function in the photosynthetic machinery and the underlying regulatory mechanisms at the whole transcriptome level remain elusive. In this study, the ZjNYC1 gene was cloned from the important warm-season turfgrass Zoysia japonica. Analysis of the subcellular localization revealed that ZjNYC1 was localized in the chloroplasts, and results of the bimolecular fluorescence complementation (BiFC) assay indicated that ZjNYC1 could interact in vivo with the NYC1-like protein, ZjNOL. Overexpression of ZjNYC1 accelerated the degradation of chlorophyll, and promoted senescence with accumulation of ABA and reactive oxygen species (ROS) in Arabidopsis. Expression of ZjNYC1 rescued the stay-green phenotype of the Arabidopsis nyc1 mutant. An integrated analysis of chlorophyll fluorescence test (JIP-test) and RNA-sequencing revealed that ZjNYC1 negatively affected the efficiency of the PSII, PSI, and the intersystem electron transport chain. Furthermore, the Calvin cycle and photorespiration were suppressed, but ABA and ethylene synthesis and signal transduction pathways were activated in the transgenic lines. Collectively, these results demonstrated that ZjNYC1 plays important roles in accelerating chlorophyll degradation and senescence, and caused negative affect on the integrity and functionality of the photosystems.

Organ-Specific Transcriptome Analysis Identifies Candidate Genes Involved in the Stem Specialization of Bermudagrass (Cynodon dactylon L.).

As an important warm-season turfgrass and forage grass species with wide applications, bermudagrass (Cynodon dactylon L.) simultaneously has shoot, stolon and rhizome, three types of stems with different physiological functions. To better understand how the three types of stems differentiate and specialize, we generated an organ-specific transcriptome dataset of bermudagrass encompassing 114,169 unigenes, among which 100,878 and 65,901 could be assigned to the Kyoto Encyclopedia of Genes and Genomes (KEGG) and the Gene Ontology (GO) terms, respectively. Using the dataset, we comprehensively analyzed the gene expression of different organs, especially the shoot, stolon and rhizome. The results indicated that six organs of bermudagrass all contained more than 52,000 significantly expressed unigenes, however, only 3,028 unigenes were enrich-expressed in different organs. Paired comparison analyses further indicated that 11,762 unigenes were differentially expressed in the three types of stems. Gene enrichment analysis revealed that 39 KEGG pathways were enriched with the differentially expressed unigenes (DEGs). Specifically, 401 DEGs were involved in plant hormone signal transduction, whereas 1,978 DEGs were transcription factors involved in gene expression regulation. Furthermore, in agreement with the starch content and starch synthase assay results, DEGs encoding starch synthesis-related enzymes all showed the highest expression level in the rhizome. These results not only provided new insights into the specialization of stems in bermudagrass but also made solid foundation for future gene functional studies in this important grass species and other stoloniferous/rhizomatous plants.

The genome of the warm-season turfgrass African bermudagrass (Cynodon transvaalensis)

Cynodon species can be used for multiple purposes and have high economic and ecological significance. However, the genetic basis of the favorable agronomic traits of Cynodon species is poorly understood, partially due to the limited availability of genomic resources. In this study, we report a chromosome-scale genome assembly of a diploid Cynodon species, C. transvaalensis, obtained by combining Illumina and Nanopore sequencing, BioNano, and Hi-C. The assembly contains 282 scaffolds (~423.42 Mb, N50 = 5.37 Mb), which cover ~93.2% of the estimated genome of C. transvaalensis (~454.4 Mb). Furthermore, 90.48% of the scaffolds (~383.08 Mb) were anchored to nine pseudomolecules, of which the largest was 60.78 Mb in length. Evolutionary analysis along with transcriptome comparison provided a preliminary genomic basis for the adaptation of this species to tropical and/or subtropical climates, typically with dry summers. The genomic resources generated in this study will not only facilitate evolutionary studies of the Chloridoideae subfamily, in particular, the Cynodonteae tribe, but also facilitate functional genomic research and genetic breeding in Cynodon species for new leading turfgrass cultivars in the future.