Habitat differentiation and environmental adaptability contribute to leaf size variations globally in C3 and C4 grasses.

The grass family (Poaceae) dominates ~43 % of Earth's land area and contributes 33 % of terrestrial primary productivity that is critical to naturally regulating atmosphere CO2 concentration and global climate change. Currently grasses comprise ~11,780 species and ~50 % of them (~6000 species) utilize C4 photosynthetic pathway. Generally, grass species have smaller leaves under colder and drier environments, but it is unclear whether the primary drivers of leaf size differ between C3 and C4 grasses on a global scale. Here, we analyzed 34 environmental variables, such as latitude, elevation, mean annual temperature, mean annual precipitation, and solar radiation etc., through a comparatively comprehensive database of ~3.0 million occurrence records from 1380 C3 and 978 C4 grass species (2358 species in total). Results from this study confirm that C4 grasses have occupied habitats with lower latitudes and elevations, characterized by warmer, sunnier, drier and less fertile environmental conditions. Grass leaf size correlates positively with mean annual temperature and precipitation as expected. Our results also demonstrate that the mean temperature of the wettest quarter of the year is the primary control for C3 leaf size, whereas C4 leaf size is negatively correlated with the difference between summer and winter temperatures. For C4 grasses, phylogeny exerts a significant effect on leaf size but is less important than environmental factors. Our findings highlight the importance of evolutionarily contrasting variations in leaf size between C3 and C4 grasses for shaping their geographical distribution and habitat suitability at the global scale.

Reponses of morphological and biochemical traits of bamboo trees under elevated atmospheric O3 enrichment.

Dwarf bamboo (Indocalamus decorus) is an O3-tolerant plant species. To identify the possible mechanism and response of leaf morphological, antioxidant, and anatomical characteristics to elevated atmospheric O3 (EO3) concentrations, we exposed three-year-old I. decorus seedlings to three O3 levels (low O3-LO: ambient air; medium O3-MO: Ambient air+70 ppb high O3-HO: Ambient air+140 ppb O3) over a growing season using open-top chambers. Leaf shape and stomatal characteristics, and leaf microscopic structure of I. decorus were examined. The results indicated that 1) the stomata O3 flux (Fst) of HO decreased more rapidly under EO3 as the exposure time increased. The foliar O3 injury of HO and MO occurred when AOT40 was 26.62 ppm h and 33.20 ppm h, respectively, 2) under EO3, leaf number, leaf mass per area, leaf area, and stomata length/width all decreased, while leaf thickness, stomatal density, width, and area increased compared to the control, 3) MDA and total soluble protein contents all showed significantly increase under HO (36.57% and 32.77%) and MO(31.91% and 19.52%) while proline contents only increased under HO(33.27%). 4) MO and HO increased bulliform cells numbers in the leaves by 6.28% and 23.01%, respectively. HO reduced the transverse area of bulliform cells by 13.73%, while MO treatments had no effect, and 5) the number of fusoid cells interspace, the transverse area of fusoid cells interspace, and mesophyll thickness of HO significantly increased by 11.16%, 28.58%, and 13.42%, respectively. In conclusion, I. decorus exhibits strong O3 tolerance characteristics, which stem from adaptions in the leaf's morphological, structural, antioxidant, and anatomical features. One critical attribute was the enlargement of the bulliform cell transverse area and the transverse area of fusoid cells interspace that drove this resistance to O3. Local bamboo species with high resistance to O3 pollution thus need to be promoted for sustained productivity and ecosystem services in areas with high O3 pollution.

Phylogenomic analysis reveals five independently evolved African forage grass clades in the genus Urochloa.

BACKGROUND AND AIMS: The grass genus Urochloa (Brachiaria) sensu lato includes forage crops that are important for beef and dairy industries in tropical and sub-tropical Africa, South America and Oceania/Australia. Economically important species include U. brizantha, U. decumbens, U. humidicola, U. mutica, U. arrecta, U. trichopus, U. mosambicensis and Megathyrsus maximus, all native to the African continent. Perennial growth habits, large, fast growing palatable leaves, intra- and interspecific morphological variability, apomictic reproductive systems and frequent polyploidy are widely shared within the genus. The combination of these traits probably favoured the selection for forage domestication and weediness, but trait emergence across Urochloa cannot be modelled, as a robust phylogenetic assessment of the genus has not been conducted. We aim to produce a phylogeny for Urochloa that includes all important forage species, and identify their closest wild relatives (crop wild relatives). Finally, we will use our phylogeny and available trait data to infer the ancestral states of important forage traits across Urochloa s.l. and model the evolution of forage syndromes across the genus. METHODS: Using a target enrichment sequencing approach (Angiosperm 353), we inferred a species-level phylogeny for Urochloa s.l., encompassing 54 species (~40 % of the genus) and outgroups. Phylogenies were inferred using a multispecies coalescent model and maximum likelihood method. We determined the phylogenetic placement of agriculturally important species and identified their closest wild relatives, or crop wild relatives, based on well-supported monophyly. Further, we mapped key traits associated with Urochloa forage crops to the species tree and estimated ancestral states for forage traits along branch lengths for continuous traits and at ancestral nodes in discrete traits. KEY RESULTS: Agricultural species belong to five independent clades, including U. brizantha and U. decumbens lying in a previously defined species complex. Crop wild relatives were identified for these clades supporting previous sub-generic groupings in Urochloa based on morphology. Using ancestral trait estimation models, we find that five morphological traits that correlate with forage potential (perennial growth habits, culm height, leaf size, a winged rachis and large seeds) independently evolved in forage clades. CONCLUSIONS: Urochloa s.l. is a highly diverse genus that contains numerous species with agricultural potential, including crop wild relatives that are currently underexploited. All forage species and their crop wild relatives naturally occur on the African continent and their conservation across their native distributions is essential. Genomic and phenotypic diversity in forage clade species and their wild relatives need to be better assessed both to develop conservation strategies and to exploit the diversity in the genus for improved sustainability in Urochloa cultivar production.

Application of magnetic resonance imaging (MRI) technology in the characterization of microstructure and moisture content of young Moso bamboo.

Bamboo nodes play a key role in the hollow structure and the rapid growth of bamboo culm. Studying on the anatomical structure of bamboo is helpful to understand its growth mechanism. Taking the noninvasive, high-resolution and accurate technical advantages of magnetic resonance imaging (MRI), we conducted cross-sectional high-resolution MRI scanning on the tip of young Moso bamboo culm (removed shoot sheath) and extracted the gray value of the MRIs by using MATLAB software to explore the differences of water distribution in nodes, proximal nodes, and internodes. The results showed that numerous vascular bundles were repeatedly twisted and rotated horizontally at the nodal diaphragms and inner wall near the nodal diaphragms of the young bamboo, forming an intricate and highly connected network. The structure protected important tissues from mechanical stress by allocating axial loads, and enabled to laterally transport water and nutrients, which was an important basis for the rapid growth of Moso bamboo in relatively short term. The signal value (also known as brightness value) of MRIs indicated that water content of vascular bundles in young bamboo culm was much higher than that of surrounding parenchyma tissues. The mean value and standard deviation of water content between pixels of internodes were significantly higher than that of nodes, and the values of that in the proximal nodes were intermediate. The development of MRI would play a significant role in the studies of bamboo anatomy, physiology, and biochemistry.

Ontogeny and anatomy of Bouteloua (Poaceae: Chloridoideae) species display a basipetal branch formation and a novel modified leaf structure in grasses.

BACKGROUND AND AIMS: Shoot ontogenesis in grasses follows a transition from a vegetative phase into a reproductive phase. Current studies provide insight into how branch and spikelet formation occur during the reproductive phase. However, these studies do not explain all the complex diversity of grass inflorescence forms and are mostly focused on model grasses. Moreover, truncated inflorescences of the non-model grass genus Urochloa (Panicoideae) with formation of primary branches have basipetal initiation of branches. Bouteloua species (Chloridoideae) are non-model grasses that form truncated inflorescences of primary branches with apical vestiges of uncertain homology at the tips of branching events and sterile florets above the lowermost fertile floret. Sterile florets are reduced to rudimentary lemmas composed of three large awns diverging from an awn column. Conflict about the awn column identity of this rudimentary lemma is often addressed in species descriptions of this genus. We test if Bouteloua species can display basipetal initiation of branches and explore the identity of vestiges and the awn column of rudimentary lemmas. METHODS: We surveyed the inflorescence ontogeny and branch/awn anatomy of Bouteloua species and compared results with recent ontogenetic studies of chloridoids. KEY RESULTS: Bouteloua arizonica has florets with basipetal maturation. Branches display basipetal branch initiation and maturation. Branch vestiges are formed laterally by meristems during early branching events. The spikelet meristem forms the awn column of rudimentary lemmas. Vestiges and sterile floret awns have anatomical similarities to C4 leaves. CONCLUSIONS: Basipetal initiation of branches is a novel feature for Chloridoideae grasses. Branch vestiges are novel vegetative grass structures. Sterile floret awn columns are likely to be extensions of the rachilla.

Light and scanning electron microscopic imaging of leaf transverse sections of indigenous fodder grasses of central Punjab, Pakistan.

The significance of grasses as fodder is enormous. However, it has been observed that different fodder grasses are identified locally with the similar vernacular names. Even same species recognized with different names. This happened due to their reduced and overlapped morphological characters. Hence comprehensive taxonomic keys were required to provide authentic identification of this grass flora. Current study established microscopic identification tools on the basis of leaf transverse anatomical features. Results demonstrated a great diversity in ribs and furrows arrangement among all studied grass members. Lolium temulentum, Phalaris minor, Poa annua, Arundo donax, Aristida adscensionis, Desmostachya bipinnata, Cenchrus biflorus and Digitaria ciliaris possessed ribs and furrows only at adaxial surfaces whereas all other species possessed this feature abaxially. Generally all the species contain three types of vascular bundles i.e. small, medium and large. Therefore, this qualitative feature is valuable only at family level, however, it found insignificant in taxa identification. Diversity was observed in bundle sheath type which could be taxonomically significant. Generally bundle sheath was found complete in most of species but in Bromus japonicus Thunb., Dactylis glomerata L., Acrachne racemosa (Heyne ex Roth) Ohwi, Chrysopogon aucheri (Boiss.) Stapf, Dichanthium annulatum (Forssk.) Stapf, Heteropogon contortus (L.) P Beauv. Ex. Roem & Schult. Eragrostis minor Host. and in Agrostis gigantea Roth. had incomplete type of sheath. Results reported great diversity in characters which could be taxonomically viable. RESEARCH HIGHLIGHTS: This research highlighted the significance of microscopic examination of leaf transverse anatomical features in field of taxonomy. Established anatomical tools would be of great importance for the identification of studied species.

Detailed macro and micromorphology of grasses caryopsis using scanning electron and light microscopy.

Micromorphology of 15 grass caryopsis was investigated through scanning electron microscopy for its implications in the identification of grasses. Both macro and micromorphological characters especially caryopsis shape and surface morphology were found significant in the taxonomic diagnosis. Shape morphology of caryopsis varied among the species and lanceolate, fusiform, narrow ellipsoidal, ovate, elliptical, plano-convex, fusiform, linear ovate, broadly elliptical, broadly pllipsoidal, plano-convex, oblique ovate, and subglobose shapes were recorded. Digitaria nodosa (3.31 × 0.7 mm) and Echinochloa crus-galli (3.26 × 1.44 mm) had the largest caryopsis size, while Acrachne racemosa (0.76 × 0.54 mm) and Eragrostis minor (0.62 × 0.38 mm) had the smallest caryopsis size. Macro and micromorphological characters were useful for the diagnosis of genus and species. Utilizing both qualitative and quantitative character taxonomic key at generic and species level were made.

Evolution of the grass leaf by primordium extension and petiole-lamina remodeling.

The sheathing leaf found in grasses and other monocots is an evolutionary innovation, yet its origin has been a subject of long-standing debate. Here, we revisit the problem in the light of developmental genetics and computational modeling. We show that the sheathing leaf likely arose through WOX-gene-dependent extension of a primordial zone straddling concentric domains around the shoot apex. Patterned growth within this zone, oriented by two polarity fields, accounts for wild-type, mutant and mosaic grass leaf development, whereas zone contraction and growth remodeling accounts for eudicot leaf development. In contrast to the prevailing view, our results suggest that the sheath derives from petiole, whereas the blade derives from the lamina of the eudicot leaf, consistent with homologies proposed in the 19th century.

grasviq: an image analysis framework for automatically quantifying vein number and morphology in grass leaves.

Beyond facilitating transport and providing mechanical support to the leaf, veins have important roles in the performance and productivity of plants and the ecosystem. In recent decades, computational image analysis has accelerated the extraction and quantification of vein traits, benefiting fields of research from agriculture to climatology. However, most of the existing leaf vein image analysis programs have been developed for the reticulate venation found in dicots. Despite the agroeconomic importance of cereal grass crops, like Oryza sativa (rice) and Zea mays (maize), a dedicated image analysis program for the parallel venation found in monocots has yet to be developed. To address the need for an image-based vein phenotyping tool for model and agronomic grass species, we developed the grass vein image quantification (grasviq) framework. Designed specifically for parallel venation, this framework automatically segments and quantifies vein patterns from images of cleared leaf pieces using classical computer vision techniques. Using image data sets from maize inbred lines and auxin biosynthesis and transport mutants in maize, we demonstrate the utility of grasviq for quantifying important vein traits, including vein density, vein width and interveinal distance. Furthermore, we show that the framework can resolve quantitative differences and identify vein patterning defects, which is advantageous for genetic experiments and mutant screens. We report that grasviq can perform high-throughput vein quantification, with precision on a par with that of manual quantification. Therefore, we envision that grasviq will be adopted for vein phenomics in maize and other grass species.

Impact of elevated air temperature and drought on pollen characteristics of major agricultural grass species.

Grass pollen allergens are known to be one of the major triggers of hay fever with an increasing number of humans affected by pollen associated health impacts. Climate change characterized by increasing air temperature and more frequent drought periods might affect plant development and pollen characteristics. In this study a one-year (2017) field experiment was conducted in Bavaria, Germany, simulating drought by excluding rain and elevated air temperature by installing a heating system to investigate their effects primarily on the allergenic potential of eight selected cultivars of the two grass species timothy and perennial ryegrass. It could be shown for timothy that especially under drought and heat conditions the allergen content is significantly lower accompanied by a decrease in pollen weight and protein content. In perennial ryegrass the response to drought and heat conditions in terms of allergen content, pollen weight, and protein content was more dependent on the respective cultivar probably due to varying requirements for their growth conditions and tolerance to drought and heat. Results support recommendations which cultivars should be grown preferentially. The optimal choice of grass species and respective cultivars under changing climate conditions should be a major key aspect for the public health sector in the future.

Developmental and biophysical determinants of grass leaf size worldwide.

One of the most notable ecological trends-described more than 2,300  years ago by Theophrastus-is the association of small leaves with dry and cold climates, which has recently been recognized for eudicotyledonous plants at a global scale1-3. For eudicotyledons, this pattern has been attributed to the fact that small leaves have a thinner boundary layer that helps to avoid extreme leaf temperatures4 and their leaf development results in vein traits that improve water transport under cold or dry climates5,6. However, the global distribution of leaf size and its adaptive basis have not been tested in the grasses, which represent a diverse lineage that is distinct in leaf morphology and that contributes 33% of terrestrial primary productivity (including the bulk of crop production)7. Here we demonstrate that grasses have shorter and narrower leaves under colder and drier climates worldwide. We show that small grass leaves have thermal advantages and vein development that contrast with those of eudicotyledons, but that also explain the abundance of small leaves in cold and dry climates. The worldwide distribution of leaf size in grasses exemplifies how biophysical and developmental processes result in convergence across major lineages in adaptation to climate globally, and highlights the importance of leaf size and venation architecture for grass performance in past, present and future ecosystems.

Responses of Phragmites australis to copper stress: A combined analysis of plant morphology, physiology and proteomics.

Few relevant research attempts have been made to determine heavy metal resistance mechanisms of rhizomatous perennial plants. Thus, it is pertinent to investigate the physiological and biochemical changes in Phragmites australis under metal-stressed conditions to facilitate the development of strategies to enhance copper (Cu) tolerance. We measured parameters related to plant growth and development, metal translocation and physiological responses of P. australis subjected to Cu stress. In addition, the differentially expressed proteins (DEP) were evaluated using the isobaric tag for relative and absolute quantification (iTRAQ) system. A large amount of copper accumulates in the roots of P.australis, but the growth parameters were not sensitive to Cu. However, the high concentration of Cu reduced the content of chlorophyll a and chlorophyll b, and the expression of important photosynthesis proteins PsbD, PsbO and PsaA were all down-regulated, so photosynthesis was inhibited. In contrast, the content of ascorbic acid and proline both increased with the increase of copper stress. P.australis fixed a large amount of Cu in its roots, limiting the migration of Cu to other parts of the plant. Moreover, Cu stress can affect photosynthesis by inhibiting the activity of PSI, PSII and LHCII. In addition, P.australis synthesizes ascorbic acid through the D-mannose/L-galactose pathway, and synthesizes proline through the ornithine pathway. Ascorbic acid and proline can increase Cu tolerance and protect photosynthesis. These results provide a theoretical basis for understanding the tolerance and repair mechanisms of plants in response to heavy metal pollution.

Unveiling the Actual Functions of Awns in Grasses: From Yield Potential to Quality Traits.

Awns, which are either bristles or hair-like outgrowths of lemmas in the florets, are one of the typical morphological characteristics of grass species. These stiff structures contribute to grain dispersal and burial and fend off animal predators. However, their phenotypic and genetic associations with traits deciding potential yield and quality are not fully understood. Awns appear to improve photosynthesis, provide assimilates for grain filling, thus contributing to the final grain yield, especially under temperature- and water-stress conditions. Long awns, however, represent a competing sink with developing kernels for photosynthates, which can reduce grain yield under favorable conditions. In addition, long awns can hamper postharvest handling, storage, and processing activities. Overall, little is known about the elusive role of awns, thus, this review summarizes what is known about the effect of awns on grain yield and biomass yield, grain nutritional value, and forage-quality attributes. The influence of awns on the agronomic performance of grasses seems to be associated with environmental and genetic factors and varies in different stages of plant development. The contribution of awns to yield traits and quality features previously documented in major cereal crops, such as rice, barley, and wheat, emphasizes that awns can be targeted for yield and quality improvement and may advance research aimed at identifying the phenotypic effects of morphological traits in grasses.

Pseudoflowers produced by Fusarium xyrophilum on yellow-eyed grass (Xyris spp.) in Guyana: A novel floral mimicry system?

Pseudoflower formation is arguably the rarest outcome of a plant-fungus interaction. Here we report on a novel putative floral mimicry system in which the pseudoflowers are composed entirely of fungal tissues in contrast to modified leaves documented in previous mimicry systems. Pseudoflowers on two perennial Xyris species (yellow-eyed grass, X. setigera and X. surinamensis) collected from savannas in Guyana were produced by Fusarium xyrophilum, a novel Fusarium species. These pseudoflowers mimic Xyris flowers in gross morphology and are ultraviolet reflective. Axenic cultures of F. xyrophilum produced two pigments that had fluorescence emission maxima in light ranges that trichromatic insects are sensitive to and volatiles known to attract insect pollinators. One of the volatiles emitted by F. xyrophilum cultures (i.e., 2-ethylhexanol) was also detected in the head space of X. laxifolia var. iridifolia flowers, a perennial species native to the New World. Results of microscopic and PCR analyses, combined with examination of gross morphology of the pseudoflowers, provide evidence that the fungus had established a systemic infection in both Xyris species, sterilized them and formed fungal pseudoflowers containing both mating type idiomorphs. Fusarium xyrophilum cultures also produced the auxin indole-3-acetic acid (IAA) and the cytokinin isopentenyl adenosine (iPR). Field observations revealed that pseudoflowers and Xyris flowers were both visited by bees. Together, the results suggest that F. xyrophilum pseudoflowers are a novel floral mimicry system that attracts insect pollinators, via visual and olfactory cues, into vectoring its conidia, which might facilitate outcrossing of this putatively heterothallic fungus and infection of previously uninfected plants.

Light and scanning electron microscopy-based foliar micro morphological tools for the identification of fodder grass taxa.

Fertile plain of Central Punjab Pakistan is rich with fodder grasses and from centuries the local inhabitants of this area have been using their regional grasses for ruminant feeding. However, they always faced difficulties in identification because of their overlapping vernacular names, more or less identical leaf shapes, indefinite variations in stem branching pattern, and reduced floral parts. Hence, the current study has provided a detailed and comprehensive micro-morphological analysis of 53 ethnobotanical fodder grass taxa. A variety of quantitative and qualitative leaf epidermal micromorphological traits was studied and results reported epidermal characters like stomatal index, silica bodies, prickles, microhairs, hook cells as most diagnostic in delimitation of species, and genera. As stomatal index was 79% in Poa annua while in its closely related species Poa infirmai was 85%. Similarly, Cenchrus ciliaris can be differentiated from Cenchrus pennisetiformis on the basis of silica body shape as butterfly shaped in former and dumbbell shaped in later one. Moreover, prickles were present in Chrysopogon aucheri while absent in Chrysopogon zizanioides. Hence, overall this study declared that diversity and variations in foliar micromorphological characters are valuable and supportive in the identification of grasses at the specific and generic level.

C4 grasses adapted to low precipitation habitats show traits related to greater mesophyll conductance and lower leaf hydraulic conductance.

In habitats with low water availability, a fundamental challenge for plants will be to maximize photosynthetic C-gain while minimizing transpirational water-loss. This trade-off between C-gain and water-loss can in part be achieved through the coordination of leaf-level photosynthetic and hydraulic traits. To test the relationship of photosynthetic C-gain and transpirational water-loss, we grew, under common growth conditions, 18 C4 grasses adapted to habitats with different mean annual precipitation (MAP) and measured leaf-level structural and anatomical traits associated with mesophyll conductance (gm ) and leaf hydraulic conductance (Kleaf ). The C4 grasses adapted to lower MAP showed greater mesophyll surface area exposed to intercellular air spaces (Smes ) and adaxial stomatal density (SDada ) which supported greater gm . These grasses also showed greater leaf thickness and vein-to-epidermis distance, which may lead to lower Kleaf . Additionally, grasses with greater gm and lower Kleaf also showed greater photosynthetic rates (Anet ) and leaf-level water-use efficiency (WUE). In summary, we identify a suite of leaf-level traits that appear important for adaptation of C4 grasses to habitats with low MAP and may be useful to identify C4 species showing greater Anet and WUE in drier conditions.

Extensive reticulate evolution within Fargesia (s.l.) (Bambusoideae: Poaceae) and its allies: Evidence from multiple nuclear markers.

Reticulate evolution resulting from hybridization and introgression has been recognized as a creative source of species and diversification in bamboos. Previous phylogenetic studies revealed that Fargesia (s.l.) (Fargesia and Yushania) was divided into the Fargesia spathe clade and the non-spathe clade. Interestingly, the Fargesia spathe clade may have originated from hybridization among other clades within Fargesia (s.l.). Understanding the hybrid origin of this clade requires a robust phylogenetic framework in which major clades within Fargesia (s.l.) are resolved. Here, we used three nuclear genes to reconstruct the evolutionary history of Fargesia (s.l.) and its allies to identify putative patterns in the origin of the Fargesia spathe clade and to examine the extent to which reticulate evolution has occurred at the interspecific level in bamboos. Bashania species form a clade with Fargesia (s.l.), which is further divided into Group I and Group II. The Fargesia spathe clade, the Alpine Bashania clade, and Fargesia yajiangensis comprise Group I, while the Bashania fargesii clade and the remaining Fargesia (s.l.) species form Group II. Incongruence between the current nuclear-based and previous plastid phylogenies demonstrate several possible hybridization events among Fargesia (s.l.) species and related taxa, which have given rise to the Fargesia spathe clade, the Phyllostachys clade, and the Ampelocalamus clade. We also detected several putative hybrid species of Fargesia (s.l.). Our results show that reticulate evolution has played a prominent role in Fargesia (s.l.) evolution, which could, in part, account for the taxonomic difficulty associated with Fargesia (s.l.) and the alpine bamboos. The study also underscores the importance of hybridization in the evolution of bamboos, at both intergeneric and intrageneric levels.

Effects of shade stress on turfgrasses morphophysiology and rhizosphere soil bacterial communities.

BACKGROUND: The shade represents one of the major environmental limitations for turfgrass growth. Shade influences plant growth and alters plant metabolism, yet little is known about how shade affects the structure of rhizosphere soil microbial communities and the role of soil microorganisms in plant shade responses. In this study, a glasshouse experiment was conducted to examine the impact of shade on the growth and photosynthetic capacity of two contrasting shade-tolerant turfgrasses, shade-tolerant dwarf lilyturf (Ophiopogon japonicus, OJ) and shade-intolerant perennial turf-type ryegrass (Lolium perenne, LP). We also examined soil-plant feedback effects on shade tolerance in the two turfgrass genotypes. The composition of the soil bacterial community was assayed using high-throughput sequencing. RESULTS: OJ maintained higher photosynthetic capacity and root growth than LP under shade stress, thus OJ was found to be more shade-tolerant than LP. Shade-intolerant LP responded better to both shade and soil microbes than shade-tolerant OJ. The shade and live soil decreased LP growth, but increased biomass allocation to shoots in the live soil. The plant shade response index of LP is higher in live soil than sterile soil, driven by weakened soil-plant feedback under shade stress. In contrast, there was no difference in these values for OJ under similar shade and soil treatments. Shade stress had little impact on the diversity of the OJ and the LP bacterial communities, but instead impacted their composition. The OJ soil bacterial communities were mostly composed of Proteobacteria and Acidobacteria. Further pairwise fitting analysis showed that a positive correlation of shade-tolerance in two turfgrasses and their bacterial community compositions. Several soil properties (NO3--N, NH4+-N, AK) showed a tight coupling with several major bacterial communities under shade stress. Moreover, OJ shared core bacterial taxa known to promote plant growth and confer tolerance to shade stress, which suggests common principles underpinning OJ-microbe interactions. CONCLUSION: Soil microorganisms mediate plant responses to shade stress via plant-soil feedback and shade-induced change in the rhizosphere soil bacterial community structure for OJ and LP plants. These findings emphasize the importance of understanding plant-soil interactions and their role in the mechanisms underlying shade tolerance in shade-tolerant turfgrasses.

ddRAD analyses reveal a credible phylogenetic relationship of the four main genera of Bambusa-Dendrocalamus-Gigantochloa complex (Poaceae: Bambusoideae).

The Bambusa-Dendrocalamus-Gigantochloa complex (BDG complex) is the most diversified and phylogenetically recalcitrant group of the paleotropical woody bamboos. Species of this complex occur in tropical and subtropical Asia and most of them are of great economic, cultural and ecological value. The lack of resolution achieved through the analyses of previous molecular datasets has long confounded its phylogenetic estimation and generic delimitation. Here, we adopted a ddRAD-seq strategy to investigate phylogenetic relationships of the four main genera (Bambusa, Dendrocalamus, Gigantochloa, and Melocalamus) in the BDG complex. A total of 102 species were sampled, and SNP data were generated. Both MP and ML analyses of the ddRAD-seq data resulted in a well-resolved topology with Gigantochloa and Melocalamus confirmed as monophyletic, and Melocalamus resolved as sister to the rest of the complex. Bambusa and Dendrocalamus were both resolved as paraphyletic. The phylogenetic relationships were mostly supported by morphological evidence including characters of the branch complement, rachilla, lodicules, filaments and stigma. We also generated and assembled complete plastid genomes of 48 representative species. There were conflicts between the plastome and the ddRAD topologies. Our study demonstrated that RAD-seq can be used to reconstruct evolutionary history of lineages such as the bamboos where ancient hybridization and polyploidy play a significant role. The four genera of the BDG complex have a complex evolutionary history which is likely a product of ancient introgression events.

Increased adaxial stomatal density is associated with greater mesophyll surface area exposed to intercellular air spaces and mesophyll conductance in diverse C4 grasses.

Mesophyll conductance (gm ) is the diffusion of CO2 from intercellular air spaces (IAS) to the first site of carboxylation in the mesophyll cells. In C3 species, gm is influenced by diverse leaf structural and anatomical traits; however, little is known about traits affecting gm in C4 species. To address this knowledge gap, we used online oxygen isotope discrimination measurements to estimate gm and microscopy techniques to measure leaf structural and anatomical traits potentially related to gm in 18 C4 grasses. In this study, gm scaled positively with photosynthesis and intrinsic water-use efficiency (TEi ), but not with stomatal conductance. Also, gm was not determined by a single trait but was positively correlated with adaxial stomatal densities (SDada ), stomatal ratio (SR), mesophyll surface area exposed to IAS (Smes ) and leaf thickness. However, gm was not related to abaxial stomatal densities (SDaba ) and mesophyll cell wall thickness (TCW ). Our study suggests that greater SDada and SR increased gm by increasing Smes and creating additional parallel pathways for CO2 diffusion inside mesophyll cells. Thus, SDada , SR and Smes are important determinants of C4 -gm and could be the target traits selected or modified for achieving greater gm and TEi in C4 species.