Effects of atmospheric CO2 concentration on transpiration and leaf elongation responses to drought in Triticum aestivum, Lolium perenne and Festuca arundinacea.

BACKGROUND AND AIMS: Leaf elongation is vital for Poaceae species' productivity, influenced by atmospheric CO2 concentration ([CO2]) and climate-induced water availability changes. Although [CO2] mitigates the effects of drought on reducing transpiration per unit leaf area, it also increases total leaf area and water use. These complex interactions associated with leaf growth pose challenges in anticipating climate change effects. This study aims to assess [CO2] effects on leaf growth response to drought in perennial ryegrass (Lolium perenne), tall fescue (Festuca arundinacea) and wheat (Triticum aestivum). METHODS: Plants were cultivated in growth chambers with [CO2] at 200 or 800 ppm. At leaf six to seven unfolding, half of the plants were subjected to severe drought treatment. Leaf elongation rate (LER) was measured daily, whereas plant transpiration was continuously recorded gravimetrically. Additionally, water-soluble carbohydrate (WSC) content along with water and osmotic potentials in the leaf growing zone were measured at drought onset, mid-drought and leaf growth cessation. KEY RESULTS: Elevated [CO2] mitigated drought impacts on LER and delayed growth cessation across species. A positive correlation between LER and soil relative water content (SRWC) was observed. At the same SRWC, perennial grasses exhibited a higher LER with elevated [CO2], likely due to enhanced stomatal regulation. Despite stomatal closure and WSC accumulation, CO2 did not influence nighttime water potential or osmotic potential. The marked increase in leaf area across species resulted in similar (wheat and tall fescue) or higher (ryegrass) total water use by the experiment's end, under both watered and unwatered conditions. CONCLUSIONS: In conclusion, elevated [CO2] mitigates the adverse effects of drought on leaf elongation in three Poaceae species, due to its impact on plant transpiration. Overall, these findings provide valuable insights into CO2 and drought interactions that may help anticipate plant responses to climate change.

Climate change and C4 and C3 grasses in a midlatitude dryland steppe.

Climate change is projected to alter the structure of plant communities due to increasing temperatures and changes to precipitation patterns, particularly in midlatitude dryland ecosystems. Modifications to climatic suitability may lead to major community changes such as altered dominant plant functional types. Previous studies have indicated that climatic suitability is likely to increase for C4 grasses and decrease for C3 grasses in the Western United States. However, if no C4 grass species currently exist to serve as a propagule source, expansion into areas of increased suitability will be limited. We conducted a field and modeling study in the Upper Green River Basin (UGRB) of Western Wyoming to determine if (1) C4 grasses are present to provide a propagule source and (2) C4 grasses are likely to increase in importance relative to C3 grasses due to climatic changes. We searched 44 sites for C4 grasses to establish presence, and modeled suitability at 35 sites using 17 Global Climate Models, two greenhouse gas Representative Concentration Pathways (RCPs; 4.5 and 8.5), and two time periods (mid- and late century; 2030-2060 and 2070-2099, respectively). We found C4 grasses at 10 of the 44 sites, indicating that there is a present propagule source. Our model projected increases in suitability for both C3 and C4 grasses across sites for all RCPs and time periods. In the mid-century RCP 4.5 scenario, the C3 functional type increased in projected biomass in 29 of 35 sites, and the C4 type increased in 31 sites. In this scenario, C3 grasses increased in projected biomass by a median 4 g m-2 (5% change), and C4 grass biomass increased by a median 8 g m-2 (21% change). Our study suggests that climate change will increase climatic suitability for grasses across the UGRB, and that all requirements are in place for C4 grasses to increase in abundance.

Dual role of BdMUTE during stomatal development in the model grass Brachypodium distachyon.

Grasses form morphologically derived, four-celled stomata, where two dumbbell-shaped guard cells (GCs) are flanked by two lateral subsidiary cells (SCs). This innovative form enables rapid opening and closing kinetics and efficient plant-atmosphere gas exchange. The mobile bHLH transcription factor MUTE is required for SC formation in grasses. Yet, if and how MUTE also regulates GC development and if MUTE mobility is required for SC recruitment is unclear. Here, we transgenically impaired BdMUTE mobility from GC to SC precursors in the emerging model grass Brachypodium distachyon. Our data indicates that reduced BdMUTE mobility severely affected the spatiotemporal coordination of GC and SC development. Furthermore, while BdMUTE has a cell-autonomous role in GC division orientation, complete dumbbell morphogenesis of GCs required SC recruitment. Finally, leaf-level gas exchange measurements showed that dosage-dependent complementation of the four-celled grass morphology was mirrored in a gradual physiological complementation of stomatal kinetics. Together, our work revealed a dual role of grass MUTE in regulating GC division orientation and SC recruitment, which in turn was required for GC morphogenesis and the rapid kinetics of grass stomata.

Ten years of directing seeding restoration in the Brazilian savanna: Lessons learned and the way forward.

Savannas and grasslands have lost almost 50% of their original cover worldwide. Therefore, the development of methods and information on open-canopy ecosystem restoration is urgent for the inclusion of these ecosystems into global and regional priorities. In the Brazilian savanna, the most diverse savanna in the world, restoration efforts focused on open ecosystems have been virtually absent, but have increased in the last 10 years. Such efforts are frequently threatened by invasive exotic grasses (IEG) that invade and dominate areas excluding native species, oftentimes aided by altered soil conditions. Long-term studies of savanna restoration trajectories are rare. In this study, we surveyed 22 savanna restoration areas established two to ten years before the study with similar restoration methods to assess their current status. We show that the current restoration methods are successful in establishing native species and allowing species turnover but they are threatened by IEG. Restoration success varies and is affected by soil conditions, IEG landscape cover and post-sowing weeding. Despite that, the simultaneous introduction of different plant functional groups allows turnover from fast to slow-growing plants. Establishing savanna native species is possible at an operational scale with current knowledge and techniques. However, native species establishment fails to prevent IEG reinfestation, which needs to be managed in restoration efforts in the Brazilian savanna.

Screening Cover Crops for Utilization in Irrigated Vineyards: A Greenhouse Study on Species' Nitrogen Uptake and Carbon Sequestration Potential.

This study examines the potential of 23 plant species, comprising 10 legumes, 9 grasses, and 4 forbs, as cover crops to enhance carbon (C) sequestration and soil nitrogen (N) in vineyards. After a 120-day evaluation period, cover crop biomass was incorporated into the soil, and grapevine seedlings were planted in its place. Among the established cover crops, the C input potential ranged from 0.267 to 1.69 Mg ha-1, and the N input potential ranged from 12.3 to 114 kg ha-1. Legume species exhibited up to threefold greater shoot dry weight (SDW) compared to grass species. Ladino white clover, Dutch white clover, and Clover blend were superior in SDW, total dry weight (TDW), total C content, and total N content. Legumes exhibited slightly higher root dry weight (RDW) than grasses, with the exception of Fall rye leading at 15 g pot-1, followed by Ladino white clover and Dutch white clover at an average of 12 g pot-1. Legumes, particularly clover blend and Alsike clover, displayed high shoot N concentration at an average of 2.95%. Root N concentration in Legumes (Fabaceae) were significantly higher at 1.82% compared to other plant families at 0.89%, while their root C/N ratio was lower at 18.3, contrasting with others at 27.7, resulting in a faster turnover. Biomass production exhibited a negative relationship (R2 = 0.51) with soil residual NO3-. Fall rye, Winfred brassica, and buckwheat had the highest N utilization efficiency (NUtE) values (ava. 121 g g-1). Alsike clover, Ladino white clover, and clover blend showed the highest N uptake efficiency (NUpE) values (ava. 75%). The Readily Available N (RAN) Reliance Index (RANRI) is introduced as a novel indicator for quantifying the extent to which a plant relies on RAN for its total N requirement. The RANRI value represents the percentage of the plant's total N sourced from RAN, ranging from 11% for legumes to 86% for grasses. This implies a substantial influx of nitrogen through a pathway independent of RAN in legumes. Grape shoot N concentration positively correlated with soil NO3- (R2 = 0.31) and cover crop C/N ratio (R2 = 0.17) but negatively correlated with cover crop TDW (R2 = 0.31). This study highlights legume plants as more effective in C and N assimilation during establishment but cautions about potential soil mineral N depletion before reaching their full biological N fixation capacity.

A comparative analysis of perennial grass-legume mixtures for biomethane production.

Examining the case of Lithuania, this study comparatively analyzed five perennial grass-legume mixtures in terms of biomethane production. Every mixture was divided into two parts: long (during the fifth year or beyond) and short (during the first four years) time periods. The analysis includes three types of perennial bell grass: Timothy, P. Ryegrass, C. Cocksfoot, and one legume grass Red clover. With this study, we aimed to evaluate how perennial grass-legume mixtures can promote biomethane uptake in Lithuania. Through analyzing the efficiency and consequences of government subsidy measures, this study aimed to address the question of how governmental assistance can promote the growth of the biomethane industry, specifically focusing on the utilization of perennial grass-legume mixtures. This study used seven financial indicators, including subsiding policy, in order to gain a deeper understanding of mixtures for biomethane production. The analysis revealed that the best mixtures for biomethane production with subsidies were the second (Red clover 35 % + Timothy 45 % + Ryegrass 20 % grass mixture) and fourth scenarios (Red clover 55 % + Ryegrass 45 % grass mixture). The first (Red clover 35 %. + Timothy 25 % + Ryegrass 20 % + Cocksfoot 20 % grass mixture), third (Red clover 55 % + Timothy 45 % grass mixture), and fifth scenarios (Red clover 55 % + Cocksfoot 45 % grass mixture) had the smallest positive effects. The results showed that, in Lithuania, in order to encourage farmers to produce biomethane, subsidy policies are needed. Incentives for engaging with this activity are necessary, as the income earned does not cover the costs incurred; unfortunately, biomethane production is unprofitable without subsidy. As such, our recommendation is to develop a long-term subsidy policy to promote biomethane production, focusing on the effectiveness, particularly in the Lithuanian context, of utilizing mixtures of perennial grasses. Further research and policy interventions are needed to address the opportunities associated with scaling synergy between perennial energy cops and environmental sustainability in bioenergy crop cultivation.

Genetic analyses of embryo homology and ontogeny in the model grass Zea mays subsp. mays.

The homology of the single cotyledon of grasses and the ontogeny of the scutellum and coleoptile as the initial, highly modified structures of the grass embryo are investigated using leaf developmental genetics and targeted transcript analyses in the model grass Zea mays subsp. mays. Transcripts of leaf developmental genes are identified in both the initiating scutellum and the coleoptile, while mutations disrupting mediolateral leaf development also disrupt scutellum and coleoptile morphology, suggesting that these grass-specific organs are modified leaves. Higher-order mutations in WUSCHEL-LIKE HOMEOBOX3 (WOX3) genes, involved in mediolateral patterning of plant lateral organs, inform a model for the fusion of coleoptilar margins during maize embryo development. Genetic, RNA-targeting, and morphological evidence supports models for cotyledon evolution where the scutellum and coleoptile, respectively, comprise the distal and proximal domains of the highly modified, single grass cotyledon.

Adaptive strategies to drought stress in grasses of the poaceae family under climate change: Physiological, genetic and molecular perspectives: A review.

Drought stress is one of the most critical abiotic factors which negatively impacts on growth, productivity, and survival of plants. Grass species have an important role in the sustainable intensification of cropping systems. This review focus on the specific drought tolerance characteristics in grass species and application of prevalent classical and molecular methods for genetic improvement of them to drought stress. Generally, grass species adapt to drought stress by utilizing more than one strategy including of changes in the root growth, photosynthetic pigments, activation of antioxidant enzymes, and accumulation of compatible osmolytes. They also have other specific characteristics consisted of summer dormancy, drought recovery, and persistence, which lead to drought adaptation after prolonged drought. Studies on different grasses, indicated that most of above mentioned traits usually have positive correlation with drought tolerance. Also, high heritability has been reported for most of them in different grasses. Therefore, an effective index might be considering in identification of drought tolerance genotypes. Recently, high-throughput imaging phenotyping and advanced molecular techniques such as genotyping-by-sequencing (GBS), RNA sequencing, genome-wide association study, and genome editing help conventional breeding methods to increase the accuracy, selection efficiency, genetic gains, and speed of breeding programs for developing drought tolerant cultivars.

Phenotypic screening of seed retention and histological analysis of the abscission zone in Festuca pratensis and Lolium perenne.

BACKGROUND: Seed retention is the basic prerequisite for seed harvest. However, only little breeding progress has been achieved for this trait in the major forage grasses. The aim of this study was to evaluate the potential of plant genetic resources of the important fodder grasses Festuca pratensis Huds. and Lolium perenne L. as source for seed retention in the breeding process. Furthermore, the morphology of the abscission zone, where shattering occurs, was studied on the cell tissue level in different developmental stages of contrasting accessions. RESULTS: 150 and 286 accessions of Festuca pratensis and Lolium perenne were screened for seed retention, respectively. Contrasting accessions were selected to be tested in a second year. We found a great variation in seed retention in Festuca pratensis and Lolium perenne, ranging from 13 to 71% (average: 35%) and 12 to 94% (average: 49%), respectively, in the first year. Seed retention was generally lower in the second year. Cultivars were within the accessions with highest seed retention in Festuca pratensis, but had lower seed retention than ecotypes in Lolium perenne. Field-shattered seeds had a lower thousand grain weight than retained seeds. Cell layers of the abscission zone appeared already in early seed stages and were nested within each other in accessions with high seed retention, while there were two to three superimposed layers in accessions with low seed retention. CONCLUSIONS: Plant genetic resources of Lolium perenne might be a valuable source for breeding varieties with high seed retention. However, simultaneous selection for high seed weight is necessary for developing successful commercial cultivars.

Optimising parameters for pilot scale steam explosion and continuous pressurised disc refining of Miscanthus and sugarcane bagasse for xylose and xylo-oligosaccharide release.

The first comparative pre-treatment study of Miscanthus (Mxg) and sugarcane bagasse (SCB) using steam explosion (SE) and pressurised disc refining (PDR) pretreatment to optimise xylose and xylo-oligosaccharide release is described. The current investigation aimed to 1) Develop optimised batch-wise steam explosion parameters for Mxg and SCB, 2) Scale from static batch steam explosion to dynamic continuous pressurised disc refining, 3) Identify, understand, and circumvent scale-up production hurdles. Optimised SE parameters released 82% (Mxg) and 100% (SCB) of the available xylan. Scaling to PDR, Miscanthus yielded 85% xylan, highlighting how robust scouting assessments for boundary process parameters can result in successful technical transfer. In contrast, SCB technical transfer was not straightforward, with significant differences observed between the two processes, 100% (SE) and 58% (PDR). This report underlines the importance of feedstock-specific pretreatment strategies to underpin process development, scale-up, and optimisation of carbohydrate release from biomass.

MicroRNA169 integrates multiple factors to modulate plant growth and abiotic stress responses.

MicroRNA169 (miR169) has been implicated in multi-stress regulation in annual species such as Arabidopsis, maize and rice. However, there is a lack of experimental functional and mechanistic studies of miR169 in plants, especially in perennial species, and its impact on plant growth and development remains unexplored. Creeping bentgrass (Agrostis stolonifera L.) is a C3 cool-season perennial turfgrass of significant environmental and economic importance. In this study, we generated both miR169 overexpression and knockdown transgenic creeping bentgrass lines. We found that miR169 acts as a positive regulator in abiotic stress responses but is negatively associated with plant growth and development, playing multiple critical roles in the growth and environmental adaptation of creeping bentgrass. These roles include differentiated spatial hormone accumulation patterns associated with growth and stress accommodation, elevated antioxidant activity that alleviates oxidative damage induced by stress, ion-channelling membrane components for maintaining homeostasis under saline conditions, and potential cross-talks with stress-regulating transcription factors such as AsHsfA and AsWRKYs. Our results unravel the role of miR169 in modulating plant development and stress responses in perennial grass species. This underlines the potential of manipulating miR169 to generate crop cultivars with desirable traits to meet diverse agricultural demands.

Rhythmic lipid and gene expression responses to chilling in panicoid grasses.

Chilling stress threatens plant growth and development, particularly affecting membrane fluidity and cellular integrity. Understanding plant membrane responses to chilling stress is important for unraveling the molecular mechanisms of stress tolerance. Whereas core transcriptional responses to chilling stress and stress tolerance are conserved across species, the associated changes in membrane lipids appear to be less conserved, as which lipids are affected by chilling stress varies by species. Here, we investigated changes in gene expression and membrane lipids in response to chilling stress during one 24 hour cycle in chilling-tolerant foxtail millet (Setaria italica), and chilling-sensitive sorghum (Sorghum bicolor), and Urochloa (browntop signal grass, Urochloa fusca, lipids only), leveraging their evolutionary relatedness and differing levels of chilling-stress tolerance. We show that most chilling-induced lipid changes are conserved across the three species, while we observed distinct, time-specific responses in chilling-tolerant foxtail millet, indicating the presence of a finely orchestrated adaptive mechanism. We detected rhythmicity in lipid responses to chilling stress in the three grasses, which were also present in Arabidopsis (Arabidopsis thaliana), suggesting the conservation of rhythmic patterns across species and highlighting the importance of accounting for time of day. When integrating lipid datasets with gene expression profiles, we identified potential candidate genes that showed corresponding transcriptional changes in response to chilling stress, providing insights into the differences in regulatory mechanisms between chilling-sensitive sorghum and chilling-tolerant foxtail millet.

Cross-scale analysis reveals interacting predictors of annual and perennial cover in Northern Great Basin rangelands.

Exotic annual grass invasion is a widespread threat to the integrity of sagebrush ecosystems in Western North America. Although many predictors of annual grass prevalence and native perennial vegetation have been identified, there remains substantial uncertainty about how regional-scale and local-scale predictors interact to determine vegetation heterogeneity, and how associations between vegetation and cattle grazing vary with environmental context. Here, we conducted a regionally extensive, one-season field survey across burned and unburned, grazed, public lands in Oregon and Idaho, with plots stratified by aspect and distance to water within pastures to capture variation in environmental context and grazing intensity. We analyzed regional-scale and local-scale patterns of annual grass, perennial grass, and shrub cover, and examined to what extent plot-level variation was contingent on pasture-level predictions of site favorability. Annual grasses were widespread at burned and unburned sites alike, contrary to assumptions of annual grasses depending on fire, and more common at lower elevations and higher temperatures regionally, as well as on warmer slopes locally. Pasture-level grazing pressure interacted with temperature such that annual grass cover was associated positively with grazing pressure at higher temperatures but associated negatively with grazing pressure at lower temperatures. This suggests that pasture-level temperature and grazing relationships with annual grass abundance are complex and context dependent, although the causality of this relationship deserves further examination. At the plot-level within pastures, annual grass cover did not vary with grazing metrics, but perennial cover did; perennial grasses, for example, had lower cover closer to water sources, but higher cover at higher dung counts within a pasture, suggesting contrasting interpretations of these two grazing proxies. Importantly for predictions of ecosystem response to temperature change, we found that pasture-level and plot-level favorability interacted: perennial grasses had a higher plot-level cover on cooler slopes, and this difference across topography was starkest in pastures that were less favorable for perennial grasses regionally. Understanding the mechanisms behind cross-scale interactions and contingent responses of vegetation to grazing in these increasingly invaded ecosystems will be critical to land management in a changing world.

Hybridization in the Subtribe Alopecurinae Dumort. (Poaceae) According to Molecular Phylogenetic Analysis: Different Ploidy Level Tells Different Origin of the Groups.

We performed next-generation sequencing of the 18S rDNA-ITS1-5.8S rDNA region along with traditional Sanger sequencing of rbcL, matK, ndhF, and ITS1-5.8S rDNA-ITS2 to clarify the hybridization pattern in the subtribe Alopecurinae and in the genus Alopecurus in particular. Our data support the hybrid origin of Alopecurus × brachystylus from hybridization between A. geniculatus (sect. Alopecurium) and A. pratensis (sect. Alopecurus). Moreover, in the rDNA of hybrid A. × brachystylus, only A. aequalis-like ribotypes from tetraploid A. geniculatus participated. Surprisingly, we found the traces of introgression of A. arundinaceus-like ribotypes not only in hybrid A. × marssonii (A. geniculatus × A. arundinaceus) but in A. aequalis s. str. as well. A high-polyploid group from the section Alopecurus, A. aggr. alpinus has undoubted hybrid origin: e. g., A. brachystachyus has rDNA from the sect. Alopecurium. Alopecurus alpinus, with its allies, is clearly distinct from other members of the sect. Alopecurus (especially by maternal line) and thus we can re-establish a previous opinion about the separate group to which A. alpinus belongs. Species from the section Colobachne (presumably Alpine grasses from Ancient Mediterranean region) probably hybridized with the A. alpinus group. Even A. myosuroides (sect. Pseudophalaris) that could be referred to the separate genus has ribotypes common with the species of the section Alopecurium (A. aequalis, A. geniculatus) in one of the accessions. Additionally, we found that the possible polyphyletic origin of the genus Limnas. Limnas stelleri is very close to Alopecurus magellanicus according to NGS data, while L. malyschevii is more or less distinct from other studied species of the genus Alopecurus.

Formation of Si nanopillars through partial sacrificing in super passivation reactive ion etching.

The vertical gate-all-around (VGAA) metal-oxide-semiconductor field-effect transistor (MOSFET) holds remarkable potential in the three-dimensional (3D) integrated circuits (ICs), primarily owing to its capacity for vertical integration. The Si nanopillar, a crucial channel in the VGAA MOSFET, is conventionally shaped via the reactive ion etching (RIE) system employing SF6/O2. Past studies have indicated that high O2gas conditions in RIE often result in Si grasses irregular nanostructures, such as nanospikes on the bottom surface, due to over-passivation. However, this study revealed that ultrahigh O2proportions (>70%), especially when combined with low chamber pressure, inhibit the development of Si grasses in the RIE system (termed as super passivation). Nevertheless, this scenario leads to the segmentation of the Si nanopillar. To address this issue, a proposed partial sacrificing method, achieved by sacrificing the upper segment of the nanopillar through prolonged processing time and reduced mask size, successfully yielded Si nanopillars without Si grasses. Furthermore, an empirical model was developed to elucidate how experimental parameters influence etching characteristics, encompassing etching rate and Si nanopillar shape, through a systematic examination of the RIE etching process. This research significantly contributes to the production of VGAA MOSFETs and 3D ICs.

Polygenic architecture of flowering time and its relationship with local environments in the grass Brachypodium distachyon.

Synchronizing the timing of reproduction with the environment is crucial in the wild. Among the multiple mechanisms, annual plants evolved to sense their environment, the requirement of cold-mediated vernalization is a major process that prevents individuals from flowering during winter. In many annual plants including crops, both a long and short vernalization requirement can be observed within species, resulting in so-called early-(spring) and late-(winter) flowering genotypes. Here, using the grass model Brachypodium distachyon, we explored the link between flowering-time-related traits (vernalization requirement and flowering time), environmental variation, and diversity at flowering-time genes by combining measurements under greenhouse and outdoor conditions. These experiments confirmed that B. distachyon natural accessions display large differences regarding vernalization requirements and ultimately flowering time. We underline significant, albeit quantitative effects of current environmental conditions on flowering-time-related traits. While disentangling the confounding effects of population structure on flowering-time-related traits remains challenging, population genomics analyses indicate that well-characterized flowering-time genes may contribute significantly to flowering-time variation and display signs of polygenic selection. Flowering-time genes, however, do not colocalize with genome-wide association peaks obtained with outdoor measurements, suggesting that additional genetic factors contribute to flowering-time variation in the wild. Altogether, our study fosters our understanding of the polygenic architecture of flowering time in a natural grass system and opens new avenues of research to investigate the gene-by-environment interaction at play for this trait.

Nutrient uptake efficiency and stoichiometry for different plant functional groups on spoil heap after hard coal mining in Upper Silesia, Poland.

Various plant functional groups (PFGs) used in the reclamation of post-mining heaps may differ in their nutrient uptake efficiency and thus in their effect on the ecosystem development. The effect of PFGs may be additionally modified by the applied reclamation measures such as e.g. topsoiling. In this study we compared the nutrient uptake efficiencies and plant stoichiometry for two PFGs (grasses and forbs) growing on the sites reclaimed by applying topsoil (TS) and unreclaimed sites on carboniferous bare rock (BR) in hard coal spoil heap in Upper Silesia (southern Poland). Basic soil parameters, including pH, texture, soil organic carbon, and nutrients (N, P, K, Ca, and Mg), were measured, and the aboveground plant biomass and nutrient content in plant tissue were determined. Forbs were characterized by a larger biomass and higher nutrient concentrations (except for P) than grasses. The TS treatment supported higher concentrations of N and P in plant tissues but not to the level ensuring more significant primary biomass production. The nutrient concentration and elemental stoichiometry in plant tissue indicated that N was the primary limiting element. However, the major growth limitation for N-fixing forbs was from P. Forbs were much more efficient in nutrient uptake than grasses, independent of the reclamation treatment. Therefore, they stimulate nutrient cycling in the restored ecosystems more than grasses.

The operation of PEPCK increases light harvesting plasticity in C4 NAD-ME and NADP-ME photosynthetic subtypes: A theoretical study.

The repeated emergence of NADP-malic enzyme (ME), NAD-ME and phosphoenolpyruvate carboxykinase (PEPCK) subtypes of C4 photosynthesis are iconic examples of convergent evolution, which suggests that these biochemistries do not randomly assemble, but are instead specific adaptations resulting from unknown evolutionary drivers. Theoretical studies that are based on the classic biochemical understanding have repeatedly proposed light-use efficiency as a possible benefit of the PEPCK subtype. However, quantum yield measurements do not support this idea. We explore this inconsistency here via an analytical model that features explicit descriptions across a seamless gradient between C4 biochemistries to analyse light harvesting and dark photosynthetic metabolism. Our simulations show that the NADP-ME subtype, operated by the most productive crops, is the most efficient. The NAD-ME subtype has lower efficiency, but has greater light harvesting plasticity (the capacity to assimilate CO2 in the broadest combination of light intensity and spectral qualities). In both NADP-ME and NAD-ME backgrounds, increasing PEPCK activity corresponds to greater light harvesting plasticity but likely imposed a reduction in photosynthetic efficiency. We draw the first mechanistic links between light harvesting and C4 subtypes, providing the theoretical basis for future investigation.

Invasive-dominated grasslands in Hawai'i are resilient to disturbance.

Non-native-dominated landscapes may arise from invasion by competitive plant species, disturbance and invasion of early-colonizing species, or some combination of these. Without knowing site history, however, it is difficult to predict how native or non-native communities will reassemble after disturbance events. Given increasing disturbance levels across anthropogenically impacted landscapes, predictive understanding of these patterns is important. We asked how disturbance affected community assembly in six invaded habitat types common in dryland, grazed landscapes on Island of Hawai'i. We mechanically disturbed 100 m2 plots in six vegetation types dominated by one of four invasive perennial grasses (Cenchrus ciliaris, Cenchrus clandestinus, Cenchrus setaceus, or Melinis repens), a native shrub (Dodonaea viscosa), or a native perennial bunchgrass (Eragrostis atropioides). We censused vegetation before disturbance and monitored woody plant colonization and herbaceous cover for 21 months following the disturbance, categorizing species as competitors, colonizers, or a combination, based on recovery patterns. In addition, we planted individuals of the native shrub and bunchgrass and monitored survival to overcome dispersal limitation of native species when exploring these patterns. We found that the dominant vegetation types showed variation in post-disturbance syndrome, and that the variation in colonizer versus competitor syndrome occurred both between species, but also within species among different vegetation types. Although there were flushes of native shrub seedlings, these did not survive to 21 months within invaded habitats, probably due to regrowth by competitive invasive grasses. Similarly, survival of planted native individuals was related to the rate of regrowth by dominant species. Regardless of colonization/competitor syndrome, however, all dominant vegetation types were relatively resilient to change. Our results highlight that the altered post-agricultural, invaded grassland landscapes in Hawai'i are stable states. More generally, they point to the importance of resident communities and their effects on species interactions and seed availability in shaping plant community response to disturbance.

Review: Nitrogen acquisition, assimilation, and seasonal cycling in perennial grasses.

Perennial grasses seasonal nitrogen (N) cycle extends the residence and reuse time of N within the plant system, thereby enhancing N use efficiency. Currently, the mechanism of N metabolism has been extensively examined in model plants and annual grasses, and although perennial grasses exhibit similarities, they also possess distinct characteristics. Apart from assimilating and utilizing N throughout the growing season, perennial grasses also translocate N from aerial parts to perennial tissues, such as rhizomes, after autumn senescence. Subsequently, they remobilize the N from these perennial tissues to support new growth in the subsequent year, thereby ensuring their persistence. Previous studies indicate that the seasonal storage and remobilization of N in perennial grasses are not significantly associated with winter survival despite some amino acids and proteins associated with low temperature tolerance accumulating, but primarily with regrowth during the subsequent spring green-up stage. Further investigation can be conducted in perennial grasses to explore the correlation between stored N and dormant bud outgrowth in perennial tissues, such as rhizomes, during the spring green-up stage, building upon previous research on the relationship between N and axillary bud outgrowth in annual grasses. This exploration on seasonal N cycling in perennial grasses can offer valuable theoretical insights for new perennial grasses varieties with high N use efficiency through the application of gene editing and other advanced technologies.