Climate, atmospheric pCO sub(2), and fire all may exert major influences on the relative abundance of C sub(3) and C sub(4) grasses in the present-day vegetation. However, the relative role of these ...factors in driving variation in C sub(3) and C sub(4) grass abundances in the paleorecord is uncertain, and C sub(4) abundance is often interpreted narrowly as a proxy indicator of aridity or pCO sub(2). We measured delta super(13)C values of individual grains of grass (Poaceae) pollen in the sediments of two sites in southeastern Australia to assess changes in the proportions of C sub(3) and C sub(4) grasses during the past 25,000 years. These data were compared with shifts in pCO sub(2), temperature, moisture balance, and fire to assess how these factors were related to long-term variation of C sub(4) grass abundance during the late Quaternary. At Caledonia Fen, a high-elevation site in the Snowy Mountains, C sub(4) grass abundance decreased from an average of 66% during the glacial period to 11% during the Holocene, primarily in response to increased pCO sub(2) and temperature. In contrast, this pattern did not exist in low-elevation savannah woodlands around Tower Hill Northwest Crater, where C sub(4) grass abundance instead varied in response to shifts in regional aridity. Fire did not appear to have strongly influenced the proportions of C sub(3) and C sub(4) grasses on the landscape at millennial timescales at either site. These patterns are similar to those of a recent study in East Africa, suggesting that elevation-related climatic differences influence how the abundance of C sub(3) and C sub(4) grasses responds to shifts in climate and pCO sub(2). These results caution against using C sub(4) plant abundance as a proxy indicator of either climate or pCO sub(2) without an adequate understanding of key controlling factors.
The radiation of a lineage and its rise to ecological dominance are distinct phenomena and driven by different processes. For example, paleoecological data has been used to show that the Cretaceous ...angiosperm radiation did not coincide with their rise to dominance. Using a phylogenetic approach, we here explored the evolution of C4 grasses and evaluated whether the diversification of this group and its rise to ecological dominance in the late Miocene were decoupled. We assembled a matrix including 675 grass species of the PACMAD clade and 2784 characters (ITS and ndhF ) to run a molecular dating analysis using three fossils as reference calibrations. We coded species as C sub( 3) vs. C sub( 4) and reconstructed ancestral states under maximum likelihood. We used the program BiSSE to test whether rates of diversification are correlated with photosynthetic pathway and whether the radiation of C sub( 4) lineages preceded or coincided with their rise to ecological dominance from ~10 Ma. C sub( 4) grass lineages first originated around 35 Ma at the time of the Eocene-Oligocene transition. Accelerated diversification of C4 lineages did not coincide with their rise to ecological dominance. C sub( 4)-dominated grasslands have expanded only since the Late Miocene and Pliocene. The initial diversification of their biotic elements can be tracked back as far as the Eocene-Oligocene transition. We suggest that shifts in taxonomic diversification and ecological dominance were stimulated by different factors, as in the case of the early angiosperms in the Cretaceous.
Niche dimensionality provides a general theoretical explanation for biodiversity-more niches, defined by more limiting factors, allow for more ways that species can coexist. Because plant species ...compete for the same set of limiting resources, theory predicts that addition of a limiting resource eliminates potential trade-offs, reducing the number of species that can coexist. Multiple nutrient limitation of plant production is common and therefore fertilization may reduce diversity by reducing the number or dimensionality of belowground limiting factors. At the same time, nutrient addition, by increasing biomass, should ultimately shift competition from belowground nutrients towards a one-dimensional competitive trade-off for light. Here we show that plant species diversity decreased when a greater number of limiting nutrients were added across 45 grassland sites from a multi-continent experimental network. The number of added nutrients predicted diversity loss, even after controlling for effects of plant biomass, and even where biomass production was not nutrient-limited. We found that elevated resource supply reduced niche dimensionality and diversity and increased both productivity and compositional turnover. Our results point to the importance of understanding dimensionality in ecological systems that are undergoing diversity loss in response to multiple global change factors.
We report results of field collections, laboratory rearing, and behavioral observations of tephritids belonging to the tribes Acanthonevrini and Gastrozonini in Malaysia and Thailand. The focus of ...the study was on general biology, seasonal history, mating, oviposition, larval biology, larval habits, and microhabitats. Host association with bamboo was unequivocally established for 31 species. Adult flies fed on liquids oozing from plants or other sources. Most species developed in the rainy season, when bamboo shoots were available. In Thailand, adult flies gathered along streams in the dry season. Observed sexual behavior patterns appeared to be simple in Gastrozonini, whereas in some Acanthonevrini, the males produced a foamy "nuptial gift," which was offered to females during courtship. Eggs were laid under sheaths or in injuries to the bamboo surface. The main obstacle to oviposition and penetration of shoots appeared to be the hard culm sheaths.Thelarvae entered feeding substrates via injuries, holes created by other insects, or by squeezing in between culm sheaths and bamboo walls. Larvae of Gastrozonini and Rioxoptilona (Acanthonevrini) fed on living or dead bamboo shoots. Larvae of other Acanthonevrini developed in water-filled internode cavities, scraping particles from walls or collecting them from the water surface. Bamboo growth stages and degree of protection by culm sheaths were used to classify microhabitats. These determined to a large extent which guilds of flies could be found. While larvae of some bamboo tephritids destroyed thin bamboo shoots or branches, most acted as secondary pests and did not cause substantial economic losses.
The micropropagation of Guadua angustifolia Kunth, commonly known as giant bamboo, using semi-solid culture medium, is reported to have low multiplication rates. This study evaluated the ...multiplication index of G. angustifolia in a temporary immersion system (RITA super( registered )), comparing results with those obtained using a semi-solid culture medium. The treatments consisted of either three or four 2-min immersions per day and use of semi-solid culture medium, which consisted of MS supplemented with 3.0 mg L super(-1) of the cytokinin benzylaminopurine (BAP). Equipment consisted of 20 vessels for automated RITA super( registered ), each containing 200 ml of culture medium. Immersions were performed for 2 min at two different frequency intervals (6 and 8 h). Large clumps of G. angustifolia with 1, 2 or 3 stems were inoculated depending on the treatment. Best results were obtained with four immersion cycles per day (every 6 h), with a multiplication index of 2.7 shoots per original explant (axillary buds) and greater rhizome growth. Overall, the temporary immersion system performed better than the semi-solid medium in terms of shoot multiplication rates and rhizome growth. Further studies should be conducted to develop an application for RITA super( registered )for use in the commercial production of G. angustifolia.
The evolution of grasses using C₄ photosynthesis and their sudden rise to ecological dominance 3 to 8 million years ago is among the most dramatic examples of biome assembly in the geological record. ...A growing body of work suggests that the patterns and drivers of C₄ grassland expansion were considerably more complex than originally assumed. Previous research has benefited substantially from dialog between geologists and ecologists, but current research must now integrate fully with phylogenetics. A synthesis of grass evolutionary biology with grassland ecosystem science will further our knowledge of the evolution of traits that promote dominance in grassland systems and will provide a new context in which to evaluate the relative importance of C₄ photosynthesis in transforming ecosystems across large regions of Earth.
Form, development and function of grass stomata Nunes, Tiago D. G.; Zhang, Dan; Raissig, Michael T.
The Plant journal : for cell and molecular biology,
February 2020, Letnik:
101, Številka:
4
Journal Article
Recenzirano
Odprti dostop
Summary
Stomata are cellular breathing pores on leaves that open and close to absorb photosynthetic carbon dioxide and to restrict water loss through transpiration, respectively. Grasses (Poaceae) ...form morphologically innovative stomata, which consist of two dumbbell‐shaped guard cells flanked by two lateral subsidiary cells (SCs). This ‘graminoid’ morphology is associated with faster stomatal movements leading to more water‐efficient gas exchange in changing environments. Here, we offer a genetic and mechanistic perspective on the unique graminoid form of grass stomata and the developmental innovations during stomatal cell lineage initiation, recruitment of SCs and stomatal morphogenesis. Furthermore, the functional consequences of the four‐celled, graminoid stomatal morphology are summarized. We compile the identified players relevant for stomatal opening and closing in grasses, and discuss possible mechanisms leading to cell‐type‐specific regulation of osmotic potential and turgor. In conclusion, we propose that the investigation of functionally superior grass stomata might reveal routes to improve water‐stress resilience of agriculturally relevant plants in a changing climate.
Significance Statement
A key challenge for plants is to efficiently use water, particularly when growing in a hot and dry climate. Stomata – cellular breathing pores on leaves that mediate gas exchange between plant and atmosphere – have a pivotal role in controlling water‐use efficiency. Stomata can adjust their pore size to balance carbon dioxide uptake with water vapour loss. Interestingly, grasses like the three most important food crops rice, maize and wheat have improved stomata that can regulate water use more efficiently by opening and closing faster than other plants. Rapid stomatal movements are linked to the grass stomata's unique morphology consisting of dumbbell‐shaped guard cells and lateral subsidiary or helper cells. Recently, work on domesticated and wild grass species has started to reveal some of the secrets regarding how grass stomata form and function more efficiently.
ABSTRACT
Poaceae (the grasses) is arguably the most successful plant family, in terms of its global occurrence in (almost) all ecosystems with angiosperms, its ecological dominance in many ...ecosystems, and high species richness. We suggest that the success of grasses is best understood in context of their capacity to colonize, persist, and transform environments (the “Viking syndrome”). This results from combining effective long‐distance dispersal, efficacious establishment biology, ecological flexibility, resilience to disturbance and the capacity to modify environments by changing the nature of fire and mammalian herbivory. We identify a diverse set of functional traits linked to dispersal, establishment and competitive abilities. Enhanced long‐distance dispersal is determined by anemochory, epizoochory and endozoochory and is facilitated via the spikelet (and especially the awned lemma) which functions as the dispersal unit. Establishment success could be a consequence of the precocious embryo and large starch reserves, which may underpin the extremely short generation times in grasses. Post‐establishment genetic bottlenecks may be mitigated by wind pollination and the widespread occurrence of polyploidy, in combination with gametic self‐incompatibility. The ecological competitiveness of grasses is corroborated by their dominance across the range of environmental extremes tolerated by angiosperms, facilitated by both C3 and C4 photosynthesis, well‐developed frost tolerance in several clades, and a sympodial growth form that enabled the evolution of both annual and long‐lived life forms. Finally, absence of investment in wood (except in bamboos), and the presence of persistent buds at or below ground level, provides tolerance of repeated defoliation (whether by fire, frost, drought or herbivores). Biotic modification of environments via feedbacks with herbivory or fire reinforce grass dominance leading to open ecosystems. Grasses can be both palatable and productive, fostering high biomass and diversity of mammalian herbivores. Many grasses have a suite of architectural and functional traits that facilitate frequent fire, including a tufted growth form, and tannin‐like substances in leaves which slow decomposition. We mapped these traits over the phylogeny of the Poales, spanning the grasses and their relatives, and demonstrated the accumulation of traits since monocots originated in the mid‐Cretaceous. Although the sympodial growth form is a monocot trait, tillering resulting in the tufted growth form most likely evolved within the grasses. Similarly, although an ovary apparently constructed of a single carpel evolved in the most recent grass ancestor, spikelets and the awned lemma dispersal units evolved within the grasses. Frost tolerance and C4 photosynthesis evolved relatively late (late Palaeogene), and the last significant trait to evolve was probably the production of tannins, associated with pyrophytic savannas. This fits palaeobotanical data, suggesting several phases in the grass success story: from a late Cretaceous origin, to occasional tropical grassland patches in the later Palaeogene, to extensive C3 grassy woodlands in the early–middle Miocene, to the dramatic expansion of the tropical C4 grass savannas and grasslands in the Pliocene, and the C3 steppe grasslands during the Pleistocene glacial periods. Modern grasslands depend heavily on strongly seasonal climates, making them sensitive to climate change.
Genomic DNA base composition (GC content) is predicted to significantly affect genome functioning and species ecology. Although several hypotheses have been put forward to address the biological ...impact of GC content variation in microbial and vertebrate organisms, the biological significance of GC content diversity in plants remains unclear because of a lack of sufficiently robust genomic data. Using flow cytometry, we report genomic GC contents for 239 species representing 70 of 78 monocot families and compare them with genomic characters, a suite of life history traits and climatic niche data using phylogeny-based statistics. GC content of monocots varied between 33.6% and 48.9%, with several groups exceeding the GC content known for any other vascular plant group, highlighting their unusual genome architecture and organization. GC content showed a quadratic relationship with genome size, with the decreases in GC content in larger genomes possibly being a consequence of the higher biochemical costs of GC base synthesis. Dramatic decreases in GC content were observed in species with holocentric chromosomes, whereas increased GC content was documented in species able to grow in seasonally cold and/or dry climates, possibly indicating an advantage of GC-rich DNA during cell freezing and desiccation. We also show that genomic adaptations associated with changing GC content might have played a significant role in the evolution of the Earth’s contemporary biota, such as the rise of grass-dominated biomes during the mid-Tertiary. One of the major selective advantages of GC-rich DNA is hypothesized to be facilitating more complex gene regulation.
Significance Our large-scale survey of genomic nucleotide composition across monocots has enabled the first rigorous testing, to our knowledge, of its biological significance in plants. We show that genomic DNA base composition (GC content) is significantly associated with genome size and holocentric chromosomal structure. GC content may also have deep ecological relevance, because changes in GC content may have played a significant role in the evolution of Earth’s biota, especially the rise of grass-dominated biomes during the mid-Tertiary. The discovery of several groups with very unusual GC contents highlights the need for in-depth analysis to uncover the full extent of genomic diversity. Furthermore, our stratified sampling method of distribution data and quantile regression-like logic of phylogenetic analyses may find wider applications in the analysis of spatially heterogeneous data.
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