A global database of C4 photosynthesis in grasses

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.

Reassessment of the risks of climate change for terrestrial ecosystems

Forecasting the risks of climate change for species and ecosystems is necessary for developing targeted conservation strategies. Previous risk assessments mapped the exposure of the global land surface to changes in climate. However, this procedure is unlikely to robustly identify priority areas for conservation actions because nonlinear physiological responses and colimitation processes ensure that ecological changes will not map perfectly to the forecast climatic changes. Here, we combine ecophysiological growth models of 135,153 vascular plant species and plant growth-form information to transform ambient and future climatologies into phytoclimates, which describe the ability of climates to support the plant growth forms that characterize terrestrial ecosystems. We forecast that 33% to 68% of the global land surface will experience a significant change in phytoclimate by 2070 under representative concentration pathways RCP 2.6 and RCP 8.5, respectively. Phytoclimates without present-day analogue are forecast to emerge on 0.3-2.2% of the land surface and 0.1-1.3% of currently realized phytoclimates are forecast to disappear. Notably, the geographic pattern of change, disappearance and novelty of phytoclimates differs markedly from the pattern of analogous trends in climates detected by previous studies, thereby defining new priorities for conservation actions and highlighting the limits of using untransformed climate change exposure indices in ecological risk assessments. Our findings suggest that a profound transformation of the biosphere is underway and emphasize the need for a timely adaptation of biodiversity management practices.

Spatial ecology of moose in Sweden: Combined Sr-O-C isotope analyses of bone and antler

The study of spatial (paleo)ecology in mammals is critical to understand how animals adapt to and exploit their environment. In this work we analysed the 87Sr/86Sr, δ18O and δ13C isotope composition of 65 moose bone and antler samples from Sweden from wild-shot individuals dated between 1800 and 1994 to study moose mobility and feeding behaviour for (paleo)ecological applications. Sr data were compared with isoscapes of the Scandinavian region, built ad-hoc during this study, to understand how moose utilise the landscape in Northern Europe. The 87Sr/86Sr isoscape was developed using a machine-learning approach with external geo-environmental predictors and literature data. Similarly, a δ18O isoscape, obtained from average annual precipitation δ18O values, was employed to highlight differences in the isotope composition of the local environment vs. bone/antler. Overall, 82% of the moose samples were compatible with the likely local isotope composition (n = 53), suggesting that they were shot not far from their year-round dwelling area. 'Local' samples were used to calibrate the two isoscapes, to improve the prediction of provenance for the presumably 'non-local' individuals. For the latter (n = 12, of which two are antlers and ten are bones), the probability of geographic origin was estimated using a Bayesian approach by combining the two isoscapes. Interestingly, two of these samples (one antler and one bone) seem to come from areas more than 250 km away from the place where the animals were hunted, indicating a possible remarkable intra-annual mobility. Finally, the δ13C data were compared with the forest cover of Sweden and ultimately used to understand the dietary preference of moose. We interpreted a difference in δ13C values of antlers (13C-enriched) and bones (13C-depleted) as a joint effect of seasonal variations in moose diet and, possibly, physiological stresses during winter-time, i.e., increased consumption of endogenous 13C-depleted lipids.

Early human selection of crops' wild progenitors explains the acquisitive physiology of modern cultivars

Crops have resource-acquisitive leaf traits, which are usually attributed to the process of domestication. However, early choices of wild plants amenable for domestication may also have played a key role in the evolution of crops' physiological traits. Here we compiled data on 1,034 annual herbs to place the ecophysiological traits of 69 crops' wild progenitors in the context of global botanical variation, and we conducted a common-garden experiment to measure the effects of domestication on crop ecophysiology. Our study found that crops' wild progenitors already had high leaf nitrogen, photosynthesis, conductance and transpiration and soft leaves. After domestication, ecophysiological traits varied little and in idiosyncratic ways. Crops did not surpass the trait boundaries of wild species. Overall, the resource-acquisitive strategy of crops is largely due to the inheritance from their wild progenitors rather than to further breeding improvements. Our study concurs with recent literature highlighting constraints of crop breeding for faster ecophysiological traits.

Diversification of flowering plants in space and time

The rapid diversification and high species richness of flowering plants is regarded as 'Darwin's second abominable mystery'. Today the global spatiotemporal pattern of plant diversification remains elusive. Using a newly generated genus-level phylogeny and global distribution data for 14,244 flowering plant genera, we describe the diversification dynamics of angiosperms through space and time. Our analyses show that diversification rates increased throughout the early Cretaceous and then slightly decreased or remained mostly stable until the end of the Cretaceous-Paleogene mass extinction event 66 million years ago. After that, diversification rates increased again towards the present. Younger genera with high diversification rates dominate temperate and dryland regions, whereas old genera with low diversification dominate the tropics. This leads to a negative correlation between spatial patterns of diversification and genus diversity. Our findings suggest that global changes since the Cenozoic shaped the patterns of flowering plant diversity and support an emerging consensus that diversification rates are higher outside the tropics.

Global distribution, climatic preferences and photosynthesis-related traits of C4 eudicots and how they differ from those of C4 grasses

C₄ is one of three known photosynthetic processes of carbon fixation in flowering plants. It evolved independently more than 61 times in multiple angiosperm lineages and consists of a series of anatomical and biochemical modifications to the ancestral C3 pathway increasing plant productivity under warm and light-rich conditions. The C4 lineages of eudicots belong to seven orders and 15 families, are phylogenetically less constrained than those of monocots and entail an enormous structural and ecological diversity. Eudicot C4 lineages likely evolved the C4 syndrome along different evolutionary paths. Therefore, a better understanding of this diversity is key to understanding the evolution of this complex trait as a whole. By compiling 1207 recognised C4 eudicots species described in the literature and presenting trait data among these species, we identify global centres of species richness and of high phylogenetic diversity. Furthermore, we discuss climatic preferences in the context of plant functional traits. We identify two hotspots of C4 eudicot diversity: arid regions of Mexico/Southern United States and Australia, which show a similarly high number of different C4 eudicot genera but differ in the number of C4 lineages that evolved in situ. Further eudicot C4 hotspots with many different families and genera are in South Africa, West Africa, Patagonia, Central Asia and the Mediterranean. In general, C4 eudicots are diverse in deserts and xeric shrublands, tropical and subtropical grasslands, savannas and shrublands. We found C4 eudicots to occur in areas with less annual precipitation than C4 grasses which can be explained by frequently associated adaptations to drought stress such as among others succulence and salt tolerance. The data indicate that C4 eudicot lineages utilising the NAD-ME decarboxylating enzyme grow in drier areas than those using the NADP-ME decarboxylating enzyme indicating biochemical restrictions of the later system in higher temperatures. We conclude that in most eudicot lineages, C4 evolved in ancestrally already drought-adapted clades and enabled these to further spread in these habitats and colonise even drier areas.

A Machine Learning Framework Identifies Plastid-Encoded Proteins Harboring C3 and C4 Distinguishing Sequence Information

C4 photosynthesis is known to have at least 61 independent origins across plant lineages making it one of the most notable examples of convergent evolution. Of the >60 independent origins, a predicted 22-24 origins, encompassing greater than 50% of all known C4 species, exist within the Panicoideae, Arundinoideae, Chloridoideae, Micrairoideae, Aristidoideae, and Danthonioideae (PACMAD) clade of the Poaceae family. This clade is therefore primed with species ideal for the study of genomic changes associated with the acquisition of the C4 photosynthetic trait. In this study, we take advantage of the growing availability of sequenced plastid genomes and employ a machine learning (ML) approach to screen for plastid genes harboring C3 and C4 distinguishing information in PACMAD species. We demonstrate that certain plastid-encoded protein sequences possess distinguishing and informative sequence information that allows them to train accurate ML C3/C4 classification models. Our RbcL-trained model, for example, informs a C3/C4 classifier with greater than 99% accuracy. Accurate prediction of photosynthetic type from individual sequences suggests biologically relevant, and potentially differing roles of these sequence products in C3 versus C4 metabolism. With this ML framework, we have identified several key sequences and sites that are most predictive of C3/C4 status, including RbcL, subunits of the NAD(P)H dehydrogenase complex, and specific residues within, further highlighting their potential significance in the evolution and/or maintenance of C4 photosynthetic machinery. This general approach can be applied to uncover intricate associations between other similar genotype-phenotype relationships.

Limited climatic space for alternative ecosystem states in Africa

One of the foundational premises of ecology is that climate determines ecosystems. This has been challenged by alternative ecosystem state models, which illustrate that internal ecosystem dynamics acting on the initial ecosystem state can overwhelm the influence of climate, and by observations suggesting that climate cannot reliably discriminate forest and savanna ecosystem types. Using a novel phytoclimatic transform, which estimates the ability of climate to support different types of plants, we show that climatic suitability for evergreen trees and C4 grasses are sufficient to discriminate between forest and savanna in Africa. Our findings reassert the dominant influence of climate on ecosystems and suggest that the role of feedbacks causing alternative ecosystem states is less prevalent than has been suggested.

Geographic distribution of C4 species and its phylogenetic structure across China

Over the past fifty years, the distribution patterns of C₄ species, across large spatial scales, are largely ignored. Here, we endeavored to examine patterns in the taxonomic and phylogenetic diversity of species with C₄ photosynthetic pathways across the broad spatial extent of China and relate those to climatic gradients. We built a database of all plants with the C₄ photosynthetic pathway in China. We analyzed the geographic distributions, taxonomic diversity, phylogenetic diversity, and phylogenetic structure of all C₄ species, as well as the three families with the most C₄ species (Poaceae, Amaranthaceae and Cyperaceae), and compared their values along temperature and precipitation gradients at two scales-the level of the province and at the 100 x 100 km grid cell. We found 644 C₄ plants (belonging to 23 families 165 genera) in China, with Poaceae (57%), Amaranthaceae (17%), Cyperaceae (13%) accounting for the majority of species. Standardized effect size values of phylogenetic distances were negative overall, indicating that C₄ species showed a phylogenetic clustering pattern. Southern China had the highest species richness and the highest degree of phylogenetic clustering. C₄ tended to be more phylogenetically over-dispersed in regions with colder and/or drier climates, but more clustered in warmer and/or wetter climates. Patterns within individual families were more nuanced. The distribution of C₄ species and its phylogenetic structure across China was constrained by temperature and precipitation. C₄ species showed a phylogenetic clustering pattern across China, while different families showed more nuanced responses to climate variation, suggesting a role for evolutionary history.

Relationships of the competitor, stress tolerator, ruderal functional strategies of grass species with lifespan, photosynthetic type, naturalization and climate

Grass species (family Poaceae) are globally distributed, adapted to a wide range of climates and express a diversity of functional strategies. We explored the functional strategies of grass species using the competitor, stress tolerator, ruderal (CSR) system and asked how a species' strategy relates to its functional traits, climatic distribution and propensity to become naturalized outside its native range. We used a global set of trait data for grass species to classify functional strategies according to the CSR system based on leaf traits. Differences in strategies in relation to lifespan (annual or perennial), photosynthetic type (C₃ or C₄), or naturalisation (native or introduced) were investigated. In addition, correlations with traits not included in the CSR classification were analyzed, and a model was fitted to predict a species' average mean annual temperature and annual precipitation across its range as a function of CSR scores. Values for competitiveness were higher in C₄ species than in C₃ species, values for stress tolerance were higher in perennials than in annuals, and introduced species had more pronounced competitive-ruderal strategies than native species. Relationships between the CSR classification, based on leaf traits, and other functional traits were analyzed. Competitiveness was positively correlated with height, while ruderality was correlated with specific root length, indicating that both above- and belowground traits underlying leaf and root economics contribute to realized CSR strategies. Further, relationships between climate and CSR classification showed that species with competitive strategies were more common in warm climates and at high precipitation, whereas species with stress tolerance strategies were more common in cold climates and at low precipitation. The findings presented here demonstrate that CSR classification of functional strategies based on leaf traits matches expectations for the adaptations of grass species that underlie lifespan, photosynthetic type, naturalization and climate.

An Update of the Cenchrinae (Poaceae, Panicoideae, Paniceae) and a New Genus for the Subtribe to Clarify the Dubious Position of a Species of Panicum L

Subtribe Cenchrinae, so-called as the "bristle clade", is a monophyletic group of panicoid grasses characterized by having sterile branches or bristles on the inflorescences in most of its species. Within this subtribe is also placed Panicum antidotale Retz., an "incertae sedis" species of Panicum L. which lacks bristles along the inflorescence. In this study, we present an update of the subtribe Cenchrinae based on molecular, morphological, and anatomical evidence to clarify the systematic position of P. antidotale in the Cenchrinae, excluding it from Panicum and establishing it in a new genus (i.e., Janochloa Zuloaga & Delfini); the morphological features distinguishing the new genus from other closely related taxa are properly discussed and an identification key to the 24 genera recognized within Cenchrinae is presented. We also add American Setaria species, not tested before, of subgenera Paurochaetium and Reverchoniae, discussing the position of these taxa in actual phylogeny of the genus as well as defining placements in the tree of Setaria species that were imprecisely located in previous analyses. A comparison with the results from other studies, comments on Stenotaphrum Trin. and a brief discussion on conflicting placements in Cenchrus and related taxa, and of Acritochaete Pilg. are also included.

The China plant trait database version 2

Plant functional traits represent adaptive strategies to the environment, linked to biophysical and biogeochemical processes and ecosystem functioning. Compilations of trait data facilitate research in multiple fields from plant ecology through to land-surface modelling. Here we present version 2 of the China Plant Trait Database, which contains information on morphometric, physical, chemical, photosynthetic and hydraulic traits from 1529 unique species in 140 sites spanning a diversity of vegetation types. Version 2 has five improvements compared to the previous version: (1) new data from a 4-km elevation transect on the edge of Tibetan Plateau, including alpine vegetation types not sampled previously; (2) inclusion of traits related to hydraulic processes, including specific sapwood conductance, the area ratio of sapwood to leaf, wood density and turgor loss point; (3) inclusion of information on soil properties to complement the existing data on climate and vegetation (4) assessments and flagging the reliability of individual trait measurements; and (5) inclusion of standardized templates for systematical field sampling and measurements.

Anthropogenic land use and urbanization alter the dynamics and increase the export of dissolved carbon in an urbanized river system

Greenhouse gas emissions from urban rivers play a crucial role in global carbon (C) cycling, this is tightly linked to dissolved C in rivers but research gaps remain. The effects of urbanization and anthropogenic land-use change on riverine dissolved carbon dynamics were investigated in a temperate river, the River Kelvin in UK. The river was constantly a source of methane (CH₄) and carbon dioxide (CO₂) to the atmosphere (excess concentration of CH₄ ranged from 13 to 4441 nM, and excess concentration of CO₂ ranged from 2.6 to 230.6 μM), and dissolved C concentrations show significant spatiotemporal variations (p < 0.05), reflecting a variety of proximal sources and controls. For example, the concentration variation of dissolved CH₄ and dissolved CO₂ were heavily controlled by the proximity of coal mine infrastructure in the tributary near the river head (~ 2 km) but were more likely controlled by adjacent landfills in the midstream section of the rivers main channel. Concentration and isotopic evidence revealed an important anthropogenic control on the riverine export of CO₂ and dissolved organic carbon (DOC). However, dissolved inorganic carbon (DIC) input via groundwater at the catchment scale primarily controlled the dynamics of riverine DIC. Furthermore, the positive relationship between the isotopic composition of DIC and CO₂ (r = 0.79, p < 0.01) indicates the DIC pool was at times also significantly influenced by soil respiratory CO₂. Both DIC and DOC showed a weak but significant correlation with the proportion of urban/suburban land use, suggesting increased dissolved C export resulting from urbanization. This research elucidates a series of potentially key effects anthropogenic activities and land-use practices can have on riverine C dynamics and highlights the need for future consideration of the direct effects urbanization has on riverine C dynamics.

Plant Evolution History Overwhelms Current Environment Gradients in Affecting Leaf Chlorophyll Across the Tibetan Plateau

AIMS

Leaf chlorophyll (Chl) is a fundamental component and good proxy for plant photosynthesis. However, we know little about the large-scale patterns of leaf Chl and the relative roles of current environment changes vs. plant evolution in driving leaf Chl variations.

LOCATIONS

The east to west grassland transect of the Tibetan Plateau.

METHODS

We performed a grassland transect over 1,600 km across the Tibetan Plateau, measuring leaf Chl among 677 site-species.

RESULTS

Leaf Chl showed a significantly spatial pattern across the grasslands in the Tibetan Plateau, decreasing with latitude but increasing with longitude. Along with environmental gradient, leaf Chl decreased with photosynthetically active radiation (PAR), but increased with water availability and soil nitrogen availability. Furthermore, leaf Chl also showed significant differences among functional groups (C₄ > C₃ species; legumes < non-legume species), but no difference between annual and perennial species. However, we surprisingly found that plant evolution played a dominant role in shaping leaf Chl variations when comparing the sum and individual effects of all the environmental factors above. Moreover, we revealed that leaf Chl non-linearly decreased with plant evolutionary divergence time. This well-matches the non-linearly increasing trend in PAR or decreasing trend in temperature during the geological time-scale uplift of the Tibetan Plateau.

MAIN CONCLUSION

This study highlights the dominant role of plant evolution in determining leaf Chl variations across the Tibetan Plateau. Given the fundamental role of Chl for photosynthesis, these results provide new insights into reconsidering photosynthesis capacity in alpine plants and the carbon cycle in an evolutionary view.

Functional structure of plant communities along salinity gradients in Iranian salt marshes

Salt marshes are unique habitats between sea or saline lakes and land that need to be conserved from the effects of global change. Understanding the variation in functional structure of plant community along environmental gradients is critical to predict the response of plant communities to ongoing environmental changes. We evaluated the changes in the functional structure of halophytic communities along soil gradients including salinity, in Iranian salt marshes; Lake Urmia, Lake Meyghan, Musa estuary, and Nayband Bay (Iran). We established 48 plots from 16 sites in four salt marshes and sampled 10 leaves per species to measure leaf functional traits. Five soil samples were sampled from each plot and 30 variables were analyzed. We examined the changes in the functional structure of plant communities (i.e., functional diversity [FD] and community weighted mean [CWM]) along local soil gradients using linear mixed effect models. Our results showed that FD and CWM of leaf thickness tended to increase with salinity, while those indices related to leaf shape decreased following soil potassium content. Our results suggest that the variations in functional structure of plant communities along local soil gradients reveal the effect of different ecological processes (e.g., niche differentiation related to the habitat heterogeneity) that drive the assembly of halophytic plant communities in SW Asian salt marshes.

Effect of fire on the palatability of plants in an African woodland savanna: varying impacts depending on plant functional groups

Fire and herbivores are two important drivers of changes in vegetation composition, quality and dynamics and both are highly related to each other. Herbivores are known to respond to fire both in terms of foraging decisions and distribution. However, little is known about the actual changes in plant chemistry following a fire event and how long these changes will last. We investigated the effect of fire on two different plant functional groups (grasses and woody species) in a woodland savanna of southern Africa. We studied chemical compounds known to be important for palatability of five perennial grass and seven woody species (trees and shrubs) common in the woodland savanna and known to be utilized by herbivores. We wanted to know if plant chemistry differs between a recently burned site (burned 2 years ago) and a control site, burned 16 years ago, and if grasses and woody species show similar relative differences between sites (i.e., the plants' response to fire). We found a clear difference in chemical composition patterns between the plant functional groups, with an almost homogenous response to fire among woody species, but higher variability in response among grass species. Furthermore, we found that woody species maintained a higher nutritional value even 2 years after burning, whereas grasses did not show clear differences among the two investigated sites. Hence, few years after burning, woody plants might still serve as an attraction for herbivores, especially browsers, in contrast to grasses. The knowledge about these differences between the two functional groups in response to fire is beneficial for the development of management strategies for large herbivores whether domestic or wild.

Beyond the Tree-Line: The C3-C4 “Grass-Line” Can Track Global Change in the World’s Grassy Mountain Systems

von Humboldt’s tree-line concept has dominated mountain ecology for almost two hundred years, and is considered a key indicator for monitoring change in biome boundaries and biodiversity shifts under climate change. Even though the concept of life zones and elevation gradients are a globally observed phenomenon, they have not been thoroughly explored for many contexts. One such example is the tree-line ecotone, a widely used conceptual tool to track climate change in many regions, which has limited application in the widespread tree-sparse, grassy systems that comprise a third of the world’s mountain systems. Among grasses (Poaceae), temperature is linked to variation in photosynthetic performance and community dominance for C3 and C4 metabolic groups, due to its role in limiting photorespiration in the C3 photosynthesis process. Here, we investigate this community shift in grassland-dominated mountains to demonstrate the role of climate in driving this transition and discuss the potential applications of this tool to mountain ecosystem conservation worldwide. For identifying grass-dominated mountains worldwide, we measured the grass-cover using satellite data. We then compiled Poaceae distribution data for ten grass-dominated mountains spanning from 42°S to 41°N and determined the temperature intervals and elevation ranges at which each genus was found, testing for effects of temperature, precipitation, and latitudinal gradients on the dominance of C3-C4 grasses. Temperature was the main driver of C3 dominance, with the richness of C3 genera tending to surpass the taxonomic dominance of C4 plants along mountain temperature gradients where the annual mean temperature was colder than ca. 14.6°C. Similar patterns were observed in eight out of ten mountains, suggesting that this may constitute an isotherm-driven ecotone. Consequently, this C3-C4 transition offers a promising tool for monitoring climate change impacts in grassy mountains. C3-C4 grass community shifts in response to environmental change will likely have major implications for fire frequency and severity, rangeland productivity and livelihoods, food security, and water budgets in mountain systems. Given the severity of the implications of global change on these social-ecological systems, we propose that a “grass-line” monitoring protocol be developed for global application.

Evolutionary innovations driving abiotic stress tolerance in C4 grasses and cereals

Grasslands dominate the terrestrial landscape, and grasses have evolved complex and elegant strategies to overcome abiotic stresses. The C4 grasses are particularly stress tolerant and thrive in tropical and dry temperate ecosystems. Growing evidence suggests that the presence of C4 photosynthesis alone is insufficient to account for drought resilience in grasses, pointing to other adaptations as contributing to tolerance traits. The majority of grasses from the Chloridoideae subfamily are tolerant to drought, salt, and desiccation, making this subfamily a hub of resilience. Here, we discuss the evolutionary innovations that make C4 grasses so resilient, with a particular emphasis on grasses from the Chloridoideae (chloridoid) and Panicoideae (panicoid) subfamilies. We propose that a baseline level of resilience in chloridoid ancestors allowed them to colonize harsh habitats, and these environments drove selective pressure that enabled the repeated evolution of abiotic stress tolerance traits. Furthermore, we suggest that a lack of evolutionary access to stressful environments is partially responsible for the relatively poor stress resilience of major C4 crops compared to their wild relatives. We propose that chloridoid crops and the subfamily more broadly represent an untapped reservoir for improving resilience to drought and other abiotic stresses in cereals.

C3 plant isotopic variability in a boreal mixed woodland: implications for bison and other herbivores

Plant isotopic baselines are critical for accurately reconstructing ancient diets and environments and for using stable isotopes to monitor ecosystem conservation. This study examines the stable carbon and nitrogen isotope compositions (δ ¹³C, δ ¹⁵N) of terrestrial C₃ plants in Elk Island National Park (EINP), Alberta, Canada, with a focus on plants consumed by grazers. EINP is located in a boreal mixed woodland ecozone close to the transition area between historic wood and plains bison habitats, and is currently home to separate herds of wood and plains bison. For this study, 165 C₃ plant samples (grasses, sedges, forbs, shrubs, and horsetail) were collected from three habitat types (open, closed, and wet) during two seasons (summer and fall). There were no statistically significant differences in the δ ¹³C or δ ¹⁵N values of grasses, sedges, shrubs and forbs. On the other hand, plant δ ¹³C and δ ¹⁵N values varied among habitats and plant parts, and the values increased from summer to fall. These results have several implications for interpreting herbivore tissue isotopic compositions: (1) consuming different proportions of grasses, sedges, shrubs, and forbs might not result in isotopic niche partitioning, (2) feeding in different microhabitats or selecting different parts of the same types of plants could result in isotopic niche partitioning, and (3) seasonal isotopic changes in herbivore tissues could reflect seasonal isotopic changes in dietary plants rather than (or in addition to) changes in animal diet or physiology. In addition, the positively skewed plant δ ¹⁵N distributions highlight the need for researchers to carefully evaluate the characteristics of their distributions prior to reporting data (e.g., means, standard deviations) or applying statistical models (e.g., parametric tests that assume normality). Overall, this study reiterates the importance of accessing ecosystem-specific isotopic baselines for addressing research questions in archaeology, paleontology, and ecology.

AusTraits, a curated plant trait database for the Australian flora

We introduce the AusTraits database - a compilation of values of plant traits for taxa in the Australian flora (hereafter AusTraits). AusTraits synthesises data on 448 traits across 28,640 taxa from field campaigns, published literature, taxonomic monographs, and individual taxon descriptions. Traits vary in scope from physiological measures of performance (e.g. photosynthetic gas exchange, water-use efficiency) to morphological attributes (e.g. leaf area, seed mass, plant height) which link to aspects of ecological variation. AusTraits contains curated and harmonised individual- and species-level measurements coupled to, where available, contextual information on site properties and experimental conditions. This article provides information on version 3.0.2 of AusTraits which contains data for 997,808 trait-by-taxon combinations. We envision AusTraits as an ongoing collaborative initiative for easily archiving and sharing trait data, which also provides a template for other national or regional initiatives globally to fill persistent gaps in trait knowledge.

Environment, phylogeny, and photosynthetic pathway as determinants of leaf traits in savanna and forest graminoid species in central Brazil

Leaf traits are closely linked to plant responses to the environment and can provide important information on adaptation and evolution. These traits may also result from common ancestry, so phylogenetic relationships also play an important role in adaptive evolution. We evaluated the effects of the closed forest environment (gallery forest) and the open savanna environment (cerrado) on the selection of leaf traits of graminoid species. The two plant communities differ in light, nutrients, and water availability, which are important drivers in the selection and differentiation of these traits. We also investigated the functional structure and the role of phylogeny in the functional organization of species, considering leaf traits. Patterns of leaf trait variation differed between forest and savanna species suggesting habitat specialization. Wider and longer leaves, with higher values of specific leaf area, chlorophyll, and nitrogen, seem to be an advantage for graminoid species growing in forest environments, while thicker leaves, with higher values of leaf dry-matter content and carbon, benefit species growing in savanna environments. We found few phylogenetic signals related to leaf traits in each environment. Therefore, the functional similarity that the gallery forest and cerrado graminoid species share within their group is independent of their phylogenetic proximity. Environmental filters affect the functional structure of communities differently, generating communities with trait values that are more distant than expected by chance in cerrado (functional dispersion), and closer than expected by chance in the gallery forest (functional convergence).

Resprouting grasses are associated with less frequent fire than seeders

Plant populations persist under recurrent fire via resprouting from surviving tissues (resprouters) or seedling recruitment (seeders). Woody species are inherently slow maturing, meaning that seeders are confined to infrequent fire regimes. However, for grasses, which mature faster, the relationships between persistence strategy and fire regime remain unknown. Globally, we analysed associations between fire regimes experienced by hundreds of grass species and their persistence strategy, within a phylogenetic context. We also tested whether persistence strategies are associated with morphological and physiological traits. Resprouters were associated with less frequent fire than seeders. Whilst modal fire frequencies were similar (fire return interval of 4-6 yr), seeders were restricted to regions with more frequent fire than resprouters, suggesting that greater competition with long-lived resprouters restricts seeder recruitment and survival when fire is rare. Resprouting was associated with lower leaf N, higher C:N ratios and the presence of belowground buds, but was unrelated to photosynthetic pathway. Differences between the life histories of grasses and woody species led to a contrasting prevalence of seeders and resprouters in relation to fire frequency. Rapid sexual maturation in grasses means that seeder distributions, relative to fire regime, are determined by competitive ability and recruitment, rather than time to reproductive maturity.

The photosynthetic pathways of plant species surveyed in Australia's national terrestrial monitoring network

The photosynthetic pathway of plants is a fundamental trait that influences terrestrial environments from the local to global level. The distribution of different photosynthetic pathways in Australia is expected to undergo a substantial shift due to climate change and rising atmospheric CO2; however, tracking change is hindered by a lack of data on the pathways of species, as well as their distribution and relative cover within plant communities. Here we present the photosynthetic pathways for 2428 species recorded across 541 plots surveyed by Australia's Terrestrial Ecosystem Research Network (TERN) between 2011 and 2017. This dataset was created to facilitate research exploring trends in vegetation change across Australia. Species were assigned a photosynthetic pathway using published literature and stable carbon isotope analysis of bulk tissue. The photosynthetic pathway of species can be extracted from the dataset individually, or used in conjunction with vegetation surveys to study the occurrence and abundance of pathways across the continent. This dataset will be updated as TERN's plot network expands and new information becomes available.

C4 herbs dominate the reservoir flood area of the Three Gorges Reservoir

Dam operations can dramatically degenerate riparian vegetation. To improve the restoration practices of reservoir riparian vegetation, it is important to understand which and how a dominant species physiologically and ecologically maintain high fitness in this type of ecosystems. We explored the compositional change of riparian plants during the long-term flood-dry-flood cycle in the reservoir flood area (RFA) of the Three Gorges Reservoir Area (TGRA), China. In total 769 vascular plant species (belonging to 415 genera in 122 families) existed in the study area before damming (prior to 2006, i.e. the natural riparian zone). Following damming (2008-2018), plant species diversity rapidly declined, with only 51 species identified in 2018 (45 genera in 22 families). Before damming, perennial herbs, annual herbs and shrubs co-dominated the study area. After damming, the proportion of shrubs decreased significantly, and the proportion of annuals to total plants increased by 20%. Alien invasive species proportion increased from 5% to 18%. Notably, the proportion of C₄ species increased significantly from 7% to 31%. Ten of the 16 dominant species in RFA since 2015 were C₄ Poaceae species. Our study indicates that dam construction could cause severe biodiversity loss of riparian plants and draw alien species invasion. Besides, C₄ herbs would dominate the RFA. A higher photosynthetic rate could help C₄ plants grow faster to cope with the nitrogen deficiency and short growth cycles in RFA. Hence, screening C₄ herbs for vegetation restoration might aid in maintaining biodiversity and ecosystem functions in flood-dry-flood reservoir flood areas.

Arbuscular Mycorrhizal Fungal Communities in the Soils of Desert Habitats

Deserts cover a significant proportion of the Earth’s surface and continue to expand as a consequence of climate change. Mutualistic arbuscular mycorrhizal (AM) fungi are functionally important plant root symbionts, and may be particularly important in drought stressed systems such as deserts. Here we provide a first molecular characterization of the AM fungi occurring in several desert ecosystems worldwide. We sequenced AM fungal DNA from soil samples collected from deserts in six different regions of the globe using the primer pair WANDA-AML2 with Illumina MiSeq. We recorded altogether 50 AM fungal phylotypes. Glomeraceae was the most common family, while Claroideoglomeraceae, Diversisporaceae and Acaulosporaceae were represented with lower frequency and abundance. The most diverse site, with 35 virtual taxa (VT), was in the Israeli Negev desert. Sites representing harsh conditions yielded relatively few reads and low richness estimates, for example, a Saudi Arabian desert site where only three Diversispora VT were recorded. The AM fungal taxa recorded in the desert soils are mostly geographically and ecologically widespread. However, in four sites out of six, communities comprised more desert-affiliated taxa (according to the MaarjAM database) than expected at random. AM fungal VT present in samples were phylogenetically clustered compared with the global taxon pool, suggesting that nonrandom assembly processes, notably habitat filtering, may have shaped desert fungal assemblages.

Continued Adaptation of C4 Photosynthesis After an Initial Burst of Changes in the Andropogoneae Grasses

C\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$_{4}$\end{document} photosynthesis is a complex trait that sustains fast growth and high productivity in tropical and subtropical conditions and evolved repeatedly in flowering plants. One of the major C\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$_{4}$\end{document} lineages is Andropogoneae, a group of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$\sim $\end{document}1200 grass species that includes some of the world’s most important crops and species dominating tropical and some temperate grasslands. Previous efforts to understand C\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$_{4}$\end{document} evolution in the group have compared a few model C\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$_{4}$\end{document} plants to distantly related C\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$_{3}$\end{document} species so that changes directly responsible for the transition to C\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$_{4}$\end{document} could not be distinguished from those that preceded or followed it. In this study, we analyze the genomes of 66 grass species, capturing the earliest diversification within Andropogoneae as well as their C\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$_{3}$\end{document} relatives. Phylogenomics combined with molecular dating and analyses of protein evolution show that many changes linked to the evolution of C\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$_{4}$\end{document} photosynthesis in Andropogoneae happened in the Early Miocene, between 21 and 18 Ma, after the split from its C\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$_{3}$\end{document} sister lineage, and before the diversification of the group. This initial burst of changes was followed by an extended period of modifications to leaf anatomy and biochemistry during the diversification of Andropogoneae, so that a single C\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$_{4}$\end{document} origin gave birth to a diversity of C\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$_{4}$\end{document} phenotypes during 18 million years of speciation events and migration across geographic and ecological spaces. Our comprehensive approach and broad sampling of the diversity in the group reveals that one key transition can lead to a plethora of phenotypes following sustained adaptation of the ancestral state. [Adaptive evolution; complex traits; herbarium genomics; Jansenelleae; leaf anatomy; Poaceae; phylogenomics.]

High silicon concentrations in grasses are linked to environmental conditions and not associated with C4 photosynthesis

The uptake and deposition of silicon (Si) as silica phytoliths is common among land plants and is associated with a variety of functions. Among these, herbivore defense has received significant attention, particularly with regard to grasses and grasslands. Grasses are well known for their high silica content, a trait which has important implications ranging from defense to global Si cycling. Here, we test the classic hypothesis that C₄ grasses evolved stronger mechanical defenses than C₃ grasses through increased phytolith deposition, in response to extensive ungulate herbivory ("C₄ -grazer hypothesis"). Despite mixed support, this hypothesis has received broad attention, even outside the realm of plant biology. Because C₃ and C₄ grasses typically dominate in different climates, with the latter more abundant in hot, dry regions, we also investigated the effects of water availability and temperature on Si deposition. We compiled a large dataset of grasses grown under controlled environmental conditions. Using phylogenetically informed generalized linear mixed models and character evolution models, we evaluated whether photosynthetic pathway or growth condition influenced Si concentration. We found that C₄ grasses did not show consistently elevated Si concentrations compared with C₃ grasses. High temperature treatments were associated with increased concentration, especially in taxa adapted to warm regions. Although the effect was less pronounced, reduced water treatment also promoted silica deposition, with slightly stronger response in dry habitat species. The evidence presented here rejects the "C₄ -grazer hypothesis." Instead, we propose that the tendency for C₄ grasses to outcompete C₃ species under hot, dry conditions explains previous observations supporting this hypothesis. These findings also suggest a mechanism via which anthropogenic climate change may influence silica deposition in grasses and, by extension, alter the important ecological and geochemical processes it affects.

Lineage-based functional types: characterising functional diversity to enhance the representation of ecological behaviour in Land Surface Models

Process-based vegetation models attempt to represent the wide range of trait variation in biomes by grouping ecologically similar species into plant functional types (PFTs). This approach has been successful in representing many aspects of plant physiology and biophysics but struggles to capture biogeographic history and ecological dynamics that determine biome boundaries and plant distributions. Grass-dominated ecosystems are broadly distributed across all vegetated continents and harbour large functional diversity, yet most Land Surface Models (LSMs) summarise grasses into two generic PFTs based primarily on differences between temperate C₃ grasses and (sub)tropical C₄ grasses. Incorporation of species-level trait variation is an active area of research to enhance the ecological realism of PFTs, which form the basis for vegetation processes and dynamics in LSMs. Using reported measurements, we developed grass functional trait values (physiological, structural, biochemical, anatomical, phenological, and disturbance-related) of dominant lineages to improve LSM representations. Our method is fundamentally different from previous efforts, as it uses phylogenetic relatedness to create lineage-based functional types (LFTs), situated between species-level trait data and PFT-level abstractions, thus providing a realistic representation of functional diversity and opening the door to the development of new vegetation models.

An operational definition of the biome for global change research

Biomes are constructs for organising knowledge on the structure and functioning of the world's ecosystems, and serve as useful units for monitoring how the biosphere responds to anthropogenic drivers, including climate change. The current practice of delimiting biomes relies on expert knowledge. Recent studies have questioned the value of such biome maps for comparative ecology and global-change research, partly due to their subjective origin. Here we propose a flexible method for developing biome maps objectively. The method uses range modelling of several thousands of plant species to reveal spatial attractors for different growth-form assemblages that define biomes. The workflow is illustrated using distribution data from 23 500 African plant species. In an example application, we create a biome map for Africa and use the fitted species models to project biome shifts. In a second example, we map gradients of growth-form suitability that can be used to identify sites for comparative ecology. This method provides a flexible framework that (1) allows a range of biome types to be defined according to user needs and (2) enables projections of biome changes that emerge purely from the individualistic responses of plant species to environmental changes.

Sheathing the blade: Significant contribution of sheaths to daytime and nighttime gas exchange in a grass crop

Despite representing a sizeable fraction of the canopy, very little is known about leaf sheath gas exchange in grasses. Specifically, estimates of sheath stomatal conductance, transpiration and photosynthesis along with their responses to light, CO₂ and vapour pressure deficit (VPD) are unknown. Furthermore, the anatomical basis of these responses is poorly documented. Here, using barley as a model system, and combining leaf-level gas exchange, whole-plant gravimetric measurements, transpiration inhibitors, anatomical observations, and biophysical modelling, we found that sheath and blade stomatal conductance and transpiration were similar, especially at low light, in addition to being genotypically variable. Thanks to high abaxial stomata densities and surface areas nearly half those of the blades, sheaths accounted for up to 17% of the daily whole-plant water use, which -surprisingly- increased to 45% during the nighttime. Sheath photosynthesis was on average 17-25% that of the blade and was associated with lower water use efficiency. Finally, sheaths responded differently to the environment, exhibiting a lack of response to CO₂ but a strong sensitivity to VPD. Overall, these results suggest a key involvement of sheaths in feedback loops between canopy architecture and gas exchange with potentially significant implications on adaptation to current and future climates in grasses.

Silicified bulliform cells of Poaceae: morphological characteristics that distinguish subfamilies

BACKGROUND

Grass phytoliths are the most common phytoliths in sediments; recognizing grass phytolith types is important when using phytoliths as a tool to reconstruct paleoenvironments. Grass bulliform cells may be silicified to large size parallelepipedal or cuneiform shaped phytoliths, which were often regarded as of no taxonomic value. However, studies in eastern Asia had identified several forms of grass bulliform phytoliths, including rice bulliform phytolith, a phytolith type frequently used to track the history of rice domestication. Identification with a higher level of taxonomic resolution is possible, yet a systematic investigation on morphology of Poaceae bulliform phytoliths is lacking. We aimed at providing a morphological description of bulliform phytoliths of Poaceae from Taiwan based on morphometric measurements in anatomical aspect. The results are important references for paleo-ecological studies.

RESULT

The morphology of grass bulliform phytoliths is usually consistent within a subfamily; the end profile is relatively rectangular in Panicoideae and Micrairoideae, whereas cuneiform to nearly circular in Oryzoideae, Bambusoideae, Arundinoideae, and Chloridoideae. Bulliform phytoliths were seldom observed in Pooideae. Certain morphotypes are limited to plants growing in specific environments. For example, large, thin, and pointed bulliform phytoliths are associated with wet habitat; Chloridoideae types are mostly from C4 plants occupying open arid places.

CONCLUSION

Grass bulliform phytoliths can be identified at least to the subfamily level, and several forms were distinguished within large subfamilies. Previously un-reported silicified cell types, i.e., arm cells and fusoids, and two special trichome phytolith types associated with bulliform phytoliths, were described. Morphometric methods were great tools for delimiting morphotypes; with refined morphological classification the association between forms and habit/habitats was revealed. The knowledge provides new ways to interpret phytolith assemblage data, and it is especially useful when the sediments are enriched in large blocky phytoliths.

Grass pollen as a trigger of emergency department presentations and hospital admissions for respiratory conditions in the subtropics: A systematic review

INTRODUCTION

It is unknown if high concentration of airborne grass pollen, where subtropical grasses (Chloridoideae and Panicoideae) dominate, is a risk factor for respiratory health. Here we systematically reviewed the association between airborne grass pollen exposure and asthma emergency department (ED) presentations and hospital admissions in subtropical climates.

OBJECTIVES

A systematic review was performed to identify and summarise studies that reported on respiratory health (asthma ED presentations and hospital admissions) and airborne grass pollen exposure in subtropical climates.

METHODS

Searches were conducted in: MEDLINE, Web of Science, Scopus, CINAHL (EBSCO), Embase and Google Scholar databases (1966-2019). Risk of bias was assessed using a validated quality assessment tool. A meta-analysis was planned, however due to the heterogeneity in study design it was determined inappropriate and instead a narrative synthesis was undertaken.

RESULTS

Nineteen studies were identified for inclusion, with a total of 598,931 asthma ED presentation participants and 36,504 asthma hospital admission participants in six countries (Australia, India, Israel, Italy, Spain, USA). The narrative synthesis found airborne grass pollen appears to have a small and inconsistent increase on asthma ED presentations (judged as: probably little effect n = 5, may have little effect n = 4, no effect n = 2 and uncertain if there is an effect n = 4) and hospital admissions (judged as: probably increase slightly n = 2 probably little effect n = 1, may have a little effect n = 1, no effect n = 3 and we are uncertain if there is an effect n = 4) in the subtropics. Furthermore, the reported effect sizes were small and its clinical relevance may be difficult to discern.

CONCLUSION

Exposure to airborne grass pollen appears to have a small and inconsistent increase on asthma ED presentations and hospital admissions in the subtropics. These findings are comparable to reported observations from studies undertaken in temperate regions.

Annual and seasonal variations in gross primary productivity across the agro-climatic regions in India

Gross primary productivity (GPP) is a vital ecosystem variable that is used as a proxy to study the functional behaviour of a terrestrial ecosystem and its ability to regulate atmospheric CO₂ by working as a carbon pool. India, having the potential terrestrial ecosystem dynamics to absorb the atmospheric carbon dioxide to some extent, is one of the least-explored regions in terms of carbon monitoring studies. The current study evaluates the applicability of a newly developed, quantum yield-based, remote sensing data-driven diagnostic model called the Southampton Carbon Flux (SCARF). This model was used to estimate the annual and seasonal variability of the terrestrial GPP over the Indian region with a spatial resolution of 1 km during 2008. This modified version of the conventional production efficiency model successfully predicted GPP using meteorological variables (PAR, air temperature and dew point temperature), the fraction of photosynthetically active radiation and quantum yield of C3 and C4 plants as the key input parameters. The annual GPP values were in the range from 0 to 4147.55 g C m^-2 year^-1, with a mean value of 1507.32 g C m^-2 year^-1. The maximum and minimum GPP were during the summer monsoon and pre-monsoon, respectively. The seasonal and annual distributions of GPP over the study area obtained using the SCARF model, and the MODIS GPP product (MOD17A2H) were similar. However, MODIS was found to underestimate the GPP in all regions and an overestimation in eastern Himalaya region. The study reveals that environmental scalars, specifically water stress, are the pivotal controlling variables responsible for the variation of GPP in India. The estimates of the GPP in different regions of the study area were made using SCARF, and an eddy covariance technique was similar. The SCARF model can be used to estimate GPP on a global scale. SCARF appears to be a better model in terms of the simplicity of the algorithm, performance and resolution. Thus, it may give higher accuracy in carbon monitoring studies.

Tracking data and retrospective analyses of diet reveal the consequences of loss of marine subsidies for an obligate scavenger, the Andean condor

Over the last century, marine mammals have been dramatically reduced in the world's oceans. We examined evidence that this change caused dietary and foraging pattern shifts of the Andean condor (Vultur gryphus) in Patagonia. We hypothesized that, after the decrease in marine mammals and the increase in human use of coastlines, condor diet changed to a more terrestrial diet, which in turn influenced their foraging patterns. We evaluated the diet by means of stable isotope analysis (δ¹³C, δ¹⁵N and δ³⁴S) of current (last decade) and historical (1841-1933) feathers. We further evaluated the movement patterns of 23 condors using satellite tracking of individuals. Condors reduced their use of marine-derived prey in recent compared with historical times from 33 ± 13% to less than 8 ± 3% respectively; however, they still breed close to the coast. The average distance between the coast and nests was 62.5 km, but some nests were located close to the sea (less than 5 km). Therefore, some birds must travel up to 86 km from nesting sites, crossing over the mountain range to find food. The worldwide reduction in marine mammal carcasses, especially whales, may have major consequences on the foraging ecology of scavengers, as well as on the flux of marine inputs within terrestrial ecosystems.

A diet rich in C3 plants reveals the sensitivity of an alpine mammal to climate change

Plant-herbivore interactions provide critical insights into the mechanisms that govern the spatiotemporal distributions of organisms. These interactions are crucial to understanding the impacts of climate change, which are likely to have an effect on the population dynamics of alpine herbivores. The Royle's pika (Ochotona roylei, hereafter pika) is a lagomorph found in the western Himalaya and is dependent on alpine plants that are at risk from climate change. As the main prey of many carnivores in the region, the pika plays a crucial role in trophic interactions. We examined topographical features, plant genera presence and seasonal dynamics as drivers of the plant richness in the pika's diet across an elevational gradient (2,600-4,450 m). We identified 79 plant genera in the faecal pellets of pikas, of which 89% were forbs, >60% were endemic to the Himalaya, and 97.5% of the diet plant genera identified followed the C3 photosynthetic pathway. We found that, during the premonsoon season, the number of genera in the pika's diet decreased with increasing elevation. We demonstrate that a large area of talus supports greater plant diversity and, not surprisingly, results in higher species richness in the pika's diet. However, in talus habitat with deep crevices, pikas consumed fewer plant genera suggesting they may be foraging suboptimally due to predation risk. The continued increase in global temperature is expected to have an effect on the distribution dynamics of C3 plants and consequently influence pika diet and distribution, resulting in a significant negative cascading effect on the Himalayan ecosystem.

Some like it hot: the physiological ecology of C4 plant evolution

The evolution of C₄ photosynthesis requires an intermediate phase where photorespiratory glycine produced in the mesophyll cells must flow to the vascular sheath cells for metabolism by glycine decarboxylase. This glycine flux concentrates photorespired CO₂ within the sheath cells, allowing it to be efficiently refixed by sheath Rubisco. A modest C₄ biochemical cycle is then upregulated, possibly to support the refixation of photorespired ammonia in sheath cells, with subsequent increases in C₄ metabolism providing incremental benefits until an optimized C₄ pathway is established. 'Why' C₄ photosynthesis evolved is largely explained by ancestral C₃ species exploiting photorespiratory CO₂ to improve carbon gain and thus enhance fitness. While photorespiration depresses C₃ performance, it produces a resource (photorespired CO₂) that can be exploited to build an evolutionary bridge to C₄ photosynthesis. 'Where' C₄ evolved is indicated by the habitat of species branching near C₃-to-C₄ transitions on phylogenetic trees. Consistent with the photorespiratory bridge hypothesis, transitional species show that the large majority of > 60 C₄ lineages arose in hot, dry, and/or saline regions where photorespiratory potential is high. 'When' C₄ evolved has been clarified by molecular clock analyses using phylogenetic data, coupled with isotopic signatures from fossils. Nearly all C₄ lineages arose after 25 Ma when atmospheric CO₂ levels had fallen to near current values. This reduction in CO₂, coupled with persistent high temperature at low-to-mid-latitudes, met a precondition where photorespiration was elevated, thus facilitating the evolutionary selection pressure that led to C₄ photosynthesis.

Poaceae em uma planície de inundação no Brasil: distribuição espacial e conservação

Resumo Com 94 espécies, Poaceae é uma das maiores famílias botânicas ocorrentes na Planície de Inundação do Alto Rio Paraná (PIAP) e seu entorno, localizada a 22º38’-22º57’S e 53º5’-53º36’O, a qual abrange áreas dos estados do Mato Grosso do Sul e do Paraná, Brasil. Sazonalmente inundável, a PIAP faz parte da Área de Proteção Ambiental Federal das Ilhas e Várzeas do Rio Paraná (APA-IVRP) e do Parque Estadual das Várzeas do Rio Ivinhema (PEVRI). Com o objetivo de ampliar os conhecimentos botânicos, ecológicos e oferecer subsídios que possam contribuir para a conservação, no presente trabalho foi avaliado o padrão de distribuição espacial das gramíneas na PIAP e no seu entorno. Para as espécies ocorrentes na PIAP foram considerados: fitofisionomia, exposição à luz, via fotossintética, condição hídrica do substrato em que preferencialmente ocorrem, classificação da morfovegetação, frequências absoluta e relativa, origem e Domínio Fitogeográfico. Os resultados mostram que as espécies distribuem-se espacialmente de acordo com a configuração geomorfológica da PIAP, aqui representadas em dois perfis esquemáticos.

Assessing the applicability of stable isotope analysis to determine the contribution of landfills to vultures' diet

Human activities cause changes to occur in the environment that affect resource availability for wildlife. The increase in the human population of cities has led to a rise in the amount of waste deposited in landfills, installations that have become a new food resource for both pest and threatened species such as vultures. In this study we used stable isotope analysis (SIA) and conventional identification of food remains from Egyptian Vultures (Neophron percnopterus) to assess the applicability of SIA as a new tool for determining the composition of the diets of vultures, a group of avian scavengers that is threatened worldwide. We focused on an expanding Egyptian Vulture population in NE Iberian Peninsula to determine the part played by landfills and livestock in the diet of these species, and aimed to reduce the biases associated with conventional ways of identifying food remains. We compared proportions of diet composition obtained with isotope mixing models and conventional analysis for five main prey. The greatest agreement between the two methods was in the categories ‘landfills’ and ‘birds’ and the greatest differences between the results from the two methods were in the categories ‘livestock’, ‘carnivores’ and ‘wild herbivores’. Despite uncertainty associated to SIA, our results showed that stable isotope analysis can help to distinguish between animals that rely on waste and so present enriched levels of δ ¹³C than those that feed on the countryside. Indeed, a high proportion of food derived from landfills (nearly 50%) was detected in some breeding pairs. Furthermore we performed GLMM analyses that showed that high values of δ ¹³C in Egyptian Vulture feathers (a proxy of feeding in landfills) are related with high levels of humanization of territories. This method has the potential to be applied to other threatened vulture species for which there is a lack of information regarding resources they are consuming, being especially important as the main causes of vultures decline worldwide are related to the consumption and availability of food resources.

Savannahs of Asia: antiquity, biogeography, and an uncertain future

The savannahs of Asia remain locally unrecognized as distinctive ecosystems, and continue to be viewed as degraded forests or seasonally dry tropical forests. These colonial-era legacies are problematic, because they fail to recognize the unique diversity of Asian savannahs and the critical roles of fire and herbivory in maintaining ecosystem health and diversity. In this review, we show that: the palaeo-historical evidence suggests that the savannahs of Asia have existed for at least 1 million years, long before widespread landscape modification by humans; savannah regions across Asia have levels of C4 grass endemism and diversity that are consistent with area-based expectations for non-Asian savannahs; there are at least three distinct Asian savannah communities, namely deciduous broadleaf savannahs, deciduous fine-leafed and spiny savannahs and evergreen pine savannahs, with distinct functional ecologies consistent with fire- and herbivory-driven community assembly. Via an analysis of savannah climate domains on other continents, we map the potential extent of savannahs across Asia. We find that the climates of African savannahs provide the closest analogues for those of Asian deciduous savannahs, but that Asian pine savannahs occur in climates different to any of the savannahs in the southern continents. Finally, we review major threats to the persistence of savannahs in Asia, including the mismanagement of fire and herbivory, alien woody encroachment, afforestation policies and future climate uncertainty associated with the changing Asian monsoon. Research agendas that target these issues are urgently needed to manage and conserve these ecosystems.This article is part of the themed issue 'Tropical grassy biomes: linking ecology, human use and conservation'.

The deforestation story: testing for anthropogenic origins of Africa's flammable grassy biomes

Africa has the most extensive C4 grassy biomes of any continent. They are highly flammable accounting for greater than 70% of the world's burnt area. Much of Africa's savannas and grasslands occur in climates warm enough and wet enough to support closed forests. The combination of open grassy systems and the frequent fires they support have long been interpreted as anthropogenic artefacts caused by humans igniting frequent fires. True grasslands, it was believed, would be restricted to climates too dry or too cold to support closed woody vegetation. The idea that higher-rainfall savannas are anthropogenic and that fires are of human origin has led to initiatives to 'reforest' Africa's open grassy systems paid for by carbon credits under the assumption that the net effect of converting these system to forests would sequester carbon, reduce greenhouse gases and mitigate global warming. This paper reviews evidence for the antiquity of African grassy ecosystems and for the fires that they sustain. Africa's grassy biomes and the fires that maintain them are ancient and there is no support for the idea that humans caused large-scale deforestation. Indicators of old-growth grasslands are described. These can help distinguish secondary grasslands suitable for reforestation from ancient grasslands that should not be afforested.This article is part of the themed issue 'The interaction of fire and mankind'.

Nutrient addition shifts plant community composition towards earlier flowering species in some prairie ecoregions in the U.S. Central Plains

The distribution of flowering across the growing season is governed by each species’ evolutionary history and climatic variability. However, global change factors, such as eutrophication and invasion, can alter plant community composition and thus change the distribution of flowering across the growing season. We examined three ecoregions (tall-, mixed, and short-grass prairie) across the U.S. Central Plains to determine how nutrient (nitrogen (N), phosphorus, and potassium (+micronutrient)) addition alters the temporal patterns of plant flowering traits. We calculated total community flowering potential (FP) by distributing peak-season plant cover values across the growing season, allocating each species’ cover to only those months in which it typically flowers. We also generated separate FP profiles for exotic and native species and functional group. We compared the ability of the added nutrients to shift the distribution of these FP profiles (total and sub-groups) across the growing season. In all ecoregions, N increased the relative cover of both exotic species and C₃ graminoids that flower in May through August. The cover of C₄ graminoids decreased with added N, but the response varied by ecoregion and month. However, these functional changes only aggregated to shift the entire community’s FP profile in the tall-grass prairie, where the relative cover of plants expected to flower in May and June increased and those that flower in September and October decreased with added N. The relatively low native cover in May and June may leave this ecoregion vulnerable to disturbance-induced invasion by exotic species that occupy this temporal niche. There was no change in the FP profile of the mixed and short-grass prairies with N addition as increased abundance of exotic species and C₃ graminoids replaced other species that flower at the same time. In these communities a disturbance other than nutrient addition may be required to disrupt phenological patterns.

Functionally dissimilar neighbors accelerate litter decomposition in two grass species

Plant litter decomposition is a key regulator of nutrient recycling. In a given environment, decomposition of litter from a focal species depends on its litter quality and on the efficiency of local decomposers. Both may be strongly modified by functional traits of neighboring species, but the consequences for decomposition of litter from the focal species remain unknown. We tested whether decomposition of a focal plant's litter is influenced by the functional-trait dissimilarity to the neighboring plants. We cultivated two grass species (Brachypodium pinnatum and Elytrigia repens) in experimental mesocosms with functionally similar and dissimilar neighborhoods, and reciprocally transplanted litter. For both species, litter quality increased in functionally dissimilar neighborhoods, partly as a result of changes in functional traits involved in plant-plant interactions. Furthermore, functional dissimilarity increased overall decomposer efficiency in one species, probably via complementarity effects. Our results suggest a novel mechanism of biodiversity effects on ecosystem functioning in grasslands: interspecific functional diversity within plant communities can enhance intraspecific contributions to litter decomposition. Thus, plant species might better perform in diverse communities by benefiting from higher remineralization rates of their own litter.