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1,418 results for “Grasses”
Data from: Restoring dryland old fields with native shrubs and grasses: does facilitation and seed source matter?
Restoration of agricultural fields is challenging, especially in arid and semi-arid ecosystems. We conducted experiments in two fields in the Great Basin, USA, which differed in cultivation history and fertility. We tested the effects of different levels of functional diversity (planting grasses and shrubs together, vs. planting shrubs alone), seed source (cultivars, local or distant wild-collections), and irrigation regime (spring or fall and spring) on restoration outcomes. We sowed either: 1) grasses and shrubs in year one, 2) shrubs only, in year one, 3) grasses in year one with herbicide, shrubs in year two, or 4) shrubs alone in year two, after a year of herbicide. We irrigated for two years and monitored for three years. Shrub emergence was highest in the lower fertility field, where increasing functional diversity by seeding grasses had a neutral or facilitative effect on shrub emergence. In the higher fertility field, increasing functional diversity appeared to have a neutral to competitive effect. After declines in shrub densities after irrigation ceased, these effects did not persist. Grasses initially suppressed or had a neutral effect on weeds relative to an unseeded control, but had neutral or facilitative effects on weeds relative to shrub-only seeding. Initially, commercial grasses were either equivalent to or outperformed wild-collected grasses, but after irrigation ceased, commercial grasses were outperformed by wild-collected grasses in the higher fertility field. Local shrubs initially outperformed distant shrubs, but this effect did not persist. Fall and spring irrigation combined with local shrubs and wild-collected grasses was the most successful strategy in the higher fertility field, while in the lower fertility field, irrigation timing had fewer effects. Superior shrub emergence and higher grass persistence indicated that the use of wild and local seed sources is generally warranted, whereas the effects of functional diversity and irrigation regime were context-dependent. A bet-hedging approach that uses a variety of strategies may maximize the chances of restoration success.
Data from: The role of climatic and geological events in generating diversity in Ethiopian grass frogs (genus Ptychadena)
Ethiopia is a world biodiversity hotspot and harbours levels of biotic endemism unmatched in the Horn of Africa, largely due to topographic—and thus habitat—complexity, which results from a very active geological and climatic history. Among Ethiopian vertebrate fauna, amphibians harbour the highest levels of endemism, making amphibians a compelling system for the exploration of the impacts of Ethiopia's complex abiotic history on biotic diversification. Grass frogs of the genus Ptychadena are notably diverse in Ethiopia, where they have undergone an evolutionary radiation. We used molecular data and expanded taxon sampling to test for cryptic diversity and to explore diversification patterns in both the highland radiation and two widespread lowland Ptychadena. Species delimitation results support the presence of nine highland species and four lowland species in our dataset, and divergence dating suggests that both geologic events and climatic fluctuations played a complex and confounded role in the diversification of Ptychadena in Ethiopia. We rectify the taxonomy of the endemic P. neumanni species complex, elevating one formally synonymized name and describing three novel taxa. Finally, we describe two novel lowland Ptychadena species that occur in Ethiopia and may be more broadly distributed.
Data from: C4 savanna grasses fail to maintain assimilation in drying soil under low CO2 compared with C3 trees despite lower leaf water demand
1) C4 photosynthesis evolved when grasses migrated out of contracting forests under a declining atmospheric CO2 concentration ([CO2]a) and drying climate around 30 million years ago. C4 grasses are hypothesised to benefit from improved plant–water relations in open habitats like savannas, giving advantages over C3 plants under low [CO2]a. But experimental evidence in a low CO2 environment is limited and comparisons with C3 trees are needed to understand savanna vegetation patterns. 2) To test whether stomatal conductance (gS) and CO2 assimilation (A) are maintained in drier soil for C4 grasses than C3 trees, particularly under low [CO2]a, we investigated photosynthesis and plant–water relations of three C3 tree and three C4 grass species grown at 800, 400 or 200 ppm [CO2]a over moderate wetting–drying cycles. 3) C4 grasses had a lower soil–to–leaf water potential gradient than C3 trees, especially at 200 ppm [CO2]a, indicating reduced leaf water demand relative to supply. Yet the dependence of gS and A on predawn leaf water potential (a measure of soil water availability) was greater for the C4 grasses than trees, particularly under low [CO2]a. 4) Our findings establish that gS and A are not maintained in drier soil for C4 grasses compared with C3 trees, suggesting that this mechanism was not prevailing in the expansion of C4–dominated grasslands under low [CO2]a. This inherent susceptibility to sudden decreases in soil water availability justifies why C4 grasses have not evolved a resistant xylem allowing operation under drought, but instead shut down below a water potential threshold and rapidly recover. We point to this capacity to respond to transient water availability as a key overlooked driver of C4 grass success under low [CO2]a.
Data from: Short-term priority over exotic annuals increases the initial density and longer-term cover of native perennial grasses
Temporal priority can affect individual performance and reproduction, as well as community assembly, but whether these effects persist over time remains unclear, and their demographic mechanisms have been little explored. The continued dominance of exotic annual grasses in California has been commonly attributed to their demonstrated early germination and rapid early growth relative to native perennial grasses. This advantage may play a crucial role in the structure of California exotic annual grasslands, as well as in the practice of native grassland restoration. We tested whether a two-week planting advantage under field conditions increased individual survival, growth, and reproduction for four native perennial grass species and whether these effects persisted over three years. We show that short-term priority significantly increased the establishment success of native perennial grasses. Increased density of native grass seedlings presaged later large increases in cover that were not evident in the first year after planting. Although priority effects at the individual level may diminish over time, short differences in emergence timing can have long-lasting effects on community structure. Earlier germination and faster initial growth of exotic annual species may help explain their unprecedented invasion and continued dominance of California grasslands. Finally, these results highlight the importance of priority effects for effective exotic annual control during native grassland restoration in California: initial control can increase the establishment of native perennial seedlings, which then results in long-term control by mature native individuals.
Data from: Experimental evaluation of the robustness of the growth-stress tolerance trade-off within the perennial grass Dactylis glomerata
1. A core tenet of functional ecology is that the vast phenotypic diversity observed in the plant kingdom could be partly generated by a trade- off between the ability of plants to grow quickly and acquire resources in rich environments vs. the ability to conserve resources and avoid mortality under stress. However, experimental demonstrations remain scarce and potentially blurred by phylogenetic constraints in cross-species analyses. Here we experimentally decoupled growth potential and stress survival by applying an off-season stress on contrasting populations of the perennial grass Dactylis glomerata exhibiting a range of seasonal dormancy. 2. Seventeen populations of D. glomerata, originating from a latitudinal gradient from Norway to Morocco, were subjected to three types of dehydration stress: winter frost in Norway, summer drought, and early spring (off-season) drought stress in the south of France. Growth rate, and two leaf traits (leaf width and leaf dry matter content) suspected to be involved in the adaptation to dehydration stress, were monitored under optimal conditions. We quantified plant dehydration survival as the amount of plant recovery after a severe stress. 3. Nordic populations were found to be winter dormant. Winter and summer dormant populations better survived frost and summer drought, respectively. However, no trade-off between growth potential and dehydration survival was detected in non-dormant plants in early spring when dehydration occurred unseasonably for all populations. Furthermore, Mediterranean populations better survived an early spring drought. 4. Our results highlight the importance of assessing plant growth potential as a response to seasonal environmental cues. They suggest that growth potential and stress survival trade-off when plants exhibit seasonal dormancy but can be functionally independent at other seasons. Consequently, the growth-stress survival relationship could be better described as a dynamic linkage rather than a constant and general trade-off. Moreover, leaf trait values, such as thinner and more lignified leaves reflecting drought adaptation, may have contributed to the improved drought-stress survival without resulting in a cost to growth. 5. Further exploration of the growth-stress survival relationship should permit deciphering the suite of plant traits and trait covariations involved in plants' responses to increasing stress.
Data from: Native grass ground covers provide multiple ecosystem services in Californian vineyards
1. The mechanisms responsible for the success or failure of agricultural diversification are often unknown. Most studies of arthropod pest management focus on enhancing the effectiveness of natural enemies, but non-crop plants can also improve or hamper pest suppression by changing the host quality of crop plants by reducing or adding available soil nutrients or water. Native perennial ground covers may provide resources and long-term habitat to resident natural enemies and be more compatible than exotic annuals for crop management in terms of competition for soil nutrients or water. 2. A three-year study was conducted in a California vineyard to examine the impacts of native perennial grasses on pests, natural enemies, crop plant condition and soil properties. Three ground cover treatments were included: bare soil with a grower standard drip irrigation, native grasses with the drip irrigation, or native grasses with the drip irrigation and an additional flood irrigation to keep the grasses green and growing during the season. 3. Numbers of leafhopper pests (Erythroneura spp.) decreased in both native grass treatments, where parasitism rates and spider densities were higher. 4. Nitrate levels in vine leaf petioles were lower in grass treatments, indicating competition with vines for soil nitrogen, which is most often considered to be detrimental. Berry weight was higher in the irrigated treatment but did not differ between the bare soil and non-irrigated native grass treatments. Grape quality (brix) was similar in the bare soil and native grass treatments, suggesting that increased soil moisture in the presence of native grasses did not compromise grape quality. In fact, leaf water stress was lower and available soil moisture higher not only in the irrigated native grass treatment but, at times, in the non-irrigated native grass treatment, in comparison to the no ground cover treatment. 5. We conclude that native grasses contributed to a reduction in leafhopper density by reducing host quality through competition with vines for soil nitrogen and providing food resources and/or habitat for natural enemies. Native grasses also improved soil water content and may be part of a water conservation program for perennial crops in dry climate regions.
Data from: Not seeing the grass for the trees: timber plantations and agriculture shrink tropical montane grassland by two-thirds over four decades in the Palani Hills, a Western Ghats Sky Island
Tropical montane habitats, grasslands, in particular, merit urgent conservation attention owing to the disproportionate levels of endemic biodiversity they harbour, the ecosystem services they provide, and the fact that they are among the most threatened habitats globally. The Shola Sky Islands in the Western Ghats host a matrix of native forest-grassland matrix that has been planted over the last century, with exotic timber plantations. The popular discourse on the landscape change is that mainly forests have been lost to the timber plantations and recent court directives are to restore Shola forest trees. In this study, we examine spatiotemporal patterns of landscape change over the last 40 years in the Palani Hills, a significant part of the montane habitat in the Western Ghats. Using satellite imagery and field surveys, we find that 66% of native grasslands and 31% of native forests have been lost over the last 40 years. Grasslands have gone from being the dominant, most contiguous land cover to one of the rarest and most fragmented. They have been replaced by timber plantations and, to a lesser extent, expanding agriculture. We find that the spatial pattern of grassland loss to plantations differs from the loss to agriculture, likely driven by the invasion of plantation species into grasslands. We identify remnant grasslands that should be prioritised for conservation and make specific recommendations for conservation and restoration of grasslands in light of current management policy in the Palani Hills, which favours large-scale removal of plantations and emphasises the restoration of native forests.
Data from: Combinations of plant water-stress and neonicotinoids can lead to secondary outbreaks of Banks grass mite (Oligonychus pratensis Banks)
Spider mites, a cosmopolitan pest of agricultural and landscape plants, thrive under hot and dry conditions, which could become more frequent and extreme due to climate change. Recent work has shown that neonicotinoids, a widely used class of systemic insecticides that have come under scrutiny for non-target effects, can elevate spider mite populations. Both water-stress and neonicotinoids independently alter plant resistance against herbivores. Yet, the interaction between these two factors on spider mites is unclear, particularly for Banks grass mite (Oligonychus pratensis; BGM). We conducted a field study to examine the effects of water-stress (optimal irrigation = 100% estimated evapotranspiration (ET) replacement, water stress = 25% of the water provided to optimally irrigated plants) and neonicotinoid seed treatments (control, clothianidin, thiamethoxam) on resident mite populations in corn (Zea mays, hybrid KSC7112). Our field study was followed by a manipulative field cage study and a parallel greenhouse study, where we tested the effects of water-stress and neonicotinoids on BGM and plant responses. We found that water-stress and clothianidin consistently increased BGM densities, while thiamethoxam-treated plants only had this effect when plants were mature. Water-stress and BGM herbivory had a greater effect on plant defenses than neonicotinoids alone, and the combination of BGM herbivory with the two abiotic factors increased the concentration of total soluble proteins. These results suggest that spider mite outbreaks by combinations of changes in plant defenses and protein concentration are triggered by water-stress and neonicotinoids, but the severity of the infestations varies depending on the insecticide active ingredient.
Data from: Consequences of seed origin and biological invasion for early establishment of a North American grass species
Local, wild-collected seeds of native plants are recommended for use in ecological restoration to maintain patterns of adaptive variation. However, some environments are so drastically altered by exotic, invasive weeds that original environmental conditions may no longer exist. Under these circumstances, cultivated varieties selected for improved germination and vigor may have a competitive advantage at highly disturbed sites. This study investigated differences in early establishment and seedling performance between wild and cultivated seed sources of the native grass, Poa secunda, both with and without competition from the invasive exotic grass, Bromus tectorum. We measured seedling survival and above-ground biomass at two experimental sites in western Montana, and found that the source of seeds selected for restoration can influence establishment at the restoration site. Cultivars had an overall advantage when compared with local genotypes, supporting evidence of greater vigor among cultivated varieties of native species. This advantage, however, declined rapidly in the presence of B. tectorum and most accessions were not significantly different for growth and survival in competition plots. Only one cultivar had a consistent advantage despite a strong decline in its performance when competing with invasive plants. As a result, cultivated varieties did not meet expectations for greater establishment and persistence relative to local genotypes in the presence of invasive, exotic species. We recommend the use of representative local or regional wild seed sources in restoration to minimize commercial selection, and a mix of individual accessions (wild, or cultivated when necessary) in highly invaded settings to capture vigorous genotypes and increase the odds native plants will establish at restoration sites.
Data from: Local context drives infection of grasses by vector-borne generalist viruses
Host characteristics commonly determine infection risk, but infection can also be mediated by regional- or local-scale variation in the biotic and abiotic environment. Experiments can clarify the relative importance of these factors. We quantified drivers of infection by barley and cereal yellow dwarf viruses (B/CYDV), a group of generalist, vector-borne grass pathogens, at hierarchically nested spatial scales (105–1 m) by planting individuals of six common grass species into five Pacific Coast grassland sites spanning 7° of latitude (> 5000 total hosts) and applying a factorial combination of nitrogen and phosphorus fertilizer. Infection differed most among experimental blocks (102–103 m scale), suggesting that local factors control infection risk; infection increased with cover of long-lived hosts and phosphorus, but not nitrogen, fertilization. For B/CYDV, local context more strongly predicts infection risk than host species traits or regional context; such spatially nested experiments can clarify the factors underlying variation in infection risk.
Data from: Adaptive evolution and divergent expression of heat stress transcription factors in grasses
Background: Heat stress transcription factors (Hsfs) regulate gene expression in response to heat and many other environmental stresses in plants. Understanding the adaptive evolution of Hsf genes in the grass family will provide potentially useful information for the genetic improvement of modern crops to handle increasing global temperatures. Results: In this work, we performed a genome-wide survey of Hsf genes in 5 grass species, including rice, maize, sorghum, Setaria, and Brachypodium, by describing their phylogenetic relationships, adaptive evolution, and expression patterns under abiotic stresses. The Hsf genes in grasses were divided into 24 orthologous gene clusters (OGCs) based on phylogeneitc relationship and synteny, suggesting that 24 Hsf genes were present in the ancestral grass genome. However, 9 duplication and 4 gene-loss events were identified in the tested genomes. A maximum-likelihood analysis revealed the effects of positive selection in the evolution of 11 OGCs and suggested that OGCs with duplicated or lost genes were more readily influenced by positive selection than other OGCs. Further investigation revealed that positive selection acted on only one of the duplicated genes in 8 of 9 paralogous pairs, suggesting that neofunctionalization contributed to the evolution of these duplicated pairs. We also investigated the expression patterns of rice and maize Hsf genes under heat, salt, drought, and cold stresses. The results revealed divergent expression patterns between the duplicated genes. Conclusions: This study demonstrates that neofunctionalization by changes in expression pattern and function following gene duplication has been an important factor in the maintenance and divergence of grass Hsf genes.
Data from: Crop-associated virus infection in a native perennial grass: reduction in plant fitness and dynamic patterns of virus detection
To understand the eco-evolutionary significance of plant viruses in nature, we must (i) quantify the effects of infection on plant fitness and (ii) recognize that native plants are increasingly exposed to crop-associated viruses. Studies of perennials are particularly needed: most of our knowledge of plant-virus interactions is from annuals, yet long-lived species dominate landscapes. Here we used aster models for life-history analysis and longitudinal measures of plant virus status to evaluate multi-year consequences of crop virus infection in a native perennial. We used Barley yellow dwarf virus acquired from wheat to inoculate seedlings of Panicum virgatum L. (switchgrass), a North American prairie grass. We grew inoculated and mock-inoculated individuals of two ecotypes for 3 years in the field. We measured plant size, infection status and fitness components. Aster modelling provided integrated multi-year measures of fitness. Crop virus inoculation reduced multi-year native plant fitness by 30% over 2 years despite generally asymptomatic infection and evidence of resistance. This reduction was greater than predicted from individual fitness components or most size measures. Ecotypes differed in response, with the lowland ecotype experiencing higher apparent recovery from infection. Virus treatment in the upland ecotype delayed flowering phenology and reduced seed filling. Synthesis. Our use of field experimentation, surveys of plant infection status and aster modelling demonstrates a rigorous and broadly applicable approach for quantifying the effects of viruses and other microbes on multi-year plant fitness. We found that a crop virus had negative multi-year effects on native plant fitness even after infection was no longer detected. Viruses may have substantial effects on native vegetation with domestication of landscapes and agricultural expansion.
Data from: Influence of gene flow on divergence dating – implications for speciation history of Takydromus grass lizards
Dating the time of divergence and understanding speciation processes are central to the study of the evolutionary history of organisms but are notoriously difficult. The difficulty is largely rooted in variations in the ancestral population size or in the genealogy variation across loci. To depict the speciation processes and divergence histories of three monophyletic Takydromus species endemic to Taiwan, we sequenced 20 nuclear loci and combined with one mitochondrial locus published in GenBank. They were analyzed by a multispecies coalescent approach within a Bayesian framework. Divergence dating based on the gene tree approach showed high variation among loci, and the divergence was estimated at an earlier date than when derived by the species tree approach. To test whether variations in the ancestral population size accounted for the majority of this variation, we conducted computer inferences using isolation-with-migration (IM) and approximate Bayesian computation (ABC) frameworks. The results revealed that gene flow during the early stage of speciation was strongly favored over the isolation model, and the initiation of the speciation process was far earlier than the dates estimated by gene- and species-based divergence dating. Due to their limited dispersal ability, it is suggested that geographic isolation may have played a major role in the divergence of these Takydromus species. Nevertheless, the current study reveals a more complex situation and demonstrates that gene flow during the speciation process cannot be overlooked and may have a great impact on divergence dating. By using multilocus data and incorporating Bayesian coalescence approaches, we provide a more biologically realistic framework for delineating the divergence history of Takydromus.
Data from: Effect of plant root symbionts on performance of native woody species in competition with an invasive grass in multispecies microcosms
The majority of terrestrial plants form mutualistic associations with arbuscular mycorrhizal fungi (AMF) and rhizobia (i.e. nitrogen fixing bacteria). Understanding these associations has important implications for ecological theory and for restoration practice. Here we tested whether the presence of AMF and rhizobia influence the performance of native woody plants invaded by a non-native grass in experimental microcosms. We planted eight plant species (i.e. Acacia acuminata, A. microbotrya, Eucalyptus loxophleba subsp. loxophleba, E. astringens, Calothamnus quadrifidus, Callistemon phoeniceus, Hakea lissocarpha and H. prostrata) in microcosms of field-conditioned soil with and without addition of AMF and rhizobia in a fully factorial experimental design. After seedling establishment, we seeded half the microcosms with an invasive grass Bromus diandrus. We measured shoot and root biomass of native plants and Bromus, and on roots, the percentage colonization by AMF, number of rhizobia-forming nodules and number of proteaceous root clusters. We found no effect of plant root symbionts or Bromus addition on performance of myrtaceous, and as predicted, proteaceous species as they rely little or not at all on AMF and rhiozbia. Soil treatments with AMF and rhiozbia had a strong positive effect (i.e. larger biomass) on native legumes (A. microbotrya and A. acuminata). However, the beneficial effect of root symbionts on legumes became negative (i.e. lower biomass and less nodules) if Bromus was present, especially for one legume, i.e. A. acuminata, suggesting a disruptive effect of the invader on the mutualism. We also found a stimulating effect of Bromus on root nodule production in A. microbotrya and AMF colonization in A. acuminata which could be indicative of legumes' increased resource acquisition requirement, i.e. for nitrogen and phosphorus, respectively, in response to the Bromus addition. We have demonstrated the importance of measuring belowground effects because the aboveground effects gave limited indication of the effects occuring belowground.
Data from: Soil aggregate stability and grassland productivity associations in a northern mixed-grass prairie
Soil aggregate stability data are often predicted to be positively associated with measures of plant productivity, rangeland health, and ecosystem functioning. Here we revisit the hypothesis that soil aggregate stability is positively associated with plant productivity. We measured local (plot-to-plot) variation in grassland community composition, plant (aboveground) biomass, root biomass, % water-stable soil aggregates, and topography. After accounting for spatial autocorrelation, we observed a negative association between % water-stable soil aggregates (0.25-1 and 1-2 mm size classes of macroaggregates) and dominant graminoid biomass, and negative associations between the % water-stable aggregates and the root biomass of a dominant sedge (Carex filifolia). However, variation in total root biomass (0-10 or 0-30 cm depths) was either negatively or not appreciably associated with soil aggregate stabilities. Overall, regression slope coefficients were consistently negative thereby indicating the general absence of a positive association between measures of plant productivity and soil aggregate stability for the study area. The predicted positive association between factors was likely confounded by variation in plant species composition. Specifically, sampling spanned a local gradient in plant community composition which was likely driven by niche partitioning along a subtle gradient in elevation. Our results suggest an apparent trade-off between some measures of plant biomass production and soil aggregate stability, both known to affect the land's capacity to resist erosion. These findings further highlight the uncertainty of plant biomass-soil stability associations.
Data from: The consequences of daily cyclic hypoxia on a European grass shrimp: from short-term responses to long-term effects
1. Salt marshes are a key coastal environment for their important role as nursery habitats for marine and estuarine fish and crustaceans. Salt marshes are variable environments where species can experience daily cyclic hypoxic stress, characterized by profound variations in oxygen partial pressure (pO2) from supersaturated conditions (~42kPa) to extremely hypoxic conditions (~3kPa) in ~12-hours. 2. Here, under laboratory conditions, we assessed the physiological consequences of exposing the shrimp Palaemon varians, a species commonly found in the salt marshes of northern Europe, to the daily cyclic hypoxic regime currently experienced in its habitat in August (7.1±1.8 hours day-1 below 4.0kPa). In the laboratory adults were kept at water pO2 <4.5kPa for 7-hours each night and in normoxic conditions for the rest of the time. 3. We recorded an acceleration of P. varians' moult cycle, which was 15% shorter in animals kept in cyclic hypoxia compared to animals in normoxia. Similarly, the pattern of expression of two cuticular proteins over an entire moult cycle indicated an effect of cyclic hypoxia on moult stage-related genes. After 16 days, morphological changes to the gills were detected, with shrimps in cyclic hypoxia having a 13.6% larger lamellar surface area (measured in µm2/mg animal) than normoxic animals, which could improve gas exchange capacity. Overall, phenotypic and morphological data indicate that faster moulting is triggered in response to cyclic hypoxia, with the benefit that gill modifications can be prompted more rapidly in order to meet oxygen requirements of the body. 4. On the first experimental day, in cyclic hypoxic exposed animals, we recorded a 50% decrease in feeding rates (during hypoxic conditions) in comparison to normoxic animals. Similarly, ammonium excretion was reduced by 66-75% during the 1st and 21st experimental day. Body size was reduced by ~4% after 28 days. Females that reproduced in cyclic hypoxic conditions reduced the amount of yolk in each egg by ~24%. Overall, results underline how, in a decapod shrimp living in a key coastal environment, many physiological parameters are impaired by a cyclic hypoxic regime that is currently found in its natural habitat.
Data from: Grass competition overwhelms effects of herbivores and precipitation on early tree establishment in Serengeti
1. Savanna ecosystems span a diverse range of climates, edaphic conditions and disturbance regimes, the complexity of which has stimulated long-standing interest in the mechanisms that maintain tree-grass coexistence. One hypothesis suggests that tree establishment is strongly limited by one or several demographic bottlenecks at early stages of the tree life cycle. A major impediment to testing this hypothesis is the lack of data on the relative strengths of different bottlenecks across key environmental gradients. 2. To identify demographic bottlenecks that limit early tree establishment (0-18 months), we conducted a series of transplant experiments with two savanna trees species (Acacia robusta and A. tortilis) across a natural rainfall and soil fertility gradient in the Serengeti ecosystem, Tanzania. We tested the interactive effects of precipitation, herbivory, seed scarification, grass competition, water limitation and tree species identity on two key life stages: germination and early seedling survival (0-2 months) and juvenile seedling survival (2-18 months). 3. Germination and early seedling survival increased as a function of rainfall, in the absence of herbivores and when seeds were scarified. Juvenile seedling survival, in contrast, decreased with rainfall but increased in the absence of herbivores. Grass removal had the single strongest (positive) effect on juvenile seedling survival of any treatment. Soil moisture monitoring and grass-addition treatments revealed that grasses negatively affected seedlings in ways that were not necessarily linked to soil moisture. 4. A demographic model combining all effects across early life stages showed that the strength of grass competition on juvenile seedling survival was the key factor limiting early tree establishment. While rainfall had an unexpected opposing effect on the two life stages, the net effect of mean annual precipitation on early tree establishment was positive. 5. Synthesis: Successful tree establishment in Serengeti is maximized by a seemingly unlikely sequence of events: (1) scarification of seeds by browsers, (2) heavy rainfall to promote germination, (3) intensive grazing (but absence of browsers) and (4) dry conditions during juvenile seedling growth (>2 months) to reduce competition with grasses. By considering a wide suite of conditions and their interactions, our experimental results are relevant to ongoing debates about savanna vegetation dynamics and structural shifts in tree:grass ratios.
Data from: Lodato et al. (2021) Functional importance and diversity of fungi during standing grass litter decomposition
<p>Although microbial participation in litter decomposition is widely known within terrestrial soils, the role and significance of microorganisms during the aerial standing litter phase of decomposition remains poorly investigated. We examined the fungi inhabiting standing leaf litter of <i>Schizachyrium scoparium</i> and <i>Schizachyrium tenerum</i> in a Longleaf Pine savanna ecosystem and estimated their contribution to litter decomposition. We identified fungal phylotypes associated with leaf litter and quantified leaf C mass loss, fungal biomass production, and microbial respiration during decomposition. These data were used to construct budgets estimating C flow into and through fungi. Significant losses in <i>S. scoparium</i> (55%) and <i>S. tenerum</i> (67%) leaf C mass were observed during standing decomposition along with concomitant increases in fungal biomass, which reached a maximum of 36 and 33 mgC/g detrital C, respectively. Cumulative fungal production during decomposition totaled 99±6 mgC/g initial detrital C in <i>S. scoparium</i> and 73±5 mgC/g initial detrital C in <i>S. tenerum</i>, indicating that 18 and 11% of the litter C was converted into fungal biomass, respectively. Corresponding estimates of cumulative fungal respiration totaled 106±7 and 174±11 mgC/g initial detrital C in <i>S. scoparium</i> and <i>S. tenerum</i>, respectively. Next generation sequencing identified several fungal phylotypes, with the majority of sequences belonging to the Ascomycota (Dothideomycetes) and Basidiomycota (Agaricomycetes). Fungal phylotypes were similar between litter species and changed over time, showing a successional pattern. These findings extend our understanding of fungal processes to standing litter in terrestrial ecosystems, and highlight the quantitative importance of fungi in C cycling processes.</p>
Data from: Fire and non-native grass invasion interact to suppress tree regeneration in temperate deciduous forests
1. While many ecosystems depend on fire to maintain biodiversity, non-native plant invasions can enhance fire intensity, suppressing native species and generating a fire–invasion feedback. These dynamics have been observed in arid and semi-arid ecosystems, but fire–invasion interactions in temperate deciduous forests, where prescribed fires are often used as management tools to enhance native diversity, have rarely been investigated. 2. Here we evaluated the effects of a widespread invasive grass on fire behaviour in eastern deciduous forests in the USA and the potential effects of fire and invasions on tree regeneration. We planted native trees into invaded and uninvaded forests, quantified fuel loads, then applied landscape-scale prescribed fires and no-burn controls, and measured fire behaviour and tree seedling and invasive plant performance. 3. Our results show that fires in invaded habitats were significantly more intense, including higher fire temperatures, longer duration and higher flame heights, even though invasions did not alter total fuel loads. The invasion plus fire treatment suppressed native tree seedling survival by 54% compared to invasions without fire, and invasions reduced natural tree recruitment by 66%. 4. We also show that invasive plant biomass did not change from one season to the next in plots where fire was applied, but invader biomass declined significantly in unburned reference plots, suggesting a positive invasive grass–fire feedback. 5. Synthesis and applications. These findings demonstrate that fire–invasion interactions can have significant consequences for invaded temperate forest ecosystems by increasing fire intensity and reducing tree establishment while promoting invasive plant persistence. To encourage tree regeneration and slow invasive spread, we recommend that forest managers remove invasions prior to applying prescribed fires or avoid the use of fire in habitats invaded by non-native grasses.
Monument a Leon Chiris in Grasse (FR)
Historical "Monument a Leon Chiris" located in the frenche city of Grasse, original build in 1914. Modeled in Autodesk Maya Textured in Substance Painter Source: https://de.m.wikipedia.org/wiki/Datei:Grasse_-_Monument_a_Leon_Chiris.jpg Source: Objaverse 1.0 / Sketchfab
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Annotated Behaviour and Observability Dataset (ABODe)
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