Major Life Forms Research Articles

Grasses in Semi-Arid Lowlands—Community Composition and Spatial Dynamics with Special Regard to the Influence of Edaphic Factors

Edaphic properties have been widely shown to influence community composition and distribution. However, the degree to which edaphic factors can affect grasses in semi-arid lowlands is still little researched. We assessed the significance of nine edaphic factors to explain the distributions of 65 grass species with various ecological traits (i.e., the ecological indicator values for their preferred habitat) in the semi-arid lowlands of Pakistan. To record information on species composition and related ecological conditions, we selected 10 random sampling locations between 2020 and 2021. For each species, we determined the important value index (IVI) and looked at the primary indicator species that were identified using the indicator species analysis approach. The major genera were Setaria, Brachiaria, and Cenchrus with 6.15% species in each followed by Aristida, Panicum, and Eragrostis with 4.61% wild grass species, Bothriochloa, Bromus, Phragmites, Polypogon, Saccharum, Poa, Echinochloa, and Dactyloctenium with 3.07% species, whereas other genera had a single species each. In total, 80% of the species were native, while only 20% were introduced species. Microphylls accounted for 49.23% of the leaf size spectra of the grass flora in the study area. The other frequent traits included macrophylls (21.53%), nanophylls (20%), and leptophylls (9.23%). The major life forms were therophytes (56.92%) followed by hemicryptophytes (38.46%) and geophytes (4.61%). The results of an ordination analysis indicated that the distribution of grasses was significantly (p ≤ 0.002) influenced by several edaphic parameters, with pH having the greatest impact on species distribution. The analyses of indicator species showed that pH and EC were the most powerful and important edaphic factors for determining the composition of plant communities and indicator species. The significant indicator species in various ecosystems were Cynodon dactylon (L.) Pers. rainer.bussmann@smnk.de and Leptochloa chinensis (L.) Nees (agroecosystem), Brachiaria reptans (L.) C.A. Gardner and C.E. Hubb, Dichanthium annulatum (Forssk.) Stapf, and Saccharum spontaneum L. (forest ecosystem), Cenchrus biflorus Roxb., Cenchrus ciliaris L., and Desmostachya bipinnata (L.) Stapf (urban ecosystem), Arundo donax L., Echinochloa crus-galli, and Phragmites australis (wetland ecosystem), and Saccharum spontaneum and Echinochloa crus-galli (L.) P. Beauv. (riparian ecosystem). We discovered that different species groupings had different habitat preferences and that soil pH had a significant beneficial effect on plant variety. These results provide a scientific roadmap for soil and plant restoration in semi-arid lowland habitats.

Humboldt's legacy: explaining the influence of environmental factors on the taxonomic and phylogenetic diversity of angiosperms along a Neotropical elevational gradient.

The scientific work of Alexander von Humboldt was influenced by his interaction with the diversity and natural wealth of the Neotropics. He proposed that climate determines plant diversity along elevational gradients based on his observations. Here, we evaluated the most prominent climate-based hypotheses in explaining plant diversity along an elevational gradient that Humboldt himself visited during his journey across Mexico. Specifically, we examined how climatic variables and forest-use intensity affected species richness and phylogenetic structure of major angiosperm life forms (trees, shrubs, epiphytes, herbs and lianas) along the Cofre de Perote mountain, Veracruz, Mexico. We analysed species richness and phylogenetic structure of angiosperms at eight sites between 30 to 3500 m a.s.l. We estimated the phylogenetic structure using a mega-phylogeny of angiosperms and the abundance-weighted net relatedness index. We considered multiple environmental factors' direct and indirect effects by applying a piecewise structural equation modelling approach. Each life form responds differently to the environmental variables included in our model; however, it is observed that temperature is the main predictor of the taxonomic and phylogenetic diversity of the angiosperms studied, both when the different life forms are grouped and separated. Potential evapotranspiration and precipitation are variables that also influence some life forms' diversity, especially taxonomic diversity. The forest-use intensity negatively affected only the taxonomic diversity of trees. These results highlight the influence of studying the different life forms of angiosperms in diversity gradient models and show the great influence that temperature has in conjunction with other environmental variables to promote the taxonomic and phylogenetic diversity of plant communities. Given the current global environmental crisis, an integrative biogeographically oriented vision based on Humboldt's method is necessary. Honouring the work of Humboldt and continuing his legacy demands more research to understand the causes behind elevational diversity gradients.

Amino acid sensor conserved from bacteria to humans

SignificanceAmino acids are the building blocks of life and important signaling molecules. Despite their common structure, no universal mechanism for amino acid recognition by cellular receptors is currently known. We discovered a simple motif, which binds amino acids in various receptor proteins from all major life-forms. In humans, this motif is found in subunits of calcium channels that are implicated in pain and neurodevelopmental disorders. Our findings suggest that γ-aminobutyric acid-derived drugs bind to the same motif in human proteins that binds natural ligands in bacterial receptors, thus enabling future improvement of important drugs.

The Natural Selection of Metabolism Explains Curvature in Fossil Body Mass Evolution

The natural selection of metabolism and mass can explain inter-specific body mass allometries from prokaryotes to mammals (Witting in Theor Popul Biol 117:23–42, https://doi.org/10.1016/j.tpb.2017.08.005, 2017a), with allometric exponents that depend on the selected metabolism and the packing of home ranges in predominately one (1D), two (2D), or three (3D) spatial dimensions. The predicted exponent for total metabolism for a 2D packing of home ranges increases from 3/4 to 7/4 when the fraction of the inter-specific body mass variation that follows from the natural selection of metabolism increases from zero to one. While a 3/4 exponent is commonly observed for inter-specific comparisons in mammals, a 7/4 exponent has so far not been reported. Yet, I detect the full range of exponents for evolution over time in the fossil record. There are no fossil data for allometric correlations between metabolism and mass, but I show that the allometry $$ \left( {\dot{w} \propto w^{{\hat{\dot{w}}}} } \right) $$ for the rate of evolution $$ \left( {\dot{w} = {\text{ d }}w/{\text{ d }}t} \right) $$ in mass (w) in physical time (t) is given by the underlying set of allometries for life history parameters, including mass-specific metabolism. The $$\hat{\dot{w}}$$ exponent describes the curvature of body mass evolution in time, with predicted values including: 3/2 (2D) for within niche evolution in small horses over 54 million years. 5/4 (2D) and 9/8 (3D) for across niche evolution of maximum mass in four mammalian clades. 3/4 (2D) for fast evolution in large horses, and maximum mass in trunked and terrestrial mammals. And 1 for maximum mass across major lifeforms during 3.5 billion years of evolution along a metabolic bound. These results integrate the inter-specific allometries of existing species with a deeper understanding of their natural selection during evolutionary diversification over millions of years.

Comparing the effects of continuous grazing and long term exclosure on floristic composition and plant diversity in rangeland ecosystems of Saral, Iran

Continuous grazing as the most common land us in Kurdistan rangeland is practiced wildly. Along with continuous grazing, long term exclosure has been implemented in research site in Saral. The main objective of this study was to investigate the changes in plant diversity, floristic composition and plant groups of the major life forms in response to 40 years of continuous grazing and long terrm exclosure in Saral rangelands, Iran. This research was conducted in cold semi-arid rangeland of Baharestan located in Saral’s agricultural and natural resources station (including grazed and excluded sites). In total, six transects were sampled in both grazed and excluded sites and ten plots were randomly placed per transect to measure vegetation and plant characteristics. Sampling was carried out in late May to early June (peak biomass) in 2017. T test was used to compare the means of total plant material, and Shannon’s diversity index was used based on the total cover percentage in both grazed and exclosure sites. Our results indicated that long-term grazing exclosure significantly increased canopy covers and species richness of annuals, perennial grasses, perennial forbs and shrubs. Conversely, continuous grazing caused some species to disappear namely Ferula haussknechtii and Prangos ferulacea. There was statistically a significant difference between litter and total plant material in experimental sites (p < 0.001). Apart from palatability, exclosure increased floristic diversity by 17.8%. Our findings elucidated that exclosure in degraded vegetation is an effective strategy and management policy to recover and restore missing vegetation cover.

Plant and Animal Reproductive Strategies: Lessons from Offspring Size and Number Tradeoffs

The tradeoff between offspring size and number is ubiquitous and manifestly similar in plants and animals despite fundamental differences between the evolutionary histories of these two major life forms. Fecundity (offspring number) primarily affects parental fitness, while offspring size underpins the fitness of parents and offspring. We provide an overview of theoretical models dealing with offspring size and fitness relationships. We follow that with a detailed examination of life-history constraints and environmental effects on progeny size and number, separately in plants and animals. The emphasis is on seed plants, but we endeavour to also summarize information from distinct animal groups - insects, fishes, reptiles, birds, and mammals. Furthermore, we analyse genetic controls on progeny size and number in two model organisms - Arabidopsis and Drosophila. Despite the deep evolutionary divergence between plants and animals, we find four trends in reproductive strategy that are common to both lineages: (i) offspring size is generally less variable than offspring number, (ii) offspring size increases with increasing parent body size, (iii) maternal genes restrict offspring size and increase offspring numbers, while zygotic genes act to increase offspring size; such parent-offspring conflicts are enhanced when there is sibling rivalry, and (iv) variation in offspring size increases under sub-optimal (harsh) environmental conditions. The most salient difference between plants and animals is that the latter tend to produce larger (fewer) offspring under sub-optimal conditions while seed plants invest in smaller (many) seeds, suggesting that maternal genetic control over offspring size increases in plants but decreases in animals with parental care. The time is ripe for greater experimental exploration of genetic controls on reproductive allocation and parent-offspring conflicts in plants and animals under sub-optimal (harsh) environments.

Trend in coral-algal phase shift in the Mandapam group of islands, Gulf of Mannar Marine Biosphere Reserve, India

The present study revealed proliferation of macro-algae modifying coral reef ecosystems in a different manner due to diseases and sedimentations in the Mandapam group of islands in the Gulf of Mannar. Benthic surveys were conducted with major attack of seven coral reefs diseases with high sedimentation rate, nine species of fleshy macro-algae (Turbinaria ornata, Turbinaria conaides, Caulerpa scalpelliformis, Caulerpa racemosa, Kappaphycus alvarezii, Padina gymnosphora, Sargassum wightii, Ulva reticulata and Calurpa lentillifera) proliferation against major corals life forms (Acropora branching, Acropora digitate, Acropora tabulate, coral massive, coral submassive, coral foliose and coral encrusting). The results confirm that diseased corals most favor to macro-algae growth (15.27%) rather than the sedimentation covered corals (8.24 %). In the degradation of coral life forms, massive corals were more highly damaged (7.05%) than any other forms. Within a short period of time (May to September), coral coverage shrank to 17.4% from 21.9%, macro-algae increased 23.51% and the average sedimentation rate attained 77.52 mg cm−2d−1 with persisting coral reef diseases of 17.59%. The Pearson correlation showed that the coral cover decreased with increasing macro-algae growth, which was statistically significant (r = −0.774, n = 100, P < 0.0005). The proliferation of the various macro-algae C. scalpellifrmis, T. ornata, C. racemosa, T. conaides, U. reticulata, S. wightii, K. alvarezii, P. gymnosphora and C. lentillifera increased with percentages of 6.0, 5.8, 5.7, 4.9, 4.2, 3.7, 2.7 and 1.9, respectively. If this trend continues, the next generation of new recruit corals will undoubtedly lead to a phase shift in Gulf of Mannar corals.

An ethnobotanical note on wild edible plants of Upper Eastern Himalaya, India

The present article deals with the documentation of tribal knowledge on wild edible plants in Upper Eastern Himalayan Region of India. In total, 269 plant species belonging to 77 families were recorded in the study area of Upper Subansiri District of Arunachal Pradesh. Dioscoreaceae, Rutaceae, Cucurbitaceae and Arecaceae were the dominant families with 16, 13, 12 and 11 plant species, respectively, while Moraceae and Asteraceae followed with 10 species each. Four major life forms were trees, shrubs, herbs and climbers. Trees made the highest proportion of the edible species (81) followed by shrubs (74), herbs (71) and climbers (37). Availability of some of these species might be a serious constraint in near future due to various anthropogenic factors. Need for undertaking vigorous environmental awareness campaign among local tribes has been stressed upon in the article for conserving this valuable biological resource of Eastern Himalayan region of India.

Evaluating methodology of current state of entomofauna diversity of agricultural landscapes in Ukraine

The range of estimates shows that reduction with strong entomological school, thorough systematization of species diversity of insects Ukraine has not yet been carried out, making it difficult to determine the state of biodiversity for ecological study of measures under the UN Convention. We believe that the assessment of agricultural landscapes is possible on entomofauna example reprezentative sample presented with constant and dominant species according to Entomological registers created in the last century. In order to better generalization of representative samples in the analytical research we grouped known advisable entomofauna of agricultural landscapes by major life forms, each of which requires adequate census methods, due to the peculiarities of each environmental group. The results of the analytical studies were drawn registers constant and dominant species of insects of agricultural landscapes steppes of Ukraine on life forms «heophyls» (heobionts, herpetobionts) and phytophyls (hortobionts, dendrobionts). Longterm studies of different faunal habitats of agricultural landscapes revealed the presence or absence of certain species of Entomological Meeting and compare existing species biodiversity literature data.

Effects of open grazing and livestock exclusion on floristic composition and diversity in natural ecosystem of Western Saudi Arabia

Livestock grazing is one of the main causes of rangeland degradation in Saudi Arabia. Fencing to exclude grazers is one of the main management practices used to restore vegetation and conserve biodiversity. The main objectives of this study were to investigate the changes in plant diversity and abundance, floristic composition and plant groups of the major life forms in response to thirty-five years of grazing exclosure in western Saudi Arabia. These vegetation attributes and palatability were compared in 30 sampling stands located in the excluded and grazed sites. Our results showed that livestock exclusion significantly increased covers, density and species richness of annuals, grasses, perennial forbs, shrubs and trees. Exclosure enhanced the abundance and richness of palatable species and depressed the development of weedy species. About 66.7% of the recorded species at the excluded site were highly palatable compared to 34.5% at the grazed site. In contrary, about 55.2% unpalatable species were found in the grazed site compared to 25.8% in the protected site. Jaccard’s similarity index between the excluded and grazed sites showed lower values of 0.39%, 0.40% and 0.31% at levels of families, genus and species, respectively. The results suggest that establishing livestock exclusion may be a useful sustainable management tool for vegetation restoration and conservation of plant diversity in degraded rangelands of arid regions.

Structure and Composition of the Natural Sal (Shorea robusta Gaertner f.) Forest, Gomtu,Southern Bhutan

Scattered pockets of natural hill Sal forest in the southern foothills of Bhutan are the only remnant forests important for protection and conservation in southernmost Bhutan. The ecological study of Sal forest in Gomtu is the first of its kind in Bhutan and is aimed at enhancing future management and conservation programmes. We wanted to understand the floristic composition, diversity, and structural traits of this forest type in detail. A total of nine plots were sampled along the altitudinal gradients; trees and epiphytic vegetation were enumerated in all the plots. A total of 91 tree species belonging to 38 families were recorded (51 trees, 30 shrubs, 7 woody climbers and 3 palm species). Floristically, two major life-forms were exhibited; deciduous forest in the upper elevations mainly dominated by Shorea robusta and evergreen broad-leaved forest at the lower elevations. The entire study area was demarcated into three different forest types using cluster analysis; a Shorea dominant one on the ridge top, a Schima dominant one with Shorea at the lower altitudes, and a riparian one at the lowest altitude. The Shorea dominated type showed relatively low diversity and species richness compared to the other two types. The total basal area of Shorea robusta was 86,786.5 cm 2 /3,200 m 2 while the stem density was 123 stem/3,200 m 2 . The basal area increased from 2,146.2 cm 2 /400 m 2 to 18,926.0 cm 2 /400 m 2 while stem density increased from 3 stems/400 m 2 to 32 stems/400 m 2 with increasing altitude. However, the maximum estimated tree height decreased from 41.3 to 22.4 m approaching ridge tops. The study provided clear evidence that the most suitable range for the hill Sal forest was from a high altitude of 600 metre above sea level down to 527 m on northwest-facing ridge slopes.

Variation of grazing‐induced vegetation changes across a large‐scale productivity gradient

AbstractQuestionsDoes the magnitude of grazing‐induced changes in species composition vary with habitat productivity? How does the sign and magnitude of grazing effects on species richness and beta‐diversity change with increasing productivity? Do major life forms exhibit consistent responses to grazing along productivity gradients?LocationSteppes and grasslands of southern South America in Argentina and Uruguay.MethodsWe evaluated grazing effects on plant composition, species richness, beta‐diversity and life‐form abundances along a ten‐fold, regional productivity gradient and within subregions of contrasting productivity, using a common sampling protocol for 23 paired grazed vs ungrazed plots. The annual integral of the normalized difference vegetation index was used as a surrogate for above‐ground net primary productivity.ResultsCompositional dissimilarity between grazed and ungrazed plots, as well as grazing‐induced differences in plant richness and beta‐diversity all increased with habitat productivity. Grazing decreased species richness in low‐productive steppes but enhanced the richness of high‐productive grasslands. On average, grazing reduced beta‐diversity in high‐productive sites but not in low‐productive sites. Dominant species were more strongly suppressed by grazing towards productive grasslands. Grazing generally decreased shrub species cover, whereas graminoid and forb cover did not consistently change with grazing through the productivity gradient.ConclusionsOur results indicate that the overall grazing effects on vegetation structure increased along a regional productivity gradient. Yet the sign of grazing impacts on species richness and beta‐diversity shifted with habitat productivity, in agreement with models of herbivore‐mediated co‐existence and species colonization in productive systems. Further, we found that narrowing the spatial extent of analysis to the subregion generally obscured grazing–productivity relationships. Biodiversity conservation programmes should carefully weigh the varied impacts of livestock grazing across productivity gradients.

Landscape-scale variation in the structure and biomass of the hill dipterocarp forest of Sumatra: Implications for carbon stock assessments

One of the first steps in estimating the potential for reducing emissions from deforestation and forest degradation (REDD) initiatives is the proper estimation of the carbon components. There are still considerable uncertainties about carbon stocks in tropical rain forest, coming essentially from poor knowledge of the quantity and spatial distribution of forest biomass at the landscape level.We evaluate the influence of site and topography on forest structure, biomass and carbon stock over a forested landscape in Sumatra. Sixteen sites were selected across a landscape of ca. 1000km2, and within each site, a network of small 0.1ha plots was laid down perpendicular to the major topographical gradient. Structural parameters for trees with diameter bigger or equal to 10cm and major life forms were recorded for each plot. The total sampled area was 70.2ha.The above-ground biomass (AGBM) in the 16 sites ranged from 271±19 to 478±38Mgha−1, with a mean of 361±7Mgha−1. This value is similar to the global ‘tropical wet forest’ estimate of Keith et al. (2009), but 23% higher than the biome default value given in the IPCC (2006) guidelines. Plots on acid tuff were the most distinctive in having fewer and smaller trees, with a resulting low AGBM. The number of stems was low, but the average tree diameter was larger on the nutrient-rich young volcanic andesitic soils. Landscape-scale variability of forest structure and dynamics was considerable. Within sites, there was little variation of mean height or mean diameter of the trees, but significant differences in stem density, basal area and AGBM between land facets. Both topography and geology appeared to affect the dynamics and the biomass of the forest.At the same time, our findings confirm the need for caution in extrapolating data from small plots to larger spatial scales when estimating carbon stocks for a given forest type or a region. Our results for C stock values for Sumatra lowland and hill dipterocarp forests (135–240Mgha−1, with a mean of 180Mgha−1) showed higher variability in C stock values at landscape level than generally reported in the literature. Based on our results, stratified sampling is recommended for biomass and carbon estimation. Within an error range of 6–8% of the AGBM, a minimum area of 4–6ha should be sufficient to estimate biomass with satisfactory accuracy at the landscape scale. Networks of several small plots across landscape are preferable to fewer larger plots, providing that the sampling is representative of the land facets in the area.

Molecular phylogenetics of Alchemilla, Aphanes and Lachemilla (Rosaceae) inferred from plastid and nuclear intron and spacer DNA sequences, with comments on generic classification

Alchemilla (the lady’s mantles) is a well known but inconspicuous group in the Rosaceae, notable for its ornamental leaves and pharmaceutical properties. The systematics of Alchemilla has remained poorly understood, most likely due to confusion resulting from apomixis, polyploidisation and hybridisation, which are frequently observed in the group, and which have led to the description of a large number of (micro-) species. A molecular phylogeny of the genus, including all sections of Alchemilla and Lachemilla as well as five representatives of Aphanes, based on the analysis of the chloroplast trnL–trnF and the nuclear ITS regions is presented here. Gene phylogenies reconstructed from the nuclear and chloroplast sequence data were largely congruent. Limited conflict between the data partitions was observed with respect to a small number of taxa. This is likely to be the result of hybridisation/introgression or incomplete lineage sorting. Four distinct clades were resolved, corresponding to major geographical division and life forms: Eurasian Alchemilla, annual Aphanes, South American Lachemilla and African Alchemilla. We argue for a wider circumscription of the genus Alchemilla, including Lachemilla and Aphanes, based on the morphology and the phylogenetic relationships between the different clades.

Changes in plant functional types in response to goat and sheep grazing in two semi-arid shrublands of SE Spain

In Mediterranean plant communities, grazing induces severe floristic changes affecting the life histories of grazed and non-grazed species. Alteration of the grazing regimen causes important changes in the structure and dynamics of the plant community and ecosystem stability. To determine the susceptibility of different plant functional types to landscape management, we measured changes in Plant Functional Types (PFTs) in response to grazing by goat and sheep in an inland dwarf-palm matorral and a marine-exposed thorny-shrub matorral in Cabo de Gata Natural Park (SE Spain). We classified the major life forms into PFTs, and identified six PFT shrubs (dwarf-palms, sclerophyllous small trees, xeric thorny-shrubs, spiny legumes, glaucous dwarf-shrubs, and xeric half-shrubs), four PFT forbs (leafy stem herbs, xeric prostrate herbs, rosette herbs, and clonal spiny herbs), and two PFT grasses (steppe and short grasses). Morphological traits measured include sclerophilly, leaf presence, leaf size, shape of leaf margins, hairiness, position of dormant buds (growth form), clonality, plant coverage, canopy structure, phenological deciduousness (drought resistance), and regeneration (reproduction type, pollination type, inflorescence position, and seed size). There was a higher correlation within and between morphological growth forms, leaf and phenological traits, than within regenerative traits (only seed size was correlated with main dispersal type). We analysed the importance of these PFTs at several sites of the two communities, which were subjected to different livestock rates. In inland and marine-exposed communities, the same PFTs decreased in response to medium-high grazing: sclerophyllous small trees ( Quercus coccifera, Olea europaea var. sylvestris), glaucous dwarf-shrubs ( Phlomis and Cistus spp.) and short grasses ( Brachypodium retussum). In both communities, the decrease of these grazing-susceptible PFTs was widely associated with an increase in steppe grasses ( Stipa tenacissima, “alfa-grass”) and xeric prostrate herbs ( Fagonia cretica, Paronichia sufruticosa), the latter of which is a reliable indicator of degradation in semi-arid systems. Instead, different PFTs behave as either grazing-averse and/or grazing-tolerant in each community: Dwarf-palms ( Chamaerops humilis) and xeric thorny shrubs ( Periploca laevigata) in the marine-exposed community, and xeric half-shrubs ( Thymus hiemalys, Sideritis osteoxylla, Teucrium spp., Artemisia herba-alba) in the inland community. The latter functional group resists disturbances, such as medium-moderate grazing and drought, in semi-arid zones and is an indicator of long-term degradation.

Effects of the fire retardant Phos-Chek on vegetation in eastern Australian heathlands

The effects of the fire retardant Phos-Chek D75R on species composition, survival and growth of eastern Australian heathland vegetation are described. Two sites in Victoria were selected, Victoria Valley in the Grampian Ranges and Marlo in East Gippsland. Both areas supported heathland vegetation that was long, unburnt and relatively undisturbed. Plots were subjected to single applications of increasing concentrations of retardant (0.5, 1.0 and 1.5 L fire retardant m−2) or no additional fire retardant (‘Control’ and ‘Water only’ treatments). A single application of Phos-Chek did not appear to significantly change species composition or projected foliage cover of the major life forms of native heathland vegetation. However, it did cause whole plant and shoot death of key species Allocasuarina paludosa, Banksia marginata, Leptospermum continentale and L. myrsinoides, and was observed to affect other species. The fertilising effect of the fire retardant generally increased shoot growth of the key species but did not significantly increase the overall height of these species. The application of fire retardant enhanced weed invasion, particularly when supplied at higher concentrations. A number of research recommendations are made from this preliminary investigation.

Corynebacterium glutamicum Glyceraldehyde-3-Phosphate Dehydrogenase Isoforms with Opposite, ATP-Dependent Regulation

Corynebacterium glutamicum gapA and gapB encode glyceraldehyde-3-phosphate dehydrogenases (GAPDHs) that differ in molecular weight and activity in the presence of ATP. Comparative genome analysis revealed that GapA, the product of gapA, represented the canonical GAPDH that is highly conserved across the three major life forms. GapB, with an additional 110-residue-long sequence upstream of its GAPDH-specific domain, was homologous only to select microbial putative GAPDHs. Upon gene disruption, the initial growth rates of the wild-type, ΔgapA and ΔgapB strains on glucose (0.77, 0.00 and 0.76 h^–1, respectively), lactate (0.20, 0.18 and 0.15 h^–1, respectively), pyruvate (0.39, 0.29 and 0.20 h^–1, respectively), and acetate (0.06, 0.06 and 0.04 h^–1, respectively), implied that GapA was indispensable for growth on glucose, that GapB, but not GapA, affected early growth on acetate, and that GapB had a greater influence on growth under gluconeogenic conditions than GapA. The disruption of either gapA or gapB showed no significant effect on the transcription of any of the other gap cluster genes although it led to reduced triosephosphate isomerase (TPI) activities. Glycolytic GAPDH activity at low in vitro ATP concentrations was solely attributed to the 35.9-kDa GapA. At higher ATP concentrations, the same activity was attributed to the 51.2-kDa GapB. Both enzymes, however, exhibited similar NADP-dependent GAPDH activities at the higher ATP concentrations. In effect therefore, the GAPDH-catalyzed reaction at low ATP concentrations was irreversible, with all the glycolytic activity strictly NAD-dependent and attributed to GapA. At higher ATP concentrations, the reaction was reversible, with glycolytic activity NAD- or NADP-dependent and attributed to GapB, while gluconeogenic activity was attributable to both GapA and GapB.

Temporal trends in species composition and plant traits in natural grasslands of Uruguay

Abstract. We report the successional trends of the major life-forms (graminoids and forbs) in natural grasslands of Uruguay over a 9-yr period after the removal of domestic herbivores. For the whole community, species richness and diversity decreased over the successional period. In graminoids we observed clear temporal trajectories in floristic composition; the rate of floristic change decreased with time and was associated with a shift in plant traits. The exclusion of large herbivores promoted erect and tall grasses with narrow leaves and greater seed length, vegetative growth constrained to the cool season and increased frequency of annual species. Forbs did not show a clear temporal trend in species composition, but there was, nevertheless, a plot-specific species turnover of this functional group that was reflected in their attributes. Species spreading by means of rhizomes, with vegetative growth restricted to the warm season. Species with larger seeds increased under grazing exclusion, as did annual and nitrogen-fixing forbs. The floristic changes induced by cattle exclusion occurred early in the succession. This early high rate of change has practical implications for management and conservation programs of the natural grasslands of Uruguay. Additionally, the shift in plant traits may be helpful in devising simple indicators of grazing impact.

LANDSCAPE-SCALE CHANGES IN PLANT SPECIES ABUNDANCE AND BIODIVERSITY OF A SAGEBRUSH STEPPE OVER 45 YEARS

Increasing demands on arid and semiarid ecosystems, which comprise one-third of Earth's terrestrial environment, create an urgent need to understand their biodiversity, function, and mechanisms of change. Sagebrush (Artemisia) steppe, the largest semiarid vegetation type in North America, is endangered because of losses to agriculture, excessive grazing, and invasive species. Establishment in 1950 of what is now designated as the Idaho National Engineering and Environmental Laboratory (southeastern Idaho, USA) created the largest existing reserve of this extensive vegetation type. We used cover, density, and frequency data for vascular plants sampled on 79 permanent plots nine times during 45 years to (1) assess long-term changes in abundance and distribution of major species and life forms, (2) assess changes in species richness and plot similarity, and (3) test the hypotheses that plant cover and stability of cover are positively associated with species richness and that invasibility is inversely relate...

Landscape-Scale Changes in Plant Species Abundance and Biodiversity of a Sagebrush Steppe over 45 Years

Increasing demands on arid and semiarid ecosystems, which comprise one-third of Earth's terrestrial environment, create an urgent need to understand their biodiversity, function, and mechanisms of change. Sagebrush (Artemisia) steppe, the largest semiarid vegetation type in North America, is endangered because of losses to agriculture, excessive grazing, and invasive species. Establishment in 1950 of what is now designated as the Idaho National Engineering and Environmental Laboratory (southeastern Idaho, USA) created the largest existing reserve of this extensive vegetation type. We used cover, density, and frequency data for vascular plants sampled on 79 permanent plots nine times during 45 years to (1) assess long-term changes in abundance and distribution of major species and life forms, (2) assess changes in species richness and plot similarity, and (3) test the hypotheses that plant cover and stability of cover are positively associated with species richness and that invasibility is inversely related to native plant cover and richness. From 1933 through 1957 the area was subject to severe drought, with annual precipitation exceeding the long-term mean only four times. Cover of shrubs plus perennial grasses was 18% in 1950, and the vegetation was heavily dominated by sagebrush. Perennial grass cover was only 0.5%. With elevated precipitation after 1957, shrub cover increased to 25% by 1965, and by 1975 cover of perennial grasses had increased 13-fold. Subsequent fluctuations in cover did not track precipitation closely. Cover and density of major species were often out of phase, and correlation analyses indicated lags of 2–5 yr in responses of species or functional groups to precipitation. Aggregate species richness of the area has not changed appreciably, but richness of shrubs, perennial grasses, and forbs per plot steadily increased from 1950 to 1995. Vegetative heterogeneity also increased, with mean similarity among plots declining from 72% to 40%. Plots having higher species richness tended to maintain higher levels of cover and to vary less in cover relative to their mean level, indicating links between species richness and function. Abundance of nonnative species was negatively correlated with cover, but not with richness of native species. Thus, adequate cover of native species can render these semiarid communities more resistant to invasion. Maintaining richness and cover of native species should be a high management priority for these ecosystems.