Dissimilar Plant Research Articles

Should we burn the Cerrado? Effects of fire frequency on open savanna plant communities

AbstractAimsTropical savanna evolved in the presence of fire, depending on it to maintain its physiognomies and biodiversity. Open ecosystems of tropical savanna burn frequently, and thus changes in fire frequency can affect their plant communities. In this study we aimed to analyze the effects of different fire frequencies on the composition, structure and post‐fire regeneration of open savanna plant communities of the Cerrado.LocationOpen savannas, Central Brazil (13°35–38′S and 47°45–51′W).MethodsWe conducted surveys in areas with different fire frequencies (fire exclusion, burned annually and burned biennially for 6 years, from 2013). Vegetation sampling was carried out before application of fire treatments in 2017, and then 1 and 2 years after. Species cover was estimated visually and later grouped into graminoids, shrubs and forbs.ResultsEvaluation of the plant communities after 6 years of fire treatment indicated that fire frequency did not affect species richness. Fire frequency did, however, promote alteration in species occurrence and abundance, resulting in three dissimilar plant communities. Regarding post‐fire regeneration, annually burned plots showed consistency in species richness and growth form cover over 6 years of annually applied fire. Biennially burned plots tended to be more variable than the other treatments, with a large increase in species richness and growth form cover in the first year after fire, succeeded by a decrease in the second year. Not all species that were recruited just after fire were able to persist in the above‐ground community in the second year after fire.ConclusionsOpen savannas of the Cerrado are highly resilient to fire, even to annual fires, with 6 years of annual fire treatments not affecting post‐fire species diversity or growth form cover. However, communities differed in species composition, which can influence their functional diversity and lead to alterations in ecosystem services. Our findings encourage long‐term studies to evaluate the resilience of areas frequently burned, as well as longer fire exclusion periods.

Codon Usage Bias for Fatty Acid Genes FAE1 and FAD2 in Oilseed Brassica Species

Codon usage bias (CUB) phenomenon varies with the species and even within the genes of the same species, where few codons are preferred more frequently than their other synonymous codons. It also categorizes the differences between species. Nucleotide compositional analysis reveals the molecular mechanisms of genes and the evolutionary relationship of a gene in dissimilar plant species. In the present study, three orthologous sequences of each FAE1 (FAE1.1, FAE1.2, and FAE1.3) and FAD2 (FAD2.1, FAD2.2, and FAD2.3) genes, from six Brassica species were accessed using the GenBank database. Further, CUB-related parameters such as nucleotide composition (AT and GC content), relative synonymous codon usage (RSCU), the effective number of codons (ENC), frequency of optimal codons (Fop), relative codon usage bias (RCBS), neutrality plot (GC12 vs. GC3), parity rule-2 [(A3/(A3 + T3) vs. (G3/(G3 + C3)], and correspondence analysis (COA) were analyzed to compare codon bias in U’s triangle Brassica species. The FAE1 genes were AT-biased and FAD2 genes were GC-biased across the studied Brassica species. RSCU values indicated that both the genes had moderate codon usage frequency for selected amino acids. The evolutionary study confirmed that codon usage preference is similar within the species grouped into the same cluster for FAE1; however, B. nigra performed differently for FAD2.2 orthologue. The high ENC value, low Fop, and RSCU value highlighted that FAE1 and FAD2 genes had a low level of gene expression and moderate preference for codon usage across the Brassicas. In addition, neutrality plot, parity rule, and correspondence analysis revealed that natural selection pressure had significantly contributed to CUB for FAE1 genes, whereas mutation and selection pressure occurred for FAD2 genes. This study would help to decode codon optimization, improve the level of expression of exogenous genes, and transgenic engineering to increase fatty acid profiling for the betterment of seed oil in Brassica species.

Genetic behavior of induced translocation heterozygote in Artemisia annua L.

From the population raised from gamma irradiated seeds at different doses (100, 200 and 300 Gy), at 100 Gyphenotypically dissimilar plant (from the control plants) was isolated. The plant was shorter and morphologically weaker in contrast to control population. The cytological studies were carried out in a plant showed segmental exchanges between heterologous chromosomes. Chromosomal associations in rings and chains along with bivalents and univalents were observed in pollen mother cells (PMCs) during microsporogenesis. Various anaphasic anomalies were also taken into account including chromatid bridges, laggards and unequal separations etc. Subsequent stages of meiosis were also found to be highly intermittent. Owing to the high frequency of chromosomal aberrations, pollen fertility in control (96.32%) were efficaciously reduced to 38.26% at dose of 100Gy. The present study has been conducted to assess cytological behavior of the induced translocation heterozygote which is first time induced through gamma irradiation in the Artemisia annua L.

Above‐belowground linkages of functionally dissimilar plant communities and soil properties in a grassland experiment

AbstractChanges in plant community composition can have long‐lasting consequences for ecosystem functioning. However, how the duration of plant growth of functionally distinct grassland plant communities influences abiotic and biotic soil properties and thus ecosystem functions is poorly known. In a field experiment, we established identical experimental subplots in two successive years comprising of fast‐ or slow‐growing grass and forb community mixtures with different forb:grass ratios. After one and two years of plant growth, we measured above‐ and belowground biomass, soil abiotic characteristics (pH, organic matter, soil nutrients), soil microbial properties (respiration, biomass, community composition), and nematode abundance. Fast‐ and slow‐growing plant communities did not differ in above‐ and belowground biomass. However, fast‐ and slow‐growing plant communities created distinct soil bacterial communities, whereas soil fungal communities differed most in 100% forb communities compared to other forb:grass ratio mixtures. Moreover, soil nitrate availability was higher after two years of plant growth, whereas the opposite was true for soil ammonium concentrations. Furthermore, total nematodes and especially bacterial‐feeding nematodes were more abundant after two years of plant growth. Our results show that plant community composition is a driving factor in soil microbial community assembly and that the duration of plant growth plays a crucial role in the establishment of plant community and functional group composition effects on abiotic and biotic soil ecosystem functioning under natural field conditions.

Investigation of Antioxidant Activity and Physicochemical Properties of Local and Branded Honeys in Sindh, Pakistan

The honey is a sweetest natural products because it have unique properties, which honey bees are collect from dissimilar plants materials. The honey is used as a nutritional purposes for human consumption and also use for medicinal and industrial purposes. The honey also an important product in the international markets. The present study was conducted to analyzed the physicochemical and antioxidant activities of different honey samples in Sindh Pakistan. The 15 honey samples were analyzed for parameters including pH, electrical conductivity, moisture, viscosity, ash%, density and antioxidant activity. The average value of pH was founded 3.78 electrical conductivity 2492 μs/cm, viscosity 12.34 mpa, moisture 15.99%, density 0.78 and average value of antioxidant activity was founded 19.12 mg/100g.

IMPACT OF ENDOPHYTIC LIPOPEPTIDES USE AGAINST SOME PLANT PATHOGENIC MICROORGANISMS

Twelve dissimilar plant associated bacterial colonies were isolated from five different tomato seedlings, the Non Ribosomal Lipopeptides genes were detected by degenerated primers technique in the twelve tomato endophytic isolates, only the long rode bacilli endophytic strains were found to harbour the lipopeptides synthetases genes, these three strains were given laboratory names of (BMG100, BMG101 and BMG102) for further pursuit. Partial sequencing of 16s RNA gene and protein profile analysis for the three bacilli isolates showed that all isolates belonged to Bacillus subtilis. The lipopeptides production by HPLC analysis revealed that all the endophytic isolates from tomato stems had the ability to produce lipopeptides except the third isolate named B. subtilis BMG102 showed no production. different levels of volumetric oxygen transfer coefficient (KLa) were used as cursors for lipopeptides production. The maximum concentration of surfactin type was about 1431, 529 and 437 mg.L-1, the plipastitin (fengycin type ) was 360 198 mg.L-1 and zero while the Mycosubtilin (iturin type) was zero, 228 and 414 mg.L-1 for the strains B. subtilis ATCC21332, BMG100 and BMG101, respectively. Surfactin production is visibly optimal at high oxygen transfer (kLa) and showed more than 0.07 S-1, while the optimum production of the fengycin and iturin could be observed at mild values of O2 transfer (kLa) which equal 0.01 and 0.015 S-1 respectively. The antibacterial - antifungal effects of the three B.subtilis extracts collected during lipopeptides productivity regimes showed inhibition activity against Pseudomonas syringae, Ralstonia solanacearum and Erwinia amylovora, as will as the antifungal activity against Aspergillus niger, Phanerochaete chrysosporium and Alternaria alternata. These results indicate potential use of B.subtilis strains as biocontrol agents, especially when considering commercial implementation. Studies regarding the lipopeptides applications, should also be considered as this will influence the efficacy of the lipopeptides against the target organisms.

Impacts of seven years of experimental warming and nutrient addition on neighbourhood species interactions and community structure in two contrasting alpine plant communities

Global change is predicted to have major impacts on alpine and arctic ecosystems. Plant fitness and growth will be determined by how plants interact with each other at smaller scales. Local-scale neighbourhood interactions may be altered by environmental pertubations, which could fundamentally affect community structure. This study examined the effects of seven years of experimental warming and nutrient addition on overall changes in the community structure and patterns of interspecific interaction between neighbouring plant species in two contrasting alpine plant communities, mesic meadow and poor heath, in subarctic Sweden. We used a network approach to quantify the dissimilarity of plant interaction networks and the average number of interspecific neighbourhood interactions over time in response to different environmental perturbations. The results revealed that combined warming and nutrient addition had significant negative effects on how dissimilar plant interaction networks were over time compared with the control. Moreover, plant–plant neighbourhood interaction networks were more dissimilar over time in nutrient-poor heath than in nutrient-rich mesic meadow. In addition, nutrient addition alone and combined nutrient addition and warming significantly affected neighbourhood species interactions in both plant communities. Surprisingly, changes in interspecific neighbourhood interactions over time in both communities were very similar, suggesting that the nutrient-poor heath is as robust to experimental environmental perturbation as the mesic meadow. Comparisons of changes in neighbouring species interactions with changes in evenness and richness at the same scale, in order to determine whether diversity drove such changes in local-scale interaction patterns, provided moderate evidence that diversity was behind the changes in local-scale interspecific neighbourhood interactions. This implied that species might interact at smaller scales than those at which community measures were made. Overall, these results demonstrated that global change involving increased nutrient deposition and warming is likely to affect species interactions and alter community structure in plant communities, whether rich or poor in nutrients and species.

Plant community composition and structural characteristics of an invaded forest in the Galápagos

Non-native species have invaded habitats worldwide, greatly impacting the structure and function of native communities and ecosystems. To better understand mechanisms of invasion impacts and how to restore highly impacted and transformed ecosystems, studies are needed that evaluate invader effects on both biotic communities and structural characteristics. On Santa Cruz Island in Galapagos we compared biotic (plant species richness, diversity, and community composition) and structural (canopy openness, forest height, and leaf litter) characteristics of a relic forest dominated by an endemic and highly threatened tree and a forest dominated by an invasive tree. The forests are located within the historical distribution of the endemic tree, which now occupies only 1% of its original extent. We found that the invaded forest had 42% lower native plant species richness and 17% less plant diversity than the endemic tree dominated forest. Additionally, with the invader there was 36% greater non-native plant species richness, 37% higher non-native plant diversity, and highly dissimilar plant composition when compared to the endemic-dominated forest. Additionally, the invaded forest had a more open and taller tree canopy and greater leaf litter cover than native forest. The presence of the invasive tree and the associated forest structural changes were the primary factors in models that best explained higher non-native diversity in the invaded forest. Our correlational results suggest that an invasive tree has significantly altered plant assemblage and forest structural characteristics in this unique ecosystem. Experiments that remove the invader and evaluate native plant community responses are needed to identify thresholds for practical restoration of this threatened and biologically unique native forest.

Root exudate cocktails: the link between plant diversity and soil microorganisms?

Higher plant diversity is often associated with higher soil microbial biomass and diversity, which is assumed to be partly due to elevated root exudate diversity. However, there is little experimental evidence that diversity of root exudates shapes soil microbial communities. We tested whether higher root exudate diversity enhances soil microbial biomass and diversity in a plant diversity gradient, thereby negating significant plant diversity effects on soil microbial properties. We set up plant monocultures and two‐ and three‐species mixtures in microcosms using functionally dissimilar plants and soil of a grassland biodiversity experiment in Germany. Artificial exudate cocktails were added by combining the most common sugars, organic acids, and amino acids found in root exudates. We applied four different exudate cocktails: two exudate diversity levels (low‐ and high‐diversity) and two nutrient‐enriched levels (carbon‐ and nitrogen‐enriched), and a control with water only. Soil microorganisms were more carbon‐ than nitrogen‐limited. Cultivation‐independent fingerprinting analysis revealed significantly different soil microbial communities among exudate diversity treatments. Most notably and according to our hypothesis, adding diverse exudate cocktails negated the significant plant diversity effect on soil microbial properties. Our findings provide the first experimental evidence that root exudate diversity is a crucial link between plant diversity and soil microorganisms.

Cascading effects of belowground predators on plant communities are density-dependent.

Soil food webs comprise a multitude of trophic interactions that can affect the composition and productivity of plant communities. Belowground predators feeding on microbial grazers like Collembola could decelerate nutrient mineralization by reducing microbial turnover in the soil, which in turn could negatively influence plant growth. However, empirical evidences for the ecological significance of belowground predators on nutrient cycling and plant communities are scarce. Here, we manipulated predator density (Hypoaspis aculeifer: predatory mite) with equal densities of three Collembola species as a prey in four functionally dissimilar plant communities in experimental microcosms: grass monoculture (Poa pratensis), herb monoculture (Rumex acetosa), legume monoculture (Trifolium pratense), and all three species as a mixed plant community. Density manipulation of predators allowed us to test for density-mediated effects of belowground predators on Collembola and lower trophic groups. We hypothesized that predator density will reduce Collembola population causing a decrease in nutrient mineralization and hence detrimentally affect plant growth. First, we found a density-dependent population change in predators, that is, an increase in low-density treatments, but a decrease in high-density treatments. Second, prey suppression was lower at high predator density, which caused a shift in the soil microbial community by increasing the fungal: bacterial biomass ratio, and an increase of nitrification rates, particularly in legume monocultures. Despite the increase in nutrient mineralization, legume monocultures performed worse at high predator density. Further, individual grass shoot biomass decreased in monocultures, while it increased in mixed plant communities with increasing predator density, which coincided with elevated soil N uptake by grasses. As a consequence, high predator density significantly increased plant complementarity effects indicating a decrease in interspecific plant competition. These results highlight that belowground predators can relax interspecific plant competition by increasing nutrient mineralization through their density-dependent cascading effects on detritivore and soil microbial communities.

Trophic phylogenetics: evolutionary influences on body size, feeding, and species associations in grassland arthropods.

Contemporary animal-plant interactions such as herbivory are widely understood to be shaped by evolutionary history. Yet questions remain about the role of plant phylogenetic diversity in generating and maintaining herbivore diversity, and whether evolutionary relatedness of producers might predict the composition of consumer communities. We tested for evidence of evolutionary associations among arthropods and the plants on which they were found, using phylogenetic analysis of naturally occurring arthropod assemblages sampled from a plant-diversity manipulation experiment. Considering phylogenetic relationships among more than 900 arthropod consumer taxa and 29 plant species in the experiment, we addressed several interrelated questions. First, our results support the hypothesis that arthropod functional traits such as body size and trophic role are phylogenetically conserved in community ecological samples. Second, herbivores tended to cooccur with closer phylogenetic relatives than would be expected at random, whereas predators and parasitoids did not show phylogenetic association patterns. Consumer specialization, as measured by association through time with monocultures of particular host plant species, showed significant phylogenetic signal, although the. strength of this association varied among plant species. Polycultures of phylogenetically dissimilar plant species supported more phylogenetically dissimilar consumer communities than did phylogenetically similar polycultures. Finally, we separated the effects of plant species richness and relatedness in predicting the phylogenetic distribution of the arthropod assemblages in this experiment. The phylogenetic diversity of plant communities predicted the phylogenetic diversity of herbivore communities even after accounting for plant species richness. The phylogenetic diversity of secondary consumers differed by guild, with predator phylogenetic diversity responding to herbivore relatedness, while parasitoid phylogenetic diversity was driven by plant relatedness. Evolutionary associations between plants and their consumers are apparent in plots only meters apart in a single field, indicating a strong role for host-plant phylogenetic diversity in sustaining landscape consumer biodiversity.

Keeping Pace with Climate Change: Stage-Structured Moving-Habitat Models

Life cycles can limit the abilities of species to track changing climatic conditions. We combined age or stage structure and a moving-habitat model to explore the effects of life history on the persistence of populations in the presence of climate change. We studied four dissimilar plant species in moving patches and found that (1) population growth rates, (2) elasticities with respect to the survival (stasis and shrinkage) components of the projection matrix, and (3) the evenness of the elasticities with respect to the components of the projection matrix all decreased as we increased the translational speeds of the patches. In addition, the value of long-distance dispersal increased with patch speed for three of the four species. Our analyses confirm that rapid growth, high fecundity, and long-distance dispersal can benefit species in moving patches. Thus, species with long generation times and limited dispersal ability are especially vulnerable to habitat movement. Stage-structured moving-habitat models can easily incorporate spatial complexity and can help us predict the effects of shifting climatic conditions.

Aphid Protein Effectors Promote Aphid Colonization in a Plant Species-Specific Manner

Microbial pathogens and pests produce effectors to modulate host processes. Aphids are phloem-feeding insects, which introduce effectors via saliva into plant cells. However, it is not known if aphid effectors have adapted to modulate processes in specific plant species. Myzus persicae is a polyphagous insect that colonizes Arabidopsis thaliana and Nicotiana benthamiana, while the pea aphid Acyrthosiphon pisum specializes on colonizing plant species of the family Fabaceae. We found that M. persicae reproduction increased on transgenic Arabidopsis, producing the M. persicae effectors C002, PIntO1 (Mp1), and PIntO2 (Mp2), whereas reproduction of M. persicae did not increase on Arabidopsis producing the A. pisum orthologs of these three proteins. Plant-mediated RNA interference experiments showed that c002- and PIntO2-silenced M. persicae produce less progeny on Arabidopsis and N. benthamiana than nonsilenced aphids. Orthologs of c002, PIntO1, and PIntO2 were identified in multiple aphid species with dissimilar plant host ranges. We revealed high nonsynonymous versus synonymous nucleotide substitution rates within the effector orthologs, indicating that the effectors are fast evolving. Application of maximum likelihood methods identified specific sites with high probabilities of being under positive selection in PIntO1, whereas those of C002 and PIntO2 may be located in alignment gaps. In support of the latter, a M. persicae c002 mutant without the NDNQGEE repeat region, which overlaps with an alignment gap in C002, does not promote M. persicae colonization on Arabidopsis. Taken together, these results provide evidence that aphid effectors are under positive selection to promote aphid colonization on specific plant species.

High value of short rotation coppice plantations for phytodiversity in rural landscapes

AbstractThe demand for wood from short rotation coppice (SRC) plantations as a renewable energy source is currently increasing and could affect biodiversity in agricultural areas. The objective was to evaluate the contribution of SRC plantations to phytodiversity in agricultural landscapes assessed as species richness, species–area relationships, Shannon indices, detrended correspondence analysis on species composition, Sørensen similarities, habitat preference proportions, and species proportions found in only one land use. Vegetation surveys were conducted on 12 willow (Salix spp.) and three poplar (Populus spp.) coppice sites as well as on surrounding arable lands, grasslands and forests in central Sweden and northern Germany. SRC plantations were richer in plant species (mean: 30 species per 100 m²) than arable land (10), coniferous forests (13) and mixed forests in Germany (12). Comparing SRC plantations with other land uses, we found lowest similarities in species composition with arable lands, coniferous forests and German mixed forests and highest similarities with marginal grassland strips, grasslands and Swedish mixed forests. Similarity depended on the SRC tree cover: at increased tree cover, SRC plantations became less similar to grasslands but more similar to forests. The SRC plantations were composed of a mixture of grassland (33%), ruderal (24%) and woodland (15%) species. Species abundance in SRC plantations was more heterogeneous than in arable lands. We conclude that SRC plantations form novel habitats leading to different plant species composition compared to conventional land uses. Their landscape‐scale value for phytodiversity changes depending on harvest cycles and over time. As a structural landscape element, SRC plantations contribute positively to phytodiversity in rural areas, especially in land use mosaics where these plantations are admixed to other land uses with dissimilar plant species composition such as arable land, coniferous forest and, at the German sites, also mixed forest.

Use of focussed beam reflectance measurement (FBRM) for monitoring changes in biomass concentration

The potential of focussed beam reflectance measurement (FBRM) as a tool to monitor changes in biomass concentration was investigated in a number of biological systems. The measurement technique was applied to two morphologically dissimilar plant cell suspension cultures, Morinda citrifolia and Centaurea calcitrapa, to a filamentous bacteria, Streptomyces natalensis, to high density cultures of Escherichia coli and to a murine Sp2/0 hybridoma suspension cell line, 3-2.19. In all cases, the biomass concentration proved to be correlated with total FBRM counts. The nature of the correlation varied between systems and was influenced by the concentration, nature, size and morphology of the particle under investigation.

Carbon dioxide enrichment alters plant community structure and accelerates shrub growth in the shortgrass steppe.

A hypothesis has been advanced that the incursion of woody plants into world grasslands over the past two centuries has been driven in part by increasing carbon dioxide concentration, [CO(2)], in Earth's atmosphere. Unlike the warm season forage grasses they are displacing, woody plants have a photosynthetic metabolism and carbon allocation patterns that are responsive to CO(2), and many have tap roots that are more effective than grasses for reaching deep soil water stores that can be enhanced under elevated CO(2). However, this commonly cited hypothesis has little direct support from manipulative experimentation and competes with more traditional theories of shrub encroachment involving climate change, management, and fire. Here, we show that, although doubling [CO(2)] over the Colorado shortgrass steppe had little impact on plant species diversity, it resulted in an increasingly dissimilar plant community over the 5-year experiment compared with plots maintained at present-day [CO(2)]. Growth at the doubled [CO(2)] resulted in an approximately 40-fold increase in aboveground biomass and a 20-fold increase in plant cover of Artemisia frigida Willd, a common subshrub of some North American and Asian grasslands. This CO(2)-induced enhancement of plant growth, among the highest yet reported, provides evidence from a native grassland suggesting that rising atmospheric [CO(2)] may be contributing to the shrubland expansions of the past 200 years. Encroachment of shrubs into grasslands is an important problem facing rangeland managers and ranchers; this process replaces grasses, the preferred forage of domestic livestock, with species that are unsuitable for domestic livestock grazing.

Succession and resilience in boreal mixedwood plant communities 15–16 years after silvicultural site preparation

Non-native plant abundance, vascular and non-vascular diversity and plant community succession were studied 10 and 15–16 years after stand initiation at two mixedwood boreal sites in northwestern Canada. At Inga Lake, five silvicultural treatments (untreated, plowed-and-inverted, rotocleared-and-mixed, burned-windrow, repeated vegetation control) created a gradient from pure broadleaf to pure white spruce ( Picea glauca [Moench] Voss) overstories. At Iron Creek, four treatments (untreated, mounded, plowed-and-inverted, vegetation control) produced a narrower range of conifer:broadleaf ratios. Both experiments were randomized block designs with 4–5 replications. Univariate ANOVA, stepwise regression and multivariate ANOVA by canonical redundancy analysis were used to address three questions: (1) did non-native species diminish over time?; (2) how was understory diversity related to overstory composition?; and (3) did highly dissimilar plant communities diverge or converge over time? Non-native cover declined three- to six-fold between the two sampling dates. Non-vascular richness generally doubled over the 5–6-year sampling interval. Understory diversity increased with treatment severity and frequency and was positively correlated with conifer overstory abundance. At Inga Lake, there was successional convergence among all treatments. Convergence was most rapid on severely burned windrows where plants originated mainly from seed, and slowest on rotocleared-and-mixed sites with a dense turf of Calamagrostis canadensis (Michx.) Beauv. At Iron Creek, the vegetation control treatment diverged slightly from untreated communities after recent manual cutting. Our results demonstrate the strong resilience of these boreal mixedwood plant communities and suggest ways that silvicultural intervention can modify stand composition and diversity to address a variety of ecosystem management goals.

Restoring Structure in Late‐Successional Sagebrush Communities by Thinning with Tebuthiuron

AbstractLate successional, dense Artemisia tridentata (big sagebrush) stands restrict associated plant species production, resulting in a monotypic, shrub‐dominated community that threatens biodiversity preservation and ecosystem function. Traditional practices to control A. tridentata can severely reduce or temporarily eliminate A. tridentata and other plant species. Thinning A. tridentata with low rates of the herbicide tebuthiuron enhances herbaceous plant production, community structure, ecosystem functioning, and biodiversity. Tebuthiuron was applied at rates of 0.11–1.0 kg ai/ha to A. tridentata‐dominated plots at Ten Sleep (1979), Lander (1993), and Waltman (1993), Wyoming. Changes in A. tridentata canopy cover, associated plant species biomass, and community composition were evaluated 13 and 14 years post‐treatment at Ten Sleep, and 2 and 4 years post‐treatment at Lander and Waltman. At all sites A. tridentata canopy cover decreased proportionally with increased tebuthiuron rate. Biomass of grasses increased as shrub biomass and cover decreased with increasing tebuthiuron rate. Forb biomass varied between treatments across sample year and site. Shifts from shrub‐dominated control to grass‐dominated treatment plots were attributable to biomass differences of A. tridentata and 2–3 grass species among treatments. The number of plant species was not significantly different between treatments at any site. Similarity indexes revealed progressively greater dissimilar plant composition between the control and sequential treatment plots of increased tebuthiuron rate. Incremental rates of tebuthiuron produce gradual changes in plant species composition without reducing species richness, which may have utility in certain restoration projects.

The molecular revolution in ectomycorrhizal ecology: peeking into the black-box.

Molecular tools have now been applied for the past 5 years to dissect ectomycorrhizal (EM) community structure, and they have propelled a resurgence in interest in the field. Results from these studies have revealed that: (i) EM communities are impressively diverse and are patchily distributed at a fine scale below ground; (ii) there is a poor correspondence between fungi that appear dominant as sporocarps vs. those that appear dominant on roots; (iii) members of Russulaceae, Thelephoraceae, and/or non-thelephoroid resupinates are among the most abundant EM taxa in ecosystems sampled to date; (iv) dissimilar plants are associated with many of the same EM species when their roots intermingle--this occurs on a small enough spatial scale that fungal individuals are likely to be shared by dissimilar plants; and (v) mycoheterotrophic plants have highly specific fungal associations. Although, these results have been impressive, they have been tempered by sampling difficulties and limited by the taxonomic resolution of restriction fragment length polymorphism methods. Minor modifications of the sampling schemes, and more use of direct sequencing, has the potential to solve these problems. Use of additional methods, such as in situ hybridization to ribosomal RNA or hybridization coupled to microarrays, are necessary to open up the analysis of the mycelial component of community structure.

Vegetation along hydrologic and edaphic gradients in a North Carolina coastal plain creek bottom and implications for restoration

We described the vegetation of two alluvial swamp forest stands along Durham Creek in Beaufort County, North Carolina, USA in relation to elevation, hydrologic, and edaphic gradients. Over 3,000 sur- veyed elevations of individual plant microsites were used in conjunction with 26 years of stream gage data to examine individual species responses to annual and growing season flooding frequencies. Direct gradient analyses combined with plot ordinations derived from detrended correspondence analysis and canonical correspondence analysis suggested that differences in vegetation between the stands were primarily the result of variations in elevation, growing season flooding frequency, percent base saturation, exchangeable acidity, and soil physical properties. Although the stands were less than 4.5 km apart and without significant inter- mediate tributaries, growing season flooding frequency and duration were magnified in the lowest elevations of the downstream stand. An elevation difference of as little as 10 cm resulted in a 20% difference in the frequency of surface flooding during the growing season. Species distributions were significantly correlated with depth to mottling (r 2 5 0.75), flooding frequency (r 2 52 0.57), elevation (r 2 5 0.70), and several soil chemical properties. The two stands had very similar annual surface flooding regimes, but subtle differences in growing season flooding frequency, soil characteristics, and disturbance history have apparently resulted in dissimilar plant community composition and structure. These results suggest that the lack of quantitative data on vegetation-environment interactions occurring at the microtopographic scale (10 21 m) in alluvial swamp forests makes precise prediction, planning, or design of created or restored wetland composition and function a formidable challenge.