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Extreme drought events during post-fire regeneration are becoming increasingly frequent in Mediterranean-type ecosystems. Understanding how plants with different traits and origins respond to such conditions during early life stages is therefore critical for assessing the effect of climate change. Here, seedlings of three Cistus (semi-deciduous malacophylls from the Mediterranean Basin) and three Ceanothus (evergreen sclerophylls from California) species, two post-fire seeder genera with contrasting leaf traits, were subjected to complete water deprivation for 3 months in a common garden experiment. The leaf and plant structure and plant tissue water relations were characterized before the drought, and the functional responses (water availability, gas exchange and fluorescence) were monitored during the drought. Both genera exhibited contrasting leaf structure and tissue water relations traits, with higher leaf area and specific leaf area as well as higher osmotic potential at maximum turgor and turgor loss point in Cistus than Ceanothus. During drought, Ceanothus showed a more conservative use of water than Cistus , with a water potential less sensitive to decreasing soil moisture and a strong decline in photosynthesis and stomatal conductance in response to water deficit, but also a level of fluorescence more responsive to drought than Cistus. However, we could not find a different degree of drought resistance between the genera. This was particularly clear between Cistus ladanifer L. and Ceanothus pauciflorus DC. the two most functionally contrasting species, but at the same time, the two most drought-resistant. Our findings demonstrate that species with different leaf traits and functional responses to water stress may not differ in their degree of drought resistance, at least during the seedling stage. This underlines the need to take general categorizations by genus or functional types with caution and to deepen our knowledge about the Mediterranean-type species ecophysiology, especially during early life stages, in order to anticipate their vulnerability to climate change. [ABSTRACT FROM AUTHOR]

Many plant species are likely to face population decline or even extinction in the coming century, especially those with a limited distribution and inadequate dispersal relative to the projected rates of climate change. The obligate seeding California endemic, Ceanothus perplexans is especially at risk, and depending on how climate change interacts with altered fire regimes in Southern California, certain populations are likely to be more at risk than others. To identify which areas within the species’ range might need conservation intervention, we modeled population dynamics of C. perplexans under various climate and fire regime change scenarios, focusing on spatially explicit patterns in fire frequency. We used a species distribution model to predict the initial range and potential future habitat, while adapting a density-dependent, stage-structured population model to simulate population dynamics. As a fire-adapted obligate seeder, simulated fire events caused C. perplexans seeds to germinate, but also killed all adults in the population. Our simulations showed that the total population would likely decline under any combination of climate change and fire scenario, with the species faring best at an intermediate fire return interval of around 30–50 years. Nevertheless, while the total population declines least with a 30–50 year fire return interval, the effect of individual subpopulations varies depending on spatially explicit patterns in fire simulations. Though climate change is a greater threat to most subpopulations, increased fire frequencies particularly threatened populations in the northwest of the species’ range closest to human development. Subpopulations in the mountainous southern end of the range are likely to face the sharpest declines regardless of fire. Through a combination of species distribution modeling, fire modeling, and spatially explicit demographic simulations, we can better prepare for targeted conservation management of vulnerable species affected by global change.

Community interaction webs describe both direct and indirect interactions among species. Changes in direct interactions often become noticeable soon after a perturbation, but time lags in the responses of many species may delay the appearance of indirect effects and lead to temporal or spatial variation in interaction webs. Accurately identifying these shifts in the field requires time‐specific, spatially differentiated interaction webs. We explore how variation in browsing affects interaction webs in a long‐unburned chaparral shrubland near the central California coast. Most prior work in chaparral focused on rapid changes for <5 years after a wildfire that were assumed to determine community patterns until the next fire. Here, we report the results of the first 15 years of an ongoing experiment monitoring how interaction webs in long‐unburned chaparral (at least 100 years postfire) respond to experimental variation in browsing by deer and rabbits on dominant shrubs (Arctostaphylos pumila, Ceanothus cuneatus var. rigidus, and Ericameria ericoides). We hypothesized that variation in browsing would directly affect foodplants, indirectly modify growth and survival of other shrubs, and impact habitat needed by herbaceous plants. We found a dynamic web of plant–herbivore and plant–plant interactions that responded rapidly to changes in deer browsing on Ceanothus followed by indirect interactions that continued developing over several years, affecting shrubs, open space, herbaceous plants, and small mammals. Experimental variation in the intensity of deer browsing led to temporal and spatial changes in interactions that produced three different community interaction webs. With deer, community webs were complex, having numerous direct and indirect interactions. Removing deer simplified the community web, changed outcomes of interactions, and reduced open space and herbaceous plant densities. Finally, changes in Ceanothus morphology without deer allowed woodrats to browse these shrubs, with negative impacts on Ceanothus growth and survival. General field observations also showed that all three alternative interaction webs occurred naturally at our fieldsite, varying across space and over time. Long‐unburned chaparral communities browsed by deer maintain high biological diversity, but maintenance of this diversity involves many key direct and indirect biotic interactions. [ABSTRACT FROM AUTHOR]

Defoliation by herbivores can reduce carbon assimilation, change plant water relations, and even shift the biotic structure of plant communities. In this study, we took advantage of a long-term deer exclosure experiment to examine the consequences of persistent deer herbivory on plant water relations and the xylem structure-function relationships in Ceanothus rigidus, a maritime chaparral shrub in coastal California. Browsed plants had thicker stems with many intertwined short distal twigs, and significantly higher sapwood-to-leaf area ratios than their non-browsed counterparts. Leaf area-specific hydraulic conductivity was similar in both browsed and non-browsed plants, but xylem area-specific conductivity was significantly lower in the browsed plants. Vessel diameters were equivalent in both plant groups, but the number of vessels on a transverse area basis was nearly 40% lower in the browsed plants, accounting for their lower transport efficiency. Mid-day in situ water potentials and losses of hydraulic conductivity due to embolism were similar in both groups of plants but stomatal conductance was higher in the browsed shrubs in the early part of the growing season. We discuss our findings in the context of whole-plant ecophysiology, and explore the consequences of herbivory on hormonal signals, wood anatomy, and xylem function.

Ceanothus verrucosus (CEVE) is a globally rare, long-lived, chaparral shrub endemic to coastal southern California (CA) and northernMexico. There is concern for CEVE persistence because of habitat loss, fire, and climate change, yet little is known about basic features of the plant, including whether it contains annual rings, plant age, and climate-growth response. Growth-ring analysis was challenging because of semi-ring-porous structure, false, andmissing rings. We successfully crossdated CEVE annual rings, primarily fromCabrillo NationalMonument, CA, using a nearby Pinus torreyana chronology. The oldest living individual had 116 rings; the oldest inner-ring date was 1873; and most of the plants established between 1894 and 1905, all older than previous estimates. CEVE mortality occurred during a dry period from the late 1940s through the early 1960s. Correlations between age and stem measurements were weak to moderate (r = 0.10 to 0.56) posing challenges for field-based estimates of plant ages, which are important for population modeling. Variability in CEVE ring width had a strong positive correlation with prior cool-season (October-April) precipitation, yet 2- to 7-day warm-season precipitation events were recorded as rare false rings in multiple years, indicating extreme plasticity in cambial phenology and growth response to moisture. [ABSTRACT FROM AUTHOR]

Abstract Frankia sp. NRRL B-16219 was directly isolated from a soil sample obtained from the rhizosphere of Ceanothus jepsonii growing in the USA. Its host plant range includes members of Elaeagnaceae species. Phylogenetically, strain NRRL B-16219 is closely related to “Frankia discariae” with a 16S rRNA gene similarity of 99.78%. Because of the lack of genetic tools for Frankia, our understanding of the bacterial signals involved during the plant infection process and the development of actinorhizal root nodules is very limited. Since the first three Frankia genomes were sequenced, additional genome sequences covering more diverse strains have helped provide insight into the depth of the pangenome and attempts to identify bacterial signaling molecules like the rhizobial canonical nod genes. The genome sequence of Frankia sp. strain NRRL B-16219 was generated and assembled into 289 contigs containing 8,032,739 bp with 71.7% GC content. Annotation of the genome identified 6211 protein-coding genes, 561 pseudogenes, 1758 hypothetical proteins and 53 RNA genes including 4 rRNA genes. The NRRL B-16219 draft genome contained genes homologous to the rhizobial common nodulation genes clustered in two areas. The first cluster contains nodACIJH genes whereas the second has nodAB and nodH genes in the upstream region. Phylogenetic analysis shows that Frankia nod genes are more deeply rooted than their sister groups from rhizobia. PCR-sequencing suggested the widespread occurrence of highly homologous nodA and nodB genes in microsymbionts of field collected Ceanothus americanus.

Estimating the spatial distribution of weeds for site-specific control is essential. Therefore, this research was conducted to predict and interpolate the spatial distribution of Amaranthus retroflexus L. populations using a Radial Basis Function Neural Network (RBF-NN) in two potato fields. Weed population data were collected from sampling 200 and 36 points, respectively, in two commercial potato fields in Jolge Rokh, of Torbat Heidarieh in Khorasan Razavi and Mojen of Shahroud in Semnan Provinces, Iran, in 2012. Some statistical tests, such as comparisons of the means, variance and statistical distribution, as well as linear regression, were used for the observed point sample data and the estimated weed seedling density surfaces to evaluate the neural network capability for predicting the spatial distribution of the weed. The results showed that the trained RBF-NN had high capability in the spatial prediction in points that were not sampled with 100% output, 0.999 coefficients, and an average error of less than 0.04 and 0.07 in the Mojen and Jolge Rokh Regions, respectively. Test results also showed that there was no significant difference between the statistical characteristics of actual data and the values predicted by the RBF-NN. According to the experimental results, the RBFNN can be used as an alternative method to estimate the spatial changes function of annual weeds with random dispersion, such as Redroot Pigweed. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Amaranthus retroflexus increased diversity and richness of soil N-fixing bacterial communities (SNB). • Heavy metal pollution (HMP) decreased number of species and richness of SNB. • Combined A. retroflexus and HMP decreased total number of all species of SNB. • Combined A. retroflexus and HMP decreased richness of SNB. Abstract Soil nitrogen (N) availability is generally considered as the mainly driving force of successful colonization of many kinds of invasive plant species. Meanwhile, the vast majority of biologically available N in ecosystems mainly originates from soil N-fixing bacterial communities (SNB) primarily via biological N-fixation. The progressive shifts in the components of heavy metal pollution (HMP) can cause obvious changes in soil microbial communities (especially SNB). This study aims to comprehensively analyze the effects of redroot pigweed (Amaranthus retroflexus L.) invasion on the community structure of SNB under Cu and Cd heavy metal soil pollution (independent copper (Cu), independent cadmium (Cd), and combined Cu and Cd) by using high-throughput sequencing. The positive effects of redroot pigweed invasion on the total number of all species, the number of species, the diversity, and the richness of SNB may be that redroot pigweed can trigger obvious variation in soil nutrient content (especially N), a key driver of the community structure of SNB, via the root exudates and/or leaf litters. The negative effects of HMP on the number of species and the richness of SNB may be attributed to the additional energy cost to SNB and/or the decreased soil pH under HMP. The effects of the combined Cu and Cd on the total number of all species and the richness of SNB were higher than those under the independent Cu and Cd. This may be due to the stronger oxidative stress under the combined heavy metals. The negative effects of redroot pigweed invasion treatment with all types of HMP on the total number of all species and the richness of SNB may be ascribed to the shifts in soil physicochemical properties (especially the stronger acidification) and the additional energy cost which can wave remarkably effects on the abundance of the nifH gene. Accordingly, the invasion of redroot pigweed may be inhibited under HMP as a result of the shifts in certain species of SNB and the decreased the total number of all species and the richness of SNB. [ABSTRACT FROM AUTHOR]

Two types of nitrogen-fixing root nodule symbioses are known, rhizobial and actinorhizal symbioses. The latter involve plants of three orders, Fagales, Rosales, and Cucurbitales. To understand the diversity of plant symbiotic adaptation, we compared the nodule transcriptomes of Datisca glomerata (Datiscaceae, Cucurbitales) and Ceanothus thyrsiflorus (Rhamnaceae, Rosales); both species are nodulated by members of the uncultured Frankia clade, cluster II. The analysis focused on various features. In both species, the expression of orthologs of legume Nod factor receptor genes was elevated in nodules compared to roots. Since arginine has been postulated as export form of fixed nitrogen from symbiotic Frankia in nodules of D. glomerata , the question was whether the nitrogen metabolism was similar in nodules of C. thyrsiflorus. Analysis of the expression levels of key genes encoding enzymes involved in arginine metabolism revealed up-regulation of arginine catabolism, but no up-regulation of arginine biosynthesis, in nodules compared to roots of D. glomerata , while arginine degradation was not upregulated in nodules of C. thyrsiflorus. This new information corroborated an arginine-based metabolic exchange between host and microsymbiont for D. glomerata , but not for C. thyrsiflorus. Oxygen protection systems for nitrogenase differ dramatically between both species. Analysis of the antioxidant system suggested that the system in the nodules of D. glomerata leads to greater oxidative stress than the one in the nodules of C. thyrsiflorus , while no differences were found for the defense against nitrosative stress. However, induction of nitrite reductase in nodules of C. thyrsiflorus indicated that here, nitrite produced from nitric oxide had to be detoxified. Additional shared features were identified: genes encoding enzymes involved in thiamine biosynthesis were found to be upregulated in the nodules of both species. Orthologous nodule-specific subtilisin-like proteases that have been linked to the infection process in actinorhizal Fagales, were also upregulated in the nodules of D. glomerata and C. thyrsiflorus. Nodule-specific defensin genes known from actinorhizal Fagales and Cucurbitales, were also found in C. thyrsiflorus. In summary, the results underline the variability of nodule metabolism in different groups of symbiotic plants while pointing at conserved features involved in the infection process. [ABSTRACT FROM AUTHOR]

Premise of the Study: Studies across diverse species have established theory for the contribution of leaf traits to plant drought tolerance. For example, species in more arid climates tend to have smaller leaves of higher vein density, higher leaf mass per area, and more negative osmotic potential at turgor loss point (πTLP). However, few studies have tested these associations for species within a given lineage that have diversified across an aridity gradient. Methods: We analyzed the anatomy and physiology of 10 Ceanothus (Rhamnaceae) species grown in a common garden for variation between and within "wet" and "dry" subgenera (Ceanothus and Cerastes, respectively) and analyzed a database for 35 species for leaf size and leaf mass per area (LMA). We used a phylogenetic generalized least squares approach to test hypothesized relationships among traits, and of traits with climatic aridity in the native range. We also tested for allometric relationships among anatomical traits. Key Results: Leaf form, anatomy, and drought tolerance varied strongly among species within and between subgenera. Cerastes species had specialized anatomy including hypodermis and encrypted stomata that may confer superior water storage and retention. The osmotic potentials at turgor loss point (πTLP) and full turgor (πo) showed evolutionary correlations with the aridity index (AI) and precipitation of the 10 species' native distributions, and LMA with potential evapotranspiration for the 35 species in the larger database. We found an allometric correlation between upper and lower epidermal cell wall thicknesses, but other anatomical traits diversified independently. Conclusions: Leaf traits and drought tolerance evolved within and across lineages of Ceanothus consistently with climatic distributions. The πTLP has signal to indicate the evolution of drought tolerance within small clades. [ABSTRACT FROM AUTHOR]

Frankia sp. NRRL B-16219 was directly isolated from a soil sample obtained from the rhizosphere of Ceanothus jepsonii growing in the USA. Its host plant range includes members of Elaeagnaceae species. Phylogenetically, strain NRRL B-16219 is closely related to 'Frankia discariae' with a 16S rRNA gene similarity of 99.78%. Because of the lack of genetic tools for Frankia, our understanding of the bacterial signals involved during the plant infection process and the development of actinorhizal root nodules is very limited. Since the first three Frankia genomes were sequenced, additional genome sequences covering more diverse strains have helped provide insight into the depth of the pangenome and attempts to identify bacterial signaling molecules like the rhizobial canonical nod genes. The genome sequence of Frankia sp. strain NRRL B-16219 was generated and assembled into 289 contigs containing 8,032,739 bp with 71.7% GC content. Annotation of the genome identified 6211 protein-coding genes, 561 pseudogenes, 1758 hypothetical proteins and 53 RNA genes including 4 rRNA genes. The NRRL B-16219 draft genome contained genes homologous to the rhizobial common nodulation genes clustered in two areas. The first cluster contains nodACIJH genes whereas the second has nodAB and nodH genes in the upstream region. Phylogenetic analysis shows that Frankia nod genes are more deeply rooted than their sister groups from rhizobia. PCR-sequencing suggested the widespread occurrence of highly homologous nodA and nodB genes in microsymbionts of field collected Ceanothus americanus. [ABSTRACT FROM AUTHOR]

North America is home to approximately 55 species of Ceanothus (Rhamnaceae), more than 30 of them endemic to the biodiversity hotspot known as the California Floristic Province. Although several species of Ceanothus are widespread in North America, most of the species are micro-endemics, known from a small number of occurrences and generally associated with special ecological conditions. As botanical exploration of North America continues, it is expected that more such micro-endemics will be discovered. However, field work is not the only way in which additional Ceanothus diversity will come to light; the strongly variable morphology of Ceanothus means that specimens are difficult to identify, and many biological entities that probably deserve taxonomic recognition are already represented in herbaria but have not yet been recognized as new. We here describe three new taxa of Ceanothus, two initially noted among existing collections, and another discovered during botanical exploration in San Diego County. All three are edaphic micro-endemics found only in the southern California Floristic Province, California. These include 1) Ceanothus foliosus var. viejasensis D. O. Burge&Rebman, restricted to gabbro-derived soils on ViejasMountain in SanDiego County, 2) Ceanothus pendletonensis D. O. Burge, Rebman, &M. R. Mulligan, found on granodiorite-derived soils of the central Santa Margarita Mountains in San Diego County, and 3) Ceanothus thyrsiflorus var. obispoensis D. O. Burge, endemic to rhyolite-derived soils near Hollister Peak in San Luis Obispo County. [ABSTRACT FROM AUTHOR]

The Santa Monica Mountains are home to many species of chaparral shrubs that provide vegetative cover and whose deep roots contribute to the stability of the steep slopes. Recently, native chaparral have been threatened by an unprecedented drought and frequent wildfires in Southern California. Besides the damage from the wildfires themselves, there is the potential for subsequent structural losses due to erosion and landslides. In this paper, we develop a mathematical model that predicts the impact of drought and frequent wildfires on chaparral plant community structure. We begin by classifying chaparral into two life history types based on their response to wildfires. Nonsprouters are completely killed by a fire, but their seeds germinate in response to fire cues. Facultative sprouters survive by resprouting but also rely on seed germination for post-fire recovery. The individual-based model presented here simulates the growth, seed dispersal, and resprouting behavior of individual shrubs across two life history types as they compete for space and resources in a rectangular domain. The model also incorporates varying annual rainfall and fire frequency as well as the competition between plants for scarce resources. The parameters were fit using seedling and resprout survivorship data as well as point quarter sampling data from 1986 to 2014 at a biological preserve within the natural landscape of the Malibu campus of Pepperdine University. The simulations from our model reproduce the change in plant community structure at our study site which includes the local extinction of the nonsprouter Ceanothus megacarpus due to shortened fire return intervals. Our simulations predict that a combination of extreme drought and frequent wildfires will drastically reduce the overall density of chaparral, increasing the likelihood of invasion by highly flammable exotic grasses. The simulations further predict that the majority of surviving shrubs will be facultative sprouting species such as Malosma laurina. [ABSTRACT FROM AUTHOR]

Chaparral wildfires typically create even-aged stands of vegetation that grow quickly in the first 2 decades following a fire. Patterns of this growth are important for understanding ecosystem productivity and re-establishment success, but are logistically challenging to measure over long time periods. We tested the utility of a novel method of using shrub growth rings to estimate stand-level biomass accumulation at an annual time scale in southern California chaparral. We examined how temporal variation in precipitation and spatial variation in solar irradiation influence that accumulation. Using field measurements and a relationship between stem basal area and aboveground biomass, we estimated current biomass levels in an 11-year-old chaparral stand, and used growth-ring diameters to estimate growth in each year from age 4 to 11 years. We found that annual growth as measured by shrub growth rings tracked closely with patterns of annual precipitation, but not with time since fire. Solar irradiation was not found to be a significant covariate with total biomass by plot, possibly due to sampling area limitations. The close relationship of annual biomass accumulation with annual precipitation indicates that shrub growth-ring measurements can provide a useful metric of stand-level recovery. [ABSTRACT FROM AUTHOR]

Woody plant expansion is a global phenomenon that alters the spatial distribution of nutrients, biomass, and fuels in affected ecosystems. Altered fuel patterns across the landscape influences ecological processes including fire behavior, fire effects, and can impact post-fire plant germination and establishment. The purpose of this study was to determine how accumulations of ground fuels beneath western juniper ( Juniperus occidentalis ssp . occidentalis) canopies, composed of litter and duff, affect post-fire species response in sagebrush steppe and to quantify fuel loading patterns. Field sampling and analysis was conducted across environmental gradients following the 2007 Tongue-Crutcher Wildfire in southwestern Idaho to determine conditions that were most influential in post-fire vegetation recovery patterns. Duff depth and fire severity were determined to be the most influential factors affecting post-fire vegetation response. Decreasing species richness and native perennial grass cover was represented along the increasing duff depth gradient. Species response grouped by fire severity revealed significant presence of cheatgrass ( Bromus tectorum) in low severity sites and a dominance of snowbrush ceanothus ( Ceanothus velutinus) in higher severity sites. Determining sub-crown surface fuel characteristics offers the potential to predict future patterns and processes as they relate to burn severity and vegetation recovery components in developing woodlands. [ABSTRACT FROM AUTHOR]

Many studies have shown the importance of air-filled porosity (VA) for optimal growth and dry weight of container-grown plants, but few have examined its effects on California native plants. Anecdotal evidence suggests that various upland native species require higher substrate aeration or less frequent irrigation than do standard nursery crops. We tested effects of VA and irrigation frequency on 15 California native species that had been identified by growers as challenging because of their aeration needs and sensitivity to overwatering. Plants were grown in substrates with 10% or 22% VA and were irrigated once (up to 574 ml) or twice daily (up to total of 972 ml). None of the applied treatments preferentially influenced plant survival or growth. Results indicate that these species may tolerate both normal and high VA values. The high survival and growth rates in these experiments indicate that growers' experiences of plant death or poor plant growth are attributable to something other than VA. [ABSTRACT FROM AUTHOR]

Open conditions created by restoration activities in ponderosa pine (Pinus ponderosa) forests of the American Southwest can lead to increases in understory plant productivity but also attract large ungulate herbivores. In this study, we remeasured buckbrush (Ceanothus fendleri) plants on permanent plots to determine effects of long-term herbivore exclusion on population abundance and potential reproduction. Results showed that survival of buckbrush was significantly lower on unprotected plots compared with plants given long-term herbivore protection. A greater proportion of the highest stem density class (> 50 stems m-2) was found on long-term protection plots compared with short-term protection or unprotected groups. The unprotected group was overwhelmingly (90%) made up of plots with less than 10 aerial stems m-2. Plots with long-term protection had a significantly greater proportion of plots in the highest flowering class (> 50% of aerial stems flowering) than unprotected plots. Logistic regression showed a strong, positive relationship (p < 0.001; R2 = 0.61) between the probability of flowering and plant height. Results indicated that short-term protection following forest restoration treatments marginally improves survival of buckbrush in these ecosystems. However, herbivory pressure remained high over the 12-year study period and detrimentally affected potential reproduction of plants exposed to large herbivores. These findings generally suggest that short-term protection may not be sufficient to conserve buckbrush populations over time and high herbivory pressure may be constraining understory responses and slowing restoration success. [ABSTRACT FROM AUTHOR]

The aim of the study was to establish whether the redroot pigweed (Amaranthus retroflexus L.), which is a common weed in potato crops can be a source of Alternaria alternata, the causal agent of Alternaria leaf blight, and to determine the genetic diversity of isolates of this pathogen infecting the weed and the potato cultivar tested. With the A. alternata isolates selected for genetic testing, homosporous cultures were obtained, from which DNA (deoxyribonucleic acid) was subsequently isolated. The genetic diversity of A. alternata isolates was determined by the RAPD-PCR (random amplification of polymorphic-polymerase chain reaction) method. Based on the results obtained, it was found that the dominant fungi present on the diseased leaves of both potato and pigweed plants were: Alternaria alternata, A. solani, Cladosporium cladosporioides, C. herbarum, Epicoccum purpurascens and Fusarium sambucinum. Presence of A. alternata as a dominant fungus on redroot pigweed suggests that if weed infestation is extensive, the pathogen is very likely to spread and its population to increase. [ABSTRACT FROM AUTHOR]

Infestation by onion thrips, Thrips tabaci Lindeman, was determined on transplants of onion (Allium cepa L.) received in Colorado during March and April from out-of-state sources (Imperial Valley, CA; near Phoenix, AZ; and southern Texas) during 2004 to 2008. In the 5 years of the study, 50 to 100% of the transplant lots sampled arrived infested with thrips. Among infested transplant lots, the overall number of thrips averaged 0.15 to 0.63 per plant, with as many as four per plant in some lots. T. tabaci was the dominant thrips species in all seasons and locations of transplant origin. In addition, 19 of 83 (23%) tested lots had plants positive for Iris yellow spot virus. Iris yellow spot virus and T. tabaci were detected in volunteer onion plants as early as 1 May, a few weeks after the summer onion crop was planted, suggesting a possible role of infected volunteer plants in perennation of the virus between onion crops. Iris yellow spot virus and T. tabaci were detected in many common weeds including blue mustard (Chorispora tenella (Pall.) DC), common purslane (Portulaca oleracea L.), field bindweed (Convolvulus arvensis L.), flixweed (Descurainia sophia Webb & Berth.), prickly lettuce (Lactuca serriola L.), and redroot pigweed (Amaranthus retroflexus L.) in early spring near onion fields in Colorado during 2006 to 2009. Confirmation that Iris yellow spot virus and Iris yellow spot virus-infective thrips overwintered in volunteer onions and some common winter annual and perennial weeds emphasizes that managing volunteer onions and weeds is important for management of iris yellow spot, in addition to planting transplants free of thrips and the pathogen. [ABSTRACT FROM AUTHOR]

Experiments were conducted to characterize the diversity of redroot pigweed populations collected from three sites in Jordan by evaluating morpho-phenological traits and by using amplified fragment length polymorphism (AFLP) analysis. Morpho-phenological evaluations conducted outdoors indicated that populations had similar phenological and morphological traits. The three populations had considerably similar diversity. However; one population was less diverse than the other two. Cluster analysis (Ward method) performed on all recorded morpho-phenological traits did not provide evidence of the presence of distinct biotypes in Jordanian redroot pigweed populations. AFLP electropherograms also were unable to define separate biotypes among the three populations. Apparently, the selection pressure imposed by herbicide applications on redroot pigweed populations is not extensive to create distinct biotypes. [ABSTRACT FROM AUTHOR]

We examined postfire regeneration of chaparral shrubs during an intense drought. This study focused on the demography and physiology of shrub species that resprout from a basal lignotuber following fire. We found significant levels of resprout mortality when intense drought occurred in the year following fire during the period of shrub recovery. Three of the seven sampled resprouting species had the greatest or near greatest levels of mortality ever recorded when compared to previous studies. Most shrub mortality occurred during the drought after individuals had resprouted (i.e. individuals survived fire, resprouted and then subsequently died). Physiological measurements of species with high mortality suggested that resprout stems were highly embolized and xylem hydraulic conductivities were close to zero during the peak of the drought. In addition, lignotubers of two of the three species experiencing high mortality were depleted of starch. Population densities of most shrub species declined after the drought compared with their prefire levels, with the exception of one drought tolerant obligate seeding species. Resprouting shrub species may deplete their carbohydrate reserves during the resprouting process, making them particularly vulnerable to drought because of the need to transpire water to acquire the CO2 that is used to supply energy to a large respiring root system. Drought appears to interact with fire by altering postfire shrub recovery and altering species abundances and composition of chaparral communities. [ABSTRACT FROM AUTHOR]

* Premise of the study: Hybridization is thought to have played an important role in diversification of the speciose shrub genus Ceanothus; putative hybrid species have been described, and data suggest that intrinsic barriers may not exist among closely related species. However, the extent to which hybridization occurs in the wild is not known, and little is understood about how extrinsic factors such as soil chemistry may influence the process. The present research focuses on the gabbro-endemic C. roderickii and the closely related soil-generalist C. cuneatus. Though the species occur peripatrically, they remain distinct across an edaphic disjunction. * Methods: AFLP was used to quantify hybridization and introgression. Biological data and experiments were used to test for prezygotic isolation. Growth trials were used to test for local adaptation and selection against hybrids. * Key results: Ceanothus cuneatus and C. roderickii were strongly differentiated morphologically and genetically, despite a lack of evidence for prezygotic barriers. Hybrids and back-crosses were present but infrequent. Finally, there was selection against hybrids in nonnative soil. * Conclusions: There is little genetic exchange between the focal species across an edaphic disjunction, despite the absence of prezygotic barriers. This result implies that soil conditions, as well as other extrinsic factors, should be considered as forces that may restrict hybridization and gene flow in Ceanothus, influencing local adaptation and speciation. Findings presented here are significant because they imply that exchange of genetic material between plants may be limited directly by the abiotic environment, rather than by the biology of the plants. [ABSTRACT FROM AUTHOR]

The effect of irrigation regimes and N rates on corn (Zea mays L.) yield and redroot pigweed (Amaranthus retroflexus L.) growth in sandy soils is not completely understood. Therefore, field experiments were conducted in a semiarid region of Iran in 2010 and 2011 to determine the influence of N rates and irrigation regimes on corn and redroot pigweed leaf area index (LAI), dry matter and grain yield, N uptake, irrigation water productivity (IWP) and N leaching loss. The experiment was conducted using a randomized complete-block design with a split-factorial arrangement of treatments in four replicates. The main plots were subjected to either a low (L) or a full (F) irrigation regime. The subplots were arranged in a factorial scheme with four N rates (0, 150, 300, and 450 kg N ha-1) and two levels of redroot pigweed interference with corn (weed free, CW0; and weedy, CW1). The results indicated that the more N was applied, the higher were corn grain yield losses in both irrigation regimes due to weed interference. The difference in corn grain yield between CW0F and CW1F treatments was 400 and 1800 kg ha-1 at N0 and N450 levels, respectively. In contrast, the difference between CW0L and CW1L reached 300 and 800 kg grain ha-1 at N0 and N450 levels, respectively. Based on the information gained in this study, we do not recommend increasing inputs (water and N), especially in sandy soils, to diminish the redroot pigweed/corn competition. [ABSTRACT FROM AUTHOR]

The article discusses a study that statistically tested species limits within the Ceanothus vestitus complex (Rhamnaceae) by using multivariate analysis on a suite of nine morphological traits that have been used in past treatments. It investigates possible alternative circumscriptions using naive statistical clustering methods and revises the taxonomy of the group based on the analyses. Results also show that only C. perplexans is significantly divergent from C. vestitus and C. pauciflorus.

Question Do variations in fire intensity within a stand determine changes in fire intensity and plant demographics in a subsequent fire? Location San Diego ( CA, USA); chaparral dominated by Adenostoma fasciculatum (resprouter) and Ceanothus greggii (seeder). Methods In 2003, a wildfire burned a young (16-yr-old) stand containing a set of experimental plots burned in 1987 with various levels of fire intensity. In 2004, all the 1987 plots were sampled for Adenostoma survival and the recruitment of both species. Similar measures were carried out in the adjacent old (75-yr) stand. Fire intensity in 2003 was estimated by a surrogate fire severity measure [minimum diameter of burned branches (branch diameter)]. Results In the young stand, branch diameter in 2003 was similar to the control plots in 1987, but lower than in the old stand. Fire intensity in 1987 did not significantly affect branch diameter in 2003. Survival of Adenostoma in the young stand was very low, much lower than after the 1987 burn and that in the old stand. Fire intensity in 1987 did not affect Adenostoma survival. Recruitment in Adenostoma increased, and in Ceanothus decreased, with increased fire intensity in 1987. Conclusions We demonstrate that there is a carry-over effect of fire intensity across a whole fire cycle on plant recruitment of the two dominant species. The 2003 fire partially reversed the relative effects on recruitment caused by elevated fire intensity in 1987. Arguably, this effect was driven by the contrasted relationships of the two species to fire intensity. Adenostoma survival in the young stand was much lower in 2003 than in 1987, despite similar branch diameter, and was also lower than in the old stand, despite higher branch diameter in this case. The causes of such mortality are unknown. [ABSTRACT FROM AUTHOR]

Mechanical mastication is increasingly used as a wildland fuel treatment, reducing standing trees and shrubs to compacted fuelbeds of fractured woody fuels. One major shortcoming in our understanding of these fuelbeds is how particle fracturing influences moisture gain or loss, a primary determinant of fire behaviour. To better understand fuel moisture dynamics, we measured particle and fuelbed drying rates of masticated Arctostaphylos manzanita and Ceanothus velutinus shrubs, common targets of mastication in fire-prone western USA ecosystems. Drying rates of intact and fractured particles did not differ when desorbing at the fuelbed surface, but these particles did dry more rapidly than underlying fuelbeds. Average response times of 10-h woody particles at the fuelbed surfaces ranged from 16 to 21 h, whereas response times of fuelbeds (composed of 1-h and 10-h particles) were 40 to 69 h. Response times did not differ between fuelbeds composed of fractured woody particles and fuelbeds composed of intact particles (P = 0.258). Particle fracturing as a result of mastication does not affect the drying rate, but the longer-than-expected response times of particles within fuelbeds underscores the needs to better understand fuel moisture dynamics in these increasingly common fuels. Through laboratory desorption experiments, we determined that fractured shrub particles from mastication fuels treatments do not dry faster than non-fractured particles in dense fuelbeds composed of equal fuel loading by diameter class. However, drying rates of fuelbeds were much slower than particles drying at their surface, indicating a propensity for moisture retention in these fuelbeds. [ABSTRACT FROM AUTHOR]

* Premise of the Study: California chaparral shrub species have different life history types: Nonsprouters (NS) are killed by fire and persist through a fire-stimulated seed bank; facultative sprouters (FS) reestablish by a combination of vegetative sprouting and seeding; and obligate sprouters (OS) reestablish exclusively by sprouting. Nonsprouters and FS establish seedlings in opencanopy postfire environments, whereas OS establish seedlings between fires in the shady understory. We hypothesized that allocation differences among seedlings of postfire sprouters and nonsprouters and regeneration niche differences would lead to contrasting patterns in biomass accumulation (NS > FS > OS, in sun; OS > FS > NS, in shade). * Methods: Seedlings of three species from each life history type were grown in sun and 75% shade. We measured net carbon assimilation and biomass accumulation after one year. * Key Results: Biomass accumulation was similar in the sun except FS>OS. In the shade, NS had lower biomass than FS and OS. Assimilation rates, nitrogen relations, and allocation differences could not fully explain biomass accumulation differences. Instead, biomass accumulation was inversely related to water-stress tolerance and shade tolerance. Additionally, OS and FS differed in root/shoot allocation even though both are sprouters. * Conclusions: Seedling growth and carbon assimilation rates were divergent among three life history types and were consistent with differences in tolerance to water stress and shade or sun regeneration niches, but not tradeoffs in sprouting-related allocation differences per se. [ABSTRACT FROM AUTHOR]

Understory shrubs play important ecological roles in forests of the western US, but they can also impede early tree growth and lead to fire hazard concerns when very dense. Some of the more common genera (Ceanothus, Arctostaphylos, and Prunus) persist for long periods in the seed bank, even in areas where plants have been shaded out. To determine shrub seed density and investigate the feasibility of managing shrub abundance by regulating the size of the soil seed bank with fire, we sampled the seed bank in 24 mixed conifer forest stands throughout northern California. Twenty stands were unburned, two had recently burned in wildfires, and two (McCloud and Jennie Springs) were subjected to experimental prescribed fires with unburned controls. Seeds were extracted from duff and soil that was collected in six layers, to a depth of 10 cm in the mineral soil. Ceanothus seeds were the most abundant (mean = 246 seeds m-2), noted at all sites and at 88 % of sampling locations within unburned sites. Arctostaphylos and Prunus seeds were less abundant (mean = 29 seeds m-2 and 6 seeds m-2, respectively), but still recorded at 64 % and 45 % of the unburned sites, respectively. The depth of seed burial varied at all unburned sites, but some seed was present even at the deepest (6 cm to 10 cm) soil layer, where seed mortality due to heat from burning is least likely. Seed density was substantially reduced, but not eliminated, by October prescribed burns at both McCloud and Jennie Springs, while seed density following July burns at Jennie Springs did not differ from the control. The abundance of buried seed indicates that restoring shrubs to forest understory should be possible even in areas where they are currently lacking. If preventing shrubs from colonizing a site is the management goal, the effectiveness of a single prescribed fire may be limited. [ABSTRACT FROM AUTHOR]

* Premise of the study: Ceanothus roderickii is an endangered shrub endemic to California. To investigate the population genetics of this species, including the genetic consequences of population fragmentation and hybridization, 10 microsatellite markers were developed. * Methods and Results: Using next-generation sequencing (454) data from a single C. roderickii individual, 10 microsatellite markers were developed. A group of 12 individuals representing all of the major C. roderickii populations were analyzed. All loci were found to be polymorphic, with a range from two to 12 alleles per locus. Observed heterozygosity ranged from 0.08 to 0.83 across loci. All 10 loci were also amplifiable in at least one other Ceanothus species. * Conclusions: Results presented here indicate the utility of our new microsatellite primers in ongoing and future studies concerning population genetics and gene flow in C. roderickii , as well as the potential applicability of these primers in similar studies on other Ceanothus species. [ABSTRACT FROM AUTHOR]

High diversity and endemism in the California Floristic Province (CFP) are an alleged response to the late Cenozoic advent of Mediterranean-type climate in this region. Ceanothus comprises two divergent subgenera with centers of diversity in the CFP. We reconstruct the evolution of Ceanothus by using DNA sequence data from the nuclear gene nitrate reductase. We find that the timing of diversification events is related to geological and climatic history. In both subgenera, diversification is characterized by recent divergence of extant taxa and geographically structured phylogenetic relationships. A strong north-south divergence of subgenus Cerastes across the Transverse Ranges indicates that phylogenetic relationships may be structured by climatically divergent regions of the CFP. Divergence-time estimation suggests that the age of extant diversification in both subgenera is ~6Ma. This agrees with the fossil record but predates the hypothesized Quaternary (2-Ma) origin of Mediterranean-type climate in the region. [ABSTRACT FROM AUTHOR]

Thinnings using cut-to-length or whole-tree harvesting systems followed by underburning were evaluated for their effects on seedling and sapling demography in a pure, uneven-aged Jeffrey pine (Pinus jeffreyi Grev. & Balf.) stand containing a minor component of California white fir (Abies concolor var. lowiana [Gord.] Lemm.). Depression of seedling counts due to forest floor disturbance associated with thinning was followed by a recovery largely confined to Jeffrey pine in the whole-tree treatment where final seedling counts exceeded those found initially. The postburn substrate was more favorable for establishment of Jeffrey pine than white fir seedlings, and the largest increase in seedling counts between the initial and final inventories occurred in the burned portion of the whole-tree treatment. Live sapling losses from thinning were greatest in the cut-to-length treatment, while underburning induced complete sapling mortality. Absent treatment, several stand and site variables influenced seedling and sapling abundance, prominent among them a propensity for mahala mat (Ceanothus prostratus Benth.) to elevate counts of white fir within both size classes. These results provide land managers insight into the impacts of six combinations of thinning and burning treatment on natural regeneration in eastern Sierra Nevada Jeffrey pine and similar dry site forest types. [ABSTRACT FROM PUBLISHER]

Mechanical mastication is a fuels treatment that converts shrubs and small trees into dense fuelbeds composed of fractured woody particles. Although compaction is thought to reduce fireline intensity, the added particle surface area due to fracturing could also influence fire behaviour. We evaluated effects of particle fracturing and moisture content (ranging from 2.5 to 13%) on fire behaviour in fuelbeds composed of masticated Arctostaphylos manzanita Parry and Ceanothus velutinus Dougl. shrubs in the laboratory. Fuelbeds composed of fractured particles did not burn with greater intensity than fuelbeds composed of intact particles, as hypothesised. Flame heights ranged from 54 to 95 cm and fireline intensity from 50 to 140 kJ s-1m-1, approximating values observed in field experiments. Masticated fuelbeds burned with shorter flame heights and longer flaming duration under higher fuel moistures, but duration of lethal heating (>60°C) above fuelbeds did not differ across the range of fuel moistures, averaging 12 min over a 0.1-m² area. Our results suggest that expected fire behaviour increases due to particle fracturing may be overwhelmed by fuelbed bulk density. The long-duration heating of burning masticated fuels may require managers to mitigate effects to trees and soils when fuel loads are high. [ABSTRACT FROM AUTHOR]

Fuel management techniques are commonly used in shrublands to reduce wildfire risk. However, more information about the ecological effects of these treatments is needed by managers and ecologists. In an effort to address this need, we performed a replicated (4 replicates per treatment) 48-ha experiment in northern California chaparral dominated by Adenostoma fasciculatum to determine the effects of two fuel reduction types (prescribed fire and mastication) and three different seasons of treatment (fall, winter, and spring) on shrub cover, height, and seedling density. Exclosures (2.5 m each) were also used to assess herbivory effects. By the third post-treatment year, prescribed fire treatments had higher shrub cover (71 ± 2%) than mastication (43 ± 4%). There was no treatment effect on shrub height, species richness, or composition. Seedling density was initially higher in prescribed fire treatments (31 ± 4 seedlings m) than mastication (3 ± 0 seedlings m); however, prescribed fire treatments experienced substantial mortality, especially spring burning, resulting in lower densities 3 years after treatments (18 ± 0 seedlings m after fall and winter fire compared to 2 ± 0 seedlings m after spring fire). A. fasciculatum remained the dominant shrub species after the treatments, and Ceanothus cuneatus recruitment was higher in fall burning. Deer herbivory only affected shrub height, especially in masticated units, resulting in heights of 55 ± 2 cm in unexclosed areas compared to 66 ± 4 cm inside exclosures by the third post-treatment year. Overall, our findings suggest that fuel treatments play an important role in shrubland community dynamics, at least in the short-term, with implications for re-treatment frequency, community structure, and wildlife habitat. [ABSTRACT FROM AUTHOR]

1. Shrubs in fire prone chaparral communities have evolved different life history types in response to fire. A key to understanding the evolution of life history type differences is to understand how physiological traits are linked to differences in life history type. Vascular adaptations are important for delivering an efficient and stable water supply to evergreen chaparral shrub leaves. This study tested for a link between vascular physiology and life history type in chaparral shrubs. 2. Chaparral shrub species along the south-western coast of North America survive wildfire by three different life histories. Non-sprouters are killed by fire and re-establish exclusively through germination of fire-stimulated seeds, facultative sprouters re-establish by a combination of vegetative sprouting and fire-stimulated seeds, and obligate sprouters re-establish exclusively by vegetative sprouting because their seeds do not survive fire. Non-sprouters and facultative sprouters establish seedlings in the open canopy post fire environment, whereas obligate sprouters establish seedlings in the shady understory of the mature chaparral canopy. 3. Seedlings of nine species (Rhamnaceae) representing three each of the different life history types were grown in deep containers in a common garden under treatments of sun and shade. Hydraulic conductance was measured using a high-pressure flow meter for all organs, and a vacuum technique was used to measure conductance of fine and woody roots. We predicted that non-sprouters would exhibit greater hydraulic efficiency than the sprouting species, and that facultative sprouters would be more efficient than the shade tolerant obligate sprouters. 4. Non-sprouters had the greatest hydraulic conductance per unit leaf and sapwood area at the whole seedling level, whereas facultative and obligate sprouters were not different. Comparing hydraulic conductance across major organs (from fine roots to leaves) showed that the hydraulic system was well coordinated. At the whole seedling level, the root system was more of a bottleneck than the shoot system. This pattern was consistent with high resistance extraxylary pathways in roots and differences in root architecture. 5. The greater hydraulic efficiency of the non-sprouter life history type is attributed to its post-fire pioneering habit and may partially explain the relatively high speciation in the non-sprouters. Lower hydraulic efficiency is associated with a sprouting life history and greater shade tolerance. The seedling root systems represent a hydraulic bottleneck that may place roots under especially intense selection. [ABSTRACT FROM AUTHOR]