Short-lived Perennial Plant Research Articles

“Realistic Choice of Annual Matrices Contracts the Range of λS Estimates” under Reproductive Uncertainty Too

Our study is devoted to a subject popular in the field of matrix population models, namely, estimating the stochastic growth rate, λS, a quantitative measure of long-term population viability, for a discrete-stage-structured population monitored during many years. “Reproductive uncertainty” refers to a feature inherent in the data and life cycle graph (LCG) when the LCG has more than one reproductive stage, but when the progeny cannot be associated to a parent stage in a unique way. Reproductive uncertainty complicates the procedure of λS estimation following the defining of λS from the limit of a sequence consisting of population projection matrices (PPMs) chosen randomly from a given set of annual PPMs. To construct a Markov chain that governs the choice of PPMs for a local population of Eritrichium caucasicum, an short-lived perennial alpine plant species, we have found a local weather index that is correlated with the variations in the annual PPMs, and we considered its long time series as a realization of the Markov chain that was to be constructed. Reproductive uncertainty has required a proper modification of how to restore the transition matrix from a long realization of the chain, and the restored matrix has been governing random choice in several series of Monte Carlo simulations of long-enough sequences. The resulting ranges of λS estimates turn out to be more narrow than those obtained by the popular i.i.d. methods of random choice (independent and identically distributed matrices); hence, we receive a more accurate and reliable forecast of population viability.

Born in the Mediterranean: Comprehensive Taxonomic Revision of Biscutella ser. Biscutella (Brassicaceae) Based on Morphological and Phylogenetic Data

Biscutella L. ser. Biscutella (= Biscutella ser. Lyratae Malin.) comprises mostly annual or short-lived perennial plants occurring in the Mediterranean basin and the Middle East, which exhibit some diagnostic floral features. Taxa in the series have considerable morphological plasticity, which is not well correlated with clear geographic or ecologic patterns. Traditional taxonomic accounts have focused on a number of vegetative and floral characters that have proved to be highly variable, a fact that contributed to taxonomic inflation mostly in northern Africa. A detailed study and re-evaluation of morphological characters, together with recent phylogenetic data based on concatenation of two plastid and one nuclear region sequence data, yielded the basis for a taxonomic reappraisal of the series. In this respect, a new comprehensive integrative taxonomic arrangement for Biscutella ser. Biscutella is presented in which 10 taxa are accepted, namely seven species and three additional varieties. The name B. eriocarpa DC. is reinterpreted and suggested to include the highest morphological variation found in northern Morocco. Its treatment here accepts two varieties, one of which is described as new (B. eriocarpa var. riphaea A. Vicente, M. Á. Alonso & M. B. Crespo). In addition, the circumscriptions of several species, such as B. boetica Boiss. & Reut., B. didyma L., B. lyrata L., and B. maritima Ten., are revisited. Nomenclatural types, synonymy, brief descriptions, cytogenetic data, conservation status, distribution maps, and identification keys are included for the accepted taxa, with seven lectotypes and one epitype being designated here.

Disappointing Survival Forecast for a Local Population of Androsace albana in a Random Environment

A local population of Andropace albana, a short-lived perennial plant, has been monitored during 10 years on permanent plots laid down in an alpine lichen heath in 2009. We summarize the outcome of monitoring as a non-autonomous matrix model of stage-structured population dynamics. The model originates from a life cycle graph constructed earlier for the stages of ontogenesis and consists of 9 annual “projection” matrices that are calibrated in a unique way from the observation data. Five of the 9 matrices have their dominant eigenvalues greater than 1, i.e., give favorable forecasts for the local population survival, while the rest four have those values less than 1, i.e., give the negative forecasts. To make the resulting prediction, we apply an original concept of the pattern-geometric averaging of given nonnegative matrices and obtain the dominant eigenvalue, λ1(G9), of the average matrix G9 markedly less than 1, indicating the population decline in the long term. The traditional method to forecast the local population is to estimate λS, the stochastic growth rate of the population in a random environment formed by a random choice from the same 9 annual matrices. Assuming the choice to be independent and equiprobable, we obtain the negative result as well, yet with higher quantitative values of λS. We associate these higher values with the artificial assumption of equal choice probability when forming the random sequence of annual matrices, each of which is indirectly reflecting the habitat conditions that have influenced the growth and development of plants during the year prior the calibration moment. This motivates the task to construct a more adequate model for choosing annual matrices, in which the probability of choice would be related to the dynamics of the real habitat factors for a given local population.

Diversification of Biscutella ser. Biscutella (Brassicaceae) followed post-Miocene geologic and climatic changes in the Mediterranean basin

Biscutella ser. Biscutella (= ser. Lyratae Malin.) is a group of mostly annual or short-lived perennial plants, with petals gradually tapering at the base and lateral intrastaminal nectaries, endemic to the Mediterranean basin and the Middle East. Recent taxonomic work has revealed that a relative morphological homogeneity occurs in Europe and Asia, but a high plasticity is found in N Africa for most of the characters traditionally used for taxonomic arrangements. This fact had generally led to overestimation of the number of taxa, which currently is reduced to ten (namely 7 species and 3 additional varieties), some of them being narrow endemics. In the present contribution, on the basis of a previous detailed morphological study carried out by the authors, the first comprehensive phylogeny based on 47 DNA sequence data including concatenation of two plastid (rpl32-trnL and trnV) and one nuclear (ITS) regions, together with the first time-calibrated phylogenetic tree, allows reappraisal of evolutionary and biogeographic relationships among the accepted taxa in the series. According to all evidence gathered in the present study, the current distribution of B. ser. Biscutella, mostly centred in the southern parts of the Mediterranean basin and the Middle East, suggests that it evolved in relation with the major geological and climatic events occurred in the Mediterranean basin and Eurasia within the last 20 million years. The origin of Biscutella is dated ca 18.75 Mya, and the radiation of the series triggered ca 5.87 Mya with the Messinian Salinity Crisis. Rapid diversification occurred coetaneously to the Intensification of Northern Hemisphere Glaciation (ca 2.86 Mya) onwards, with parallel large-amplitude aridity cycles in Africa and southwestern Asia. In recent times, the divergence of lineages became faster in the W Mediterranean (ca 1.54 to 0.43 Mya), mostly related to geographical and ecological patterns of specialisation. In many cases, the distribution of the current species is apparently linked to ancient glacial refuges in S Mediterranean basin.

Status of Endangered La Graciosa Thistle Cirsium scariosum var. loncholepis (Asteraceae) in Coastal Southern California

La Graciosa thistle Cirsium scariosum var. loncholepis (Asteraceae) is a biennial or short-lived perennial plant (usually 10 to 100 cm tall) that is endemic to southwestern San Luis Obispo County and western Santa Barbara County in coastal southern California, and little has been published regarding it. The taxon was listed as threatened under the California Endangered Species Act in 1990 and endangered under the U.S. Endangered Species Act in 2000. At Federal listing in 2000, La Graciosa thistle was known from 17 occurrences, 8 of which were likely extirpated. As of 2019, it is known from 21 occurrences of which five are extant, 15 are likely extirpated and 1 has unknown status. La Graciosa thistle exists as groups of individuals in wetland habitats in an arid and semi-arid landscape, and the five extant occurrences are associated with the Callender Dunes and Guadalupe Dunes in San Luis Obispo County. The plants flower once and then die, with a probable life span of 2 to 6 yr. Seed dispersal is by wind and also likely by water, and the taxon appears to have only a minimally persistent soil seed bank. The primary threat to La Graciosa thistle in 2019 is reduced water/lack of water, with groundwater decline as the likely major cause, along with hydrological alteration, drought and climate change. The groundwater decline appears to result primarily from extraction for urban, agricultural and industrial uses, and it is exacerbated by drought and climate change. In 2019, La Graciosa thistle meets the IUCN criteria for endangered.

Aggregation may or may not eliminate reproductive uncertainty

In matrix population models, there cannot be any ‘reproductive uncertainty’ when the life cycle graph contains only one reproductive stage. Otherwise, it is logical to expect that aggregating all the reproductive stages into a single one would exclude the very basis of uncertainty. However, can the aggregation change principally the model characteristics such as the dominant eigenvalue λ1 of the projection matrix, thus signifying the aggregation failure? I demonstrate that it can with the data mined in a case study on the dynamics of a local stage-structured population of Eritrichium caucasicum, a short-lived perennial plant species inhabiting an alpine lichen heath. Frobenius Theorem for nonnegative matrices specifies the upper and lower bounds for λ1 via the row (or column) sums of matrix elements, and the lower bound, when it exceeds the maximal possible λ1 of the original, disaggregated matrix, does explain why the aggregation may fail to eliminate reproductive uncertainty.

Status of the Endangered Chorro Creek Bog ThistleCirsium fontinalevar.obispoense(Asteraceae) in Coastal Central California

Chorro Creek bog thistle Cirsium fontinale var. obispoense (Asteraceae) is a biennial or short-lived perennial plant up to 2 m tall that occurs only in San Luis Obispo County, west of the outer coast ranges. It was listed as endangered under the California Endangered Species Act in 1993 and the U.S. Endangered Species Act in 1994. Chorro Creek bog thistle is a serpentine endemic, occupying perennial seeps and springs in serpentine soil and rock in western San Luis Obispo County from north of San Simeon Creek to south of the city of San Luis Obispo. At federal listing in 1994 Chorro Creek bog thistle was known from nine occurrences (one of these presumed extirpated) and with an estimate of <3,000 individuals. In 2016 the conservation status of Chorro Creek bog thistle is substantially improved because of an increased number of known occurrences along with an increased number of occurrences that are protected. Only two of nine known occurrences were protected in 1994, whereas 10 of 21 occurrences are protected in 2016. There are many other locations with habitat that have not been searched, in particular on private land. It is highly likely that additional unknown occurrences exist in San Luis Obispo County, and possibly also in Monterey County to the north and Santa Barbara County to the south. In consideration of the available information, we conclude that Chorro Creek bog thistle is still endangered. However, when using the international standards of IUCN, we assign the category data deficient because of the limitations of our data.

Nondestructive estimation of growth year in ginseng cultivars using the means of mathematical modeling on the basis of allometry.

Growth-year authentication has extraordinary significance for plant growth, structure and development research, and has a wide range of applications in value assessment of economic crops. Panax ginseng is the most commonly used medicinal plant in Asian countries. The fix number of growth-year is an important quality evaluation which is difficult to be obtained accurately in current technical conditions. Preliminary authentication theory for growth-year has been described in previous studies using a short-lived perennial medicinal plant (Paeonia lactiflora pall.) as the research material. In this research, we focused on the growth-year estimation in ginseng cultivars, and attempt to explore the age estimation method for vascular plants according to mathematical simulation of the root structure development. Micro data was obtained from 204 individuals of 3 different kinds of ginseng cultivars, which have a series of gradient age and a clear growth record. Outer diameter of the vascular cambium (b) and the radius of cross section (r) were measured with ordinary stereo microscope. We further designed and established two different kinds of authentication model based on the taproot structure development for growth year authentication (P =β*M-α and M = K*X1 (a) (1) X2 (a) (2) ). Moreover, the models were applied to identify the growth year of ginseng without damage using Micro-CT or DEI reconstruction. A potential method, have been recently described, the age of ginseng can be analyzed by telomere length and telomerase activity. However, we found that there are different results indicated in other species. We concluded that microscopic methods perceived currently were provided a more effective means for growth-year authentication.

PM 9/20 (1) Parthenium hysterophorus

PM 9/20 (1) <i>Parthenium hysterophorus</i>

Dianthus barbatus-A New Host of Stolbur Phytoplasma in Serbia.

Sweet William (Dianthus barbatus, Caryophyllaceae) is a biennial or short-lived perennial plant native to southern Europe, from the Pyrenees to the Carpathians and the Balkans. During the summers of 2012 and 2013, phytoplasma-like symptoms were observed on D. barbatus plants on a Serbian plantation (Pancevo, 44°51'49″ N, 20°39'33″ E, 80 m ASL). Only seven symptomatic plants were observed in the summer of 2012. Disease incidence in 2013 was estimated to be less than 1% but increased during 2014 to 4%. Affected plants, showing symptoms of leaf reddening, malformation, and proliferation; flower bud deficiency; and abnormal shoot production, were tested for phytoplasmas. Samples were collected from seven symptomatic and three symptomless plants each year (20 samples), and total nucleic acid was extracted from midrib tissue using a method that includes a phytoplasma enrichment step and DNA purification by chloroform/phenol (3). Oligonucleotide primers specific to the phytoplasma 16S to 23S rRNA intergenic spacer region were used in polymerase chain reaction (PCR) assays on DNA extracted from Sweet William plants (1,3). Using phytoplasma universal primer pairs P1/P7 and P1/16S-Sr, phytoplasma-specific 1.8- and 1.5-kb amplicons were obtained from four and six symptomatic plants collected in 2012 and 2013, respectively. Nested PCR with R16F2n/R2 primers yielded ~1.2-kb amplicons from DNAs of all symptomatic plants (1). No amplicon was generated in PCRs conducted with DNA templates from symptomless plants. Restriction fragment length polymorphism (RFLP) analysis of amplified 1.2-kb fragments was performed using four endonucleases (AluI, Tru1I, HhaI, and HpaII). Comparative analysis was done using RFLP patterns of Stolbur (Stol), Aster Yellows (AY), Flavescence Doree-C (FD-C), Poinsettia Branch-Inducing (PoiBI), and Clover Yellow Edge (CYE) phytoplasmas. PCR-RFLP patterns from tested samples were identical to those of the Stol reference strain, indicating that diseased Sweet William was affected by phytoplasma belonging to the 16SrXII-A (Stolbur) group. The sequence of a 1.2-kb rDNA PCR product derived from sample Tk9 (deposited under accession number KM401436 in NCBI GenBank) showed the closest identity (100%) to those of Bulgarian corn (KF907506.1), Iranian 'Bois Noir' (KJ637208.1), and two Serbian phytoplasmas (KJ174507.1 from Calendula officinalis and KF614623.1 from Paeonia tenuifolia), all belonging to the 'Candidatus Phytoplasma solani' Stolbur subgroup. Previously, Aster Yellows Phytoplasma (16SrI) had been detected in two Dianthus species: D. barbatus (Sweet William) and D. caryophyllus (carnation) (2). This is the first record of the 16SrXII-A phytoplasma subgroup being associated with yellowing and reddening of D. barbatus in Serbia. The Stolbur phytoplasma occurrence on Sweet William is significant for the management of the disease in Serbia.

Physicochemical and biological properties of luteolin-7-O-β-d-glucoside (cynaroside) isolated from Anthriscus sylvestris (L.) Hoffm.

A simple method for isolation of luteolin-7-O-β-d-glucoside (cynaroside) from a short-lived perennial plant Anthriscus sylvestris (L.) Hoffm. is described. Cynaroside was isolated in high purity as documented by high-performance liquid chromatography (HPLC), thermal, and nuclear magnetic resonance (NMR) analyses. Isolated cynaroside shows biological activity especially against Gram-negative bacteria, exhibits antimutagenic activity, suppresses biofilm formation of Pseudomonas aeruginosa and Staphylococcus aureus, and increases frequency of mutations leading to ciprofloxacin resistance in Salmonella typhimurium. Additionally, electron paramagnetic resonance (EPR) spectroscopy and 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) assay confirmed its antioxidant and radical scavenging activity. In situ EPR and ultraviolet–visible (UV–Vis) spectroelectrochemical experiments were performed to follow the oxidation reactions of cynaroside in dimethyl sulfoxide solutions. The primary oxidation step takes place on the 1,2-dihydroxybenzene subunit leading to an unstable semiquinone anion radical as proved by EPR spectroscopy and quantum chemical calculations. Spectroelectrochemical and antioxidant studies indicate an important role of the deprotonated form of cynaroside in its redox and antioxidant behavior.

A Quantitative Genetic Signature of Senescence in a Short-Lived Perennial Plant

The evolution of senescence (the physiological decline of organisms with age) poses an apparent paradox because it represents a failure of natural selection to increase the survival and reproductive performance of organisms. The paradox can be resolved if natural selection becomes less effective with age, because the death of postreproductive individuals should have diminished effects on Darwinian fitness [1, 2]. A substantial body of empirical work is consistent with this prediction for animals, which transmit their genes to progeny via an immortal germline. However, such evidence is still lacking in plants, which lack a germline and whose reproduction is diffuse and modular across the soma. Here, we provide experimental evidence for a genetic basis of senescence in the short-lived perennial plant Silene latifolia. Our pedigree-based analysis revealed a marked increase with age in the additive genetic variance of traits closely associated with fitness. This result thus extends to plants the quantitative genetic support for the evolutionary theory of senescence.

Molecular characterization of Chilli leaf curl virus and satellite molecules associated with leaf curl disease of Amaranthus spp

Amaranthus, collectively known as amaranth, is an annual or short-lived perennial plant used as leafy vegetables, cereals and for ornamental purposes in many countries including India. During 2011, leaf samples of Amaranthus plants displaying leaf curling, leaf distortion, leaf crinkling and yellow leaf margins were collected from Banswara district, Rajasthan in India. Full-length clones of a monopartite begomovirus, a betasatellite and an alphasatellite were characterized. The complete nucleotide sequence of the isolated begomovirus features as a typical 'Old World' begomovirus with the highest nucleotide per cent identity with Chilli leaf curl virus and hence, considered as an isolate of Chilli leaf curl virus. The complete nucleotide sequences of betasatellite and alphasatellite possess maximum nucleotide identity with Tomato yellow leaf curl Thailand betasatellite and Chilli leaf curl alphasatellite, respectively. This is the first report of the association of chilli-infecting begomovirus and satellite molecules infecting a new host, Amaranthus, causing leaf curl disease.

The triple helix of Plantago lanceolata: Genetics and the environment interact to determine population dynamics

The theory of evolution via natural selection predicts that the genetic composition of wild populations changes over time in response to the environment. Different genotypes should exhibit different demographic patterns, but genetic variation in demography is often impossible to separate from environmental variation. Here, we asked if genetic variation is important in determining demographic patterns. We answer this question using a long-term field experiment combined with general linear modeling of deterministic population growth rates (lambda), deterministic life table response experiment (LTRE) analysis, and stochastic simulation of demography by paternal lineage in a short-lived perennial plant, Plantago lanceolata, in which we replicated genotypes across four cohorts using a standard breeding design. General linear modeling showed that growth rate varied significantly with year, spatial block, and sire. In LTRE analysis of all cohorts, the strongest influences on growth rate were from year x spatial block, and cohort x year x spatial block interactions. In analysis of genetics vs. temporal environmental variation, the strongest impacts on growth rate were from year and year x sire. Finally, stochastic simulation suggested different genetic composition among cohorts after 100 years, and different population growth rates when genetic differences were accounted for than when they were not. We argue that genetic variation, genotype x environment interactions, natural selection, and cohort effects should be better integrated into population ecological studies, as these processes should result in deviations from projected deterministic and stochastic population parameters.

Comparative population genetic structure in a plant-pollinator/seed predator system

Comparative analyses of spatial genetic structure of populations of plants and the insects they interact with provide an indication of how gene flow, natural selection and genetic drift may jointly influence the distribution of genetic variation and potential for local co-adaptation for interacting species. Here, we analysed the spatial scale of genetic structure within and among nine populations of an interacting species pair, the white campion Silene latifolia and the moth Hadena bicruris, along a latitudinal gradient across Northern/Central Europe. This dioecious, short-lived perennial plant inhabits patchy, often disturbed environments. The moth H.bicruris acts both as its pollinator and specialist seed predator that reproduces by laying eggs in S.latifolia flowers. We used nine microsatellite markers for S.latifolia and eight newly developed markers for H.bicruris. We found high levels of inbreeding in most populations of both plant and pollinator/seed predator. Among populations, significant genetic structure was observed for S.latifolia but not for its pollinator/seed predator, suggesting that despite migration among populations of H.bicruris, pollen is not, or only rarely, carried over between populations, thus maintaining genetic structure among plant populations. There was a weak positive correlation between genetic distances of S.latifolia and H.bicruris. These results indicate that while significant structure of S.latifolia populations creates the potential for differentiation at traits relevant for the interaction with the pollinator/seed predator, substantial gene flow in H.bicruris may counteract this process in at least some populations.

Current and potential distribution of Senecio madagascariensis Poir. (fireweed), an invasive alien plant in Japan

The short-lived perennial (sometimes annual) plant, Senecio madagascariensis Poir. (fireweed) is native to South Africa and Madagascar. This plant is an invasive weed becoming naturalized over a wide range of the world, and has caused agricultural damage mainly due to its toxicity to livestock. In Japan, fireweed was first found in 1976, and has been spreading throughout the country. In this study, the current distribution of fireweed in Japan was investigated. Using a maximum entropy ecological niche modeling algorithm, the relationship between the distribution records of fireweed and climatic variables was modeled, and the potential distribution of fireweed was predicted. Many growing sites of fireweed have been observed on the Pacific coast and Seto Inland Sea coast. The northern and southern ends of the current distribution were the Pacific coast of southern Tohoku (36.9172°N, 140.8613°E) and southern Kyushu (31.5654°N, 130.3438°E), respectively. The results of modeling showed that mean temperature in the warmest quarter was the most influential predictor, and suggested that geographical distribution of fireweed in Japan is restricted mainly by temperature, not by precipitation. The predicted areas of potential distribution were mainly on the Pacific coast and eastern Seto Inland Sea coast. Of the regions where fireweed had not been found, the following regions were predicted as potential distribution areas of fireweed: southern Kanto region along Tokyo Bay, coastal area of western Tokai region, western part of Seto Inland Sea coast and northern Kyushu. The Pacific coast of central Tohoku (39.058°N, 141.843°E) was predicted as the northern end of the potential distribution, and Amami-oshima Island (28.304°N, 129.519°E) as the southern end.

Plant Induced Defenses Depend More on Plant Age than Previous History of Damage: Implications for Plant-Herbivore Interactions

Herbivore-induced plant responses can significantly change as a function of plant developmental stage and previous history of damage. Yet, empirical tests that assess the combined role of multiple damage events and age-dependent constraints on the ability of plants to induce defenses within and among tissues are scarce. This question is of particular interest for annual and/or short-lived perennial plant species, whose responses to single or multiple damage events over a growing season are likely to interact with ontogenetic constraints in affecting a plant's ability to respond to herbivory. Using Plantago lanceolata and one of its specialist herbivores, Junonia coenia, we examined the effect of plant ontogeny (juvenile vs. mature developmental stages) and history of damage (single and multiple damage events early and/or late in the season) on plant responses to leaf damage. Plant responses to herbivory were assessed as induced chemical defenses (iridoid glycosides) and compensatory regrowth, in both above- and below-ground tissues. We found that constitutive concentration of iridoid glycosides markedly increased as plants matured, but plant ability to induce chemical defenses was limited to juvenile, but not mature, plant stages. In addition, induced defenses observed 7d following herbivory in juvenile plants disappeared 5wk after the first herbivory event, and mature plants that varied considerably in the frequency and intensity of damage received over 5wk, did not differ significantly in their levels of chemical defenses. Also, only small changes in compensatory regrowth were detected. Finally, we did not observe changes in below-ground tissues' defenses or biomass a week following 50% removal of leaf tissues at either age class or history of damage. Together, these results suggest that in P. lanceolata and perhaps other systems, ontogenetic trajectories in plant growth and defenses leading to strong age-dependent induced responses may prevail over herbivore-induced indirect interactions.

Fine-scale spatial genetic structure and gene dispersal in Silene latifolia

Plants are sessile organisms, often characterized by limited dispersal. Seeds and pollen are the critical stages for gene flow. Here we investigate spatial genetic structure, gene dispersal and the relative contribution of pollen vs seed in the movement of genes in a stable metapopulation of the white campion Silene latifolia within its native range. This short-lived perennial plant is dioecious, has gravity-dispersed seeds and moth-mediated pollination. Direct measures of pollen dispersal suggested that large populations receive more pollen than small isolated populations and that most gene flow occurs within tens of meters. However, these studies were performed in the newly colonized range (North America) where the specialist pollinator is absent. In the native range (Europe), gene dispersal could fall on a different spatial scale. We genotyped 258 individuals from large and small (15) subpopulations along a 60 km, elongated metapopulation in Europe using six highly variable microsatellite markers, two X-linked and four autosomal. We found substantial genetic differentiation among subpopulations (global F(ST)=0.11) and a general pattern of isolation by distance over the whole sampled area. Spatial autocorrelation revealed high relatedness among neighboring individuals over hundreds of meters. Estimates of gene dispersal revealed gene flow at the scale of tens of meters (5-30 m), similar to the newly colonized range. Contrary to expectations, estimates of dispersal based on X and autosomal markers showed very similar ranges, suggesting similar levels of pollen and seed dispersal. This may be explained by stochastic events of extensive seed dispersal in this area and limited pollen dispersal.

Edaphic environment, gall midges, and goldenrod clonal expansion in a mid-successional old-field

During the middle stage of old-field succession, genets of clonal plants vie to take over space from annual and short-lived perennial plants. We studied factors that may influence the relative rates of expansion of Solidago altissima genets in an old-field population attacked by the gall midge Rhopalomyia solidaginis . Genets growing in more clayey soil expanded more slowly, as evidenced by differences in rhizome growth. Edaphic conditions also affected galling frequencies, with genets in more sandy soil having twice as many galls. Gall midges reduced goldenrod stem growth, and stem height was positively correlated with rhizome growth. For a given stem height, galled ramets allocated relatively more biomass to rhizome growth than ungalled ramets. The end result was that galled ramets produced the same number and sizes of rhizomes as ungalled ramets.

Photosynthesis in an invasive grass and native forb at elevated CO2 during an El Niño year in the Mojave Desert.

Annual and short-lived perennial plant performance during wet years is important for long-term persistence in the Mojave Desert. Additionally, the effects of elevated CO2 on desert plants may be relatively greater during years of high resource availability compared to dry years. Therefore, during an El Niño year at the Nevada Desert FACE Facility (a whole-ecosystem CO2 manipulation), we characterized photosynthetic investment (by assimilation rate-internal CO2 concentration relationships) and evaluated the seasonal pattern of net photosynthesis (A net) and stomatal conductance (g s) for an invasive annual grass, Bromus madritensis ssp. rubens and a native herbaceous perennial, Eriogonum inflatum. Prior to and following flowering, Bromus showed consistent increases in both the maximum rate of carboxylation by Rubisco (V Cmax) and the light-saturated rate of electron flow (J max) at elevated CO2. This resulted in greater A net at elevated CO2 throughout most of the life cycle and a decrease in the seasonal decline of maximum midday A net upon flowering as compared to ambient CO2. Eriogonum showed significant photosynthetic down-regulation to elevated CO2 late in the season, but the overall pattern of maximum midday A net was not altered with respect to phenology. For Eriogonum, this resulted in similar levels of A net on a leaf area basis as the season progressed between CO2 treatments, but greater photosynthetic activity over a typical diurnal period. While g s did not consistently vary with CO2 in Bromus, it did decrease in Eriogonum at elevated CO2 throughout much of the season. Since the biomass of both plants increased significantly at elevated CO2, these patterns of gas exchange highlight the differential mechanisms for increased plant growth. The species-specific interaction between CO2 and phenology in different growth forms suggests that important plant strategies may be altered by elevated CO2 in natural settings. These results indicate the importance of evaluating the effects of elevated CO2 at all life cycle stages to better understand the effects of elevated CO2 on whole-plant performance in natural ecosystems.