Increase In Shoot Density Research Articles

Long-Term Population Changes of a Fire-Adapted Plant Subjected to Different Fire Seasons

Abstract Long-term studies of the responses of plant populations to fire can inform adaptive management of ecosystems. I present results of an analysis of responses of a fire-adapted plant, Pityopsis graminifolia (Michx.) Nutt. (silkgrass goldenaster), to season of fire from 2001 to 2005 in a longleaf pine (Pinus palustris P. Miller) sandhill community in north Florida. Replicated May-burned and January-burned plots had been burned biennially from 1986 to 2004. Previous work in the early 1990s showed that populations of this species benefited more from fires during the peak lightning fire season (i.e., May) than from January fires. In 2001, however, shoot densities in both treatments were substantially lower than in 1992 and remained relatively low through March 2005. Shoot densities were significantly higher in May-burned plots than in January-burned plots between 2001 and 2005. May fires significantly increased shoot densities in 2002 (relative to January fires), but did not in 2004. Shoot densities in ...

Managing Tree-of-Heaven (Ailanthus altissima) in Parks and Protected Areas: A Case Study of Rondeau Provincial Park (Ontario, Canada)

The Carolinian Life Zone in southwestern Ontario, Canada is valued because it represents an almost disjunct ecosystem (i.e., one that is typical of the mid-Atlantic United States, rather than the rest of Canada or the nearby states in the United States). The landscape of the Carolinian Life Zone has undergone dramatic transformation, especially in recent decades as agriculture, urbanization, and recreation have intensified. One of the most apparent changes is the invasion of exotic plant species that exacerbates the need for mass restoration efforts. Within the Carolinian Life Zone, Rondeau Provincial Park has experienced an influx of nonindigenous, invasive species in recent years. Tree-of-heaven (Ailanthus altissima) is one example. The infestation is still relatively localized to (mainly) the park, slowly spreading, and manageable as long as something is done immediately. We examined the effects of hand-pulling and mulching, cut stump and glyphosate application, cut stump alone, and the EZJect Capsule Injection System (using glyphosate) on the management of A. altissima within the park. Cut stump and glyphosate treatment was most effective and efficient in its control of young A. altissima shoots because it limits disturbance and has acceptable capital and operating costs. Hand-pulling and mulching was the second choice, mainly because of the risk of additional disturbance that increased shoot densities 1 year after treatment. Cut stump alone was not effective, worsened the infestation, and is not recommended for this species. The EZJect system was effective at managing mature, seed-producing shoots, although the somewhat higher capital costs mean that the system probably should be purchased for management of several invasive tree species to make it more cost-effective.

Sexual reproduction, clonal diversity and genetic differentiation in patchily distributed populations of the temperate forest herb Paris quadrifolia (Trilliaceae)

Clonal plant species have been shown to adopt different strategies to persist in heterogeneous environments by changing relative investments in sexual reproduction and clonal propagation. As a result, clonal diversity and genetic variation may be different along environmental gradients. We examined the regional and local population structure of the clonal rhizomatous forest herb Paris quadrifolia in a complex of forest fragments in Voeren (Belgium). Relationships between population size (the number of shoots), shoot density (the number of shoots per m2) and local growth conditions were investigated for 47 populations. Clonal diversity and genetic variation within and among 19 populations were investigated using amplified fragment length polymorphism markers. To assess the importance of sexual reproduction, seed set, seed weight and germination success were determined in 18 populations. As predicted, local growth conditions largely affected population distribution, size and density of P. quadrifolia. Populations occurring in moist and relatively productive sites contained significantly more shoots. Here, shoots were also much more sparsely distributed compared to populations occurring in dry and relatively unproductive sites, where shoots showed a strongly aggregated distribution pattern. Clonal diversity was relatively high, compared with other clonal species (G/N ratio=0.43 and Simpson's D=0.81). Clonal diversity significantly (P<0.01) decreased with increasing shoot density while molecular genetic variation was significantly (P<0.01) affected by population size and local environmental conditions. Lack of recruitment and out-competition of less-adapted genotypes may explain the decreased genetic variation in dry sites. Analysis of molecular variance revealed significant genetic variation among populations (PhiST=0.42, P<0.001), whereas pairwise genetic distances were not correlated to geographic distances, suggesting that gene flow among populations is limited. Finally, the number of generative shoots, the number of seeds per fruit and seed weight were significantly and positively related to population size and local growth conditions. We conclude that under stressful conditions populations of clonal forest plant species can slowly evolve into remnant populations characterized by low levels of genetic variation and limited sexual reproduction. Conservation of suitable habitat conditions is therefore a prerequisite for effective long-term conservation of clonal forest plant species.

Rendimiento de plantas de tomate injertadas y efecto de la densidad de tallos en el sistema hidropónico

El cultivo de tomate en primavera con baja densidad inicial de plantas y luego aumentar-se la densidad efectiva mediante el desarrollo de tallos laterales, cuando las integrales diarias de radiación son altas, parece ser una manera prometedora de incrementar el número de frutos m-2 y uniformizar el tamaño del fruto; y presenta la ventaja adicional de requerir-se un menor número de plantas para la superficie de cultivo. Por lo tanto, se ha llevado a cabo un ensayo cuyo objetivo ha sido evaluar los efectos de la densidad de tallos sobre el rendimiento y la uniformidad de los frutos de un cultivo de tomate injertado y no injertado. El cultivo se realizó de marzo a julio de 1998, en las condiciones de invernadero en Almería (sudeste español). La densidad inicial de plantación fue de 2,4 y 3,0 plantas m-2, en el caso de las plantas no injertadas, que presentaban un único tallo en el transplante; y 1,2 plantas m-2 en las plantas injertadas, que tenían dos tallos (2,4 tallos m-2). A partir del mes de abril, mediante el desarrollo de tallos laterales (cuando el tratamiento así lo exigía) se pasó a tener las siguientes densidades: 2,4; 3,0 y 3,5 tallos m-2 (plantas injertadas y no injertadas); y 3,0 plantas no injertadas m-2 a un tallo durante todo el ciclo. Los resultados muestran que plantas de tomate injertadas y transplantadas a dos tallos tuvieron igual producción total, pero frutos de tamaño más uniforme, que plantas no injertadas transplantadas a un tallo y con doble densidad de plantas. Dentro del rango de 2,4 a 3,5 tallos m-2, una mayor densidad de tallos aumentó la producción precoz y dio un tamaño más uniforme de frutos, no afectando su peso promedio y la producción total. La adición de tallos laterales (3,0 tallos m-2) supuso una reducción de un 20% en el rendimiento total, pero vino acompañada por un ahorro de un 21% y de un 39% en el número de plantas no injertadas e injertadas, respectivamente, necesarias para la misma superficie; asimismo, dio un tamaño más uniforme de fruto, comparando con plantas cultivadas desde el inicio del ciclo en alta densidad (3,0 plantas m-2 sin adición de tallos laterales).

The importance of plant root characteristics in controlling concentrated flow erosion rates

AbstractWhile it has been demonstrated in numerous studies that the aboveground characteristics of the vegetation are of particular importance with respect to soil erosion control, this study argues the importance of separating the influence of vegetation on soil erosion rates into two parts: the impact of leaves and stems (aboveground biomass) and the influence of roots (belowground biomass). Although both plant parameters form inseparable constituents of the total plant organism, most studies attribute the impact of vegetation on soil erosion rates mainly to the characteristics of the aboveground biomass. This triggers the question whether the belowground biomass is of no or negligible importance with respect to soil erosion by concentrated flow. This study tried to answer this question by comparing cross‐sectional areas of concentrated flow channels (rills and ephemeral gullies) in the Belgian Loess Belt for different cereal and grass plant densities. The results of these measurements highlighted the fact that both an increase in shoot density as well as an increase in root density resulted in an exponential decrease of concentrated flow erosion rates. Since protection of the soil surface in the early plant growth stages is crucial with respect to the reduction of water erosion rates, increasing the plant root density in the topsoil could be a viable erosion control strategy. Copyright © 2003 John Wiley &amp; Sons, Ltd.

REGROWTH STRATEGY OF HARVESTED POPULATION OF PHRAGMITES AUSTRALIS FROM THE RHIZOME ASPECTS

Regrowth dynamics of common reed Phragmites australis after harvesting were investigated in a swampy section of Akigase-Park (35°51'N, 139°35'E). Shoots were harvested in June 2000 and July 2000. Observations were conducted from April 2001 to December 2001 particularly focusing on the reserve allocation to new to old rhizomes. Harvesting increased shoot density, however, decreased shoot diameter, shoot height and shoot biomass in the following season. Newly formed rhizomes were not affected by cutting event. Although 1-year-old rhizomes, produced in the treatment performed year, were decreased compared with a control stand. Older (3 to 5-years-old) rhizomes also reduced by consuming reserve materials for recovery from cutting damage.These results imply that young reed communities are easily injured by accidental damages because of their small reservations. For wetland management, harvesting in June most efficiently suppress reed stands.

Competition betweenSphagnum magellanicumandEriophorum angustifoliumas affected by raised CO2and increased N deposition

The competition between peat mosses (Sphagnum) and vascular plants as affected by raised CO2and increased N deposition was studied in a glasshouse experiment by exposing peat monoliths with monocultures and mixtures ofSphagnummagellanicumandEriophorumangustifoliumto ambient (350 ppmv) or raised (560 ppmv) atmospheric CO2concentrations, combined with low (no N addition) or high (5 g m−2yr−1added) N deposition. Growth of the two species was monitored for three growing seasons. The presence ofEriophorumdid not affectSphagnumbiomass, becauseEriophorumdensity did not become high enough to severely shade the moss surface. In contrast,Sphagnumhad a negative effect onEriophorumbiomass, particularly on the number of flowering stems. Possibly, the presence of a livingSphagnumlayer decreased nutrient availability toEriophorumby immobilising nutrients mineralised from the peat. Raised CO2and/or increased N deposition did not change these competitive relationships betweenSphagnumandEriophorum, but had independent effects. Raised CO2had a positive effect both onSphagnumandEriophorumbiomass, though onEriophorumthe effect was transient, probably because of P limitation. Nitrogen addition had a direct negative effect onSphagnumheight growth in the first growing season, but by the third year an increased shoot density had cancelled this out, so no N effect onSphagnumbiomass was present at the end of the experiment. The response ofEriophorumto N addition was small; N availability appeared not to limit its growth.

MACROALGAL CANOPIES CONTRIBUTE TO EELGRASS (ZOSTERA MARINA) DECLINE IN TEMPERATE ESTUARINE ECOSYSTEMS

Loss of eelgrass (Zostera marina) habitat from temperate estuaries worldwide often coincides with increased macroalgal accumulations resulting from increased delivery of anthropogenic nitrogen. We conducted macroalgal enclosure/exclosure experiments dur- ing summer 1998 within eelgrass populations in two estuaries of Waquoit Bay, Massachu- setts, USA, to evaluate how increased macroalgal biomass affects density, recruitment, growth rate, and production of eelgrass. One estuary featured a low nitrogen loading rate and sustained a relatively pristine eelgrass population with a 2 cm high macroalgal canopy. The other estuary had a sixfold higher nitrogen loading rate and a declining eelgrass population with a 9 cm high macroalgal canopy. Experimental units were 1 X 1 m plots of eelgrass fenced within 50 cm high plastic mesh that excluded or included macroalgae at canopy heights ranging from 0 to 25 cm. In both estuaries, rates of eelgrass loss increased, largely a result of decreased recruitment, and growth rates decreased (due to decreased rates of leaf appearance) with increasing macroalgal canopy height. Aboveground summer production in both estuaries decreased exponentially as macroalgal canopy heights in- creased. We conclude that macroalgal cover is a proximate cause for loss of eelgrass in the higher N estuary since, upon removal of macroalgae, we observed an increase in shoot density, a 55% increase in summer growth, and a 500% increase in summer aboveground net production. Based on summer growth data and density of shoots in our experimental plots the following spring, we suggest that the negative impacts of macroalgal canopies persist, but also that eelgrass recovery upon removal of macroalgae may be possible. To identify the mechanisms by which macroalgae potentially inhibit eelgrass production, we measured changes in nutrient and oxygen concentrations resulting from macroalgal canopies and estimated the relative importance of summer standing stocks of phytoplankton, epiphytes, and macroalgae to potential shading of eelgrass in both estuaries. We document both (1) unfavorable biogeochemical conditions (lowered redox conditions and potentially toxic concentrations of NH4+) imposed by the presence of macroalgal canopies and (2) potential light limitation of eelgrass by standing stocks of producers in the higher N estuary, with estimates of light reduction via macroalgae numerically more important than light sequestration by phytoplankton and epiphytes for newly recruiting shoots. Increased ma- croalgal biomass associated with increased nitrogen loading to estuaries can lead to eelgrass disappearance, and we identify an approximate 9-12-cm critical macroalgal canopy height at which eelgrass declines.

EFFECTS OF NITROGEN APPLICATION TIMING ON GROWTH AND QUALITY OF A TURFGRASS MIXTURE

A 3-year field study was conducted to determine the influence of nitrogen (N) application timing on the growth and quality of a turfgrass mixture consisting of perennial ryegrass (Lolium perenne L.), Kentucky bluegrass (Poa pratensis L.), creeping red fescue (Festuca rubra var. rubra L.), and chewings fescue (Festuca rubra var. commutata Gaud.) under irrigated conditions. Nitrogen was applied annually at the rate of 30 g m−2 year−1, with six application regimes: control (no N), single spring (30 g m−2), single fall (30 g m−2), spring + fall (15 + 15 g m−2), spring + summer + fall (10 + 10 + 10 g m−2), and monthly from April through September (5 g m−2). Color, turf quality, clipping weights, and shoot density were correlated with fertilizer rates and application timing in this study. Fertilization monthly or every 2 months resulted in more uniform color and turf quality and less clipping weights than with comparable heavy spring and fall fertilizations. Heavy N applications in the fall did not cause winter injury and produced significantly darker color and more uniform appearance in early spring than other N applications. All N-fertilization regimes increased shoot density, but spring fertilization stimulated density the most. Nitrogen applied monthly or every 2 months was enough to enhance the color, turf quality, and shoot density of the turf during the growing season but did not greatly affect the growth rate.

Influence of herbivory, competition and soil fertility on the abundance of Cirsium arvense in acid grassland

Summary 1. The extent to which the weed Cirsium arvense (creeping thistle) may be controlled by manipulating interspecific competition and herbivory was examined in two factorial experiments in order to identify non‐chemical herbicide‐based control methods for the weed. 2. In the first experiment, a single spring cultivation of grassland intensively grazed by rabbits led to a 25‐fold increase in C. arvense cover within 3 months, the effects of which were still present the following summer. As well as destroying the competing perennial vegetation, cultivation created and dispersed small root fragments (3–5 cm in length) from which almost all shoot recruitment occurred. 3. Fencing the cultivated plots against rabbits decreased the cover of C. arvense because ungrazed regrowth from palatable/grazing intolerant species reduced recruitment of C. arvense seedlings and shoots. Seedling competition, in the form of a wildflower seed mix sown soon after cultivation, reduced C. arvense cover on fenced plots to pre‐cultivation levels. 4. In the second experiment, conducted in a permanent grassland, C. arvense shoot densities on plots fenced against rabbits and treated as a hay meadow were about one‐eighth of those found on rabbit‐grazed plots where competing vegetation was kept short. Adventitious shoot recruitment was greater on soil disturbances such as molehills and rabbit scrapes than in intact vegetation. Seedling recruitment occurred only on soil disturbances such as molehills. 5. Lime and nitrogen fertilizer application to the fenced grassland increased the standing biomass of competing species, which reduced C. arvense shoot density. Outside the fences, rabbit grazing was so concentrated on the competing species of the nitrogen‐fertilized and limed areas that C. arvense benefited from competitive release, exhibiting increased shoot density. Cirsium arvense showed pronounced competitive release from grasses, with greater shoot densities where grasses were removed with selective herbicides than where no plant species were removed. 6. Exclusion of insects and molluscs with chemical pesticides had no effect on shoot or seedling recruitment or overall shoot density on cultivated soil or in permanent grassland. 7. It is concluded that combinations of management procedures that encourage interspecific competition, such as sowing crops soon after cultivation and delaying grazing of them, and nitrogen fertilizer application and non‐ or reduced grazing of intact grasslands, will help reduce C. arvense abundance.

Do nutrient availability and plant density limit seagrass colonization in the Baltic Sea?

Seagrasses continue to decline at an alarming rate throughout the planet's temperate regions. After a decline recolonization or restoration starts from small patches of single shoots which then propagate vegetatively. We investigated the effects of plant density within a patch and nutrient resources on growth and survival of eelgrass (Zostera marina L.), the dominant seagrass species in the northern temperate zone. We created small (0.5 m') eelgrass patches by planting single shoots in circular plots at high (20 cm) and low (40 cm distance between shoots) density. In a factorial design, the sediment was nutrient-enriched (1) though biodeposition of transplanted mussels (Meus edulisL.) (2) by a slow- release NPK-fertilizer or (3) not enriched. The experiment was run over 1 growth period at a relatively nutrient-poor site (<30 pm01 NH4+ l-' porewater) in the Baltic Sea. Mussels increased NH4+ concen- trations and the fertihzer increased both NH4+ and Pod3- in the sediment porewater and the overlying water column, but this had only limited effects on eelgrass shoot growth rates and increase in shoot density, which were high overall (up to 75 mm shoot-' d-l, doubling shoot density every 3 mo). In contrast, increased plant density had clear positive effects on shoot growth, area1 expansion of patches and increase in shoot density. These results suggest that nutrient availability is not a major factor in eelgrass patch colonization or survival in the Baltic. Positive interactions among eelgrass shoots appear to be more important than competitive processes, during the early stages of recolonization.

Changes in Seagrass-Associated Fish and Crustacean Communities on Florida Bay Mud Banks: The Effects of Recent Ecosystem Changes?

The fauna of seagrass-covered mud banks in Florida Bay, documented in the mid 1980s prior to recent seagrass die-off, phytoplankton blooms, and other ecosystem changes, was reexamined in the mid 1990s for faunal changes that might be associated with environmental perturbations. During both decades, decapod crustaceans and fishes were collected with 1-m2 throw traps from seagrass beds at six sites that differ in the amount of freshwater and/or marine influence and in seagrass community metrics. The most common faunal changes were declines in seagrass-canopydwelling forms and increases in benthic forms. At three sites with relatively lush seagrass meadows, above-ground seagrass standing crop declined and abundance of the benthic predatory fishOpsanus beta increased. The degree of faunal change among these sites appeared to be related either to salinity variability or to the degree of exposure to the ecosystem changes that have taken place in Florida Bay. At two sites with poorly developed seagrass meadows, seagrass standing crop and canopy height did not change significantly between decades, but there was an increase in shoot density and total leaf area. The animal communities at these sites were characterized by significant increases in the abundance of benthic crustaceans. At the site on the edge of Rankin Lake, the basin where seagrass die-off was first observed in Florida Bay during 1987, seagrass standing crop, canopy height, shoot density, and leaf area declined significantly between decades, but species richness of both crustaceans and fishes increased. The abundance of canopy-dwelling crustaceans and fishes declined markedly at this site, whereas the abundance of benthic forms less dependent on seagrass cover generally increased. In retrospect, we believe the fauma at this site during the 1980s, characterized by high productivity but few species, was already showing signs of the stresses that led to the seagrass die-off that began in 1987.

Experimental demography of the old‐field perennialSolidago altissima: the dynamics of the shoot population

1Control strategies are needed for the clonal speciesSolidago altissima, which is an aggressive invader in Europe that propagates vegetatively by persistent rhizomes that produce annual shoots.2The shoot dynamics of a population ofS. altissimathat had invaded an old‐field site in 1984 were studied from 1987 to 1992. Shoots from 120 genets of the same cohort were followed in relation to their parent genets. We assessed the effect of yearly mowing, yearly cutting of rhizomes and repeated removal of close neighbour plants on growth, survival, probability of reproduction and flux of these shoots.3In unmown plots, both shoot survival until the end of the growing season and the proportion of shoots producing seeds decreased (59% to 36% and 67% to 32%, respectively, from 1988 to 1992). The proportion of rhizomes producing shoots, however, rose (fromc. 50% to more than 90%) so that annual shoot density increased almost fivefold by the end of the study, when it had almost reached equilibrium.4In contrast, shoot density in mown plots remained roughly constant from 1988 to 1992, after an increase from 1987 to 1988. Shoots were much smaller and a smaller proportion of them reproduced than in unmown plots.5Rhizome cutting (reduced clonal integration) produced a small but consistent decrease in height and in the percentage of sexually reproducing shoots.6The removal of close neighbour plants increased shoot density, and a higher percentage of these shoots survived and reproduced.7Experimental demographic studies thus show that (i) continued regular mowing reduces the production of both seeds and shoots, and so would prevent further spread of an invadingS. altissimapopulation; (ii) clonal integration may contribute to the species’ success as an invader because disconnected rhizomes produce smaller shoots with a lower chance of sexual reproduction; and (iii) competition decreases shoot density, mainly as a consequence of reduced shoot survival, and can therefore controlS. altissimagrowth.

Experimental evidence that herbivory increases shoot density and productivity in a subtropical turtlegrass (Thalassia testudinum ) meadow.

The sea urchin, Lytechinus variegatus, has been estimated to consume between 50 and 90% of annual net aboveground production in selected turtlegrass (Thalassia testudinum) meadows in the eastern Gulf of Mexico. Nevertheless, turtlegrass persists where sea urchin grazing is intense. We hypothesized that turtlegrass productivity is stimulated by grazing, as has been reported from terrestrial grassland systems, and that this best explains the persistence of heavily grazed turtlegrass in St. Joseph Bay, Fla. This hypothesis was tested by manipulating sea urchin densities (0, 10, and 20 individuals/m2) in 1-m2 enclosures. These densities encompass the range of average densities at the study site and those reported in the literature. Changes in turtlegrass abundance (e.g., short shoot density and biomass), production by short shoots, and leaf width were monitored in these enclosures during the summer. Repeated-measures ANOVA showed that production by short shoots, leaf density/shoot, and leaf width decreased over time in all treatments. Leaf density/shoot and leaf width were not significantly impacted by grazing, nor did grazing significantly reduce seagrass biomass, but it did lead to significantly higher densities of short shoots than found in control cages. Our results indicate that turtlegrass compensates for the effects of sea urchin herbivory by increasing the recruitment of short shoots during the growing season. We estimate that this increased shoot density led to a 40% increase in net aboveground primary production (g dry weight/m2) in grazing treatments, which helps to explain the lack of significant reductions of sea grass biomass during the growing season.

‘Grasslands G27’ red clover (Trifolium pratense L.)

‘Grasslands G27’ red clover was bred from the tetraploid cultivar ‘Grasslands Pawera’, with selection aimed at reducing the concentration of the isoflavone, formononetin. Selection proceeded for seven generations and resulted in the formononetin level being less than half of that in Pawera under sward conditions. This reduction increases ewe ovulation, conception, and lambing rates by a significant amount.Other characteristics of G27, probably a consequence of reduced formononetin level, are increased palatability and reduced disease tolerance. Since both of these characters would tend to reduce sward persistence, G27 was selected also for increased shoot density and prostrateness to help counteract these weaknesses.

Seasonal variation in the intertidal seagrass Zostera noltii Hornem.: coupling demographic and physiological patterns

The considerable seasonal variation in biomass (2–130 g ash-free dry weight (AFDW) m −2) and cover of intertidal Zostera noltii Hornem. in the Zandkreek estuary (SW Netherlands) was mainly caused by changes in shoot density (1000–23000 m −2) and not in shoot size (shoot weight 1–3.6 mg AFDW, shoot leaf area 0.3–1.5 cm 2). The spring increase in shoot density was realised through continuous monopodial branching of the rhizome, which commenced when light available during low tide increased above 15 E m −2 day −1, in mid April. Branching stopped by the end of July, about 6 weeks before the onset of the annual biomass decline, due to a combination of: (a) self-shading during low tide; (b) high respiratory demand by the expanded rhizome network; (c) the seasonal decline in light availability during late summer. Nutrients were probably not limiting since concentrations in shoots remained high: 3.6% N and 0.6% P of dry weight are seasonal means. During the period of maximal biomass the primary rhizome axes decayed, leaving single shoots on short pieces of rhizome, the former secondary axes. The rapid decline in biomass from mid September onwards could be attributed to grazing by herbivorous migratory waterfowl. It was estimated that brent geese, Branta bernicla (L.), and wigeon, Anas penelope L. (about 200 and 300 birds, respectively, on the bed of 30 ha) together removed 45 g AFDW m −2 month −1, whilst autumn storms were insignificant. As established experimentally, winter survival was by single shoots enclosing an active meristem, and not by rhizome fragments without leaves. Sucrose was the main storage carbohydrate. The rhizome was the main storage organ, with maximal carbohydrate content observed in mid July (190 mg g −1 dry weight, sucrose + starch in glucose weight equivalents), and a gradual decline during autumn and winter. We estimated that the storage carbohydrates could cover 28% of the respiratory needs during winter, which would necessitate a substantial photosynthesis to meet the remaining 72%. From iteratively fitted photosynthesis-light curves we conclude that this intertidal Z. noltii population is high-light adapted compared with permanently submerged seagrasses and freshwater angiosperms: estimates for the light compensation point (LCP) and half-saturation constant ( K m) were comparatively high (July LCP and K m: 98 μE m −2 s −1 and 236 μE m −2 s −1, respectively), maximum photosynthetic rate was high ( P max: 236 μg O 2 g −1 AFDW min −1) and the initial slope of the curve was low (α: 0.63 μg O 2 g −1 AFDW min −1/μE m −2 s −1). Estimated daily oxygen balances confirmed that positive net photosynthesis was largely limited to low tide daylight in this turbid estuary (mean high tide light attenuation coefficient: 2.1 m −1).

Fruit Environment and Crop Level Effects on Pinot noir. III. Composition and Descriptive Analysis of Oregon and British Columbia Wines

Pinot noir vines growing in the Okanagan Valley of British Columbia (BC) and near Alpine, Oregon (OR), were subjected to three canopy management treatments [10 shoots/m row, 20 shoots/m row, Scott Henry (vertical canopy division) with 10-shoots/m canopy; 15-shoots/m row in OR only] in combination with two crop levels (full crop, half crop) in a factorialized treatment arrangement. BC wine titratable acidity (TA) and pH were reduced slightly by Scott Henry training in two of three years, but anthocyanins increased in Scott Henry wines in only one of three years. OR ethanol and wine TA increased (1 of 2 years) and pH decreased (2 of 2 years) with increasing shoot density, while Scott Henry training increased both ethanol and anthocyanins and reduced TA and pH compared to non-divided canopies. Reducing crop level increased ethanol and anthocyanins in OR wines, but BC half-crop wines had higher TA, pH, anthocyanins, and ethanol. BC wines from 1989, 1991, and 1992, and the 1990 and 1991 OR vintages were assessed by consensus-type descriptive analysis by a BC sensory panel. The tasters were able to distinguish between canopy treatments and/or crop levels in the 1989 wines using these descriptors: vegetative (aroma and flavor); black pepper aroma; chocolate aroma; and astringency. The 1991 and 1992 BC wines and the 1990 and 1991 OR wines were distinguished using cherry, berry, anise, bell pepper, and grassy aromas; cherry, currant, berry, and bell pepper flavors; color, astringency, and aftertaste (finish). Means of the five vintages from both wine regions indicated that clove, bell pepper, and grassy aromas were least in 10-shoots/m and Scott Henry canopy treatments. Cherry and anise aromas were also highest in Scott Henry wines, but many flavors, color, and finish were not increased by vertical canopy division. Scott Henry trellising is nonetheless recommended for situations where high vine vigor may contribute to vegetative aromas and flavors in Pinot noir wines. Reducing crop level increased color, currant aroma, astringency, and intensity of finish independent of canopy treatment.

Shoot Density Affects `Riesling' Grapevines I. Vine Performance

`Riesling' grapevines (Vitis vinifera L.) were subjected for 4 years (1987-90) to three shoot densities (16, 26, and 36 shoots/m of row) combined with three crop-thinning levels (1, 1.5, and 2 clusters/shoot) in a factorialized treatment arrangement. Weight of cane prunings per vine (vine size) decreased linearly with increasing shoot density and clusters per shoot. Cane periderm formation (in terms of percent canes per vine with &gt;10 ripened internodes) was inhibited by increased shoot density, while vine winter injury (primarily bud and cordon) increased slightly in a linear fashion with increasing clusters per shoot. Canopy density and leaf area data suggested that fruit clusters were most exposed to sunlight at a shoot density of 26 shoots/m of row due to reduced lateral shoot growth and a trend toward slightly smaller leaves. Yield, clusters per vine, and crop load (yield per kilogram of cane prunings) increased with increasing shoot density and clusters per shoot, while other yield components (cluster weight, berries per cluster, and berry weight) decreased. Soluble solids and pH of berries and juices decreased with increasing shoot density and clusters per shoot, but titratable acidity was not substantially affected. Free volatile terpenes increased in berries and juices in 1989 with increasing shoot density, as did potentially volatile terpenes in 1990. Shoot densities of 16 to 26 shoots/m of row are recommended for low to moderately vigorous `Riesling' vines to achieve economically acceptable yields and high winegrape quality simultaneously.

Shoot Density Affects `Riesling' Grapevines II. Wine Composition and Sensory Response

`Riesling' grapevines (Vitis vinifera L.) were subjected for 4 seasons (1987-90) to three shoot densities (16, 26, and 36 shoots/m of row) combined with three crop-thinning levels (1, 1.5, and 2 clusters per shoot) in a factorial design. Wines were made from all treatment combinations in 1989. Aroma compounds such as trans-3-hexen-1-ol, linalool, and linalool oxides 1 and 2 in many cases decreased in nonaged and aged wines by increasing shoot density and clusters per shoot, while cis-3-hexen-1-ol increased. Aging wines increased concentrations of cis-3-hexen-1-ol, citronellol, α-terpineol, and the linalool oxides, while linalool decreased. Tasters identified aged wines from the lowest shoot densities and clusters per shoot as having the most ripe-fruit flavor and the least green-fruit flavor and perceived acidity. Flavor descriptors were correlated with linalool, cis-3-hexen-1-ol, and linalool oxide 1. Shoot densities of 20 to 25 shoots/m of row are recommended for low to moderately vigorous `Riesling' vines to achieve economically acceptable yields and high wine quality simultaneously.

Effects of fire season and soil fertility on clonal growth in a pyrophilic forb, Pityopsis graminifolia (Asteraceae)

We experimentally manipulated fire season in a longleaf pine sandhill community in north Florida in 1990 and 1992. We determined the size and demography of shoots, rhizomes, and clones of Pityopsis graminifolia from late 1990 to early 1993. In addition, we examined shoot responses to seasonal variation in canopy/litter removal and soil fertility in 1992. May fires caused a higher short‐term rate of increase in shoot density than did either January fires or August fires. The combination of canopy/litter removal and mineral nutrient addition as part of the clipping experiment revealed a similar effect on shoot density in May. Fire season influenced clone structure. May fires resulted in greater numbers of shoots/clone than did January or August fires. January‐burned plots had clones and rhizomes that contained larger (but fewer) shoots than did May‐burned or August‐burned plots. We suggest that such variation in clone structure may indicate a greater capacity of clones to grow laterally following May fires than following either January or August fires. This capacity is positively associated with the likelihood that longleaf pine savannas will be burned by lightning fires at different times during the year.