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Biomass harvesting removes unmarketable vegetative material from timber harvests for use as cellulosic bioenergy, leaving only leaf litter. To test whether biomass harvests negatively affect red-backed salamander (Plethodon cinereus) populations, we set up coverboard arrays at 10 sites (mean 3.29 ha, range 2.35-4.61 ha) with varying degrees of biomass harvesting at the Southeast Purdue Agricultural Center (SEPAC) in Jennings County, Indiana. We monitored salamander artificial cover object (AGO) arrays within each site from spring 2012 to fall 2015 and marked all salamanders with visible implant elastomers, generating capture histories for all individuals. Using Program MARK and Pollock s robust design we developed 10 a priori candidate models to test salamander population parameters, with variations on capture probability, recapture probability, survival, emigration, and immigration, as well as a set of models comparing preharvest and postharvest data. To incorporate precipitation events, we classified sessions as wet or dry based on total rainfall prior to sampling. The best performing models were those that incorporated the year, season, and amount of precipitation when estimating capture probabilities. Linear regression results showed percentage of canopv cover and Downed Coarse Woody Derbies (DCWD) were significant predictors of salamander abundance. We also found no significant relationships between survival, DCWD, and canopy cover. Our results suggest DCWD has some impact on variations in population sizes of red-backed salamanders, although other factors are likely contributing as well., Introduction In response to increasing gas prices and the depletion of fossil fuels, the use of renewable biofuels as an alternative energy source is becoming a realistic option (Janowiak and [...]

Species richness has been shown to increase biomass production of plant communities. Such overyielding occurs when a community performs better than its component monocultures due to the complementarity or dominance effect and is mostly detected in substrate-bound plant communities (terrestrial plants or submerged macrophytes) where resource use complementarity can be enhanced due to differences in rooting architecture and depth. Here, we investigated whether these findings are generalizeable for free-floating phytoplankton with little potential for spatial differences in resource use. We performed aquatic microcosm experiments with eight phytoplankton species belonging to four functional groups to determine the manner in which species and community biovolume varies in relation to the number of functional groups and hypothesized that an increasing number of functional groups within a community promotes overyielding. Unexpectedly, we did not detect overyielding in any algal community. Instead, total community biovolume tended to decrease with an increasing number of functional groups. This underyielding was mainly caused by the negative dominance effect that originated from a trade-off between growth rate and final biovolume. In monoculture, slow-growing species built up higher biovolumes than fast-growing ones, whereas in mixture a fast-growing but low-productive species monopolized most of the nutrients and prevented competing species from developing high biovolumes expected from monocultures. Our results indicated that the magnitude of the community biovolume was largely determined by the identity of one species. Functional diversity and resource use complementarity were of minor importance among free-floating phytoplankton, possibly reflecting the lack of spatially heterogeneous resource distribution. As a consequence, biodiversity-ecosystem functioning relationships may not be easily generalizeable from substrate-bound plant to phytoplankton communities and vice versa. Key words: biomass production; functional diversity; negative dominance effect; overyielding; phytoplankton primary producer; resource use complementarity; species richness, underyielding.

Under optimal partitioning theory (OPT), plants preferentially allocate biomass to acquire the resource that most limits growth. Within this framework, higher root mass under low nutrients is often assumed to reflect an allocation response to build more absorptive surface. However, higher root mass also could result from increased storage of total nonstructural carbohydrates (TNC) without an increase in non-storage mass or root surface area. To test the relative contributions of TNC and non-storage mass as components of root mass responses to resources, we grew seedlings of seven northern hardwood tree species (black, red, and white oak, sugar and red maple, American beech, and black cherry) in a factorial light x nitrogen (N) greenhouse experiment. Because root mass is a coarse metric of absorptive surface, we also examined treatment effects on fine-root surface area (FRSA). Consistent with OPT, total root mass as a proportion of whole-plant mass generally was greater in low vs. high N. However, changes in root mass were influenced by TNC mass in all seven species and were especially strong in the three oak species. In contrast, non-storage mass contributed to increased total root mass under low N in three of the seven species. Root morphology also responded, with higher fine-root surface area (normalized to root mass) under low vs. high N in four species. Although biomass partitioning responses to resources were consistent with OPT, our results challenge the implicit assumption that increases in root mass under low nutrient levels primarily reflect allocation shifts to build more root surface area. Rather, root responses to low N included increases in: TNC, non-storage mass and fine-root surface area, with increases in TNC being the largest and most consistent of these responses. The greatest TNC accumulation occurred when C was abundant relative to N. Total nonstructural carbohydrates storage could provide seedlings a carbon buffer when respiratory or growth demands are not synchronized with photosynthesis, flexibility in responding to uncertain and fluctuating abiotic and biotic conditions, and increased access to soil resources by providing an energy source for mycorrhizae, decomposers in the rhizosphere, or root uptake of nutrients. Key words: biomass allocation; biomass partitioning; fine roots; .fine root surface area; optimal partitioning theory; soil resources; storage; total nonstructural carbohydrates.

We examined a series of eight pea genotypes differing in three naturally occurring allelic mutations, i.e., af (afila), st (stipules reduced), and tl (tendril-less) and three species, five cultivars, and one interspecific hybrid of tomato differing in SP (SELFPRUNING) allele composition to determine whether different phenotypes ontogenetically express different biomass partitioning patterns compared to the isometric poatitioning pattern and an interspecilic 3/4 scaling 'rule'' governing annual growth with respect to body mass. The slopes and 'elevations' (i.e., a and log [beta], respectively) of log-log linear regression curves of bivariate plots of leaf. stem, and root dry mass and of annual growth vs. total body mass were used to assess pattern homogeneity. The annual growth of all pea and tomato phenotypes complied with the 3/4 growth rule. The biomass partitioning patterns of all tomato phenotypes were statistically indistinguishable from the isometric pattern as were those of the pea wild type and three singlemutant genotypes. However, significant departures from the isometric (and pea wild type) biomass allocation pattern were observed for three genotypes, all of which were homozygous for the af allele. These results open the door to explore the heritability and genetics underlying the allometry of biomass partitioning patterns and growth. Key words: af (afila); allometry; Fabaceae; Lycopersicon esculentum; Lycopersicon pennellii; Lycopersicon pbnpinellifolium; leaf morphology; Piston sativum; scaling relationships; Solanaceae.

Understanding the dependency of ecosystem processes on spatial and temporal scales is crucial in current efforts to model ecosystem responses to global change. Here we present a case of nonlinear interactions between temporal and spatial scales in a high spatial- and temporal-resolution study of fine-root biomass responses to edaphic and climatic variation in a lowland tropical rain forest (La Selva, Costa Rica). The spatiotemporal variation in fine roots in this forest was considerably greater than that for aboveground live biomass and litterfall. Standing stocks of both live and dead fine roots varied strongly during a seven-year period (up to 10-fold) and across two edaphic gradients with different soil nutrient and water variation (up to four-fold). Fine-root biomass decreased with soil fertility and volumetric soil water content, but responses across a landscape gradient (decreasing with total soil P and K and increasing with N:P ratio between two Oxisols with different weathering) differed from those across a topographic gradient in older Oxisols (increasing with total Fe and A1 and decreasing with Ca, Mg, and C:N ratio down the slopes). The spatial contrasts across the landscape gradient (but not in the topographic gradient) changed substantially through time, and they, in fact, disappeared entirely by the middle of the study interval. Shortterm monitoring of belowground standing biomass could thus lead to important biases when quantifying root responses. The positive time x gradient interaction in fine-root biomass across soil types (but not downslope) also indicates nonlinear changes in spatial patterns across temporal scales, so studies on temporal responses also need to be spatially explicit at narrow scales. This interaction also appears to be more complex than previously recognized: semester-averaged fine-root biomass was negatively correlated with soil water content in the preceding semester, but the relationship was restricted to residual Oxisols. To increase the accuracy of global carbon cycle models in the future, a critical complement to observations of ecosystem processes at regional and global scales will be quantifying these processes through multiple years and across the substantial edaphic gradients that typically exist within landscapes. Key words: aboveground biomass; Costa Rica, La Selva Biological Station; ecological scale; ecological stoichiometry; nitrogen; nutrient ratios; phosphorus; soil fertility gradients; soil moisture; soil nutrients.

Patterns of resource availability and heterogeneity shape the composition, productivity, and dynamics of plant assemblages in a wide variety of terrestrial ecosystems. Despite this, the responses of plant assemblages to simultaneous changes in the availability and heterogeneity of more than a single resource are virtually unknown. To fill this gap, microcosms consisting of assemblages formed by Lolium perenne, Plantago lanceolata, Anthoxantum odoratum, Holcus lanatus, and Trifolium repens were grown in a factorial experiment with the following treatments: nutrient availability (NA), water availability (WA), spatial nutrient heterogeneity (NH), and temporal water heterogeneity (WH). Assemblages exhibited precise root foraging patterns in response to nutrient heterogeneity, which were modified by NA and WA. A series of two- and three-way interactions involving the four factors evaluated determined biomass production, the belowground:aboveground biomass ratio, the patterns of root biomass allocation with depth, and the relative contribution to aboveground biomass of Lolium and Anthoxanthum. In all cases, these interactions explained significant amounts of the variation found in the data. Our study demonstrates that considering the interactions between resource availability and heterogeneity allows for a refinement of predictions that can detectably reduce the error associated with extrapolating from single factor analyses. Key words: Anthoxantum odoratum; competition, global change; Holcus lanatus; Lolium perenne; microcosm; plant assemblages; Plantago lanceolata; resource availability; resource heterogeneity; Trifolium repens.

Most natural local systems exchange organisms with a regional pool of species through migration and dispersal. Such metacommunity processes of interconnected multispecies assemblages are likely to affect local dynamics of both species and processes. We present results from an artificial marine outdoor rock pool system in which we investigated the factors of (1) local grazer richness and composition, and (2) connectivity of local patches to a regional species pool, and their effects on algal biomass. Local species richness of six grazers was manipulated in both open and closed pools, which were embedded in a regional species pool containing all six grazers. Grazer richness showed significant net biodiversity effects on grazing in the closed, but not in the open, system. Grazer composition, on the other hand, showed significant effects on grazing in both open and closed systems, depending on which species were initially present. The two most efficient grazers were able to compensate for less efficient grazers in species mixtures, hence ensuring the function of grazing. The efficiency of top-down control of algal biomass in open systems thus depends on which particular species are lost. Further, differences in grazing between the open and closed system changed over time due to temporal dynamics in grazer composition. The results emphasize the importance of including system connectivity in experimental designs to allow an extrapolation of biodiversity ecosystem-functioning relationships to natural systems. Key words: compensation effect; composition; diversity; ecosystem function; grazing; marine; metacommunity; open system; rock pools; species identity.

Abstract: Wild rice (Zizania palustris L.) litter accumulation may inhibit plant growth and production both by physically suppressing seedling emergence and by nitrogen immobilization in fresh litter. This latter mechanism [...]

Abstract: Carbon (C) modeling and carbon dioxide (C[O.sub.2]) flux measurements in peatlands are dependent on the distribution and productivity of vegetation in a system with a high degree of spatial [...]

The invasive grass Microstegium vimineum grows in low light beneath the canopy of eastern forests in North America by reiteration of modules (phytomers) along a tiller. Basal phytomers are vegetative; terminal phytomers produce a raceme of chasmogamous (CH) spikelets plus an axillary raceme of cleistogamous (CL) spikelets. Additional subterminal phytomers with CL racemes mature basipetally. Allocation to culms, leaves, and CH and CL within phytomers was examined in relation to light conditions for a population in New Jersey, USA. Plants were reared in a greenhouse from seed families of parents in deep shade (2-8% full sun) or sunny, edge habitats. Primary tillers were subdivided into phytomers, dried, and weighed. Tillers from field habitats were similarly treated. For vegetative and subterminal phytomers, allocation to leaves and CH was greatest for the shady habitat. CL allocation decreased from terminal to reproductively immature subterminal phytomers. CH and CL mass was positively correlated with leaf mass, suggesting that reproduction is determined by available photosynthate. CH mass showed a genetic correlation with leaf mass. Developmental plasticity in modular allocation allows Microstegium to maximize fitness when conditions are favorable (e.g., high light along forest edges) by continual maturation of CL caryopses on axillary racemes. Key words: annual grass; chasmogamy; cleistogamy; invasive species; Microstegium vimineum; phytomers; Poaceae.

Canopy-forming plants and algae commonly contribute to spatial variation in habitat complexity for associated organisms and thereby create a biotic patchiness of communities. In this study, we tested for interaction effects between biotic habitat complexity and resource availability on net biomass production and species diversity of understory macroalgae by factorial field manipulations of light, nutrients, and algal canopy cover in a subtidal rocky-shore community. Presence of algal canopy cover and/or artificial shadings limited net biomass production and facilitated species diversity. Artificial shadings reduced light to levels similar to those under canopy cover, and net biomass production was significantly and positively correlated to light availability. Considering the comparable and dependent experimental effects from shadings and canopy cover, the results strongly suggest that canopy cover controlled net biomass production and species diversity by limiting light and thereby limiting resource availability for community production. Canopy cover also controlled experimental nutrient effects by preventing a significant increase in net biomass production from nutrient enrichment recorded in ambient light (no shading). Changes in species diversity were mediated by changes in species dominance patterns and species evenness, where canopy cover and shadings facilitated slow-growing crust-forming species and suppressed spatial dominance by Fucus vesiculosus, which was the main contributor to net production of algal biomass. The demonstrated impacts of biotic habitat complexity on biomass production and local diversity contribute significantly to understanding the importance of functionally important species and biodiversity for ecosystem processes. In particular, this study demonstrates how loss of a dominant species and decreased habitat complexity change the response of the remaining assembly to resource loading. This is of potential significance for marine conservation since resource loading often promotes low habitat complexity and canopy species are among the first groups lost in degraded aquatic systems. Key words: Baltic Sea; biodiversity; canopy cover; coastal ecosystems; ecosystem function; eutrophication; Fucus vesiculosus; macroalgae; marine diversity; subtidal ecology.

Evergreen broad-leaved tropical forests can have high rates of productivity and large accumulations of carbon in plant biomass and soils. They can therefore play an important role in the global carbon cycle, influencing atmospheric C[O.sub.2] concentrations if climate warms. We applied meta-analyses to published data to evaluate the apparent effects of temperature on carbon fluxes and storages in mature, moist tropical evergreen forest ecosystems. Among forests, litter production, tree growth, and belowground carbon allocation all increased significantly with site mean annual temperature (MAT); total net primary productivity (NPP) increased by an estimated 0.2-0.7 Mg C*[ha.sup.-1] *[yr.sup.-1]*[degrees][C.sup.-1]. Temperature had no discernible effect on the turnover rate of aboveground forest biomass, which averaged 0.014 [yr.sup.-1] among sites. Consistent with these findings, forest biomass increased with site MAT at a rate of 5-13 Mg C*[ha.sup].[degrees][C.sup.-1]. Despite greater productivity in warmer forests, soil organic matter accumulations decreased with site MAT, with a slope of -8 Mg C*[ha.sup.-1]*[degrees][C.sup.-1] indicating that decomposition rates of soil organic matter increased with MAT faster than did rates of NPP. Turnover rates of surface litter also increased with temperature among forests. We found no detectable effect of temperature on total carbon storage among moist tropical evergreen forests, but rather a shift in ecosystem structure, from low-biomass forests with relatively large accumulations of detritus in cooler sites, to large-biomass forests with relatively smaller detrital stocks in warmer locations. These results imply that, in a warmer climate, conservation of forest biomass will be critical to the maintenance of carbon stocks in moist tropical forests. Key words: belowground carbon allocation; carbon cycle; carbon turnover; decomposition; forest biomass; forest productivity; global warming; mean annual temperature; meta-analysis; net primary productivity; soil organic matter; tropical evergreen forests.

In this study we explored the effect of the physical environment and the availability of prey (biomass and taxonomic composition) on the patterns of prey capture and reproduction on five populations of Pinguicula moranensis (Lentibulariaceae) in areas ranging from pine-oak forests to desert scrublands. Environmental variation was summarized using principal factor analysis. Prey availability and prey capture increased toward the shadiest, most humid, and fertile population. The probability of reproduction and average bud production per population did not follow the same tendency because both fitness components peaked at the middle of the environmental gradient. These results suggest that the benefits derived from carnivory are maximized at sites fulfilling a trade-off between light, moisture, and prey availability. We also found that the taxonomic composition of both the available prey and that of the prey captured by plants varied among populations. The results also indicated that the prey captured by plants are not a random sample of prey available within populations. Overall, the results from this study revealed a marked amount of heterogeneity in the physical and biotic environment among the populations of P. moranensis, which has the potential to affect the outcome of the interaction between this carnivorous species and its prey. Key words: carnivorous habit; environmental heterogeneity; insectivorous plants; Lentibulariaceae; Pinguicula.

Abundance of invasive plants is often attributed to their ability ot outcompete native species. We compared resource acquisition and allocation of the invasive annual grass Bromus madritensis subsp. rubens with that of two native Mojave Desert annuals, Vulpia octoflora and Descurainia pinnata, in a glasshouse experiment. Each species was grown in monoculture at two densities and two levels of N availability to compare how these annuals capture resources and to understand their relative sensitivities to environmental change. During >4 mo of growth, Bromus used water more rapidly and had greater biomass and N content than the natives, partly because of its greater root-surface area and its exploitation of deep soils. Bromus also had greater N uptake, net assimilation and transpiration rates, and canopy area than Vulpia. Resource use by Bromus was less sensitive to changes in N availability or density than were the natives. The two native species in this study produced numerous small seeds that tended to remain dormant, thus ensuring escape of offspring from unfavorable germination conditions; Bromus produced fewer but larger seeds that readily germinated. Collectively, these traits give Bromus the potential to rapidly establish in diverse habitats of the Mojave Desert, thereby gaining an advantage over coexisting native species. Key words: Bromus madritensis subsp. rubens; desert ephemerals; introduced annual grasses; Mojave Desert; nitrogen uptake; plant biomass; Poaceae; root system; seed production; Vulpia octoflora; water uptake.

Ammophila breviligulata, American beachgrass, and Spartina patens, salt meadow hay, have been grazed by feral horses on the dunes of Assateague Island for hundreds of years; however, because of a significant increase in the horse population since the 1960s, overgrazing and dune erosion have become problems. Grazing was assessed on foredunes of four different morphologies along a 21-km stretch of the Maryland portion of the island using 17 exclosure plot pairs. In addition to decreased cover and biomass of the two species, plant structure was significantly affected by grazing. Leaf length and width, stem diameter, and stem density of A. breviligulata and stem diameter of S. patens were reduced in the grazed plots. Especially sensitive to grazing were reproductive characteristics. Percentage of plants in flower, height of flowering stems, and inflorescence length were all significantly reduced by grazing (nongrazed individuals measured). Species composition was not affected by horse accessibility. Key words: American beachgrass; Ammophila breviligulata; Assateague Island; dune morphology; feral horses; grazing; Poaceae; sand dune; Spartina patens.

We examined the allometry and mechanical properties of the peduncles of Hieracium pilosella and other species in the Asteraceae (H. aurantiacum, Taraxicum officinale, Tragopogon pratensi) to evaluate the hypothesis that tapered, tubular, and non-septate peduncles optimize the trade-offs among stem biomass allocation, elevating flowers and thus their wind-dispersed fruits, and the requirement for a factor of safety against mechanical failure. This hypothesis was evaluated by comparing peduncle morphometry (e.g., biomass M, floral biomass [M.sub.s] and length L) and mechanical properties (e.g., bending rigidity EI) for populations growing in windy and windsheltered sites as well as transplants between sites. Regardless of ambient wind speeds, [M.sub.s] [alpha] [L.sup.4/3] and EI [alpha] [L.sup.11/4) [alpha] [M.sub.s.sup.(5/3)], whereas [M.sub.f]/[M.sub.s] [alpha] [L.sup.-1.15], i.e., peduncles disproportionately increase in their biomass as they increase in length, but mechanically support a disproportionately smaller floral biomass relative to their biomass. Calculations show that the tall peduncles from wind-sheltered sites have a larger fruit dispersal range and a lower factor of safety than the shorter peduncles produced in open sites. These and other observations are interpreted to indicate that tubular peduncles enhance relative fitness in terms of propagule dispersal (but not propagule number per stein) while maintaining a sufficient factor of safety against mechanical failure. Key words: allometry; Asteraceae; Brazier buckling; flexural stiffness; fruit dispcrsal; Hieracium pilosella; plant biomechanics; winding loading.

1 Submergence of coastal wetlands in Louisiana is currently rapid and widespread. A number of factors contribute to this loss of habitat, including the activities of herbivores. The objective of this study was to examine the effects of large mammals, predominantly nutria and wild boar, on processes controlling soil elevation in coastal marshes. 2 Effects of herbivores on soil and vegetation were assessed by the use of paired fenced and unfenced plots over two successive growing seasons. Above-ground biomass, litter production, changes in soil elevation, vertical soil accretion, shallow subsidence, below-ground production of roots and rhizomes, the thickness of the root zone, soil bulk density, and soil organic matter were measured. 3 Above-ground biomass, below-ground production, soil elevation and the expansion of the root zone decreased due to herbivore activity. Litter production, the rate of soil surface accretion and shallow soil subsidence were all higher in grazed compared to ungrazed plots, while soil organic matter and bulk density did not differ significantly between treatments. 4 The results indicate that herbivores can have a negative effect on soil building processes, primarily by reducing below-ground production and expansion of the root zone. Where natural rates of mineral sediment deposition are high, coastal marshes are expected to persist, despite herbivore activities. However, where sediment inputs are substantially less, herbivores may lead to destruction of habitat. Keywords: coastal wetlands, habitat destruction, herbivory, soil development, wetland loss

A study was conducted to characterize a couple of cellulase components from a marine hyperthermophile, Thermotoga neopolitana. The molecular masses of the enzymes were obtained using sodium dodecyl sulfate while polysaccharase activity was determined through the release of reducing sugars by the Somogyi-Nelson technique. Results indicated that the cellulase components may be determined as a polycistronic mRNA. Findings also suggested cellobiose correlated with cellulase production in Trichoderma reesei and in Thermomonospora fusca.

1 A dwarf shrub heath in subarctic Sweden was subjected to factorial manipulation of air temperature, water and nutrient supply for 5 years. The responses of the vegetation to the perturbations were then assessed by point intercept (quadrat) analysis followed by determination of above-ground biomass. 2 Nineteen vascular and 23 non-vascular species (or species groups) were recorded and the most dramatic response was that of the grass Calamagrostis lapponica to nutrient addition, with abundance being stimulated by a factor of more than 18 compared with plots not subjected to nutrient addition. Calamagrostis lapponica did not show any significant responses to temperature or water alone but there was a synergistic interaction between all three variables. 3 The abundance of the dominant dwarf shrubs (Empetrum hermaphroditum, Vaccinium vitis-idaea, V. myrtillus and V. uliginosum) was unaffected by the perturbations but elevated temperature stimulated the biomass of V. uliginosum by 125% and total shrub biomass by 16%. The low ratio of current year's growth to standing biomass may have concealed other responses of the dwarf shrub group to the perturbations. 4 The response of the non-vascular flora to the perturbations was either neutral or negative, with lichens showing the most dramatic responses. Lichen biomass on temperature- and nutrient-amended plots was 56% and 18%, respectively, of that on unperturbed plots. Nutrients also exerted a negative effect on the biomass of bryophytes, and the combined biomass of lichens and bryophytes on nutrient-treated plots was almost a third of that on plots which did not receive additional nutrients. 5 Total above-ground biomass was not affected by the perturbations but the total number of interceptions determined by point quadrat analysis was greater on the elevated temperature and nutrient-treated plots. Point quadrat analysis also revealed an accumulation of litter and standing dead material in response to the nutrient and temperature perturbations, both singly and in combination, suggesting a faster turnover of plant material. 6 Both temperature and nutrients increased canopy height and also interacted synergistically such that together they resulted in a mean canopy height of 14.9cm compared with 8.0 cm in plots subjected to neither perturbation. 7 Nutrient addition lowered species richness by 17.7%, mainly through its impact on the mosses and lichens. 8 In general, nutrient addition elicited the greatest response, followed by temperature, with water exerting little measurable influence. There were a number of important interactions that were often synergistic, and some involved water. 9 Species' responses were highly individualistic and changes in the community were mediated through the response of a small number of key species already present in the community, with no invasion of new species. In the short term at least, floristic diversity may decline as understorey species become less abundant and immigration by new species is inhibited by the dominance of clonal angiosperms. Keywords: biomass, nutrients, species abundance, temperature, water

1 Canopy-level C[O.sub.2] exchange and biomass were measured monthly for 9 consecutive months during 1990 on grazed and non-grazed portions of a Danish salt marsh dominated by Spartina anglica. The empirical measurements were used to calibrate a model of canopy photosynthesis and soil respiration that was subsequently integrated to provide estimates of annual net ecosystem production (NEP). 2 Standing total and green biomass on the non-grazed site reached maxima during September of 1.9 [+ or -] 0.2 and 1.1 [+ or -] 0.2 kgm-2 ([+ or -] 1 SD, n = 3), respectively. Corresponding maxima (0.8 [+ or -] 0.1 and 0.5 [+ or -] 0.05 kg [m.sup.-2]), were achieved during July at the grazed site. 3 Sediment organic matter as a percentage of dry weight was 31.6% and 5% at the non-grazed and grazed sites, respectively. Accounting for the higher sediment bulk density at the grazed site meant that concentrations of organic carbon were 0.027 and 0.021 g [cm.sup.-3] at non-grazed and grazed sites, respectively. Thus, the fraction of NEP removed by grazing animals significantly reduced the accumulation of sediment organic matter. 4 Estimate of NEP varied between 17 and 38 mol [m.sup.-2] [year.sup.-1] of carbon at the grazed site and between 5 and 38 mol [m.sup.-2] [year.sup.-1] at the non-grazed site, depending on assumptions about canopy geometry. Soil respiration, 36 mol [m.sup.-2] [year.sup.-1], did not differ between sites. Canopy respiration was less (21 mol [m.sup.-2] [year.sup.-1]) at the grazed site than at the non-grazed site (28 mol [m.sup.-2] [year.sup.-1]), and accounted for 22-29% and 2841% of gross photosynthesis at grazed and non-grazed sites, respectively. The decrease in canopy respiration compensated the grazed canopy for losses to herbivores. 5 A canopy photosynthesis model was used to calculate a theoretical envelope of canopy biomass, termed the production window, inside of which NEP is positive and outside of which NEP is negative. The production window is bisected by the optimum canopy biomass, which is the theoretical biomass at which NEP is maximized. The seasonality of NEP is determined by the trajectory of actual canopy biomass through the production window. It was shown that canopy biomass on the grazed site was close to the theoretical optimum biomass late in the season, while the non-grazed canopy biomass was supraoptimal. Keywords: grazing, model, net ecosystem production, photosynthesis, respiration

1 Acer mono is one of the earliest germinating species in hardwood forests of northern Japan. To evaluate the advantage of early germination for the seedling establishment, differences in the temporal pattern of leaf development between the seedlings and overstorey trees were investigated, together with the timing of dry mass gain and allocation, survival and mortality agents of seedlings. These traits were contrasted at four sites with different types of foliage phenology in the overstorey trees (FU-1 and FU-2, forest understorey in which overstorey trees unfolded and shed the leaves as a flush and succeedingly, respectively; SG, small gaps; and FE, forest edge). 2 Seasonal growth patterns of the seedlings were greatly affected by the differences in the coupling of leaf development between the seedlings and the overstorey trees. For early germinating cohorts of Acer mono, 79, 61, 50 and 53% of annual dry mass gain occurred within 2 months of germination, in FU-1, FU-2, SG and FE, respectively. After this point (canopy closure) mass increment decreased abruptly in both FU sites, but continued to increase in both SG and FE. Seedling mass, however, increased after September again in FU-2 but not in FU-1, mainly due to earlier leaf shedding of the canopy trees in FU-2. 3 After canopy closure, leaf mass ratio was greatest in FU-1 where light was most limited, but lowest in FE. In contrast, root mass ratio was greatest in FE but lowest in FU-1 where soil moisture was most abundant. These traits might lead to the optimization of growth by making all resources equally limiting even after canopy closure in forest understorey. 4 Higher seedling survival resulting from early germination was observed in all four sites, since predators and pathogens selectively attacked late germinating individuals. The advantage of early germination was greater in both FU-1 and FU-2 than in FE, mainly due to large differences in available light for early vs. late germinating individuals in both FU sites compared with the FE site. 5 These observations suggest that phenological traits of A. mono such as rapid germination in early spring and earlier deployment of leaves compared with overstorey trees has been selected to maximize annual mass gain and survival in understorey habitats of deciduous broad-leaved forests. Keywords: causes of mortality, biomass allocation, RGR, light, shade avoidance

Gynodioecy is a breeding system in which hermaphrodites coexist with male steriles. Theoretical models predict that without any compensation in female fitness male steriles will disappear from a population due to their reproductive disadvantage. In the present study I investigated whether male-sterile (MS), partially male-sterile (IN), and hermaphroditic (H) plants of Plantago lanceolata differed in reproductive growth and allocation. Offspring of three interpopulation crosses segregating all three sex morphs were grown under nitrogen-limited conditions in a growth chamber. Independent of the genetic background MS plants attained a higher vegetative and reproductive dry mass and a higher reproductive output than H plants, whereas IN plants had intermediate values. When corrected for the mass of the pollen, the dry mass differences between the sex morphs were much reduced but still present. However, when whole-plant allocation was expressed on the basis of nitrogen, the differences between the sex morphs disappeared. Thus the sex morphs took up similar amounts of nitrogen but distributed them differently. The MS and IN plants used the nitrogen saved by not producing pollen for additional vegetative as well as reproductive growth. The data presented in this study suggest that resource compensation is one of the main mechanisms responsible for the maintenance of MS and IN plants in gynodioecious P. lanceolata. Key words: biomass allocation; compensation; gynodioecy; male sterility; Plantaginaceae; Plantago lanceolata; reproductive growth.

We tested whether effects of competition and herbivory on plant growth depend on the aboveground biomass of vegetation. Our objective was to test theoretical predictions about the site-dependence of biotic mechanisms of plant population regulation. Biomass ranged from a mean of 64 to 776 g/m² at the eight study sites, which included six old fields and two herbaceous plant communities near water. To measure effects of competition, 4-5 wk old plants of a perennial grass (Poa compressa) were transplanted into plots where neighboring plants were either left intact or removed and after 4 mo the shoot mass of transplants was compared in the two treatments. Transplants were caged in both treatments to exclude herbivores. Removing neighbors increased transplant shoot mass significantly at all sites, indicating that transplants experienced less competition for resources when their neighbors were removed. Regression analysis indicated that the increase in shoot mass due to neighbor removal was significantly greater at sites with higher biomass. This result supports theories that predict competition should increase with increasing biomass. To measure effects of herbivory, the growth of caged and uncaged plants was compared. Caging transplants did not increase their shoot mass significantly at the two sites with the lowest biomass. However, shoot mass was significantly greater for caged transplants than for uncaged transplants at all other sites. Caged transplants lost less tissue to herbivores such as small mammals and molluscs. Regression analysis indicated that the increase in shoot mass due to caging was significantly greater at sites with higher biomass. The combined effect of herbivory and competition was measured by comparing transplant growth in plots where transplants were caged and neighbors were removed with the growth of transplants in plots where transplants were not caged and neighbors were left intact. Transplant shoot mass was significantly greater where herbivores were excluded and neighbors were removed, especially at sites with high biomass. Our results indicate that competition and herbivory each have a greater effect on plant growth at sites with higher biomass and that herbivory has less effect than competition on plant growth at sites with relatively low biomass., Key words aboveground biomass; competition; herbivory; old field: Ontario, Canada; plant growth; Poa; population regulation. INTRODUCTION One goal of plant ecologists is to develop a model of population density regulation [...]

We compared growth and biomass allocation patterns of Lonicera japonica, an invasive vine in the southeastern United States, and its native congener, L. sempervirens, among three herbivory treatments. Growth and biomass variables were calculated at nine harvest dates across 14 mo under no herbivory, insect herbivory, and mammal and insect herbivory. In the absence of herbivory, L. sempervirens accumulated greater biomass and had higher growth rates than L. japonica. Lonicera sempervirens, however, experienced more herbivore damage than L. japonica, particularly due to the combined effects of insect and mammal herbivory. Total biomass accumulation and greater allocation to leaves and stems indicate a compensatory response to herbivory by L. japonica. These attributes in response to herbivory coupled with lower herbivory in its new range compared to L. sempervirens could give L. japonica a substantial advantage over its native congener.

Abstract. Foodchain models predict strong positive response of algal biomass to total phosphorus (TP) in odd-link ecosystems where grazers are controlled by planktivores and no significant response of algal biomass in even-link ecosystems where grazers are released from planktivore predation. On the other hand, resource- or ratio-dependent models predict proportional increase in algal biomass with increasing TP. These predictions were tested with field data from a large number of north temperate lake ecosystems exhibiting a wide range of TP. Instead of using the traditional approach of the number of trophic links present in an ecosystem, I used the presence vs. absence or near absence of large Daphnia and planktivorous fish to indicate the functional dominance of odd vs. even links. Results showed that algal biomass response to TP is stronger in dominant odd-link ecosystems than in dominant even-link ecosystems, which is consistent with the predictions of foodchain models. The significant positive slope of the relationship of algal biomass to total phosphorus for dominant even-link ecosystems is not consistent with foodchain models. In addition, a nonlinear response pattern of algal biomass to total phosphorus appears to be inconsistent with both foodchain and ratio-dependent models. Results also showed that even-link ecosystems produce proportionately lower algal biomass, demonstrating that grazers can modify ratio dependence of algal biomass. Overall, algal biomass appears to be both predator and ratio dependent because grazers are capable of modifying algal response to nutrients, and algae show positive response to nutrients even in the presence of large grazers.

Abstract. The woody [C.sub.3] Prosopis glandulosa (honey mesquite) and [C.sub.4] perennial grass Schizachyrium scoparium (little bluestem) were grown along a gradient of daytime carbon dioxide concentrations from near 340 to 200 [micro]mol/mol air in a 38 m long controlled environment chamber. We sought to determine effects of historical and prehistorical increases in atmospheric [CO.sub.2] concentration on growth, resource use, and competitive interactions of a species representative of [C.sub.4]-dominated grasslands in the southwestern United States and the invasive legume P. glandulosa. Increasing [CO.sub.2] concentration stimulated [N.sub.2] fixation by individually grown P. glandulosa and elicited in [C.sub.3] seedlings a similar relative increase in leaf intercellular [CO.sub.2] concentration, net assimilation rate, and intrinsic water use efficiency (leaf net assimilation rate/stomatal conductance). Aboveground biomass of P. glandulosa was not altered by [CO.sub.2] concentration, but belowground biomass and whole-plant water and nitrogen use efficiencies increased linearly with [CO.sub.2] concentration in seedlings that were grown alone. Biomass produced by P. glandulosa that was grown with S. scoparium was not affected by [CO.sub.2] concentration. Stomatal conductance declined and leaf assimilation rates of S. scoparium at near maximum incident light increased at higher [CO.sub.2] concentration, but there was no effect of [CO.sub.2] concentration on biomass production or whole-plant water use efficiency of the [C.sub.4] grass. Rising [CO.sub.2] concentration, especially the 27% increase since the beginning of the 19th century, may have contributed to more abundant P. glandulosa on [C.sub.4] grasslands by stimulating the shrub's growth or reducing the amount of resources that the [C.sub.3] required. Much of the potential response of P. glandulosa to [CO.sub.2] concentration, however, appears to be contingent on the shrub's escaping competition with neighboring grasses.

1 Species composition and biomass of vascular plants were determined in a matrix of 29 sites on the wet eastern slope of Mauna Loa volcano, Hawaii. 2 Sites were sampled at five or six altitudes (914-2438 m a.s.l.) on each of five known-age lava flows (5, 47, 137, 300 and 3400 years BP). 3 The resultant age - climate matrix was used to examine patterns of biomass accumulation, species distribution, and diversity during primary succession. 4 Biomass increased with substrate age and ranged from 0 to over 36 000 g m to the -2 across the matrix. Generally, biomass increased as altitude decreased, although the maximum value was observed at intermediate altitude on the oldest flow. 5 Community composition varied dramatically with substrate age and climate; species richness ranged from 0 to 30 species plot to the -1, with the maximum at low altitude on the oldest flow. 6 Succession was more rapid at low than at high altitude, but followed distinct compositional trajectories at each altitude. A number of species were found solely or primarily as specialists at a particular altitude and/or successional position, while others exhibited broad niches.

1 Year-to-year growth dynamics of a long-lived woodland perennial herb, Paris tetraphylla, were investigated based on the diffusion model. The past biomass growth of each harvested individual was traced back by measuring the rhizome volume between stem scars. The population density was 2.47 m to the -2. Interference between individuals was therefore expected to be almost absent. 2 Two-year field observations revealed that there was little mortality and only a few recruits by seed. Branching of rhizomes (vegetative reproduction or clonal growth) was also very rare. Mean absolute growth rate per year of individuals of biomass x at year t (defined as the G(t,x) function representing averaged species characteristics) was nearly 0 irrespective of x and t, whilst variance of absolute growth rates per year of individuals of biomass x at year t (defined as the D(t,x) function which is caused by environmental fluctuations, genetic variation, etc.) was proportional to x(super b) where b ranged between 1 and 2. 3 Theoretically estimated stationary size distributions of individual biomass based on the above results agreed well with the observed ones, suggesting that the Paris tetraphylla population was already long lived and that the size structure was at a stationary state. The variation factor D(t,x), but not the deterministic factor G(t,x), determined the stationary size structure of the population. 4 It was shown theoretically that fluctuations in mortality rate and the magnitude of the D(t,x) function around the values estimated from the field data affect the stationary size distribution only a little. Therefore, the Paris tetraphylla population studied here is regarded as a stable system. As mortality rate decreases and/or the magnitude of the D(t,x) function increases, stability of size structure increases. 5 The growth and size-structure dynamics of Paris tetraphylla are in striking contrast to those of most crowded annuals and trees, where one-sided or strongly asymmetric competition between individuals is the major determinant of size structure and brings about its stability through the G(t,x) function. Therefore, there are two types of stable plant communities: in one type, such as in most crowded annuals and trees, growth, size structure and stability are governed mainly by the G(t,x) function (i.e. effect of the D(t,x) function is relatively small), and in the other mainly by the D(t,x) function such as in P. tetraphylla studied here and the sparse populations. However, the inverse J-shaped size distribution of individual biomass or stem diameter is common to both types.

Grassland communities dominated by Festuca scabrella or by Stipa curtiseta and Agropyron dasystachyum were burned experimentally in spring or autumn. Forb, shrub and graminoid biomasses were greater in the unburned Festuca community than in the Stipa-Agropyron type. Spring and autumn burning delayed early season growth of graminoids in both grassland types in the 1st growing season after fire. Peak green biomass was reached later in the season in burned plots relative to reference areas. Plant growth in the spring of the 2nd yr after fire was more rapid in burned plots and peak biomass was reached earlier than in the reference plots. Autumn burning reduced forb biomass significantly early in the growing season during 1 of 3 yr that this parameter was measured. No effect of burning on shrub biomass was detected. Autumn and spring burning of Festuca grassland reduced peak, green, graminoid biomass production in the 1st and 2nd yr after fire; autumn burning had the most negative effect. Reductions in graminoid biomass after burning Stipa-Agropyron stands were smaller than in the Festuca community. Nitrogen concentrations in F. scabrella shoots regrown after fire were higher than those from the reference areas. Soil water content during the growing season, and snow trapping were reduced by burning. Peak green biomass and total graminoid biomass in Festuca grassland recovered to the level of the reference plots 2-3 yr after burning. Recovery was slower in the Stipa-Agropyron community.

Boltonia decurrens (Torrey & Gray) Wood, a perennial species endemic to the Illinois River Valley, is threatened with extinction. Construction of a system of dikes along the Illinois River has altered flood patterns during the last 100 years, converting wet prairies and natural marshes to cropland. Remaining shore habitats have been modified by heavy siltation and altered flooding regimes. Boltonia decurrens is now confined to areas that are disturbed by occasional cropping, disappearing from sites after 3 to 5 years of natural succession. This study was conducted to determine the role of light and water availability upon growth and reproduction. Our data indicate that under greenhouse conditions B. decurrens requires high levels of light for optimal photosynthesis and growth, and is more sensitive to reductions in growth light level than to moderate drought-stress. This sensitivity to light regime may help explain its disappearance from disturbed areas after several years of natural succession. If B. decurrens is overtopped by fast-growing species, it could be shaded to the extent that growth and seed production would be severely affected, increasing the likelihood of its extinction.

The impacts of autumn or spring burning on Symphoricarpos occidentalis were studied in Fescue Prairie in central Saskatchewan. Symphoricarpos density increased two- to three-fold over preburn density in the 1st 2 growing seasons following a burn. Individual shoot weights were approximately one-third those of plants in reference (unburned) sites. Leaves that were approximately two to three times larger, combined with increased stem densities, enabled plants in burned stands to re-establish a leaf area index equal to reference sites within 2 mo of growth in the 1st growing season. Total standing crop of S. occidentalis was reduced only for the early part of the 1st growing season following burning. In the 1st growing season following burning, xylem water potentials and stomatal conductance of burned plants equalled or exceeded those of reference sites. A delayed effect of burning was expressed in the 2nd growing season, with soil moisture, xylem water potentials and turgor potentials being lower in burned plants than in the reference. Flexibility in resource allocation, with a larger proportion of biomass in leaves, and unaffected or improved water status are adaptive features that enable S. occidentalis to regain its position in the plant community the 1st growing season following disturbance by burning. One-time burning in autumn or spring should not reduce the dominance of S. occidentalis in this region.

Growth of vegetative and reproductive structures in Artemisia tridentata is temporally separated during the growing season; vegetative growth occurs during spring and early summer when soil moisture is most abundant, while reproductive growth occurs during summer and fall when soil moisture may be limiting. Vegetative and reproductive structures may therefore exhibit contrasting efficiencies of resource acquisition and investment resulting from temporal differences in resource availability during their development. We examined the effect of water stress on growth, photosynthesis, and resource investment for vegetative and reproductive modules of Artemisia tridentata by applying supplemental water. No differences were observed in vegetative biomass between shrubs in the two watering treatments. Growth of vegetative structures occurred in the spring when water was not limiting, and shrubs in both watering treatments exerted little stomatal control over water loss. Conversely, reproductive growth occurred through the summer when water was limiting, and supplemental watering increased reproductive growth. Shrubs conserved water during summer by abscising leaves and lowering stomatal conductance of both vegetative and reproductive modules in response to decreases in xylem pressure potential and increases in evaporative demand. Leaf abscission can occur without decreasing the amount of carbon available for reproductive growth because inflorescences are capable of positive photosynthetic rates comparable to vegetative leaves. Water stress did not alter tissue construction costs or carbon and nitrogen contents for either vegetative or reproductive modules. Resource limitations were, however, reflected in the efficiency of water use during tissue construction; floral leaves and floral heads of shrubs not receiving supplemental water were produced with higher water-use efficiency. Conservative use of water during production of vegetative modules would offer no advantage to A. tridentata because neighboring species are also most active at this time. Reproductive growth in A. tridentata occurs during summer when neighboring species are largely dormant, and so efficient use of water may allow development of reproductive structures to continue throughout the summer even with limited supplies of water.

The allometry of reproductive biomass M was determined for one moss (Polytrichum commune), four pteridophytes (Psilophyton princeps, Psilotum nudum, Lycopodium lucidulum, and L. clavatum), six gymnosperms (Larix decidua, Pseudotsuga douglasii, Tsuga canadensis, Pinus rigida, Picea abies, and Taxus baccata), and two angiosperms (Crataegus sp. and Quercus bicolor). Biomass M was measured for individual and grouped reproductive organs and regressed as a function of stem diameter D measured proximal to M for representative reproductive stems from each species. Published data for Cooksonia pertoni were used to estimate sporangial M. The data from this vascular plant fossil were compared to those from other species. Least squares regression of the entire data set yielded M = 0.12D(super 2.9) (r squared = 0.94, N = 215), indicating that M, on the average, compiled with M proportional to D(super alpha approximately equal to 3.0). The allometries of the moss, pteridophyte, gymnosperm, and angiosperm species, however, were M = 0.46D(super 4.6) (r squared = 0.99, N = 41), M = 0.07D(super 3.2) (r squared = 0.91, N = 65), M = 0.56D(super 2.2) (r squared = 0.92, N = 85), and M = 0.44D(super 1.8) (r squared = 0.97, N = 21), respectively, indicating that the proportionality M is proportional to D(super alpha approximately equal 3.0 recedes with finer taxonomic resolution. The data for Cooksonia were found to comply with the allometry of Polytrichum when the regression curve of this moss was extrapolated into the size range of the fossil species. Analyses showed that intraspecific allometric scaling factors alpha were dependent upon the manner in which plant stems taper. Species or portions of branching systems with alpha > 4.0 had essentially untapered stems (e.g., Polytrichum commune, Psilotum nudum, twigs of Larix decidua); species with alpha < 2.2 had tapered stems resulting from secondary growth in most cases. The evolution of tapered primary stems and secondary growth was interpreted to alter reproductive allometry.

1. Allocation of biomass and nitrogen were studied for 1 year in experimental populations of Carex diandra, C. rostrata and C. lasiocarpa (species from mesotrophic fens) and C. acutiformis (a species from eutrophic fens). These species were grown at two levels of N supply (3 center dot 3 and 20 center dot 0 g N m to the -2 year to the -1, respectively). 2. At low N supply, total biomass did not differ between the species. At high N supply, the total biomass of C. lasiocarpa and C. acutiformis ('high-productive species') significantly exceeded that of C. diandra and C. rostrata ('low-productive species'). In all species, percentage nitrogen allocation to the leaves exceeded percentage biomass allocation to the leaves. 3. The high-productive species had a higher shoot:root ratio, a higher percentage biomass allocation to the leaves (leaf weight ratio, LWR), a higher total nitrogen content and a higher percentage nitrogen allocation to the leaves than the low-productive species. However, the low-productive species had higher leaf nitrogen concentrations (on a weight basis) than the high-productive species. 4. Parameters which are related to light interception, such as the specific leaf area (SLA: m squared of leaf per kg of leaf), the leaf area ratio (LAR: m squared of leaf per kg of plant), the leaf area index (LAI: m squared of leaf per m squared of soil) and the ratio between total leaf area and total root length, did not differ consistently between the high-productive and the low-productive species. 5. Compared with the high-productive species, the low-productive species invested relatively more biomass and nitrogen in plant parts which contribute to the acquisition of below-ground resources. 6. At low N supply, there was a decrease in all species of the shoot:root ratio, LWR, LAR, LAI, and the ratio between total leaf area and total root length. 7. The rank order of potential productivity of the species in this study did not match the rank order of nitrogen availability in their natural habitat. It is suggested that the distribution of these species is not only determined by their potential productivity, but also by specific demands on the water chemistry and by their competitive ability.

1. A growth analysis was conducted on seven annual/perennial pairs of grasses (six congeneric and one pair taken at random) grown in a hydroponic culture system under constant, productive conditions, in order to investigate the mechanisms responsible for the higher relative growth rate (RGR) of annuals as compared to perennials. 2. All the production parameters (RGR, relative leaf production rate, unit leaf rates), were higher in annuals than in perennials. There were very few differences between the two life forms in biomass allocation to the different organs (except a higher allocation to sheaths in perennials). The specific leaf areas and the leaf area ratios were higher in annuals, whereas the dry-weight:fresh-weight ratios of all the organs were higher in perennials. These differences between annuals and perennials were almost systematic when the comparisons were made within a given genus, but not when they were made between annuals and perennials in different genera. 3. The wide range of RGR obtained for the 14 species also permitted general relationships between RGR and the various components of growth to be discussed. RGR was significantly correlated with: (i) unit leaf rate, (ii) specific leaf area, (iii) leaf area ratio, (iv) dry-weight:fresh-weight ratio of the whole plant, and (v) dry-weight:fresh-weight ratio of roots. Surprisingly, RGR was not correlated with any of the biomass allocation parameters. The single factor that best explained the differences in RGR was the specific leaf area. 4. If, as has been hypothesized elsewhere, the annual life form is derived from the perennial one, the results presented here suggest that the same morphological changes have occured repeatedly in different genera. It is argued that these changes, which are probably correlated with differences in anatomical features, mainly affect the specific (i.e. per unit weight or area) uptake capacities of the plant organs, leading to the higher seedling growth rate observed in annuals.

1. Veronica chamaedrys, V. montana and V. officinalis were grown in either shaded or unshaded conditions in a field experiment lasting 18 months. V. officinalis failed to grow beneath shading as a result of slug grazing. Between May and October of the first year, unshaded V. officinalis had the highest relative growth rate (RGR) and shading significantly reduced RGR in both V. chamaedrys and V. montana but to a greater extent in V. chamaedrys. 2. The proportion of biomass allocated to roots was rapidly reduced by shading, but at the end of the experiment differences between species and light environments were negligible. Root phenology was unaffected by shading. In unshaded plants, allocation to stem (SWR) was higher in both V. chamaedrys and V. montana than in V. officinalis. Shading increased SWR and allocation to petioles but only altered stem phenology. The difference in SWR between shaded and unshaded plants of V. montana became less with time. Total allocation to leaves (TLWR) in unshaded plants was ranked V. montana > V. officinalis > V. chamaedrys. The contribution of dead leaves to TWLR was greatest in unshaded plants. Shading increased TLWR in V. chamaedrys but not in V. montana. 3. In unshaded plants, biomass allocation to sexual reproduction was ranked V. officinalis > V. chamaedrys > V. moiziana. Whilst shading reduced allocation to sexual reproduction in V. chamaedrys, it increased allocation in V. montana. Inflorescences were subdivided into: pedicels plus peduncles; capsules plus calyces; and seeds. A second quotient (|relative allocation') was devised by expressing the biomass allocated to each of these subgroups as a proportion of the total allocated to inflorescences. Whereas shading had no influence on relative allocation in V. montana, there was an increase in the pedicel + peduncle component in V. chamaedrys. Pedicels + peduncles accounted for 50% of inflorescence biomass in unshaded V. chamaedrys, but only 30% in V. montana and V. officinalis. Relative allocation to seeds was ranked V. montana > V. officinalis > V. chamaedrys. 4. Growth form, photosynthetic characteristics and slug grazing all hindered the proliferation of V. officinalis under shading. V. officinalis had a high RGR and allocated c. 25% of plant biomass to inflorescences. 5. Shading modified allocation within and between vegetative and reproductive organs of V. chamaedrys. V. chamaedry did not acclimatize to shading; increases in SWR in the second year, coinciding with tree canopy expansion, were supplementary to those incurred in the first year. 6. Shading had little effect on the allocation of biomass within either vegetative or reproductive organs of V. montana: changes detected in previous short-term experiments were transient. At high irradiances, V. montana was susceptible to chlorophyll photodegradation and could not sustain sexual reproductive output.

In Carpinteria Salt Marsh, Salicornia virginica (pickleweed) grows at lower marsh elevations than does Arthrocnemum subterminalis (Parish's glasswort). Standing biomass of both species was greatest immediately adjacent to their abrupt border, suggesting that conditions for plant growth were best here. We utilized field experiments, in which growth rates of naturally occurring and transplanted individuals of both species were measured in four marsh zones, to investigate the role of edaphic factors and competition in maintaining this zonation pattern. The frequency of flooding, and hence soil waterlogging, was greatest at lower marsh elevations, whereas salinity was highest at higher marsh elevations. Consequently, it was not clear, a priori, which part of the marsh had the most severe physical conditions. In our field experiments, both Salicornia and Arthrocnemum grew better in the two middle marsh zones (high Salicornia zone and Arthrocnemum zone) than in either the low marsh (low Salicornia zone), where flooding was frequent and soils were waterlogged, or the high marsh (transition zone), where soil salinity was extremely high during much of the year and plant water potentials very low. However, Salicornia appeared better able to tolerate flooding, and so persisted in the low Salicornia zone, whereas Arthrocnemum appeared better able to tolerate high salinities, and so persisted in the transition zone. Interspecific competition was most important in the relatively benign middle marsh zones, where each species excluded the other from a portion of this prime habitat. In this marsh, flooding, soil salinity, and competition all interacted to determine plant zonation patterns, but the relative importance of these factors varied at different elevations. Key words: Arthrocnemum; competition; edaphic conditions; halophytes; physical gradient; Salicornia; salt marsh; soil salinity; tidal flooding; zonation.

(1) The relative magnitudes of environmental vs. genetic influences on the growth of Scirpus americanus and Scirpus maritimus were examined in an intertidal marsh on the Fraser River Delta, British Columbia. Intraspecific comparisons at the high and low parts of an elevational gradient were made for shoot, inflorescence, root, rhizome and corm mass over a 16-month period. (2) S. americanus plants on the high marsh had greater shoot densities, flowering frequencies, above- and below-ground masses than plants growing on the low marsh. Shoot density of S. maritimus was highest on the low marsh but its flowering frequency, and above- and below-ground masses were greatest on the high marsh. At all sites sampled, vegetative reproductive effort exceeded sexual reproductive effort; within each species, total reproductive effort on the high marsh exceeded that measured on the low marsh. (3) Shoot growth rates were calculated after controlling for below-ground mass and the duration of tidal exposure. For both species, low-marsh stands had higher shoot growth rates per gram below-ground mass per hour of tidal exposure than high-marsh stands, but shoot mass [m.sup.-2] was greatest on the high marsh. Enhanced plant mass on the high marsh is associated with larger below-ground reserves, but is ultimately a product of prolonged aerial exposure. (4) Reciprocal field-transplant experiments indicated that the high- and low-marsh populations of S. americanus and S. maritimus consist of different genotypes which show similar phenotypes when grown in a common environment. Genotypes moved into new environments grew as well as the residents, suggesting that there is no local genetic differentiation.

Potted fireweeds plants, Epilobium angustifolium L., were grown both from seed and root segments and subjected to early, late, and continuous defoliation and to apical excision during a single growing season. Seed-grown plants and root regenerates compensated completely for the early defoliation treatment and did not differ significantly from controls with respect to the dry weight of any yield component. Late defoliation significantly reduced the weight of flowers and fruit in seed-grown plants and root regenerates, and the annual increment of root weight in root regenerates. Continuous defoliation (early + late) significantly reduced the weight of flowers in seed-grown plants and the weight of both flowers and fruit in root regenerates. Apical excision significantly increased the total weight, shoot weight, and root weight of seed-grown plants but did not significantly affect any yield component in root regenerates. Reproductive allocation, defined as the percentage of total biomass in flowers and fruit, was significantly reduced in both seed-grown plants and root regenerates by the late and continuous defoliation treatments.

A sequential coring approach was used to measure root biomass and production over 1 year in four different communities within the Great Dismall Swamp. A second method, an implanted bag technique, was also used to measure root production, and values were generally lower using this technique. On all sites, fine roots were the most dynamic root component. Both biomass (1,887 g/[m.sup.2]) and production (354-989 g [m.sup.-2] [yr.sup.-1]) were highest on the mixed hardwood site, the least flooded site, and second highest on the cedar site, the site with the longest duration of soil saturation (1,033 g[m.sup.2] and 274-366 g [m.sup.-2] [yr.sup.-1). The maple-gum (696 g/[m.sup.2] and 59-91 g [m.sup.-2 yr.sup.-1) and cypress (824 g/[m.sup.2] and 68-308 g [m.sup.-2] [yr.sup.-1) sites had similarly low amounts of biomass and rates of production. Environmental parameters that influenced production include frequency and duration of flooding, and soil type. Peaks in belowground production were observed on the most productive sites (mixed hardwood and cedar) in summer and late fallwinter; the other two sites exhibited little seasonal variability. The least flooded stand appears to allocate a greater percentage of net primary production belowground than the more extensively flooded stands. The ratio of above- and belowground allocation appears to change in response to a flooding gradient. This has major implications for ecosysten functions as carbon allocation patterns determine the array of litter types generated (leaves vs. roots) which affect decomposition rates and nutrient availability.