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The effect of zooplankton species diversity on trophic structure and temporal stability of total zooplankton biomass is examined. Results reveal that increased zooplankton diversity significantly altered the size structure of algae, increasing the relative abundance of large, grazer-resistant algae.

The effects on the temporal dynamics of each of the endoparasitic nematodes Meloidogyne maritima, Heterodera arenaria and Pratylenchus penetrans by the presence of the other two species are investigated. Results reveal that Meloidogyne maritima is suppressed, both in abundance and in time of first appearance in the new root layer, by the addition of the endoparasitic nematodes Heterodera arenaria and Pratylenchus penetrans, while the other two are not affected.

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

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

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.

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.

(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.

Mass loss of senescing leaves is an important part of plant biomass turnover and has consequences for assessment of ecosystem productivity, ecosystem nutrient use efficiency, and plant nutrient resorption efficiency. Data on mass loss are scarce and often based on leaf area as the reference base.