Showing papers on "Productivity (ecology) published in 1986"

Partitioning herbivory and its effects on coral reef algal communities

Abstract: Coral reef herbivores were classified into three functional groups according to criteria describing the frequency and intensity of disturbance to the algal community created by their herbivory. These herbivore groups included: microherbivores, which have small foraging ranges ( 1-100 cm2) and a high frequency of grazing any point within their range; the echinoid Diadema antillarum, which has intermediate-size foraging ranges (0.5-1 M2) and intermediate frequencies of grazing any one area within an individual's range; and herbivorous fishes, with large foraging ranges (up to 0.5 ha) and the lowest grazing frequencies at any one site. Algal communities on experimental coral-settling plates were subjected to treatments designed to detect the effects of grazing by representatives of each functional herbivore group on algal biomass, community structure, and primary productivity in a backreef/reefcrest habitat in St. Croix, United States Virgin Islands. Abundances of microherbivores and herbivorous fishes (mainly juvenile scarids) fluctuated over time, while Diadema antillarum abundance remained relatively constant. Grazing intensity (as mea- sured by the rate of algal biomass removal and algal standing crop under different grazing regimes) was greatest for D. antillarum; grazing by D. antillarum resulted in low-biomass, highly productive algal turfs (02 release per unit chlorophyll a per unit time: 1 1.3-22.4 /ug -ug- g h-'). Algal turfs grazed by D. antillarum were dominated by epilithic and endolithic filamentous and crustose species. Grazing by herbivorous fishes led to algal communities with algal turfs of higher biomass than in D. antillarum- grazed treatments; these communities became dominated by a single algal species (Sphacelaria tri- buloides). Fish-grazed algal communities had lower biomass-specific productivity rates than algal turfs grazed by D. antillarum (2.4-8.4 gug -ugg- h'-). Microherbivore-grazed and ungrazed treatments had the lowest biomass-specific productivity rates and eventually became dominated by a few macroalgal species. Although algal biomass in sea urchin-grazed treatments was only 25-50% of the biomass values in treatments not grazed by sea urchins, productivity per unit area was not significantly lower in the former treatments, suggesting a positive effect of sea urchin grazing on algal productivity. This positive effect is a result of the reduction of algal self-shading when grazing is intense and/or the input of regenerated nutrients from D. antillarum excretions. Coral reef plant-herbivore interactions are similar to those in terrestrial grassland-herbivore sys- tems. As in many terrestrial systems, plant-herbivore interactions result in higher overall ecosystem primary productivity and apparently facilitate the flow of energy and materials in this case from the highly productive algal turf component to higher levels in the reef trophic web.

Importance of Ice Edge Phytoplankton Production in the Southern Ocean

Abstract: B efore the mid-1970s, biological oceanographers considered the Southern Ocean a region characterized by high primary productivity during the short austral summer, this large, pulsed productivity apparintly supported the elevated biomasses observed among higher trophic levels since the early whaling expeditions. Enhanced productivity was thought to follow from increased sunlight during the summer and extremely high nutrient concentrations brought to the surface by a massive circumpolar divergence (Deacon 1982). Several investigators believed that as the amount of incident light increased seasonally, primary production also increased when the critical

Nutrients and the productivity of estuarine and coastal marine ecosystems

Abstract: SUMMARY Recent research on estuarine and coastal marine systems has revealed two particularly interesting things about nutrients and productivity. First is the observation that these areas are among the most intensively fertilized environments on earth. Second is the common finding that much of the characteristically high primary productivity of these shallow waters is supported by nutrients released or recycled by pelagic and benthic microheterotrophs. Since nutrient inputs to coastal areas have probably been increasing and are likely to continue to do so, it is particularly important to understand the relationship between nutrient loading and nutrient cycling and the extent to which their interactions may set the levels of primary and secondary production in coastal systems. That some direct relationship exists between the input of nutrients and the productivity of higher trophic levels has been a principle of marine ecology since the turn of the century. It is surprisingly difficult, however, to find q...

The Role of Bryophytes in Nutrient Cycling in the Taiga

Abstract: The bryophytes of the boreal forest are interesting in that they may form a minor element of the community in terms of biomass, while simultaneously being a major element in terms of cover and primary productivity. Even more importantly, the mosses may control ecosystem function through rapid nutrient uptake and through their effects on both the thermal environment of the soil and associated development of permafrost. Consequently, mosses can have major effects on vascular plant productivity and nutrient cycling in the ecosystem.

Phytoplankton bloom dynamics of the western Ross Sea ice edge—I. Primary productivity and species-specific production

Abstract: During the austral summer in 1983, studies of primary productivity within a phytoplankton bloom associated with a receding ice edge in the western Ross Sea, Antarctica were conducted. Primary production was elevated within the ice-edge bloom, with integrated euphotic zone production averaging 40.1 mg C m−2h−1. The production was elevated in regions where the ice melt had created a strong vertical stability, and was decreased outside the zone of melt-water influence. Microautoradiographic analyses and species abundance data showed that a single species of diatom, Nitzschia curta, a species generally considered to be epontic, contributed up to 93% of the total productivity and 70% of the number of phytoplankton cells. Growth rates determined from autoradiography and carbon estimates based on cell volume as well as those determined from bulk production data agreed well and ranged from 0.1 to 0.5 divisions per day. No difference in growth rates between populations within and from outside the bloom was noted, an observation which we believe reflects the recent mixing of the phytoplankton as vertical stability weakened. We conclude that the bloom was seeded by algae released from melting ice, and that an ice-edge bloom can have substantial impact on the biogeochemical cycles and foodweb dynamics of the Southern Ocean.

Phytoplankton production in two east coast estuaries: Photosynthesis-light functions and patterns of carbon assimilation in Chesapeake and Delaware Bays

Abstract: Chesapeake Bay is a large and productive estuary that has received close scrutiny in recent years because of indications that its water quality and biota have been damaged by man's activities. Data on primary production for the estuary as a whole, however, are surprisingly sparse. We describe here the distribution of photosynthetic carbon assimilation by phytoplankton in Chesapeake Bay, and relate productivity patterns to hydrographic characteristics of the estuary. Between March 1982 and April 1983, a series of four cruises was conducted on Chesapeake Bay, and two cruises on the urbanized Delaware Bay for comparison. The upper Chesapeake and Delaware were highly turbid with high concentrations of suspended particulate matter and dissolved inorganic nutrients. Low chlorophyll concentrations were usually found in these areas of high turbidity, despite the abundance of nutrients, suggesting light limitation. Application of Wofsy's (1983) model of phytoplanton growth confirmed this suggestion. Chlorophyll and productivity maxima usually occurred seaward of the turbidity maxima where light penetration increased and suffient nutrients were present to support active phytoplankton growth. Further seaward of the chlorophyll maxima in the Chesapeake, the photic zone depth increased, concentrations of nutrients decreased, and phytoplankton biomass decreased, suggesting that nutrient availability, rather than light, controlled phytoplankton growth in the lower portion of the estuary. In contrast to the Chesapeake, Delaware Bay was more turbid, had generally higher nutrient concentrations, and was lower in phytoplankton productivity. The chlorophyll maxima and region of rapid phytoplankton growth occurred further toward the lower estuary and shelf regions in Delaware Bay because the high turbidity extended further seaward. Nutrients were never depleted at the shelf end of the estuary sufficiently to retard phytoplankton growth. Photosynthesis-irradiance (P-I) curves from simulated in situ and constant intensity incubations showed a strong correlation of the light-limited slope (aB) with the light-saturated rate ( P m B ) on each cruise. Spatial variations in P m B corresponded to patterns of phytoplankton abundance, as did integral production (PP) and carbon-based growth rates (μC, μm), and photosynthetic parameters varied significantly with temperature.

Limnetic Herbivory: Effects on Phytoplankton Populations and Primary Production

Abstract: Population—level and ecosystem—level responses of phytoplankton to grazing by zooplankton were determined in nutrient—enriched and unenriched enclosures in Peter Lake, Michigan. Species—specific net growth rates were determined, and chlorophyll a, primary production (PPR), and alkaline phosphatase activity (APA) were determined for each of three size categories of phytoplankton: 75μm. Thirteen of 16 dominant algal taxa were nutrient limited. Zooplankton reduced APA, an indicator of nutrient deficiency. Growth rates of grazed, nutrient—limited algae (< 30 μm) increased at low levels of zooplankton μμm) nutrient—limited algae increased or did not change as zooplankton biomass increased. These species—specific responses resulted in four— to fivefold changes in chlorophyll concentration and PPR. Overall, the stimulatory effect of nutrient regeneration by zooplankton overrode losses due to grazing, and caused net increases in phytoplankton biomass and productivity.

Significance of atmospheric-derived fixed nitrogen on productivity of the Sargasso sea

Abstract: Recently, it has been suggested that marine primary productivity can be influenced by direct inputs of fixed inorganic nitrogen (NO−3, NO−2 and NH+4) from atmospheric deposition, and that this may be important in shaping trends of productivity in coastal areas1 It is known that anthropogenic contaminants are transported from North America to the Sargasso Sea, affecting the chemistry of rain water over this oligotrophic ocean area Here we present data collected between 1982 and 1984 as part of the Western Atlantic Ocean Experiment (WATOX) by a wet-only precipitation collector on Bermuda Our measurements of the anthropogenic fixed nitrogen in the rainwater samples are discussed in the context of the amount of nitrogen required to support ‘new’ primary production in the Sargasso Sea We show that the effects of atmospheric deposition are insignificant

Effect of Stream Acidification on Periphyton Composition, Chlorophyll, and Productivity

Abstract: We determined periphyton community composition, cell number and biovolume, chlorophyll a density, and areal and chlorophyll-specific primary productivity along a pH (4.5–6.4) and total monomeric al...

The seasonality of phytoplankton in the North American Great Lakes, a comparative synthesis

Abstract: The phytoplankton and productivity of the North American Great Lakes has been studied extensively by Fisheries and Oceans Canada during the past 15 years to monitor the impact of nutrient and contaminant loading on the plankton of the ecosystem. Lakewide cruises were conducted at monthly intervals mainly during the spring to fall period. This provided extensive biomass, species, size, productivity and nutrient concentration data for the Great Lakes. These data were collected using the Utermohl inverted microscope technique together with standardized taxonomic, productivity and data-handling procedures. These standardized methodologies were applied to all the Great Lakes which resulted in a comprehensive phycological and ecological data base for the first time. These data form the basis for the evaluation of the complex phenomenon of seasonality.

Studies of larval herring (Clupea harengus L.) patch in the Buchan area. IV. Zooplankton distribution and productivity in relation to hydrographic features

Abstract: The distribunon and activity of zooplankton were recorded across a temperature front and in relation to phytoplankton distribution in the Buchan area during the last half of September. Egg laying rates of the copepods Acartia tonsa and Temora longicornis, determined in shipboard experiments, closely followed the concentration of chlorophyll, and varied between 0 and an equivalent of 58% body C d. The rates peaked in mixed and particularly frontal water and decreased with increasing intensity of temperature stratification. Copepod egg production rates of three copepod species, inferred from the ratio of egg to female biomass in the water column showed the same magnitude and pattern of variation. Accordingly, the abundance of copepod eggs was highest in mixed and transitional water and declined in stratified water. The distribution of successively older copepod stages showed de creasingly interpretable relationships to hydrography and abundance of phytoplankton. Copepod production in absolute terms showed a similar relation to hydrography as did the specific (egg) production rates, and varied between Ca. 200-300 eg C m3 d1 in mixed and frontal water and between 50-150 g C m3 d’ in stratified water. Total copepod biomass showed a different relation to hydrography than did production, viz. it was higher jo stratified than in mixed and transitional water. However, biomäss peaks were evident in transitional water for small sized (30-200 sm) cope pods, and in the course of the study an additional peak of total copepod biomass evolved in transitional water. Tt is suggested that in the Buchan area frontal water may provide the best longterm average feeding conditions for herring larvae, even though the conditions at any specific point in time may be somewhat different.

The life cycle, population dynamics and productivity of Melanoides tuberculata (Muller, 1774) (Gastropoda: Prosobranchia: Thiaridae) in Hong Kong

Abstract: An investigation of the life cycle, population dynamics and secondary productivity of the viviparous snail Melanoides tuberculuta inhabiting flooded furrows and irrigation ditches at Ping Long, New Territories, Hong Kong, was undertaken between March 1982 and March 1983. There was a single peak in juvenile recruitment coinciding with the warmer months; hatchlings grew quickly and were sexually mature before the next breeding season. Large animals experienced high mortality and few individuals survived until a second breeding season. Secondary productivity and the production: biomass (P:B) ratio of the population (13.43 g shell–free dry weight m−2 yr−1 and 4.81, respectively) were high and exceeded values of these parameters recorded for freshwater prosobranch populations in temperate regions. Ping Long M. tuberculata were exclusively female, as is typical of most populations of this species. Animals > 3.0 mm shell width (90–120 days old) had eggs and developing larvae in the brood pouch, and fully–developed larvae were recorded from brood pouches throughout the study although release of hatchlings was distinctly seasonal. A comparison of life cycle parameters of Malaysian M. turberculata with those of the Ping Long population revealed a marked similarity. The significance of such similarity and the importance of parthenogenicity in the life cycle of this widely distributed snail is discussed. Melanoides tuberculata exhibits the characteristics of an opportunist or ‘fugitive’ species and, by virtue of its reproductive strategies and high productivity, is able to colonize rapidly and temporarily dominate vacant habitats.

On the leaf litter community of the Amazonian blackwater stream Tarumazinho

Abstract: A study of the benthic leaf litter community of the Tarumazinho, a centralAmazonian stream (03° S, 60° W) is presented This small tributary of the Rio Negro is of theblackwater type with a very low nutrient content The sampling stations were towards themouth of the tributary where it flowed through annually inundated forest and the work wascarried out during the low water season Previous studies concluded that these acid waters wereof very low productivity and held impoverished faunas However, this study showed that leaflitter banks held a diverse aquatic community of unexpectedly high biomass This was becausethe banks supplied food and shelter and were available during the low water period when otherhabitats had dried out The macrofauna was dominated by fish and shrimps From an examina-tion of gut contents a food web was produced Primary consumers were found to take mainlydetritus and fungi and it was concluded that allochthonous inputs were the main source ofenergy and nutrients No feeding specialists were found and all the predators took prey frommore than one trophic levelKEY WORDS: Amazonia, benthic community, blackwaters, freshwater ecology, food web, leaflitter, stream macrofaunaINTRODUCTION

Distribution and abundance of benthic microalgae in a shallow southwestern Australian estuarine system

Abstract: Measurements were made of benthic microalgal biomass (chlorophyll mg m-2) and concentration (chlorophyll, µg g-1 dry weight of sediment) from the Peel-Harvey estuarine system, Western Australia. Most chlorophyll was in the top 1 cm of sediment, and less than 10 % of chlorophyll a was non-functional as determined by hexane extraction. Highest biomass occurred at shallow sites and on coarse sandy sediments. Biomass was higher in Harvey (202 mg m-2) than Peel (107 mg m-2) in summer when there was a large population of microalgae in Peel; biomass was similar in winter (Harvey 163 mg m-2, Peel 151 mg m-2). Biomass increased with the onset of riverine nutrient input and decreased when blooms occurred in the water column. Except during Nodularia blooms, the biomass (chlorophyll) of benthic microalgae greatly exceeded (e g 40 times) the biomass of chlorophyll in the water column above. In summer much of the chlorophyll of the water column was due to wind stirring of benthic microalgae. The possible importance of benthic microalgae to the productivity of shallow systems is emphasized.

Environmental Productivity Indices for a Chihuahuan Desert Cam Plant, Agave Lechuguilla

Abstract: Productivity of Agave lechuguilla, a commercially harvested plant that occurs over vast areas of the Chihuahuan Desert, was measured using conventional dry mass changes in the field and was predicted based on physiological responses to environmental variables in the laboratory. An environmental productivity index (EPI) was constructed as the product of indices for water status, leaf temperature, and photosynthetically active radiation (PAR). Each of these component indices was assigned a maximum value of unity when that variable was not limiting net CO2 uptake over a 24—h period. Soil water potential, daily air and leaf temperatures, and PAR in the planes of the leaves at the field site in Coahuila, Mexico, could thus be quantitatively described in terms of their effect on net CO2 uptake. Water status proved to be the most important of the three variables considered, nearly all leaf unfolding occurring during the relatively wet summer and early fall. The rosette habit and low leaf area index (1.23) for the plant groups monitored led to a relatively uniform and high level of PAR over the leaves. Seasonal changes in PAR proportionally affected both the modest daytime net CO2 uptake and the predominant nighttime net CO2 uptake for this crassulacean acid metabolism plant, while seasonal variations in temperature had relatively small effects on net CO2 uptake over a 24—h period. EPI was highly correlated with the number of new leaves unfolding each month in the field (°2 °0.83); counting unfolding leaves in a nondestructive method of estimating productivity. For the 1—yr study period EPI averaged 0.28, which led to a predicted annual dry mass gain per unit leaf area of 0.68 kg/m2. Field measurements indicated that the actual dry mass gain was about half this value, the difference representing photosynthate needed for constructing and maintaining folded leaves, stem, and roots. The productivity of A. lechuguilla per unit ground area explored by its roots was 0.38 kg.m—2.yr—1, which although much less than for agricultural crops, is still much greater than the average productivity for desert ecosystems.

Bacterial biomass in warm-core Gulf Stream ring 82-B: mesoscale distributions, temporal changes and production

Abstract: The distribution of bacterioplankton biomass and productivity in warm-core Gulf Stream ring 82-B generally corresponded to the physical and dynamical structure of the ring. Mean cell volumes were uniform for 4 months, but were larger by a factor of 2–3 in the high velocity (frontal) region (HVR) near the ring edge. As a result of this gradient and higher abundances, water column biomass and production were highest in the front, which appeared to be a local maximum in those properties. In this regard bacterioplankton contrasted strongly to phytoplankton, which exhibited strong local maxima at the center of the ring in June. In April when the water column inside the ring was isothermal to 450 m, bacterial biomass and production were low and uniform to 250 and 50 m, respectively. Bacterioplankton responded dramatically to the vernal restratification of the ring. In June when the surface layer was characterized by a strong pycnocline at 10–40 m, bacterial biomass and production often had strong subsurface maxima, and were 3 and 5 times greater than in April, respectively. Abundance exceeded 1.5 × 10 9 cells l −1 at ring center and exceeded 3 × 10 9 l −1 in the HVR. Turnover rates for the euphotic zone bacterioplankton as a whole were 0.24 d −1 in April, 0.56 d −1 in June, and 0.27 d −1 in August at ring center. Bacterial production averaged 12% of hourly primary production (range 1–32%), suggesting that bacteria control a significant and sometimes large portion of the carbon cycling in the euphotic zone. These data suggest that warm-core rings are sites of enhanced variability of bacterioplankton properties in the open sea. Furthermore, the data strongly support recent work showing that frontal zones are sites of locally enhanced bacterial biomass and production. In the ring system as a whole, the euphotic zone bacterioplankton biomass and production were comparable to and occasionally greater than the biomass and production of the >64 μm zooplankton, especially in the HVR. Bacterioplankton appear to carry out a major fraction of the heterotrophic carbon cycling in oceanic frontal regions.

Biomass and Productivity of Three Phytoplankton Size Classes in

Abstract: Primary productivity of three size classes of phytoplankton ( 22 /zm) was measured monthly at six sites within San Francisco Bay throughout 1980. These sites in the three principal embayments were chosen to represent a range of environments, phytoplankton communities, and seasonal cycles in the estuary. Temporal variations in productivity for each size class generally followed the seasonality of the corresponding fraction of phytoplankton biomass. The 5-22 ~m size class accounted for 40 to 50% of the annual production in each embayment, but production by phytoplankton >22 ttm ranged from 26% in the southern reach to 54% of total phytoplankton production in the landward embayment of the northern reach. A productivity index is derived that predicts daily productivity for each size class as a function of ambient irradiance and integrated chlorophyll a in the photic zone. For the whole phytoplankton community and for each size class, this index was constant and estimated as =0.76 g C m -2 (g chlorophyll a Einstein) -1. The annual means of maximum carbon assimilation numbers were usually similar for the three size classes. Spatial and temporal variations in size-fractionated productivity are shown to be primarily due to differences in biomass rather than size-dependent carbon assimilation rates.

The contribution of crassulacean acid metabolism to the annual productivity of two aquatic vascular plants

Abstract: Net annual productivity and annual carbon budgets were determined for populations of Littorella uniflora var. americana and Isoetes macrospora in a mesotrophic and oligotrophic lake in northern Wisconsin, to assess the contribution of Crassulacean Acid Metabolism (CAM) to annual productivity of the species in their natural environment. Nocturnal carbon accumulation (CAM), daytime uptake of external CO2 via the C3 mechanism, and refixation of endogenously generated CO2 from daytime respiration were the sources of carbon income. CAM activity as diurnal acid rhythms reached maxima of 89 to 182 μeq·g-1 leaf fresh weight for the various populations.

Biomass and productivity of three phytoplankton size classes in San Francisco Bay.

Abstract: Primary productivity of three size classes of phytoplankton ( 22 μm) was measured monthly at six sites within San Francisco Bay throughout 1980. These sites in the three principal embayments were chosen to represent a range of environments, phytoplankton communities, and seasonal cycles in the estuary. Temporal variations in productivity for each size class generaly followed the seasonality of the corresponding fraction of phytoplankton biomass. The 5–22 μm size class accounted for 40 to 50% of the annual production in each embayment, but production by phytoplankton >22 μm ranged from 26% in the southern reach to 54% of total phytoplankton production in the landward embayment of the northern reach. A productivity index is derived that predicts daily productivity for each size class as a function of ambient irradiance and integrated chlorophylla in the photic zone. For the whole phytoplankton community and for each size class, this index was constant and estimated as ≅0.76 g C m−2 (g chlorophylla Einstein)−1. The annual means of maximum carbon assimilation numbers were usually similar for the three size classes. Spatial and temporal variations in size-fractionated productivity are shown to be primarily due to differences in biomass rather than size-dependent carbon assimilation rates. *** DIRECT SUPPORT *** A01BY034 00005

Secondary production of an intertidal mussel ( Mytilus edulis L.) population in the Eastern Scheldt (S.W. Netherlands)

Abstract: We monitored an intertidal mussel (Mytilus edulis L.) population between June 1981 and June 1982 in the Eastern Scheldt estuary (S.W. Netherlands). Density and biomass of the population remained relatively constant over the study period. The shell length growth was described by a Gompertz growth curve. The parameters of this equation were estimated from a log-log-modified Ford-Walford plot of the growth-ring data. The slope of the relationship between animal weight and shell length is season-dependent, mainly due to the spawning cycle in larger mussels. Secondary production is estimated with the growth rate method. In the calculated growth rates the change in slope of the length-weight relationship is incorporated, as well as differences in length growth rates between summer and winter. Secondary production amounts to 156 g AFDW m−2a −1 (expressed per m2 of mussel bank). P:B is 0.50 a−1. The mussel productivity is probably a limiting factor for the density of overwintering Oystercatchers (Haematopus ostralegus).

Seasonal growth and productivity ofMacrocystis integrifolia in British Columbia, Canada

Abstract: The seasonal growth rates and nitrogen and carbon fluxes were estimated for two subtidalMacrocystis integrifolia Bory kelp forests in British Columbia, Canada from changes in population structure through time. Mean relative growth rates of the forests varied from a high of 4.3% d-1 to a low of-3.6% d-1. Mean net assimilatioon rates of carbon (a photosynthesis analog) varied from a high of 0.66 g C m-2 of foliage d-1 to a low of-0.87 g C m-2 d-1. The leaf area index ranged from 0.3 to 11.9. Annual carbon input on a foliage area basis was calculated at 250 g C m-2 yr-1. Annual carbon input to the forest was estimated at 1 300 g C m-2 of ocean bottom yr-1. The yearly nitrate nitrogen input to the forest was estimated at 60 g N m-2 of ocean bottom yr-1. The net ecosystem production varied from-520 to +31 g C m-2 of ocean bottom yr-1. The intra-forest, inter-forest and seasonal variabilities of these productivity parameters are discussed.

Utilization of growth parameters of eelgrass, Zostera marina, for productivity estimation under laboratory and in situ conditions

Abstract: Allometry was used for monitoring aboveground growth of the marine angiosperm Zostera marina L. Dry weight was regressed with leaf length and width, allowing estimation of aboveground net productivity and biomass of individual plants. At the termination of the experiment, rhizome productivity of the same plants was determined by harvesting. Plants in shaded and unshaded seawater tanks were monitored from June until September, 1976; in situ plants were also monitored at Point Judith Pond, Rhode Island, USA. Unshaded plants had shorter leaves, a lower net productivity, lower biomass, and a lower aboveground-torhizome productivity ratio than shaded plants. Unshaded plants had a higher rate of rhizome branching and the resulting new shoot formation than in situ plants.