Invasion by a Perennial Herb Increases Decomposition Rate and Alters Nutrient Availability in Warm Temperate Lowland Forest Remnants

We determined the impact of the invasive herb, Tradescantia fluminensis Vell., on litter decomposition and nutrient availability in a remnant of New Zealand lowland podocarp–broadleaf forest. Using litter bags, we found that litter beneath mats of Tradescantia decomposed at almost twice the rate of litter placed outside the mat. Values of k (decomposition quotient) were 9.44±0.42 yrs for litter placed beneath Tradescantia and 5.42±0.42 yrs for litter placed in native, non-Tradescantia plots. The impact of Tradescantia on decomposition was evident through the smaller forest floor mass in Tradescantia plots (2.65±1.05 t ha⁻¹) compared with non-Tradescantia plots (5.05±1.05 t ha⁻¹), despite similar quantities of annual leaf litterfall into Tradescantia plots (6.85±0.85 t ha⁻¹ yr⁻¹) and non-Tradescantia plots (7.45±1.05 t ha⁻¹ yr⁻¹). Moreover, there was increased plant nitrate available, as captured on resin bags, in Tradescantia plots (25.77 ± 8.32 cmol(−)/kg resin) compared with non-Tradescantia plots (9.55±3.72 cmol(−)/kg resin). Finally, the annual nutrient uptake by Tradescantia represented a large proportion of nutrients in litterfall (41% N, 61% P, 23% Ca, 46% Mg and 83% K), exceeded the nutrient content of the forest floor (except Ca), but was a small proportion of the topsoil nutrient pools. Taken together, our results show that Tradescantia increases litter decomposition and alters nutrient availability, effects that could influence the long-term viability of the majority of podocarp–broadleaf forest remnants affected with Tradescantia in New Zealand. These impacts are likely mostly due to Tradescantia's vegetation structure (i.e., tall, dense mats) and associated microclimate, compared with native ground covers. This revised version was published online in July 2006 with corrections to the Cover Date.     

Tradescantia‐based models: a powerful looking glass for investigation of photoacclimation and photoadaptation in plants

Here, we summarize diverse evidence from species that belong to the genus Tradescantia, which we propose as handy and versatile models for studies of the ecology of photosynthesis and the mechanisms of photoacclimation in higher plants. A valuable feature of this genus is the amazingly broad range of ecological niches occupied by its species: from shady understory of tropical rainforest to deserts and semideserts. The former habitats demand shade tolerance (e.g. that featured by Tradescantia fluminensis), whereas the latter requires succulence and/or high light stress tolerance (evident in e.g. Tradescantia navicularis). At the same time, the acclimative traits of Tradescantia species seem quite moderate at first glance. Certainly, their basic principles of acclimation seem to differ in some aspects from the ones typical for most of other higher plants. This review presents a systematic analysis of irradiance responses of Tradescantia species studied on different timescales. The specifics of Tradescantia responses to irradiance make the plants of this genus a ‘multitool’ for studies in this field. Similarity of irradiance acclimation patterns is a characteristic feature in the ecologically contrasting Tradescantia species, which may inspire further insights into physiology and evolution of plants.     

Shrub expansion alters forest structure but has little impact on native mammal occurrence

The expansion (or encroachment) of shrubs in forests and woodlands is generally considered a serious threat to biodiversity. The effects of shrub expansion on forest fauna, however, are poorly understood and likely to depend on the availability of key resources in shrub‐encroached forest. Coranderrk Bushland, like many conservation reserves in south‐eastern Australia, is considered threatened by the spread of an indigenous shrub. We investigated the associations between cover of Yarra burgan (Kunzea leptospermoides (Myrtaceae)), vegetation structure and the occurrence of terrestrial native mammals within the reserve, basing our predictions on prior knowledge of burgan growth habits and fauna habitat preferences. We quantified burgan cover and other potentially important habitat attributes using structure surveys, and used motion‐sensing cameras to detect terrestrial mammals. Dense burgan cover was associated with less grass, a sparser understorey, and more cryptogams, dead trees and coarse woody debris. However, there was no evidence that these changes negatively affected native mammals: burgan cover had little influence on the occurrence of any species except swamp wallabies (Wallabia bicolor), which occurred in all areas of the reserve but shifted from sites with high burgan cover during the day to sites with low cover at night. Our findings contrast with those from grassland shrub‐expansion studies, where fauna generally show strong responses to shrub cover. The effects of shrub expansion on forest fauna may be mitigated by the greater pre‐existing structural diversity in forests or the longer time required for structural changes to be fully realized. The large quantities of dead wood in areas with high shrub cover may also provide compensatory resources for small mammals, while the proximity to un‐encroached areas may enable large herbivores to move between dense shelter and forage. Shrub‐encroached forests clearly provide resources for some native fauna, and management strategies need to consider the potential impacts of shrub removal on these taxa.     

Abundance and Spread of the Invasive Red Algae, <Emphasis Type="Italic">Kappaphycus</Emphasis> spp., in Kane’ohe Bay,Hawai’i and an Experimental Assessment of Management Options

Several species of Kappaphycus were intentionally introduced into Kane’ohe Bay, Hawai’i in the 1970s. Subsequent research has demonstrated that these algae have spread rapidly throughout the bay and can be found in a variety of reef habitats overgrowing and killing corals. This study was conducted to (a) quantify Kappaphycus spp. abundance both spatially and temporally, and (b) investigate control options including manual removal and the use of biocontrol agents. Kappaphycus spp. distribution has increased in the bay over the period between surveys conducted in 1999 and 2002, with variation among reefs. The biomass of Kappaphycus spp. removed, and the amount of time required to manually remove them from the reef varied with habitat type, but in all cases amounted to at least 10 kg/m² requiring almost 2 person-hours to clear 1 m². Re-growth of the algae following their removal was rapid at most sites, likely due to the experimentally demonstrated ability of the algae to re-grow from minute attachment points and the low palatability of the algae to native herbivorous fishes. The native sea urchin, Tripneustes gratilla, reduced the biomass of Kappaphycus spp. in small experimental enclosures and may be a useful biocontrol agent. Because Kappaphycus spp. are still spreading in Kane’ohe Bay and can overgrow over 50% cover on some reefs, we recommend that rapid management action be taken to prevent further damage and spread to other Hawaiian coral reefs.     

Genotoxic effects in <Emphasis Type="Italic">Tradescantia</Emphasis> plant (clone 2) induced by benzo(a)pyrene

This work surveys the genetic toxicity of benzo(a)pyrene added to soil for Tradescantia plants (clone 02). Different adaptation levels of Tradescantia (clone 02) to soil pollution with benzo(a)pyrene have been estimated. Plant adaptation was not observed at the morphological level, but found for the physiological and genetic (with every adaptation stage) levels. The products of benzo(a)pyrene metabolism act as auxin on plants influencing the growth of root biomass and the cell size.     

Response of Tradescantia albiflora to growth irradiance: Change versus changeability

Most chloroplasts undergo changes in composition, function and structure in response to growth irradiance. However, Tradescantia albiflora, a facultative shade plant, is unable to modulate its light-harvesting components and has the same Chl a/Chl b ratios and number of functional PS II and PS I reaction centres on a Chl basis at all growth irradiances. With increasing growth irradiance, Tradescantia leaves have the same relative amount of chlorophyll—proteins of PS II and PS I, but increased xanthophyll cycle components and more zeaxanthin formation under high light. Despite high-light leaves having enhanced xanthophyll cycle content, all Tradescantia leaves acclimated to varying growth irradiances have similar non-photochemical quenching. These data strongly suggest that not all of the zeaxanthin formed under high light is necessarily non-covalently bound to major and minor light-harvesting proteins of both photosystems, but free zeaxanthin may be associated with LHC II and LHC I or located in the lipid bilayer. Under the unusual circumstances in light-acclimated Tradescantia where the numbers of functional PS II and PS I reaction centres and their antenna size are unaltered during growth under different irradiances, the extents of PS II photoinactivation by high irradiances are comparable. This is due to the extent of PS II photoinactivation being a light dosage effect that depends on the input (photon exposure, antenna size) and output (photosynthetic capacity, non-radiative dissipation) parameters, which in Tradescantia are not greatly varied by changes in growth irradiance.This revised version was published online in October 2005 with corrections to the Cover Date.     

Cover crop and conidia delivery system impacts on soil persistence of Metarhizium anisopliae (Hypocreales: Clavicipitaceae) in sugarbeet

The sugarbeet root maggot, Tetanops myopaeformis (Röder), is a major North American pest of sugarbeet, Beta vulgaris L. Previous research suggests that moderate T. myopaeformis control is possible with the entomopathogen Metarhizium anisopliae (Metch.) Sorok. We conducted a three-year (2002–2004) experiment to assess impacts of oat, Avena sativa L. and rye, Secale cereale L., cover crops on persistence of corn grit-based granular or spray formulations of M. anisopliae isolate ATCC 62176 (i.e. MA 1200) applied at 8×10¹² viable conidia/ha in sugarbeet. More colony forming units (CFUs) were detected immediately after application [0 days after treatment (DAT)] in spray plots than granule-treated plots. However, 76–92% declines in CFUs per gram of soil occurred in spray plots within 30 DAT. Substantially (i.e. 83–560%) more rainfall occurred in June 2002 than during June of any other year. Subsequently, 71–670% increases in CFU concentrations occurred by 60 DAT in M. anisopliae granule-treated plots with oat or rye cover crops that year. CFU density increases were higher in cover crops in 2002, but no significant cover crop effects were detected. Conidia persisted for up to 30 DAT in M. anisopliae spray plots and 60 DAT in granule-treated plots in 2002; however, no increases occurred in the years with less June rainfall. Trends suggest that M. anisopliae aqueous sprays result in greater conidia concentrations than granules at sugarbeet plant bases in June during T. myopaeformis oviposition and larval establishment on host plants. Increases are possible when delivering conidia via granules, but high post-application rainfall could be necessary for conidia production.     

Chloroplast translocations induced by light pulses

The effect of single blue-light pulses on chloroplast rearrangement was studied in the leaves of Tradescantia albiflora, Chlorophytum elatum, and Lemna trisulca. For measuring translocations in terrestrial plants the method of transmission changes was used; translocations in the water plant Lemna were studied by direct microscopic observation and counting. Strong light (30 W m^-2) applied in the form of short pulses, shorter than a lag period of translocations, induces some transient effects in the following dark period. With short pulses, transient rearrangements of chloroplasts to a weak-light position were found. With longer pulse duration, biphasic responses took place in Tradescantia and Lemna: The initial movement to a partial strong-light position was followed by a wave of translocation to a weak-light arrangement. In Chlorophytum this type of response appeared only in a narrow fluence range. The validity of the reciprocity law in relation to fluence rate and time of irradiation was confirmed for Tradescantia. The results may give us an insight into the kinetics of the primary effects of light in the translocation process.     

Monitoring the effects of <Emphasis Type="Italic">Rodolia cardinalis</Emphasis> on <Emphasis Type="Italic">Icerya purchasi</Emphasis> populations on the Galapagos Islands

In January 2002, the first biological control program was implemented on the Galapagos Islands with the release of the Australian coccinellid Rodolia cardinalis Mulsant to control the invasive cottony cushion scale, Icerya purchasi Maskell. This was the first time that Galapagos authorities had approved the introduction of a biological control agent to this iconic archipelago and, because of this precedent, it was important to monitor and evaluate its behaviour soon after its introduction. Surveys were carried out after the release of R. cardinalis in 2002 to confirm establishment on Santa Cruz Island. In 2009, seven years post-release, a broader survey was done to document spread throughout the archipelago. Directly after the release of R. cardinalis in 2002, a predator exclusion study and field observations were carried out on scale insect populations on white mangrove (Laguncularia racemosa [L.] Gaertn. F.) on Santa Cruz Island to document impact. In less than three months after R. cardinalis was released in 2002, populations of I. purchasi on white mangrove that were exposed to the predator in the exclusion experiment, or were monitored in the field, had declined by 99–100%. Results suggest that R. cardinalis played a key role in this decline, possibly in combination with high rainfall. Rodolia cardinalis dispersed quickly after its release and by 2009 was found in a wide variety of habitats on seven of the eight islands surveyed that had records of I. purchasi. Two of these were self-introductions. Further monitoring is recommended to determine whether this biological control agent has successfully reduced scale insect numbers on other valued plant species.     

Control of <Emphasis Type="Italic">Lepidium latifolium</Emphasis> (perennial pepperweed) and recovery of native plants in tidal marshes of the San Francisco Estuary

Several management techniques are effective in controlling Lepidium latifolium (perennial pepperweed) in rangelands and hay meadows; however, this invader’s rapid spread into sensitive aquatic habitats throughout the western US calls for alternative control strategies. To evaluate control methods for use in tidal marshes of San Francisco Estuary, we tested chemical, mechanical, and biological methods in field and greenhouse experiments. In a field experiment in three brackish marshes spanning the estuary, application of the herbicide glyphosate to re-growth of L. latifolium following hand-removal reduced L. latifolium cover by an average of 80% after 2 years and led to a 60% increase in native vegetation cover. Glyphosate alone was less effective at reducing L. latifolium cover (20% decrease) and increasing native cover (34% increase). Preliminary tests of a potential biological control, a native parasitic plant, were not successful, thus plots intended for field trials were instead used to test the newly approved herbicide imazapyr, which showed promise in controlling L. latifolium. An additional greenhouse experiment found large reductions in stem lengths with either glyphosate following clipping or imazapyr with or without clipping, all significantly more so than glyphosate alone. We conclude that an integrated management approach of applying glyphosate following mechanical removal can be effective at reducing L. latifolium cover and allowing recovery of native tidal marsh plants, providing a useful solution for controlling smaller, accessible infestations of the invader. Our preliminary tests of imazapyr suggest that it may be very effective at controlling L. latifolium in tidal marshes, although further assessment of non-target effects and native plant recovery are needed to evaluate its relative merit.     

Livestock Predation—Insights From Problem Animal Control Registers in Botswana

Abstract: Problem Animal Control Registers, where farmers report livestock losses due to predators as a prerequisite for financial compensation, allow quantifying the human-predator conflict. We analyzed such registers from the Kweneng District of Botswana to assess the impact of native predators on livestock over 3 years. Leopards (Panthera pardus), lions (Panthera leo), wild dogs (Lycaon pictus), brown hyenas (Hyaena brunnea), and cheetahs (Acinonyx jubatus) altogether claimed 2,272 head of livestock. During 2002, the year with the highest impact, the number of animals reported depredated (954) represented 0.34% of the livestock in the district. Leopards and lions caused 64% of the losses. Leopard livestock predation mainly affected calves and was consistent over the district and over time. In contrast, lion predation concentrated on adult cattle, was characterized by local hot spots close to reserve borders, decreased with increasing distance to a reserve, and increased during 2002, an unusually dry year. Interviews with 60 farmers and herders within 30 km of Khutse and Central Kalahari Game Reserves revealed an annual loss of 2.2% of their livestock to predators. Here, small farms (max. 100 domestic animals) suffered relatively higher losses than large, commercial farms, not only due to predation (small farms: 11.7%; large farms: 1.0%) but also from other causes (small: 12.6%; large: 2.8%), even though herders on large farms guarded 5 times more livestock per person than those on small farms. To reduce livestock predation in most of the district where lions are absent, we recommend maternity corrals for pregnant females and calves to better protect vulnerable calves during day and night. In areas close to a reserve where lions roam, herders' incentives to keep all livestock protected in a corral at night have to be enhanced because, according to the registers, only 3 predation cases were reported to have happened inside a corral.     

Plastids in sieve elements and their companion cells

Summary Plastids have been identified in the sieve elements and/or companion cells of 14 monocotyledon species. In contrast to earlier reports, plastids are present in the sieve elements of Smilax and the companion cells of Tradescantia. The development and fine structure of the sieve-element plastids in Smilax do not differ from the type found in all of the 230 angiosperm species we have studied so far contain prominent plastids. The companion cells are easily identified by their specialized plasmatic connections with the sieve elements. The leucoplasts in the companion cells of Tradescantia are identical with those reported for many angiosperms.     

EFFECTS OF SPACE FLIGHT (BIOSATELLITE II) AND RADIATION ON FEMALE GAMETOPHYTE DEVELOPMENT IN TRADESCANTIA

The mode of female gametophyte development and the cytological effects of orbital flight factors, with and without radiation, on embryo sac development were studied in Tradescantia clone 02 flown in Biosatellite II. One package of 32 rooted inflorescences was exposed during the free-flight phase of the two-day orbital flight to about 220 R gamma radiation from an ⁸⁵Sr source, and a nonirradiated package was flown as a flight control. Two similar packages, one irradiated and one unirradiated, were maintained in a ground-based vehicle as concurrent nonflight controls. Various postflight ground experiments were conducted in an attempt to associate with specific flight factors the effects observed in the orbited plants. Mature ovaries were fixed daily as the flowers opened for at least 20 days after the treatment, sectioned, stained, and analyzed for the rate of embryo sac abortion and other developmental abnormalities. The embryo sac in Tradescantia clone 02 is eight-nucleate with a Polygonum type of development. Irradiation during megasporogenesis produced an increased rate of embryo sac abortion and this radiation effect was greater in the environment of the flight vehicle than in the nonflight vehicle. This effect may be due to an increase in concentration of ethylene in the flight vehicle. A synergism between some undetermined flight factor and radiation was found to produce underdeveloped embryo sacs. Malfunctioning of the spindle, most probably due to free flight, was evidenced by the increased number of embryo sacs with misoriented nuclei.     

A Model for the Spread of an Invasive Weed, <Emphasis Type="Italic">Tradescantia fluminensis</Emphasis>

Tradescantia fluminensis is an invasive weed and a serious threat to native forests in eastern Australia and New Zealand. Current methods of eradication are often ineffective, so understanding the growth mechanisms of Tradescantia is important in formulating better control strategies. We present a partial differential equation (PDE) model for Tradescantia growth and spatial proliferation that accounts for Tradescantia’s particular creeping and branching morphology, and the impact of self-shading on plant growth. This is the first PDE model to represent a weed that spreads via a creeping growth habit rather than by seed dispersal. We use a travelling wave analysis to investigate how Tradescantia extends to colonise new territory. Numerical simulations and analysis show that the model provides a good qualitative representation of the behaviour of this plant. This model provides a foundation for assessing different control and eradication strategies for Tradescantia.     

Abundance and Distribution of Native and Alien Grasses in a “Cerrado” (Brazilian Savanna) Biological Reserve1

Several species of African grasses brought to Brazil as cattle forage have spread widely, outcompeting native herb species. The open forms of Brazilian savanna (“campo cerrado” and “campo sujo”) are the most affected by such invasions, because their structure is open, permitting enough sunlight into the lower strata. The invasion of alien forage grasses occurs in almost every cerrado nature reserve. This study was carried out in the “Cerrado de Hmas Biological Reserve”, Pirassununga, São Paulo State, Brazil, with the following objectives: (a) to compare the abundance of native and alien grass species; (b) to verify the importance of such alien grasses in the community; (c) to identity distribution patterns for the alien grass species in a gradient from the edge (highly disturbed) to the center (less disturbed) of the reserve; and (d) to explore the distribution of native and alien grasses in the search for possible competitive interactions. Using the “point method,” a total of 260 points was sampled and 52 species were recorded. The four most frequent species (FA = absolute frequency) were two native (Echinolaena inflexa [Poir.J Chase [FA = 38.85%] and Diandrostachya chrysotrix [Nees] Jacues Felix [FA = 15.38%]) and two alien African species (Melinis minutiflora Beauv. [FA = 33.08%] and Brachiaria decumbens Stapf [FA = 13.85%]). M. minutiflora and E. inflexa had higher values of absolute vigor (67.69 and 59.62%, respectively), relative vigor (28.16 and 24.80%, respectively), and cover (100.77 and 98.47, respectively), indicating higher biomasses and densities and their dominance in the community. B. decumbens presented the highest number of contacts per point, showing the highest stratification. To detect possible edge–center distribution gradients, correspondence analysis was done, initially using all the recorded species and subsequently only the four more frequent grasses, with similar results: (a) the alien grasses, especially M. minutiflora, did not show a distinct distribution gradient from edge to center, but occurred over the whole reserve; (b) no distinct ecotonal band around the reserve (edge–belt) was detected, the whole reserve seeming to be “ecotonal”; and (c) E. inflexa and M. minutiflora showed similar phytosociological patterns, and spatial distribution; association between these two species was statistically significant.     

Population structure and population dynamic of Pulsatilla patens (L.) Mill. in relation to vegetation characteristics

In 2003, the last existing population of Pulsatilla patens in Germany was studied in the nature reserve “Garchinger Heide”, a calcareous grassland north of Munich. The aim of our study was to evaluate the endangerment of the species in ancient and young grasslands of the nature reserve. Therefore, the size, structure and generative reproduction of the population in relation to vegetation characteristics were investigated. Total population size and mean density of individual plants in different zones of the nature reserve were determined by a GPS-supported counting and compared to a mapping of 1991. The population structure was analyzed by counting the number of individuals of different age–state classes on 4 m² plots in ancient and young grasslands of the nature reserve. The cover of phanerogams, cryptogams, litter and bare soil was studied in order to characterize habitat quality.In 2003, about 9700 individuals of P. patens were counted which means that population size strongly decreased in comparison to 1991 (about 27 000). In the ancient grasslands, the number of individuals of all age–state classes of P. patens correlated negatively with the cover of phanerogams and litter. In contrast, phanerogam and cryptogam cover had a positive influence on the number of individuals of all age–state classes on a topsoil-removal site due to protection from desiccation. This site was the only one in the nature reserve, where population size increased between 1991 and 2003. The large population size indicates that short-term endangerment or extinction of the species in the nature reserve is not very likely. Nevertheless, the management of the nature reserve has to be optimized in order to prevent a further long-term decrease of the population size of P. patens.     

DIFFERENTIAL RESPONSES OF PLANT FOLIAGE TO SIMULATED ACID RAIN

Experiments were performed to show the responses of foliage of several clones of Tradescantia sp., Pteridium aquilinum, Quercus palustris, and Glycine max to simulated acid rain. These experiments were performed to (a) predict the relative sensitivities of foliage of these plants to acid rain, and (b) identify leaf surface and anatomical alterations to simulated acid rain that may be used to diagnose acid rain injury. Plants were exposed to simulated rain at pH levels of 5.7, 3.4, 3.1, 2.9, 2.7, 2.5, and 2.3. Sporophyte leaves of bracken fern {P. aquilinum) were most sensitive to simulated acid rain among the species tested. About 10% of the surface area of older leaves of P. aquilinum was injured after exposure to 10 rainfalls at pH 2.5 (a single 20-min rainfall daily). Foliage of pin oak (Q. palustris) exhibited less than one-percent leaf area injury after exposure to simulated rain at pH 2.5 after 10 rainfalls (one 20-min rainfall daily). The responses of soybeans (G. max) and spiderwort (Tradescantia sp.) were intermediate between these two extremes. Histological observations show that lesion development results in collapsed leaf tissue in all four species. Gall formation that resulted from both cell hypertrophy and hyperplasia occurred in lesions of Tradescantia, and Q. palustris. Limited hyperplastic and hypertrophic reactions occurred in G. max foliage after exposure to simulated acid rain but no leaf galls resulted. Sporophyte foliage of P. aquilinum exhibited a “granular” type abnormality in the cytoplasm prior to the collapse of some epidermal cells injured by simulated rain. Injury occurred most frequently near vascular tissues and trichomes in all four species. In general, plant species that show cell hyperplasia and hypertrophy of leaf tissues after exposure to simulated acid rain are injured less than species that do not show these responses.     

Photodynamic injury to heated leaves

Summary The leaves of Tradescantia fluminensis Vell, were kept in light and darkness after short-term heating (5 min and 10 min) at different temperatures. In light temperature causing injury was 10° lower than in darkness. A considerable destruction of chlorophyll occurred when the heated leaves were kept in light. If the light intensity was 4,000 lux or even lower the damage to cells was not accompanied by bleaching of chlorophyll. Light produced no effect on unheated leaves. In variegated white-green leaves of Chlorophytum elatum R. Br. light injured only green parts of leaf blades. The minimal light intensity which brought about injury of Tradescantia leaves in experimental conditions was 1,000 lux. Light of the same intensity accelerated death of heated isolated leaves of Cucumis sativus L.Light damage to Tradescantia leaves occurred when the action of light was accompanied by that of high temperature.In an atmosphere of nitrogen the injurious effect of light sharply decreased.It is suggested that the injury of heated leaves in light is caused by photooxydation which is sensitized by chlorophyll and occurs at the expense of photochemical energy which is not used in photosynthesis. Photosynthesis itself is repressed by heating.     

Elevated carbon dioxide affects the patterning of subsidiary cells in Tradescantia stomatal complexes

The influence of elevated CO₂ concentration (670 ppm) on thestructure, distribution, and patterning of stomata in Tradescantialeaves was studied by making comparisons with plants grown atambient CO₂. Extra subsidiary cells, beyond the normal complementof four per stoma, were associated with nearly half the stomatalcomplexes on leaves grown in elevated CO₂. The extra cells sharedcharacteristics, such as pigmentation and expansion, with thetypical subsidiary cells. The position and shape of the extrasubsidiary cells in face view differed in the green and purplevarieties of Tradescantia. Substomatal cavities of complexeswith extra subsidiary cells appeared larger than those foundin control leaves. Stomatal frequency expressed on the basisof leaf area did not differ from the control. Stomatal frequencybased on cell counts (stomatal index) was greater in leavesgrown in CO₂-enriched air when all subsidiary cells were countedas part of the stomatal complex. This difference was eliminatedwhen subsidiary cells were included in the count of epidermalcells, thereby evaluating the frequency of guard cell pairs.The extra subsidiary cells were, therefore, recruited from theepidermal cell population during development. Stomatal frequencyin plants grown at elevated temperature (29 C) was not significantlydifferent from that of the control (24 C). The linear aggregationsof stomata were similar in plants grown in ambient and elevatedCO₂. Since enriched CO₂ had no effect on the structure or patterningof guard cells, but resulted in the formation of additionalsubsidiary cells, it is likely that separate and independentevents pattern the two cell types. Plants grown at enrichedCO₂ levels had significantly greater internode lengths, butleaf area and the time interval between the appearance of successiveleaves were similar to that of control plants. Porometric measurementsrevealed that stomatal conductance of plants grown under elevatedCO₂ was lower than that of control leaves and those grown atelevated temperature. Tradescantia was capable of regulatingstomatal conductance in response to elevated CO₂ without changingthe relative number of stomata present on the leaf. Key words: Elevated CO₂, stomata, subsidiary cells, patterning