Nutrient-rich Habitats Research Articles

Root morphological and physiological plasticity of perennial grass species and the exploitation of spatial and temporal heterogeneous nutrient patches

Root morphological and physiological characteristics of four perennial grass species were investigated in response to spatial and temporal heterogeneous nutrient patches. Two species from nutrient-rich habitats (i.e. Holcus lanatus and Lolium perenne) and two species from nutrient-poor habitats (i.e. Festuca rubra and Anthoxanthum odoratum) were included in the study. Patches were created by injecting equal amounts of nutrient solution into the soil either on one location (i.e. spatial heterogeneity) or on several, alternating locations (i.e. temporal heterogeneity) within the pot. The consequences of changes in root morphology and the implications for the exploitation of the nutrient patches by individual plants were quantified by the amount of 15N captured from the enriched patches. The effects of nutrient heterogeneity on the acquisition of nutrients by species were determined by comparing the total nitrogen and phosphorus acquisition of the species in the two heterogeneous habitats with the total nitrogen and phosphorus acquisition in a homogeneous treatment. In this homogeneous treatment the same amount of nutrient solution was supplied homogeneously over the soil surface. The experiment lasted for 27 days and comprised one harvest.

Mineral ion, nitrogen and organic solute pattern in sedges(Carex Spp.) – a contribution to the physiotype concept. II. Culture experiments

Summary Field studies on Carex species (C hoo & A lbert 1999) suggest that this genus represents a uniform physiotype. In order to ascertain whether this physiological stability in the field can also be found under controlled conditions with a varied nutrient supply, five Carex species native to wet-acidic oligotrophic ( c. rostrata, C. limosa ), moist-eutrophic ( c. acutiformis ), mesotrophic flysch-sandstone ( c. pilosa ) and meso-eutrophic saline ( c. distans ) habitats were cultivated under three different nutrient regimes. In addition to plant matter and total N, plants were analyzed for inorganic ions (K, Na, Mg, Ca, CI, NO 3 , SO 4 , P i ), organic acids, low molecular weight carbohydrates, amino acids, and osmolality. While C. acutiformis , being adapted to nutrient-rich habitats, could not maintain a high growth under low nutrient availability, C. limosa and C. rostrata , being adapted to nutrient-poor habitats, were able to maintain or even to increase their growth. C. acutiformis and C. distans reduced the below-ground to above-ground biomass ratio under eutrophic conditions, while C. limosa maintained this ratio and C. pilosa even increased it. Despite differences in the nutrient regimes, changes in the main osmotic patterns of the investigated species were rather limited. The following trends were observed: levels of amino acids and total N increased with the nutrient supply, but were inversely correlated to sugar contents. Fluctuations of total amino acid levels were paralleled by changes of asparagine (Asn) contents, suggesting a key role for asparagine as a potential N-storage compound. Compared to oligo- and mesotrophic conditions, eutrophic plants generally showed the lowest total sugar contents. The ionic changes stemming from increased eutrophication showed the same pattern for all investigated species, indicating quite similar characteristics of the mineral ion and organic acid metabolism. Generally, Carex species under oligo- to mesotrophic conditions adequately met their ion demands by efficient metabolic uptake processes; on the other hand, under eutrophic conditions, a balanced uptake of nutrient ions was achieved by efficient regulatory processes that also prevent the uptake of potentially toxic amounts of ions. Based on these results as well as on those in C hoo & A lbert (1999), we assume that Carex species represent a relatively uniform physiotype enabling this genus to cope successfully with a broad variety of environmental conditions.

Leaf and StemIn Vitro Digestibility for Grasses and Dicotyledons of Meadow Plant Communities in Spring

The aim of this study was to improve prediction of the herbage digestibility of meadow plant communities rich in species. The variability of the in vitro dry matter digestibility (IVDMD) at a given date could result both from the species which constitute the plant community and from the variability in the proportion of the different plant components in relation to growth conditions. In order to separate the two factors, we studied the IVDMD change in spring, through the NIRS procedure, one month before and one month after the flowering stage of the main species. This was done for two sets of plant communities with very different botanical composition, dominated by species such as Dactylis glomerata and Chaerophyllum aureum (three) or Festuca rubra and Sanguisorba minor (two plant communities). The IVDMD of dicotyledons was higher than those of grasses both for leaf blades and for stems. The leaf blade IVDMD was quite stable throughout the period studied while those of grasses decreased by about 100 g kg -1 . The stem IVDMD for grasses as for dicotyledons first decreased quickly the month before the flowering stage of the main species, and then move slowly the next month. The difference in IVDMD between those species which were mostly in nutrient-rich habitats was 20 (stems of dicotyledons) to 80 g kg -1 (leaf blades of grasses) higher when compared to those species which were mostly in nutrient-poor habitats. These results, obtained for leaf blades and stems of sets of species with different habitat characteristics, were in agreement with those of the literature on swards which are almost always pure. For modelling the digestibility change for such plant communities through a growth period, we propose to use the IVDMD values characteristic of a given set of species, as outlined above, and the proportion of the different plant components in the herbage.

Ostracode speciation following Middle Ordovician extinction events, north central United States

Abstract Studies by several workers show that major extinctions of trilobites, echinoderms, brachiopods and gastropods (but not conodonts) occurred at the horizon of a middle Ordovician K-bentonite (Deicke metabentonite) in the north central United States. Extinctions of Ostracoda are also represented at the Deicke horizon. The metabentonite, a Rocklandian stage ash fall the age of which is approximately 454 Ma, middle Caradocian, originated in the eastern United States. About 160 species of Ostracoda have been recorded in the middle and upper Ordovician of the north central USA. Ostracode speciation was low prior to the Deicke extinction event, consisting of a few eoleperditiids, leperditellids, drepanellids, aparchitids and bairdiids of the Glenwood and Platteville formations (Blackriveran-early Rocklandian). Following the extinction event, during the next approximately 1.5 Ma, 85 ostracode species appeared in the uppermost Platteville Limestone and in the overlying Decorah Shale (late Rocklandian-early Shermanian). The known Ostracoda species durations averaged about 2 Ma, although some are only half that length of time. Additional episodes of ash falls, following the Deicke and associated episodes, occurred in the next approximately 7.5 Ma in the region. The preceding Decorah ostracode fauna disappeared from the area and about 50 recorded new or immigrant taxa appeared following the last volcanic event in the late Edenian and Maysvillian stages (Dubuque and Maquoketa formations). Species duration during this time interval apparently averaged less than in the Decorah, about 1 Ma. The volcanic episodes appear to have provided nutrient-rich habitats that resulted in evolutionary spurts in the Ostracoda, following at least two of the episodes. Duration of the species was perhaps related to the total nutrient budget provided by the ash falls as well as to salinity regimes, palaeoclimates and other factors.

Accumulation of Amino Acids in Forest Plants in Relation to Ecological Amplitude and Nitrogen Supply

Summary 1. Field experiments were conducted to examine how total nitrogen (N) concentration and accumulation of free amino acids in boreal forest plants were affected by nitrogen supply. Nine species, including grasses, herbs and one ericaceous dwarf shrub, were fertilized with ammonium and nitrate (30 g N m-2), respectively. Leaves, rhizomes and roots were harvested 10 and 65 days after fertilization. The experiments were done in two spruce-dominated forest ecosystems that differed in biodiversity and productivity. 2. With some exceptions, ammonium fertilization gave the largest increase in both total N concentration and amino acid accumulation. The increase in total N was largely caused by an increase in amino acid N. 3. Glutamine N showed the largest response to fertilization and dominated the amino acid N pool 10 days after fertilization. Fertilization gave a more significant effect in the less productive forest. 4. At the end of the growing season, 65 days after fertilization, species typical of nutrient-rich habitats (Filipendula ulmaria, Lactuca alpina and Poa remota), had mainly accumulated asparagine, while species typical of poorer habitats (Geranium sylvaticum, Maianthemum bifolium and Vaccinium myrtillus), had accumulated arginine in rhizomes and roots as a response to increased N availability.

Nitrate reductase activity in vegetation below an arctic bird cliff, Svalbard, Norway.

. Vegetated sites below bird‐nesting cliffs are uniquely nutrient‐rich habitats in the otherwise nutrient‐poor arctic environment. Plants from six distinct vegetation zones below such a cliff at 79° N, Svalbard, Norway, were collected for analysis under greenhouse conditions. Leaf nitrate reductase activity (NRA) was analysed in 42 species representing 25 % of the Svalbard vascular flora. The species mean NRA values ranged from 0.37 to 8.34 μmols of nitrite ions formed per gram of plant fresh weight per hour. Species in the vegetated zone growing closest to recent guano deposits had the highest NRA values, (mean = 4.47) whereas plants growing farther below the cliff had significantly lower values (mean = 0.55).A similar pattern was detected in a duplicate set of plants induced with 15 mM KNO3; vegetation zone means for NRA ranged from 5.08 to 0.98 μmols of nitrite ions formed per gram of plant fresh weight per hour. Maximally induced species NRA values were highest in the first zones below the cliff and decreased downslope. This gradient paralleled the steep soil nitrate gradient, which decreased from 13.84 mg/l at the cliffbase to 1.03 mg/l downslope. Correspondingly, soil ammonium ions in the vegetation zones ranged between 1.96 mg/l at the cliff‐base to 0.03 mg/l downslope. Correlations between NRA and soil nitrate provide a systematic basis for assigning scalar ‘nitrogen figures’ as indicators of habitat preference, here for the first time applied to arctic species.

Meristem activity and biomass production as response mechanisms in two forest herbs.

Actaea spicata and Geranium sylvaticum are deciduous rosette herbs, frequently coexisting in nutrient-rich forests of boreal Sweden. A. spicata is restricted to this habitat whereas G. sylvaticum has a wider ecological amplitude. To explore the different distributions of these species we studied the growth mechanisms by which they responded to nutrient and light supply. Plants raised from seeds were grown under four combinations of light and nutrient supplies and growth was followed for 20 weeks. Growth responses were measured as biomass accumulation and meristem activity, i.e. leaf development by shoot meristems. Biomass accumulation and meristem activity were affected by nutrient and light treatments. However, A. spicata responded more to nutrients, whereas G. sylvaticum responded more to light, and low resource supply shortened the time during which shoot meristems of A. spicata developed leaves without a corresponding effect on biomass accumulation. In G. sylvaticum, the periods of leaf development and biomass accumulation were the same, but a relationship between high development rates and peak allocation of biomass to shoot meristems indicated a storage function of these during leaf development. We conclude that the inflexible growth of A. spicata, mainly affected by nutrient supply, makes it less competitive in open habitats and restricts it to shaded, nutrient-rich habitats. G. sylvaticum should be more successful in habitats subjected to unpredictable disturbances, due to a flexible growth morphology and a dynamic function of meristems that buffers against variation in nutrient supply and facilitates positive light responses. Meristematic data should be included in interspecific comparisons on growth responses to different resource supplies. Unless species have the same growth mechanism, it is not satisfactory to study biomass-related traits alone, as internal constraints concerning plant development might confuse the interpretation.

The ability of several high arctic plant species to utilize nitrate nitrogen under field conditions.

The ability to utilize NO inf3sup- in seven high arctic plant species from Truelove Lowland, Devon Island, Canada was investigated, using an in vivo assay of maximum potential nitrate reductase (NR) activity and applications of 15N. Plant species were selected on the basis of being characteristic of nutrient-poor and nutrient-rich habitats. In all species leaves were the dominant site of NR activity. Root NR activity was negligible in all species except Saxifraga cernua. NO inf3sup- availability per se did not appear to limit NR activity of the species typically found on nutrient-poor sites (Dryas integrifolia, Saxifraga oppositifolia, and Salix arctica), or in Cerastium alpinum, as leaf NR activities remained low, even after NO inf3sup- addition. 15NO inf3sup- uptake was limited in D. integrifolia and Salix arctica. However, the lack of field induction of NR activity in C. alpinum and Saxifraga oppositifolia was not due to restricted nitrate uptake, as 15NO inf3sup- labelled NO inf3sup- entered the roots and shoots of both species. Leaf NR activity rates were low in three of the species typical of nutrient-rich habitats (O. digyna, P. radicatum and Saxifraga cernua), sampled from a site containing low soil NO inf3sup- . Additions of NO inf3sup- significantly increased leaf NR activity in these latter species, suggesting that potential NR activity was limited by the availability of NO inf3sup- . 15N labelled NO inf3sup- was taken up by O. digyna. P. radicatum and Saxifraga cernua. Although two species (D. integrifolia and Salix arctica) showed little utilization of NO inf3sup- , we concluded that five of the seven selected high arctic plant species (C. alpinum, O. digyna, P. radicatum, Saxifraga cernua and Saxifraga oppositifolia) do have the potential to utilize NO inf3sup- as a nitrogen source under field conditions, with the highest potential to utilize NO inf3sup- occurring in three of the species typically found on fertile habitats.

A Comparative Study of the Growth and Morphology of Eight Grass Species from Habitats with Different Nutrient Availabilities

1. To find out which properties enable plant species to dominate in nutrient-poor habitats and which properties benefit species in nutrient-rich habitats, we studied the growth and morphology of eight perennial grass species from habitats with contrasting soil fertilities in a pot experiment under controlled conditions in a glasshouse. 2. The species were grown under nutrient-poor and nutrient-rich conditions. Ranked from the least responsive to the most responsive to the supply of nutrients they were: Festuca ovina, F. rubra, Anthoxanthum odoratum, F. arundinacea, Alopecurus pratensis, F. pratensis, Arrhenatherum elatius, Lolium perenne. 3. The response correlated positively with the Ellenberg nitrogen number of the species. No differences in initial relative growth rate were found between the species, but after 4 weeks the plant dry weight increased with increasing nitrogen number as a result of variation in embryo plus endosperm weight. 4. Species characteristic of nutrient-rich hayfields are taller and show a more homogeneous vertical distribution of photosynthetic area than the species from nutrient-poor habitats, which have most of their leaf area below 15 cm. Species from the nutrient-poor habitats allocated less dry matter to the roots and consequently more to the shoot, than species from nutrient-rich conditions. However, leaf and root morphology seem to be most clearly adapted to the habitat. 5. Species from nutrient-rich habitats have a higher specific leaf area (SLA) than species from nutrient-poor habitats, while species from nutrient-poor habitats had more root length per unit root weight (SRL) than species from nutrient-rich habitats.

The Clone Architecture of Rumex alpinus (Polygonaceae)

Rumex alpinus is a perennial species with a monopodial rhizome consisting of annual growth segments which are products of individual seasons. In nutrient-rich habitats, R. alpinus is a strong dominant suppressing other species under its dense canopy. The rhizome pattern and dynamics of a stand of R. alpinus were studied in the Krkonose Mts, Czechoslovakia. Rhizomes of R. alpinus remain alive for 13.0±3.2 (mean±S.D.) yr. Segment width can be used as an estimate of shoot biomass since these variables are closely correlated. The long-term growth dynamics of R. alpinus stands was simulated by a stochastic model. This enabled prediction of a) the fate of individual ramets within the stand, b) the number of genets in the stand, c) successive changes in spatial pattern, and d) lateral extension of the stand (...)

Competition and Nitrogen Loss from Plants in Grassland Ecosystems

Adaptation of plant populations to nutrient—poor environments may follow two essentially different pathways: maximizing the assimilation of nutrients or minimizing the loss of nutrients. Our hypothesis was that plant species that are adapted to nutrient—poor soils can replace species that are characteristic for relatively nutrient—rich habitats by features that enable them to restrict their nutrient losses. We chose Festuca rubra and Arrhenatherum elatius as species to test this hypothesis. In a long—term field experiment in a hayfield it was observed that Festuca was very common and Arrhenatherum was almost absent in the unfertilized plots, whereas after fertilization Festuca disappeared and Arrhenatherum increased strongly. It was hypothesized that differences in nutrient and carbon losses resulting from mowing were responsible for the different success of the two species in the unfertilized plots. A pot experiment was carried out in a greenhouse with clipped and unclipped and with unfertilized and fertilized treatments in a factorial design with four series. In the fertilized treatments Arrhenatherum replaced Festuica; its heavier seeds resulted in more rapid early growth and its more erect architecture enabled it to overtop Festuca after some time. In the two unfertilized treatments Festuca replaced Arrhenatherum, but much more rapidly in the clipped pots than in the unclipped ones. Losses of nitrogen due to clipping were much greater in Arrhenatherum than in Festuca because of the strongly increased allocation of nitrogen to aboveground parts in Arrhenatherum in response to clipping. It was concluded that differences in nitrogen loss resulting from clipping have an important impact upon the competitive balance between plant species under nutrient—poor conditions.

Plant spinescence in arid southern Africa: does moisture mediate selection by mammals?

The prediction that spinescence in plants increases with aridity, soil fertility and mammalian herbivory was examined at regional and local scales in southern Africa. Spinescence tended to increase with aridity. Within arid areas, vegetation of moist, nutrient-rich habitats was more spinescent than that of the surrounding dry plains. Spinescence in plants of drainage lines and pans in arid southern Africa occurs in a wide range of genera and appears to have been selected by the effect of large mammals which concentrate on these moist patches. It is concluded that spinescence may be selected by breakage as well as herbivory, and that in arid areas moisture may be important in mediating mammalian selection of spinescence.

Diurnal routine O 2 consumption at different O 2 concentrations by Colossoma macropomum and Colossoma brachypomum (Teleostei: Serrasalmidae)

1. 1. Colossoma macropomum and C. brychypomum were found to reveal a bimodal diurnal pattern of V o 2 which persisted at all levels of O 2 concentration. V o 2 increased around dawn and dusk. This seemed to be a response to the light on/off stimuli rather than being endogenous. 2. 2. When there is a diurnal rhythm with a morning minimum in the O 2 concentration, the maximum V o 2 of C. macropomum occurred at dawn, while that of C. brachypomum occurred at dusk. 3. 3. V o 2 of pond fish was by the factor 0.6−0.8 lower than in fish from natural water bodies. 4. 4. The experimental results suggest that these two species, which have somewhat similar diets, occupy separate temporal niches in the nutrient-rich habitats of the Amazon floodplains.

SPIROGYRA SPECIES AND ACCOMPANYING ALGAE FROM DUNE WATERS IN THE NETHERLANDS

SUMMARY A survey is given of the occurrence of filamentous algae from dune pools situated in the calcium carbonate-rich dune area at Oostvoorne and Egmond-Castricum as well as the calcium carbonatepoor Wadden area at Terschelling. Spirogyra and Oedogonium were important and often dominant components at these sites and were represented by at least 35 and 20 species respectively. Accompanying species belonged to Zygnema, Mougeotia, Bulbochaete, Microspora and Tribonema. In several pools Chara was dominant. Mass occurrence of filamentous algae was frequently observed. The seasonal dynamics of the components in floating mats were described. Periodicity phenomena of components and individual Spirogyra and Oedogonium species were studied. A peak in spore production of Spirogyra was situated in the second half of May and the first half of June. Based on physico-chemical data, the water of most of the investigated pools can be characterized as mesotrophic freshwater with a moderate or high amount of calcium and bicarbonate. Water quality differences between Terschelling (low alkalinity) and Egmond-Castricum/Oostvoorne (high alkalinity) were reflected in their species composition. Most of the species from the dune pools are also known from other more nutrient-rich habitats in The Netherlands, but there are differences in quantities and combinations of species.

Species Competitive Ability and Position Along a Natural Stress/Disturbance Gradient

We tested the prediction that plant species that grow in undisturbed, nutrient—rich habitats tend to have higher competitive abilities than those found in disturbed or nutrient—poor habitats. The distributions of seven species (Eriocaulon septangulare, Rhynchospora fusca, Hypericum ellipticum, Juncus pelocarpus, Lysimachia terrestris, Dulichium arundinaceum, and Drosera intermedia) were measured along a gradient of exposure to wave action on the shore of Axe Lake, Ontario. The exposure gradient incorporates disturbance, through the removal of plant biomass, and stress, through the creation of a gradient in sediment organic content, nutrient concentrations, and fine particle sizes. Species distributions on the exposure gradient were quantified by determining the mean sediment organic content of the quadrats containing each species. Competitive abilities were measured as relative increase in dry mass per plant, in a field experiment in which species were grown together in all pairwise combinations (N = 10 replicates). Species had significantly heterogeneous competitive abilities (P < .01). Species found on exposed, nutrient—poor shores (e.g., E. septangulare) had low competitive abilities, while those growing on sheltered, nutrient—rich shores (e.g., D. arundinaceum) had high competitive abilities. Competitive ability was significantly correlated with mean position on the exposure gradient.

The growth of Drosera intermedia in nutrient-rich habitats: the role of insectivory and interspecific competition

This study used field experiments to test whether insectivory confers any benefit on Drosera intermedia Hayne growing on lakeshores characterized by high sediment organic content and dense vegetation. Ramets were grown in pots containing organic shoreline sediment for one summer at Axe Lake, Ontario. Insect availability was controlled by nylon mesh. Biomass accumulated by D. intermedia was not affected by insect availability. In a second experiment, when D. intermedia was grown with ramets of Lysimachia terrestris (L.) BSP., the exclusion of insects significantly reduced the biomass accumulated by D. intermedia. These results suggest that insectivory may be important in reducing the effect of interspecific competition on D. intermedia growing in nutrient-rich habitats.

An ecological validation of a taxonomic distinction: the ecology of Acanthocyclops vernalis and A. robustus (Crustacea: Copepoda)

Long-standing taxonomic problems involving the vernalis complex of freshwater cyclopoid copepods of the genus Acanthocyclops have now been largely resolved, at least in Europe. Two species, A. vernalis and A. robustus, are recognizable on unambiguous morphological criteria, but each shows variation of a simular kind. Ecological data confirm this distinction. Ecological preferences are themselves reflected by the distribution patterns displayed in a restricted, but not small, area encompassing a diversity of environments. A. vernalis is eurytopic but displays a preference for acidic, calcium-poor waters, low in total ions, and is exclusively benthic. By contrast A. robustus does not colonize strongly acidic waters (min. pH 6.42) and is restricted to alkaline, or weakly acidic, nutrient-rich habitats. In some situations it becomes pelagic. While A. vernalis extends throughout the area frequented by A. robustus, the latter fails to colonize large tracts of upland country for which A. vernalis shows a definite preference and where it is common and widespread.

Variability of pressure adaptation in deep sea bacteria

Isolations of pressure-adapted deep sea bacteria from depths of 1,400 to 5,100 m resulted in a variety of psychrophilic barotolerant and barophilic strains. Growth rates determined at different pressures indicated a gradual transition between the two types of pressure-adapted isolates. The presence of barotolerant bacteria in deep water, sustained by sinking particulate matter, causes the nonbarophilic response of natural populations, i.e., increased growth after decompression. With increasing pressure-adaptation in barophilic isolates the maximum growth rates at optimum pressures decrease. Thus, the observed general slow-down of microbial activity in the deep sea takes effect regardless of the common occurrence of psychrophilic and barophilic bacteria. The highest degree of barophilism was observed in isolates from nutrient-rich habitats such as intestinal tracts of deep sea animals or decaying carcasses. Detailed studies with an isolate, growing barophilically on a complex as well as a single-carbon-source medium, showed that (1) culturing at pressures lower than optimal for growth resulted in the formation of cell filaments, (2) growth was unaffected by repeated compression/decompression cycles and (3) no perceptible differences in the distribution of radiolabeled carbon from an amino acid mixture occurred in cells grown at, below and above the pressure optimal for growth.

The effect of potassium on growth of Carex species from swamp habitats varying from oligotrophic to eutrophic and comparison of physiological reactions of Carex species to P stress and K stress

In a growth experiment at potassium levels varying between 0.001 mM and 3.0 mM potassium, relative growth rate (RGR) and other growth parameters were determined in Carex species: C. rostrata Stokes, C. limosa L., C. lasiocarpa Ehrh., C. diandra Schrank and C. acutiformis Ehrh., listed in order of increasing nutrient availability of their habitats. Carex species of nutrient poor sites did grow faster at low potassium concentration than species from nutrient rich habitats. The RGR of C. limosa was not affected by the K concentration, even at the lowest potassium concentration (0.001) mM) used. At high potassium availability Carex species from nutrient‐rich sites responded with greatly increased RGR, whereas the Carex from nutrient‐poor sites absorbed potassium in excess of immediate growth requirements: luxury consumption. A comparison is made of the physiology of the Carex species as affected by stress and abundance of phosphate and potassium.

A COMPARISON OF THE REACTION TO A LOCALIZED SUPPLY OF PHOSPHATE IN PLANTAGO MAJOR, PLANTAGO LANCEOLATA AND PLANTAGO MEDIA*

SUMMARY Plantago major ssp. major, P. lanceolata and P. media have been compared with respect to their ability to adapt themselves to a localized availability of phosphate. The growth and phosphorus content of plants of the three species were followed during 4–5 weeks in a divided-roots-experiment where at the start of the experiment about 25% of the root mass received a complete nutrient solution and the remaining roots a solution without phosphate. The dry matter production of the treated plant is slightly depressed in P. major but unaffected in P. lanceolata and P. media. In all species the P-supplied roots of the treated plant show a stimulated relative growth rate and a stimulated rate of P-uptake. These stimulations are smallest in P. major which also shows the lowest rate of P-uptake in control plants uniformly supplied with a complete nutrient solution. These facts point to the need for a more uniform supply of phosphate to the root system of P. major relative to P. lanceolata and P. media, correlating well with the nutrient-rich habitat of P. major. The stimulated rate of uptake of phosphate after localization of the P-supply appears to be correlated with (a) lower P-concentration in the shoot, (b) lower P-concentration in the phloem and (c) lower concentration of inorganic phosphate in the root.