Differences in nitrate uptake of species from habitats rich or poor in nitrogen when grown at low nitrate concentrations,using a new growth technique

Summary A method is described for culturing plants at extremely low nutrient concentrations. Using a Braun infusion pump, a fixed amount of nitrate or ammonium was supplied continuously to plants growing in a culture vessel at a rate limiting the uptake of the plants. At a very low nitrogen concentration an equilibrium was established where uptake rate of the plants is equal to the rate of supply by the infusion pump. The nitrogen concentrations reached appeared to be in the order of 1 μM. The method compared the nitrate uptake byHypochaeris radicata L.ssp.radicata, H. radicata ssp.ericetorum Van Soest andUrtica dioica L. and ammonium uptake byH. radicata ssp.radicata andH. radicata ssp.ericetorum. Plants were cultivated in monocultures or in mixed cultures (two species per culture vessel). For the mixed cultures competition for nitrate (or ammonium) between the species was maintained for long periods. The capacities of the uptake systems of two subspecies ofH. radicata from places different in nitrogen supply and pH were adapted equally well to both low nitrate and low ammonium concentrations. Apparently factors other than nitrogen uptake play a part in the distribution of the subspecies. The capacity of the uptake system ofU. dioica, a nitrophilous species, was lower than that ofH. radicata ssp.radicata, a species from places poorer in nitrogen. This difference is related to the different distribution of the two species in the field. The present results are compared with those of previous experiments where K_m and V_max were measured and the significance of both parameters is discussed.     

Two ecologically distinct subspecies ofHypochaeris radicatal L.

Summary The present paper is part of a series of papers comparing two ecologically distinct subspecies ofHypochaeris radicata L.Hypochaeris radicata ssp.radicata grows in more fertile soils thanH. radicata ssp.ericetorum.The dry-weight yield of plants grown from seeds was measured after a 25 days culture period on varying levels of nitrate. Roots and shoots were analyzed for total organic nitrogen and free nitrate. Dry-weight yield showed an almost identical response over the whole range of nitrate concentrations used. The chemical analysis did not reveal differences between the subspecies that could explain the distribution in the field. In a second experiment the growth rate of the two subspecies was measured under optimal nitrate supply during a two month period. Both subspecies exhibited initially the same relative growth rate but one month after sowing the growth rate of both subspecies declined, with a sharper decline in ssp.ericetorum resulting in an 82 per cent difference in dry-weight between both subspecies two months after sowing. Some pronounced formative differences became evident. Shoot to root ratio of ssp.ericetorum showed little response to increasing nitrate concentrations whereas ssp.radicata was clearly responsive in this respect.The contribution of the tap root in total plant dry-weight was relatively higher in ssp.Ericetorum. The decline in growth rate and the formative differences can explain the absence of ssp.ericetorum from nutrient rich soils. when grown on ammonium ssp.radicata had a slightly but not significantly higher yield than ssp.ericetorum. The difference was even greater at low pH. It is concluded that both subspecies are adapted to ammonium nutrition at pH 4.5 as well as at pH 6 and that the absence of ssp.radicata from acidic soils cannot be explained by the low pH. The possibility that both subspecies have different abilities to reduce their growth when nitrate resources become limiting, and yet remain capable for further growth and reproduction is discussed.Grassland species research group, publ. no.16.     

Two ecologically distinct subspecies ofHypochaeris radicata L.

Summary Uptake and assimilation of nitrate by two subspecies ofHypochaeris radicata L. were investigated under laboratory conditions as well as in the field.H. radicata ssp.radicata grows on relatively nitrogen-richer soils thanH. radicata ssp.ericetorum. Attempts were made to relate nitrate uptake and nitrate assimilation in the two subspecies to their different distribution in the field.No differences between the two subspecies with respect to nitrate uptake and nitrate assimilation were observed under laboratory conditions. In plants from the field intact tissue nitrate reductase was higher in ssp.radicata than in ssp.ericetorum. The nitrate reductase activity of both subspecies responded positively to nitrate addition.The significance of nitrate uptake capacity and the level of nitrate reductase for the distribution of plants in the field is here discussed.Grassland species research group, publ. no.15.     

Heterotrophic nitrification in a health soil demonstrated by anin situ method

Summary Nitrate reductase activity (NRA) in the leaves of two subspecies ofHypochaeris radicata was taken as a parameter for nitrate production in the soilin situ. Ammonium addition to the soil ofH. radicata ssp.radicata (soil pH 6.2) resulted in an increase of NRA, thus indicating nitrate formation by chemolithotrophic nitrifiers after a certain time-lag. Addition of ammonium to the soil ofH. radicata ssp.ericetorum (soil pH 4.3) dit not affect NRA in the leaves. Tests based on the MPN method failed to demonstrate the occurrence of chemolithotrophic nitrifiers in this soil. However, the addition of peptone led to an increase of NRA within seven days, which indicates the presence of heterotrophic nitrifying organisms. The results obtainedin situ were confirmed in a laboratory experiment, where soil samples were incubated in the presence and absence of (NH₄)₂SO₄ or peptone. The addition of ammonium led to a decrease in the production of nitrate to zero as compared with the control in the acid soil of ssp.ericetorum, whereas the addition of peptone resulted in nitrate levels amounting to about twice the control value. In the soil of ssp.radicata nitrate formation showed a rapid increase, compared with the control, after the addition of ammonium as well as after the addition of peptone.Grassland species research group, publication no27     

Efficiency of Root Respiration in Relation to Growth Rate, Morphology and Soil Composition

Root growth respiration and root maintenance respiration rate of the following species were determined: Hypochaeris radicata L. ssp. radicata L., H. radicata ssp. ericetorum Van Soest, Plantago lanceolata L., P. major L. ssp. major, P. major ssp. pleiosperma Pilgcr, P. maritime L., Senecio viscosus L., S. vulgaris L. and Urtica dioica L. A high root growth respiration (i.e. the amount of oxygen consumed for synthesis of a given weight of root material) implied a high maintenance respiration rate (i.e. the amount of oxygen consumed per unit of time and dry weight, but not connected with growth). High values of both components reflect a low efficiency of root respiratory processes. The efficiency of root respiration, as determined by the values for root growth respiration and root maintenance respiration rate could not be demonstrated to be of advantage in adaptation to soil conditions, as e.g. nitrogen content, moisture content and pH. It is concluded that (he degree of ‘wasteful utilization of sugars’ in roots, i.e. such consumption of sugars as cannot be related to structural growth, storage of carbohydrates or maintenance processes, depends on imbalance of transport of sugars from the shoot to the roots with utilization of sugars for synthesis of root material. The results are discussed in relation to Brouwer's explanation for the equilibrium between the growth of shoots and of roots. Root growth rate in the present species appears limited by a factor produced in the shoot under light conditions, and which factor is distinct from carbohydrates. The evidence presented shows that relatively inefficient root respiration does not imply a low growth rate. In regulation of plant growth the growth rate itself and also the shoot to-root ratio may be more important than the regulation of the efficiency of energy metabolism.     

Two ecologically distinct subspecies ofHypochaeris radicata L.

Summary Two subspecies ofHypochaeris radicata were compared with respect to differences in drought tolerance. The soil water content of the sites ofH. radicata ssp. ericetorum Van Soest was always lower than that ofH. radicata L. ssp.radicata throughout a great part of the growing season. Two water culture experiments were conducted at different light intensities. Water stress was induced by addition of NaCl to the culture solution. Both subspecies accumulated free proline andmyo-inositol during water stress. The results are compared with those of field observations. In all experiments with stress application ssp.radicata showed heavier wilting symptoms than ssp.ericetorum, concomittantly with a lower osmotic potential of the cell sap, a higher percentage of dry-weight and irreversible desiccation of older leaves in some experiments after stress application. The observed effects are attributed to the higher transpiration rate maintained by ssp.radicata during stress. Free proline accumulation depended on the severity of the internal stress rather than on the applied level of external stress. At low light intensity the stress resulted in a significantly higher proline accumulation in ssp.ericetorum than in ssp.radicata whereas at high light intensity this was the reverse. No differences inmyo-inositol accumulation were observed in the water culture experiments. Since ssp.ericetorum occurs in a nitrogen poor environment, the effect of nitrogen deprivation on accumulation of free proline andmyo-inositol was investigated. Both subspecies tended to accumulate less proline under such conditions especially ssp.radicata. Accumulation ofmyo-inositol was not favoured by nitrogen deprivation in the water culture experiments. Neither of the subspecies accumulated proline during the sampling period in the field presumably as a result of the wet summer. Leaves of whole plants collected in the field and subsequently subjected to water deprivation showed a high capacity to accumulate free proline. The level ofmyo-inositol in the field was higher in ssp.ericetorum than in either ssp.radicata or control plants in the water culture experiments. When the cytoplasmic volume is estimated as 10% of the total cell volume, free proline andmyo-inositol account for 44–69% of the osmotic potential. It is concluded that ssp.ericetorum is better adapted to the drier environment by its higher capacity to accumulate proline and reduce transpiration during stress. Grassland species research group, publication no41.     

Lipid Composition of the Roots of Plantago Species: Response to Alteration of the Level of Mineral Nutrition and Ecological Significance

In a study of the adaptation of Plantago species to their specific environment the lipid composition of the roots of several species: Plantago major L. ssp. major, Plantago major L. ssp. pleiosperma Pilger, Plantago lanceolata L., Plantago media L., Plantago maritima L., Plantago coronopus L. was studied as well as the effect of the nutritional regime. Upon exposure to low-salt conditions Plantago major L. ssp. major L. and Plantago maritima L. maintained the level of free sterols in the roots, despite a depressed level of total sterols, and the root lipids were more saturated than under high-salt conditions. Both factors may reduce nutrient leakage from the roots to the low-salt condition. Upon exposure to low-salt conditions, all Plantago species showed a decreased level of galactolipid (exception: Plantago coronopus) and a decreased level of sitosterol (exception: Plantago maritima); the latter being compensated by an elevated level of cholesterol + tocopherol in Plantago major ssp. pleiosperma, Plantago lanceolata and Plantago media. Plantago coronopus was the only species which under low-salt conditions showed an increased level of free sterols, among which cholesterol was the most important; thus indicating a high degree of regulation of membrane permeability under alternating nutritional conditions. The level of sulfolipid was kept constant in all Plantago species, with the highest level observed in Plantago maritima. The role which various lipids may play in maintenance of membrane integrity under alternating nutritional conditions is discussed.     

The effect of nitrate concentration in a flowing solution system on growth and nitrate uptake of twoPlantago species

Summary Juvenile plants ofPlantago lanceolata andP. major ssp.major were grown in a flowing solution system at 7.5 mM or 9.5 M NO₃. The parameters investigated were: RGR, shoot weight percentage, leaf length, length of main root axis, shoot concentrations of major ions and organic N, and the specific uptake rate for NO₃. At 9.5 M NO₃ growth ofP. major was not hampered, whereas shoot growth and leaf length ofP. lanceolata were reduced. The NO₃ concentration ofP. lanceolata decreased more than that ofP. major. The different performances of the species at 9.5 M NO₃ were associated with different specific uptake rates. In both treatments the root system ofP. major was shorter than that ofP. lanceolata. P. lanceolata accumulated more NO₃ in the leaves. The performance of thePlantago species is discussed in relation to the availability of nutrients in their habitats.Grassland Species Research Group. Publication no. 37.     

Ammonium and nitrate nutrition inPlantago lanceolata L. andPlantago major L. ssp.major

With the aims (1) to test whether the different natural occurrence of twoPlantago species in grasslands is explained by a different preference of the species for nitrate or ammonium; (2) to test whether the different occurrence is explained by differences in the flexibility of the species towards changes in the nitrogen form; (3) to find suitable parameters as a tool to study ammonium and nitrate utilization of these species at the natural sites in grasslands, plants ofPlantago lanceolata andP. major ssp.major were grown with an abundant supply of nitrate, ammonium or nitrate+ammonium as the nitrogen source (0.5 mM). The combination of ammonium and nitrate gave a slightly higher final plant weight than nitrate or ammonium alone. Ammonium lowered the shoot to root ratio inP. major. Uptake of nitrate per g root was faster than that of ammonium, but from the mixed source ammonium and nitrate were taken up at the same rate. In vivo nitrate reductase activity (NRA) was present in both shoot and roots of plants receiving nitrate. When ammonium was applied in addition to nitrate, NRA of the shoot was not affected, but in the root the activity decreased. Thus, a larger proportion of total NRA was present in the shoot than with nitrate alone. In vitro glutamate dehydrogenase activity (GDHA) was enhanced by ammonium, both in the shoot and in the roots.In vitro glutamine synthetase activity (GSA) was highest in roots of plants receiving ammonium. Both GDHA and GSA were higher inP. lanceolata than inP. major. The concentration of ammonium in the roots increased with ammonium, but it did not accumulate in the shoot. The concentration of amino acids in the roots was also enhanced by ammonium. Protein concentration was not affected by the form of nitrogen. Nitrate accumulated in both the shoot and the roots of nitrate grown plants. When nitrate in the solution was replaced by ammonium, the nitrate concentration in the roots decreased rapidly. It also decreased in the shoot, but slowly. It is concluded that the nitrogen metabolism of the twoPlantago species shows a similar response to a change in the form of the nitrogen source, and that differences in natural occurrence of these species are not related to a differential adaptation of nitrogen metabolism towards the nitrogen form. Suitable parameters for establishing the nitrogen source in the field are thein vivo NRA, nitrate concentrations in tissues and xylem exudate, and the fraction of total reduced nitrogen in the roots that is in the soluble form, and to some extent thein vitro GDHA and GSA of the roots. Grassland Species Research Group. Publ. no 118.     

Nitrate production in the rhizosphere of Plantago species

Summary The production of nitrate in an old established dune grassland soil and its uptake by plants was studied by comparing amounts of mineral nitrogen and numbers of nitrifying bacteria in the rhizosphere on the one hand, and on the other accumulated nitrate and levels of nitrate reductase (NaR) of individual plants of three Plantago species,i. e., P. major, P. lanceolata andP. coronopus. For these three Plantago species andP. media basal levels of NaR in the absence of nitrate were determined in plants grown in culture solutions. The basal NaR levels ofP. major andP. media (species occurring on nutrient-rich soils) were significantly higher than those ofP. lanceolata andP. coronopus (species found on nutrient-poor soils). NaR activity increased in the presence of nitrate and was suppressed by ammonium.From the numbers of nitrifying bacteria in the rhizosphere and NaR activity in the leaves it was concluded that nitrate was produced in the root environments of the three Plantago species and that the compound was taken up by the plants. NaR activities and numbers of nitrifying bacteria were higher for individuals ofP. major than for those ofP. lanceolata andP. coronopus. No correlation was found between the ammonium levels and the numbers of nitrifying bacteria in the soil, and no indications of inhibition of nitrifying bacteria in the rhizosphere were obtained. For individuals ofP. lanceolata a correlation was found between the numbers of nitrifying bacteria in the soil and NaR activity in the leaves. The results are discussed in relation to the ecological habitats of the three species.Grassland Species Research Group Publication No.38.     

Variations in pollen proportions of Plantago lanceolata and P. major/media at a Neolithic lake dwelling,Lake Chalain,France

Detailed pollen analytical investigations at a Neolithic lake dwelling site on Lake Chalain, Jura, France, show very characteristic variation in the Plantago lanceolata and P. major/media pollen curves in the period during which settlements are recorded (3030–2630 cal. B.C.). At first, P. lanceolata is the more important taxon but P. major/media representation gradually rises, to become the more important taxon in the uppermost settlement phase. After considering the present day ecology and phytosociology of the Plantago species in question, i.e. P. lanceolata, P. major and P. media, and the available archaeozoological and archaeological information, it is suggested that the changes in the representation of these two pollen taxa are the result of a change in the farming economy, at ca. 2800 cal. B.C., which involved a substantial rise in the numbers of domesticated grazing animals and more intensive land use.     

Anti-mitotic and anti-genotoxic effects of Plantago lanceolata aqueous extract on Allium cepa root tip meristem cells

Plantago is the most important genus of Plantaginaceae family and is used in traditional medicine around the world for different purposes. Plantago coronopus L., Plantago major L., Plantago media L. and Plantago lanceolata L. are most commonly used species of Plantago in traditional medicine in Turkey. The main goal of this study was to investigate the eventual anti-mitotic and anti-genotoxic effects of P. lanceolata L. leaf aqueous extracts (15 g/L and 30 g/L) on Allium cepa L. root tip meristem cells which were treated with 0.7% hydrogen peroxide. For this purpose, two different experiments were performed under the same conditions. In the first experiment, Allium cepa onion bulbs were treated with 0.7% H₂O₂ for 1 h. After the H₂O₂ treatment, the onion bulbs were treated with two different concentrations (15 g/L and 30 g/L) of P. lanceolata extracts for 24 h. In the second experiment, A. cepa onion bulbs were treated with two different extract concentrations (15 g/L and 30 g/L) for 24 h and then with 0.7% H₂O₂ for 1 h. The test concentrations were determined according to doses which are recommended in alternative medicinal usage by people. As positive and negative control 0.7% H₂O₂ and tap water was used, respectively. As a result, it was determined that aqueous extracts reduced mitotic index and chromosome aberrations in treatment groups in comparison with controls. These results showed that P. lanceolata aqueous extracts have anti-mitotic and anti-genotoxic effects.     

Efflux of Potassium from Wheat Roots Induced by Changes in the Water Potential of the Root Medium

Growth of Plantago major L., ssp. major L. and ssp. pleiosperma Pilger and P. maritime L. was followed at two levels of mineral nutrition (low-salt and high-salt). In addition the response of transfer of plants from low-salt conditions to high-salt conditions and vice versa was studied. Growth of the studied Plantago species was strongly stimulated by high-salt conditions. The Ca²⁺- and Mg²⁺-stimulated ATPase activity of microsomal preparations of the roots was also studied. In P. major ssp. major and P. maritime a major pH optimum was observed at pH 6.5, and in addition a second pH optimum was found at pH 8.0. High-salt plants of these two species were characterized by biphasic stimulation curves for Ca²⁺ and Mg²⁺, whereas P. major ssp. pleiosperma showed a monophasic pattern. The ATPase activity per g dry weight of P. major and P. maritima was highest in high-salt plants. The species investigated here are adapted to relatively nutrient-rich conditions, and the properties of ATPases (K_m, K_max, protein content) and the growth responses are discussed in relation to this ecological property.     

Cyanide-Resistant Root Respiration and Tap Root Formation in Two Subspecies of Hypochaeris radicata

Root respiration of the tap root forming species Hypochaeris radicata L. was measured during tap root formation. A comparison was made of two subspecies: H. radicata L. ssp. radicata L., a subspecies from relatively rich soils, and H. radicata L. ssp. ericetorum Van Soest, a subspecies from poor acidic soils. Root respiration was high and to a large extent inhibited by hydroxamic acid (SHAM) before the start of the tap root formation, indicating a high activity of an alternative non-phosphorylative electron transport chain. The rate of root respiration was much lower and less sensitive to SHAM when a considerable tap root was present. However, root respiration was also cyanide-resistant when a tap root was present, indicating that the alternative pathway was still present. A decreased rate of root respiration coincided with an increase of the content of storage carbohydrates, mainly in the tap root. The level of reducing sugars was constant throughout the experimental period, and it was concluded that the activity of the alternative oxidative pathway was significant in oxidation of sugars that could not be utilized for purposes like energy production, the formation of intermediates for growth or for storage. Root respiration decreased after the formation of a tap root. This decrease could neither be attributed to a gradual disappearance of the alternative chain, nor to a decreased level of reducing sugars. No differences in respiratory metabolism between the two subspecies have been observed, suggesting that a high activity of the alternative oxidative pathway is not significant in adaptation of the present two subspecies to relatively nutrient-rich or poor soils.     

Comparison of Plantago Species from Nutrient-rich and Nutrient-poor Conditions: Growth Response, ATPases and Lipids of the Roots, as Affected by the Level of Mineral Nutrition

Two groups of Plantago species, one of relatively nutrient-rich habitats (Plantago major L., P. major L. ssp. pleiosperma Pilger and P. martrima L.) and the other of relatively nutrient poor habitats (P. lanceolata L., P. media L. and P. coronopus L.), were compared with respect to the response of the plants to alterations of the level of mineral nutrition. The comparison deals with growth response and root cell membrane functions (Ca²⁺ and Mg²⁺ stimulated ATPases and lipids). As far as these parameters are concerned species from relatively nutrientpoor habitats are not much affected by bringing the plants to high-salt conditions, while the reverse was true for species from relatively nutrient-rich habitats when transferred to low salt medium.     

Establishment of Plantago lanceolata L. and Plantago major L. among grass

Summary Establishment of Plantago lanceolata and P. major ssp major among grass was studied in a field experiment in which survival and selection on date of seedling emergence and plant size was investigated in relation to the vegetation structure. P. major — in contrast to P. lanceolata — was not able to establish itself in grass because of its lower competitive ability caused by later germination, smaller seedling size, and shorter leaves. In both species there was selection for early germination. For P. lanceolata a significant correlation was found between the strength of selection and the light climate, determined by the structure of the grass sward. Plants that germinated early were at an advantage because they were larger, especially the leaves, when compared with plants that germinated late. It seems likely that selection was mainly by competition for light. Contrary to expectation P. major-seedlings had a higher shade tolerance than those of P. lanceolata. The performance of both species is discussed in relation to their different life strategies.Grassland species research group publication no 142     

Genetic structure and differentiation of Plantago major reveals a pair of sympatric sister species

Seeds of the widespread weed Plantago major were collected from 10 European countries, as well as Trinidad and North America. The seed collections were from populations of two taxa which are ecologically rather than geographically separated and formally recognized as the subspecies Plantago major ssp. major and P.m. ssp. intermedia (also called P.m. ssp. pleiosperma). Eight polymorphic allozyme loci and 73 random-primed DNA fragments were scored, as well as 11 morphological characters. Complete concordance between morphological traits and genetic data provides evidence that these two taxa, although very similar, are distinct species. They are both widespread, they are broadly sympatric and capable of interbreeding. However, slight morphological and ecological differences coincide with genetic clustering of populations from widely separated locations. In addition, P. major and P. intermedia differ in their population structure: P. intermedia has greater genetic diversity among populations and less genetic variance within populations than P. major. We suggest that differences between the two species in their levels of selfing may explain the distinctive genetic structure of each species. We hypothesize a link between selfing rate and lifespan of the two taxa. P. major is characterized by lower genetic variation among populations, a higher rate of outcrossing, longer lifespan and production of fewer seeds per seed capsule. P. intermedia is more highly structured with much differentiation among populations, a higher rate of inbreeding and it often grows as an annual.     

Host plant species affects the quality of the generalist Trichoplusia ni as a host for the polyembryonic parasitoid Copidosoma floridanum

Diet of herbivorous insects can influence both the herbivores and their natural enemies. We examined the direct and indirect effects of diet on the interactions between the polyphagous herbivore Trichoplusia ni Hübner (Lepidoptera: Noctuidae) and its polyembryonic parasitoid Copidosoma floridanum Ashmead (Hymenoptera: Encyrtidae). To determine how host plant species and host plant iridoid glycoside content affect host caterpillars and their parasitoids, parasitized and unparasitized T. ni were given leaves of either Plantago lanceolata L., which contains the iridoid glycosides aucubin and catalpol, Plantago major L. (Plantaginaceae), which contains only aucubin, or Taraxacum officinale F.H. Wigg (Asteraceae), which contains neither. Survival of unparasitized T. ni was much lower when fed P. major compared with the other two host plants, whereas pupae were smallest when fed T. officinale and developed most slowly when fed P. lanceolata as larvae. Neither aucubin nor catalpol were detected in intact Plantago‐fed T. ni larvae or their hemolymph, and only trace amounts of aucubin were detected in frass, suggesting that these compounds are mostly metabolized in the midgut and are not encountered by the parasitoid. Copidosoma floridanum clutch size was almost doubled when reared from P. lanceolata‐fed T. ni compared with T. officinale‐fed larvae and tripled compared with P. major‐fed larvae, although the percent of parasitoids surviving to adulthood was uniformly high regardless of host diet. The observed variation in C. floridanum fitness among host diets is likely mediated by the effect of the diets on host quality, which in turn may be influenced more by other factors in the host plants than their iridoid glycoside profiles. Interactions between plant metabolites, generalist herbivores like T. ni, and their parasitoids may be predominantly indirect.     

Isolation of polymorphic microsatellite loci in Plantago major and P. intermedia

Plantago major and P. intermedia are two closely related inbreeding species. The isolation of polymorphic codominant microsatellite markers will provide valuable tools to investigate the reproductive isolation and the evolution of the two species. The isolation of microsatellite loci was achieved using a membrane enrichment method. Primers were designed to microsatellite flanking sequences and were analysed using fluorescent labels. Results indicated that nine out of the 10 loci amplified in both species, and that all the loci were polymorphic. The amplification of the loci was tested in a variety of Plantago species and was shown to be limited.     

Genetic differentiation in Plantago major L. in growth and P uptake under conditions of P limitation

To study possible adaptive mechanisms inbred lines from three populations of Plantago major from sites that were found to differ in P availability were compared. In a pot experiment the growth and P uptake either in the presence or absence of Glomus fasciculatum was determined. Under these P-limited conditions it was shown by partitioning the relative growth rate (RGR, in mg g^-1 day^-1) in the components root weight ratio (RWR, in g_roots g_plant ^-1), specific P uptake rate (SPUR, in mol P g_roots ^-1 day^-1), and P-efficiency (PEFF, in mg mol P^-1), that the increase in RGR of mycorrhizal infected plants was related to an increase in SPUR, and a decrease in RWR and PEFF. P. major ssp. major had a lower RGR (related to a lower PEFF and SPUR) and a higher RWR than P. major ssp. pleiosperma. In a second experiment three inbred lines were compared upon P depletion in a nutrient solution. The P. major ssp. major line had a lower RGR and higher RWR, and a higher accumulation of P in the roots than the P. major ssp. pleiosperma lines under optimal growing conditions. There were no differences among the inbred lines in the relative contribution of inorganic P to the total P concentration in the shoot. The results are discussed in relation to the characteristics of the habitats of the investigated P. major populations.