Dauciform Roots Research Articles

Carex parva and Carex scabrirostris adopt diverse response strategies to adapt to low-light conditions.

In recent years, the visible light intensity of lawns has significantly decreased due to obstructions caused by urban shading objects. Carex has a competitive advantage over other turfgrass in low-light conditions and extensive management. Therefore, exploring their survival strategy in low-light environments is of great significance. This study focuses on two species of Carex, Carex parva and Carex scabrirostris, and investigates their response to low-light conditions (150 μmol/m2/s) by simulating urban lawn conditions. Biomass allocation characteristics, leaf anatomical features, biochemical parameters, root morphology and photosynthetic parameters were measured. (a) Peroxidase activity, specific leaf area, and relative water content are key factors influencing the photosynthetic capacity of the two Carex species. (b) Under low-light conditions, photosynthetic parameters, leaf physiological indicators, and biomass allocation of the two Carex species were significantly affected (p<0.05). Both Carex species increased their investment in leaf biomass, maintained lateral root growth, and cleared reactive oxygen species to maintain their physiological balance. (c) In the simulated urban low-light environment, neither C. parva nor C. scabrirostris produced dauciform roots. In terms of response strategies, C. scabrirostris is a high-photosynthesis investing species with high productivity under low-light conditions, whereas C. parva exhibits minimal response, indicating a slow investment. C. scabrirostris has greater potential for application in low-light environments compared to C. parva. These results provide a theoretical basis for the cultivation and application of these two Carex species, as well as the expansion of turfgrass germplasm resources.

Not only phosphorus: dauciform roots can also influence aboveground biomass through root morphological traits and metal cation concentrations

BackgroundPhosphorus in the soil is mostly too insoluble for plants to utilize, resulting in inhibited aboveground biomass, while Carex can maintain their aboveground biomass through the presence of dauciform roots. However, dauciform roots lead to both morphological and physiological changes in the root system, making their primary mechanism unclear.MethodsA greenhouse experiment was conducted on three Carex species, in which Al-P, Ca-P, Fe-P, and K-P were employed as sole phosphorus sources. The plants were harvested and assessed after 30, 60 and 90 days.Results(1) The density of dauciform roots was positively correlated with root length and specific root length, positively influencing aboveground biomass at all three stages. (2) The aboveground phosphorus concentration showed a negative correlation with both dauciform root density and aboveground biomass in the first two stages, which became positive in the third stage. (3) Aboveground biomass correlated negatively with the aboveground Al concentration, and positively with Ca and Fe concentration (except Al-P). (4) Root morphological traits emerged as critical factors in dauciform roots’ promotion of aboveground biomass accumulation.ConclusionDespite the difference among insoluble phosphorus, dauciform roots have a contributing effect on aboveground growth status over time, mainly by regulating root morphological traits. This study contributes to our understanding of short-term variation in dauciform roots and their regulatory mechanisms that enhance Carex aboveground biomass under low available phosphorus conditions.

Recovering from trampling: The role of dauciform roots to functional traits response of Carex filispica in alpine meadow.

In the natural habitats of China, dauciform roots were only described in degraded alpine meadows. It was found that the presence of dauciform roots of Carex filispica was related to the advantage of multiple functional traits after trampling, reflecting short-term resistance. However, the long-term response of dauciform roots to trampling and the recovery of C. filispica with and without dauciform roots to trampling require further studies. In this study, different intensities of trampling (0, 50, 200 and 500 passages) were performed in an alpine meadow. One year later, individuals with and without dauciform roots were separated and their functional traits related to the economic spectrum of leaves and roots were measured as a reflection of recovery from trampling. The results showed that: (1) 1 year after trampling, the number of dauciform roots showed an increase with trampling intensity; (2) 1 year later, there was no significant difference in the response of economic spectrum traits among trampling intensities, or between plants with and without dauciform roots; (3) the number of dauciform roots was positively correlated with the leaf area of both individuals with and without dauciform roots, as well as with the biomass of those without dauciform roots; and (4) plants with more resource-conservative roots showed an advantage after trampling recovery: specifically, plants with dauciform roots showed such an advantage in the control group, which was lost with a leaning towards resource-acquisitive roots and an increased density of dauciform roots once trampled. In contrast, plants without dauciform roots showed a significant advantage of conservative roots only after trampling. In conclusion, the presence of dauciform roots is related to the plants' position on the root economic spectrum, thereby influencing the recovery of C. filispica from trampling. Carex filispica showed strong recovery from trampling after 1 year, which makes it an adequate choice for ecological restoration in alpine meadows. Dauciform roots showed a positive correlation with the aboveground growth of both plants with and without them, however, it requires a lab-controlled study to confirm whether there is indeed a positive effect on the growth of neighbouring plants.

Dauciform roots affect the position of the neighboring plants on the economic spectrum in degraded alpine meadows.

Special root structures that can dissolve insoluble phosphorus locked in soil are supposed to contribute not only to the growing status of themselves but also to the neighbouring plants. However, whether dauciform roots have any effect on the neighbouring plants and how does it respond to meadow degradation had not been studied. Alpine meadows with different degradation statuses were selected and the functional traits of Carex filispica and the co-occurring species Polygonum viviparum were measured to explore their response to degradation, as well as the response of Polygonum viviparum to the dauciform roots of Carex filispica. The results showed that 1) the number of dauciform roots decreased with the intensifying degradation, positively related to available phosphorus in the soil and negatively related to the aboveground phosphorus of Carex filispica. 2) Carex filispica and Polygonum viviparum are similar in specific leaf area and specific root area, yet different in the phosphorus content. The available phosphorus in the soil was negatively related to the aboveground phosphorus of Carex filispica and positively related to that of Polygonum viviparum. 3) When lightly degraded, the proportion of dauciform roots had positive effects on the aboveground resource-acquiring traits of Polygonum viviparum, which were no longer significant at heavy degradation. 4) Polygonum viviparum and Carex filispica without dauciform roots have similar performance: a decrease of belowground carbon with the increasing degradation, and a trend toward resource conservation with the increasing proportion of dauciform roots, which did not exist in Carex filispica with dauciform roots. Our study found that dauciform roots had a beneficial effect on the resource acquisition of their neighbouring plants. However, due to the uncontrollable nature of natural habitats, whether this effect is stable and strong enough to be performed in ecological restoration requires further lab-controlled studies.

Dauciform roots affect functional traits of Carex filispica under nitrogen and phosphorus fertilization in alpine meadow

Over recent decades, there has been a severe nitrogen-deposition in alpine meadows which often leads to phosphorus limitation of plant productivity. In these high-altitude localities, Cyperaceae have an increasing biomass while other functional groups decrease. Meanwhile, Cyperaceae are known to have the ability of producing dauciform roots, which are formed under phosphorus limitation, but in China, are only described in these high-altitude places. So, is the superiority of Cyperaceae and the formation of dauciform roots in high-altitude localities related to the accumulation of nitrogen? And is there a link between them? A Carex filispica dominated community in Baima Snow Mountain was selected and quantitative fertilization with four levels of nitrogen and three levels of phosphorus was performed. After 2 weeks, Carex filispica individuals with and without dauciform roots were separated and analyzed for their regular root properties, dauciform root properties, biomass and chemical traits of above- and belowground parts. The total cover of the community declined under phosphorus limitation with increasing nitrogen supply, while the relative cover difference of Carex filispica increased with increasing nitrogen supply and decreased with increasing phosphorus supply. Dauciform roots had a more significant response to nitrogen supply than to phosphorus supply and they were formed the most at a low supply of nitrogen. The biomass and root properties of individuals with dauciform roots were enhanced by nitrogen supply and inhibited by phosphorus supply, while those of individuals without dauciform roots were often enhanced by phosphorus supply. Individuals with and without dauciform roots showed two different mechanisms, and were limited by significantly different factors, which can explain the opposite performance of Cyperaceae after nitrogen and phosphorus supply in previous studies.

What role do dauciform roots play? Responses of Carex filispica to trampling in alpine meadows based on functional traits.

In China, dauciform roots were hardly studied and only reported in alpine meadows, where sedges showed a different tendency from other functional groups such as grasses and forbs with degradation. In addition, Carex species were proved to have shifting scaling relationships among LES (leaf economics spectrum) traits under disturbance. So, are these unique performances of sedges related to the presence of dauciform roots, and if so, how? An alpine meadow dominated by Carex filispica in Baima Snow Mountain was selected, and quantitative trampling was performed (0, 50, 200, and 500 passes). The cover and dauciform root properties of Carex filispica were measured, as well as the morphological, chemical traits and biomass of leaves and roots, their correlations and the differences between individuals with and without dauciform roots were analyzed. After the trampling, individuals with dauciform roots showed multiple resource-acquisitive traits: Larger, thicker leaves, more aboveground biomass, higher efficiency of nutrient utilization, and slenderer roots. Additionally, they had a tighter correlation among belowground biomass, morphological and chemical traits, as well as dauciform root properties and morphology of leaves, suggesting that their traits were more related than those without dauciform roots. The presence of dauciform roots in Carex filispica was related to advantages in multiple traits after trampling, which is consistent with and might be responsible for the unique performances of sedges.

Formation of dauciform roots by Japanese native Cyperaceae and their contribution to phosphorus dynamics in soils

Formation of dauciform roots by Japanese native Cyperaceae and their contribution to phosphorus dynamics in soils

A common-mesocosm experiment recreates sawgrass (Cladium jamaicense) phenotypes from Everglades marl prairies and peat marshes.

PremiseThe southern Florida Everglades landscape sustains wetlands of national and international importance. Sawgrass (Cladium jamaicense), the dominant macrophyte in the Everglades, has two phenotypes that vary in size and density between Everglades marl prairies and peat marshes. Marl prairies have recently been hypothesized to be a newly formed habitat developed after European colonization as a result of landscape‐scale hydrologic modifications, implying that sawgrass marl phenotypes developed in response to the marl habitat. We examined whether sawgrass wetland phenotypes are plastic responses to marl and peat soils.MethodsIn a common‐mesocosm experiment, seedlings from a single Everglades population were grown outdoors in field‐collected marl or peat soils. Growth and morphology of plants were measured over 14 mo, while soil and leaf total nitrogen, total phosphorus, total carbon, and plant biomass and biomass allocation were determined in a final harvest.ResultsSawgrass plant morphology diverged in marl vs. peat soils, and variations in morphology and density of mesocosm‐grown plants resembled differences seen in sawgrass plants growing in marl and peat habitats in Everglades wetlands. Additionally, sawgrass growing in marl made abundant dauciform roots, while dauciform root production of sawgrass growing in peat was correlated with soil total phosphorus.ConclusionsSawgrass from a single population grown in marl or peat soils can mimic sawgrass phenotypes associated with marl vs. peat habitats. This plasticity is consistent with the hypothesis that Everglades marl prairies are relatively new habitats that support plant communities assembled after European colonization and subsequent landscape modifications.

Restoration of wetlands: successes and failures on scalds comprising an iron oxide clogged layer with areas of acid sulfate soils

This paper reports on successes and failures experienced over nearly two decades while attempting to remediate degraded scalds typified by iron clogged layersinterspersed with patches of acid sulphate soil on the Eastern Dundas Tablelands in Victoria, Australia. In 2004 (Gardner et al. I Overview Plant Soil 267:51–59, 2004a, Plant Soil 267:85–95, b), it was suggested that redox processes similar to acid sulfate soil reactions were acting to exacerbate and amplify salinity effects in the landscape. Soil permeability to 1 m depth was measured and compared to that at 3-5 m depths. Additional analysis of soils in the discharge zone were undertaken (mineralogy, SEM, XRF, XRD) to seek evidence of typical acid sulfate reactions which had not been found in 2004. Water quality (EC, pH) and hydraulic pressures were measured in 2005- 2006, after shallow trenchs were dug across the site, and revegetation attempted with a range of native species. Following observations of improved growth at leaking peizometers, those with above ground water levels were drilled to allow water to escape. Assessment of revegetation outcomes were conducted in 2006 and 2016. Soil permeability was lower in the upper 1 m layer of the soil than at 3-5m depth, Clear evidence of acid sulfate soil mineralogy was found, however small scale variation was the norm. Clogging of soil macropores was observed, which could be manually cleared. Fracturing the soil to increase discharge either with explosives or excavation of both shallow and deep trenchs failed because the increased discharge was insufficient to overcome evaporation and salt concentration, and redox processes continued which would eventually clog the soil again. Success was achieved with leaking piezometers to 4.5 m depth, which allowed the groundwater to reach the surface without reducing ferric oxides. Rushes planted at the discharge point maintained an oxidised environment thereby halting the redox processes. Evaporation effects were prevented because the increased discharge occurred at a point. This combination allowed a range of native species to flourish and after 10 years, to spread beyond what we estimate the leaking piezometers would support. Evaporation causing concentration of salts is very important, but this is linked to the redox processes, which cause soil clogging and reduced permeability, and thus the evaporation and salt issue. Success was achieved when the reduced groundwater could access the surface in an oxidised environment, at a sufficient rate to prevent salt concentration by evaporation. The revegetation has expanded beyond what could be supported by the original discharge, suggesting that the plants are breaking the clogged soil layers and increasing discharge. The successful colonising species typically produce specialised structures such as dauciform and proteoid roots which are able to reduce and chelate iron oxides.

How functional is a trait? Phosphorus mobilization through root exudates differs little between Carex species with and without specialized dauciform roots.

Root structures secreting carboxylates and phosphatases are thought to enhance a plant's phosphorus (P) acquisition. But do closely related species with and without such structures really differ in root exudation, P mobilization, or ecological niche? We investigated this by comparing 23 European Carex species with and without 'dauciform roots' (DRs). Plants grown in pots with sand were screened for DR formation, phosphatase activities, carboxylate exudation, and utilization of various organic and inorganic P compounds. Ecological niches were compared using ecological indicator values and nutrient concentrations of plant shoots in natural habitats. Species of subgenus Carex formed DRs, while species of subgenus Vignea did not. Species with DRs had higher root diesterase activity than species without DRs, exuded more citrate but less oxalate and less total carboxylates, and allocated less biomass to roots. Species with and without DRs showed similar growth responses to different forms of P and different amounts of P supplied; their natural habitats do not differ in soil fertility or degree of P limitation. Despite some differences in physiological function, DRs did not influence the P acquisition and nutritional niche of European Carex species, suggesting that species with and without DRs do not exhibit distinct P-acquisition strategies.

Taxonomic and ecological patterns in root traits of Carex (Cyperaceae)

Plants can develop various root traits which may contribute to their nutrient acquisition. We investigated the occurrence of five root traits among species of genus Carex to determine their frequency, mutual associations and dependence on taxonomy (subgenus) or habitat. Root samples of 40 species were collected in their natural habitats within Russia and Belarus. They were examined microscopically to quantify the abundance of AM-fungal hyphae (H), arbuscules (A) and vesicles (V), dark septate endophyte (DSE), typical (long) root hairs (TRH), bulbous (shortened) root hairs (BRH) and dauciform roots (DR). The frequency of root traits decreased in the order TRH (100% of the species), DSE (80%), BRH (43%), A and V (25%) and DR (23%). Most species possessed 2–4 different traits, but up to five were possible, even on a single plant. Traits occurred largely independently of each other. DR were only found in subgenus Carex and mainly in grasslands. DSE and BRH were more abundant in subgenus Carex. BRH were most abundant in wetlands, TRH were shortest and thinnest in grasslands. A diversity of root traits exists in the genus Carex, with variation both among and within species. The abundance and size of traits exhibits some taxonomic and ecological patterns, which differ for each trait.

Regulation of dauciform root formation and root phosphatase activities of sedges (Carex) by nitrogen and phosphorus

Dauciform roots (DR) are formed by some Cyperaceae under phosphorus (P) deficiency. To advance our understanding of their physiological function, I ask: Is DR formation regulated by shoot P status or external P supply? How does it respond to nitrogen (N)? Do DR enhance root monoesterase, diesterase or phytase activities and ability to utilize organic P? Greenhouse experiments were carried out with two Carex species grown in sand with (1) different combinations of N and P supply, (2) local supply of N or P to root halves, and (3) different organic P forms. Carex flava produced DR in all treatments. The density of DR and phosphatase activities increased with N supply; they were regulated by shoot P status and external N (but not P) supply. All phosphatase activities increased with DR density. Carex muricata produced no DR and had lower diesterase activity than C. flava but both species grew equally well with diester-P. DR and phosphatase activities are regulated by both N and P supply. Similar growth responses to nutrients in both species suggest small costs and benefits of DR under experimental conditions but confirmation is needed for plants grown on natural soils.

Means for soil nutrient uptake in sedges with different ecological strategies

The prevalence of arbuscular mycorrhizas and nonsymbiotic modifications of absorbing organs (dauciform roots) has been studied in species of the genus Carex with competitive (C) and stress-tolerant (S) types of Grime-Ramenskii’s ecological strategies. The groups of C- and S-strategists do not differ in the ability to form mycorrhizas. Dauciform roots are more frequent in S-strategists, which accounts for a higher diversity of means for soil nutrient uptake in this group, compared to S-strategists.

Ectomycorrhizal fungi associated with two species of Kobresia in an alpine meadow in the eastern Himalaya

The diversity of ectomycorrhizal fungi (EMF) on Kobresia filicina and Kobresia capillifolia in an alpine meadow in China’s southwestern mountains, one of the word’s hotspots of biodiversity, was estimated based on internal transcribed spacer rDNA sequence analysis of root tips. Seventy EMF operational taxonomical units (OTUs) were found in the two plant species. Dauciform roots with EMF were detected in species of Kobresia for the first time. OTU richness of EMF was high in Tomentella/Thelophora and Inocybe, followed by Cortinarius, Sebacina, the Cenococcum geophilum complex, and Russula. Tomentella/Thelophora and Inocybe were general and dominant mycobiont genera of the two sedges. Besides the C. geophilum complex, the ascomycete components Hymenoscyphus and Lachnum were also detected on the two plants. Alpine plants in different geographical regions share similar main genera and/or families of EMF while harboring predominantly different mycobiont species; most of the members detected by us have not been found elsewhere. Significant differences in the profile of EMF occurrences were not found between the two plant species and among the three sampling seasons in our sample size.Electronic supplementary materialThe online version of this article (doi:10.1007/s00572-009-0287-5) contains supplementary material, which is available to authorized users.

Mobilization and Acquisition of Sparingly Soluble P‐Sources by Brassica Cultivars under P‐Starved Environment II. Rhizospheric pH changes, Redesigned Root Architecture and Pi‐Uptake Kinetics

Non-mycorrhizal Brassica does not produce specialized root structures such as cluster or dauciform roots but is an effective user of P compared with other crops. In addition to P-uptake, utilization and remobilization activity, acquisition of orthophosphate (Pi) from extracellular sparingly P-sources or unavailable bound P-forms can be enhanced by biochemical rescue mechanisms such copious H(+)-efflux and/or carboxylates exudation into rhizosphere by roots via plasmalemma H(+) ATPase and anion channels triggered by P-starvation. To visualize the dissolution of sparingly soluble Ca-phosphate (Ca-P), newly formed Ca-P was suspended in agar containing other essential nutrients. With NH(4)(+) applied as the N source, the precipitate dissolved in the root vicinity can be ascribed to rhizosphere acidification, whereas no dissolution occurred with nitrate nutrition. To observe in situ rhizospheric pH changes, images were recorded after embedding the roots in agar containing bromocresol purple as a pH indicator. P-tolerant cultivar showed a greater decrease in pH than the sensitive cultivar in the culture media (the appearance of typical patterns of various colors of pH indicator in the root vicinity), and at stress P-level this acidification was more prominent. In experiment 2, low P-tolerant class-I cultivars (Oscar and Con-II) showed a greater decrease in solution media pH than low P-sensitive class-II (Gold Rush and RL-18) cultivars, and P-contents of the cultivars was inversely related to decrease in culture media pH. To elucidate P-stress-induced remodeling and redesigning in a root architectural system, cultivars were grown in rhizoboxes in experiment 3. The elongation rates of primary roots increased as P-supply increased, but the elongation rates of the branched zones of primary roots decreased. The length of the lateral roots and topological index values increased when cultivars were exposed to a P-stress environment. To elucidate Pi-uptake kinetics, parameters related to P influx: maximal transport rate (V(max)), the Michaelis-Menten constant (K(m)), and the external concentration when net uptake is zero (C(min)) were tested in experiment 4. Lower K(m) and C(min) values were better indicative of the P-uptake ability of the class-I cultivars, evidencing their adaptability to P-starved environmental cues. In experiment 5, class-I cultivars exuded two- to threefold more carboxylates than class-II cultivars under the P-stress environment. The amount and types of carboxylates exuded from the roots of P-starved plants differed from those of plants grown under P-sufficient conditions. Nevertheless, the exudation rate of both class-I and class-II cultivars decreased with time, and the highest exudation rate was found after the first 4 h of carboxylates collection. Higher P uptake by class-I cultivars was significantly related to the drop in root medium pH, which can be ascribed to H(+)-efflux from the roots supplied with sparingly soluble rock-P and Ca(3)(PO(4))(2). These classical rescue strategies provided the basis of P-solubilization and acquisition from sparingly soluble P-sources by Brassica cultivars to thrive in a typically stressful environment.

Specialized ‘dauciform’ roots of Cyperaceae are structurally distinct, but functionally analogous with ‘cluster’ roots

When grown in nutrient solutions of extremely low [P] (<or=1.0 microm), the sedge Schoenus unispiculatus Benth. (Cyperaceae) develops dauciform roots, which are short and carrot shaped, and produce dense numbers of long root hairs. It has been suggested that dauciform roots of monocotyledonous sedges function to acquire P from nutrient-poor, P-fixing soils in a manner similar to that of cluster (proteoid) roots developed by some dicotyledonous species, but without evidence to substantiate this claim. To elucidate the ecophysiological role of dauciform roots, we assessed carboxylate exudation, internal carboxylate and P concentrations and O(2) uptake rates during dauciform root development. We showed that O(2) consumption was fastest [9 nmol O(2) g(-1) fresh mass (FM) s(-1)] and root [P] greatest (0.4 mg P g(-1) FM) when dauciform roots were young and rapidly developing. Citrate was the most abundant carboxylate in root tissues at all developmental stages, and was most concentrated (22.2 micromol citrate g(-1) FM) in young dauciform roots, decreasing by more than half in mature dauciform roots. Peak citrate-exudation rates (1.7 nmol citrate g(-1) FM s(-1)) occurred from mature dauciform roots, and were approximately an order of magnitude faster than those from roots of species without root clusters, and similar to those of mature proteoid (cluster) roots of Proteaceae. Both developing and mature dauciform roots had the capacity to acidify (but not alkalinize) the rhizosphere. Anatomical studies showed that epidermal cells in dauciform roots were greatly elongated in the transverse plane; epidermal cells of parent roots were unmodified. Although structurally distinct, the physiology of dauciform roots in sedges appears to be analogous to that of proteoid roots of Proteaceae and Fabaceae, and hence, dauciform roots would facilitate access to sorbed P and micronutrients from soils of low fertility.

Functional significance of dauciform roots: exudation of carboxylates and acid phosphatase under phosphorus deficiency in Caustis blakei (Cyperaceae)

Caustis blakei produces an intriguing morphological adaptation by inducing dauciform roots in response to phosphorus (P) deficiency. We tested the hypothesis that these hairy, swollen lateral roots play a similar role to cluster roots in the exudation of organic chelators and ectoenzymes known to aid the chemical mobilization of sparingly available soil nutrients, such as P. Dauciform-root development and exudate composition (carboxylates and acid phosphatase activity) were analysed in C. blakei plants grown in nutrient solution under P-starved conditions. The distribution of dauciform roots in the field was determined in relation to soil profile depth and matrix. The percentage of dauciform roots of the entire root mass was greatest at the lowest P concentration ([P]) in solution, and was suppressed with increasing solution [P], while in the field dauciform roots were predominantely located in the upper soil horizons, and decreased with increasing soil depth. Citrate was the major carboxylate released in an exudative burst from mature dauciform roots, which also produced elevated levels of acid phosphatase activity. Malonate was the dominant internal carboxylate present, with the highest concentration in young dauciform roots. The high concentration of carboxylates and phosphatases released from dauciform roots, combined with their prolific distribution in the organic surface layer of nutrient-impoverished soils, provides an ecophysiological advantage for enhancing nutrient acquisition.

ADAPTATIONS OF CAUSTIS BLAKEI TO LOW PHOSPHORUS CONDITIONS AND ITS SUSCEPTIBILITY TO PHOSPHORUS TOXICITY

Attempts to domesticate Australian native plants into conventional nursery production systems have been hampered by the sensitivity of a number of species to the essential mineral element phosphorus (P). However, this toxic response to P is highly variable, with sensitive and non-sensitive species present in the same genus. This paper presents details of a solution culture experiment examining the P absorption and internal requirement of the P-sensitive Australian native plant Caustis blakei. This study shows that with increasing solution P concentration above 10 μM, Caustis growth steadily declines. At these concentrations P toxicity symptoms were also evident and associated with accumulation of up to 1.2% P in the shoot at solution P of 250 μM. In contrast, under P limiting conditions, Caustis appears to be highly efficient in its acquisition and internal use of P. This is demonstrated by the fact that the highest total dry weight of 12.8g was achieved at solution P of 1.0 μM. Adaptations for low-P conditions by Caustis include an increased root to shoot ratio and the formation of dauciform roots at very low solution P concentrations ≤ 1 μM. Current research explores the role of dauciform roots in the production of organic acid and acid phosphatase exudates in response to P deficiency.

Effects of Ca- and Fe-rich Seepage on P Availability and Plant Performance in Calcareous Dune Soils

Ca- and Fe-rich seepage in wet dune slacks often sustains oligotrophic, species rich vegetation as a result of reduced P availability. While this effect has been attributed to pH buffering, we tested whether Ca- and Fe-rich seepage also immobilised P in calcareous soils with a strong pH buffer. Two oligotrophic species (Carex flacca and Schoenus nigricans) and two eutrophic species (Calamagrostis epigejos and Molinia caerulea) were planted in experimental sods. After 4 months supply with water of seepage or infiltration quality, with or without the addition of P, soil P fractions and a number of plant physiological responses were measured. A field validation was performed in a flow-through lake in calcareous dunes where the seepage flow had been restored recently. The readily available water soluble P fraction (Pw) was reduced by more than 80% by seepage, both in the greenhouse experiment and in the field, but the P Olsen-inorganic fraction was unaffected. All four test species had elevated N: P ratios in aboveground tissues when treated with seepage, indicating that seepage water had indeed reduced P availability to plants. Formation of dauciform roots by Carex flacca was diminished by P addition to less than 25% of treatments without P addition, indicating sensitivity to P availability, while seepage on average halved production of these root structures. Dauciform root formation by Schoenus nigricans was unaffected by the P addition and the hydrological treatment. Biomass of the test species in the experiment as well as vegetation biomass and relative abundance of oligotrophic species in the field were unrelated to seepage patterns, suggesting that compensatory mechanisms enabled the plants to sustain biomass production within the time frame of this experiment. In conclusion, Ca- and Fe-rich seepage can lower P availability in soils with a strong pH buffer. In the long term, this may create favourable conditions for species that have low P requirements or efficient P uptake. In the short term, however, existing vegetation seems to be resilient to changes in P supply.

The nonmycorrhizal root – a strategy for survival in nutrient‐impoverished soils

The nonmycorrhizal root – a strategy for survival in nutrient‐impoverished soils