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Leaf absorption of mineral nutrients in carnivorous plants stimulates root nutrient uptake

2002; Wiley; Volume: 155; Issue: 1 Linguagem: Inglês

10.1046/j.1469-8137.2002.00441.x

1469-8137

Lubomı́r Adamec,

Light effects on plants

New PhytologistVolume 155, Issue 1 p. 89-100 Free Access Leaf absorption of mineral nutrients in carnivorous plants stimulates root nutrient uptake Lubomír Adamec, Corresponding Author Lubomír Adamec Institute of Botany of the Academy of Sciences of the Czech Republic, Section of Plant Ecology, Dukelská 135, CZ-379 82 Třeboň, Czech RepublicAuthor for correspondence: Lubomír Adamec Tel: +420 333 721156 Fax: +420 333 721136 Email: adamec@butbn.cas.czSearch for more papers by this author Lubomír Adamec, Corresponding Author Lubomír Adamec Institute of Botany of the Academy of Sciences of the Czech Republic, Section of Plant Ecology, Dukelská 135, CZ-379 82 Třeboň, Czech RepublicAuthor for correspondence: Lubomír Adamec Tel: +420 333 721156 Fax: +420 333 721136 Email: adamec@butbn.cas.czSearch for more papers by this author First published: 18 June 2002 https://doi.org/10.1046/j.1469-8137.2002.00441.xCitations: 68AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Summary • The mineral nutrition of terrestrial carnivorous plants was investigated under glasshouse conditions to elucidate ecophysiological adaptations of this plant group. • In Drosera capillaris and D. capensis, absorption of N, P, K, and Mg from insects was relatively efficient (> 43%), whereas that of Ca was not. Carnivorous plants (D. capensis, D. peltata, D. scorpioides, and Dionaea muscipula) exhibited a high efficiency of re-utilization of N (70–82%), P (51–92%), and K (41–99%) from senescing leaves. Re-utilization of Mg was low or negative, and that of Ca highly negative. • In a growth experiment, foliar nutrient supply led to markedly increased growth and nutrient accumulation in D. capillaris, D. aliciae, and D. spathulata. In all the three species tested it was demonstrated that leaf-supplied nutrients were accumulated in the plant biomass and even stimulated root nutrient uptake. • These results suggest that the main physiological effect of leaf nutrient absorption from prey is a stimulation of root nutrient uptake. Introduction The majority of terrestrial carnivorous plants grow in bog and fen soils, in which they encounter persistent unfavourable conditions. The soils are usually wet or waterlogged, mostly acid, and usually poor in available mineral nutrients (N, P, K, Ca, Mg; Juniper et al., 1989, Adamec, 1997a). Thus, carnivory in most terrestrial plants may be considered as an adaptation to all of these stress factors. The basic questions of mineral nutrition of carnivorous plants that have been raised by biologists in the last decades are related to the relative importance of foliar and root mineral nutrient uptake, the identification of the elements from prey bodies, the uptake of which is for plant growth, the relationship between the uptake of organic and mineral nutrients from prey, and the nature of interactions between the foliar and root uptake of mineral nutrients (Lüttge, 1983; Juniper et al., 1989; Adamec, 1997a). However, our knowledge of the principal processes of mineral nutrition of carnivorous plants is still very fragmentary. On the basis of many glasshouse growth experiments, it has been concluded that terrestrial carnivorous plant species differ greatly in their ability to use soil or foliar mineral nutrient supply. Accordingly, carnivorous plants have been classed with three main ecophysiological groups (Adamec, 1997a). Plants in the group of ‘nutrient requiring species’ markedly increase their growth due to both soil and leaf nutrient supply and their root nutrient uptake may be stimulated by foliar uptake. Plants in the group of ‘root-leaf nutrient competitors’ grow better and accumulate more nutrients because of both root and leaf nutrient uptake. However, competition occurs between root and leaf nutrient uptake. Plants in the third group of ‘nutrient modest species’ have roots with a very low nutrient uptake capacity and rely on leaf nutrient uptake. The aim of this present study is to elucidate the principal processes of mineral nutrition of some terrestrial carnivorous plant species under glasshouse conditions. The physiological efficiency of mineral nutrient uptake (N, P, K, Ca, Mg) from model prey (fruit flies, mosquitoes) was investigated in Drosera capillaris and D. capensis as a difference in nutrient content between intact and spent carcasses. The efficiency of the re-utilization of the nutrients from senescent leaves of D. capensis, D. peltata, D. scorpioides, and Dionaea muscipula was investigated as a comparison of tissue nutrient content in adult and senescent leaves. A growth experiment was performed to reveal the effect of foliar mineral nutrient supply on root nutrient uptake in Drosera capillaris, D. aliciae, and D. spathulata. Thus, the hypothesis that foliar mineral nutrient supply can stimulate root nutrient uptake (Hanslin & Karlsson, 1996; Adamec, 1997a) was tested. Materials and Methods Mineral nutrient uptake from prey The proportions of total N, P, K, Ca, and Mg absorbed from model prey were investigated in two perennial, evergreen sundew species, low erect Drosera capensis L. (native to South Africa) and rosette-leaved D. capillaris Poir. (America). Both species have a relatively high capacity for mineral nutrient uptake both by leaves and roots (Adamec, 1997a). The subadult D. capensis plants grown from root cuttings were 8–12 cm high, with 15–25 adult leaves, while adult D. capillaris plants grown from seeds had rosette diameters of 4.2–4.5 cm, with 15–17 adult leaves. Neither species flowered during this study. The plants were grown in plastic 10 × 10 × 10 cm pots in organic soils with c. 10% (v/v) of vermiculite; the D. capensis in conifer needle mould (see Table 1a) and D. capillaris in acid fen soil (Table 1c; Adamec et al., 1992). The pots with the plants were placed in a 0.84-m2 white polypropylene container 0.4 m high, filled with water to a depth of 2–3 cm. The insect-proof container was covered with a nylon net (mesh diameter 470 µm) and a neutral-density plastic foil to reduce irradiance. In this way, the plants were protected from overheating. In summer, the irradiance on the level of plants was 12–15% of that in an open area outdoors. The container with the plants was maintained in a naturally lit glasshouse. Daily temperatures at plant level fluctuated between 20 and 36°C and relative air humidity (RH) between 60 and 90% during the day, and between 16 and 22°C and 80–96% RH at night. This manner of cultivation and the summer microclimatic conditions were the same for all plants used throughout this study. Table 1. Available nutrient content and pH values in soils used for growing carnivorous plants throughout the study Soil type Initial pH NH4+-N PO4-P K Ca Mg mg kg−1(d. wt) (A) Conifer leaf mould (1999) 4.20 27 8.7 229 342 337 (B) Conifer leaf mould (2000) 4.38 151 4.7 267 720 484 (C) Acid fen soil (1999) 4.10 31 17 47 569 74 (D) Acid fen soil + sand (2000) 4.16 23 5.7 30 260 143 One mixed soil sample was analysed. As a model prey, fruit flies Drosophila melanogaster and mosquitoes Culex pipiens were used. The former species is the one that has been most commonly used in similar studies (Adamec, 1997a). D. melanogaster (strain Oregon R) flies were cultured from the egg stage in a carbohydrate-rich medium. Adult flies (d. wt, c. 0.30 mg) were narcotized with ether and stored frozen at −15°C in a vial until used. The mosquitoes (d. wt c. 1.63 mg) were caught by a fine net in a forest, narcotized, and stored similarly. On 20 June 1999, two fruit flies were put on the centre of adult leaves of both Drosera species. The distance between the two flies on the same leaf was c. 10 mm in D. capensis and 2–3 mm in D. capillaris. This treatment was replicated for three adult leaves in each of 11 plants of both species, totalling six flies per plant. The tentacles and leaves surrounded the dead flies in a similar manner to that observed with live flies. After 15 days, the spent carcasses were carefully removed by fine forceps and put in mineralization glass flasks. One mosquito each was put on two adult leaves of each of seven D. capensis plants. The spent carcasses were removed and analysed after 22 days. The experiment on feeding D. capillaris on fruit flies was repeated on 11 June 2000. In this case, the plants were grown in a similar substrate but watered by distilled water (Table 1d). Thus, the tissue nutrient content in the leaves of these plants was somewhat lower than that in the 1999 season (cf. Table 2) and the relationship between the tissue nutrient content and nutrient absorption efficiency could be estimated. Table 2. Elemental content in standard prey (fruit flies, Drosophilia melanogaster and mosquito Culex pipiens) Element Prey Content (µg per prey) SE n % of d. wt of prey SE N Fruit fly 18.8 0.8 8 6.3 0.3 P ″ 2.6 0.2 8 0.88 0.06 K ″ 2.7 0.1 8 0.89 0.03 Ca ″ 0.16 0.01 8 0.05 0.002 Mg ″ 0.30 0.01 8 0.10 0.004 N Mosquito 65.9 11.4 5 4.1 0.7 P ″ 28.7 2.7 4 1.8 0.2 K ″ 13.1 1.1 4 0.81 0.07 Ca ″ 17.0 1.8 4 1.0 0.01 Mg ″ 6.2 0.1 4 0.38 0.004 Mean elemental content per one prey and in prey d. wt are shown. n, number of independent samples analysed. Two flies were always used for analyses of N, two for P, and four for K, Ca, and Mg analyses, or one mosquito for each of the analyses. As a control, intact frozen flies and mosquitoes were analysed. Absorption of the nutrients from the prey was expressed as a difference in nutrient content between the intact and spent carcasses (Dixon et al., 1980). Six to 10 parallel analyses of fruit flies and 4–5 of mosquitoes were performed on each plant species. Mineral nutrient re-utilization The proportions of N, P, K, Ca, and Mg re-utilized (recycled) from senescing leaves were studied in Drosera capensis, microstilt D. scorpioides Planch. (Australia), tuberous D. peltata Thunb. (Australia), and in erect-rosette Venus flytrap Dionaea muscipula Ell. (USA), and compared with tissue nutrient content in adult and senescent leaves. D. peltata was grown from tubers, D. scorpioides from in vitro cultured plants, while Dionaea muscipula was grown from plant cuttings. All these species have erect leaves which are usually not in contact with the soil. In June, a further 12 D. capensis plants, grown on conifer needle mould (Table 1a), were selected. They were of the same size as in a parallel study of nutrient uptake from prey. Three younger adult leaves of approximately the same age and size were selected from each plant. To obtain a measure of the relationship between the d. wt of adult and senescent leaves the selected leaves were tagged by a fine silicon ring on their petiole. The approximate ‘leaf area’ of the ribbon-like carnivorous part of leaf laminae with tentacles (i.e. traps) was estimated as a multiple of leaf length times leaf width. In each selected leaf, these parameters were measured by a plastic caliper; leaf length to the nearest 0.5 mm, and leaf width to the nearest 0.2 mm. In each plant, one selected and measured leaf was excised and its carnivorous lamina dried (80°C) and weighed. The plants with the tagged leaves were allowed to grow for further 2–3 months (by the end of September) until the complete senescence of leaf laminae took place. In order to prevent any contact of the senescent leaves with the soil in the pots, the senescing leaves were supported gently by a fine isolated wire. The brown colour of the leaf traps was the criterion for a complete leaf senescence. The leaf laminae were excised as soon as they had become fully senescent, dried and weighed. Linear correlation between the ‘leaf area’ of adult leaves and d. wt of senescent leaves was calculated. Tissue N, P, K, Mg, and Ca content in adult and senescent leaves was estimated in 7–13 parallel leaf samples. The same experiment was performed with Dionaea muscipula. The subadult plants were grown in conifer needle mould with vermiculite watered by distilled water (Table 1b). The length and width of both lobes of the snapping traps were measured independently. Thus, the total ‘leaf area’ is the sum of ‘leaf areas’ of the both leaf lobes. All mineral nutrient analyses were repeated 9–10 times. A similar experiment was performed with Drosera peltata plants grown in a fen soil (Table 1d) and watered by distilled water. From 12 plants, leaf laminae of c. 50 adult (17th March) and c. 60 senescent leaves (27th April) were excised. All mineral nutrient analyses were performed four times. A preliminary experiment was also performed with adult Drosera scorpioides plants grown in a fen soil (Table 1d) and watered by distilled water. From 10 plants, leaf laminae of 12 adult and c. 40 senescent leaves were excised. Due to the small size of the leaves, only two parallel nutrient analyses were performed. For the calculation of nutrient re-utilization in this species and D. peltata, the decrease of d. wt of adult D. capensis leaves was used. No plants of any of the four species were allowed to flower during the experiment. It was only necessary to excise developing flower stalks in D. capensis. Growth experiment A growth experiment was performed on three perennial rosette Drosera species to reveal the efficiency of foliar mineral nutrient supply on root mineral nutrient uptake from soil (Adamec et al., 1992). The seeds of D. capillaris, D. aliciae Hamet (South Africa), and D. spathulata Labill. (Australia) were sown on a fen soil with perlite in an insect-proof container in the glasshouse on 15th November 1999. On 27th April 2000, 90 homogeneous seedlings (rosette diameter c. 10–12 mm) of each of the three species were carefully selected. Eighty randomly selected seedlings of each species with intact root systems were planted in 16 10 × 10 × 10 cm plastic pots (five seedlings per pot) in a filamentous fen soil with c. 10% (v/v) of washed sand (Table 1d). Initial root length of the seedlings was measured. In 10 plants of each species, initial root and shoot d. wt (80°C) was measured. In each species, 20 seedlings in four pots represented controls or fertilized treatment for the growth experiment. For 5 d after the transplantation, all plants were sprayed gently with distilled water to reduce their transpiration. Every week from 3 May until 6 June 2000, one drop of a mineral nutrient solution (volume 2 µl) was placed onto each of the two largest leaves of all plants in the fertilized variant using an automatic micropipette. The same nutrient solution (in mM, NH4NO3 2.5; KH2PO4 0.74; MgSO4 0.41; CaCl2 1.0; FeCl3 0.016) was used as in the previous study (Adamec et al., 1992). Every week from 15 June to 23 August, a further 3 µl drops of the solution were dropped in the same way. In D. spathulata, the plants were fertilized only until 26th July. The control plants were treated in the same way with the same volume of distilled water. Thus, during the whole growth experiment, 90 µl of the nutrient solution or distilled water was supplied to each D. capillaris and D. aliciae plant, while only 66 µl was supplied to each D. spathulata plant. In total, 6.44 µg N, 2.21 µg P, 2.32 µg K, 3.57 µg Ca, and 0.80 µg Mg was supplied to each fertilized D. capillaris and D. aliciae plant, while 73.3% of this amount was supplied to D. spathulata during the experiment. In D. capillaris and D. aliciae, parallel sets of 20 seedlings in four pots were treated in the same way. At the end of the growth experiment, they were used for root respiration measurements. The 3-µl drops were checked by weighing and their true volume could be greater by 20–25%. During the growth experiment in the glasshouse, all pots with the plants stood in distilled water in the same insect-proof plastic container as above, but its height was 30 cm and the irradiance on the level of plants was c. 19.5% of that in the open. In the container, all pots with the plants had their position changed by rotation regularly every week. D. capillaris and D. aliciae were grown for 125 d, to 30 August, while D. spathulata was grown for 95 d, to 31 July Longest leaf length (± 0.5 mm), number of live leaves, and occurrence of flower organs were estimated in all plants at 1-month intervals. At the end of the experiment, the plants were carefully released from the fen soil and their excised roots washed thoroughly with tap water until all attached soil particles were removed. Root length was measured with a plastic ruler. Roots, shoots, and reproductive organs at each stage of development were dried (80°C) and weighed to the nearest 0.01 mg. Dead parts of the organs were removed. Tissue N, P, K, Mg, and Ca content in roots, shoots and reproductive organs, both at the beginning and the end of the experiment, were estimated in 3–5 parallel samples from different pots. Several organs from one pot were usually pooled together. The efficiency of utilization of single leaf-supplied nutrients for their own accumulation in the final total plant biomass (i.e. stimulation of root nutrient uptake from soil) was calculated for each species as (F–C): S; where F, total nutrient content in the leaf-fertilized variant; C, total nutrient content in controls; S, total nutrient content supplied onto the leaves (Aldenius et al., 1983; Adamec et al., 1992; Hanslin & Karlsson, 1996; Adamec, 1997a). At the end of the growth experiment, oxygen-based respiration rate was measured in whole roots of the parallel Drosera plants as a criterion of their metabolic activity. For one measurement, roots of three plants (f. wt, 5–20 mg) were pooled. Respiration rate was measured in the 50 times diluted mineral nutrient solution, which was used in the growth experiment, in an 8-ml stirred thermostatted chamber at 22.0 ± 0.1°C and in darkness, using a Clark-type oxygen sensor (Labio, Prague, Czech Republic) and a pen recorder (Adamec, 1997b). Oxygen concentration during the measurements was 80–90% of saturation. Origin of the plant material The plant material of Dionaea muscipula, Drosera capensis, D. capillaris, D. peltata, D. aliciae, and D. spathulata was provided from the carnivorous plant collection in the Institute of Botany at Třeboň, Czech Republic, D. scorpioides from a private collection at Ostrava, Czech Republic, and D. capillaris seeds from the Botanical Garden at Liberec, Czech Republic. Chemical analyses Values of pH in the soils were measured with a pH electrode in soil suspensions (1 g of soil f. wt + 4 ml of distilled water). Available mineral nutrient content in the soils was determined using an extracting solution (1.22 M sodium acetate and 0.52 M acetic acid, pH 4.80, 5 min) after Morgan and Wolf (Wolf, 1982). In soil extracts filtered through GF/C glass microfiber filters (Whatman, Maidstone, UK), NH4 ± N and PO4-P concentrations were determined colorimetrically by an automatic FIAstar 5010 Analyzer (Tecator, Höganäs, Sweden), while K, Ca, and Mg concentrations were estimated by atomic absorption flame spectrometry using an analyzer SpectrAA 640 (Varian Techtron, Melbourne, Australia). The nutrient solution used for leaf nutrient supply in the growth experiment was analyzed in the same way and its exact composition was: NH4 ± N, 42.6 mg l−1; NO3−-N, 29.0 mg l−1; PO4-P, 24.6 mg l−1; K+, 25.8 mg l−1; Ca2+, 39.7 mg l−1; Mg2+, 8.86 mg l−1. This composition was used for all calculations. NO3−-N concentrations were also determined using the FIAstar 5010 Analyzer. NO3−-N was determined using a Cd reductor and the sulphanilamide method, to form a diazo compound, with N-(1-naphtyl)-ethylenediamine dihydrochloride. NH4 ± N was determined colorimetrically in an acid-base indicator, after alkalization of the sample and the diffusion of the released NH3 through a gas-permeable membrane, and PO4-P using the phosphomolybdate blue method (for all methods see Ruzicka & Hansen, 1981). Mineral content of intact and spent fruit flies and mosquitoes was estimated in diluted mineralized samples. For N analyses, the carcasses were mineralized with 0.2 ml of 98% H2SO4 (190°C, 6 h), for P, with 0.15 ml of 60% HClO4 (170°C, 3 h), and for K, Ca, and Mg analyses, with 0.15 ml of 65% of HNO3 (140°C, 30 min). Dry plant biomass was mineralized in the same way in 12 ml mineralization flasks. When necessary, larger plant organs were ground in a minimortar. About 1.0–2.5 mg of d. wt was mineralized for N analyses, 1.5–4.0 mg for P, and 2.0–4.5 mg for cation analyses. N, P, and cation concentrations in the mineralizates were determined as above. Blank samples were used for all mineralization methods. Nutrient analyses always included plants from different pots. Where possible all paired data were statistically evaluated by a two-tailed paired t-test. Since the biometric data for the groups of five plants within the same pots in the growth experiment are dependent on each other, means of four parallel pots were always taken into account. Other data were processed by one-way ANOVA (Tukey HSD test). Results The total mineral content in intact mosquitoes as model prey was about 3.5–109 times greater than that in fruit flies (Table 2). Per unit d. wt, mosquitoes were a richer source of Ca and Mg than fruit flies. Absorption of N, P, K, and Mg from both prey species was relatively efficient (> 43%) in D. capillaris and D. capensis. However, neither species of Drosera could absorb Ca from fruit flies, only D. capensis could from calcium-rich mosquitoes (Table 3). In both plant species, 43–62% N, 61–97% P, 60–96% K, and 57–92% Mg were absorbed from the two prey species. With the exception of K, the efficiency of nutrient absorption from fruit flies was greater in the D. capillaris variant with lower tissue nutrient content than in that with greater content (cf. Table 4). Table 3. Mineral nutrient absorption from standard prey (fruit flies, Drosophila melanogaster and mosquito Culex pipiens) by Drosera capillaris and Drosera capensis Species Nutrient Prey Content (µg per prey) SE n Absorbed nutrient (%) D. capillaris a N Fruit fly 9.4 0.6 7 50.3 ″ P ″ 0.28 0.04 6 89.5 ″ K ″ 0.36 0.07 6 86.5 ″ Ca ″ 0.25 0.04 6 −54.1 ″ Mg ″ 0.13 0.02 6 57.4 D. capillaris b N Fruit fly 7.2 0.5 10 61.6 ″ P ″ 0.093 0.010 9 96.5 ″ K ″ 1.1 0.2 10 59.8 ″ Ca ″ 0.18 0.02 10 −10.7 ″ Mg ″ 0.069 0.015 10 76.5 D. capensis N Fruit fly 10.8 0.8 7 42.9 ″ P ″ 0.22 0.06 7 91.6 ″ K ″ 0.095 0.019 6 96.4 ″ Ca ″ 0.49 0.05 6 −206 ″ Mg ″ 0.12 0.02 6 59.7 D. capensis N Mosquito 37.1 7.6 5 43.7 ″ P ″ 11.2 2.0 5 61.2 ″ K ″ 0.79 0.26 4 94.0 ″ Ca ″ 7.2 0.7 4 57.6 ″ Mg ″ 0.53 0.11 4 91.5 n, number of independent samples analysed. aplants with higher mineral nutrient content in leaves. b plants with lower mineral nutrient content in leaves. The negative sign indicates accumulation of the nutrient in the prey. Mean mineral nutrient content remaining in one digested prey and mean percentage of absorbed nutrient are shown. Table 4. Tissue nutrient content in leaves of Drosera capillaris plants used in two experiments on nutrient absorption from fruit flies Water for watering N P K Ca Mg % d. wt Tap water 1.51–1.65 0.081–0.095 1.54–2.02 0.52–0.53 0.36–0.38 Distilled water 1.12–1.30 0.031–0.042 1.30–1.55 0.45–0.51 0.25–0.26 Duplicate values are always shown. All four carnivorous species exhibited a high efficiency of N, P, and K re-utilization (recycling) from senescent leaves, whereas a considerable loss of Ca (−32 to −119% of the initial amount) or slight Mg re-utilization or loss to the leaves (33 to −75%; Table 5). The efficiency of re-utilization of N was 70–82%, P 51–92%, and of K 41–99%. Thus, K was the most efficiently re-utilized element from senescing leaves of all species except for D. peltata. As available Ca and Mg content in all soils used throughout the study was relatively high (Table 1) Ca and Mg plant tissue content was also relatively high. This fact could influence the patterns of Ca and Mg absorption from prey and re-utilization. The following linear correlation was obtained in adult Drosera capensis leaves between ‘leaf area’ (A) in mm2 and d. wt. (mg) of leaf traps: A = 22.7 d. wt + 118.7 (n = 12; r= 0.84; P < 0.01), while A = 42.9 d. wt + 53.4 (n = 16; r= 0.78; P < 0.01) in senescent leaves. In Dionaea muscipula, the correlation was found in adult leaves: A = 17.5 d. wt + 70.4 (n = 17; r= 0.93; P < 0.01), while A = 21.8 d. wt + 95.8 (n = 16; r= 0.94; P < 0.01) in senescent leaves. Thus, before they senesced adult Drosera capensis leaves lost on average 30% of d. wt and Dionaea muscipula leaves 28%. Table 5. Re-utilization of N, P, K, Ca, and Mg from senescing carnivorous plant leaves Element Content in adult leaves Content in senescent leaves Re-utilization (% of initial amount) (% d. wt) SE n (% d. wt) SE n Drosera capensis N 1.42 0.12 10 0.36 0.05 9 82.4 ± 3.5 P 0.12 0.01 9 0.014 0.003 7 92.2 ± 2.3 K 1.48 0.07 10 0.45 0.09 10 79.0 ± 4.9 Ca 0.46 0.04 10 1.23 0.14 13 –87.8 ± 59.1 Mg 0.24 0.01 10 0.43 0.03 13 –23.2 ± 14.1 Drosera peltata N 1.70 0.13 4 0.54 0.06 4 77.8 ± 3.8 P 0.12 0.01 4 0.025 0.002 4 85.7 ± 1.7 K 1.17 0.05 4 1.00 0.14 4 40.7 ± 10.1 Ca 0.26 0.03 4 1.05 0.06 4 −187 ± 50 Mg 0.22 0.01 4 0.44 0.02 4 −44.6 ± 15.7 Drosera scorpioides N 1.62 − 2 0.70 – 2 69.8 P 0.048 – 2 0.0088 – 2 87.2 K 2.56 – 2 0.088 – 2 97.6 Ca 0.34 – 2 0.63 – 2 −31.9 Mg 0.31 – 2 0.30 – 2 33.2 Dionaea muscipula N 2.16 0.11 10 0.60 0.09 10 80.1 ± 3.7 P 0.21 0.01 10 0.15 0.02 9 50.6 ± 8.8 K 1.20 0.09 10 0.017 0.007 10 99.0 ± 0.4 Ca 0.34 0.04 10 1.05 0.06 10 −119 ± 66 Mg 0.19 0.01 10 0.47 0.03 10 −75.2 ± 19.4 Values of mean leaf tissue elemental content are shown for adult and senescent leaves. Percentage of re-utilized elements was corrected for the decrease in d. wt of senescent leaves by 30.0% of that of adult leaves in Drosera capensis, D. peltata, and D. scorpioides, and by 28.1% in Dionaea muscipula. A negative sign indicates accumulation of the nutrient in senescent leaves. Mean values ±1 SE are shown where possible; n, number of independent samples analysed. In all three Drosera species, leaf nutrient supply resulted in marked growth enhancement (Fig. 1, Table 6). After 64 d, the fertilized variants of D. capillaris and D. aliciae differed statistically significantly (at least at P < 0.05) from the nonfertilized controls in length of the longest leaf and the number of live leaves (Fig. 1a,b). In D. spathulata, the only statistically significant difference was in leaf length after 64 d (Fig. 1c). At the end of the growth experiment after 125 d, the fertilized variants of D. capillaris and D. aliciae differed statistically significantly from the nonfertilized controls in root length, root d. wt, shoot d. wt, and total d. wt. However, in D. spathulata after 95 d, leaf nutrient supply led to a statistically significant increase only in total d. wt (Table 6). At the end of the experiment, the increase of total plant d. wt in the fertilized variant was 88% greater than in the controls in D. capillaris, 120% in D. aliciae, and 81% in D. spathulata. The relative growth rates (RGR) of the controls of all three species ranged from 0.010–0.013 d−1, and from 0.014–0.018 d−1 in the variants. In the three Drosera species, no control plants flowered. Leaf nutrient supply enhanced flowering in D. capillaris and D. spathulata. Flowering attained 25% in D. capillaris and 85% in D. spathulata. The former species allocated on average c. 8% of the total plant d. wt to reproductive biomass, while the latter species allocated 26%. Figure 1Open in figure viewerPowerPoint Longest leaf length (circles) and number of live leaves (triangles) of Drosera capillaris (a), Drosera aliciae (b), and Drosera spathulata (c) during the growth experiment. Full symbols and full lines, plants fertilized with mineral nutrient solution onto the leaves; empty symbols and dotted lines, plants treated with drops of distilled water (controls). Mean values ±1 SE intervals are always shown; n= 4 parallel pots. Table 6. Results of growth experiment on Drosera seedlings in a glasshouse Parameter D. capillaris D. aliciae D. spathulata Controls Fertilized Controls Fertilized Controls Fertilized Initial root length (cm) 5.06 ± 0.43 2.81 ± 0.26 4.20 ± 0.32 Final root length (cm) 7.97 ± 0.30 9.47 ± 0.51* 4.65 ± 0.24 5.41 ± 0.14* 7.98 ± 0.70 8.56 ± 0.26ns Initial root d. wt (mg) 0.53 0.17 0.35 Final root d. wt (mg) 1.34 ± 0.08 2.01 ± 0.13** 0.76 ± 0.15 1.62 ± 0.11** 1.05 ± 0.18 1.35 ± 0.11ns Initial shoot d. wt (mg) 1.52 ± 0.24 0.83 ± 0.08 1.24 ± 0.15 Final shoot d. wt (mg) 5.84 ± 0.49 8.71 ± 0.53** 4.23 ± 0.24 8.14 ± 0.26** 4.39 ± 0.62 4.94 ± 0.19ns Final reproduct d. wt (mg) 0.00 0.95 ± 0.40 0.00 0.00 0.00 2.26 ± 0.37 Total initial plant d. wt (mg) 2.05 1.00 1.58 Total final plant d. wt (mg) 7.18 ± 0.57 11.7 ± 1.06** 4.99 ± 0.39 9.76 ± 0.37** 5.44 ± 0.80 8.55 ± 0.67* Final root : shoot ratio 0.23 0.21 0.18 0.20 0.24 0.19