Influence of phosphorus level on VA Mycorrhizal colonization and growth of cowpea cultivars

Vesicular-arbuscular mycorrhizal (VAM) associations often vary according to the abundance of available soil phosphorus (P). Therefore, understanding the response of crop plants to colonization by VAM fungi necessitates the study of the response of colonized and noncolonized plants, from a range of cultivars, to differing levels of P. Cowpea is grown throughout the world, often on impoverished soils in which it can benefit from formation of mycorrhizae. The present study was conducted to determine the response of four cultivars of cowpea (Vigna unguiculata (L.) Walp.), varying in nitrogen fixation capacity, to inoculation withGlomus fasciculatum at four levels of added P in the rooting medium. In a greenhouse experiment, four cowpea cultivars, Mississippi Silver, Brown Crowder, Six Week Browneye and MI 35, were grown with and without the mycorrhizal fungus at four levels of added P, 0, 10, 20 and 30 ppm. Root colonization (%) was negatively correlated with P content of the growth medium and shoot P concentration. Intraspecific variability was shown for shoot dry weight and leaf area in response to inoculation withG. fasciculatum at different P levels. The range of P required in the growth medium which allowed benefit fromG. fasciculatum was identified for individual cultivars using shoot dry weight and leaf area, and collectively across cultivars for other parameters.     

Growth of mycorrhizal tomato and mineral acquisition under salt stress

 High salt levels in soil and water can limit agricultural production and land development in arid and semiarid regions. Arbuscular mycorrhizal fungi (AMF) have been shown to decrease plant yield losses in saline soils. The objective of this study was to examine the growth and mineral acquisition responses of greenhouse-grown tomato to colonization by the AMF Glomus mosseae [(Nicol. And Gerd.) Gerd. and Trappe] under varied levels of salt. NaCl was added to soil in the irrigation water to give an EC_e of 1.4 (control), 4.7 (medium) and 7.4 dS m^–1 (high salt stress). Plants were grown in a sterilized, low P (silty clay) soil-sand mix. Mycorrhizal colonization was higher in the control than in saline soil conditions. Shoot and root dry matter yields and leaf area were higher in mycorrhizal than in nonmycorrhizal plants. Total accumulation of P, Zn, Cu, and Fe was higher in mycorrhizal than in nonmycorrhizal plants under both control and medium salt stress conditions. Shoot Na concentrations were lower in mycorrhizal than in nonmycorrhizal plants grown under saline soil conditions. The improved growth and nutrient acquisition in tomato demonstrate the potential of AMF colonization for protecting plants against salt stress in arid and semiarid areas. Accepted: 21 February 2000     

Immobilization of tissue iron on calcareous soil: differences between calcicole and calcifuge plants

Deficiency of P and sometimes of micronutrients, especially Fe, is of importance to the calcicole–calcifuge behaviour of plants. Calcifuge species are unable to solubilize these elements or keep them metabolically active in sufficient amounts on calcareous soils. To demonstrate if calcicole, calcifuge and ‘soil indifferent’ species differ in Fe nutrition dynamics, samples of such species were transplanted on a slightly acid silicate soil (pH BaCl₂ ca 4.0) and on a calcareous soil (pH BaCl₂ ca 7.2). Plants were grown in a computer‐controlled greenhouse at a soil moisture content of 50–60% water holding capacity and with additional light (ca 160 μE s^?1 m^?2, 12 h d^?1) if ambient light was <120 μE s^?1 m^?2.
The calcifuge species developed chlorosis when grown on the calcareous soil, whereas the other species did not. Calcareous‐soil grown plants had less 1,10‐phenanthroline extractable Fe in their leaf tissues than the silicate‐grown plants whereas total leaf Fe showed more species specific properties. The ratio of 1,10‐phenanthroline extractable to total Fe in the leaves was significantly lower in the calcifuges than in the calcicoles when grown on the calcareous soil. ‘Soil indifferent’ species did not differ much from the calcicoles. Root Fe, fractioned as DCB extractable ‘plaque’ on the root surface and Fe remaining in the root after DCB extraction, showed no distinct pattern of DCB‐Fe related to the different categories, but remaining root Fe tended to be lower in the calcifuges compared to the two other categories. Leaf colour estimated by a colour scale correlated well with chlorophyll a+b content measured in the leaves of two calcifuges. Leaf P concentrations did not differ between the different categories but were more species dependent.
We conclude that chlorosis in calcifuge species is related to an immobilization of Fe in physiologically less active forms in the tissue, if plants are forced to grow on a calcareous soil, whereas calcicole and ‘soil indifferent’ species are able to retain a much higher share of their leaf Fe in metabolically active form. This probably decreases the vitality and may exclude calcifuge plants from calcareous soil. We consider this property, previously almost unconsidered in an ecological context, as important to the calcifuge–calcicole behaviour of plants.     

Trifluralin-induced chlorosis in soybeans (Glycine max (L.) Merr.) grown on clayey,high pH soils

Summary The cause of leaf chlorosis, frequently observed on soybeans (Glycine max (L.) Merr.) grown on high pH soils of the Mississippi Blackland Prairie, is thought to be low Fe availability and restricted rooting. Three greenhouse experiments were conducted using two soils, Sumter, a Rendollic Eutrocrept and Okolona, a Typic Chromudert; nine soybean cultivars differing in Feefficiency; and trifluralin (α-α-α-trifluoro-2,6-dinitro-N, N-di-propyl-p-toludine). Trifluralin at rates greater than 0.56 kg/ha caused chlorosis which was more severe on the Sumter, a soil low in available Fe. Fe-efficient cultivars were more resistant to the chlorosis induced by trifluralin than the Fe-inefficient cultivars. It was concluded that the chlorosis is an Fe deficiency caused by reduced uptake. The herbicide-induced chlorosis can be avoided by proper dosage and placement of the herbicide.     

Endophytic fungi (Neotyphodium coenophialum) affect the growth and mineral uptake, transport and efficiency ratios in tall fescue (Festuca arundinacea)

Neotyphodium coenophialuminteracts mutualistically with its host grasses. Tall fescue (Festuca arundinacea Schreb.) plants infected by the fungal endophyte,Neotyphodium coenophialum(Morgan-Jones and Gams) Glenn, Bacon and Hanlin, often perform better than non-infected plants, especially in limited resource environments. However, there is a scarcity of information about endophyte-grass ecotypes interaction in Andisols of temperate regions. Clones of three tall fescue ecotypes (Fukaura, Koiwai and Showa) either infected with N. coenophialum (E+) or noninfected (E–) were grown in Andisols (Black Andisol: naturally low content of phosphorus, high in other nutrients; Red Andisol: naturally high content of phosphorus, low in other nutrients) for 133 days in a controlled environment. Cumulative shoot dry weight, daily regrowth rates (tiller number, plant height and shoot dry matter) after clippings and nutrient uptake, transport and efficiency ratios were measured. In Black Andisol, E+ plants had significantly higher cumulative shoot dry weight as well as daily regrowth rates than E– plants, while in Red Andisol the reverse was true. Among the ecotypes studied, Showa had the highest shoot growth. Significantly higher phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) uptake as well as transport were identified in E+ vs. E– plants grown in Black Andisol. With few exceptions, values for nutrient efficiency ratios were not significantly different between E+ and E– plants grown in both soils. Significant three-way interaction (endophyte × ecotype × soil) for cumulative shoot dry weight and regrowth rate revealed that the ecotype specific regrowth responses to endophyte infection were depended on soil nutrient conditions. Vegetative growth and nutrient acquisition in tall fescue varied with ecotype and were modified by abiotic (soil fertility status) as well as biotic (endophyte infection) factors.     

Soil chemical limitations to growth and development of Veronica officinalis L. and Carex pilulifera L.

Veronica officinalis and Carex pilulifera, widespread plants of acid soils in Europe, were grown in 50 soils of natural and seminatural ecosystems representing a wide range of soil chemical properties. The experiment was performed in a greenhouse at a soil moisture content of 55–65% WHC, ca. 60% R.H. of the air, temperature 14–16°C at night and 19–21°C by day; additional light 70 W m^-2 12 h d^-1. Properties closely related to soil acidity precluded growth of V. officinalis and limited the growth rate of C. pilulifera at soil pH-KCl < ca. 3.4. In slightly-moderately alkaline (calcareous) soils, growth was primarily limited by insufficient phosphate uptake. A low growth rate of C. pilulifera. in such soils was related to low concentrations of exchangeable soil phosphate and low tissue concentrations of phosphorus. However, in high-pH soils, secondary effects due to suboptimum trace element (probably Fe) conditions, giving rise to symptoms of chlorosis, were also indicated. The highest growth rates of both species were invariably measured in soils of intermediate acidity having very high concentrations of exchangeable phosphate. Multiple regression tests on the entire material indicated that 65–75% of the variability in several growth functions could be accounted for, when two or more soil characters were included in the equation. Besides phosphate, exchangeable Zn (in C. pilulifera) and nitrate (in V. officinalis) were of considerable importance in accounting for growth rates.     

Effects of labile soil carbon on nutrient partitioning between an arctic graminoid and microbes

We measured partitioning of N and P uptake between soil microorganisms and potted Festuca vivipara in soil from a subarctic heath in response to factorial addition of three levels of labile carbon (glucose) combined with two levels of inorganic N and P. The glucose was added to either non-sterilized or sterilized (autoclaved) soils in quantities which were within the range of reported, naturally occurring amounts of C released periodically from the plant canopy. The aims were, firstly, to examine whether the glucose stimulated microbial nutrient uptake to the extent of reducing plant nutrient uptake. This is expected in nutrient-deficient soils if microbes and plants compete for the same nutrients. Secondly, we wanted to test our earlier␣interpretation that growth reduction observed in graminoids after addition of leaf extracts could be caused directly by labile carbon addition, rather than by phytotoxins in the extracts. Addition of high amounts of N did not affect the microbial N pool, whereas high amounts of added P significantly increased the microbial P pool, indicating a luxury P uptake in the microbes. Both plant N and in particular P uptake increased strongly in response to soil sterilization and to addition of extra N or P. The increased␣uptake led to enhanced plant growth when both elements were applied in high amounts, but only led to increased tissue concentrations without growth responses when the nutrients were added separately. Glucose had strong and contrasting effects on plant and microbial N and P uptake. Microbial N and P uptake increased, soil inorganic N and P concentrations were reduced and plant N and P uptake declined when glucose was added. The responses were dose-dependent within the range of 0–450 μg C g⁻¹ soil added to the non-sterilized soil. The opposite responses of plants and microbes showed that plant acquisition of limiting nutrients is dependent on release of nutrients from the soil microbes, which is under strong regulation by the availability and microbial uptake of labile C. Hence, we conclude, firstly, that the microbial populations can compete efficiently with plants for nutrients to an extent of affecting plant growth when the microbial access to labile carbon is high in nutrient deficient soils. We also conclude that reduced growth of plants after addition of leaf extracts to soil can be caused by carbon-induced shifts in nutrient partitioning between plants and microbes, and not necessarily by phytotoxins added with the extracts as suggested by some experiments. Received: 15 February 1997 / Accepted: 12 July 1997     

Reaction of incompatible isolate of Pyricularia grisea on rice leaves stripped of epicuticular wax reflects blast conduciveness of soils

Upland rice cultivars were evaluated in the greenhouse for susceptibility to the rice blast disease caused by Pyricularia grisea Sacc., on two upland soils from the Philippines previously considered to be “blast conducive” and “blast non-conducive”. Under monocyclic inoculation tests plants grown in conducive soil showed significantly greater lesion development than plants of the same cultivar grown in non-conducive soil: cultivars considered to be susceptible to the isolates used showed increased number of susceptible-type lesions; resistant cultivars showed increased number of hypersensitive resistant-type lesions. A similar effect was observed under polycyclic tests where several generations of the pathogen were allowed to develop on the test plants. Dilution of conducive soil with non-conducive soil resulted in a corresponding reduction of disease severity, although this was most pronounced on resistant cultivars. Removal of leaf epicuticular waxes (LEW) using organic solvents increased the number of resistant-type lesions on resistant cultivars grown in both soils following inoculation. Susceptible plants were not suitable for quantifying the relative blast conduciveness of a soil because of the extreme environmental sensitivity of the bioassay and the tendency of lesions to coalesce. Comparing numbers of resistant-type lesions on leaves of plants stripped of LEW and inoculated with an incompatible P. grisea isolate among plants grown in different soils proved to be a satisfactory means of distinguishing the relative blast conduciveness of soils under controlled conditions. This method was field tested in eastern India and results corroborated farmer assessment of which soils were blast conducive. Using incompatible isolate-cultivar combinations and LEW-free leaves is proposed as a simple bioassay for assessing blast conduciveness of soils and should prove useful in regional characterization of rice blast risk.     

Effects of mycorrhizal fungus isolates on mineral acquisition by Panicum virgatum in acidic soil

 Plant ability to withstand acidic soil mineral deficiencies and toxicities can be enhanced by root-arbuscular mycorrhizal fungus (AMF) symbioses. The AMF benefits to plants may be attributed to enhanced plant acquisition of mineral nutrients essential to plant growth and restricted acquisition of toxic elements. Switchgrass (Panicum virgatum L.) was grown in pH_Ca (soil:10 mM CaCl₂, 1 : 1) 4 and 5 soil (Typic Hapludult) inoculated with Glomus clarum, G. diaphanum, G. etunicatum, G. intraradices, Gigaspora albida, Gi. margarita, Gi. rosea, and Acaulospora morrowiae to determine differences among AMF isolates for mineral acquisition. Shoots of mycorrhizal (AM) plants had 6.2-fold P concentration differences when grown in pH_Ca 4 soil and 2.9-fold in pH_Ca 5 soil. Acquisition trends for the other mineral nutrients essential for plant growth were similar for AM plants grown in pH_Ca 4 and 5 soil, and differences among AMF isolates were generally higher for plants grown in pH_Ca 4 than in pH_Ca 5 soil. Both declines and increases in shoot concentrations of N, S, K, Ca, Mg, Zn, Cu, and Mn relative to nonmycorrhizal (nonAM) plants were noted for many AM plants. Differences among AM plants for N and Mg concentrations were relatively small (<2-fold) and were large (2- to 9-fold) for the other minerals. Shoot concentrations of mineral nutrients did not relate well to dry matter produced or to percentage root colonization. Except for Mn and one AMF isolate, shoot concentrations of Mn, Fe, B, and Al in AM plants were lower than in nonAM plants, and differences among AM plants for these minerals ranged from a low of 1.8-fold for Fe to as high as 6.9-fold for Mn. Some AMF isolates were effective in overcoming acidic soil mineral deficiency and toxicity problems that commonly occur with plants grown in acidic soil. Accepted: 14 June 1999     

Plantago lanceolata L. and Rumex acetosella L. differ in their utilisation of soil phosphorus fractions

To establish relationships between soil phosphorus (P) fractions and leaf P, a mycorrhizal species (Plantago lanceolata L.) was compared with a typically non-mycorrhizal species (Rumex acetosella L.) in a glasshouse experiment. The plants were grown in 40 soils from non-fertilised, abandoned pastures or abandoned arable fields and leaf P concentration were found to be related to various soil P fractions after six weeks of growth. The differences in the P fractions in soil can account for a large share of the variation in leaf P concentration in both species, but the two species differed in their utilisation of P fractions. Leaf P concentration of R. acetosella was more related to extractable soil P than that of P. lanceolata. Rumex acetosella showed a higher maximum P concentration. The P fractions accounting for the largest share of the variation in leaf P concentration was the Bray 1 extractable and the weak oxalate (1 mM) extractable P, and for P. lanceolata also the Na₂SO₄+NaF extractable P fraction. P extracted with these methods accounted for up to 80% of the variation in P concentration in leaves of R. acetosella and 65% of the variation in leaves of P. lanceolata. More P extractable with weak oxalate, Na₂SO₄+NaF and strong oxalate (50 mM) was released from the soil than was taken up by the plants during the experimental period. The Bray 1 extractable P fraction, however, decreased in both unplanted and planted soils. Phosphatase release was not induced in any of the plants during the experimental period, indicating that they were not mobilising soil organic P. However, some of the methods extracted a large share of the organic P and still explained much of the variation in leaf P concentration. Mycorrhizal colonisation of P. lanceolata was inversely related to the extractable soil P. The consistently fast P uptake of R. acetosella indicates that this species have a high demand for P. The differences in P utilisation between R. acetosella and P. lanceolata could be caused by their different mycorrhizal status.     

Response of cassava to VA mycorrhizal inoculation and phosphorus application in greenhouse and field experiments

Cassava (Manihot esculenta Crantz) was grown in the greenhouse and in the field at different levels of phosphorus applied, with or without inoculation with VA mycorrhiza in sterilized or unsterilized soil. When grown in a sterilized soil to which eight levels of P had been applied the non-inoculated plants required the application of 3200 kg P ha⁻¹ to reach near-maximum yield of plant dry matter (DM) at 3 months. Inoculated plants, however, showed only a minor response to applied P. Mycorrhizal inoculation in the P check increased top growth over 80 fold and total P uptake over 100 fold. Relating dry matter produced to the available P concentration in the soil (Bray II), a critical level of 15 ppm P was obtained for mycorrhizal and 190 ppm P for non-mycorrhizal plants. This indicates that the determination of critical levels of P in the soil is highly dependent on the degree of mycorrhizal infection of the root system. In a second greenhouse trial with two sterilized and non-sterilized soils it was found that in both sterilized soils, inoculation was most effective at intermediate levels of applied P resulting in a 15–30 fold increase in DM at 100 kg P ha⁻¹. In the unsterilized soil inoculation had no significant effect in the quilichao soil, but increased DM over 3 fold in the Carimagua soil, indicating that the latter had a native mycorrhizal population less effective than the former. When cassava was grown in the field in plots with 11 levels of P applied, uninoculated plants grown in sterilized soil remained extremely P deficient for 4–5 months after which they recuperated through mycorrhizal infection from unsterilized borders or subsoil. Still, after 11 months inoculation had increased root yields by 40%. In the non-sterilized soil inoculation had no significant effect as the introduced strain was equally as effective as the native mycorrhizal population. These trials indicate that cassava is extremely dependent on an effective mycorrhizal association for normal growth in low-P soils, but that in most natural soils this association is rapidly established and inoculation of cassava in the field can only be effective in soils with a low quantity and quality of native mycorrhiza. In that case, plants should be inoculated with highly effective strains.     

Growth and elemental content of several sagebrush-steppe species in unburned and post-wildfire soil and plant effects on soil attributes

Fire is the principal means of stand renewal in big sagebrush-steppe communities of western North America. Plant growth following fire may be influenced by heat-induced changes in the nutrient status of the soil. Moreover, post-wildfire pioneer plant species may alter soil properties, and thereby, impact subsequent plant recruitment. Our study compared the growth and elemental content of big sagebrush (Artemisia tridentata), squirreltail (Elymus elymoides), cheatgrass (Bromus tectorum), and Indian ricegrass (Achnatherum hymenoides), grown under greenhouse conditions in post-wildfire and similar unburned soil. We also examined soil attributes following plant growth. Cheatgrass and squirreltail, grown in post-wildfire soil, had significantly (p≤0.05) greater aboveground mass than plants grown in unburned soil. As compared with unburned soil, post-wildfire soil engendered the following significant (p≤0.05) differences in leaf elemental content: 1) big sagebrush had higher levels of P and lower levels of Mn; 2) squirreltail accumulated more P and N; and 3) all grass species had higher SiO₂ content. Following harvest of plants, post-wildfire soil generally contained significantly (p≤0.05) more KCl-extractable ortho-P, NH _inf4 ⁺ , and SO ₄ ⁻ , than unburned soil. Plant growth in both burned and unburned soils fostered a significant (p≤0.05) increase in the bicarbonate-extractable pool of P as compared with unplanted controls. Soil Kjeldahl-N was significantly (p≤0.05) greater after plant growth in burned treatments as compared with the control. This study demonstrates that post-wildfire soil can have a stimulatory effect on plant growth for some species. Squirreltail deserves consideration as a post-wildfire revegetation species. Furthermore, pioneer plant growth following wildfires can attenuate soil properties and therefore influence plant succession.     

Changes in root morphology of white lupin (Lupinus albus L.) and its adaptation to soils with heterogeneous alkaline/acid profiles

The ability of Lupinus albus L. to adapt to a heterogeneous soil profile containing acid subsoil below limed topsoil of the same type, and to utilize nutrients by significantly altering its root system structure, was investigated using specially constructed soil profile tubes. Plants grown in homogeneous acid profiles had the fastest growth while those grown in homogeneous limed-soil profiles showed the slowest growth and exhibited some chlorosis after 19 days. Limed topsoil combined with an acid subsoil profile initially retarded plant growth similar to that in a homogeneous limed soil. However, after 68 days significantly greater growth had occurred in the limed/acid soil treatment relative to the homogeneous limed soil, indicating plants had benefited from the acid subsoil stratum. Plants in the homogeneous limed soil profile had lower concentrations of P, Fe and Mn in shoots compared with those in heterogeneous soils. In contrast, the concentration of Ca increased by 74%, due mainly to an increase in the water-soluble Ca fraction. When grown in a heterogeneous limed/acid soil profile, concentrations of P, Ca, K, Mg, Fe, Mn and Zn in shoots were comparable to those grown in a soil with a homogeneous acid profile. Although total root production was lower in the homogeneous limed-soil profile compared to the acid-soil containing profiles, cluster root mass was maintained at a level comparable with that in acid soil. The roots in heterogeneous soil profiles exhibited extensive plasticity, demonstrating a root-type specific, morphological response to the soil conditions. Within the acid subsoil of a heterogeneous profile, there was a large increase in cluster root mass compared with non-cluster roots. The proliferation of cluster roots in acid soil below limed topsoil may enhance the plant's ability to exploit this soil and facilitate the cultivation of L. albus on limed soil. This revised version was published online in August 2006 with corrections to the Cover Date.     

Acquisition of Cu, Zn, Mn and Fe by mycorrhizal maize (Zea mays L.) grown in soil at different P and micronutrient levels

Sustainability of soil-plant systems requires, among other things, good development and function of mycorrhizal symbioses. The effects of P and micronutrient levels on development of an arbuscular mycorrhizal fungus (AMF) and uptake of Zn, Cu, Mn and Fe by maize (Zea mays L.) were studied. A pot experiment with maize either inoculated or not with Glomus intraradices was conducted in a sand:soil (3 :1) mix (pH 6.5) in a greenhouse. Our goal was to evaluate the contribution of mycorrhizae to uptake of Cu, Zn, Mn and Fe by maize as influenced by soil P and micronutrient levels. Two levels of P (10 and 40 mg kg⁻¹ soil) and three levels of a micronutrient mixture: 0, 1X and 2X (1X contained, in mg kg⁻¹ soil, 4.2 Fe, 1.2 Mn, 0.24 Zn, 0.06 Cu, 0.78 B and 0.036 Mo), were applied to pots. There were more extraradical hyphae at the low P level than at the high P level when no micronutrients were added to the soil. Root inoculation with mycorrhiza and application of micronutrients increased shoot biomass. Total Zn content in shoots was higher in mycorrhizal than non-mycorrhizal plants grown in soils with low P and low or no micronutrient addition. Total Cu content in shoots was increased by mycorrhizal colonization when no micronutrients were added. Mycorrhizal plants had lower Mn contents than non-mycorrhizal plants only at the highest soil micronutrient level. AMF increased total shoot Fe content when no micronutrients were added, but decreased shoot Fe when plants were grown at the high level of micronutrient addition. The effects of G. intraradices on Zn, Cu, Mn, and Fe uptake varied with micronutrient and P levels added to soil. Accepted: 27 December 1999     

盐土和沙土对新疆常见一年生盐生植物生长和体内矿质组成的影响

选用古尔班通古特沙漠南缘荒漠-绿洲交错带常见的一年生盐生植物盐角草、刺毛碱蓬、叉毛蓬、猪毛菜和碱地肤为材料,比较了它们在原状盐土和沙土中的生长及体内矿质元素组成的差异。结果表明：① 原状盐土0—100 cm各土层的pH值低于沙土,但电导率和含水量明显高于沙土;② 原状盐土中生长的植物干重是沙土中生长植物干重的7—118倍,后者的根冠比是前者的2—6倍。③ 体现肉质化程度的地上部含水率为52%—81%,中低耐盐植物含水率在两种土壤中差异显著,强耐盐植物差异不显著;④ 5种一年生盐生植物地上部氮浓度为11—34 g/kg,在有效氮含量高的盐土上植物氮浓度也高;磷浓度为1—4 g/kg,在有效磷高的盐土上植物磷浓度也较高（盐角草除外）;但沙土中的植物地上部钾浓度明显高于盐土中植株的地上部钾浓度,这与两种土壤在0—60 cm土层中的钾浓度差异相反;⑤ 尽管原状盐土0—100 cm土层中的水溶性钙、镁、钠、氯、硫浓度显著高于沙土,盐土与沙土中生长的植物地上部钠、水溶性氯和硫的浓度比值远远低于土壤中的相应元素浓度的比值,甚至盐土中的植株钙、镁浓度等于或显著低于沙土中生长的植物。表明盐土不仅影响一年生盐生植物的生长,也显著影响这些植物对矿质元素的吸收和累积。一年生盐生植物能够选择性吸收不同生境中的矿质元素。本研究期望为进一步深入研究盐生植物耐盐的适应机制提供依据,也可为植物修复盐碱土的品种选择提供参考。     

Effect of salinity on nutrient content of the leafs of coconut seedlings

Two experiments were carried out with coconut seedlings grown in polybags filled with soils from maritime and forest environments. Salination treatments of 0, 2, 4, 6, 8, 10 and 12 g of common salt were applied to each polybag seedling fortnightly. The youngest open leaf, which was next to the spear leaf, of each seedling was sampled for chemical analysis after 12 months of seedling growth. Na and Cl content of leaf increased appreciably as a consequence of increased salt application while N, K, Ca and, to a lesser extent, P decreased with salinity. N and K content were higher in leaves of coconut plants grown in the forest soil while Na content was higher in those grown in the maritime soil. Antagonistic effects also occurred between Na and K, and Ca and P in both soils.     

Contrasting response of seedlings of two tropical species Clusia minor and Clusia multiflora to mycorrhizal inoculation in two soils with different pH

Differences in mycotrophic growth and response to phosphorus (P) fertilization were studied in seedlings of two woody native species: Clusia minor L. and Clusia multiflora H.B.K. from a cloud montane forest of tropical America. Greenhouse investigation was undertaken to determine the relationships between mycorrhizal dependency of host species associated with P utilization and growth in two different soils contrasting in pH (acidic and neutral) and nutrient content. Four treatments were performed: sterilized soil; sterilized soil plus 375 mg/kg of triple superphosphate (TSP); sterilized soil inoculated with Scutellospora fulgida (20 g/pot); and sterilized soil plus S. fulgida and TSP, with 10 replications per treatment for the two species. Results showed that both Clusia species presented high growth response to increasing P availability, which indicates that the root morphology (magnolioid roots) of these species is not a limiting factor for the incorporation of P from soils. Plants inoculated with arbuscular mycorrhizal fungi (AMF) in acidic soil had significantly increased shoot and root biomass, leaf area and height, in comparison to the biomass of P-fertilized plants and nonmycorrhizal plants. In neutral soil, seedlings of C. minor and C. multiflora were negatively affected by inoculation with AMF. In contrast, a significant decrease in growth was observed when inoculated plants were compared with noninoculated plants on neutral soil. Results indicate that an increase in the availability of a limiting nutrient (P) can turn a balanced mutualistic relationship into a less balanced nonmutualistic one.     

城市绿化植物-凋落物-土壤系统碳氮磷化学计量特征研究

以福建福州市常见的15种乔木、灌木和草本绿化植物为对象,连续2年取样测定了这些植物、凋落物、立地土壤、土壤微生物量C、N、P含量,探讨城市绿化植物-凋落物-土壤系统生态化学计量特征,为中国城市绿化植物的生态功能恢复与植被重建提供科学依据。结果表明:(1)绿化植物不同器官C、N、P含量均表现为草本灌木乔木、C含量N含量P含量、叶茎根,呈现出叶的富集作用;绿化植物各器官化学计量比(C/N、C/P、N/P)也表现出基本一致的乔木灌木草本的变化趋势;各绿化植物对N的再吸收率极显著高于对P的再吸收率(P0.01),绿化植物N和P再吸收率表现为乔木灌木草本,不同绿化植物对N的再吸收率差异均显著(P0.05),对P的再吸收率差异均不显著(P0.05)。(2)绿化植物凋落物C、N、P含量基本表现为草本灌木乔木,其中不同绿化植物凋落物P含量差异不显著。(3)绿化植物立地土壤C、N、P含量表现为草本灌木乔木,但其N/P差异不显著;土壤微生物量C、N、P含量基本表现为草本灌木乔木,其相应的C/N、C/P、N/P差异均不显著。(4)植物-土壤-凋落物-土壤微生物量(C、N、P)均随着生长季温度的升高而降低,随着年降水量的增加而升高,P素的回归系数绝对值明显低于C素和N素;植物-凋落物-土壤的C与N含量、N与P含量、C/P与N/P、以及土壤和植物的C/N与N/P之间均呈显著正相关关系,而凋落物的C/N与N/P之间呈显著负相关关系;典范对应CCA排序中,植物高度、冠幅、茎粗、比叶面积和叶面积指数对植物-凋落物-土壤-土壤微生物量C、N、P含量和C/N、C/P和N/P具有较大影响作用,其中高度、冠幅和茎粗与比叶面积和叶面积指数呈负相关关系,与凋落物-土壤-土壤微生物量C、N、P含量呈负相关关系,与植物C、N、P含量呈正相关关系;而凋落物-土壤-土壤微生物量C、N、P含量与其C/N、C/P和N/P均具有一定的正相关关系。     

<Emphasis Type="Italic">Rhizophagus manihotis</Emphasis> promotes the growth of rhizobia-nodulated <Emphasis Type="Italic">Vigna luteola</Emphasis> L in phosphorus deficient acid montane soils devoid of ground cover vegetation

The failure of Vigna luteola L. to colonize tropical montane regions of Venezuela with acid P-deficient soils that lack vegetation has been mainly attributed to the inability of indigenous arbuscular mycorrhizal fungi (AMFi) to be effective suppliers of P to this host plant. To test this hypothesis, Vigna luteola plants were grown in non sterile soil collected from this habitat. Plants became nodulated by indigenous rhizobia (Nod⁺) and the roots were colonized by AMFi (AMFi⁺). Some plants were inoculated with the arbuscular mycorrhizal fungus Rhizophagus manihotis (AMFg⁺). Other plants were fertilized with 6 mM nitrate and 2 mM P to inhibit nodulation (Nod^-) and AMFi colonization (AMFi^-), respectively and these served as controls. The Nod⁺AMFi⁺ plants displayed the smallest shoot and nodule dry weights upon harvest, the poorest AMF colonization, lowest foliar mineral content (N, P, Mg, Mn, Fe, Zn, and Cu), highest leaf ureide concentrations and lowest soil dehydrogenase, urease and acid phosphatase activities. Greater growth, nodulation, nutrient uptake, photosynthesis, catabolism of ureides in leaves, leaf superoxide dismutase and soil enzymatic activities were found in Nod⁺AMFg⁺ plants. The Nod^-AMFg⁺ plants grew even better attributed to their higher P uptake that was allocated mainly to the photosynthetic apparatus rather than to N₂-fixation. The results showed that V. luteola plants inoculated with R. manihotis and nodulated by indigenous rhizobia are capable successfully of colonizing open montane regions devoid of ground cover vegetation. The Nod⁺AMFg⁺ plants had greater growth, nodulation and root colonization by AMFg resulting in improved nutrient condition, enhanced uptake of nitrate and high catabolism of ureides in leaves than Nod⁺AMFi⁺ plants. However, more research is needed before the inoculation of open montane regions with AMFg can be recommended to land managers since a) the enhanced N₂ fixation rate in Nod⁺AMFg⁺ plants have an extra cost of 1.2 mg P kg⁻¹ leaf dry weight plant⁻¹ which could places an extra burden on the plants grown in the P-deficient soils, and b) the possible impact of AMFg on the microbiology of these former forest soils must be assessed.     

Plant Seeds as Mineral Nutrient Resource for Seedlings--A Comparison of Plants from Calcareous and Silicate Soils

Mineral nutrients of seeds constitute a significant source ofessential elements to seedlings and developing individuals ofvascular plants. In spite of their potential ecological significance,seed nutrient pools have attracted little attention with respectto calcifuge–calcicole behaviour of plants. The objectivesof this study were, therefore, to compare concentrations of13 macro- and micronutrients (K, Rb, Mg, Ca, Mn, Fe, Co, Cu,Zn, Mo, B, P and S) in seeds and leaves of 35 mainly herbaceousvascular plant species growing on both limestone (calcareous)and silicate (non-calcareous) soils. Concentrations of Rb andCo in seeds of plants originating from limestone soils were,on average, about half of those from silicate soils. Concentrationsof Mn, Mg, Zn and P of seeds were, or tended to be, lower orslightly lower in limestone-soil plants, whereas mean Ca andMo concentrations were higher. Comparing seed and leaf concentrationsof the same species from limestone and silicate soils generallydemonstrated a high P enrichment ratio, but a particularly lowK enrichment ratio in seeds, valid for both types of soil. Itwas also apparent that Fe and Mn, micronutrients which are lessreadily solubilized and taken up by plants on limestone soils,had significantly higher seed:leaf concentration ratios in plantsfrom limestone than from silicate soils, whereas the oppositewas true for Ca. This indicates a ‘strategy’ tosatisfy the demand of seedlings for elements which are lessreadily available in the soil.Copyright 1998 Annals of BotanyCompany Seed, leaf, plant, nutrient, content, calcareous, silicate, acid, soil.