The effect of sodicity on cotton: plant response to solutions containing high sodium concentrations

Solution culture was used to investigate whether the high solution Na concentrations and Na:Ca ratios found in sodic soils could directly affect the early growth and nutrient uptake of cotton (Gossypium hirsutum L.). Cotton was grown in nutrient solutions with three Na:Ca ratios (46:1, 4:1 and 0.2:1 mM) and three electrical conductivities (EC) (2.5, 4.25 and 6 dS m^?1) combined in a factorial design with four replicates. Most cotton growth parameters (including shoot and root dry weight, fruit number and weight) were unaffected by increasing solution EC or Na:Ca ratio, but at the highest Na concentration (56.6 mM), plant height was reduced. It was concluded that young cotton has the ability to tolerate solution Na concentrations up to those found in moderately sodic soils. Increasing solution Na:Ca increased plant root and shoot concentrations and plant accumulation for Na, and decreased them for Ca. Increasing EC also increased plant Na concentration and accumulation. Shoot K and P concentrations decreased with EC, but actually increased as the sodicity (Na:Ca ratio) of the nutrient solution increased. The results suggest that the low K and P concentrations commonly found in cotton grown in sodic soils are not a direct result of Na:Ca ratio in the soil solution.     

Isolation of tomato strains varying in potassium acquisition using a sand-zeolite culture system

One hundred tomato strains, representing widely diverse geographic areas, were evaluated in a sand-zeolite culture medium for their response to both low (0.25 mM) and adequate (1.0 mM) K levels. Three types of strains differing in K acquisition were classified: (1) efficient strains characterized by their ability to acquire K under low-K stress and with dry matter accumulation comparable to the strains grown under adequate-K supply, (2) inefficient strains that grew well under adequate-K supply but with a low capacity to acquire K at low-K stress and correspondingly lesser dry weight production, and (3) slowly growing strains featured by low K content in tissue and low dry matter accumulation irrespective of external K levels. The efficient and slowly growing strains came mostly from South and Central America, where tomato originated and was domesticated. Strains from other regions, however, mostly showed inefficiency in K acquisition. Two distinct features associated with the efficiency of K acquisition were identified. One was the proliferation of root length and another was high net K-influx rates per unit root length under low-K stress. Our results suggested that mechanisms for efficient acquisition of nutrients were lost during the cultivation of plants, and centers of plant origin and domestication contain valuable genetic resources for improving plant efficiency in nutrient acquisition.     

Luxury uptake of magnesium by peas,Pisum sativum

Increasing the magnesium (Mg) concentration of vegetables (biofortification) will often require ‘luxury’ uptake where the whole‐plant concentration of Mg (c_p) is greater than required for maximum yield. Our aim was to quantify some of the physiological factors influencing luxury uptake of Mg to aid subsequent development of agronomic techniques for biofortification. Peas, Pisum sativum, were used as a test species. A sand culture experiment related vegetative growth and c_p for plants grown with a range of Mg and potassium (K) supply rates. We developed a model of Mg uptake including feedback control exerted by c_p. The model was parameterised with results from a solution culture experiment and then used to explore ways to increase luxury uptake of Mg. Feedback control of Mg uptake by c_p was weak. Biomass did not increase if the Mg concentration exceeded 0.11% in the whole plant or 0.13% in the shoots. Values obtained in the field are often larger than this. Our results indicate that luxury uptake of Mg by peas is readily achieved, provided that there is ample supply of Mg²⁺ to the root surfaces. In field soils though, transport of Mg²⁺ to the roots may limit uptake and cation exchange processes restrict the ability of Mg fertilisers to substantially increase Mg uptake. Increasing root growth will usually increase Mg uptake, but c_p may not rise if biomass is also increased.     

Multielement Isotope Ratios of Vegetables from Integrated and Organic Production

In this paper we discuss the use of isotope ratios as indicators of organic production. Few studies have investigated the influence of plant nutrition on the isotopic signatures of plants. As plant nutrition is often significantly different between integrated and organic production systems the isotope ratios in the plants may reflect this. Plant samples from a 2-year field-experiment were analyzed for ¹⁵N, ¹³C and ³⁴S content of the bulk-material and ¹⁸O-content of the leaf water. In this experiment cabbages (Brassica oleracea v. capitata f. alba cv. Rolly), onions (Allium cepa cv. Alisa Craig), lettuces (Lactuca sativa v. capitata cv. Ponchito) and Chinese cabbage (Brassica pekinesis cv. Parkin) were cultivated according to good agricultural practices for integrated and organic production. No differences in the δ ³⁴S and δ ¹⁸O values of the plants grown under the two production systems were observed. The organically produced vegetables were significantly enriched in ¹⁵N and depleted in ¹³C compared to those grown under the integrated system.     

Antimicrobial action and efficiency of silver-loaded zeolite X

Aims: To synthesize silver-loaded zeolite X and establish the extent to which it persist in its antimicrobial action against strains of Escherichia coli K12W-T, Pseudomonas aeruginosa NCIMB8295 and Staphylococcus aureus NCIMB6571. Methods and Results: The antimicrobial action and efficacy of silver-loaded zeolite X on Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa were investigated. Zeolite X was synthesized and loaded with Ag⁺ by ion exchange. This resulted in 2·0% (w/w) loading of Ag⁺ in the zeolite framework and 5·8% (w/w) on the zeolite. Escherichia coli and Pseudomonas aeruginosa and Staphylococcus aureus suspended in tryptone soya broth were exposed to 0·15, 0·25, 0·5 or 1·0 g l⁻¹ of silver-loaded zeolite X for a period up to 24 h. No viable cells were detected for any of the three micro-organisms within 1 h. Silver-loaded zeolite X, retrieved three times from the first exposure cultures, was washed with de-ionized water and added to fresh bacterial suspensions. The results showed that the silver-loaded zeolite X retained its antimicrobial action. Conclusions: Silver-loaded zeolite X persisted in its antimicrobial action against all three micro-organisms. Significance and Impact of the study: The results are significant for the longevity of antimicrobial action of silver-loaded zeolite X.     

Relationships between soil potassium supply characteristics based on soil solution concentration and buffer power and field responses of winter wheat and maize

The relationship between soil K supply, characterised by the soil solution K concentration and the soil K buffer power, and plant K status was investigated for field grown crops. The study was carried out in 15 K fertilisation trials with maize and wheat covering a wide range of agricultural soils and K level. Soil K buffer power was obtained through sorption–desorption curves. For each trial the critical K concentration in the soil solution was deduced from the relationship between the K concentration in the soil solution and the K concentration in shoot tissue water, which was considered as a relevant indicator of the plant K status. At sufficient K levels, the maximal K concentration in the shoot tissue water of maize (145 mM) was lower than that of wheat (175 mM) but the percentages of the critical K concentration in plant tissue water to this maximal K concentration were similar for the two plant species with an average of 75%. The critical K concentration in the soil solution varied between soils. However, a close correlation was found between the critical K concentration in soil solution and the inverse of the soil buffer power at this concentration (r ²=0.981) or the inverse of the square of buffer power (r ²=0.989). On a wide range of soils and field conditions, these two indicators were more able to account for K availability and plant response than exchangeable K content or K saturation ratio of the CEC.     

Effect of soil K, Ca and Mg saturation and endomycorrhization on growth and nutrient uptake of sugar maple seedlings

Nutrient imbalances of declining sugar maple (Acer saccharum Marsh.) stands in southeastern Quebec have been associated with high exchangeable Mg levels in soils relative to soil K and Ca. A greenhouse experiment was set up to test the hypothesis that the equilibrium between soil exchangeable K, Ca, and Mg ions influences the growth and nutrient status of sugar maple seedlings. Also tested was whether endomycorrhization can alter nutrient acquisition under various soil exchangeable basic cations ratios. Treatments consisted of seven ratios of soil exchangeable K, Ca, and Mg making up a total base saturation of 58%, and a soil inoculation treatment with the endomycorrhizal fungus Glomus versiforme (control and inoculated), in a complete factorial design. Sugar maple seedlings were grown for 3 months in the treated soils. Plant shoot elongation rate, dry biomass and nutrient concentrations in foliage were influenced by the various ratios of soil cations. The predicted plant biomass and foliar K concentration were highest at a soil Ca saturation of 38%, a soil K saturation of 12%, and a soil Mg saturation of 8%. Potassium concentration in foliage was dependent on the level of Ca and Mg saturation in the soil when soil K saturation was close to 12%. Foliar Ca and Mg levels were more dependent on their corresponding levels in soil than foliar K. Colonization by G. versiforme did not influence seedling growth and macronutrient uptake. The results confirm that growth and nutrition of sugar maple are negatively affected by imbalances in exchangeable basic cations in soils.     

Toxic effects of Ni2+ on growth of cowpea (Vigna unguiculata)

Despite the importance of Ni-polluted soils throughout the world, comparatively little is known about the activity of Ni²⁺ required to reduce plant growth and the effects that Ni²⁺ toxicity has on the plant. Cowpea (Vigna unguiculata (L.) Walp. cv Caloona) was grown in dilute nutrient solutions to investigate the effect of Ni²⁺ activity on shoot and root growth. A Ni²⁺ activity of 1.4 μM was found to cause a 10% reduction in the relative fresh mass of the root and shoots. The primary site of Ni²⁺ toxicity was the shoots, with the younger leaves displaying an interveinal chlorosis (possibly a Ni-induced Fe deficiency) at Ni²⁺ activities ≥1.7 μM. Lateral root formation was inhibited in the two highest Ni²⁺ treatments (3.3 and 5.1 μM), and the roots growing at the highest Ni²⁺ activity were short and stubby and brown in color. However, no other symptoms of toxicity were observed on the roots at lower Ni²⁺ activities.     

Screening willow clones for Radiocesium uptake at varying potassium supply in solution culture

Transfer of radiocesium from soils to the wood of willows is generally low. Therefore, willow short rotation coppice for energy production is a possible alternative land use in areas contaminated by radiocesium. A large number of willow clones are available differing in, for example, biomass production or nutrient uptake. In order to select a clone with a high biomass production and a low radiocesium uptake, 12 clones were screened in nutrient solutions, spiked with ¹³⁴Cs. Radiocesium concentrations in the plants varied less than twofold between the clones. Shoot radiocesium concentrations were significantly related to shoot potassium concentrations (R² = 0.55).

In a second experiment, four of these clones were grown in solution culture at varying K concentrations (0.08 to 2 mM). The radiocesium uptake was more affected by K supply than by the type of clone. The shoot radiocesium concentrations were reduced between 3.5‐ and 5.2‐fold by increasing the K supply from 0.08 to 0.4 mM, A further increase to 2 vaM did not affect radiocesium uptake. We conclude that intervarietal differences between willow clones were of less significance in determining radiocesium concentrations in the shoots than the impact of external K concentrations.     

Phytoremediation potential of some agricultural plants on heavy metal contaminated mine waste soils,salem district,tamilnadu

The Pot culture experiment performed for phytoextraction potential of selected agricultural plants [millet (Eleusine coracana), mustard (Brassica juncea), jowar (Sorghum bicolor), black gram (Vigna mungo), pumpkin (Telfairia occidentalis)] grown in metal contaminated soils around the Salem region, Tamilnadu, India. Physiochemical characterization of soils, reported as low to medium level of N, P, K was found in test soils. The Cr content higher in mine soils than control and the values are 0.176 mg/L in Dalmia soil and 0.049 mg/L in Burn &; Co soil. The germination rate low in mine soil than control soils (25 to 85%). The content of chlorophyll, carotenoid, carbohydrate and protein decreased in mine soils than control. The morphological parameters and biomass values decreased in experimental plants due to metal accumulation. Proline content increased in test plants and ranged from 0.113 mg g^?1 to 0.858 mg g^?1 which indicate the stress condition due to toxicity of metals. Sorghum and black gram plants reported as metal tolerant capacity. Among the plants, Sorghum produced good results (both biomass and biochemical parameters) which equal to control plant and suggests Sorghum plant is an ideal for remediation of metal contaminated soils.     

Isolation,identification and characterization of soil microbes which degrade phenolic allelochemicals

Aims: To isolate and characterize microbes in the soils containing high contents of phenolics and to dissolve the allelopathic inhibition of plants through microbial degradation. Methods and Results: Four microbes were isolated from plant soils using a screening medium containing p‐coumaric acid as sole carbon source. The isolates were identified by biochemical analysis and sequences of their 16S or 18S rDNA, and designated as Pseudomonas putida 4CD1 from rice (Oryza sativa) soil, Ps. putida 4CD3 from pine (Pinus massoniana) soil, Pseudomonas nitroreducens 4CD2 and Rhodotorula glutinis 4CD4 from bamboo (Bambusa chungii) soil. All isolates degraded 1 g l^?1 of p‐coumaric acid by 70–93% in inorganic and by 99% in Luria‐Bertani solutions within 48 h. They also effectively degraded ferulic acid, p‐hydroxybenzoic acid and p‐hydroxybenzaldehyde. The microbes can degrade p‐coumaric acid and reverse its inhibition on seed germination and seedling growth in culture solutions and soils. Low pHs inhibited the growth and phenolic degradation of the three bacteria. High temperature inhibited the R. glutinis. Co²⁺ completely inhibited the three bacteria, but not the R. glutinis. Cu²⁺, Al³⁺, Zn²⁺, Fe³⁺, Mn²⁺, Mg²⁺ and Ca²⁺ had varying degrees of inhibition for each of the bacteria. Conclusions: Phenolics in plant culture solutions and soils can be decomposed through application of soil microbes in laboratory or controlled conditions. However, modification of growth conditions is more important for acidic and ions‐contaminated media. Significance and Impact of the Study: The four microbes were first isolated and characterized from the soils of bamboo, rice or pine. This study provides some evidence and methods for microbial control of phenolic allelochemicals.     

Mobilization of non-exchangeable K by ryegrass in five Moroccan soils with and without mica

Intensive cropping of Italian ryegrass (Lolium multiforum L.) in pots was used to assess the contribution of non-exchangeable K to plant uptake. The soils used were: two soils high in mica (illite) developed on recent alluvium plus two smectitic (beidellitic) soils and a soil of mixed mineralogy rich in mica. Four K treatments were used (0, 28.6, 143, and 286 mg kg^-1 soil) with 8 successive monthly cuttings. A response of plant K uptake to added K was observed in all soils. Both 1.0 M NH₄0Ac and 0.2 M CaCl₂ extractable K were depleted to a minimum level specific for each soil. The minima were lower in the old upland soils compared to the young alluvial soils. Uptake of K by Italian ryegrass induced K release from the non-exchangeable K to replenish the plant available pool of K ions. The release of mica interlayer K in the alluvial and in the high K smectitic soil supplied sufficient K to plants even under intensive cropping. The rate of mobilization of interlayer K was low in the smectitic soil with lower K. The lowest release rate was in the old high mica soil. Iron coatings may have inhibited mobilization of interlayer K. The rates of mobilization cannot be predicted from mineralogical and K-extraction data only. The rates of K uptake and the rates of K release by ryegrass under intensive cropping are potential values which can be used for modelling K availability to plants in the soils studied.     

不同生境外生菌根真菌对铝胁迫的响应

以南北方不同生境下的10株外生菌根真菌为研究对象,采用液体培养的方法,研究了铝对不同菌根真菌的生物量、有机酸分泌及养分含量的影响,以期筛选出抗铝性强的优良菌株,并探讨其抗铝机理。结果表明:外生菌根真菌Sl 08抗铝性最强;Pt 715、Ld 03、Bo 11、Sl 01、Bo 15也具有不同程度的耐铝性;Sl 14、Gc 99、Cg 04抗铝性较差;Sg 11抗铝性最差。来自南方酸性森林土壤的菌株总体抗铝性强于来自北方石灰性土壤的菌株,这表明外生菌根真菌的铝耐受能力与其原始生境有着密切的联系。外生菌根真菌能分泌多种有机酸,且不同菌株分泌的有机酸种类不同。其中,受铝胁迫分泌量增加最多的是草酸。研究中,铝胁迫能增加大多数铝抗性菌株的草酸分泌量,其中铝抗性最强的Sl 08表现最为明显。但铝胁迫并没有促进具备一定铝抗性的Bo 11和Sl 01草酸的分泌量,同时在铝敏感的菌株中均观察到了草酸分泌量的增加。这表明分泌草酸可能并不是外生菌根真菌抵抗铝毒的唯一途径。对各菌株铝胁迫下对氮,磷及钾的吸收研究表明,除铝敏感菌株Sl 14外,铝胁迫均能促进各供试菌株对氮,磷或钾的吸收。综上,在一定铝浓度下,一些外生菌根真菌可通过增加草酸分泌来抵御铝毒。此外,铝胁迫下外生菌根真菌还可通过调控氮、磷、钾等营养元素的吸收来抵抗铝毒,即通过增加对营养元素的吸收来增强其在铝胁迫下的生存能力,这可能是其抵御铝胁迫的应激反应之一。     

Tomato (Lycopersicon esculentum L.) nutrient and lead uptake affected by zeolite and DTPA in a lead‐polluted soil

• Development of alleviation strategies, which enhance plant growth under heavy metal stress, is important. Inorganic (zeolite) and organic (diethylene triamine penta‐acetic acid, DTPA) amendments affecting the alleviation of lead (Pb) stress in a calcareous soil were tested by investigating leaf nutrient uptake of tomato (Lycopersicon esculentum L.) plants.
• Experimental quantities of lead (Pb) at 0, 50, 100 and 150 mg·kg^?1 soil, zeolite (clinoptilolite) at 0%, 0.5% and 1%, and DTPA at 0, 50 and 100 mg·kg^?1 soil were tested in a factorial experiment with three plant replicates.
• According to the anova , Pb, zeolite, DTPA and their interactions significantly affected plant concentrations of nitrogen (N), potassium (K), iron (Fe), zinc (Zn), copper (Cu), manganese (Mn) and lead (Pb). With increasing DTPA concentration at different levels of zeolite and Pb, plant concentrations of macro‐ and micronutrients significantly increased. Increasing soil Pb increased leaf Pb concentration and decreased the uptake of N, K, Fe, Zn, Cu and Mn. Although with increasing Pb concentration the uptake of macro‐ and micronutrients decreased in tomato, the use of zeolite and DTPA alleviated this stress by increasing nutrient uptake compared to the control. Interestingly, however, increased levels of zeolite and DTPA led to a decreased uptake of nutrients by plants (compared with control), indicating the absorption of such nutrients by the two amendments and their partial release for further plant use.
• Zeolite and DTPA may alleviate the negative effects of soil Pb on tomato growth by decreasing nutrient leaching and increasing plant nutrient uptake.

     

Monitoring uptake and contents of Mg,Ca and K in Norway spruce as influenced by pH and Al,using microprobe analysis and stable isotope labelling

In a model system using intact spruce trees (Picea abies [L.] Karst.) we followed the path of magnesium, calcium and potassium during uptake into the root and during long-range transport into the shoot, by multiple stable isotope labelling. The roots of two- and three-year-old spruce trees originating from soil culture were removed from the soil and, in part or in toto, exposed to labelling solutions containing the stable isotopes ²⁵Mg or ²⁶Mg, ⁴¹K and ⁴²Ca or ⁴⁴Ca. Optical-emission-spectroscopy (ICP-OES) of plant fractions and labelling solutions was combined with the quantitative analysis of stable isotope ratios in sections of shock frozen, cryosubstituted material using the laser-microprobe-mass-analyser (LAMMA). This combination allowed us to distinguish, both in bulk samples and on the cellular level between (i) the fraction of elements originally present in the plant before the start of the labelling, (ii) the material taken up from the labelling solution into the plant and (iii) any material released by the plant into the labelling solution.In single-root labelling experiments, roots of three-year-old spruce trees, grown in nursery soil, were exposed to various pH conditions. The exchange of Mg and Ca with the labelling solution was nearly 100% in the cell walls of the mycorrhized finest roots. This exchange was only slightly affected by a step down to pH 3.5. The absolute Mg and Ca content in the cell walls was moderately reduced by incubation at pH 3.5 and strongly reduced in the presence of Al at this pH. After a pH 3.5 and 2 mM Al treatment we found Al in the xylem cell walls and the cortex cell lumina at elevated concentrations. To analyse the combined effect of high Al and high proton concentrations on the long-range transport, we used a split-root system. The root mass of an intact two-year-old spruce tree, grown in mineral soil, was divided into even parts and both halves incubated in solutions with two sets of different stable isotopes of Mg and Ca (side A: no Al, ²⁵Mg and ⁴²Ca; side B: +Al, ²⁶Mg and ⁴⁴Ca) and ⁴¹K on both sides. We observed a large uptake of Mg, Ca and K into the plant and a pronounced release. The net uptake of all three elements was lower from the Al-doted solution. In cross-sections of the apical shoot we found after seven-day labelling period about 60–70% of the Mg and Ca and 30% of the K content in the xylem cell walls originating from both labelling solutions. The clear majority of the Mg and Ca label originated from the Al-doted side.     

Characterization of the 1,25-dihydroxycholecalciferol-stimulated calcium influx pathway in CaCo-2 cells

The present studies were conducted to investigate the mechanisms underlying the 1,25-dihydroxycholecalciferol (1,25(OH)₂D₃)-induced increase in intracellular Ca²⁺ ([Ca²⁺] _i ) in individual CaCo-2 cells. In the presence of 2mm Ca²⁺, 1,25(OH)₂D₃-induced a rapid transient rise in [Ca²⁺] _i in Fura-2-loaded cells in a concentration-dependent manner, which decreased, but did not return to baseline levels. In Ca²⁺-free buffer, this hormone still induced a transient rise in [Ca²⁺] _i , although of lower magnitude, but [Ca²⁺] _i then subsequently fell to baseline. In addition, 1,25(OH)₂D₃ also rapidly induced⁴⁵Ca uptake by these cells, indicating that the sustained rise in [Ca²⁺] _i was due to Ca²⁺ entry. In Mn²⁺-containing solutions, 1,25(OH)₂D₃ increased the rate of Mn²⁺ influx which was temporally preceded by an increase in [Ca²⁺] _i . The sustained rise in [Ca²⁺] _i was inhibited in the presence of external La³⁺ (0.5mm). 1,25(OH)₂D₃ did not increase Ba²⁺ entry into the cells. Moreover, neither high external K⁺ (75mm), nor the addition of Bay K 8644 (1 μm), an L-type, voltage-dependent Ca²⁺ channel agonist, alone or in combination, were found to increase [Ca²⁺] _i , 1,25(OH)₂D₃ did, however, increase intracellular Na⁺ in the absence, but not in the presence of 2mm Ca²⁺, as assessed by the sodium-sensitive dye, sodium-binding benzofuran isophthalate. These data, therefore, indicate that CaCo-2 cells do not express L-type, voltage-dependent Ca²⁺ channels. 1,25(OH)₂D₃ does appear to activate a La³⁺-inhibitable, cation influx pathway in CaCo-2 cells.     

Influence of the phenolic compound bearing species Ledum palustre on soil N cycling in a boreal hardwood forest

The effects of the understory shrub Ledum palustre on soil N cycling were studied in a hardwood forest of Interior Alaska. This species releases high concentrations of phenolic compounds from green leaves and decomposing litter by rainfall. Organic and mineral soils sampled underneath L. palustre and at nearby non-Ledum sites were amended with L. palustre litter leachates and incubated at controlled conditions. We aimed to know (i) whether L. palustre presence and litter leachate addition changed net N cycling rates in organic and mineral soils, and (ii) what N cycling processes, including gross N mineralization, N immobilization and gross N nitrification, were affected in association with L. palustre. Our results indicate that N transformation rates in the surface organic horizon were not affected by L. palustre presence or leachate addition. However, mineral soils underneath L. palustre as well as soils amended with leachates had significantly higher C/N ratios and microbial respiration rates, and lower net N mineralization and N-to-C mineralization compared to no Ledum and no leachates soils. No nitrification was detected. Plant presence and leachate addition also tended to increase both gross N mineralization and immobilization. These results suggest that soluble C compounds present in L. palustre increased N immobilization in mineral soils when soil biota used them as a C source. Increases in gross N mineralization may have been caused by an enhanced microbial biomass due to C addition. Since both plant presence and leachate addition decreased soil C/N ratio and had similar effects on N transformation rates, our results suggest that litter leachates could be partially responsible for plant presence effects. The lower N availability under L. palustre canopy could exert negative interactions on the establishment and growth of other plant species.     

Nitrogen dynamics in alpine ecosystems of the northern Caucasus

Net N mineralization, nitrification, microbial biomass N and ¹⁵N natural abundance were studied in a toposequence of representative soils and plant communities in the alpine zone of the northern Caucasus. The toposequence was represented by (1) low-productive alpine lichen heath (ALH) of wind-exposed ridge and upper slope; (2) more productive Festuca varia grassland (FG) of middle slope; (3) most productive Geranium gymnocaulon/Hedusarum caucasicummeadow (GHM) of lower slope; (4) low-productive snowbed community (SBC) of the slope bottom. N availability, net N mineralization and nitrification were higher in soils of alpine grassland and meadow of the middle part of the toposequence compared with soils of lichen heath and snowbed community of extreme habitats in the alpine zone. There was no correlation between intensities of N transformation processes and favorable (low soil acidity, low C/N ratio, long vegetation period, relatively high temperature, absence of hydromorphic features) and unfavorable (opposite) factors, indicating that the intensity of N mineralization and nitrification in the alpine soils is controlled by a complex combination of these factors. Potential net N mineralization and nitrification in alpine soils determined in the short-term laboratory incubation were considerably higher than those determined in the long-term field incubation. The differences of potential nitrification between soils of various plant communities did not correspond to the field determined pattern indicating the importance of on-site climatic conditions for control of nitrification in high mountains. The result of comparison of N transformation potentials in incubated and native soils indicated that nitrification potential was significantly increased after long-term soil incubation. It means that net nitrification determined in the field was probably overestimated, especially in the meadow soils. A soil translocation experiment indicated that low temperature was an important factor limiting net N mineralization and nitrification in alpine soils: net N mineralization and especially nitrification increased when alpine soils were translocated into the subalpine zone and mean annual temperature increased by about 3°C. Additional N input increased N availability (NH₄ ⁺-N) and potential nitrification in soils of the lower part of the toposequense (GHM and SBC), and potential net N mineralization in two soils of extreme habitats (ALH and SBC). A positive correlation was found between soil ¹⁵N and net N mineralization and nitrification; the relative ¹⁵N enrichment was characteristic of grassland and meadow ecosystems. ¹⁵N of total soil N pool increased during the field mineralization experiment; there was a positive tendency between the change in ¹⁵N and net N mineralization and nitrification, however the relationship was not significant. Foliar ¹⁵N of dominant plant species varied widely within community, however, a tendency of higher foliar ¹⁵N for species growing on the soils with higher net N mineralization, nitrification and ¹⁵N was observed.     

喜钙和嫌钙植物对外源Ca2+的生长生理响应

以喜钙植物伞花木和嫌钙植物大白杜鹃为实验材料,以Hoagland营养液并设置其Ca2+浓度分别为0、5、10、25、50mmol/L培养试验,比较不同浓度外源Ca2+对其生长、叶绿素含量、渗透调节和矿质元素积累的影响,探索喜钙植物生长的适应特征,为喀斯特地区喜钙植物嗜钙机制研究提供基础资料。结果显示:(1)随着外源Ca2+浓度的增加,伞花木植株高度、茎粗以及叶干重、叶长、叶宽和叶形指数均得到不同程度提高,叶绿素和可溶性蛋白质含量增加,脯氨酸和可溶性糖含量无显著变化;而嫌钙植物大白杜鹃的生长却受到抑制,叶绿素和蛋白质含量降低,脯氨酸和可溶性糖含量增加;当Ca2+浓度为50mmol/L时,伞花木叶绿素和蛋白质含量分别为2.99mg/g和17.10mg/g,大白杜鹃叶绿素和蛋白质含量分别为1.39mg/g和14.30mg/g。(2)在实验设置的钙范围内,Ca2+可促进伞花木对P、N吸收并稳定体内Ca、K动态;而低浓度的Ca2+(<10mmol/L)促进大白杜鹃对Ca累积,抑制N、P吸收。     

Microbial community utilization of recalcitrant and simple carbon compounds: impact of oak-woodland plant communities

Little is known about how the structure of microbial communities impacts carbon cycling or how soil microbial community composition mediates plant effects on C-decomposition processes. We examined the degradation of four ¹³C-labeled compounds (starch, xylose, vanillin, and pine litter), quantified rates of associated enzyme activities, and identified microbial groups utilizing the ¹³C-labeled substrates in soils under oaks and in adjacent open grasslands. By quantifying increases in non-¹³C-labeled carbon in microbial biomarkers, we were also able to identify functional groups responsible for the metabolism of indigenous soil organic matter. Although microbial community composition differed between oak and grassland soils, the microbial groups responsible for starch, xylose, and vanillin degradation, as defined by ¹³C-PLFA, did not differ significantly between oak and grassland soils. Microbial groups responsible for pine litter and SOM-C degradation did differ between the two soils. Enhanced degradation of SOM resulting from substrate addition (priming) was greater in grassland soils, particularly in response to pine litter addition; under these conditions, fungal and Gram + biomarkers showed more incorporation of SOM-C than did Gram – biomarkers. In contrast, the oak soil microbial community primarily incorporated C from the added substrates. More ¹³C (from both simple and recalcitrant sources) was incorporated into the Gram – biomarkers than Gram + biomarkers despite the fact that the Gram + group generally comprised a greater portion of the bacterial biomass than did markers for the Gram – group. These experiments begin to identify components of the soil microbial community responsible for decomposition of different types of C-substrates. The results demonstrate that the presence of distinctly different plant communities did not alter the microbial community profile responsible for decomposition of relatively labile C-substrates but did alter the profiles of microbial communities responsible for decomposition of the more recalcitrant substrates, pine litter and indigenous soil organic matter.