Pots Of Sand Research Articles

Nostoc, Microcoleus and Leptolyngbya inoculums are detrimental to the growth of wheat (Triticum aestivum L.) under salt stress

This study investigated the effect of cyanobacterial inoculants on salt tolerance in wheat. Unicyanobacterial crusts of Nostoc, Leptolyngbya and Microcoleus were established in sand pots. Salt stress was targeted at 6 and 13 dS m−1, corresponding to the wheat salt tolerance and 50 % yield reduction thresholds, respectively. Germinated wheat seeds were planted and grown for 14 (0 and 6 dS m−1) and 21 (13 dS m−1) days by which time seedlings had five emergent leaves. The effects of cyanobacterial inoculation and salinity on wheat growth were quantified using chlorophyll fluorescence, inductively coupled plasma-optical emission spectrometry and biomass measurements. Chlorophyll fluorescence was negatively affected by soil salinity and no change was observed in inoculated wheat. Effective photochemical efficiency correlated with a large range of plant nutrient concentrations primarily in plant roots. Inoculation negatively affected wheat biomass and nutrient concentrations at all salinities, though the effects were fewer as salinity increased. The most likely explanation of these results is the sorption of nutrients to cyanobacterial extracellular polymeric substances, making them unavailable for plant uptake. These results suggest that cyanobacterial inoculation may not be appropriate for establishing wheat in saline soils but that cyanobacteria could be very useful for stabilising soils.

Influence of N deficiency and salinity on metal (Pb, Zn and Cu) accumulation and tolerance by Rhizophora stylosa in relation to root anatomy and permeability

Effects of N deficiency and salinity on root anatomy, permeability and metal (Pb, Zn and Cu) translocation and tolerance were investigated using mangrove seedlings of Rhizophora stylosa. The results showed that salt could directly reduce radial oxygen loss (ROL) by stimulation of lignification within exodermis. N deficiency, oppositely, would reduce lignification. Such an alteration in root permeability may also influence metal tolerance by plants. The data indicated that a moderate salinity could stimulate a lignified exodermis that delayed the entry of metals into the roots and thereby contributed to a higher metal tolerance, while N deficiency would aggravate metal toxicity. The results from sand pot trail further confirmed this issue. This study provides a barrier property of the exodermis in dealing with environments. The plasticity of root anatomy is likely an adaptive strategy to regulate the fluxes of gases, nutrients and toxins at root–soil interface.

Overexpression of transcription factor ZmPTF1 improves low phosphate tolerance of maize by regulating carbon metabolism and root growth

A bHLH (basic helix-loop-helix domain) transcription factor involved in tolerance to Pi starvation was cloned from Zea mays with an RT-PCR coupled RACE approach and named ZmPTF1. ZmPTF1 encoded a putative protein of 481 amino acids that had identity with OsPTF1 in basic region. Real-time RT-PCR revealed that ZmPTF1 was quickly and significantly up-regulated in the root under phosphate starvation conditions. Overexpression of ZmPTF1 in maize improved root development, enhanced biomass both in hydroponic cultures and sand pots, and the plants developed more tassel branches and larger kernels when they were grown in low phosphate soil. Compared with wild type, overexpressing ZmPTF1 altered the concentrations of soluble sugars in transgenic plants, in which soluble sugars levels were lower in the leaves and higher in the roots. Overexpression of ZmPTF1 enhanced the expression of fructose-1,6-bisphosphatase and sucrose phosphate synthase1 participated in sucrose synthesis in the leaves but decreased them in the root, and reduced the expression of genes involved in sucrose catabolism in the roots. The modifications on the physiology and root morphology of the plants enhanced low phosphate tolerance and increased the yield under low phosphate conditions. This research provides a useful gene for transgenic breeding of maize that is tolerant to phosphate deficiency and is helpful for exploring the relationship between sugar signaling and phosphate concentrations in cells.

Excessive sulfur supply reduces cadmium accumulation in brown rice ( Oryza sativa L.)

Human activities have resulted in cadmium (Cd) and sulfur (S) accumulation in paddy soils in parts of southern China. A combined soil–sand pot experiment was conducted to investigate the influence of excessive S supply on iron plaque formation and Cd accumulation in rice plants, using two Cd levels (0, 1.5 mg kg −1) combined with three S concentrations (0, 60, 120 mg kg −1). The results showed that excessive S supply significantly decreased Cd accumulation in brown rice due to the decrease of Cd availability and the increase of glutathione in rice leaves. But excessive S supply obviously increased Cd accumulation in roots due to the decrease of iron plaque formation on the root surface of rice. Therefore, excessive S supply may result in loss of rice yield, but it could effectively reduce Cd accumulation in brown rice exposed to Cd contaminated soils.

Improving phosphorus acquisition of white clover (Trifolium repens L.) by transgenic expression of plant-derived phytase and acid phosphatase genes

Phosphate is one of the least available macronutrients restricting crop production in many ecosystems. A phytase gene (MtPHY1) and a purple acid phosphatase gene (MtPAP1), both isolated from the model legume Medicago truncatula, were introduced into white clover (Trifolium repens L.) by Agrobacterium-mediated transformation. The transgenes were driven by the constitutive CaMV35S promoter or the root-specific MtPT1 promoter. Transcripts were detected in roots of the transgenic plants. Phytase or acid phosphatase (APase) activities in root apoplasts of the transgenic plants were increased up to three-fold compared to the wild type control. After the plants were grown 80 days in sand pots supplied with organic phosphorus (Po) as the sole P source, dry weights of shoot tissues of the best performing transgenic plants almost doubled that of the control and were comparable to the counterparts supplied with inorganic phosphorus (Pi). Relative biomass production of the transgenics under Po treatment was over 90% and 80% of that from the Pi treatment when the plants were grown in hydroponics (40 days) and sand pots (80 days), respectively. In contrast, biomass of the wild type controls under Po treatment was only about 50% of the Pi treatment in either hydroponic cultures or sand pots. In addition, shoot P concentrations of the transgenic plants were significantly increased compared to the control. Transgenic plants accumulated much higher amounts of total P (up to 2.6-fold after 80 days of growth) than the control in Po supplied sand pots. The results showed that transgenic expression of MtPHY1 or MtPAP1 in white clover plants increased their abilities of utilizing organic phosphorus in response to P deficiency.

RESPONSE OF FOLLOWING WINTER CROP SEED GERMINATION AND SEEDLING GROWTH TO RICE STRAW EXTRACT AND RESIDUES

The allelopathic potential of rice straw cv. Giza 178 was evaluated on the germination and seed-ling growth of squash, turnip, lentil wheat, Egyptian berseem and flax. Germination percentage and rate of all studied crop seeds were not affected significantly by aqueous extracts of rice straw, ex-cept for the rate of germination of flax which was delayed by increasing the extract concentration. Shoot length of flax was inhibited by 10.2% with 0.1% dilution, but was stimulated for wheat shoot length by5.6% at undiluted extracts. Seedling length of turnip and flax was stimulated by 46.9& 16.2%, respectively¸ with undiluted extracts. Seed-ling growth response depended on the extract concentration. Squash seedling fresh weight was stimulated by 9.3% at undiluted extract. How-ever all other crop seedling fresh weight was not significantly affected.Residues from rice straw placed in pots of sand had no significant effect on the emergence per-centage and rate of all studied crops, except for emergence percentage of Egyptian berseem and wheat which was increased and the rate of emer-gence of turnip and lentil which were delayed by increasing residue concentration. The flax emerged seedling shoot length and lentil seedling length were inhibited by 9.6% and 14.3%¸ respec-tively, in the presence of low rice straw residues as compared with control. The fresh weight of turnip, lentil, squash and wheat emerged seedling were stimulated by 3.3%, 8.4%, 22.8% and 26.4%¸ re-spectively¸ at higher residue concentration (1%).The stimulation effect by undiluted extract, and higher residue concentration from rice straw tissue may contain water-soluble compounds that exert allelopathic effect on the growth of studied crops under controlled environmental and greenhouse conditions, and it may be recommend to incorpo-rate rice straw in the soil at higher concentration under field conditions. However more research is needed to identify these possible allelopathic com-pounds and demonstrate their potential field condi-tions.

Effect of transpiration on Pb uptake by lettuce and on water soluble low molecular weight organic acids in rhizosphere

The effect of transpiration (high and low) on Pb uptake by leaf lettuce and on water soluble low molecular weight organic acids (LMWOAs) in rhizosphere has been studied. After two weeks of growth the plants were cultured in greenhouse for more four weeks and two days. Pb(NO 3) 2 solutions of different concentrations (100, 200, and 300 mg l −1 of Pb) were then added to the quartz sand pots of different plants and studies were initiated. Blank experiments (without treating the quartz sand pots with Pb(NO 3) 2 solutions) were also run in parallel. No significant differences in the growth of the plants with the concentrations of added Pb(NO 3) 2 solutions were observed by both low and high transpirations at the end of the 0, 3rd, and 10th days of studies. The total evaporation of the volatiles during 10 days did not depend on the concentration of Pb 2+ but with high transpiration the rate of evaporation was significantly higher than with low transpiration. Uptake of Pb by shoots and roots of the plants was found to be proportional to the concentration of various Pb(NO 3) 2 solutions added and more accumulation was observed in roots than in shoots at the end of 3rd and 10th days. High transpiration created more Pb uptake than low transpiration did. One volatile acid, propionic acid and nine non-volatile acids, lactic, glycolic, oxalic, succinic, fumaric, oxalacetic, d-tartaric, trans-aconitic, and citric acids in rhizosphere quartz sands were identified and quantified by gas chromatography (GC) analysis. d-Tartaric and citric acids were major among the non-volatile acids. The amount of LMWOAs in rhizosphere quartz sands increased with the higher amount of Pb uptake and also with the duration of studies. The total quantities of the LMWOAs in the rhizosphere quartz sands were significantly higher under high transpiration with 300 mg l −1 Pb solution addition at the end of 10th day. The present study shows prominent correlation between transpiration and uptake of heavy metal and interesting correlation between Pb contaminated level and quantity of water soluble LMWOAs in rhizosphere quartz sands. The latter thus deserves of further studies.

Effect of soil fertility and transpiration rate on young wheat plants ( Triticum aestivum) Cd/Zn uptake and yield

Using treated wastewater for crop irrigation can provide more adequate supply of high quality water for human consumption, but their heavy metal applications and synergetic effect must be regulated to ensure no physiological problems for both the plant and its consumer. The objective of the present project was to measure the influence of transpiration rate and soil fertility on Cd and Zn uptake by young wheat plants ( Triticum aestivum) grown in triplicate sand pots, using two types of sands with a low and high fertility, monitored from days 7 to 30 (day 0 was emergence) with solutions containing various levels of Cd/Zn (0/0, 0.01/0, 0.10/0, 0.50/0, 0/25, 0.01/25, 0.10/25, 0.50/25 and 0.50/50 mg/L). Two growth chambers each with a different vapor pressure deficit (VPD) induced different transpiration rates, monitored from days 7 to 30. On days 15 and 30, three plants were removed from each pot, to measure their dry mass and Cd and Zn content. For the plants grown using soil 2, the roots were also collected and analyzed on day 30. Heavy metal treatments had no effect on transpiration rates per plant dry matter weight. VPD had no effect on plant transpiration rate and dry mass for soil 1, while it did from days 15 to 30 for soil 2, richer in P and K. The synergetic effect between Cd and Zn was quite variable, depending on the soil nutrient level, irrigation period and VPD or transpiration rate. In general, faster or higher plant dry mass accumulation tended to enhance the synergetic effect between Cd and Zn. In general, higher Cd levels generally decreased Zn uptake and higher Zn generally increased Cd uptake. For both soils, Zn decreased Cd uptake when applied under 5.6 mg/kg of soil, while it increased Cd uptake at higher applications. Soil nutrients were found to compete against heavy metals for plant uptake. Poorer soils also lead to a more efficient use of irrigation water per dry mass yield but to higher plant Cd and Zn content with risks of exceeding toxic levels. The level of Cd and Zn found in the shoot depended on the irrigation water Cd and Zn levels and the transpiration rate while the ratio of Cd to Zn found in the shoot depended more on the soil adsorption capability and the adsorption synergy between Cd and Zn.

Interstock-induced mechanism of increased growth and salt resistance of orange (Citrus sinensis) trees.

Interstocks improve the growth and salt resistance of lemon (Citrus limon (L.) Burm. f.) trees, but their effects on orange (Citrus sinensis (L.) Osbeck) trees are unknown. We grew 'Cleopatra' mandarin (CM) seedlings, budded trees of 'Salustiano' orange (SAO) on CM, 'Valencia Late' orange (VLO) on CM (VLO/CM), and interstock trees VLO/SAO/CM in pots of sand watered with nutrient solution containing 5 (control) or 50 mM NaCl for 12 weeks. Plants were harvested on six successive occasions and the time trends in relative growth rate (RGR) and its components were estimated by fitting a Richards function regression to the harvest data. At low and high salinities, the VLO/SAO/CM combination had higher mean RGR than VLO/CM. Under control conditions, the increase in RGR caused by the interstock was the result of an increase in leaf mass fraction (LMF; leaf dry mass/plant dry mass ratio). Increases in net assimilation rate on a leaf mass basis (NARm) and LMF contributed equally to the increase in RGR in saline conditions, their growth response coefficients being 0.52 and 0.48, respectively. The structural modifications, specific leaf area (SLA) and leaf area ratio (LAR; leaf area:plant dry mass ratio), had a slight influence on the reduction in RGR by salinity. However, NARm had a large influence on RGR, except in CM. The interstock-induced mechanism increased biomass allocation to the assimilatory organs and, under saline conditions, increased Cl- and Na+ allocations to roots. Thus, the flux of ions to the leaves was either delayed or reduced or both. The dilution of imported ions by foliar growth reduced ion concentrations in leaves, resulting in higher NARm, which together with higher LMF, increased RGR.

Induction of Multiple Bud Clumps from Inflorescence Tips and Regeneration of Salt-tolerant Plantlets in Beta vulgaris

We developed an efficient method for sugar beet multiplication in vitro from excised immature inflorescence tips. On Murashige & Skoog medium supplemented with 4.4 μM 6-benzylamino- purine and 1.3 μM naphthaleneacetic acid, multiple bud clumps were induced from segments of inflorescence tips. The clumps proliferated rapidly. By radiation of small bud clumps at an appropriate dose and by directional selection for NaCl tolerance, we obtained salt-tolerant bud clumps and regenerated plantlets. The plants were vernalized and self-pollinated. The seeds of the regenerated plants were sown in pots of sand and irrigated every day with a solution of 342 mM NaCl. Some of the seeds germinated and grew normally in the 342 mM NaCl solution, exhibiting higher salt-tolerance than the control ones; such seedlings after the saline selection were transplanted to soil and the plants grew normally and produced plump root tuber similar to controls. The seeds from two selected lines germinated and grew for a few weeks in 513 mM NaCl solution before the seedlings withered. In saline soil where the salt concentration was about 154 mM, the yields of tuber from the plants of three salt-tolerant lines were about 45–50 tons ha−1, approximately 2.6–2.9 times of the controls. It is concluded that we have got salt-tolerant materials with good agronomic traits for sugar beet breeding via selection in vitro.

Role of mycorrhizal fungi and phosphorus in the arsenic tolerance of basin wildrye.

Revegetation of arsenic (As)-rich mine spoils is often impeded by the lack of plant species tolerant of high As concentrations and low nutrient availability. Basin wildrye [Leymus cinereus (Scribner & Merr.) A. Löve] has been observed to establish naturally in soils with elevated As content and thus may be useful for the stabilization of As-contaminated soils. An experiment was conducted to evaluate how variable phosphorus (P) concentrations and inoculation with site-specific arbuscular mycorrhizal fungi influence As tolerance of basin wildrye. Basin wildrye was grown in sterile sand in the greenhouse for 16 weeks. Pots of sterile sand were amended to create one of four rates of As (0, 3, 15, or 50 mg As kg(-1)), two rates of P (3 or 15 mg P kg(-1)), and +/-mycorrhizal inoculation in a 2 x 4 x 2 factorial arrangement. After 16 weeks of growth, plants were harvested, shoots and roots thoroughly washed, and the tissue analyzed for total shoot biomass, total root and shoot As and P concentrations, and degree of mycorrhizal infection. Basin wildrye was found to be tolerant of high As concentrations allowing for vigorous plant growth at application levels of 3 or 15 mg As kg(-1). Arsenic was sequestered in the roots, with 30 to 50 times more As in the roots than shoots under low P conditions. Mycorrhizal infection did not confer As tolerance in basin wildrye nor did mycorrhizal fungi influence biomass production. Phosphorus concentrations of 15 mg kg(-1) effectively inhibited As accumulation in basin wildrye. Basin wildrye has the potential to be used for stabilization of As-rich soils while minimizing exposure to grazing animals following reclamation.

Improvement in growth and salt resistance of lemon (Citrus limon) trees by an interstock-induced mechanism.

Interstocks can reduce toxic ion accumulations in leaves of budded citrus trees, but the mechanism is not understood. We grew sour orange (Citrus aurantium L.; SO) seedlings, budded trees of 'Salustiano' orange (Citrus sinensis L. Osbeck; SAO) on SO, 'Verna' lemon (Citrus limon L. Burm. f; VL/SO) and interstock trees (VL/SAO/SO) in pots of sand watered with nutrient solution containing 5 (control) or 50 mM NaCl (saline treatment) for 12 weeks. Plants were harvested in six successive harvests and time trends in relative growth rate (RGR) and its components were estimated by fitting a Richards function regression to the harvest data. The VL/SAO/SO trees in saline conditions had higher mean RGR than VL/SO trees in control conditions. Increases in both net assimilation rate on a leaf mass basis (NARw) and leaf mass fraction (LMF) contributed equally to a twofold increase in RGR of VL/SAO/SO trees in saline conditions. In control conditions, the increase in RGR caused by the interstock had growth response coefficients of GRC(NARw) = 0.20 and GRC(LMF) = 0.80. Structural modifications-specific leaf area, leaf area ratio and LMF-had a slight influence on the salt-induced changes in RGR, whereas NARw had a large influence. Salinity decreased root mass fraction (RMF) and increased stem mass fraction (SMF). In contrast, the interstock decreased SMF and increased LMF and RMF. The VL/SAO/SO trees had the highest RMF and proportionally higher Cl- and Na+ allocations in roots than the other plant types. In saline conditions, reductions in leaf ion transport rate and dilution of imported ions by foliar growth nearly halved ion accumulations in leaves of VL/SAO/SO trees.

The production and utilisation of monoclonal antibodies for identification of a Frankia strain utilised as inoculum for Casuarina equisetifolia

Monoclonal antibodies were raised against Frankia 0RS020607, a strain isolated originally by H.G. Diem from nodules of Casuarina equisetifolia from Senegal. One of these antibodies, mAb8C5, was shown by ELISA to have high, but not absolute specificity for 0RS020607. This antibody was employed to investigate the mobility and persistence of 0RS020607 in plantations of C. equisetifolia. Seedlings were inoculated in pots of sand in a forest nursery with 0RS020607, with local crushed nodule suspensions or were left uninoculated. They were planted out after 5 months in experimental plots on a moderately fertile black soil site and on a low organic, oxidised red soil site. Compared with crushed nodule inoculated seedlings or uninoculated controls, growth of seedlings at transplant was improved by inoculation with Frankia 0RS020607. However, 4 years after transplant to experimental plots, the growth of trees receiving different treatments was similar. The possibility that movement of ORS 020607 between treatment plots contributed to new nodulation and enhanced growth of uninoculated trees was tested using mAb8C5 in ELISA of Frankia mycelium, extracted from the nodules of trees of the three treatments. No significant differences in reactivity were detected between nodules from uninoculated and 0RS020607 inoculated trees at either the black or the red soil sites, showing that 0RS020607 moved between treatment plots at both sites. However, at both sites, nodules from plots of trees that were inoculated originally with local crushed nodules gave reactions in ELISA that were significantly lower than values for 0RS020607 inoculated trees, possibly due to the competitive effects for new nodulation of enhancement of the indigenous population of Frankia. Serological techniques using antibodies of high specificity against Frankia strains have value for rapid screening of field samples as a preliminary for further analysis by more discriminatory techniques based on assays of genetic polymorphisms.

Tratamento de matrizes de cravo (Dianthus caryophyllus L., Caryophyllaceae) com nitrogênio e calogênese in vitro

Indução de calogênese eficiente e multiplicação celular rápida são pré-requisitos fundamentais em biotecnologia de plantas. Sucesso na calogênese é dependente dos componentes do meio de cultura e da qualidade dos explantes. Neste trabalho é relatada a influência do tratamento de matrizes de Dianthus caryophyllus L. com nitrogênio na indução de calogênese in vitro. Mudas de cravo cultivadas em vasos contendo areia foram tratadas com soluções nutritivas contendo 5 níveis de nitrogênio. Explantes folha, entrenós e nó foram coletados aos 30, 45 e 60 dias após início dos tratamentos e inoculados em meio de cultura contendo os sais básicos e vitaminas de Murashige & Skoog (1962), suplementado com 1 g L-1 de caseína hidrolizada, 2 mimol L-1 de cinetina e 3 mimol L-1 de 2,4-D para indução da calogênese. Ao longo dos 60 dias de tratamento com as soluções nutritivas, as matrizes de cravo não apresentaram sintomas visíveis de deficiência ou de excesso do nutriente nitrogênio. O tratamento com nitrogênio afetou a calogênese avaliada em massa de matéria fresca e seca. A produção da massa de matéria fresca de calos foi proporcional ao tratamento com nitrogênio até concentração de 267 mg L-1 para explantes folha por durante 30 dias. Tratamentos mais prolongados (45 e 60 dias) afetaram negativamente a calogênese e foram inversamente proporcionais a concentração de nitrogênio na solução nutritiva.

Influence of Chloride and Transpiration on Net15NO3−Uptake Rate byCitrus Roots

Three-month-old Carrizo citrange (hybrid of Citrus sinensis L. Osbeck×Poncirus trifoliata Blanco) seedlings were grown in controlled environment chambers in pots of fine sand. Plants were irrigated with either non-saline or saline solutions over a 3-week period. After these treatments, plants were transferred to vessels containing a 5 m m15NO3K (96% atom excess15N) solution, and transpiration as well as concentration of15N and Cl−in roots, stem and leaves were measured after 24 h. Transpiration and15NO3−uptake rates were inhibited after exposure to NaCl and the concentration of salt pre-treatment determined the intensity of this inhibitory effect. To determine the effect of transpiration on NO3−absorption, net15NO3−uptake rate was measured in salt stressed and non-stressed plants exposed to different light intensities or relative humidities and also in detached roots. Reduction in NO3−uptake was more closely related to Cl−antagonism from salt stress than to reduced transpiration rate.

Effect of ammonium or nitrate nutrition on net photosynthesis, growth, and activity of the enzymes nitrate reductase and glutamine synthetase in blueberry, raspberry and strawberry

Blueberry, raspberry and strawberry may have evolved strategies for survival due to the different soil conditions available in their natural environment. Since this might be reflected in their response to rhizosphere pH and N form supplied, investigations were carried out in order to compare effects of nitrate and ammonium nutrition (the latter at two different pH regimes) on growth, CO2 gas exchange, and on the activity of key enzymes of the nitrogen metabolism of these plant species. Highbush blueberry (Vaccinium corymbosum L. cv. 13–16–A), raspberry (Rubus idaeus L. cv. Zeva II) and strawberry (Fragaria × ananassa Duch. cv. Senga Sengana) were grown in 10 L black polyethylene pots in quartz sand with and without 1% CaCO3 (w: v), respectively. Nutrient solutions supplied contained nitrate (6 mM) or ammonium (6 mM) as the sole nitrogen source. Compared with strawberries fed with nitrate nitrogen, supply of ammonium nitrogen caused a decrease in net photosynthesis and dry matter production when plants were grown in quartz sand without added CaCO3. In contrast, net photosynthesis and dry matter production increased in blueberries fed with ammonium nitrogen, while dry matter production of raspberries was not affected by the N form supplied. In quartz sand with CaCO3, ammonium nutrition caused less deleterious effects on strawberries, and net photosynthesis in raspberries increased as compared to plants grown in quartz sand without CaCO3 addition. Activity of nitrate reductase (NR) was low in blueberries and could only be detected in the roots of plants supplied with nitrate nitrogen. In contrast, NR activity was high in leaves, but low in roots of raspberry and strawberry plants. Ammonium nutrition caused a decrease in NR level in leaves. Activity of glutamine synthetase (GS) was high in leaves but lower in roots of blueberry, raspberry and strawberry plants. The GS level was not significantly affected by the nitrogen source supplied. The effects of nitrate or ammonium nitrogen on net photosynthesis, growth, and activity of enzymes in blueberry, raspberry and strawberry cultivars appear to reflect their different adaptability to soil pH and N form due to the conditions of their natural environment.

Cotton Seedling Root Growth Responses to Light Reflected to the Shoots from Straw‐Covered versus Bare Soil

Poor seedling establishment can severely impact cotton(Gossypium hirsutum L.) when grown in a double‐crop sequence following wheat(Triticum aestivum L.). My objective was to determinw whether the light spectrum reflected from wheat straw to the cotton seedlings could be a contributing factor. Cotton was planted in 3 L pots of loamy sand which was screened to remove old plant residue. Pots were arranged in groups of five and covered with 122‐ by 122‐ by 2‐ cm polystyrene foam insulation panels which had 5 ‐cm holes centered over each pot. Panels were covered with fresh wheat straw, weathered straw, or bare soil so that different far‐red to red( FR/R) light ratios were reflected. Insulation maintained the same soil temperature (±0.5) in all pots regardless of surface cover. Each pot was thinned to a single seedling that emerged on the same day. Leaf area and stem length were measured on seedlings cut at the soil surface 1 wk after emergenc. Roots were washed free of soil, spread on paper, covered with transparent plastic, and photocopied. Root lengths were measured on the photocopies. Stems, leaves, and roots from each plant were dried and weighed. The fresh wheat straw reflected the highest FR/R ratio and resulted in seedlings with the least root length, lowest root weight, longest stems, and lowest root/ shoot weight ratio. This 2‐yr glasshouse study show that the spectral environmen over fresh straw can contribute to modified seedling morphology and suggests that it should be considered when developing management practices for no‐till double‐crop cotton.

The synergism between SO 2 oxidation and manganese leaching on spruce needles — A chamber experiment

Four year old spruce ( Picea abies (L.) Karst.) seedlings were planted in sand pots and supplied with nutrient solution. Three groups were formed, differing only in manganese nutrition (0.5 ppm, 2.5 ppm, 12.5 ppm, respectively). After three months, five individuals of each group were transferred to a dew chamber. For the next seven weeks the trees were sprayed in the evenings, the relative humidity overnight was kept high and the droplets were collected directly from the needles in the mornings. The trees were sprayed with HNO 3 (pH 3.4) during the first three weeks to reduce the natural buffering capacity of the needles. After this time, the trees were sprayed with KCl (1 mM) solution, and NaHSO 3 was added to the chamber resulting in SO 2 concentrations usually between 50 and 150 μg m −3. Needles and water samples were analysed. Foliar Ca seemed to be only a short-time buffer even under optimal Ca supply. A highly significant influence of managanese supply on manganese in needles and droplets was observed, as well as on sulphate, H + and calcium concentrations in the droplets. The SO 2 flux to trees treated with 12.5 ppm Mn was about twice as high as to trees treated with 0.5 ppm Mn. The conclusion is that this is due to a synergism between manganese leaching and catalysis of the SO 2 oxidation by the leached Mn 2+ ions. The results suggest a positive feedback between (moderate) acidification of soils and SO 2 and NH 3 inputs to terrestrial ecosystems.

Utilization of Phosphorus Substrates by Contrasting Common Bean Genotypes

Phosphorus deficiency limits common bean (Phaseolus vulgaris L.) production in tropical soils, where P may be bound to recalcitrant organic matter, or with aluminum or iron oxides. In a previous study, we showed that P‐efficient genotypes perform well in contrasting soils, suggesting that interactions with specific soil constituents did not account for genetic variation. To confirm this finding, a study was done to determine if contrasting bean genotypes differ in their ability to recover P from different P compounds. Six genotypes were planted in pots of silica sand in which P was supplied at four levels as KH2PO4, CaHPO4, inositol hexaphosphoric acid (IP6), FePO4, or AIPO4. Most results could be explained as a function of relative aqueous solubilities of the P sources. KH2PO4 gave the greatest uptake and growth and FePO4 the least. No differences were observed in the ability of the six genotypes to acquire P from the Al, Fe, or IP6 sources. Andean genotypes, especially the Peruvian landrace G19833, extracted more P from CaHPO4 than Mesoamerican genotypes. G19833 was capable of acidifying the rhizosphere more than other genotypes. We conclude that (i) differential ability to mobilize P from Fe, Al, and organic ligands does not account for genetic variation in P efficiency, and (ii) Andean germplasm has superior ability to mobilize P from Ca sources, which may be useful in utilizing phosphate rock fertilizers.

Nitrogen availability to grain sorghum from organic and inorganic sources on sandy and clayey soil surfaces in a greenhouse pot study

In a greenhouse pot study, we examined the availability of N to grain sorghum from organic and inorganic N sources. The treatments were15N-labeled clover residues, wheat residues, and fertilizer placed on a sandy clay loam and loamy sand soil surface for an 8-week period. Soil aggregates formed under each soil texture were measured after 8 weeks for each treatment. Significantly greater 15N was taken up and recovered by grain sorghum in sandy clay loam pots compared with loamy sand pots. Greater 15N recovery was consistently observed with the inorganic source than the organic sources regardless of soil texture or time. Microbial biomass C and N were significantly greater for sandy clay loam soil compared with the loamy sand. Microbial biomass 15N was also significantly greater in the sandy clay loam treatment compared to the loamy sand. The fertilizer treatment initially had the greatest pool of microbial biomass 15N but decreased with time. The crop residue treatments generally had less microbial biomass 15N with time. The crop residues and soil texture had a significant effect on the water-stable aggregates formed after 8 weeks of treatments. Significantly greater water-stable aggregates were formed in the sandy clay loam than the loamy sand. Approximately 20% greater water-stable aggregates were formed under the crop residue treatments compared to the fertilizer only treatment. Soil texture seemed to be one of the most important factors affecting the availability of N from organic or inorganic N sources in these soils.