Shoot Growth Of Wheat Research Articles

Porous Minerals Improve Wheat Shoot Growth and Grain Yield through Affecting Soil Properties and Microbial Community in Coastal Saline Land

Soil salinization has become a major environmental factor severely threatening global food security. The application of porous minerals could significantly ameliorate soil fertility and promote plant productivity under salt stress conditions. However, the effects of porous minerals on improving the salt resistance of grain crops in coastal saline soils is not fully studied. In this work, the shoot growth and grain yield of wheat plants grown in coastal saline fields, respectively amended with the four naturally available porous minerals, diatomite, montmorillonite, bentonite and zeolite, were assessed. The application of porous minerals, especially zeolite, significantly improved the biomass and grain yield of wheat plants under saline conditions, as demonstrated by the augmented plant fresh mass (14.8~61.2%) and increased seed size (3.8~58.8%) and number (1.4~57.5%). Soil property analyses exhibited that porous-mineral amendment decreased soil sodium content and sodium absorption ratio, and increased soil nutrients in both the rhizosphere and nonrhizosphere of wheat plants. Further quantitative-PCR and 16S high-throughput sequencing analysis revealed that porous-mineral application also remarkably increased the abundance of bacterial 16S rRNA (0.8~102.4%) and fungal 18S rRNA (89.2~209.6%), and altered the composition of the soil microbial community in the rhizosphere of wheat. Our findings suggest that zeolite could be used as an ideal salt soil amendment, and the changes in soil properties and microorganisms caused by the application of porous minerals like zeolite improved the salt resistance of wheat plants in coastal saline land, leading to increased shoot growth and seed production.

Proper Delay of Phosphorus Application Promotes Wheat Growth and Nutrient Uptake under Low Phosphorus Condition

It is widely known that root morphology has different response mechanisms at different phosphorus (P) levels. However, the effects of P application times on wheat (Triticum aestivum L.) root morphology and, therefore, on growth and nutrient uptake are still unclear. In this study, we investigated the feedback from the physiological indexes of wheat on different P application times after planting. Compared with the P application at planting, the shoot biomass with delayed P application for 21 days (d) increased by 11.8% (p < 0.05). Compared with the P application at planting, the shoot P uptake with delayed P application for 14–21 days increased by 38.4–71.2%, while the shoot N uptake and K uptake with delayed P application for 21 days increased by 16.0% and 14.1% (p < 0.05). Compared with the P application at planting, P use efficiency, N use efficiency, and K use efficiency with delayed P application for 21 days increased by 16.4%, 12.4%, and 12.4%. Delayed P application for 14–21 days promoted wheat shoot growth, nutrient (P, N, and K) uptake, and their use efficiencies. This is particularly important for optimizing the P fertilizer input and nutrient management for wheat growth.

Exploring the relationship between deep roots and shoot growth of wheat under different soil moisture: A large soil column experiment 1

The root system is the main organ for crops to absorb water. Crops adjust the growth of underground roots to obtain the most suitable growth state according to environmental changes. However, there is still a lack of research on how deep root systems affect crop growth. Therefore, this study designed a soil column experiment with a 3 m transparent glass tube depth. The soil moisture was controlled to be 50% (W1, water shortage), 70% (W2, suitable), and 90% (W3, surplus) of the maximum field capacity, respectively, and cut off the deep root system under 50 cm at the jointing stage of wheat. To explore the growth state of the deep root system under different soil moisture and its effects on the photosynthetic characteristics, growth characteristics, yield, and water use efficiency of wheat. The results showed that the W1 and W3 treatments increased the length of the deep root system at the heading stage of wheat by 15.5% and 1.3%, respectively, compared with the W2 treatment. The root system of W1 is distributed in deeper soil, while the root system of W3 is more distributed at 50–80 cm. After root cutting, the root system grows fastest under W3, followed by W1, indicating that crop root growth is affected by soil moisture and crop demand characteristics. Unlike the root response, aboveground growth, photosynthetic physiology, and canopy temperature of wheat increased with soil moisture, suggesting that below-ground and aboveground crop growth is not synergistic under soil moisture limitation. Cutting roots reduced wheat yield by 15.3% under W1. However, under W3 treatment, root cutting would reduce the short-term water consumption of wheat, but it would cause the regrowth of underground roots and increase the growth of aboveground parts, increasing the total water consumption of crops. While under W2, cutting the root can reduce the water consumption while maintaining the wheat yield. Therefore, maintaining appropriate soil moisture by adjusting irrigation strategies is an important measure to regulate the growth of wheat underground and above ground and ensure efficient production. At the same time, crops pay more attention to the function of deep root systems when water is scarce.

Ionomic and metabolic responses of wheat seedlings to PEG-6000-simulated drought stress under two phosphorus levels.

BackgroundWheat (Triticum aestivum L.) is a major food crop worldwide. Low soil phosphorus content and drought are the main constraints on wheat production in Xinjiang, China.MethodsIn this study, the ionic and metabolic responses of one wheat variety (“Xindong20”) to drought stress simulated by using polyethylene glycol 6000 (PEG-6000) were investigated under low phosphorus (LP) and conventional phosphorus (CP) conditions by analysing wheat mineral elements and metabolites. Besides, due to xanthohumol was the metabolite with the most significant difference in expression detected in “Xindong 20”, two wheat variety “Xindong20 and Xindong 23” were selected to conduct the germination test simultaneously, to further verify the function of xanthohumol in wheat growth. Xanthohumol was mixed with PEG solution (20%) to prepare PEG solutions with different concentrations (0%, 0.1%, 0.5%, and 1%) of xanthohumol. Then wheat grains were soaked in the solutions for 20 hours, followed by a germination test. After 7 days, the indicators including shoot length, max root length, and root number were determined to identify whether the metabolite was beneficial to improve the drought tolerance of wheat.ResultsThe results showed that the root density and volume of wheat in LP treatment were higher than those in CP treatment. The roots underwent programmed cell death both in LP and CP treatments under PEG-6000-simulated drought stress, however, the DNA degradation in root cells in LP treatment was lower than that in CP treatment after rehydration for 3 d. Before drought stress, the malondialdehyde (MDA) content in shoot and the peroxidase (POD) activity in root in LP treatment were significantly higher than those in CP treatment, while the soluble sugar content and chlorophyll content in LP treatment were significantly lower than those in CP treatment. During drought stress, the POD activity maintained at a high level and the soluble sugar content gradually increased in LP treatment. After rehydration, the MDA content still maintained at a high level in LP treatment, the superoxide dismutase (SOD) activity increased, and the contents of soluble sugar and chlorophyll were significantly higher than those in CP treatment. The analysis of mineral elements and metabolites showed that the wheat in CP treatment was more sensitive to drought stress than that in LP treatment. Besides, the effect of drought stress was greater on shoot than on root in CP treatment, while it was opposite in LP treatment. The effect of drought stress on sugar metabolism gradually increased. Germination assays showed that 0.1% exogenous xanthohumol addition could significantly increase the shoot length of the two wheat varieties under drought stress.ConclusionAppropriate low phosphorus supply could increase antioxidant enzyme activity in wheat, and enhance sugar metabolism to regulate osmotic balance, as well as the accumulation of various organic acids to maintain the intracellular ion homeostasis. Therefore, compared to the conventional phosphorus supply level, appropriate low phosphorus supply can significantly improve the drought tolerance of wheat. Additionally, addition of 0.1% exogenous xanthohumol, an important differential expressed metabolite in drought-stressed wheat, could effectively promote wheat shoot growth under drought stress.

Subcellular Element Distribution in Shoots of Wheat Grown in an Acidic Soil with Native AMF Extraradical Mycelium

Soil acidity can reduce crop growth by increasing bioavailable soil Al, Fe, and/or Mn to toxic levels. The presence of an intact extraradical mycelium (ERM) of arbuscular mycorrhizal fungi (AMF), developed by the native Ornithopus compressus in the acidic soil, can increase wheat growth and prevent symptoms of Mn toxicity. To understand the protective effect of the intact ERM of this native plant on wheat element balance and distribution, in the present study, shoot Al, Fe, K, Zn, Na, and Si levels and their subcellular partitioning were determined by inductively coupled plasma mass spectrometry (ICP-MS), for the first time, for this system. In undisturbed soil, where an intact ERM structure is maintained, wheat shoot growth was promoted, probably due to faster root mycorrhizal colonization. The levels of potentially toxic Al and Fe were reduced, the proportions of the macronutrient K and micronutrient Zn were higher in the symplast, and the Na proportion increased in the vacuole, while Si increased in the apoplast. Overall, the undisturbed soil from O. compressus treatment appeared to influence the uptake and distribution of essential and beneficial elements, as a strategy to reduce the negative effect of soil acidity on wheat growth. Understanding the dynamics of element distribution influenced by stress-adapted AMF on wheat growth can provide more sustainable approaches to intensive agriculture.

The HMA2 Gene Expression in Leaves of Introgressive Wheat Lines under Zn Optimum and Deficiency Content in Root Environment.

In two introgressive lines of bread wheat (15-7-1 and 15-7-2), which differ in the allelic status of the Gpc-B1 gene, the expression of the gene encoding the HMA2 transport protein in flag leaves under optimum Zn content in substrate (2 µМ) and in its deficiency (0 µМ) was investigated. This is the first study to show that the plants carrying functional allele of the Gpc-В1 gene (line 15-7-1) have a higher level of TaHMA2 transcripts than the plants with nonfunctional allele of the Gpc-В1 gene (line 15-7-2) both at optimum Zn content in substrate and at its deficiency. Importantly, the high TaHMA2 gene expression did not affect the wheat shoot growth but correlated with a high Zn concentration in the aboveground part of plants. It is assumed that the NAC transcription factor encoded by the Gpc-В1 gene may be involved in the regulation of the ТаНМА2 gene expression.

Spatial allocation effects within a potentization basic research model – evidence for field-like effects of homeopathic preparations?

Background: The mode of action of ultramolecular homeopathic preparations is still unknown. Interactions between objects or entities can be grouped in four main general scientific categories: material, force-/field-like, entanglement-like or informational. Should homeopathic preparations have a field-like mode of action, there is greater probability of cross-contamination as long as the means to “shield” objects from each other is unknown. A field-like interaction would also lead to treatment at a distance effects that are distance-dependent. Aims: We analysed a set of experiments with Arsenicum album 45x treated wheat seedlings regarding a possible distance-dependent cross-contamination. Materials and Methods: We performed an a posteriori analysis of a set of 17 independent experiments [1,2] with wheat seedlings pre-treated with 1‰ arsenic. Three treatments were applied (Arsenicum album 45x, water 45x, or unpotentized water) with 150 seedlings in each treatment group per experiment. Seedlings were arranged in hanging plastic bags side-by-side in identically treated blocks of 10 seedlings. The 3x15 blocks were coded and randomly allocated to the three treatments. Wheat shoot length was measured after 7 days. Treatment effects were analysed as function of the position (1–10) within the blocks of 10 seedlings. Results: Analyzing all data, Arsenicum album 45x exerted an inhibiting effect (–3.2%, p=0.01) compared to both water and water 45x. When restricting the analysis to the outermost seedlings of all subgroups (pos. 1, 10), the treatment effect vanished (0.3%, p=0.92). In contrast, the innermost seedlings of all subgroups (pos. 5, 6) showed a treatment effect of –5.6% (p=0.02). Intermediate pairs of positions (pos. 2–4, 7–9) showed intermediate effects. Regarding shoot length, dependency on spatial position was observed for the plants of the water control groups, but not for the plants treated with Arsenicum album 45x. Conclusions: Whilst the effect of Arsenicum album 45x on wheat-shoot growth was not dependent on the spatial position within the subgroup, the water-control plants became smaller the closer they were to Arsenicum album 45x-treated seedlings. This observation is compatible with the existence of a field-like effect of homeopathic dilutions. Another possible explanation that cannot be ruled out by the present experiments, is contamination through the gas-phase. Future investigations of ultramolecular homeopathic preparations should control any such effects since they may mask treatment effects, leading to false-negative results. Closer investigation of the nature of this distance-dependent effect might contribute to identification of the mode of action of ultramolecular homeopathic preparations.

Effect of Triton X-100 on the wheat and lettuce growth and contaminant absorption

This study was set to study the effects of surfactants on crops using Triton X-100, one of widely used surfactants for various purposes including agricultural uses, as a target surfactant. The effects of Triton X-100 on the growth of wheat and lettuce were studied and the germination and shoot growth of wheat were not significantly affected by Triton X-100. With lettuce, the increasing Triton X-100 concentrations tend to negatively affect the growth, possibly due to the absorption of Triton X-100 by lettuce. The average lettuce fresh mass was reduced by 31% when Triton X-100 concentration increased from 0 to 240 mg L−1. This may mean that chemicals dissolved or mobilized by Triton X-100 can be absorbed by lettuce. The Cd mobilization was facilitated with Triton X-100, and the absorption of procymidone in soil by lettuce was greater when Triton X-100 was applied (i.e., 0.18 mg kg−1) than when water was applied (i.e., 0.15 mg kg−1), although they were statistically not different (p-value > 0.05). The average lettuce masses in the presence of residual procymidone in soil and Triton X-100 (16 g) were lower than that of the control soils (20 g), although they were statistically not different (p-value > 0.05). The results suggest that surfactants contained in pesticide formulations can potentially affect crop growth and absorption of other contaminants. Therefore, the residual surfactants and active ingredients in pesticide formulations need to be properly managed to protect the environment and to produce crops free of contaminants.

Role of alkyl silatranes as plant growth regulators: comparative substitution effect on root and shoot development of wheat and maize

The present investigation reports the stimulating effects of different substituted alkyl silatranes (3a-3e) on the early seedling growth of wheat (Triticum aestivum) and maize (Zea mays). Seeds of these plants were exposed to six different concentrations (0, 10, 50, 100, 200 and 500 µmol L-1 ). The results revealed that different substitutions (3a-3e) had different effects on root and shoot elongation. Silatranes (3a-3e) were synthesized employing microwave irradiation by a solvent-mediated transesterification reaction, thereby reducing reaction times from several hours under conventional reflux conditions to 15 min under microwave irradiation. It was of interest that the effect of these silatranes did not show a dose-dependent relationship but an optimum concentration, which was 100 µmol L-1 for maize and 200 µmol L-1 for wheat. γ-Aminopropyl silatranes (3b and 3e) gave the best results in maize, whereas γ-chloropropyl silatrane (3a) was most efficient for wheat at these optimum concentrations. All the synthesized silatranes were effective in promoting root and shoot growth of wheat and maize. Furthermore, an efficient green microwave methodology was successful for the synthesis of silatranes. These observations pave the way for silatranes as efficient plant growth regulators for crops. © 2018 Society of Chemical Industry.

Effect of Boron Toxicity on Oxidative Stress and Genotoxicity in Wheat (Triticum aestivum L.).

Boron (B) toxicity, which occurs in semi-arid and arid environments, can adversely affect the growth and yield of many plants. The aim of this study was to determine the effects of different concentrations of boric acid (3, 6, 9 and 12mM) on growth, oxidative stress and genotoxicity parameters in root and shoot tissues of wheat seedlings. Our results indicate that B stress inhibits root and shoot growth of wheat in a concentration-dependent manner, and leads to increases in TBARS and H2O2 contents in shoot tissue. Moreover, our findings suggest that high concentrations of B may exert a genotoxic effect on wheat. To the best of our knowledge, this is the first report to evaluate the effect of B stress on genotoxicity in both root and shoot tissues of wheat.

Phytotoxicity of soilborne glyphosate residues is influenced by the method of phosphorus fertiliser application

Glyphosate use has increased in recent decades with the adoption of minimum tillage techniques and the emergence of glyphosate-tolerant crop cultivars. There is evidence that glyphosate residues are common in cropping soils at sowing, but any potential impact of these residues on crop growth is not known. This study aimed to determine concentrations of soilborne glyphosate that are phytotoxic to common crop species and investigate any interactions between glyphosate residues and phosphorus (P) fertiliser. A pot study examined the impact of soilborne glyphosate residues on the growth of wheat (Triticum aestivum L.) and narrow leaf lupin (Lupinus angustifolius L) seedlings in a sandy soil with a low P buffering capacity in the absence or presence of P fertiliser applied as a liquid to the topsoil. A second pot study investigated whether the phytotoxic effects of soilborne glyphosate residues on lupin growth in the presence of P fertiliser could be mitigated by banding the P fertiliser (as superphosphate) as per standard practice by farmers. Wheat was more tolerant of glyphosate residues than lupin, with glyphosate levels up to 14.8 mg kg−1 having no effect on wheat shoot growth at 48 days after sowing (DAS), while lupin shoot growth at 48 DAS had an ED10 (i.e. a 10% yield reduction) of glyphosate at 6.4 mg kg−1 in the absence of P fertiliser. When P fertiliser was applied, wheat shoot biomass had an ED10 of 5.8 mg glyphosate kg−1 soil while lupins had an ED10 of 3.4 mg glyphosate kg−1 soil. When P fertiliser (superphosphate) was banded at sowing, lupins grown adjacent to band were unaffected by glyphosate whereas the shoot weights of lupins planted above the band were significantly reduced by 68% in soil containing 1.3 mg kg−1 glyphosate and 81% in soil containing 3.4 mg kg−1 glyphosate. Where P fertiliser was applied, growth reductions in lupin seedlings were observed at soil glyphosate concentrations that have been observed in farmers’ fields, suggesting that glyphosate residues may be problematic in sandy soils with low P buffering capacities. Banding of P fertiliser exacerbated, rather than mitigated, the phytotoxicity of glyphosate residues to lupins where P fertiliser was banded directly beneath the seed.

Effect of Postsowing Compaction on Cold and Frost Tolerance of North China Plain Winter Wheat

Improper postsowing compaction negatively affects soil temperature and thereby cold and frost tolerance, particularly in extreme cold weather. In North China Plain, the temperature falls to 5 degrees below zero, even lower in winter, which is period for winter wheat growing. Thus improving temperature to promote wheat growth is important in this area. A field experiment from 2013 to 2016 was conducted to evaluate effects of postsowing compaction on soil temperature and plant population of wheat at different stages during wintering period. The effect of three postsowing compaction methods—(1) compacting wheel (CW), (2) crosskill roller (CR), and (3) V-shaped compacting roller after crosskill roller (VCRCR)—on winter soil temperatures and relation to wheat shoot growth parameters were measured. Results showed that the highest soil midwinter temperature was in the CW treatment. In the 20 cm and 40 cm soil layer, soil temperatures were ranked in the following order of CW > VCRCR > CR. Shoot numbers under CW, CR, and VCRCR treatments were statistically 12.40% and 8.18% higher under CW treatment compared to CR or VCRCR treatments at the end of wintering period. The higher soil temperature under CW treatment resulted in higher shoot number at the end of wintering period, apparently due to reduced shoot death by cold and frost damage.

Enhanced root and shoot growth of wheat (Triticum aestivum L.) by Trichoderma harzianum from Turkey.

It is well known that Trichoderma species can be used as biocontrol and plant growth promote agent. In this study, Trichoderma harzianum isolates were evaluated for their growth promotion effects on wheat in greenhouse experiments. Two isolates of T. harzianum were used. The experimental design was a randomized complete block with three replications. Seeds were inoculated with conidial suspensions of each isolate. Wheat plants grown in steriled soil in pots. T. harzianum T8 and T15 isolates increased wheat length, root dry weight and shoot dry weight according to untreated control. Turkish isolates T8 and T15 did not produce damage in seeds nor in plants.

Alternative management of a problematic weed of wheat Avena fatua L. by metabolites of Trichoderma

Wild oat (Avena fatua L.) is a problematic weed of wheat (Triticum aestivum L.) in Pakistan. The present study was designed to evaluate the herbicidal activity of culture filtrates of four Trichoderma spp., namely T. harzianum, T. pseudokoningii, T. reesei and T. viride, against this weed species. In a laboratory bioassay, original (100%) and diluted (50%) culture filtrates of T. harzianum and T. pseudokoningii significantly reduced shoot and root growth of A. fatua seedlings. Only original culture filtrates of T. reesei exhibited significant effects, while the effect of filtrates of T. viride was insignificant against shoot and root growth of the target weed species. Generally, original concentrations of culture filtrates of all Trichoderma spp., except T. harzianum, significantly reduced various parameters of root and shoot growth of wheat seedlings. In foliar spray bioassay, pot-grown 1-wk and 2-wk old A. fatua and wheat seedlings were sprayed with 100% culture filtrates of the four Trichoderma spp. thrice with 5 d interval each. Culture filtrates of all except T. viride significantly diminished root and shoot biomass of A. fatua plants in 1-wk old plants. The effect of foliar spray on root and shoot growth of wheat was insignificant. Present study concludes that metabolites of T. harzianum, T. reesei and T. pseudokoningii contain herbicidal constituents for the management of A. fatua.

Legume residue influence arbuscular mycorrhizal colonisation and P uptake by wheat

Legumes have been shown to increase growth and P uptake of the following cereal. This could, in part, be due to nutrients released by the decomposing legume residues. To investigate the effect of P added with legume residues on wheat growth, P uptake and arbuscular mycorrhizal (AM) colonisation, a number of experiments were conducted with different legume residues added to a soil with low P availability under conditions in which N was not limiting. Young and mature faba bean shoots (FYS, FMS) and mature chickpea shoots (CP) were added to soil at different rates (0.5–2%, w/w) with the P concentration being the greatest in the young faba bean shoots and least in the mature chickpea residues. Other treatments included addition of inorganic P at different rates (0–80 mg P kg−1). Available P, growth and P uptake and AM colonisation of wheat were measured after 6 weeks. As expected, inorganic P addition increased growth and P uptake but decreased AM colonisation. The effect of the residues was more complex. AM colonisation was not correlated with available P in the soil amended with residues, whereas there was significant negative correlation between available P and AM colonisation in the treatments with inorganic P. Addition of FYS increased wheat shoot growth and P uptake and decreased AM colonisation. However, FMS and CP addition not only decreased wheat growth and P uptake but also AM colonisation despite low soil P availability. It is concluded that addition of some legume residues can improve the growth of subsequent cereals, but others have a negative effect on wheat growth and AM colonisation which cannot be explained solely by soil P availability.

Isopathic treatment effects of Arsenicum album 45x on wheat seedling growth – further reproduction trials

Two experimental studies on wheat preintoxicated with Arsenic trioxide yielded a significant shoot growth increase after an isopathic application of Ars-alb 45x. One independent reproduction trial however, yielded an effect inversion: wheat shoot growth was significantly decreased after application of Ars-alb 45x. In this study we investigated the role of three potential confounding factors on the experimental outcome: geographical location of the experiments, influence of the main experimenter, and seed sensitivity to Arsenic poisoning. Laboratory-internal reproducibility was assessed by meta-analysis. Wheat poisoned with Arsenic trioxide was cultivated in vitro in either Ars-alb 45x, water 45x, or unpotentised water. Treatments were blinded and randomised. Shoot length was measured after 7 days. The stability of the experimental set-up was assessed by systematic negative control (SNC) experiments. The SNC experiments did not yield significant differences between the three groups treated with unpotentised water. Thus the experimental set-up seemed to be stable. We did not observe any shoot growth increase after a treatment with Ars-alb 45x in any of the newly performed experiments. In contrast, the meta-analysis of all 17 experiments performed (including earlier experiments already published) yielded a statistically significant shoot growth decrease (-3.2%, p=0.017) with isopathic Ars-alb 45x treatment. This effect was quantitatively similar across all five series of experiments. Ultramolecular Ars-alb 45x led to statistically significant specific effects in arsenic poisoned wheat when investigated by two independent working groups. Effect size and effect direction differ, however. The investigated factors (geographical location, experimenter, seed sensitivity to Arsenic poisoning) did not seem to be responsible for the effect inversion. Laboratory external reproducibility of basic research into homeopathic potentisation remains a difficult issue.

Phosphorus acquisition and wheat growth are influenced by shoot phosphorus status and soil phosphorus distribution in a split‐root system

AbstractRoot proliferation and greater uptake per unit of root in the nutrient‐rich zones are often considered to be compensatory responses. This study aimed to examine the influence of plant phosphorus (P) status and P distribution in the root zone on root P acquisition and root and shoot growth of wheat (Triticum aestivum L.) in a split‐root soil culture. One compartment (A) was supplied with either 4 or 14 mg P (kg soil)–1, whereas the adjoining compartment (B) had 4 mg P kg–1 with a vertical high‐P strip (44 mg kg–1) at 90–110 mm from the plant. Three weeks after growing in the split‐root system, plants with 4 mg P kg–1 (low‐P plants) started to show stimulatory root growth in the high‐P strip. Two weeks later, root dry weight and length density in the high‐P strip were significantly greater for the low‐P plants than for the plants with 14 mg P (kg soil)–1. However, after 8 weeks of growth in the split‐root system, the two P treatments of compartment A had similar root growth in the high‐P strip of compartment B. The study also showed that shoot P concentrations in the low‐P plants were 0.6–0.8 mg g–1 compared with 1.7–1.9 mg g–1 in the 14 mg P kg–1 plants after 3 and 5 weeks of growth, but were similar (1.1–1.4 mg g–1) between the two plants by week 8. The low‐P plants had lower root P concentration in both compartments than those with 14 mg P kg–1 throughout the three harvests. The findings may indicate that root proliferation and P acquisition under heterogeneous conditions are influenced by shoot P status (internal) and soil P distribution (external). There were no differences in the total root and shoot dry weight between the two P treatments at weeks 3 and 5 because enhanced root growth and P uptake in the high‐P strip by the low‐P plants were compensated by reduced root growth elsewhere. In contrast, total plant growth and total root and shoot P contents were greater in the 14 mg P kg–1 soil than in the low‐P soil at week 8. The two P treatments did not affect the ratio of root to shoot dry weight with time. The results suggest that root proliferation and greater P uptake in the P‐enriched zone may meet the demand for P by P‐deficient plants only for a limited period of time.

Increased degradation of phenanthrene in soil by Pseudomonas sp. GF3 in the presence of wheat

A phenanthrene-degrading bacterial strain Pseudomonas sp. GF3 was examined for plant-growth promoting effects and phenanthrene removal in soil artificially contaminated with low and high levels of phenanthrene (0, 100 and 200 mg kg −1) in pot experiments. Low and high phenanthrene treatments significantly decreased the growth of wheat. Inoculation with bacterial strain Pseudomonas sp. GF3 was found to increase root and shoot growth of wheat. Strain GF3 was able to degrade phenanthrene effectively in the unplanted and planted soils. Over a period of 80 days the concentration of phenanthrene in soil in which wheat was grown was significantly lower than in unplanted soil ( p < 0.05 ). At the end of the 80-d experiments, 62.2% and 42.3% of phenanthrene had disappeared from planted soils without Pseudomonas sp. GF3 when the phenanthrene was added at 100 and 200 mg kg −1 soil, respectively, but 84.8% and 70.2% of phenanthrene had disappeared from planted soils with the bacterial inoculation. The presence of vegetation significantly enhances the dissipation of phenanthrene in the soil. There was no significant difference in soil polyphenol oxidase activities among the applications of 0, 100 and 200 mg kg −1 of phenanthrene. However, the enzyme activities in planted and unplanted soils inoculated with the strain Pseudomonas sp. GF3 were significantly higher than those of non-inoculation controls. The bacterial isolate was also able to colonize and develop in the rhizosphere soil of wheat after inoculation.

Solubilization of potassium-bearing minerals by a wild-type strain of Bacillus edaphicus and its mutants and increased potassium uptake by wheat

Two potassium (K)-bearing minerals, Nanjing feldspar and Suzhou illite, were used to investigate K mobilization by the wild-type strain NBT of Bacillus edaphicus, also labeled MPs+, selected for high activity in mobilizing potassium from minerals, and by four of its UV + LiCl mutants, MPs++, MPs+1, MPs+2, and MPs-. In liquid cultures, the five bacterial strains showed better growth on Suzhou illite than on Nanjing feldspar. Suzhou illite was the better potassium source for the growth of the wild type and the MPs++, MPs+1, and MPs+2 mutants. Solubilization of K from its sources by the wild-type NBT and the MPs++ mutant resulted mostly from the action of organic acids and capsular polysaccharides. Oxalic acid seemed to be a more active agent for the solubilization of Nanjing feldspar. Oxalic and tartaric acids were likely involved in the solubilization of Suzhou illite. The MPs- mutant did not produce any organic acid or capsular polysaccharide when grown on the above two K sources. In a pot experiment, wheat (Triticum aestivum L.) 'Yangmai-158' was grown in a yellow-brown soil that had low available K. After inoculation with bacterial strains, B. edaphicus NBT and its four mutants, MPs++, MPs+1, MPs+2, and MPs- (in separate tests), the root growth and shoot growth of wheat were significantly increased by B. edaphicus NBT and the mutants MPs++ and MPs+1. Bacterial inoculation also resulted in significantly higher N, P, and K contents of plant components. The bacteria were able to survive in the wheat rhizosphere soils after root inoculation.

Ammonium versus Nitrate Nutrition of Plants Stimulates Microbial Activity in the Rhizosphere

Using an alkaline calcareous soil, pot experiments were conducted to elucidate the effects of NH4 + vs. NO3 ) nutrition (50 or 100 mg kg )1 soil) of wheat and maize on microbial activity in the rhizosphere and bulk soils. Dicyandiamide was used as nitrification inhibitor to maintain NH4 + as the predominant N source for plants grown in NH4 + -treated soil. While maize grew equally well on both N sources, root and shoot growth of wheat was higher under NH4 + than under NO3 ) nutrition. Bacterial population density on roots, but not in the rhizosphere soil, was higher under NH4 + than under NO3 – supplied at 150 mg N kg )1 soil; whereas at both N levels applied, NH4 + compared to NO3 ) nutrition of wheat and maize significantly increased microbial biomass in the rhizosphere soil. Under both plant species, NH4 + vs. NO3 ) nutrition also increased aerobic and anaerobic respiration, and dehydrogenase activity in the rhizosphere. As microbial activity in the planted bulk and unplanted soils was hardly affected by the N-source, we hypothesize that the stimulation by NH4 + of the rhizosphere microbial activity was probably due to higher availability of root exudates under NH4 + than under NO3 ) nutrition.