Stomatal and nonstomatal regulation of water use in cotton, corn, and sorghum

Stomata of corn (Zea mays L.) and sorghum (Sorghum bicolor L.) responded to changes in leaf water potential during the vegetative growth phase. During reproductive growth, leaf resistances were minimal and stomata were no longer sensitive to bulk leaf water status even when leaf water potentials approached −27 bars. Stomata of corn, cotton (Gossypium hirsutum L.), and sorghum appear to respond to changes in the humidity deficit between the leaf and air and in this manner, regulated transpirational flux to some degree. Distinct differences in water transport efficiency were observed in the three species. Under nonlimiting soil water conditions, sorghum exhibited the greatest efficiency of water transport while under limiting soil moisture conditions, cotton appeared most efficient. Corn was the least efficient with respect to nonstomatal regulation of water use. Differences in drought tolerance among the three species are partially dependent on stomatal regulation of water loss, but efficiency of the water transport system may be more related to drought adaptation. This is particularly important since stomata of all three species did not respond to bulk leaf water status during a large portion of the growing season.     

A seed respiration-based index of cold-sensitivity during imbibition in four macrothermal species

A research was carried out to evaluate the influence of temperature on seed respiration response of maize, cotton, grain sorghum and sunflower during imbibition, and to define reliable indices for a fast evaluation of cold-sensitivity at germination level in plants. The seed respiration activity was measured during seed imbibition at 25 °C (optimal) and 15 °C (suboptimal) constant temperatures, using a homemade respiration chamber adapted to an infrared gas analyzer. At 15 °C, sunflower and sorghum maintained high levels of seed germination (≥90 %), whilst this last dropped in cotton (36.7 %) and maize (27.8 %). With respect to this, cotton and maize seem to be cold sensitive during germination. Instantaneous seed respiration during imbibition versus temperature or thermal time could not be used as a good indicator for cold tolerance, since the levels of CO₂ recorded at 15 °C in cotton (higher than the other species) and maize (similar to that of sorghum and sunflower) did not correspond to adequate seed germination. Differently, the rates (b coefficient of linear regressions) of accumulation of CO₂ respired at optimal and suboptimal temperatures during the first hours of imbibition (up to approximately 24 h from the start of experiment), were significantly different in maize and cotton, whilst they did not differ in sorghum and sunflower. Therefore, the shift between slopes may represent a reliable index for seed cold-sensitivity assessment during early germination.     

Changes in physiological,biochemical, and growth parameters of sorghum in the presence of phenanthrene

Physiological, biochemical, and growth parameters of sorghum (Sorghum bicolor (L.) Moench) plants grown in the presence of phenantrene (10 and 100 mg/kg soil) were examined. Activities of intracellular tyrosinases, peroxidases, and laccase-like oxidases were analyzed in 1 and 2 months after planting. The tyrosinase activity in root and leaf tissues correlated positively throughout the experiment with the level of soil pollution. The oxidase activity was apparent only in the first month; it also correlated positively with the concentration of phenanthrene. Intracellular peroxidases exhibited the highest activity; positive correlation of this activity with the level of soil contamination was observed in the first period of observations. The soil pollutant had a negative impact on growth characteristics (germination capacity, survival rate, and accumulation of plant biomass). In addition, soil contamination with phenanthrene reduced the total content of photosynthetic pigments and changed their ratio. The maximum extent of phenanthrene elimination in soil was found to occur in the root zone of sorghum plants at high-level contamination, which indicates a significant contribution of plants to the decomposition (binding) of this xenobiotic.     

Effects of crop rotation, tillage, and fertilizer applications on sorghum head insects

Rotations, tillage, and fertilizer treatments can affect yield, costs, and profitability in sorghum, Sorghum bicolor (L.) Moench, depending on their effects on pests. Rotation or planting different crops reduces soil erosion and pests that build up when a field is planted to the same crop each year. Minimum tillage reduces the number of trips over a field, lessening soil compaction and reducing costs. We examined the effects of fertilizer, tillage, and rotation with cotton, Gossypium hirsutum L., on sorghum head insects during three sampling periods each year from 2000 to 2003. We found that fertilizer treatments did not affect pests or predators. Also, predators were unaffected by rotation and tillage, which some years affected Helicoverpa zea (Boddie) and Oebalus pugnax (F.), both pests that feed on developing sorghum kernels, thereby reducing yield. In 2000, H. zea densities were greater in continuous sorghum, regardless of tillage practice, than in sorghum-cotton rotation. However, in 2003, H. zea densities were greater in minimum tillage plots within sorghum- cotton rotation than minimum tillage plots within continuous sorghum. In 2000, in sorghum- cotton rotation, O. pugnax densities were greater in minimum tillage than conventional tillage plots, whereas in continuous sorghum the opposite was true, O. pugnax were greater in conventional tillage. Also, O. pugnax were greater in sorghum- cotton rotation than in continuous sorghum. In 2002, O. pugnax densities were greater in conventional than minimum tillage plots. These results suggest that rotation of sorghum with cotton can sometimes reduce H. zea, but this reduction may occur with increased density of O. pugnax. Also, reducing tillage may reduce O. pugnax in some instances.     

Spatial and Temporal Variation of Roots, Arbuscular Mycorrhizal Fungi, and Plant and Soil Nutrients in a Mature Pinot Noir (Vitis vinifera L.) Vineyard in Oregon, USA

Soil and crop management practices may influence biomass growth and yields of cotton (Gossypium hirsutum L.) and sorghum (Sorghum bicolorL.) and sequester significant amount of atmospheric CO₂in plant biomass and underlying soil, thereby helping to mitigate the undesirable effects of global warming. This study examined the effects of three tillage practices [no-till (NT), strip till (ST), and chisel till (CT)], four cover crops [legume (hairy vetch) (Vicia villosa roth), nonlegume (rye) (Secale cerealeL), hairy vetch/rye mixture, and winter weeds orno covercrop], and three N fertilization rates (0, 60–65, and 120–130 kg N ha ^–1) on the amount of C sequestered in cotton lint (lint + seed), sorghum grain, their stalks (stems + leaves) and roots, and underlying soil from 2000 to 2002 in central Georgia, USA. A field experiment was conducted on a Dothan sandy loam (fine-loamy, kaolinitic, thermic, Plinthic Kandiudults). In 2000, C accumulation in cotton lint was greater in NT with rye or vetch/rye mixture but in stalks, it was greater in ST with vetch or vetch/rye mixture than in CT with or without cover crops. Similarly, C accumulation in lint was greater in NT with 60 kg N ha ^–1 but in stalks, it was greater in ST with 60 and 120 kg N ha ^–1 than in CT with 0 kg N ha ^–1. In 2001, C accumulation in sorghum grains and stalks was greater in vetch and vetch/rye mixture with or without N rate than in rye without N rate. In 2002, C accumulation in cotton lint was greater in CT with or without N rate but in stalks, it was greater in ST with 60 and 120 kg N ha ^–1 than in NT with or without N rate. Total C accumulation in the above- and belowground biomass in cotton ranged from 1.7 to 5.6 Mg ha ^–1 and in sorghum ranged from 3.4 to 7.2 Mg ha ^–1. Carbon accumulation in cotton and sorghum roots ranged from 1 to 14% of the total C accumulation in above- and belowground biomass. In NT, soil organic C at 0–10 cm depth was greater in vetch with 0 kg N ha ^–1 or in vetch/rye with 120–130 kg N ha ^–1 than in weeds with 0 and 60 kg N ha ^–1 but at 10–30 cm, it was greater in rye with 120–130 kg N ha ^–1 than in weeds with or without rate. In ST, soil organic C at 0–10 cm was greater in rye with 120–130 kg N ha ^–1 than in rye, vetch, vetch/rye and weeds with 0 and 60 kg N ha ^–1. Soil organic C at 0–10 and 10–30 cm was also greater in NT and ST than in CT. Since 5 to 24% of C accumulation in lint and grain were harvested, C sequestered in cotton and sorghum stalks and roots can be significant in the terrestrial ecosystem and can significantly increase C storage in the soil if these residues are left after lint or grain harvest, thereby helping to mitigate the effects of global warming. Conservation tillage, such as ST, with hairy vetch/rye mixture cover crops and 60–65 kg N ha ^–1 can sustain C accumulation in cotton lint and sorghum grain and increase C storage in the surface soil due to increased C input from crop residues and their reduced incorporation into the soil compared with conventional tillage, such as CT, with no cover crop and N fertilization, thereby maintaining crop yields, improving soil quality, and reducing erosion.     

Cs phytoremediation by Sorghum bicolor cultivated in soil and in hydroponic system

Cs accumulation characteristics by Sorghum bicolor were investigated in hydroponic system (Cs level at 50–1000 μmol/L) and in soil (Cs-spiked concentration was 100 and 400 mg/kg soil). Two varieties of S. bicolor Cowly and Nengsi 2# grown on pot soil during the entire growth period (100 days) did not show significant differences on the height, dry weight (DW), and Cs accumulation. S. bicolor showed the potential phytoextraction ability for Cs-contaminated soil with the bioaccumulation factor (BCF) and the translocation factor (TF) values usually higher than 1 in soil system and in hydroponic system. The aerial parts of S. bicolor contributed to 86–92% of the total removed amounts of Cs from soil. Cs level in solution at 100 μmol/L gave the highest BCF and TF values of S. bicolor. Cs at low level tended to transfer to the aerial parts, whereas Cs at high level decreased the transfer ratio from root to shoot. In soil, the plant grew well when Cs spiked level was 100 mg/kg soil, but was inhibited by Cs at 400 mg/kg soil with Cs content in sorghum reaching 1147 mg/kg (roots), 2473 mg/kg (stems), and 2939 mg/kg (leaves). In hydroponic system, average Cs level in sorghum reached 5270 mg/kg (roots) and 4513 mg/kg (aerial parts), without significant damages to its biomass at 30 days after starting Cs treatment. Cs accumulation in sorghum tissues was positively correlated with the metal concentration in medium.     

Above- and below-ground responses of C3–C4 species mixtures to elevated CO2 and soil water availability

We evaluated the influences of CO₂[Control, ～ 370 µ mol mol ^{? 1}; 200 µ mol mol ^{? 1} above ambient applied by free‐air CO₂ enrichment (FACE)] and soil water (Wet, Dry) on above‐ and below‐ground responses of C₃ (cotton, Gossypium hirsutum) and C₄ (sorghum, Sorghum bicolor) plants in monocultures and two density mixtures. In monocultures, CO₂ enrichment increased height, leaf area, above‐ground biomass and reproductive output of cotton, but not sorghum, and was independent of soil water treatment. In mixtures, cotton, but not sorghum, above‐ground biomass and height were generally reduced compared to monocultures, across both CO₂ and soil water treatments. Density did not affect individual plant responses of either cotton or sorghum across the other treatments. Total (cotton + sorghum) leaf area and above‐ground biomass in low‐density mixtures were similar between CO₂ treatments, but increased by 17–21% with FACE in high‐density mixtures, due to a 121% enhancement of cotton leaf area and a 276% increase in biomass under the FACE treatment. Total root biomass in the upper 1.2 m of the soil was not influenced by CO₂ or by soil water in monoculture or mixtures; however, under dry conditions we observed significantly more roots at lower soil depths ( > 45 cm). Sorghum roots comprised 81–85% of the total roots in the low‐density mixture and 58–73% in the high‐density mixture. CO₂‐enrichment partly offset negative effects of interspecific competition on cotton in both low‐ and high‐density mixtures by increasing above‐ground biomass, with a greater relative increase in the high‐density mixture. As a consequence, CO₂‐enrichment increased total above‐ground yield of the mixture at high density. Individual plant responses to CO₂ enrichment in global change models that evaluate mixed plant communities should be adjusted to incorporate feedbacks for interspecific competition. Future field studies in natural ecosystems should address the role that a CO₂‐mediated increase in C₃ growth may have on subsequent vegetation change.     

Soil and root populations of fluorescent Pseudomonas spp. associated with seedlings and field-grown plants are affected by sorghum genotype

Sorghum [Sorghum bicolor (L.) Moench] is valued for bioenergy, feed and food. Potential of sorghum genotypes to support differing populations of root- and soil-associated fluorescent Pseudomonas spp. or Fusarium spp., in two soils, was assessed. Culturable pseudomonads were enumerated from roots and soil of sorghum (Redlan and RTx433) and wheat (Lewjain) seedlings repeatedly grown in cycled soils in the growth chamber. Pseudomonads and Fusarium spp. were assessed from roots and soil of field-grown sorghum along with biological control traits hydrogen cyanide (HCN) and 2,4-diacetylphlorogluconol (phl) production. After four 4-week cycles, soil associated with Redlan seedlings had greater numbers of fluorescent pseudomonads than Lewjain. In dryland field conditions, RTx433 roots had greater numbers of pseudomonads than Redlan before anthesis but similar numbers after. There were no differences in numbers of pseudomonads from dryland soil or roots or soil of irrigated plants. Percentages of HCN-producing root isolates and phl soil isolates declined on irrigated Redlan plants, but percentages of HCN-producers increased in dryland conditions. Redlan roots had greater percentages of Fusarium isolates in the Gibberella fujikuroi complex. Results indicated that sorghum genotype affected root-associated populations of fluorescent Pseudomonas spp. and Fusarium spp. across soil environments.     

Effect of dew from cotton and soybean foliage on activity of Heliothis nuclear polyhedrosis virus

The ionic composition of dew collected from foliage of cotton and soybean plants as well as its potential for inactivation of Heliothis NPV were compared. Cotton dew had a mean pH of 8.8 and was more alkaline than soybean dew (pH 7.8). Cotton dew had a higher concentration of ions that did soybean dew but there was no qualitative difference in the cation content of dew from the two hosts. In bioassay tests, no loss of activity occurred when polyhedra were held in dew of either plant species. If the dew in which polyhedra were suspended was air-dried and resuspended daily in deionized water, polyhedra in soybean dew remained active but in cotton dew retained little activity after 7 days. Also, electron microscopical examination of polyhedra pelleted from these cotton dew preparations showed much dissolution after 7 days. Although there was dissolution of polyhedra in cotton dew when dried, an examination of polyhedra on the upper surface of either plant species in the field showed little degradation after 7 days.     

Water uptake efficiency and above- and belowground biomass development of sweet sorghum and maize under different water regimes

Background and aims

Lately sweet sorghum (S) has attracted great interest as an alternative feedstock for biofuel production due to its high yielding potential and better adaptation to drought than maize (M). However, little is known about the response of newly developed sweet sorghum genotypes to water deficits, especially at the root level and its water uptake patterns. The objective of this study was to compare the water uptake capacity, growth and developmental characteristics at the root and canopy levels of a sweet sorghum hybrid (Sorghum bicolor cv. Sucro 506) with those of maize (Zea mays cv. PR32F73) at two water regimes.

Methods

The trial was setup in a total of 20 rhizotrons (1?m³), where calibrated soil moisture probes were installed for monitoring and adjusting the soil moisture content to 25% (well-watered, W) and 12% (drought stress, D).

Results

DS was able to sustain its physiological activity close to that of WS plants, while maize was not. The biomass production potential of DS was reduced about 38%, while in maize the reduction was 47%. The water use efficiency (WUE), however, was increased by 20% in sweet sorghum and reduced in 5% in maize. Moreover, in contrast to maize the root length density and water uptake capacity of DS was enhanced. Root water uptake efficiency in DM was sustained close to its potential, but not in sweet sorghum.

Conclusions

In summary, the better adaptation to drought of sweet sorghum is explained by increased WUE, sustained physiological activity and enlarged root system. It is also associated with a reduced water uptake efficiency compared to its control but maintained compared to maize.     

Cellular anamnesis in earthworms

The quantitative response of coelomic cells associated with first- and second-set Eisenia xenografts transplanted to Lumbricus hosts at 20 ° C was compared with autografts and nonspecific wounds. Coelomocyte numbers were significantly lower in response to first than second-set xenografts. Coelomocytes also increased in association with autografts and nonspecific wounds, but the reaction is short lived, and essential for early wound healing and repair. Such nonspecific increases are different from subsequent specific immunologic longer-lasting coelomocyte responses. First-set xenografts induced a relatively slow increase in coelomocytes, which declined after 3–4 days postgrafting. By contrast, second-set xenografts caused an accelerated rise in coelomocytes, usually 20 to 30% greater than the maximum coelomocyte response induced by first-set xenografts. The mean survival time for first-set xenografts (non-self) was 17 ± 1 days, but repeat second-sets were rejected in an accelerated time of 6 ± 1 days. Autografts (self) are never destroyed. After priming with a first-set xenograft, this heightened coelomocyte reaction, to a second-set xenograft, was interpreted as an anamnestic response. The memory response is measurable in two ways: grossly as accelerated rejection of repeat xenografts, and at the cellular level, heightened coelomocyte numbers. Specific cellular immunity is demonstrable phylogenetically at the level of annelid worms.     

不同作物轮作对连作高粱生长及其根际土壤环境的影响

以高粱连作5年为对照(CK),研究了高粱连作3年轮作苜蓿(T₁)和葱(T₂),对下茬高粱生长、根际土壤微生物及土壤酶活性的影响.结果表明:与CK相比,轮作改善了高粱地上部的生长;T₁增产16.5%,效果明显.轮作也促进了高粱根系的生长,T₁和T₂处理的高粱总根长是CK的1.3和1.4倍,根总表面积是CK的1.6和1.5倍,根体积是CK的2.2和1.6倍,根系生物量是CK的2.0和1.3倍,T₁促进了根系在10 cm以下土层中的分布.借助Biolog法对穗花期根际土壤微生物群落功能多样性分析表明,T₁和T₂处理根际土壤微生物活性显著高于CK,且Shannon多样性指数分别是CK的1.2和1.1倍;轮作提高了根际土壤蔗糖酶活性.综上,轮作苜蓿比轮作葱更能改善高粱根际土壤环境,提高土壤微生物活性和酶活性,控制高粱连作障碍,提高高粱产量.     

A 2-Year Field Study Shows Little Evidence That the Long-Term Planting of Transgenic Insect-Resistant Cotton Affects the Community Structure of Soil Nematodes

Transgenic insect-resistant cotton has been released into the environment for more than a decade in China to effectively control the cotton bollworm (Helicoverpa armigera) and other Lepidoptera. Because of concerns about undesirable ecological side-effects of transgenic crops, it is important to monitor the potential environmental impact of transgenic insect-resistant cotton after commercial release. Our 2-year study included 1 cotton field where non-transgenic cotton had been planted continuously and 2 other cotton fields where transgenic insect-resistant cotton had been planted for different lengths of time since 1997 and since 2002. In 2 consecutive years (2009 and 2010), we took soil samples from 3 cotton fields at 4 different growth stages (seedling, budding, boll-forming and boll-opening stages), collected soil nematodes from soil with the sugar flotation and centrifugation method and identified the soil nematodes to the genus level. The generic composition, individual densities and diversity indices of the soil nematodes did not differ significantly between the 2 transgenic cotton fields and the non-transgenic cotton field, but significant seasonal variation was found in the individual densities of the principal trophic groups and in the diversity indices of the nematodes in all 3 cotton fields. The study used a comparative perspective to monitor the impact of transgenic insect-resistant cotton grown in typical ‘real world’ conditions. The results of the study suggested that more than 10 years of cultivation of transgenic insect-resistant cotton had no significant effects–adverse or otherwise–on soil nematodes. This study provides a theoretical basis for ongoing environmental impact monitoring of transgenic plants.     

Development of a viral insecticide: concept to commercialization

About 18 months ago, on December 8, 1970, the Food and Drug Administration officially granted the Heliothis nucleo polyhedrosis virus (NPV) the status of temporary exemption from requirement of a tolerance. This NPV, registered for use against Heliothis on cotton, has also been extensively tested on Heliothis species attacking corn, sorghum, tobacco and truck crops. This was the first time an insect virus had been officially registered by a federal agency for use as an insecticide. More recently Spain has registered this virus, and other governments also are in the process of registering the virus.The historical and technical development of this virus from concept to commercialization is the subject of this presentation. The virus, first isolated from diseased Heliothis attacking cotton in the Rio Grande Valley in Texas, was successfully developed through laboratory, pilot-plant, and commercial phases. At each phase the virus was evaluated on the basis of: (1) its safety to man, animals, and plants; (2) its production feasibility and costs; and (3) its effectiveness against the specific target pest. Currently, two companies (International Minerals and Chemical Corporation, Libertyville, Ill., and Nutrilite Products, Inc., Buena Vista, Calif.) are producing the Heliothis NPV under their trade names Viron/H and Biotrol VHZ, respectively, for experimental programs and for limited sales.     

套作棉根际与非根际土壤酶活性和养分的变化

在棉麦两熟双高产条件下研究了棉花根际与非根际土壤酶活性和养分含量的变化.结果表明,套作棉土壤脲酶、蔗糖酶、蛋白酶及过氧化氢酶活性随生育进程的变化趋势与单作棉表现一致,但整个生育期套作棉根际与非根际土壤各种酶活性均明显高于单作棉.套作棉根际与非根际土壤养分含量在麦棉共生期低于单作棉或差异较小,而在麦收后则显著高于单作棉.套作棉土壤养分含量随生育进程的变化趋势与单作棉大体相同,但一些养分的吸收高峰晚于单作棉.无论套作棉还是单作棉,根际土壤酶活性和养分含量高于非根际.土壤各养分含量与土壤脲酶、蔗糖酶和蛋白酶活性呈显著(P=0.0,n=32)或极显著(P=0.01,n=32)相关,与土壤过氧化氢酶活性相关不显著.     

Soil Solution Phosphorus Status and Mycorrhizal Dependency in Leucaena leucocephala

A phosphorus sorption isotherm was used to establish concentrations of P in a soil solution ranging from 0.002 to 0.807 μg/ml. The influence of P concentration on the symbiotic interaction between the tropical tree legume Leucaena leucocephala and the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus fasciculatum was evaluated in pot experiments. The level of mycorrhizal infection in Leucaena roots increased as the concentration of P was raised from 0.002 to 0.153 μg/ml. Higher levels of P depressed mycorrhizal infection, but the level of infection never declined below 50%. Periodic monitoring of P contents of Leucaena subleaflets indicated that significant mycorrhizal activity was detected as early as 17 days after planting, with the activity peaking 12 to 16 days thereafter. The highest level of mycorrhizal activity was associated with a soil solution P level of 0.021 μg/ml. Even though the mycorrhizal inoculation effect diminished as the concentration of P in the soil solution was increased, mycorrhizal inoculation significantly increased P uptake and dry-matter yield of Leucaena at all levels of soil solution P examined. The concentration of P required by nonmycorrhizal L. leucocephala for maximum yield was 27 to 38 times higher than that required by mycorrhizal L. leucocephala. The results illustrate the very high dependence of L. leucocephala on VAM fungi and the significance of optimizing soil solution phosphorus for enhancing the benefits of the VAM symbiosis.     

Possible role of alternative respiration in temperature rise of water stressed plants

Role of alternative respiration, a thermogenic pathway, was evaluated in temperature rise of water stressed plants. Transpiration rate, plant temperature and respiratory dynamics were monitored in field grown irrigated and unirrigated sorghum(Sorghum vulgare Pers.) hybrid CSH 6 and pearl millet(Pennirelum typhoider (Burm. f.) Stapt and Hubbard) var. J 104 for 22 days. Transpiration rate of irrigated plants was always higher than the unirrigated plants. But the plant temperature and the alternative respiration activity of irrigated plants was always lower than unirrigated plants. The reduction in transpiration rate of unirrigated pearl millet was more as compared to unirrigated sorghum. Nonetheless, alternative respiration activity was higher in unirrigated sorghum as compared to unirrigated pearl millet. Temperature of unirrigated sorghum plants increased by 10.4°C during 22 days and it was 8.0°C higher than irrigated sorghum at day 22. Stressed pearl millet showed an increase of 3.9°C during 22 days and it was 2.9°C higher than the irrigated pearl millet at day 22. It is suggested that the heat released because of the alternative respiration activity also contributes towards temperature rise of water stressed plants.     

Effect of sorghum seedlings, and previous crop, on soil fluorescent Pseudomonas spp.

Hypotheses in which sorghum seedlings [Sorghum bicolor (L.) Moench] of different genotypes will differentially modify soil microorganisms and will affect subsequent planting of wheat (Triticum aestivum L.) seedlings, were tested. Wheat cultivar Lewjain, and sorghum genotypes Redlan and RTx433, were planted into soils previously planted with wheat or sorghum in growth chamber experiments. Total culturable fungi and oomycetes, and fluorescent Pseudomonas spp. numbers (cfu) were determined. Pseudomonads were screened for hydrogen cyanide (HCN) production, for the presence of the phlD gene for 2,4-diacetylphloroglucinol production (Phl) and for a region of the operon involved in phenazine-1-carboxylic acid (PCA) production. Pasteurized soils were inoculated with rifampicin-marked strains of Pseudomonas fluorescens then planted with Lewjain, Redlan and RTx433 to assess rhizosphere and soil colonization. Effects of plant species, sorghum genotype and previous crop on culturable fungi and oomycetes, and pseudomonad numbers (cfu g^?1 soil) were statistically significant. Soils planted with RTx433 or Lewjain had greater numbers of fungal cfu than soils planted with Redlan. When Lewjain seedlings were grown in soil previously planted with RTx433, there were greater numbers of fungal cfu than when Lewjain was planted into Redlan soil. Wheat planted into wheat soil resulted in statistically significantly fewer numbers of pseudomonads than when planted into sorghum soil. Overall, percentages of HCN-producing pseudomonads increased, especially when wheat seedlings were planted in wheat soil. For most treatments, percent of isolates with Phl declined, except when Redlan was planted into Redlan soil, which resulted in increased Phl isolates. When rifampicin-marked P. fluorescens isolates were applied to pasteurized soil, sorghum seedlings sustained rhizosphere and soil populations similar to those on wheat. Sorghum genotypes may differ in associations with soil microorganisms, suggesting that they may differentially affect numbers of fluorescent pseudomonads in cropping systems.     

利用发光酶基因标记技术跟踪棉花根圈中的绿针假单胞菌PL9L

采用细菌转化和杂交的方法,成功地将全套发光酶基因标记系统Tn7luxCDABE引入绿针假单胞菌(Pseudomonas chlororaphis)PL9,得到稳定的发光标记菌PL9L。采用发光菌落平板计数法和X射线胶片自显影法,通过盆栽试验和盒裁试验,研究了发光标记菌PL9L在棉花根圈的定殖动态和分布规律。盆栽试验结果表明,在灭菌土盆栽中,播种后6d左右PL9L在棉花根圈的定殖水平达最高(31×109cfu/g根土),播种后56d左右趋向稳定,PL9L数量为17×102cfu/g根土;未灭菌土盆载中,播种后8d左右PL9L的定殖水平达最高(11×109cfu/g根土),46d左右趋向稳定,菌数为14×102cfu/g根土。盒栽试验结果表明,PL9L可从种子向根尖方向扩散,但并不与根的伸长生长同步,播种后36d,灭菌土盒栽中PL9L可扩散至种子下方120cm以内,而未灭菌土盒栽中PL9L扩散至110cm以内。在棉花根尖区域均未检测到PL9L。     

Chemistry and Microbial Functional Diversity Differences in Biofuel Crop and Grassland Soils in Multiple Geographies

We obtained soil samples from geographically diverse switchgrass (Panicum virgatum L.) and sorghum (Sorghum bicolor L.) crop sites and from nearby reference grasslands and compared their edaphic properties, microbial gene diversity and abundance, and active microbial biomass content. We hypothesized that soils under switchgrass, a perennial, would be more similar to reference grassland soils than sorghum, an annual crop. Sorghum crop soils had significantly higher NO₃ ^? -N, NH₄ ⁺ -N, SO₄ ^2? -S, and Cu levels than grassland soils. In contrast, few significant differences in soil chemistry were observed between switchgrass crop and grassland soils. Active bacterial biomass was significantly lower in sorghum soils than switchgrass soils. Using GeoChip 4.0 functional gene arrays, we observed that microbial gene diversity was significantly lower in sorghum soils than grassland soils. Gene diversity at sorghum locations was negatively correlated with NO₃ ^? -N, NH₄ ⁺ -N, and SO₄ ^2? -S in C and N cycling microbial gene categories. Microbial gene diversity at switchgrass sites varied among geographic locations, but crop and grassland sites tended to be similar. Microbial gene abundance did not differ between sorghum crop and grassland soils, but was generally lower in switchgrass crop soils compared to grassland soils. Our results suggest that switchgrass has fewer adverse impacts on microbial soil ecosystem services than cultivation of an annual biofuel crop such as sorghum. Multi-year, multi-disciplinary regional studies comparing these and additional annual and perennial biofuel crop and grassland soils are recommended to help define sustainable crop production and soil ecosystem service practices.