Petroleum-degrading microbial numbers in rhizosphere and non-rhizosphere crude oil-contaminated soil

Phytoremediation can be a cost-effective and environmentally acceptable method to clean up crude oil-contaminated soils in situ. Our research objective was to determine the effects of nitrogen (N) additions and plant growth on the number of total hydrocarbon (TH)-, alkane-, and polycyclic aromatic hydrocarbon (PAH)-degrading microorganisms in weathered crude oil-contaminated soil. A warm-season grass, sudangrass (Sorghum sudanense (Piper) Stapf), was grown for 7 wk in soil with a total petroleum hydrocarbon (TPH) level of 16.6 g TPH/kg soil. Nitrogen was added based upon TPH-C:added total N (TPH-C:TN) ratios ranging from 44:1 to 11:1. Unvegetated and unamended controls were also evaluated. The TH-, alkane-, and PAH-degrading microbial numbers per gram of dry soil were enumerated from rhizosphere and non-rhizosphere soil for vegetated pots and non-rhizosphere soil populations were enumerated from non-vegetated pots. Total petroleum-degrading microbial numbers were also calculated for each pot. The TH-, alkane-, and PAH-degrading microbial numbers per gram of dry soil in the sudangrass rhizosphere were 3.4, 2.6, and 4.8 times larger, respectively, than those in non-rhizosphere soil across all N rates. The presence of sudangrass resulted in significantly more TH-degrading microorganisms per pot when grown in soil with a TPH-C:TN ratio of 11:1 as compared to the control. Increased plant root growth in a crude oil-contaminated soil and a concomitant increase in petroleum-degrading microbial numbers in the rhizosphere have the potential to enhance phytoremediation.     

Differential Tolerance of Cool- and W arm-Season Grasses to TNT -Contaminated Soil

Plants can be used for effective and economical remediation of soil provided they are tolerant or resistant to the contaminants. Greenhouse experiments were conducted to determine the tolerance of the cool-season grasses: smooth bromegrass (Bromus inermus Leyss.) and tall fescue (Festuca arundinaceae Schreb), and the warm-season grasses: big bluestem (Andropogon gerardii Vitman) and switchgrass (Panicum virgatum L.) to TNT (2,4,6-trinitrotoluene) in soil. TNT-contaminated soil was mixed with uncontaminated soil to obtain water-extractable TNT concentrations ranging from 71 to 435 mg kg^-1, corresponding to acetonitrile-extractable concentrations of 278 to 3115 mg kg^-1. Germination, shoot and root dry weight, and root area were measured in response to TNT concentrations in the soil mixtures. Germination and height of the warm-season grass species were more sensitive than the cool-season grass species to increasing TNT concentrations in soil. Significant reductions in shoot and root growth were observed in cool-season grasses at lower TNT concentrations in soil compared with warm-season grasses in the soil mixtures. Results indicated that the warm-season grasses can be established in soil containing less than 86 mg of water-extractable TNT kg^-1, based on 80% of measured growth in uncontaminated control soil.     

Influence of organic and inorganic soil amendments on plant growth in crude oil-contaminated soil

Phytoremediation can be a viable alternative to traditional, more costly remediation techniques. Three greenhouse studies were conducted to evaluate plant growth with different soil amendments in crude oil-contaminated soil. Growth of alfalfa (Medicago sativa L., cultivar: Riley), bermudagrass (Cynodon dactylon L., cultivar: Common), crabgrass (Digitaria sanguinalis, cultivar: Large), fescue (Lolium arundinaceum Schreb., cultivar: Kentucky 31), and ryegrass (Lolium multiflorum Lam., cultivar: Marshall) was determined in crude oil-contaminated soil amended with either inorganic fertilizer, hardwood sawdust, papermill sludge, broiler litter or unamended (control). In the first study, the addition of broiler litter reduced seed germination for ryegrass, fescue, and alfalfa. In the second study, bermudagrass grown in broiler litter-amended soil produced the most shoot biomass, bermudagrass produced the most root biomass, and crabgrass and bermudagrass produced the most root length. In the third study, soil amended with broiler litter resulted in the greatest reduction in gravimetric total petroleum hydrocarbon (TPH) levels across the six plant treatments following the 14-wk study. Ryegrass produced more root biomass than any other species when grown in inorganic fertilizer- or hardwood sawdust + inorganic fertilizer-amended soil. The studies demonstrated that soil amendments and plant species selection were important considerations for phytoremediation of crude oil-contaminated soil.     

几种狼尾草属观赏植物在北京地区的生长特性

在北京地区气候条件下评价了狼尾草‘紫光’（Pennisetum alopecuroides（L．）Spreng‘Ziguang’）、绒毛狼尾草（Pennisetum setaceum（Forssk．）Chiov．）、羽绒狼尾草（Pennisetum villosum R．Br．ex Fresen）、狼尾草‘小兔子’（Pennisetum alopecuroides Desv．ex Ham‘Little Bunny’）和东方狼尾草（Pennisetum orientale Willd．ex Rich．）的田间生长状况、越冬存活率、根系生物量分布和繁殖特性。结果表明,这5种植物在北京地区气候条件下,能正常发芽、生长、抽穗、开花和结实。其中狼尾草‘紫光’、绒毛狼尾草植株高大,分蘖旺盛,盛花期花序高度达135CH和156cm,植株茎数达156和217个／株,地上生物量达608．7和535．3g/株,根系密集分布空间在距地表10～40cm,距茎秆0～30cm。狼尾草‘小兔子’和东方狼尾草株型矮小,株高为40cm,植株茎数分别为162和108个／株,地上生物量分别为124．2和39．8g／株,根系密集分布空间为距地表10～30cm,距茎秆15～30cm。羽绒狼尾草的茎秆半匍匐生长,分蘖能力强,盛花期花序高为79cm,植株茎数为389个／株,地上生物量高达619．9g／株,根系密集区为距地表0～30am,距茎秆0～30cm。狼尾草‘紫光’、狼尾草‘小兔子’和东方狼尾草在北京地区能安全越冬,成活率为100％,羽绒狼尾草和绒毛狼尾草在自然条件下不能越冬,成活率为0。5种狼尾草都可以播种和分株的方式扩繁。     

Rhizosphere interactions, carbon allocation, and nitrogen acquisition of two perennial North American grasses in response to defoliation and elevated atmospheric CO2

Carbon allocation and N acquisition by plants following defoliation may be linked through plant-microbe interactions in the rhizosphere. Plant C allocation patterns and rhizosphere interactions can also be affected by rising atmospheric CO(2) concentrations, which in turn could influence plant and microbial responses to defoliation. We studied two widespread perennial grasses native to rangelands of western North America to test whether (1) defoliation-induced enhancement of rhizodeposition would stimulate rhizosphere N availability and plant N uptake, and (2) defoliation-induced enhancement of rhizodeposition, and associated effects on soil N availability, would increase under elevated CO(2). Both species were grown at ambient (400 μL L(-1)) and elevated (780 μL L(-1)) atmospheric [CO(2)] under water-limiting conditions. Plant, soil and microbial responses were measured 1 and 8 days after a defoliation treatment. Contrary to our hypotheses, we found that defoliation and elevated CO(2) both reduced carbon inputs to the rhizosphere of Bouteloua gracilis (C(4)) and Pascopyrum smithii (C(3)). However, both species also increased N allocation to shoots of defoliated versus non-defoliated plants 8 days after treatment. This response was greatest for P. smithii, and was associated with negative defoliation effects on root biomass and N content and reduced allocation of post-defoliation assimilate to roots. In contrast, B. gracilis increased allocation of post-defoliation assimilate to roots, and did not exhibit defoliation-induced reductions in root biomass or N content. Our findings highlight key differences between these species in how post-defoliation C allocation to roots versus shoots is linked to shoot N yield, but indicate that defoliation-induced enhancement of shoot N concentration and N yield is not mediated by increased C allocation to the rhizosphere.     

Bacterial endophytes enhance phytostabilization in soils contaminated with uranium and lead

The combined use of plants and bacteria is a promising approach for the remediation of polluted soil. In the current study, the potential of bacterial endophytes in partnership with Leptochloa fusca (L.) Kunth was evaluated for the remediation of uranium (U)- and lead (Pb)-contaminated soil. L. fusca was vegetated in contaminated soil and inoculated with three different endophytic bacterial strains, Pantoea stewartii ASI11, Enterobacter sp. HU38, and Microbacterium arborescens HU33, individually as well as in combination. The results showed that the L. fusca can grow in the contaminated soil. Bacterial inoculation improved plant growth and phytoremediation capacity: this manifested in the form of a 22–51% increase in root length, 25–62% increase in shoot height, 10–21% increase in chlorophyll content, and 17–59% more plant biomass in U- and Pb-contaminated soils as compared to plants without bacterial inoculation. Although L. fusca plants showed potential to accumulate U and Pb in their root and shoot on their own, bacterial consortia further enhanced metal uptake capacity by 53–88% for U and 58–97% for Pb. Our results indicate that the combination of L. fusca and endophytic bacterial consortia can effectively be used for the phytostabilization of both U- and Pb-contaminated soils.     

Growth and Arbuscular Mycorrhizal Fungal Colonization of Two Prairie Grasses Grown in Soil from Restorations of Three Ages

I compared growth and arbuscular mycorrhizal fungal (AMF) colonization of two prairie grasses (Wild rye [Elymus canadensis] and Little bluestem [Schizachyrium scoparium]), an early‐ and a late‐dominating species in prairie restorations, respectively, grown in soil from restored prairies of differing age, soil characteristics, and site history. There were no consistent patterns between restoration age and soil inorganic nutrients or organic matter. The oldest restoration site had higher soil mycorrhizal inoculum potential (MIP) than 2‐ and 12‐year‐old restorations. However, MIP did not translate into actual colonization for two species grown in soils from the three restorations, nor did MIP relate to phosphorus availability. There were significant differences in root mass and colonization among Wild rye plants but not among Little bluestem plants grown in soils from the three restorations. Wild rye grown in 2‐year‐old restoration soil had significantly higher AMF colonization than when it was grown in soils from the 12‐ and 17‐year‐old restorations. Wild rye grown in 2‐year‐old restoration soil also had higher colonization than Little bluestem grown in 2‐ and 12‐year‐old restoration soils. Little bluestem had no significant correlations between shoot biomass, root biomass or colonization, and concentrations of soil P, total N, or N:P. However, for Wild rye, total soil N was positively correlated with root mass and negatively correlated with colonization, suggesting that in this species, mycorrhizae may affect N availability. Collectively, these results suggest that soil properties unrelated to restoration age were important in determining differences in growth and AMF colonization of two species of prairie grasses.     

镍胁迫下产铁载体细菌对花生的促生性

【目的】挖掘镍耐受性强、产铁载体活性高的植物根际促生细菌,研究镍胁迫下产铁载体细菌对花生的促生作用及其对花生吸收镍的影响。【方法】利用CAS(Chrome azurol S)培养基对花生根际产铁载体细菌定性筛选及定量测试获得产铁载体能力强的菌株,16S r RNA基因相似性及系统进化分析鉴定产铁载体细菌,并用含Ni~(2+)牛肉膏蛋白胨培养基测试细菌对Ni的耐受性;通过花生盆栽实验,测试花生的株高、根长、生物量、氮磷钾含量及镍含量来分析镍胁迫下产铁载体细菌对花生的影响。【结果】从花生根际分离筛选产铁载体芽孢杆菌5株,其中HSGJ1产铁载体能力最强,培养2 d后产156.56 mg/L的铁载体。HSGJ1对Ni~(2+)具有较强的耐受性,最小致死浓度为150 mg/L。在50、100 mg/kg的Ni~(2+)盆栽基质中,HSGJ1能够有效地促进花生的生长、增加花生的生物量及氮磷钾含量,并使花生根部和地上部分的镍含量降低。【结论】产铁载体芽孢杆菌HSGJ1是一株优良的植物根际促生细菌,可应用于镍污染农耕土壤的作物种植中,以提高作物在镍胁迫下的抗逆性,降低作物对镍的富集量,具有较好的应用价值。     

Soil temperature and flooding effects on two species of citrus

Summary Rough lemon (Citrus jambhiri Lush.) and sour orange (C. aurantium L.) seedlings were grown at constant soil temperatures of 16, 24, and 33 C for 3 months. Shoot and root growth of rough lemon was greatest at 33 C while growth of sour orange was greatest at 24 C. There were no significant effects of soil temperature on shoot: root ratio, leaf water potential or stomatal conductance. The hydraulic conductivity of intact root systems of both species was highest when seedlings were grown at 16 C. Thus, acclimation through greater root conductivity at low soil temperature may have compensated for decreased root growth at 16 C and negated effects of soil temperature on plant water relations. Half the plants growing at each soil temperature were subsequently flooded. Within 1 week, the soil redox potential (Eh) dropped below zero mV, reaching a minimum Eh of –250mV after 3 weeks of flooded conditions. Flooded plants exhibited lower root conductivity, a cessation of shoot growth, lower leaf water potentials, lower stomatal conductances, and visual sloughing of fibrous roots. Decreases in root conductivity in response to flooding were large enough to account for the observed decreases in stomatal conductance.Florida Agricultural Experiment Stations Journal Series No. 4080.     

Effects of species of VA-mycorrhizal fungi on growth and mineral uptake of sorghum at different temperatures

Sorghum [Sorghum bicolor (L.) Moench] plants were grown in growth chambers at 20, 25 and 30°C in a low P Typic Argiudoll (3.65 µg P g^–1 soil, pH 8.3) inoculated with Glomus fasciculatum, Glomus intraradices, and Glomus macrocarpum to determine effects of vesicular-arbuscular mycorrhizal fungi (VAMF) species on plant growth and mineral nutrient uptake. Sorghum root colonization by VAMF and plant responses to Glomus species were temperature dependent. G. macrocarpum colonized sorghum roots best and enhanced plant growth and mineral uptake considerably more than the other VAMF species, especially at 30°C. G. fasciculatum enhanced shoot growth at 20 and 25°C, and mineral uptake only at 20°C. G. intraradices depressed shoot growth and mineral uptake at 30°C. G. macrocarpum enhanced shoot P, K, and Zn at all temperatures, and Fe at 25 and 30°C above that which could be accounted for by increased biomass. Sorghum plant growth responses to colonization by VAMF species may need to be evaluated at different temperatures to optimize beneficial effects.     

The dependence of root system properties on root system biomass of 10 North American grassland species

Dependence of the properties of root systems on the size of the root system may alter conclusions about differences in plant growth in different environments and among species. To determine whether important root system properties changed as root systems aged and accumulated biomass, we measured three important properties of fine roots (tissue density, diameter, and C:N) and three biomass ratios (root:shoot, fine:coarse, and shallow:deep) of monocultures of 10 North American grassland species five times during their second and third years of growth. With increasing belowground biomass, root tissue density increased and diameter decreased. This may reflect cortical loss associated with the aging of roots. For non-legumes, fine root C:N decreased with increasing root biomass, associated with decreases in soil solution NO^{3 –} concentrations. No changes in fine root C:N were detected with increasing belowground biomass for the two legumes we studied. Among all 10 species, there were generally no changes in the relative amounts of biomass in coarse and fine roots, root:shoot, or the depth placement of fine roots in the soil profile as belowground biomass increased. Though further research is needed to separate the influence of root system size, age of the roots, and changes in nutrient availability, these factors will need to be considered when comparing root functional traits among species and treatments.     

Phytoremediation of arsenic contaminated soil by Pteris vittata L. II. Effect on arsenic uptake and rice yield

A greenhouse experiment evaluated the effect of phytoextraction of arsenic from a contaminated soil by Chinese Brake Fern (Pteris vittata L.) and its subsequent effects on growth and uptake of arsenic by rice (Oryza sativa L.) crop. Pteris vittata was grown for one or two growing cycles of four months each with two phosphate sources, using single super phosphate (SSP) and di-ammonium phosphate (DAP). Rice was grown on phytoextracted soils followed by measurements of biomass yield (grain, straw, and root), arsenic concentration and, uptake by individual plant parts. The biomass yield (grain, straw and rice) of rice was highest in soil phytoextracted with Pteris vittata grown for two cycles and fertilized with diammonium phosphate (DAP). Total arsenic uptake in contaminated soil ranged from 8.2 to 16.9 mg pot(-1) in first growing cycle and 5.5 to 12.0 mg pot(-1) in second growing cycle of Pteris vittata. There was thus a mean reduction of 52% in arsenic content of rice grain after two growing cycle of Pteris vittata and 29% after the one growing cycle. The phytoextraction of arsenic contaminated soil by Pteris vittata was beneficial for growing rice resulted in decreased arsenic content in rice grain of <1 ppm. There was a mean improvement in rice grain yield 14% after two growing cycle and 8% after the one growing cycle of brake fern.     

施氮对空心莲子草(Alternanthera philoxeroides)和莲子草(Alternanthera sessilis)种间关系的影响

自然界的氮素释放总是呈现出空间和时间上的异质性,但关于异质性氮释放对于入侵植物和本地植物种间关系影响的研究相对较少。将入侵植物空心莲子草(Alternanthera philoxeroides)和同属本地植物莲子草(Alternanthera sessilis)分别进行单种种植(12株,无种间竞争)和混种种植(每种6株,有种间竞争),模拟大气氮湿沉降设置由两种不同施氮总量(15g N m~(-2)a~(-1)和30g N m~(-2)a~(-1))和两种不同施氮频率(每5天1次和每15天1次)交叉组成的4种施氮处理,并以不施氮为对照。施氮总量的增加显著促进了两种植物的生长,但对两种植物的种间竞争关系没有显著影响。施氮频率对两种植物的生长以及种间竞争关系都没有显著影响。两种植物在面对竞争时表现出不同的生物量分配策略,空心莲子草将更多的生物量分配到茎,而莲子草将更多的生物量分配到根。在全球变化的背景下,大气氮湿沉降可能会改变两种植物的种群结构和动态,但可能对这两种植物的种间关系影响较小。     

Effects of inoculation of a plant growth promoting rhizobacterium <Emphasis Type="Italic">Burkholderia</Emphasis> sp. D54 on plant growth and metal uptake by a hyperaccumulator <Emphasis Type="Italic">Sedum alfredii</Emphasis> Hance grown on multiple metal contaminated soil

Batch experiments were designed to characterize a multiple metal resistant bacterium Burkholderia sp. D54 isolated from metal contaminated soils in the Dabaoshan Mine in South China, and a follow-up experiment was conducted to investigate the effects of inoculating the isolate on plant growth and metal uptake by Sedum alfredii Hance grown on soils collected from a heavily contaminated paddy field in Daxing County, Guangxi Zhuang Automounous Region, Southwest China. Our experiments showed that strain D54 produced indole acetic acid (IAA), siderophores, 1-aminocyclopropane-1-carboxylate (ACC) deaminase, and solubilizing inorganic phosphate and solubilized insoluble metal bearing minerals. Bacterial inoculation significantly enhanced S. alfredii biomass production, and increased both shoot and root Cd concentration, but induced little variation in root/shoot Pb concentration and shoot Zn concentration. Despite this, the total shoot and root uptake of Cd, Pb and Zn in S. alfredii inoculated with D54 increased greatly compared to the non-inoculated controls. It was concluded that inoculation with strain D54 could help S. alfredii grow better on metal contaminated soils, produce more biomass, and remove more metals from soil, which implies improved efficiency of phytoextraction from metal contaminated soil. The knowledge gained from the present experiments constitutes an important advancement in understanding of the interaction between plant growth-promoting bacteria and hyperaccumulators with regard to plant ability to grow and remove the multiple heavy metals from soils.     

Fermentability of eastern gamagrass, big bluestem and sand bluestem grown across a wide variety of environments

Plant biomass has attracted interest as a feedstock for biofuels production, but much of this work has been focused on relatively few plant species. In this study, three relatively-unstudied species of warm-season perennial grasses, grown at multiple locations in the eastern and central US and harvested over a three year period, were examined for fermentability via in vitro ruminal gas production and dry matter digestibility assays, and near-infrared reflectance calibrations were developed for these fermentation parameters. Big bluestem (Andropogon gerardii Vitman) displayed greater fermentability than did sand bluestem (Andropogon hallii Hack) or eastern gamagrass [Tripsacum dactyloides (L.) L.], but displayed lower biomass yields. The bluestems also displayed lower N contents and less variation in fermentability over different growth environments (geographic locations and harvest years), suggesting a more consistent biomass quality than for eastern gamagrass. Thus, in addition to their use as forage for ruminant animals, bluestems may be of particular interest as feedstocks for bioconversion to ethanol and other products via direct microbial fermentation (consolidated bioprocessing) schemes, and thus merit additional efforts to enhance biomass yield potential.     

Role of mycorrhizal infection in the growth and reproduction of wild vs. cultivated plants

Summary We tested the hypothesis that mycorrhizal infection benefits wild plants to a lesser extent than cultivated plants. This hypothesis stems from two observations: (1) mycorrhizal infection improves plant growth primarily by increasing nutrient uptake, and (2) wild plants often possess special adaptations to soil infertility which are less pronounced in modern cultivated plants. In the first experiment, wild (Avena fatua L.) and cultivated (A. sativa L.) oats were grown hydroponically at four different phosphorus levels. Wild oat was less responsive (in shoot dry weight) to increasing phosphorus availability than cultivated oat. In addition, the root: shoot ratio was much more plastic in wild oat (varying from 0.90 in the low phosphorus solution to 0.25 in the high phosphorus solution) than in cultivated oat (varying from 0.44 to 0.17). In the second experiment, mycorrhizal and non-mycorrhizal wild and cultivated oats were grown in a phosphorus-deficient soil. Mycorrhizal infection generally improved the vegetative growth of both wild and cultivated oats. However, infection significantly increased plant lifespan, number of panicles per plant, shoot phosphorus concentration, shoot phosphorus content, duration of flowering, and the mean weight of individual seeds in cultivated oat, while it had a significantly reduced effect, no effect, or a negative effect on these characters for wild oat. Poor positive responsiveness of wild oat in these characters was thus associated with what might be considered to be inherent adaptations to nutrient deficiency: high root: shoot ratio and inherently low growth rate. Infection also increased seed phosphorus content and reproductive allocation.     

Effect of Root and Shoot Meristem Temperature on Shoot to Root Dry Matter Partitioning and the Internal Concentrations of Nitrogen and Carbohydrates in Maize and Wheat

Maize (Zea mays L.) and spring wheat (Triticum aestivum L.)were grown in nutrient solution at uniformly high air temperature(20 °C), but different root zone temperatures (RZT 20, 16,12 °C). To manipulate the ratio of shoot activity to rootactivity, the plants were grown with their shoot base includingthe apical meristem either above (i.e. at 20 °C) or withinthe nutrient solution (i.e. at 20, 16 or 12 °C). In wheat, the ratio of shoot:root dry matter partitioning decreasedat low RZT, whereas the opposite was true for maize. In bothspecies, dry matter partitioning to the shoot was one-sidedlyincreased when the shoot base temperature, and thus shoot activity,were increased at low RZT. The concentrations of non-structuralcarbohydrates (NSC) in the shoots and roots were higher at lowin comparison to high RZT in both species, irrespective of theshoot base temperature. The concentrations of nitrogen (N) inthe shoot and root fresh matter also increased at low RZT withthe exception of maize grown at 12 °C RZT and 20 °Cshoot base temperature. The ratio of NSC:N was increased inboth species at low RZT. However this ratio was negatively correlatedwith the ratio of shoot:root dry matter partitioning in wheat,but positively correlated in maize. It is suggested that dry matter partitioning between shoot androots at low RZT is not causally related to the internal nitrogenor carbohydrate status of the plants. Furthermore, balancedactivity between shoot and roots is maintained by adaptationsin specific shoot and root activity, rather than by an alteredratio of biomass allocation between shoot and roots.Copyright1994, 1999 Academic Press Wheat, Triticum aestivum, maize, Zea mays, root temperature, shoot meristem temperature, biomass allocation, shoot:root ratio, carbohydrate status, nitrogen status, functional equilibrium     

Effects of earthworms and organic litter distribution on plant performance and aphid reproduction

Human management practices and large detritivores such as earthworms incorporate plant litter into the soil, thereby forming a heterogeneous soil environment from which plant roots extract nutrients. In a greenhouse experiment we investigated effects of earthworms and spatial distribution of ¹⁵N-labelled grass litter on plants of different functional groups [Lolium perenne (grass), Plantago lanceolata (forb), Trifolium repens (legume)]. Earthworms enhanced shoot and root growth in L. perenne and P. lanceolata and N uptake from organic litter and soil in all plant species. Litter concentrated in a patch (compared with litter mixed homogeneously into the soil) increased shoot biomass and ¹⁵N uptake from the litter in L. perenne and enhanced root proliferation in P. lanceolata when earthworms were present. Growth of clover (T. repens) was rather independent of the presence of earthworms and organic litter distribution: nevertheless, clover took up more nitrogen in the presence of earthworms and exploited more ¹⁵N from the added litter than the other plant species. The magnitude of the effects of earthworms and organic litter distribution differed between the plant species, indicating different responses of plants with contrasting root morphology. Aphid (Myzus persicae) reproduction was reduced on P. lanceolata in the presence of earthworms. We suggest that earthworm activity may indirectly alter plant chemistry and hence defence mechanisms against herbivores.     

Responses of Pinus clausa, Pinus serotina and Pinus taeda seedlings to anaerobic solution culture. I. Changes in growth and root morphology

Seedlings of pond pine ( Pinus serotina Michx.), sand pine [ P. clausa (Engelm.) Sarg.] and two edaphic seed sources of loblolly pine ( P. taeda L., dry- and wet-site seed sources) were grown in non-circulating, continuously flowing solution culture under aerobic (250 μ M O₂) and anaerobic (≤ 23 μ M O₂) conditions. Survival was 100% for all seedlings at 11 weeks. Although shoot height, biomass and leaf emergence of loblolly and pond pine seedlings were not significantly affected by 15 or 30 days of anaerobic growth conditions, root biomass was significantly reduced. Sand pine suffered the largest reduction in biomass, showing extensive root dieback and shoot chlorosis with retarded leaf development. These anaerobically induced symptoms of flooding injury were less severe in dry-site loblolly pine, and absent in wet-site loblolly and pond pine seedlings. Adventitious or new, secondary roots, and stem or taproot lenticels were particularly abundant under the 30-day anaerobic treatment in wet-site loblolly and pond pine seedlings, present to a lesser degree in dry-site loblolly pine, and nearly absent in sand pine seedlings. These results indicate that much of the immediate damage from flooding is due to the anoxic condition of the root rather than to the build-up of phytotoxins or soil nutrient imbalances. On the basis of overall seedling vigor, root plasticity and growth, we suggest the following flooding-tolerance/intolerance species (seed source) gradient: pond pine ≥ wet-site loblolly pine > dry-site loblolly pine > sand pine.     

丛枝菌根真菌对羊草生物量和氮磷吸收及土壤碳的影响

采用大田试验的方法在内蒙古锡林格勒草原进行牧草接种试验,通过灭菌和未灭菌两种土壤研究接种丛枝菌根真菌Glomus mosseae和Glomus claroidium对内蒙古典型草原优势种羊草生长的影响.结果显示,接种丛枝菌根真菌对羊草的地上部干重未产生显著影响,但向未灭菌土壤中接种能显著增加羊草根系量,同时接种G.mosseae显著增加了地上部的N、P含量及吸收量,有效地改善了植株N、P营养,提高了牧草品质;2种菌对根系的营养吸收影响不同,接种G.mosseae在灭菌土壤和未灭菌土壤中均能显著增加根系的N、P吸收量,而接种G.claroidium仅在土壤未灭菌状态下增加根系N、P吸收量;接种对土壤中的菌丝密度未产生显著影响,但接种后土壤中微生物量碳有增加的趋势,短期内难以观察到接种对土壤有机碳的影响.研究表明,丛枝菌根真菌能够提高牧草对N、P吸收,促进牧草的生长,改善牧草品质,增强牧草根际微生物量碳.