丛枝菌根真菌对红花生长及根际土壤微环境的影响

为提高红花产量与品质,通过田间试验研究了接种丛枝菌根真菌对红花生长、产量以及根际微环境的影响。试验设计4个处理:摩西球囊霉菌(Glomus mosseae)单菌接种组(GM)、根内球囊霉菌(Glomus intraradics)单菌接种组(GI)、G.mosseae与G.intraradices混合菌接种组(H)、不接种的对照组(CK),测定了红花伸长期的生物量、丛枝菌根真菌侵染率、土壤有机质含量、土壤酶活性、土壤pH值及根际土壤碱解氮、速效钾、有效磷含量等指标。结果表明:3个接种组丛枝菌根真菌均有侵染,混合菌接种组侵染率最大(69.00%);与对照组相比,接种组的生物量和产量均明显提高(P<0.05),其中接种混合菌的效果最大,红花生物量、花绒产量、单株籽粒质量比对照组分别提高35.67%、17.79%、24.86%;接种组根际土壤碱解氮含量、速效钾含量、全磷含量均降低,而土壤有机质含量、速效磷含量和磷酸酶活性均提高;红花生物量、产量、土壤有效磷含量、磷酸酶活性与丛枝菌根真菌侵染率呈显著正相关关系。说明红花丛枝菌根的形成改善了根际土壤微环境,提高了土壤肥力,从而促进红花生长,增加红花产量,根际效应与丛枝菌根真菌的种类有关。

Effect of Different Arbuscular Mycorrhizal Fungi Strains on Mineral Nutrition and Antioxidant Enzymes of Chrysanthemum morifolium

[Objective] The purpose was to study the effects of different arbuscular mycorrhizal fungi strains（AMF）on the mineral nutrition and antioxidant enzymes of Chrysanthemum morifolium.[Method] The pot experiment was conducted in the greenhouse,C.morifolium ＇Jinba＇ was inoculated with five kinds of AMF,N,P,K,malondial dehyde（MDA）content,as well as the superoxide dismutase（SOD）,peroxidase（POD） and catalase（CAT） activity in roots,leaves and petals of C.morifolium were measured at seedling and flowering stages.[Result] The G.i,G.e and G.m treatments could promote mineral nutrient absorption,increase N,P,K content in roots,leaves and petals of C.morifolium compared with the control without inoculation.The G.d、G.e and G.m treatments could significantly reduce MDA content in roots and petals,thus alleviating membrane permeability and lipid peroxidation.The G.i treatments could also improve the SOD,POD and CAT activities of C.morifolium,thereby increasing the capability of scavenging oxygen free radicals.[Conclusion] According to the comprehensive analysis,G.i was screened out as the best strain to improve mineral nutrition and antioxidant enzyme activities of C.morifolium.

Effects of Arbuscular Mycorrhizal Fungi on Upland Rice Oxidative Stress Induced by Cu and Pb Contamination in Soil

[Objective] This study aimed to investigate the effect of arbuscular mycor-rhizal fungi on upland rice oxidative stress induced by Cu and Pb contamination in soil. [Method] The upland rice seeds were sowed in pots, in which the soil was previously mixed with a certain amount of Glomus mosseae and 0, 100 and 200 mg/kg Cu, or 0, 300 and 600 mg/kg Pb. In the control treatment, Glomus mosseae was inactivated before mixed into the soil. Then, the physiological and chemical properties of the aboveground parts of rice plants were measured at mature stage. [Result] Compared with the control treatment （NM）, Glomus mosseae （GM） treat-ment inhibited the POD, CAT and SOD activity while increased the soluble protein content under 100 mg/kg Cu and 300 mg/kg Pb treatment, improved the POD and CAT activity and soluble protein content while decreased SOD activity under 200 mg/kg Cu. SOD and POD activity showed no significant difference between NM and GM treatment under 600 mg/kg Pb, but the CAT activity was enhanced and soluble protein content was decreased. [Conclusion] This study wil provide theoretical refer-ence for bioremediation of soil heavy metal pol ution.

Soil microbial community composition and its driving factors in alpine grasslands along a mountain elevational gradient

Understanding the vertical distribution patterns of soil microbial community and its driving factors in alpine grasslands in the humid regions of the Tibet Plateau might be of great significance for predicting the soil microbial community of this type of vegetation in response to environmental change. Using phospholipid fatty acids （PLFA）, we investigated soil microbial community composition along an elevational gradient （3094-4131 m above sea level） on Mount Yajiageng, and we explored the impact of plant functional groups and soil chemistry on the soil microbial community. Except for Arbuscular Mycorrhizal fungi （AM fungi） biomarker 18：2ω6,9 increasing significantly, other biomarkers did not show a consistent trend with the elevational gradient. Microbial biomass quantified by total PLFAs did not show the elevational trend and had mean values ranging from 1.64 to 4.09 ktmol per g organic carbon （OC）, which had the maximum value at the highest site. Bacterial PLFAs exhibited a similar trend with total PLFAs, and its mean values ranged from 0.82 to 1.81 μmol （g OC）-1. The bacterial to fungal biomass ratios had the minimum value at the highest site, which might be related to temperature and soil total nitrogen （TN）. The ratios of Gram-negative to Gram-positive bacteria had a significantly negative correlation with soil TN and had the maximum value at the highest site. Leguminous plant coverage and soil TN explained 58% of the total variation in the soil microbial community and could achieve the same interpretation as the whole model. Other factors may influence the soil microbial community through interaction with leguminous plant coverage and soil TN. Soil chemistry and plant functional group composition in substantial amounts explained different parts of the variation within the soil microbial community, and the interaction between them had no impact on the soil microbial community maybe beeause long-term grazing greatly reduces litter. In sum, although there were obvious differences in soil microbial communities along the elevation gradient, there were no clear elevational trends found in general. Plant functional groups and soil chemistry respectively affect the different aspects of soil microbial community. Leguminous plant coverage and soil TN had important effects in shaping soil microbial community.

Effects of arbuscular mycorrhizal fungi on carbon assimilation and ecological stoichiometry of maize under combined abiotic stresses

Arbuscular mycorrhizal fungi(AMF)enhance plant tolerance to abiotic stresses like salinity and improve crop yield.However,their effects are variable,and the underlying cause of such variation remains largely unknown.This study aimed to assess how drought modifed the effect of AMF on plant resistance to high calcium-saline stress.A pot experiment was performed to examine how AMF inoculation affects the growth,photosynthetic activity,nutrient uptake and carbon(C),nitrogen(N)and phosphorus(P)stoichiometric ratio(C:N:P)of maize under high calcium stress and contrasting water conditions.The results showed that high calcium stress signifcantly reduced mycorrhizal colonization,biomass accumulation,C assimilation rate and C:N stoichiometric ratio in plant tissues.Besides,the adverse effects of calcium stress on photosynthesis were exacerbated under drought.AMF inoculation profoundly alleviated such reductions under drought and saline stress.However,it barely affected maize performance when subjected to calcium stress under well-watered conditions.Moreover,watering changed AMF impact on nutrient allocation in plant tissues.Under well-watered conditions,AMF stimulated P accumulation in roots and plant growth,but did not induce leaf P accumulation proportional to C and N,resulting in increased leaf C:P and N:P ratios under high calcium stress.In contrast,AMF decreased N content and the N:P ratio in leaves under drought.Overall,AMF inoculation improved maize resistance to calcium-salt stress through enhanced photosynthesis and modulation of nutrient stoichiometry,particularly under water defcit conditions.These results highlighted the regulatory role of AMF in carbon assimilation and nutrient homeostasis under compound stresses,and provide signifcant guidance on the improvement of crop yield in saline and arid regions.

Arbuscular Mycorrhiza Prevents Suppression of Actual Nitrification Rates in the (Myco-)Rhizosphere of Plantago lanceolata

The vast majority of herbaceous plants engage into arbuscular mycorrhizal (AM) symbioses and consideration of their mycorrhizal status should be embodied in studies of plant-microbe interactions. To establish reliable AM contrasts, however, a sterilized re-inoculation procedure is commonly adopted. It was questioned whether the specific approach is sufficient for the studies targeting the bacterial domain, specifically nitrifiers, a group of autotrophic, slow growing microbes. In a controlled experiment mycorrhizal and non-mycorrhizal Plantago lanceolata were grown up in compartmentalized pots to study the AM effect on nitrification rates in the plant rhizosphere. Nitrification rates were assayed following an extensive 3-week bacterial equilibration step of the re-inoculated soil and a 13-week plant growth period in a controlled environment. Under these specific conditions, the nitrification potential levels at harvest were exceptionally low, and actual nitrification rates of the root compartment of non-mycorrhizal P. lanceolata were significantly lower than those of any other compartment. It is then argued that the specific effects should be attributed to the alleged higher growth rates of non-mycorrhizal plants that are known to occur early in the AM experiment. It is concluded that the specific experimental approach is not suitable for the study of microbes with slow growth rates.

Effect of Carbon and Nitrogen Availability on Metabolism of Amino Acids in Germinating Spores of Arbuscular Mycorrhizal Fungi

The effects of carbon （C） and nitrogen （N） sources on N utilization and biosynthesis of amino acids were examined in the germinating spores of the arbuscular mycorrhizal （AM） fungus Glomus intraradices Schenck ＆ Smith after exposure to various N substrates, CO2, glucose, and/or root exudates. The N uptake and de novo biosynthesis of amino acids were analyzed using stable isotopic labeling with mass spectrometric detection. High-performance liquid chromatography-based analysis was used to measure amino acid levels. In the absence of exogenous N sources and in the presence of 25 mL L^-1 CO2, the germinating AM fungal spores utilized internal N storage as well as C skeletons derived from the degradation of storage lipids to biosynthesize the free amino acids, in which serine and glycine were produced predominantly. The concentrations of internal amino acids increased gradually as the germination time increased from 0 to 1 or 2 weeks. However, asparagine and glutamine declined to the low levels; both degraded to provide the biosynthesis of other amino acids with C and N donors. The availability of exogenous inorganic N （ammonium and nitrate） and organic N （urea, arginine, and glutamine） to the AM fungal spores using only CO2 for germination generated more than 5 times more internal free amino acids than those in the absence of exogenous N. A supply of exogenous nitrate to the AM fungal spores with only CO2 gave rise to more than 10 times more asparagine than that without exogenous N. In contrast, the extra supply of exogenous glucose to the AM fungal spores generated a significant enhancement in the uptake of exogenous N sources, with more than 3 times more free amino acids being produced than those supplied with only exogenous CO2. Meanwhile, arginine was the most abundant free amino acid produced and it was incorporated into the proteins of AM funsal spores to serve as an N storage compound.

Nitrogen addition overrides the effects of Stellera chamaejasme litter on the growth of Leymus chinensis and its associated mycorrhizal fungi

Rapid spread and growth of plants that are poisonous to animals produce large amounts of plant litter in degraded grasslands.Nitrogen(N)input may promote the growth of these poisonous plants and alter the rhizosphere microbes and arbuscular mycorrhizal fungi(AMF)in particular.However,it is unclear how poisonous plant litter affects the growth of palatable plants and their associated AMF in the rhizosphere and whether and how N deposition may mediate these effects.A greenhouse experiment was performed to test the combined effects of litter addition of a poisonous plant,Stellera chamaejasme,and N addition on the growth of a dominant grass,Leymus chinensis,AMF characteristics and soil properties.Litter addition significantly increased the ramet number and aboveground biomass of L.chinensis and soil available phosphorus(AP)concentration and decreased the spore density of AMF.However,the interaction of both treatments had no significant effects on traits of L.chinensis and AMF properties.Stellera chamaejasme liter positively affected L.chinensis by increasing AP and negatively affected AMF by combining balanced changes in soil nutrients and litter-induced allelopathic compositions.High N addition may alleviate soil N limitation and inhibit litter decomposition,thus overriding the litter's effects on L.chinensis and AMF.These findings imply that it is necessary to objectively and comprehensively evaluate the ecological functions of poisonous plants beyond their harmful effects on livestock.Simultaneously,N deposition should be an indispensable factor in predicting the relationships between poisonous plants and edible plants indegraded grasslands.