丛枝菌根真菌对石漠化地区造林苗木生长的影响

西南石漠化地区生态环境脆弱,地表土壤贫瘠干旱,植被退化严重且恢复困难,当地造林苗木成活率低,抗逆性差。为提高石漠化地区造林苗木的成活率和生长,利用丛枝菌根真菌地表球囊霉(Glomus versiforme)和根内球囊霉(Rhizophagus intraradices)混合菌剂接种茶条木(Delavaya toxocarpa)、降香黄檀(Dalbergia odorifera)、香椿(Toona sinensis)、喜树(Camptotheca acuminata)和任豆(Zenia insignis)培育菌根苗,然后移栽于石漠化荒坡地,研究丛枝菌根真菌对造林苗木成活率和生长的影响。结果表明:苗木移栽一年后,5种苗木接菌处理菌根侵染率为48.5%~69.5%,均高于对照苗木;菌根苗木成活率比未接菌处理增加8.9%~14.9%,保存率比对照增加11.5%~22.6%;接菌处理株高比对照增加14.4%~44.6%,基径比对照增加7.6%~31.7%;接种丛枝菌根真菌促进了苗木养分吸收,接种植株磷含量显著高于未接种处理;接种苗木生物量显著高于未接种处理,5个树种中,香椿苗木菌根依赖性最高,达到26.0%,任豆苗木最低,为9.1%;菌根苗在石漠化生境下的成活率和生长速度高于非菌根苗,表明菌根苗木在石漠化地区植被修复中具有较好的应用前景。     

AM真菌对采煤沉陷区黄花菜生长及根际土壤养分的影响

于陕北黄土沟壑采煤沉陷区内布设试验小区,对黄花菜(Hemerocallis citrina Baroni)接种丛枝菌根真菌(arbuscular mycorrhizal fungi,AMF)—摩西管柄囊霉菌,通过测定黄花菜光合性能、植株生长、抗逆性、土壤养分含量、根际微生物数量等,揭示AM真菌对黄花菜生长和土壤养分的影响。结果表明,黄花菜种植3—5个月后,接种AM真菌显著提高了黄花菜株高、冠幅及其根系菌根侵染率、菌丝密度。与不接种对照区相比,接种AM真菌后黄花菜叶片的光合速率、可溶性糖含量和过氧化氢酶活性分别提高了51%、12%、79%。接种AM真菌处理区黄花菜根际土壤的电导率、有机质、碱解氮和速效钾含量等均显著高于对照区,细菌数量和磷酸酶活性的菌根贡献率分别达77%和24%。表明采煤沉陷区扰动土壤接种AM真菌具有增强土壤微生物活性、改善土壤肥力和提高黄花菜植株抗逆性的作用,对促进陕北黄土沟壑采煤沉陷区经济作物生长和提高土壤质量具有重要现实生态意义。     

接种菌根真菌对青冈栎幼苗耐旱性的影响

利用丛枝菌根真菌摩西球囊霉(Glomus mosseae)、根内球囊霉(Glomus intraradices)和外生菌根真菌彩色豆马勃(Pisolithus tinctorius)对石漠化地区造林树种青冈栎(Cyclobalanopsis glauca)幼苗进行接种试验。在大棚盆栽条件下模拟土壤干旱胁迫,研究菌根真菌对青冈栎生长和耐旱性的影响。结果表明:在土壤干旱条件下,接种菌根处理植株生物量显著高于未接种处理(P0.05),菌根依赖性随土壤水分含量降低而升高;未接种处理植株叶绿素含量在土壤干旱条件下显著降低(P0.05),除接种Pisolithus tinctorius处理外,其它接种处理叶绿素含量无显著变化。土壤干旱使植株体内脯氨酸和可溶性糖含量上升,在中度干旱条件下,接种处理可溶性糖含量均显著高于对照处理,接种Glomus intraradices、Pisolithus tinctorius处理脯氨酸含量显著低于对照(P0.05);在重度干旱条件下,接种Glomus mosseae和Glomus intraradices处理可溶性糖含量显著高于对照处理(P0.05),而相应的脯氨酸含量显著低于对照处理。当土壤水分含量在田间持水量55%—65%时,接种处理植株SOD、POD和CAT酶活性显著高于未接种处理(P0.05),在土壤水分含量降至35%—45%时,Glomus mosseae和Glomus intraradices处理SOD酶活性显著高于对照,并且所有接种处理POD酶活性均显著高于对照。此外,在水分干旱条件下,植株全磷和全钾含量也显著高于未接种处理(P0.05)。研究表明,丛枝菌根真菌和外生菌根真菌均能够侵染青冈栎幼苗根系;在干旱胁迫条件下,接种菌根真菌能够提高青冈栎植株生物量、抗氧化酶活性、增加植株可溶性糖含量和促进植株养分吸收,提高植株耐旱性,从而使青冈栎幼苗在岩溶干旱环境下更容易存活。     

接种微生物对大豆生长及其根际土壤的影响

对沙土中的大豆接种丛枝菌根真菌及丛枝菌根真菌与解磷菌和根瘤菌联合接种, 动态监测大豆的生长状况和营养吸收情况。结果表明, 在沙土中, 根瘤菌与丛枝菌根真菌的组合效应对豆科植物营养元素的改善最为有效。接种丛枝菌根真菌以及丛枝菌根真菌与其他微生物联合应用对宿主矿质营养吸收尤其是磷吸收有明显的促进作用, 种植30 d、45 d 和64 d 接菌处理植物叶片的平均全磷含量比对照分别高1.45%、73%和56%。接种微生物使植物从土壤中吸收氮、磷、钾元素的强度比对照高, 接菌植物根际土壤养分浓度低于对照。接菌植物生物量显著高于对照, 单接种丛枝菌根真菌处理、双接种丛枝菌根真菌与解磷菌、双接种丛枝菌根真菌与根瘤菌以及丛枝菌根真菌、解磷菌与根瘤菌三种菌剂混合处理的总生物量分别比对照高出181%、134%、153%和89%。丛枝菌根真菌与解磷菌和根瘤菌三种菌剂混合接种对植物的促生作用并不明显。     

红皮云杉外生菌根菌单接种及混合接种对苗木生长的影响

以提高外生菌根真菌对红皮云杉苗木促生长效果为目的,在前期研究的基础上,采用菌株配对培养的方法对获得的云杉外生菌根真菌进行混合接种菌株组合筛选;采用沟施菌剂方法,对3年生红皮云杉移床苗进行外生菌根菌菌株组合野外混合接种试验,同时以各菌株野外单接种作为对照,研究外生菌根真菌单接种及混合接种对红皮云杉苗木生长的影响。试验结果表明:供试菌株及菌株组合对红皮云杉苗木生长均有一定的促进作用。菌株L15促生长效果最佳,接种100d苗木高生长高于对照30.88%,地径高于对照15.29%。组合L15/025与L15/009促苗木生长效果低于单接种L15的效果,高于单接种009和025的效果。接种菌株010和组合L15/025的苗木与对照相比,叶绿素含量提高差异显著,叶绿素a水平分别高于对照59.15%、54.61%,叶绿素b水平分别高于对照76.34%和67.78%。除接种菌株010的苗木外,其他处理苗木其过氧化氢酶活性与对照相比均有所降低。所有处理苗木的根系活力均低于对照。综上,外生菌根菌高效菌株与一般菌株混合接种会弱化高效菌株自身接种效果;苗木过氧化氢酶活性、苗木根系活力与苗木的生物量间无相关性。     

水分胁迫下AM真菌对沙打旺生长和抗旱性的影响

利用盆栽试验研究了水分胁迫条件下接种AM真菌对优良牧草和固沙植物沙打旺(Astragalus adsurgens Pall.)生长和抗旱性的影响。在土壤相对含水量为70%、50%和30%条件下,分别接种摩西球囊霉(Glomus mosseae)和沙打旺根际土著菌,不接种处理作为对照。结果表明,水分胁迫显著降低了沙打旺植株(无论接种AM真菌与否)的株高、分枝数、地上部干重和地下部干重,并显著提高了土著AM真菌的侵染率,对摩西球囊霉的侵染率无显著影响。接种AM真菌可以促进沙打旺生长和提高植株抗旱性,但促进效应因土壤含水量和菌种不同而存在差异。不同水分条件下,接种AM真菌显著提高了植株菌根侵染率、根系活力、地下部全N含量和叶片CAT活性。土壤相对含水量为30%和50%时,接种株地上部全N、叶片叶绿素、可溶性蛋白、脯氨酸含量和POD活性显著高于未接种株;接种AM真菌显著降低了叶片MDA含量;接种土著AM真菌的植株株高、分枝数、地上部和地下部干重显著高于未接种株。土壤相对含水量为30%时,接种AM真菌显著增加了地上部全P含量和叶片相对含水量;接种摩西球囊霉的植株株高、分枝数、地上部和地下部干重显著高于未接种株。水分胁迫40d,接种AM真菌显著提高了叶片可溶性糖含量。水分胁迫80d,接种株叶片SOD活性显著增加。菌根依赖性随水分胁迫程度增加而提高。沙打旺根际土著菌接种效果优于摩西球囊霉。水分胁迫和AM真菌的交互作用对分枝数、菌根侵染率、叶片SOD、CAT和POD活性、叶绿素、脯氨酸、可溶性蛋白、地上部全N和全P、地下部全N和根系活力有极显著影响,对叶片丙二醛和地下部全P有显著影响。AM真菌促进根系对土壤水分和矿质营养的吸收,改善植物生理代谢活动,从而提高沙打旺抗旱性,促进其生长。试验结果为筛选优良抗旱菌种,充分利用AM真菌资源促进荒漠植物生长和植被恢复提供了依据。     

模拟岩溶旱钙土壤基质中AM真菌对玉米幼苗光合生长的影响

利用盆栽试验,探讨了AM真菌在模拟岩溶区干旱、高钙及其双重胁迫的土壤基质中对玉米幼苗光合生长的影响。结果表明:玉米幼苗的菌根侵染率在不同处理下的大小顺序为对照干旱双重胁迫高钙。无论接种与否,干旱、高钙及其双重胁迫均导致玉米幼苗生物量、净光合速率下降。未接种AM真菌条件下,玉米幼苗生物量在干旱、高钙及其双重胁迫下较对照分别低3.2%、63.7%、76.0%,净光合速率较对照分别低33.4%、86.9%、98.8%;接种AM真菌条件下,玉米幼苗生物量在干旱、高钙及其双重胁迫下较对照分别低16.3%、78.4%、80.2%,净光合速率较对照分别低9.7%、92.8%、91.7%。与同种条件下的非菌根植株相比,干旱及双重胁迫下的菌根植株生物量、叶绿素含量、光合蒸腾速率、最大光化学效率,以及P吸收均呈上升趋势;高钙胁迫下的菌根植株叶绿素含量、最大光化学效率有所增加,但生物量、光合蒸腾速率以及N、P的吸收未体现菌根促进效应。AM真菌与干旱及双重胁迫的交互作用对玉米幼苗的净光合速率影响显著,与高钙交互作用对玉米幼苗净光合速率无显著影响。AM真菌能够通过促进玉米幼苗N、P吸收及叶绿素含量增加,光化学效率、气孔导度增大,从而提高玉米幼苗光合作用能力促进生长。实验结果对岩溶生态系统中合理利用菌根技术及制定合理的农业生产措施具有重要的理论和实践意义。     

接种乳黄粘盖牛肝菌和荧光假单胞菌对油松苗生长及猝倒病的影响

在盆栽条件下研究了单接种外生菌根真菌乳黄粘盖牛肝菌(SL)、单接种荧光假单胞菌(PF)、双接种(SL+PF)和不接种菌剂(CK)4个处理对油松苗生长、盆栽土壤指标、油松苗生理生化指标及猝倒病发生的影响.结果显示:(1)不同接种处理的油松苗成活率、生长状况及根系活力均高于对照,且SL+PF促生效果最好,其成活率、苗高、地径、地上干重、总干重及根系活力分别比对照提高22.10%、36.16%、44.86%、124.14%、161.54%和100%.(2)双接种可同时有效提高土壤酶活性和土壤养分含量,土壤脲酶、碱性磷酸酶和蔗糖酶活性均与速效氮、速效磷和有机碳呈显著或极显著正相关.(3)接种病原菌前后油松苗的MDA含量表现为CK>PF>SL>SL+PF,SOD、CAT和PAL活性均为SL+PF>SL>PF>CK,但接种病原菌前后不同处理酶活性增长幅度不同,CAT和PAL活性均以SL+PF增幅最大,分别比对照增长76.18%和112.64%.(4)接种处理的油松苗猝倒病发病率及病情指数均低于对照,且以SL+PF抗病效果最好,分别比对照降低60.94%和70.55%.研究表明,接种菌根真菌可有效提高土壤酶活性和土壤养分含量,增强植株体内的抗氧化酶活性,从而促进油松苗生长,抑制猝倒病的发生,菌根促生菌荧光假单胞菌增强了菌根真菌的作用.     

基于五室培养法的接菌紫花苜蓿受损根系模拟修复研究

本研究以紫花苜蓿为寄主植物,采用五室培养系统按照根系在土壤中分布的体积比例定量模拟根系损伤,初步探讨紫花苜蓿和菌根真菌共生体的协同修复作用及其生态效应。结果表明,在不同的试验设计中,接种菌根有效地缓解了根系损伤带来的不利影响,双侧接菌在植株生物量、菌根侵染效果以及收集到的矿质元素浓度等均高于单侧接菌和对照,土壤有效磷含量在伤根前后仍维持在10 mg/kg。接菌改善了紫花苜蓿根际微环境,在一定程度上减缓根系损伤对植物的负面影响,有利于采煤沉陷区地表植被的修复。     

接种不同VA菌根真菌对红三叶草利用不同磷源的影响

以红三叶草为材料,利用三室隔网培养方法,研究了施用不同磷源条件下,接种VA菌根真菌(Glomusmosseae和Glomusversiforme)对外加有机磷源及土壤有机磷的利用效率.植物生长10周后,测定植株干物重、含磷量、菌根侵染率及根系长度.结果表明接种菌根真菌能明显增加植株干物重和含磷量.接种条件下无机磷(KH2PO4)对植株生长的促进作用大于有机磷(Na-phytate)处理,接种Glomusversoiforme的作用明显大于接种Glomusmosseae.接种Glomusmosseae,植株对磷酸二氢钾中磷的吸收量明显大于植酸钠,而接种Glomusversiforme时则植株对植酸钠的磷吸收量明显高于磷酸二氢钾.上述结果说明接种两菌种对不同磷源的作用不同,接种Glomusmosseae可提高磷酸二氢钾中磷的利用率,接种Glomusversiforme则可提高对植酸钠的磷利用率.     

Arbuscular mycorrhiza can depress translocation of zinc to shoots of host plants in soils moderately polluted with zinc

There is increasing and widespread interest in the maintenance of soil quality and remediation strategies for management of soils contaminated with organic pollutants and trace metals or metalloids. There is also a growing body of evidence that arbuscular mycorrhizal (AM) fungi can exert protective effects on host plants under conditions of soil metal contamination. Research has focused on the mechanisms involved and has raised the prospect of utilizing the mutualistic association in soil re-vegetation programmes. In this short paper we briefly review this research, summarize some recent work and highlight some new data which indicate that the alleviation of metal phytotoxicity, particularly Zn toxicity, by arbuscular mycorrhiza may occur by both direct and indirect mechanisms. Binding of metals in mycorrhizal structures and immobilization of metals in the mycorrhizosphere may contribute to the direct effects. Indirect effects may include the mycorrhizal contribution to balanced plant mineral nutrition, especially P nutrition, leading to increased plant growth and enhanced metal tolerance. Further research on the potential application of arbuscular mycorrhiza in the bioremediation or management of metal-contaminated soils is also discussed.     

The mobilisation and fate of soil and rock phosphate in the rhizosphere of ectomycorrhizal Pinus radiata seedlings in an Allophanic soil

A pot experiment was conducted to investigate the uptake of Zn from experimentally contaminated calcareous soil of low nutrient status by maize inoculated with the arbuscular mycorrhizal (AM) fungus Glomus caledonium. EDTA was applied to the soil to mobilize Zn and thus maximize plant Zn uptake. The highest plant dry matter (DM) yields were obtained with a moderate Zn addition level of 300 mg kg^?1. Plant growth was enhanced by mycorrhizal colonization when no Zn was added and under the highest Zn addition level of 600 mg kg^?1, while application of EDTA to the soil generally inhibited plant growth. EDTA application also increased plant Zn concentration, and Zn accumulation in the roots increased with increasing EDTA addition level. The effects of inoculation with G. caledonium on plant Zn uptake varied with Zn addition level. When no Zn was added, Zn translocation from roots to shoots was enhanced by mycorrhizal colonization. In contrast, when Zn was added to the soil, mycorrhizal colonization resulted in lower shoot Zn concentrations in mycorrhizal plants. The P nutrition of the maize was greatly affected by AM inoculation, with mycorrhizal plants showing higher P concentrations and P uptake. The results indicate that application of EDTA mobilized soil Zn, leading to increased Zn accumulation by the roots and subsequent plant toxicity and growth inhibition. Mycorrhizal colonization alleviated both Zn deficiency and Zn contamination, and also increased host plant growth by influencing mineral nutrition. However, neither EDTA application nor arbuscular mycorrhiza stimulated Zn translocation from roots to shoots or metal phytoextraction under the experimental conditions. The results are discussed in relation to the environmental risk associated with chelate-enhanced phytoextraction and the potential role of arbuscular mycorrhiza in soil remediation.     

水分胁迫下丛枝菌根真菌对枳实生苗生长和渗透调节物质含量的影响

采用盆栽试验研究了水分胁迫下接种丛枝菌根真菌摩西球囊霉(Glomaus mosseae)对枳[Poncirustrifoliat(L.)Raf.]实生苗的生长和渗透调节物质含量的影响.结果表明,在土壤含水量为20%、16%和12%条件下,接种G.mosseae能够增加植株的生长(株高、茎粗、叶面积、地上部干重、地下部干重和植株干重),促进植株根系活跃吸收面积和根际土壤有效磷的吸收,提高叶片和根系可溶性糖含量的积累,降低叶片脯氨酸含量,增强植株的水分利用效率(达20%～40%),使枳实生苗的抗旱能力得到增强.土壤含水量为20%和16%条件下接种G.mosseae对植株的效果较土壤含水量为12%条件下更显著.12%的土壤含水量严重抑制Gmosseae的侵染,说明丛枝菌根侵染程度轻,其对植物的效果也差.     

丛枝菌根真菌对植物生长影响的研究

菌根是自然界中一种极为普遍和重要的共生现象,其中分布最为广泛的菌根类型就是丛枝菌根,可以增强植物从土壤中获取水分的能力,改善植物根系对磷、镉等矿质元素及养分的吸收,从而促进植物的生长。本文综述了丛枝菌根真菌对植物生长影响的概况。有关丛枝菌根真菌对植物水分和矿质营养的利用,尤其是磷素营养的研究较为深入,而对植物光合特性的研究较少,这些研究工作为深入理解菌根真菌与植物的相互关系提供基础资料。     

Does the sequence of plant dominants affect mycorrhiza development in simulated succession on spoil banks?

The aim of this field study was to examine how the development of arbuscular mycorrhizal fungi (AMF) on coal mine spoil banks is affected by the presence of plants with different mycorrhizal status. A 3-year trial was conducted on the freshly created spoil bank Vršany, North-Bohemian coal basin, the Czech Republic. Three plant species – non-mycotrophic annual Atriplex sagittata, highly mycotrophic annual Tripleurospermum inodorum (both dominants of early stages of succession) and facultatively mycotrophic Arrhenatherum elatius (a perennial grass species of the later stage of succession) – were planted on 1 m² plots over 3 years in different sequences that simulated the progress of succession on spoil banks. The development of AMF populations was monitored by evaluation of mycorrhizal colonization of plant roots and by measurement of the mycorrhizal inoculation potential (MIP) of soil. These two parameters were compared between plots inoculated with the mixture of three AMF isolates – Glomus mosseae BEG95, G. claroideum BEG96 and G. intraradices BEG140 – (“inoculated plots”) and plots exposed only to natural dispersal of AMF propagules (“uninoculated plots”). Highly colonized roots of plants together with a high MIP of soil in uninoculated plots were already found at the end of the first season, indicating rapid natural dispersal of AMF propagules. Root colonization of facultatively mycotrophic and non-mycotrophic plants in later years was affected by the mycorrhizal status of the previous plant species. The MIP of soil continuously increased throughout the experiment; in uninoculated plots, the MIP was temporarily decreased if plant species of higher mycotrophy were replaced by species of lower mycotrophy. The results lead to the conclusion that AMF colonize freshly formed sites very quickly and reproduce or accumulate in the soil, which leads to increasing MIP values. However, this infective potential can be decreased if non-mycotrophic plants predominate on the site.     

Extraradical mycelium of arbuscular mycorrhizal fungi radiating from large plants depresses the growth of nearby seedlings in a nutrient deficient substrate

The effect of arbuscular mycorrhiza (AM) on the interaction of large plants and seedlings in an early succession situation was investigated in a greenhouse experiment using compartmented rhizoboxes. Tripleurospermum inodorum, a highly mycorrhiza-responsive early coloniser of spoil banks, was cultivated either non-mycorrhizal or inoculated with AM fungi in the central compartment of the rhizoboxes. After two months, seedlings of T. inodorum or Sisymbrium loeselii, a non-host species colonising spoil banks simultaneously with T. inodorum, were planted in lateral compartments, which were colonised by the extraradical mycelium (ERM) of the pre-cultivated T. inodorum in the inoculated treatments. The experiment comprised the comparison of two AM fungal isolates and two substrates: spoil bank soil and a mixture of this soil with sand. As expected based on the low nutrient levels in the substrates, the pre-cultivated T. inodorum plants responded positively to mycorrhiza, the response being more pronounced in phosphorus uptake than in nitrogen uptake and growth. In contrast, the growth of the seedlings, both the host and the non-host species, was inhibited in the mycorrhizal treatments. Based on the phosphorus and nitrogen concentrations in the biomass of the experimental plants, this growth inhibition was attributed to nitrogen depletion in the lateral compartments by the ERM radiating from the central compartment. The results point to an important aspect of mycorrhizal effects on the coexistence of large plants and seedlings in nutrient deficient substrates.     

Associations of dominant plant species with arbuscular mycorrhizal fungi during vegetation development on coal mine spoil banks

Among plants colonizing mine spoil banks in Northern Bohemia the first colonizers, mainly ruderal annuals fromChenopodiaceae andBrassicaceae were found not to be associated with arbuscular mycorrhizal fungi (AMF). These species cultivated in pots with soil from four sites in different succession stages of the spoil bank did not respond to the presence of native or non-native AMF. All grass species studied (Elytrigia repens, Calamagrostis epigejos andArrhenatherum elatius) were found moderately colonized in the field and they seemed to be facultative mycotrophs, because their response to mycorrhiza in the experiment was negligible.Carduus acanthoides was found to be highly colonized in the field, however, it did not show growth response to AMF in the pot experiment. The AMF native in four sites on the spoil banks showed high infectivity but low effectiveness in association with colonizing plants compared to the non-native isolateG. fistulosum BEG23. In general, dependence on AMF in the cultivation experiment was rather low, regardless of the fact that plants were found to be associated with AMF either in the field or in pots. Occurrence and effectiveness of mycorrhizal associations might relate primarily to the mycotrophic status of each plant species rather than to the age of the spoil bank sites studied.     

Effect of arbuscular mycorrhizal fungi inoculation on root traits and root volatile organic compound emissions of Sorghum bicolor

Volatile organic compounds (VOCs) emitted by plant roots have important functions that can influence the rhizospheric environment. The aim of this study was to examine the effects of arbuscular mycorrhizal (AM) fungi on the profile of root VOCs. Sorghum (Sorghum bicolor) plants were grown in pots inoculated with either Glomus mosseae or Glomus intraradices, which formed mycorrhiza with the roots. Control plants were grown in pots inoculated with sterile inoculum and did not form mycorrhiza. Forty-four VOCs were determined using headspace solid-phase microextraction (HS-SPME) and gas chromatography–mass spectrometry (GC-MS). Alkanes were the most abundant type of VOCs emitted by both mycorrhizal and non-mycorrhizal plants. Both the quantity and type of volatiles were dramatically altered by the presence of AM fungi, and these changes had species specificity. Compared with non-mycorrhizal plants, mycorrhizal plants emitted more alcohols, alkenes, ethers and acids but fewer linear-alkanes. The AM fungi also influenced the morphological traits of the host roots. The total root length and specific root length of mycorrhizal plants were significantly greater than those of non-mycorrhizal plants; however, both the incidence and length of root-hair were dramatically decreased. Our findings confirm that AM fungi can alter the profile of VOCs emitted by roots as well as the root morphology of sorghum plants, indicating that AM fungi have the potential to help plants adapt to and alter soil environments.     

Arbuscular mycorrhizal fungi in terms of symbiosis-parasitism continuum

Arbuscular mycorrhizal fungi are forming the most wide-spread mycorrhizal relationships on Earth. Mycorrhiza contributes to phosphorous acquisition, water absorption and resistance to diseases. The fungus promotes the absorption of nutrients and water from soil, meanwhile the host plant offers photosynthetic assimilates in exchange, like carbohydrates, as energy source. The plant benefits from the contribution of symbiotic partner only when nutrients are in low concentrations in soil and the root system would not be able to absorb sufficiently the minerals. When the help of mycorrhizal fungi is not necessarily needed, the host plant is making an economy of energy, suppressing the development of fungi in the internal radicular space. In this moment, the nature of relationship turns from symbiotic to parasitic, triggering a series of defensive reactions from the plant. Also, there were several cases reported when the presence of arbuscular mycorrhizal fungi negatively influenced the host plant. For example, in adverse environmental conditions, like very high temperatures, instead of determining a higher plant biomass and flowering, the mycorrhiza reduces the growth of the host plant. We conducted a pot experiment with hydroponic culture to examine the effect of arbuscular mycorrhiza on development of French marigold as a host plant. As experimental variants, the phosphorous content in nutrient medium and temperature varied. Plants were artificially infected with arbuscular mycorrhizal fungi using a commercial inoculum containing three fungal species, as following: Glomus intraradices, Glomus etunicatum and Glomus claroideum. Colonization intensity and arbuscular richness were checked using root staining with aniline blue and estimation with the Trouvelot method. To observe the differences between plants from the experimental variants, we examined the number of side shoots, flower buds and fully developed flowers, fresh biomass and total leaf area. Results show that adverse climatic conditions, like temperature shock at the beginning of growing period modified the nature of symbiosis. In this case, the physiological parameters were reduced at colonized plants, while usual, constant growing conditions permitted the normal, efficient and beneficial development of symbiosis.     

Ecological Design is More Important Than Compensatory Mitigation for Successful Restoration of Alpine Spoil Heaps

Spoil heaps of surplus rock from hydropower tunnel construction negatively impact alpine landscapes unless restored. Such spoil heaps have been created for more than 100 years, but we still lack knowledge about the relative importance of compensatory mitigation (seeding and fertilization), spoil‐heap construction method, local environmental factors, and regional climatic factors for restoration success. We studied the species composition of 19 alpine spoil heaps in Western Norway and their undisturbed surroundings using ordination and statistical modeling. Substrate grain size was the principal factor explaining differences in species composition between spoil heaps and their surroundings. Soil characteristics, that is, organic matter content and pH, and reutilization of topsoil were also important. Seeding and fertilization had negligible effects on restoration success. Slow recovery was observed for total vegetation cover and species richness of vascular plants and lichens while bryophyte cover recovered rapidly. Lower bryophyte cover and bryophyte and vascular plant species richness on older than on younger spoil heaps indicated recent changes in spoil‐heap construction practices that favor plant colonization. Our results indicate that spoil‐heap design is more important for restoration success than compensatory mitigation. We therefore suggest spoil heaps designed with a fine‐grained top substrate preferably from stockpiled local topsoil, with uneven surface topography that mimics natural topographic variation, and recommend discontinuation of seeding and fertilization.