【作者】 何跃军；

【导师】 钟章成； 董鸣；

【作者基本信息】 西南大学 ， 生态学， 2012， 博士

【摘要】 丛枝菌根真菌(arbuscular mycorrhizae fungi, AMF)如何利用土壤养分资源供给宿主植物生长是当前菌根生态研究的热点问题。水土流失严重的南方喀斯特地区,生境异质性高,喀斯特生境中的植物个体是如何通过AMF吸收并利用土壤中的养分资源来维持植物的生长,从而实现生态系统的营养循环和养分平衡的问题还没有认识清楚。喀斯特生境中AMF是否具有分解有机物并利用其养分的能力一直未见报道,土壤养分含量是如何调节了这一过程的发生?喀斯特生境中具有较高的AMF多样性,这些菌种是如何共同维持植物生长所需要的土壤养分资源的?养分的形态是如何通过AMF影响了植物生长和土壤性质的?这些问题的明确对阐明喀斯特生态系统养分维持机制具有重要意义。为此,本文进行了如下的两个试验,旨在探索喀斯特土壤中AMF是否具有分解枯落物的腐生营养能力以及多菌种的混合效应对宿主植物的共生发育和土壤性质的影响。具体的试验方法为：试验一是以喀斯特地区适生植物香樟(Cinnamomum camphor a)为研究对象、采用隔室分离系统、温室控制实验以及15N同位素示踪方法,以喀斯特土壤作为基质接种AMF。分室系统隔室装置(用20um或0.45umm尼龙网双层隔离)对香樟幼苗进行幼套球囊霉(Glomus etunicatum)接种后,在根际周围施加外源无机氮NH4NO3,相邻隔室施加15N标记的黑麦草(Lolium perenne)枯落物,以检测AMF的腐生营养能力和外源氮对枯落物分解的影响；试验二采用相同的装置对香樟接种幼套球囊霉和摩西球囊霉(Glomus mosseae)的混合接种,相邻隔室用15N标记的(NH4)2SO4处理,并在12周后种植黑麦草,以检测AMF混合接种对香樟幼苗共生发育和土壤养分转移的影响。所有苗木培养15周后测定了隔室幼苗生理生化及土壤生化指标：侵染率、菌丝体密度、根系性状特征、光合指标、植株和土壤氮、磷含量,δ15N值、微生物量氮、微生物量碳、碱性磷酸酶和蛋白酶活性等。主要的试验结果如下：(1)外源氮调节AMF对-土壤枯落物分解和养分转移施加外源N提高了相邻隔室菌丝密度,净光合速率、根系直径、根体积和生物量的积累；施加外源N提高了植株根、茎、叶各部分的N：P比率,但植株总N摄取量没有显著影响；施加外源N降低了香樟叶片δ15N值；提高了隔室微生物量碳、微生物量氮和有机碳的含量,也提高了微生物量C：N比率；施加外源N对隔室碱性磷酸酶和蛋白酶活性没有显著影响,但菌丝隔离对二者影响显著。隔网对菌丝阻隔显著降低了相邻隔室菌丝体密度、苗高、地径,叶绿素含量和净光合速率,从而降低了生物量的积累；菌丝隔网对植株N：P比率没有显著影响,但是显著降低了植株N和P的摄取量和N：P比率；降低了幼苗叶片的δ15N值和微生物量C：N比率。试验结果表明：试验处理对香樟幼苗侵染率没有显著影响,但是显著改变了相邻隔室菌丝体密度。菌丝体的阻隔改变了根系形态特征和植株生物量；试验证实了AMF具有腐生营养能力,促进了土壤枯落物的分解并吸收其释放的15N供应给宿主植物利用；香樟幼苗优先利用根际周围N维持生长；在低N状态下,香樟植株通过AMF菌丝体更多地利用了相邻隔室枯落物分解释放的15N；施加根际外源氮有利于AMF对隔室枯落物的分解,但降低了植株对枯落物氮的利用；根际高N状态下植株的N、P摄取量较大,相邻隔室微生物量碳、氮含量和菌丝体密度提高。(2)AMF混合接种对宿主植物无机养分的吸收和转移效应混合接种处理对侵染率和菌丝体密度没有显著影响；混合接种提高了香樟幼苗生长和生物量的积累,改变了根系性状特征如根长、根体积等,但差异不显著；混合接种处理对净光合速率没有显著影响；混合接种提高了根和茎的N：P比率,也提高了植株总N摄取量,但总P摄取量效应不显著,也显著提高植株总体的N：P比率；混合接种提高了香樟叶片δ15N值,降低了相邻隔室土壤和黑麦草叶片的815N值；混合接种显著降低了相邻隔室的微生物量C,也降低了土壤微生物量的C：N比率；混合接种提高了相邻隔室碱性磷酸酶和蛋白酶活性。菌丝隔网对菌丝阻隔显著影响了相邻隔室菌丝体密度,降低了根、茎、叶生物量、根长、根体积、叶绿素含量和净光合速率；隔网显著降低了植株N、P摄取量和N：P比率、15N值,但相邻隔室土壤和黑麦草叶片δ15N值显著高于其他处理；隔网显著降低了隔室土壤的微生物量N和微生物量C及其比率；隔网对相邻隔室全N、碱解N和有效P有显著的降低作用,但是相邻隔室碱性磷酸酶和蛋白酶活性则提高。试验结果表明：混合接种对香樟幼苗侵染率和相邻隔室菌丝体密度没有显著影响。菌丝网的阻隔改变了根系形态特征和植株生物量。AMF混合接种效应提高了相邻隔室养分的利用,促进植株生长,改变了共生体系中的根系性状特征和生物量的积累和植株体内N、P的摄取、土壤酶活性和微生物量C、N等。菌丝体显著影响了植株养分的利用,从而影响到光合作用和生物量的积累。混合接种促进了植株利用更多的远距离的无机养分,而这些养分的利用时通过菌丝体吸收并转移获得的。(3)养分形态和AMF菌丝对宿主植物共生发育建成及土壤性质的影响双因素方差分析结果表明：养分形态(有机和无机养分)对香樟幼苗生长发育的影响主要是通过影响了根系生物量改变了植株总生物量的积累,光合速率和叶绿素a的含量也显著受养分形态的影响,而菌丝对植株的生物量积累以及形态建成均有显著或较大的影响；香樟幼苗总N和总P摄取量受有机养分或无机养分的影响不显著,但是对摄取养分的N：P比率影响显著,而菌丝隔网对N：P比率影响不显著,养分形态和菌丝隔网交互作用对N的摄取影响显著,但对P的摄取不显著。交互作用主要是影响了植株茎的生物量来影响植株总的生物量的,养分形态对根系性状没有显著影响,但是这些指标主要受到菌丝隔网的显著影响,他们共同影响了植株的光合和叶绿素含量；土壤有效态的N和P含量受养分形态和菌丝网影响显著,他们共同影响了土壤微生物量C,而微生物量N则主要受到菌丝隔网的影响。试验结果表明土壤养分的形态对植株生长所需要的养分和土壤生化过程产生显著影响,AM菌丝体在植物养分利用方面起到了显著的调节作用,植株生长维持所需的养分与其在土壤中存在的形态和AM菌丝状况有关。综上所述,AM真菌具有促进土壤有机物分解的能力,根际养分的高低对植株养分利用和有机物分解产生显著的作用,多菌种的混合效应在植株养分利用和维持生长方面具有显著的正效应,植株生长在一定程度上受到土壤养分形态和菌丝体状况的影响,这两个因素共同作用并影响了植物-AM-土壤共生体系的生化过程。更多还原

【Abstract】 How arbuscular mycorrhiza fungi (AMF) utilize soil nutrients and supports host plant growth are intriguing. In the south Karst ecosystem with high soil erosion, mycorrhizal fungi can be extremely important for nutrient cycling. Researchers have been focused on the questions of saprotrophic ability on AMF for long. It has not been reported for the saprotrophic ability on decomposing organic matter and utilizing nutrients in Karst habitat to maintain nutritional balance of the ecosystem. How nitrogen mediates the process? How high diversity of AMF species maintains nutrients need of plant growth? How nutrients form and hypha affet plant growth and soil characteristics? It is important significance to know these questions for revealing mechanisms of nutrient cycle in Karst ecosystem. Therefore, two experiments were conducted in order to study the saprotrophic ability of litter decoompositon via AMF mycelium and the mixed effets of multiple AMF species to symbiotic development of host plant and soil property in this thesis. The experimental measurements are as follows.Experiment1:The effects of inoculation of Cinnamomum camphora seedlings with AMF were investigated. C.camphora seedlings were inoculated with Glomus etunicatum in isolated compartments with soils from a Karst area. Exogenous nitrogen of NH4NO3was added in rhizosphere soil and litter of15N Lolium perenne labeled with15N was applied in TEST soil in order to study the saprotrophic ability and the effects of exogenous nitrogen on decomposition. Experiment2:C.camphora seedlings were inoculated with two AMF species of G. etunicatum and G. mosseae, the adjacent compartment was applied (NH4)2SO4with15N labeled and planted Lolium perenne after12weeks in TEST. The aim was to test mixed inoculation with AMF species to host plant After15weeks treatments, the following was investigated:the colonized rate, mycelium density; photosynthesis and growth characteristics, plants and soil nitrogen and phosphorus status and815N;soil microbial nitrogen and carbon content, alkaline phosphatase and protease acitivity.(1) Exogenous nitrogen mediated litter decomposition and nutrient transportation for host plant by AMFExogenous nitrogen application increased mycelium density, plants photosynthesis rate and growth. It also increased N:P in root, stem and leaf. However, the total amount of nitrogen uptake was not affected. The application of exogenous nitrogen decreased utilization of15N from but increased soil microbial carbon, nitrogen, organic carbon, microbial C:N and alkaline phosphatase and protease activity in the neighbor compartments. The isolation interrupted mycelium extension and decreased mycelium density, plants height and stem diameter, leaf chlorophyll content and photosynthesis rate and consequently biomass accumulation. The isolation did not change the plants N:P remarkably, but decreased nitrogen and phosphorus uptake. It also decreased leaf815N value and soil microbial C:N. In conclusion, the results indicated that exogenous nitrogen application did not change the colonized rate of C.camphora seedlings, but did affected the mycelium density in the neighbor compartments significantly. The isolation altered root characteristics and plants growth. AMF was saprophytic, promoted soil litter decomposition and uptake and transphere the15N to the host plants. C.camphora seedlings preferred to utilize the rhizophere soil nitrogen. Under the conditions of low level nitrogen supply, the plants utilized more15N released from the neighbor compartments. Application of exogenous nitrogen promoted soil litter decomposition but decreased its utilization by the plants; in contrast, with high level of nitrogen supply, the plants uptake much more nitrogen and phosphorus and microbial carbon, nitrogen content and mycelium density were also increased in the neighbor compartments.(2) Mixed inoculation with AMF affected uptake and transportation of inorganic nutrients for host plants in Karst soilMixed inoculation did not significantly affect mycelium density in the neighbor compartments and colonized rate of Cinnamomum camphora seedlings in this experiment.It affected photosynthesis of C.camphora seedlings significantly, and also promoted growth, such as biomass accumulation, root length and volume, although not significantly. Mixed inoculation increased N:P in the roots, stems and the plants as a whole and total nitrogen uptake, but did not affect total phosphorus uptake. This treatments also increased δ15N value of the leaves, but decreased δ15N value of the soil and Lolium perenne leaves in the neighbor compartments. It also decreased soil microbial C:N, but increased alkaline phosphatase and protease activity significantly. The isolation affected the mycelium density in the neighbor compartments and it decreased biomass accumulation of root, stem and leaf and root length and volume, leaf chlorophyll content and photosynthesis rate, nitrogen and phosphours uptake and N:P value. The0.45um net isolation decreased significantly815N value of C.camphora seedlings leaves,but the815N value of the soil and the Lolium perenne leaves in the neighbor compartments was significantly much higher than in the other treatments. The net isolation also decreased the soil microbial carbon and nitrogen content and the C:N value. It also decreased significantly the content of total nitrogen, alkali soluble nitrogen and available phosphorous respectively. It increased alkaline phosphatase and protease activity in the neighbor compartments.In conclusion, the treatments did not affected the colonized rate of the C.camphora seedlings, but they significantly altered the mycelium density in the neighbor compartments. The isolation changed the root morphology and plants total biomass. Mixed AMF inoculation increased nutrients utilization and promoted plants growth, affected the root morphology, biomass and nitrogen and phosphorus accumulation and. The improvement was mainly the consequent of changed soil enzyme activity and microbial carbon and nitrogen and nutrients utilization. The mycelium affected significantly the plants nutrients utilization, and consequent photosynthesis and biomass accumulation. The mixed inoculation promoted utilization nutrients from distance farer away via mycelium uptake and transfer.(3) Effects of nutrients from and AMF mycelium on symbiotic development of host plant and soil characteristicsThe two-ANOVA indicated that the total amount of nitrogen and phosphorus uptake by the C.camphora seedlings was not affected significantly by the organic or inorganic nutrients, but the N: P uptake was. The net isolation did not changed N:P, though. The interaction of nutrients form (organic or inorganic) and net isolation affected nitrogen uptake but not phosphorus uptake. The significant effects on plant total biomass were mainly due to changes of stem biomass. The nutrients form did not affected root morphology remarkably which was mainly affected by net isolation. Both nutrients form (organic or inorganic) and net isolation affected the chlorophyll content and plants photosynthesis, soil available nitrogen and phosphorus and soil microbial carbon. The soil microbial nitrogen was mainly affected by the net isolation. In conclusion, the soil nutrients form affected the soil biochemical processes; both soil form and AM mycelium regulated plants nutrients utilization.In summary, AM fungi promoted soil organic matter decomposition; rhizosphere nutrients availability affected soil organic matter decomposition and plants nutrients utilization significantly. Mixed AM fungi species inoculation imposed positive effects on nutrients utilization and plants growth. Plants growth was affected by soil nutrients form and AM mycelium. Both factors contributed to the Plant-AM fungi-Soils system processes.更多还原