不同浓度和形态磷处理下内生真菌感染对高羊茅的影响

以感染内生真菌(endophyte-infected,EI)和不感染内生真菌(endophyte-free,EF)的高羊茅(Festuca arundinacea Schreb.)为材料,在温室沙培条件下研究内生真菌对高羊茅适应缺磷及利用不同形态磷肥的影响。结果表明,1)缺磷条件下,高羊茅EI和EF植株生长差异不显著;正常供磷条件下,高羊茅EI植株拥有更多分蘖数和绿叶数。说明正常供磷条件下内生真菌改善了宿主高羊茅的生长。2)与水溶性磷相比,高羊茅根有机酸和酸性磷酸酶(acid phosphatase,APase)活性在难溶性磷条件下显著增加,而根总酚含量无显著变化。在水溶性磷条件下,高羊茅EI植株根总酚含量显著高于EF植株,此时EI植株比EF植株拥有更多分蘖数和绿叶数,说明在水溶性磷条件下内生真菌对宿主地上部生长具有一定贡献。在难溶性磷条件下,虽然高羊茅EI植株根总酚含量仍然高于EF植株,但同时EI植株根有机酸含量显著低于EF植株,因此内生真菌感染只是增大了宿主植物的根冠比,而对分蘖数和绿叶数等无显著影响,说明内生真菌对宿主利用难溶性磷贡献不大。可见,内生真菌对宿主植物的生长在水溶性磷条件下更有利。     

干旱胁迫下内生真菌感染对羽茅的生理生态影响

本研究在田间环境下对感染和未感染内生真菌的天然宿主羽茅（Achnatherum sibiricum (L. ) Keng）进行了干旱胁迫实验,结果发现在干旱胁迫下,内生真菌感染对宿主植物的营养生长、生物量累积和叶绿素含量都没有显著影响,但对宿主植株光系统II光化学效率（Fv/Fm）的维持产生了有利效应。同时,内生真菌感染缓解了宿主植物细胞膜的旱害程度,表现在与未感染植株相比,感染植株的丙二醛（MDA）含量显著降低,但内生真菌的感染并未促使宿主植物体内保护酶如超氧化物歧化酶（SOD）和过氧化氢酶（CAT）活性的增加,只是显著增加了类胡萝卜素的含量。因此我们推测在羽茅中,内生真菌对宿主植物的保护作用可能更多的体现在非酶系统上。     

黑麦草-内生真菌共生体对磷缺乏的生理生态反应

选取感染和未感染的黑麦草为材料,在田间盆栽条件下研究内生真菌感染对宿主植物抵抗磷胁迫方面的贡献。结果表明,土壤中缺磷或内生真菌感染对黑麦草地上部生长的影响不显著,但内生真菌感染对植株地下部生长和生理指标有明显影响。缺磷条件下,内生真菌感染有助于黑麦草地下部分的生长,表现在根系总长度更长,生物量更大;同时根中酚类物质和有机酸的含量也显著高于未感染植株,但因酚类物质和有机酸总量增加的同时并未伴随着二者浓度的增加,由此推测,内生真菌在改变宿主黑麦草根系代谢活动方面的贡献有限。此外,内生真菌感染显著提高了宿主植物的磷利用效率,这可能和缺磷条件下内生真菌感染植株具有更高的酸性磷酸酶活性有关。     

内生真菌感染对黑麦草抗盐性的影响

以感染内生真菌的多年生黑麦草（Lolium perenne L．）（SR4000）为实验材料,建植内生真菌感染（EI）和不感染（EF）的黑麦草种群,并对其进行盐胁迫实验,通过观察生长和生理生态指标的变化,分析内生真菌对宿主植物抗盐性的影响。结果表明,内生真菌感染对宿主黑麦草的营养生长没有增益效应,相反在高盐浓度下,EI种群的分蘖能力和地上部分生物量均低于EF种群;但内生真菌能够改变宿主种群生物量的分配格局,将更大比例的生物量分配于根系。在高盐浓度下,内生真菌感染可导致黑麦草叶内的脯氨酸含量显著增加、可溶性糖含量显著降低,但对PSⅡ光化学效率Fv/Fm值的变化没有影响。总体来看,内生真菌感染并未改善宿主黑麦草的抗盐性。     

盐碱胁迫对染内生菌和不染菌苇状羊茅根系丛枝菌根真菌群落多样性和组成的影响

香柱菌属Epichloë内生真菌存在于宿主植物地上部组织,不仅能提高宿主植物对生物与非生物逆境的抗性,而且能对周围环境中的微生物产生影响。该研究以染内生菌(endophyte-infected,EI)和不染菌(endophyte-free,EF)苇状羊茅Festuca arundinacea为实验材料,探究内生真菌和不同水平盐碱胁迫处理对宿主根系丛枝菌根真菌(arbuscular mycorrhizal fungi,AMF)群落多样性和组成的影响。结果表明,内生真菌和盐碱胁迫处理对苇状羊茅根系AMF多样性影响存在交互作用。EF苇状羊茅根系AMF多样性随盐碱胁迫处理水平的增加而降低,内生真菌的存在缓解了这一效应,在200和400 mmol/L盐碱胁迫处理下,内生真菌感染增加了苇状羊茅根系AMF多样性;此外,内生真菌感染改变了苇状羊茅根系AMF群落组成,降低了优势属Funneliformis相对多度,增加了Claroideoglomus、Glomus和unclassified AMF相对多度。结构方程模型结果表明,内生真菌通过间接增加土壤总磷浓度对苇状羊茅根系AMF多样性产生影响。本研究为筛选盐碱污染区生态修复的植物-微生物共生体提供基础。     

内生真菌种类和母本基因型对内生真菌-禾草共生体叶形状和叶面积的影响

Epichloë内生真菌感染能够影响宿主植物的生长发育, 但关于内生真菌感染对宿主植物叶形状和叶面积的研究很少。该研究以羽茅(Achnatherum sibiricum)为实验材料, 采用长宽系数计算和扫描测定叶面积相结合的方法探究内生真菌种类和羽茅母本基因型对羽茅-内生真菌共生体叶形状和叶面积的影响。结果表明: 内生真菌感染与否、内生真菌种类和宿主母本基因型对反映叶形状的叶校正系数、叶片长度、宽度和长宽比均无显著影响, 经计算与验证, 确定了羽茅叶片的校正系数为0.594 9。采用该校正系数及叶长宽计算的叶面积与实测叶面积无显著差异, 且二者均未受到内生真菌感染与否、内生真菌种类或宿主植物母本基因型的显著影响。     

Effects of endophyte fungal species and host plant genotype on the leaf shape and leaf area of endophyte-grass symbionts

Epichloë内生真菌感染能够影响宿主植物的生长发育, 但关于内生真菌感染对宿主植物叶形状和叶面积的研究很少。该研究以羽茅(Achnatherum sibiricum)为实验材料, 采用长宽系数计算和扫描测定叶面积相结合的方法探究内生真菌种类和羽茅母本基因型对羽茅-内生真菌共生体叶形状和叶面积的影响。结果表明: 内生真菌感染与否、内生真菌种类和宿主母本基因型对反映叶形状的叶校正系数、叶片长度、宽度和长宽比均无显著影响, 经计算与验证, 确定了羽茅叶片的校正系数为0.594 9。采用该校正系数及叶长宽计算的叶面积与实测叶面积无显著差异, 且二者均未受到内生真菌感染与否、内生真菌种类或宿主植物母本基因型的显著影响。     

刈割干扰和养分添加条件下Epichloë内生真菌感染对羽茅所在群落多样性和生产力的影响

Epichloë内生真菌感染能够影响宿主植物的种内和种间竞争力, 但目前关于内生真菌感染对宿主植物所在群落多样性和生产力影响的研究较少。该研究以感染(E+)和不感染(E-)内生真菌的羽茅(Achnatherum sibiricum)及其原生境中常见的5种植物构建人工群落, 探究在不同养分水平和刈割条件下内生真菌对宿主植物群落的影响。结果表明: 内生真菌对宿主植物群落多样性的影响同刈割与否有关。在无刈割条件下, 内生真菌感染对宿主群落多样性无显著影响; 在刈割条件下, 内生真菌感染显著增加了宿主群落的多样性, 其原因在于内生真菌感染显著增加了群落中多度较小的冰草(Agropyron cristatum)和大针茅(Stipa grandis)等的多度, 而显著降低了优势种羊草(Leymus chinensis)的多度。内生真菌感染对群落生产力未见显著影响。研究发现养分添加对内生真菌作用的影响只出现在宿主植物水平, 而对宿主植物所在群落未产生显著影响, 内生真菌对宿主羽茅的促进作用只出现在养分添加条件下。     

不同传播方式的内生真菌感染对羽茅的生理生态影响北大核心CSCD

通过田间试验,研究了垂直传播的Neotyphodium属内生真菌和水平传播的Epichloё属内生真菌对羽茅(Achnatherum sibiricum)生理生态的影响。结果表明:Neotyphodium属内生真菌感染对羽茅的株高和叶长有显著的正效应,而Epichloё属内生真菌感染对羽茅株高和叶长的增益作用较少。感染Neotyphodium属内生真菌的羽茅最大净光合速率显著高于感染Epichloё属内生真菌的羽茅,Neotyphodium属内生真菌显著提升了羽茅的气孔限制值和水分利用效率,而实验测定的第一年结果显示:Epichloё属内生真菌对羽茅的各个光合指标具有明显的负效应(胞间CO2浓度除外)。Neotyphodium属内生真菌感染使得宿主植物积累的可溶性糖含量显著高于感染Epichloё属内生真菌的羽茅和不染菌的羽茅植株。感染Epichloё属内生真菌的羽茅中氮含量显著高于感染Neotyphodium属内生真菌的羽茅。总之,内生真菌的传播方式是影响羽茅生理生态学特性的一个因素,并且垂直传播的内生真菌对羽茅生长和生理特性的益处高于水平传播的内生真菌。     

内生真菌感染对禾草宿主生境土壤特性和微生物群落的影响

以羊草(Leymus chinensis)-内生真菌共生体为研究对象, 分别在野外样地和室内盆栽两种实验条件下研究了内生真菌感染对土壤特性和微生物群落结构的影响。结果显示：在处理时间较长并伴随有枯落物分解的羊草样地中, 内生真菌感染促进了土壤氮(N)的积累, 提高了30天培养时间内土壤初始碳(C)矿化速率和前3天土壤矿化量和土壤矿化总量; 而在处理时间较短且没有地上枯落物分解的盆栽羊草中, 内生真菌感染对土壤的C、N含量及C矿化均无显著影响。无论是野外样地还是室内盆栽实验, 内生真菌感染均未引起土壤微生物磷脂脂肪酸种类的变化, 但内生真菌感染均有提高土壤微生物生物量的趋势, 内生真菌显著增加了盆栽羊草土壤中细菌、革兰氏阴性细菌、真菌磷脂脂肪酸含量和磷脂脂肪酸总量, 增加了羊草样地土壤中革兰氏阳性细菌和放线菌的磷脂脂肪酸含量。总体看来, 内生真菌感染能够改变土壤N积累和C矿化率, 并且改变土壤中微生物群落的结构, 这有助于进一步认识内生真菌与羊草之间的共生关系及其在生态系统C、N循环中所起的作用。     

Endophytic fungus improves growth and metal uptake of Lolium arundinaceum Darbyshire ex. Schreb

The effect of endophyte infection on plant growth, cadmium (Cd) uptake, and Cd translocation was investigated using tall fescue (Lolium arundinaceum) grown in greenhouses in contaminated solution. Endophyte infection significantly increased tiller number and biomass of the host grass under both control and Cd-stress conditions. Endophyte infection not only enhanced Cd accumulation in tall fescue, but also improved Cd transport from the root to the shoot. Under 20 mg L(-1) Cd stress, the phytoextraction efficiency of endophyte-infected (EI) tall fescue was 2.41-fold higher than endophyte-free plants. Although the total Cd accumulation in EI tall fescue was insufficient for practical phytoextraction applications, the observed high biomass production and tolerance of stress from abiotic factors including heavy metals, gives endophyte/plant associations the potential to be a model for endophyte-assisted phytoremediation of metal-polluted soils.     

Leaf endophyte Neotyphodium coenophialum modifies mineral uptake in tall fescue

Neotyphodium coenophialum (Morgan-Jones and Gams) Glenn, Bacon and Hanlin, a fungal endophyte found primarily in shoots of tall fescue (Festuca arundinacea Shreb.), can modify rhizosphere activity in response to phosphorus (P) deficiency. In a controlled environment experiment, two cloned tall fescue genotypes (DN2 and DN4) free (E-) and infected (E+) with their naturally occurring endophyte strains were grown in nutrient solutions at low P (3.1 ppm) or high P (31 ppm) concentrations for 21 d. Endophyte infection increased root dry matter (DM) of DN4 by 21% but did not affect root DM of DN2. Under P deficiency, shoot and total DM were not affected by endophyte but relative growth rate was greater in E+ than E- plants. In high P nutrient solution, E+ plants produced 13% less (DN2) or 29% more (DN4) shoot DM than E- plants. Endophyte affected mineral concentrations in roots more than in shoots. Regardless of P concentration in nutrient solution, E+ DN2 accumulated more P, Ca, Zn and Cu but less K in roots than E- plants. When grown in high P nutrient solution, concentrations of Fe and B in roots of E+ DN2 plants were reduced compared with those of E- plants. Concentrations of P, Ca and Cu in roots of DN4 were less, but K was greater in E+ than E- plants. In shoots, E+ DN2 had greater concentrations of Fe and Cu than E- DN2, regardless of P concentration in nutrient solution. Genotype DN4 responded to endophyte infection by reducing B concentration in shoots. Nutrient uptake rates were affected by endophyte infection in plants grown in low P nutrient solution. A greater uptake rate of most nutrients and their transport to shoots was observed in DN2, but responses of DN4 were not consistent. Results suggest that endophyte may elicit different modes of tall fescue adaptation to P deficiency. This revised version was published online in June 2006 with corrections to the Cover Date.     

Does Fungal Endophyte Infection Improve Tall Fescue’s Growth Response to Fire and Water Limitation?

Invasive species may owe some of their success in competing and co-existing with native species to microbial symbioses they are capable of forming. Tall fescue is a cool-season, non-native, invasive grass capable of co-existing with native warm-season grasses in North American grasslands that frequently experience fire, drought, and cold winters, conditions to which the native species should be better-adapted than tall fescue. We hypothesized that tall fescue’s ability to form a symbiosis with Neotyphodium coenophialum, an aboveground fungal endophyte, may enhance its environmental stress tolerance and persistence in these environments. We used a greenhouse experiment to examine the effects of endophyte infection (E+ vs. E−), prescribed fire (1 burn vs. 2 burn vs. unburned control), and watering regime (dry vs. wet) on tall fescue growth. We assessed treatment effects for growth rates and the following response variables: total tiller length, number of tillers recruited during the experiment, number of reproductive tillers, tiller biomass, root biomass, and total biomass. Water regime significantly affected all response variables, with less growth and lower growth rates observed under the dry water regime compared to the wet. The burn treatments significantly affected total tiller length, number of reproductive tillers, total tiller biomass, and total biomass, but treatment differences were not consistent across parameters. Overall, fire seemed to enhance growth. Endophyte status significantly affected total tiller length and tiller biomass, but the effect was opposite what we predicted (E−>E+). The results from our experiment indicated that tall fescue was relatively tolerant of fire, even when combined with dry conditions, and that the fungal endophyte symbiosis was not important in governing this ecological ability. The persistence of tall fescue in native grassland ecosystems may be linked to other endophyte-conferred abilities not measured here (e.g., herbivory release) or may not be related to this plant-microbial symbiosis.     

Neotyphodium Coenophialum-Infected Tall Fescue and Its Potential Application in the Phytoremediation of Saline Soils

The growth response of endophyte-infected (EI) and endophyte-free (EF) tall fescue to salt stress was investigated under two growing systems (hydroponic and soil in pots). The hydroponic experiment showed that endophyte infection significantly increased tiller and leaf number, which led to an increase in the total biomass of the host grass. Endophyte infection enhanced Na accumulation in the host grass and improved Na transport from the roots to the shoots. With a 15 g l^?1 NaCl treatment, the phytoextraction efficiency of EI tall fescue was 2.34-fold higher than EF plants. When the plants were grown in saline soils, endophyte infection also significantly increased tiller number, shoot height and the total biomass of the host grass. Although EI tall fescue cannot accumulate Na to a level high enough for it to be termed a halophyte, the increased biomass production and stress tolerance suggested that endophyte / plant associations had the potential to be a model for endophyte-assisted phytoextraction in saline soils.     

Restoration of Native Warm Season Grassland Species in a Tall Fescue Pasture Using Prescribed Fire and Herbicides

Pastures dominated by tall fescue (Schedonorus phoenix (Scop.) Holub) cover much of the eastern United States, and there are increasing efforts to restore native grassland plant species to some of these areas. Prescribed fire and herbicide are frequently used to limit the growth of tall fescue and other non‐natives, while encouraging native grasses and forbs. A fungal endophyte, commonly present in tall fescue, can confer competitive advantages to the host plant, and may play a role in determining the ability of tall fescue plants to persist in pastures following restoration practices. We compared vegetation composition among four actively restored subunits of a tall fescue pasture (each receiving different combinations of prescribed fire and/or herbicide) and a control. We also measured the rate of endophyte infection in tall fescue present within each restoration treatment and control to determine if restoration resulted in lower tall fescue cover but higher endophyte infection rates (i.e. selected for endophyte‐infected individuals). Tall fescue cover was low in all restoration treatments and the control (1.1–17.9%). The control (unmanaged) had higher species richness than restoration treatments and plant community composition was indicative of succession to forest. Restoration practices resulted in higher cover of native warm season grasses, but in some cases also promoted a different undesirable species. We found no evidence of higher fungal endophyte presence in tall fescue following restoration, as all subunits had low endophyte infection rates (2.2–9.3%). Restoration of tall fescue systems using prescribed fire and herbicide may be used to promote native grassland species.     

Soil organic carbon fractions differ in two contrasting tall fescue systems

The value of tall fescue (Festuca arundinacea Schreb.) for C sequestration in addition to forage production and soil conservation is of current interest. However, studies relating to the impacts of endophyte infected (E+) and endophyte free (E?) tall fescue on soil organic matter fractions are few. This study examined how E+ and E? growth affected soil C fractions 4 years after establishment. The study site was at the University of Kentucky research farm, Lexington, Kentucky, USA. From soil cores in replicated fields we measured total C, particulate organic matter C (POM C), microbial biomass C (MBC), mineralizable C (Min C), C in aggregates, and aggregate distribution at depths of 0 to 15 and 15 to 30 cm. Significant effects between E+ and E- fescue were sometimes observed for MBC, Min C, C in micro-aggregates, and aggregate distribution, but not for total C, and POM C. At 0?C15 cm MBC (E+ 26% greater than E?), Min C (E+ 43% lower than E?), C associated with micro-aggregates (E+ 15% lower than E?), and micro-aggregates (46% more micro-aggregates in E+ than E?), were affected by endophyte infection, confirming hypotheses that early changes in soil properties were reflected in labile C fractions and soil structure. Endophyte infection status in tall fescue has quantifiable effects on C sequestration and soil structure, achievable in a relatively short period that can be used to monitor conservation efforts and the consequences of pasture renovation strategies.     

Endophytes inconsistently affect plant communities across Schedonorus arundinaceus hosts

Fungal endophytes in cool-season grasses may affect communities at multiple trophic levels. However, it is unclear whether community-scale endophyte effects arise due to the endophyte itself or as a result of unique, endophyte–host interactions. We used a long-term field experiment to test whether common-toxic (CT) and non-ergot alkaloid-producing (novel) endophytes in Schedonorus arundinaceus (tall fescue) forage cultivars consistently affect communities across tall fescue hosts. Tilled plots (2 × 2 m; Guelph, ON) were seeded with Georgia 5 and Jesup cultivars containing either the CT or AR542 (novel) endophyte and allowed to be re-colonized by plant species from the local propagule pool. Non-seeded control plots were included to assess effects of seeding the non-native grass. We assessed plant, invertebrate, soil moisture, and soil nutrient responses to the endophyte–cultivar treatments after four growing seasons. Seeding tall fescue affected plant species abundances, but not richness, and did not consistently alter soil moisture and nutrient pools. Endophyte identity in the tall fescue cultivars affected the communities, but effects were not consistent between cultivars. Within Georgia 5, the AR542 endophyte reduced tall fescue abundance and altered the invertebrate community relative to CT plots. Within Jesup, the AR542 endophyte reduced species evenness and decreased soil moisture during dry periods relative to CT plots. Endophyte effects were not consistent between cultivars, and it is probable that the community-scale effects of endophyte infection in tall fescue cultivars arise due to unique interactions between cultivar and endophyte.     

Host Status of Endophyte-Infected and Noninfected Tall Fescue Grass to Meloidogyne spp

Tall fescue grass cultivars with or without endophytes were evaluated for their susceptibility to Meloidogyne incognita in the greenhouse. Tall fescue cultivars evaluated included, i) wild-type Jesup (E+, ergot-producing endophyte present), ii) endophyte-free Jesup (E-, no endophyte present), iii) Jesup (Max-Q, non-ergot producing endophyte) and iv) Georgia 5 (E+). Peach was included as the control. Peach supported greater (P ≤ 0.05) reproduction of M. incognita than all tall fescue cultivars. Differences in reproduction were not detected among the tall fescue cultivars and all cultivars were rated as either poor or nonhosts for M. incognita. Suppression of M. incognita reproduction was not influenced by endophyte status. In two other greenhouse experiments, host susceptibility of tall fescue grasses to two M. incognita isolates (BY-peach isolate and GA-peach isolate) did not appear to be related to fungal endophyte strain [i.e., Jesup (Max-Q; nontoxic endophyte strain) vs. Bulldog 51 (toxic endophyte strain)]. Host status of tall fescue varied with species of root-knot nematode. Jesup (Max-Q) was rated as a nonhost for M. incognita (BY-peach isolate and GA-peach isolate) and M. hapla, a poor host for M. javanica and a good host for M. arenaria. Bulldog 51 tall fescue was also a good host for M. arenaria and M. javanica, but not M. incognita. Jesup (Max-Q) tall fescue may have potential as a preplant control strategy for M. incognita and M. hapla in southeastern and northeastern United States, respectively.