Native Plant Growth and Seedling Establishment in Soils Influenced by Bromus Tectorum

The invasion of 40 million hectares of the American West by cheatgrass (Bromus tectorum L.) has caused widespread modifications in the vegetation of semi-arid ecosystems and increased the frequency of fires. In addition to well-understood mechanisms by which cheatgrass gains competitive advantage, it has been implicated in reducing arbuscular mycorrhizal fungi (AMF) abundance and taxa diversity. We evaluated this possibility at a high elevation site in a two-pronged approach. To test whether cheatgrass changed native AMF communities in ways that affected subsequent native plant growth, we grew cheatgrass and native plants in native soils and then planted native plants into these soils in a greenhouse experiment. We found that cheatgrass-influenced soils did not inhibit native plant growth or AMF sporulation or colonization. To test whether soils in cheatgrass-dominated areas inhibited establishment and growth of native plants, cheatgrass was removed and six seeding combinations were applied. We found that 14.02 ±  seedlings · m⁻² established and perennial native plant cover increased fourfold over the three years of this study. Glyphosate reduced cheatgrass cover to less than 5% in the year it was applied but did not facilitate native plant establishment or growth compared with no glyphosate. We conclude that cheatgrass influence on the soil community does not appear to contribute to its invasion success in these high elevation soils. It appears that once cheatgrass is controlled on sites with sufficient native plant abundance, there may be few lingering effects to inhibit the natural reestablishment of native plant communities.     

A Comparison of Bromus tectorum Growth and Mycorrhizal Colonization in Salt Desert vs. Sagebrush Habitats

Cheatgrass (Bromus tectorum) has recently invaded marginal low-elevation salt desert habitats across the Great Basin. We tested the hypothesis that cheatgrass seed produced in populations from the more stressful salt desert vs. upland sagebrush habitats should grow differently in salt desert soils compared to adjacent upland sagebrush soil, and vice versa. We evaluated growth, incidence of flowering, and arbuscular mycorrhizal fungi (AMF) colonization of plants grown in the soils from which their seeds were collected vs. in the reciprocal soils from the nearest sagebrush or salt desert site in three large basins in northern Nevada. Simultaneously we measured nutrient cations, available nitrogen and phosphorus, percent carbon and nitrogen, texture, and dry-down characteristics in all soils. We found that salt desert soils were generally more nutrient poor and more saline than their upland (sagebrush) counterparts; salt desert soils also generally had a higher percentage of sand compared to their upland counterparts and were consistently drier. The most dramatic plant responses to soil and seed source were 1) lower aboveground biomass of mature plants in most salt desert soils compared to sagebrush soils, or lower biomass in plants grown from salt desert seed; 2) lower root:shoot ratios in plants grown in salt desert soil across two of three basins, irrespective of seed source; 3) a higher percentage of flowering individuals from salt desert seed sources at harvest, irrespective of soil source; 4) depressed AMF colonization of plants in salt desert soils; and 5) strong influence exerted by seed source on AMF, whereby sagebrush-originating plants grown in sagebrush soils had greater AMF colonization compared to salt desert soils but salt desert-originating seedlings had very low AMF colonization rates irrespective of soil source. These results suggest that both population level and soil-based controls are important as this widespread weed moves into marginal habitat.     

Soil Moisture Enhancement Techniques Aid Shrub Transplant Success in an Arid Shrubland Restoration

In arid and semi-arid environments, where low and unpredictable rainfall is typical, establishment of perennial vegetation can be enhanced with modest increases in soil moisture. We evaluated methods for promoting shrub transplant establishment. We transplanted approximately 1 000 3-mo-old seedlings in April 2004, 2005, and 2006, using a full-factorial design with combinations of three treatments: addition of mycorrhizae spores to the root zone, addition of a hydrogel to the root zone, and placement of a wood obstruction south of the plant. We planted three shrubs: big sagebrush (Artemisia tridentata Nutt. ssp. tridentate), four wing saltbush (Atriplex canescens [Pursh] Nutt.), and rubber rabbitbrush (Ericameria nauseosa [Pall. ex Pursh] G.L. Nesom & Baird ssp. nauseosa) in a 1.2-ha area. The summer months of 2004 and 2006 were dry, leading to low survivorship (< 1%). With higher rainfall in summer 2005, transplant survivorship was ～18%. For the 2005 transplants, A. tridentata had the highest survivorship after one growing season (31.0%), followed by A. canescens (20.6%) and E. nauseosa (6.9%). Placing a wood obstruction near the plant was significant in the statistical model to describe short-term overall transplant survival and survival of A. tridentata. Placing hydrogel in the root zone also explained short-term overall transplant survival, as well as survival of E. nauseosa. However, by 4.5 yr after transplanting, there was no significant treatment effect on survival. Thus, for transplanting shrub seedlings on arid or semi-arid sites, we recommend some form of resource enhancement technique to increase short-term survival. In this experiment, both the obstruction and hydrogel treatments were effective. We recommend the obstruction treatment since slash is often readily available onsite, has low labor requirements and cost, and it increased transplant survival of A. tridentata, a species of conservation concern; however, other treatments may be appropriate for individual species.     

Anthelmintic efficacy of hydro-methanolic extracts of Larrea tridentata against larvae of Haemonchus contortus

An in vitro study was conducted to determine the anthelminthic activity of hydro-methanolic extracts of Larrea tridentata on sheathed and exsheathed larvae of Haemonchus contortus. Larvae of the parasite were incubated at 20–25 °C in hydro-methanolic extracts at concentrations of 12.5, 25, 50, 100, and 200 mg/mL for 24, 48, or 72 h. Ivermectin and water were the positive and negative controls, respectively. Total phenolic compounds of leaves of L. tridentata were 97.88?±?10.45 mg/g of dry matter. Other compounds detected in this shrub by HPLC-mass spectrometry were sesamin, galocatechin, peonidin 3-O rutinoside, methyl galangin, epigallocatechin 7-O-glucuronide, and epigalocatechin. Mortality rate of sheathed and exsheathed H. contortus was low (16–34%) with doses ≤?100 mg/mL of the extracts. At 200 mg/ml, the hydro-methanolic extracts of L. tridentata killed 32.1 and 68.4% of sheathed and exsheathed larvae, respectively, regardless of incubation time. The effective concentration of the L. tridentata extract for 50% larvae mortality (EC₅₀) after 24 h of incubation was 36 mg/mL (CI?=?6–94). Microscopic observations revealed damage to the cuticle of this parasite exposed to extracts of L. tridentata. These in vitro results provided evidence that L. tridentata extracts possess anti-Haemonchus contortus properties, particularly during the exsheathed stage of this nematode. It would be necessary to assess the safety of this shrub in vivo and also to carry out in vivo efficacy studies.

     

Spectrophotometry of Artemisia tridentata to Quantitatively Determine Subspecies

Ecological restoration is predicated on our abilities to discern plant taxa. Taxonomic identification is a first step in ensuring that plants are appropriately adapted to the site. An example of the need to identify taxonomic differences comes from big sagebrush (Artemisia tridentata). This species is composed of three predominant subspecies occupying distinct environmental niches, but overlap and hybridization are common in ecotones. Restoration of A. tridentata largely occurs using wildland collected seed, but there is uncertainty in the identification of subspecies or mix of subspecies from seed collections. Laboratory techniques that can determine subspecies composition would be desirable to ensure that subspecies match the restoration site environment. In this study, we use spectrophotometry to quantify chemical differences in the water-soluble compound, coumarin. Ultraviolet (UV) absorbance of A. tridentata subsp. vaseyana showed distinct differences among A.t. tridentata and wyomingensis. No UV absorbance differences were detected between A.t. tridentata and wyomingensis. Analyses of samples from > 600 plants growing in two common gardens showed that UV absorbance was unaffected by environment. Moreover, plant tissues (leaves and seed chaff) explained only a small amount of the variance. UV fluorescence of water-eluted plant tissue has been used for many years to indicate A.t. vaseyana; however, interpretation has been subjective. Use of spectrophotometry to acquire UV absorbance provides empirical results that can be used in seed testing laboratories using the seed chaff present with the seed to certify A. tridentata subspecies composition. On the basis of our methods, UV absorbance values < 2.7 would indicate A.t. vaseyana and values > 3.1 would indicate either A.t. tridentata or wyomingensis. UV absorbance values between 2.7 and 3.1 would indicate a mixture of A.t. vaseyana and the other two subspecies.     

干旱胁迫下AMF对枳生长和活性氧代谢的影响

在正常水分和干旱胁迫下,研究丛枝菌根真菌(AMF)Funneliformis mosseae对枳生长和活性氧代谢的影响。结果表明：6 周的干旱处理显著抑制了枳根系菌根侵染率和植株生长。接种AMF能显著增加正常水分和干旱胁迫下枳株高、茎粗、叶片数,也显著降低叶片丙二醛、过氧化氢和超氧阴离子自由基含量,并显著增强叶片超氧化物歧化酶(主要是Mn-SOD和Cu/Zn-SOD)、过氧化物酶和过氧化氢酶的活性。研究揭示了菌根化植株具有更高的抗氧化防御能力,导致较低的氧化伤害,从而增强植物的抗旱性。     

丛枝菌根真菌强化高梁幼苗修复锶污染土壤的研究

研究选用高粱为修复植物开展锶污染土壤治理,通过添加不同丛枝菌根真菌(arbuscular mycorrhizal fungi,AMF),包括地球囊霉、地表球囊霉、摩西球囊霉、透光球囊霉,比较不同AMF对幼苗期高粱修复锶污染土壤的调控作用。结果表明,与对照组(non-AMF)相比,AMF处理组的菌根侵染率均高于50%。与未接种AMF相比,接种AMF的高粱的生物量、株高和根长都显著增加(P<0.05),地球囊霉侵染高粱的地上和根生物量分别增加54.72%和53.26%,摩西球囊霉分别增加49.82%和37.92%。接种AMF的高粱都表现出显著的菌根依赖性(P<0.05),说明丛枝菌根真菌促进高粱生长。其中最显著的是地球囊霉和摩西球囊霉,菌根依赖性分别为154.44%和147.61%。AMF处理的高粱,其叶片和根中的锶含量与对照相比显著增加(P<0.05),转运系数都高于1。地球囊霉侵染后高粱的地上部分和根中的锶含量分别增加了86.05%和30.18%。接种地球囊霉、摩西球囊霉和地表球囊霉后,土壤中的全磷含量和速效磷含量显著降低(P<0.05)。全磷减少了15.89%20.32%,速效磷减少了12.98%18.49%。接种AMF显著增加了土壤磷酸酶活性(P<0.05),与对照相比,增加了21.43%30.36%。地球囊霉、摩西球囊霉和地表球囊霉接种处理显著增加了土壤转化酶活性,增加了25.77%28.87%。综上所述,AMF能够促进高粱幼苗对锶的富集能力和耐受性,其中,接种地球囊霉的效果最好。     

Arbuscular Mycorrhizal Fungi Can Accelerate the Restoration of Degraded Spring Grassland in Central Asia

Three years of field inoculation experiments were carried out in a central Asian desert to understand the effects of arbuscular mycorrhizal fungi (AMF) on the restoration process of degraded grassland. The results indicate that the biomass, density, and cover of ephemerals improved significantly after inoculation with AMF. Compared to the control treatment, aboveground biomass per plant of the mycorrhizal plant species Erodium oxyrrhynchum, Hyalea pulchella, Trigonella arcuata, and Schismus arabicus significantly increased in mycorrhizal treatment, but no significant differences were observed in the nonmycorrhizal species Alyssum linifolim and Ceratocarpus arenarius between mycorrhizal and control treatments. The total seedling numbers per square meter in the mycorrhizal treatment were much more than control treatment in all 3 yr. Inoculation with AMF increased the total cover of ephemeral plants from 7% to 14% in 2005, 15% to 38% in 2006, and 39% to 62% in 2009 than control treatment. Moreover, community productivity (shoot dry weight, grams per square meter) in mycorrhizal treatments significantly increased from 6 to 29 in 2005, 11 to 36 in 2006, and 27 to 81 in 2009 compared with the control treatment. It is concluded that AMF can speed up the regeneration process of grassland and this may be used as an effective biological approach in the restoration of degraded desert ephemeral plant communities.     

Outplanting Wyoming Big Sagebrush Following Wildfire: Stock Performance and Economics

Finding ecologically and economically effective ways to establish matrix species is often critical for restoration success. Wyoming big sagebrush (Artemisia tridentata subsp. wyomingensis) historically dominated large areas of western North America, but has been extirpated from many areas by large wildfires; its re-establishment in these areas often requires active management. We evaluated the performance (survival, health) and economic costs of container and bare-root stock based on operational plantings of more than 1.5 million seedlings across 2 200 ha, and compared our plantings with 30 other plantings in which sagebrush survival was tracked for up to 5 yr. Plantings occurred between 2001 and 2007, and included 12 combinations of stock type, planting amendment, and planting year. We monitored 10 500 plants for up to 8 yr after planting. Survival to Year 3 averaged 21% and was higher for container stock (30%) than bare-root stock (17%). Survival did not differ among container-stock plantings, whereas survival of bare-root stock was sometimes enhanced by a hydrogel dip before planting, but not by mycorrhizal amendments. Most mortality occurred during the first year after planting; this period is the greatest barrier to establishment of sagebrush stock. The proportion of healthy stock in Year 1 was positively related to subsequent survival to Year 3. Costs were minimized, and survival maximized, by planting container stock or bare-root stock with a hydrogel dip. Our results indicate that outplanting is an ecologically and economically effective way of establishing Wyoming big sagebrush. However, statistical analyses were limited by the fact that data about initial variables (stock quality, site conditions, weather) were often unrecorded and by the lack of a replicated experimental design. Sharing consistent data and using an experimental approach would help land managers and restoration practitioners maximize the success of outplanting efforts.     

Plant Age and Growing Season Nutritional Content Relationships of Three Artemisia tridentata Subspecies

The effect of plant age on growing season chemical compositions and rumen fermentation characteristics was determined for three subspecies of big sagebrush: basin (Artemisia tridentata [Nutt.] subsp. tridentata), mountain (A. tridentata subsp. vaseyana [Rybd.] Beetle), and Wyoming (A. tridentata subsp. wyomingensis [Beetle and Young]). In vitro dry matter (IVDMD) and organic matter (IVOMD) disappearance, ammonia nitrogen (NH₃N), and volatile fatty acid (VFA) content were determined at the end of two fermentation periods (24 h and 48 h) by combining rumen inocula with age-classified vegetative samples from each sagebrush subspecies. An additional one-way analysis of variance was performed to investigate potential differences among subspecies in IVDMD, IVOMD, total VFA, and NH₃N following a 48-h fermentation period. Crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), and acid detergent lignin (ADL) components were also compared among sagebrush subspecies. Age class responses were variable across the spectrum of sagebrush subspecies and response variables. Where plant age effects were indicated, the small numeric differences probably have little biological or ecological significance. Mountain sagebrush was lower in IVOMD and total VFA concentrations (P < 0.0001) than basin and Wyoming. NH₃N concentration and CP were higher (P < 0.0001) in basin sagebrush than the other two subspecies, while Wyoming sagebrush was higher in NDF, ADF, and ADL than basin and mountain subspecies (P < 0.0001). NH₃N concentration for all three subspecies was lower than the minimum level (20 mg · 100 mL^?1) required for uninhibited rumen activity. Overall, this research questions the contention that older sagebrush plants offer less nutritional value than younger ones, at least for growing season conditions. The results also provide information that can be utilized in designing supplementation strategies for domestic animals on diets with characteristically high utilization of big sagebrush.     

The influence of vesicular‐arbuscular mycorrhizas on production and nutrition of white clover

Inoculating white clover seedlings with E3 and Glomus tenuis vesicular‐arbuscular mycorrhizas produced slight increases in dry matter production in unsterilized field plots at Cedara, Natal. Phosphorus levels in plant tops showed no increases due to mycorrhizas but crude protein content of all mycorrhizal plants were higher than those of non‐mycorrhizal plants.     

高寒退化草地委陵菜根围丛枝菌根菌(AMF)分离鉴定及促生效应

从祁连山高寒退化草地优势植被钝裂委陵菜根围分离丛枝菌根真菌(AMF),鉴定并研究其促生效果,为农业生产和生态修复提供服务。用湿筛倾析—蔗糖离心法提取土壤AMF孢子,按形态挑出大量相同孢子并用燕麦盆栽法扩繁;通过形态学和18S rRNA基因分析鉴定;并通过燕麦盆栽试验(CK:不接菌;处理A:接种根内根孢囊霉(AMF1);处理B:接种本研究分离菌株AMF2)探寻AMF对燕麦苗期的促生作用。结果表明,分离扩繁出一株含量最多的丛枝菌根真菌AMF2,经形态学鉴定发现AMF2孢子颜色为白色、奶白色、黄棕色;孢子椭球形、球状、近球形;孢子直径在90~120 μm;18S基因测序获得有效序列长度为673 bp,并与NCBI blast比对发现AMF2与根内根孢囊霉相似度为100%,故结合两种鉴定方法鉴定为根内根孢囊霉,GenBank序列号MK311327。盆栽试验表明,处理A和B的AMF侵染率达到70%和61%,根活力较CK相比,分别提高了206%和123%;AMF2使燕麦苗期株高、茎粗、叶绿素b含量分别增加11%、21%和3%,AMF1对燕麦苗期地上部分促生作用较弱;两种根内球囊霉均能够增加燕麦根系总根长、根体积、根表面积,降低根平均直径,特别是对直径0~1.0 mm根的影响,其中AMF2对燕麦苗期生长的促生效果较好。综上,本研究筛选得到的AMF2为根内根孢囊霉,不仅丰富了我国AMF菌种库,还为高寒退化草地生态修复提供了有效途径。     

Simulating Current Successional Trajectories in Sagebrush Ecosystems With Multiple Disturbances Using a State-and-Transition Modeling Framework

Disturbances and their interactions play major roles in sagebrush (Artemisia spp. L.) community dynamics. Although impacts of some disturbances, most notably fire, have been quantified at the landscape level, some have been ignored and rarely are interactions between disturbances evaluated. We developed conceptual state-and-transition models for each of two broad sagebrush groups—a warm-dry group characterized by Wyoming big sagebrush (Artemisia tridentata Nutt. subsp. wyomingensis Beetle & Young) communities and a cool-moist group characterized by mountain big sagebrush (Artemisia tridentata Nutt. subsp. vaseyana [Rydb.] Beetle) communities. We used the Vegetation Dynamics Development Tool to explore how the abundance of community phases and states in each conceptual model might be affected by fire, insect outbreak, drought, snow mold, voles, sudden drops in winter temperatures (freeze-kill), livestock grazing, juniper (Juniperus occidentalis var. occidentalis Hook.) expansion, nonnative annual grasses such as cheatgrass (Bromus tectorum L.), and vegetation treatments. Changes in fuel continuity and loading resulted in average fire rotations of 12 yr in the warm-dry sagebrush group and 81 yr in the cool-moist sagebrush group. Model results in the warm-dry sagebrush group indicated postfire seeding success alone was not sufficient to limit the area of cheatgrass domination. The frequency of episodes of very high utilization by domestic livestock during severe drought was a key influence on community phase abundance in our models. In the cool-moist sagebrush group, model results indicated at least 10% of the juniper expansion area should be treated annually to keep juniper in check. Regardless, juniper seedlings and saplings would remain abundant.     

松嫩平原盐碱化羊草群落中AM真菌物种资源及侵染率研究

本研究在松嫩平原西部12个地区15个重度盐碱化草地中,调查了羊草群落天然斑块中AM真菌的种类和分布、AM真菌羊草根系的侵染能力及土壤pH值的影响。共分离出AM真菌4属11种,其中球囊霉属(Glomus)占总物种数的72.42%,在各调查样点中出现频度最高,其中摩西球囊霉(G. mossea)出现频度达100.0%。土壤pH强烈抑制盐碱化草地中羊草天然群落斑块中AM真菌的物种丰富度,但对孢子密度的影响未达到显著水平。AM真菌对羊草根系的侵染频率和侵染强度显著正相关。AM真菌对羊草根系的侵染频率和侵染强度随着AM物种数量的增加而增强,随着土壤pH的增加而下降。在盐碱化羊草地中存在较丰富的侵染羊草根系的AM真菌资源,研究结果为筛选和利用耐盐碱AM真菌菌株以恢复和重建松嫩盐碱化羊草草地生态系统提供了理论依据。     

不同磷水平下丛枝菌根真菌(AMF)对狗牙根生长与再生的影响

采用盆栽试验研究了3个施磷水平(20,40,100 mg/kg)下,接种丛枝菌根真菌(AMF)菌种摩西球囊霉和聚丛球囊霉对刈割后狗牙根生长与再生的影响。结果表明,1)狗牙根根系能与摩西球囊霉和聚丛球囊霉形成良好的共生关系,其中单一接种聚丛球囊霉菌种处理的侵染率最高。2)狗牙根地上部氮、磷浓度呈极显著正相关,暗示着氮、磷积累可能存在协同效应。3)4次刈割条件下,与AMF共生的狗牙根具有较高的再生速度和较大的生物量,表明菌根化有利于增强刈割后狗牙根的再生能力。4)施磷水平对狗牙根的生长与再生产生显著影响,尤其是土壤施磷量40 mg/kg比20或100 mg/kg更能显著增加刈割后地上部生物量的积累,并加快再生生长的速度。因此,建议在日常养护管理中,可根据狗牙根再生特性和养分吸收情况来接种AMF菌剂并进行适当施肥,以保证狗牙根的生长和增强其刈割后的再生能力。     

Relationship among ovarian follicular status,developmental competence of oocytes,and anti‐Müllerian hormone levels: A comparative study in Japanese wild boar crossbred gilts and Large White gilts

The aim of this study was to investigate the ovarian follicular development, developmental competence of oocytes, and plasma anti‐Müllerian hormone (AMH) levels of Japanese wild boar crossbred (wild hybrid) gilts, whose litter size is inferior to that of European breeds. Ovary and plasma samples were collected from two different breeds of gilts (wild hybrid and Large White breeds). The ovaries from the wild hybrid gilts had a lower average numbers of secondary follicles and vesicular follicles in ovarian cross‐sections and of good quality oocytes collected from ovarian follicles as compared with those from Large White gilts (p < 0.05). The development rate to the blastocyst stage of good quality oocytes after in vitro maturation, fertilization and culture was also lower (p < 0.05) in wild hybrid gilts than in Large White gilts. Plasma AMH levels with >0.16 ng/ml were detected in 8.3% of the examined wild hybrid gilts and 33% of the Large White gilts. These results indicate that the low reproductive performance of wild hybrid breed may result in part from low numbers of vesicular follicles and good quality oocytes, and low developmental competence of oocytes. Moreover, plasma AMH levels may support low number of vesicular follicles in ovaries of wild hybrid gilts.     

毛乌素沙地密集型克隆植物根围AM真菌多样性及空间分布

在毛乌素沙地选设3个样地,系统研究2种密集型克隆植物白沙蒿和黑沙蒿根围丛枝菌根真菌的多样性、分布及共生体结构特征。结果显示,AM真菌的分布及多样性与宿主植物和土壤条件密切相关,黑沙蒿根围AM真菌的孢子密度高于白沙蒿,水肥条件较好的榆林样地黑沙蒿根围孢子密度最高。本试验共分离出AM真菌6属20种,其中地球囊霉(Glomus geosporum)是黑沙蒿根围的优势菌种,光壁无梗囊霉(Acaulospora laevis)为白沙蒿根围的优势菌种。2种沙蒿根围孢子密度在3个样地均与土壤深度显著负相关,最大值出现在0~20 cm表层土。菌丝侵染率与泡囊侵染率呈显著正相关,丛枝侵染率与菌丝圈百分率显著正相关。丛枝侵染率与宿主植物须根在土壤中的分布变化密切相关。分析表明,2种沙蒿均为典型的丛枝菌根植物,其优异固沙性能的主要原因之一是特化根系与丛枝菌根真菌共生互补的结果。同时,荒漠土壤-植物-菌根最佳组合的优势菌种的筛选,可为毛乌素沙地植被恢复提供材料和依据。     

Role of Grazing Intensity on Shaping Arbuscular Mycorrhizal Fungi Communities in Patagonian Semiarid Steppes

Arbuscular mycorrhizal fungi (AMF) are vital for maintaining ecosystem structure and functioning and can be affected by complex interactions between plants and herbivores. Information found in the literature about how ungulate grazing affects AMF is in general contradictory but might be caused by differences in grazing intensities (GIs) among studies. Hence we studied how different GIs affect the composition, diversity, and abundance of AMF communities in a semiarid steppe of Patagonia. We predicted that 1) total AMF spore abundance (TSA) and diversity would decrease only under intense-grazing levels and 2) AMF species spore abundance would depend on their life-history strategies and on the GI. To test our predictions, we compared AMF communities among nongrazed (NG), moderately grazed (MG, 0.1–0.3 sheep ha¹), and intensely grazed sites (IG, > 0.3 sheep ha¹). GI was the most important factor driving changes in TSA and diversity, regardless of host plant identity. TSA, diversity, and evenness significantly decreased in IG sites but were not affected by MG. AMF species spore abundance varied depending on their life-history strategies and GI. Families with high growth rates like Glomeraceae and probably Pacisporaceae showed the highest spore abundance in all sites but decreased under IG. Species with higher carbon demands like Gigasporaceae showed low spore abundance and frequency in NG and MG sites and were absent in IG sites. In contrast, species with low growth rates, but efficient carbon usage, like Acaulosporaceae, showed low spore abundance in all sites but increased in IG sites compared with NG or MG sites. We conclude that intensification of grazing reduces AMF diversity and abundance, with the likely loss of AMF benefits for plants, such as improved nutrient and water uptake and soil aggregation. Therefore, sustainable grazing systems should be designed to improve or restore AMF communities, particularly in degraded rangelands, like the Patagonian steppes.     

模拟放牧对高寒草甸丛枝菌根真菌的影响

采用植物样方调查与丛枝菌根（AM）真菌的形态分子鉴定等方法分析了模拟放牧对地上植物及地下AM真菌群落的影响。结果表明：随着放牧程度的增加,地上植物的物种丰富度显著降低,但AM真菌的物种丰富度没有显著变化;AM真菌总侵染率与丛枝侵染率随着放牧强度的增加显著降低,但泡囊侵染与土壤AM真菌的孢子密度均不受放牧强度的显著影响;模拟放牧对植物群落组成具有显著影响,但AM真菌的群落组成不受放牧的影响。以上结果表明较植物群落而言,AM真菌对放牧干扰具有较高的耐受性,凸显了在放牧干扰条件下,AM真菌在维持高寒草甸生物多样性过程中的作用。     

接种AMF替代磷肥促进退化草地黄花苜蓿的补播建植

退化草地土壤肥力和有益微生物的降低是补播植物建植的主要限制因子。为探究植物共生菌与施肥对补播豆科的退化草地群落结构和生产力的影响,本研究选取黄花苜蓿(Medicago falcate)、羊草(Leymus chinensis)和冷蒿(Artemisia frigida)进行盆栽试验。结果表明：(1)与不接种相比,接种丛枝菌根真菌(Arbuscular mycorrhizal fungi,AMF)使黄花苜蓿的地上生物量显著提高259.54%;不接种加施磷肥比不施肥下黄花苜蓿地上生物量显著提高465.93%,而双接种加施磷肥比不施肥下黄花苜蓿的地上生物量仅显著提高46.58%;(2)与不接种相比,接种AMF使羊草的地上生物量显著降低60.66%;不接种加施磷肥比不施肥时羊草地上生物量显著提高34.49%;(3)不接种加施磷肥比不施肥下冷蒿地上生物量显著提高149.32%;接种AMF时,冷蒿地上生物量在氮磷同施处理下较其它施肥处理平均显著提高129.39%。因此,在退化草地中补播黄花苜蓿时,为减少肥料用量及节约成本,可通过接种AMF替代施用磷肥。