Effect of long-term nitrogen fertilization on mycorrhizal fungi associated with a dominant grass in a semiarid grassland

We studied the diversity of arbuscular mycorrhizal fungi (AMF) in semiarid grassland and the effect of long-term nitrogen (N) fertilization on this fungal community. Root samples of Bouteloua gracilis were collected at the Sevilleta National Wildlife Refuge (New Mexico, USA) from control and N-amended plots that have been fertilized since 1995. Small subunit rDNA was amplified using AMF specific primers NS31 and AM1. The diversity of AMF was low in comparison with other ecosystems, only seven operational taxonomic units (OTU) were found in B. gracilis and all belong to the genus Glomus. The dominant OTU was closely related to the ubiquitous G. intraradices/G. fasciculatum group. N-amended plots showed a reduction in the abundance of the dominant OTU and an increase in AMF diversity. The greater AMF diversity in roots from N-amended plots may have been the result of displacement of the dominant OTU, which facilitated detection of uncommon AMF. The long-term implications of AMF responses to N enrichment for plant carbon allocation and plant community structure remain unclear.     

Host Identity Impacts Rhizosphere Fungal Communities Associated with Three Alpine Plant Species

Fungal diversity and composition are still relatively unknown in many ecosystems; however, host identity and environmental conditions are hypothesized to influence fungal community assembly. To test these hypotheses, we characterized the richness, diversity, and composition of rhizosphere fungi colonizing three alpine plant species, Taraxacum ceratophorum, Taraxacum officinale, and Polemonium viscosum. Roots were collected from open meadow and willow understory habitats at treeline on Pennsylvania Mountain, Colorado, USA. Fungal small subunit ribosomal DNA was sequenced using fungal-specific primers, sample-specific DNA tags, and 454 pyrosequencing. We classified operational taxonomic units (OTUs) as arbuscular mycorrhizal (AMF) or non-arbuscular mycorrhizal (non-AMF) fungi and then tested whether habitat or host identity influenced these fungal communities. Approximately 14% of the sequences represented AMF taxa (44 OTUs) with the majority belonging to Glomus groups A and B. Non-AMF sequences represented 186 OTUs belonging to Ascomycota (58%), Basidiomycota (26%), Zygomycota (14%), and Chytridiomycota (2%) phyla. Total AMF and non-AMF richness were similar between habitats but varied among host species. AMF richness and diversity per root sample also varied among host species and were highest in T. ceratophorum compared with T. officinale and P. viscosum. In contrast, non-AMF richness and diversity per root sample were similar among host species except in the willow understory where diversity was reduced in T. officinale. Fungal community composition was influenced by host identity but not habitat. Specifically, T. officinale hosted a different AMF community than T. ceratophorum and P. viscosum while P. viscosum hosted a different non-AMF community than T. ceratophorum and T. officinale. Our results suggest that host identity has a stronger effect on rhizosphere fungi than habitat. Furthermore, although host identity influenced both AMF and non-AMF, this effect was stronger for the mutualistic AMF community.     

桐-药复合经营模式下泡桐丛枝菌根真菌群落结构特征

采用Illumina MiSeq高通量测序技术,研究江西鄱阳湖周边平原岗地的泡桐纯林及桐-药复合经营模式(泡桐-玉竹、泡桐-麦冬和泡桐-射干)下泡桐丛枝菌根真菌(arbuscular mycorrhizae fungi, AMF)群落结构特征。研究发现,泡桐AMF群落主要由球囊霉科、巨孢囊霉科、无梗囊霉科和多孢囊霉科组成,其中球囊霉科真菌占绝对优势,但不同科的相对丰度在不同经营模式下仍存在差异。与泡桐纯林相比,桐-药复合经营模式会降低泡桐菌根侵染率及AMF群落多样性。只有泡桐-射干经营模式中的泡桐含有多孢囊霉科真菌,且相对多度占2.73%。研究结果表明桐-药复合经营模式下中药材种类的差异会不同程度地改变泡桐AMF的群落结构。这为进一步研究桐-药复合经营模式下泡桐AMF的生态功能和资源利用提供了科学依据。     

Species richness and spore abundance of arbuscular mycorrhizal fungi across distinct land uses in Western Brazilian Amazon

Arbuscular mycorrhizal fungi (AMF) were surveyed for species richness and abundance in sporulation in six distinct land uses in the western Amazon region of Brazil. Areas included mature pristine forest and sites converted to pasture, crops, agroforestry, young and old secondary forest. A total of 61 AMF morphotypes were recovered and 30% of them could not be identified to known species. Fungal communities were dominated by Glomus species but Acaulospora species produced the most abundant sporulation. Acaulospora gedanensis cf., Acaulospora foveata, Acaulospora spinosa, Acaulospora tuberculata, Glomus corymbiforme, Glomus sp15, Scutellospora pellucida, and Archaeospora trappei sporulated in all land use areas. Total spore numbers were highly variable among land uses. Mean species richness in crop, agroforestry, young and old secondary forest sites was twice that in pristine forest and pasture. fungal communities were dominated in all land use areas except young secondary forest by two or three species which accounted for 48% to 63% of all sporulation. Land uses influenced AMF community in (1) frequency of occurrence of sporulating AMF species, (2) mean species diversity, and (3) relative spore abundance. Conversion of pristine forest into distinct land uses does not appear to reduce AMF diversity. Cultural practices adopted in this region maintain a high diversity of arbuscular mycorrhizal fungi.     

Nitrogen and phosphorus additions impact arbuscular mycorrhizal abundance and molecular diversity in a tropical montane forest

Increased nitrogen (N) depositions expected in the future endanger the diversity and stability of ecosystems primarily limited by N, but also often co‐limited by other nutrients like phosphorus (P). In this context a nutrient manipulation experiment (NUMEX) was set up in a tropical montane rainforest in southern Ecuador, an area identified as biodiversity hotspot. We examined impacts of elevated N and P availability on arbuscular mycorrhizal fungi (AMF), a group of obligate biotrophic plant symbionts with an important role in soil nutrient cycles. We tested the hypothesis that increased nutrient availability will reduce AMF abundance, reduce species richness and shift the AMF community toward lineages previously shown to be favored by fertilized conditions. NUMEX was designed as a full factorial randomized block design. Soil cores were taken after 2 years of nutrient additions in plots located at 2000 m above sea level. Roots were extracted and intraradical AMF abundance determined microscopically; the AMF community was analyzed by 454‐pyrosequencing targeting the large subunit rDNA. We identified 74 operational taxonomic units (OTUs) with a large proportion of Diversisporales. N additions provoked a significant decrease in intraradical abundance, whereas AMF richness was reduced significantly by N and P additions, with the strongest effect in the combined treatment (39% fewer OTUs), mainly influencing rare species. We identified a differential effect on phylogenetic groups, with Diversisporales richness mainly reduced by N additions in contrast to Glomerales highly significantly affected solely by P. Regarding AMF community structure, we observed a compositional shift when analyzing presence/absence data following P additions. In conclusion, N and P additions in this ecosystem affect AMF abundance, but especially AMF species richness; these changes might influence plant community composition and productivity and by that various ecosystem processes.     

Simulated Nitrogen Deposition Causes a Decline of Intra- and Extraradical Abundance of Arbuscular Mycorrhizal Fungi and Changes in Microbial Community Structure in Northern Hardwood Forests

Increased nitrogen (N) deposition caused by human activities has altered ecosystem functioning and biodiversity. To understand the effects of altered N availability, we measured the abundance of arbuscular mycorrhizal fungi (AMF) and the microbial community in northern hardwood forests exposed to long-term (12 years) simulated N deposition (30 kg N ha⁻¹ y⁻¹) using phospholipid fatty acid (PLFA) analysis and hyphal in-growth bags. Intra- and extraradical AMF biomass and total microbial biomass were significantly decreased by simulated N deposition by 36, 41, and 24%, respectively. Both methods of extraradical AMF biomass estimation (soil PLFA 16:1ω5c and hyphal in-growth bags) showed comparable treatment responses, and extraradical biomass represented the majority of total (intra-plus extraradical) AMF biomass. N deposition also significantly affected the microbial community structure, leading to a 10% decrease in fungal to bacterial biomass ratios. Our observed decline in AMF and total microbial biomass together with changes in microbial community structure could have substantial impacts on the nutrient and carbon cycling within northern hardwood forest ecosystems.     

Reduced aboveground tree growth associated with higher arbuscular mycorrhizal fungal diversity in tropical forest restoration

Establishing diverse mycorrhizal fungal communities is considered important for forest recovery, yet mycorrhizae may have complex effects on tree growth depending on the composition of fungal species present. In an effort to understand the role of mycorrhizal fungi community in forest restoration in southern Costa Rica, we sampled the arbuscular mycorrhizal fungal (AMF) community across eight sites that were planted with the same species (Inga edulis, Erythrina poeppigiana, Terminalia amazonia, and Vochysia guatemalensis) but varied twofold to fourfold in overall tree growth rates. The AMF community was measured in multiple ways: as percent colonization of host tree roots, by DNA isolation of the fungal species associated with the roots, and through spore density, volume, and identity in both the wet and dry seasons. Consistent with prior tropical restoration research, the majority of fungal species belonged to the genus Glomus and genus Acaulospora, accounting for more than half of the species and relative abundance found on trees roots and over 95% of spore density across all sites. Greater AMF diversity correlated with lower soil organic matter, carbon, and nitrogen concentrations and longer durations of prior pasture use across sites. Contrary to previous literature findings, AMF species diversity and spore densities were inversely related to tree growth, which may have arisen from trees facultatively increasing their associations with AMF in lower soil fertility sites. Changes to AMF community composition also may have led to variation in disturbance susceptibility, host tree nutrient acquisition, and tree growth. These results highlight the potential importance of fungal–tree–soil interactions in forest recovery and suggest that fungal community dynamics could have important implications for tree growth in disturbed soils.     

Nitrogen Fertilization Has a Stronger Effect on Soil Nitrogen-Fixing Bacterial Communities than Elevated Atmospheric CO2

Biological nitrogen fixation is the primary supply of N to most ecosystems, yet there is considerable uncertainty about how N-fixing bacteria will respond to global change factors such as increasing atmospheric CO₂ and N deposition. Using the nifH gene as a molecular marker, we studied how the community structure of N-fixing soil bacteria from temperate pine, aspen, and sweet gum stands and a brackish tidal marsh responded to multiyear elevated CO₂ conditions. We also examined how N availability, specifically, N fertilization, interacted with elevated CO₂ to affect these communities in the temperate pine forest. Based on data from Sanger sequencing and quantitative PCR, the soil nifH composition in the three forest systems was dominated by species in the Geobacteraceae and, to a lesser extent, Alphaproteobacteria. The N-fixing-bacterial-community structure was subtly altered after 10 or more years of elevated atmospheric CO₂, and the observed shifts differed in each biome. In the pine forest, N fertilization had a stronger effect on nifH community structure than elevated CO₂ and suppressed the diversity and abundance of N-fixing bacteria under elevated atmospheric CO₂ conditions. These results indicate that N-fixing bacteria have complex, interacting responses that will be important for understanding ecosystem productivity in a changing climate.     

模拟大气氮沉降对中国森林生态系统影响的研究进展

人类活动加剧了活性氮的生产和排放,并导致氮沉降日益增加并全球化。目前,人类活动对全球氮循环的干扰已经超出了地球系统安全运行的界限。中国已成为全球氮沉降的高发区域,高氮沉降已经威胁到生态系统的健康和安全,并成为生态文明建设过程中亟待理清和解决的热点问题。对国际上和中国森林生态系统模拟氮沉降研究的概况进行了综述,并从生物学和非生物学两大过程重点阐述模拟氮沉降增加对中国主要森林生态系统影响的研究进展。中国自2000年以后才开始重视大气氮沉降产生的生态环境问题,中国科学院华南植物园在国内森林生态系统模拟氮沉降试验研究上做出了开创性的贡献。模拟氮沉降研究表明,持续高氮输入将会显著改变森林生态系统的结构和功能,并威胁生态系统的健康发展,特别是处于氮沉降热点区域的中国中南部。森林生态系统的氮沉降效应依赖于系统的氮状态、土地利用历史、气候特征、林型和林龄等。最后,对未来的研究提出了一些建议,包括加强长期跟踪研究和不同气候带站点之间的联网研究,特别是在森林生态系统对长期氮沉降响应与适应的过程机制、地下碳氮吸存潜力研究、以及与其他全球变化因子的耦合研究等方面,以期为森林生态系统的可持续发展提供理论基础和管理依据。     

Decrease in diversity and changes in community composition of arbuscular mycorrhizal fungi in roots of apple trees with increasing orchard management intensity across a regional scale

Understanding which factors drive the diversity and community composition of arbuscular mycorrhizal fungi (AMF) is important due to the role of these soil micro‐organisms in ecosystem functioning and current environmental threats to AMF biodiversity. Additionally, in agro‐ecosystems, this knowledge may help to evaluate their use in making agriculture more sustainable. Here, we used 454‐pyrosequencing of small subunit rRNA gene amplicons to quantify AMF diversity and community composition in the roots of cultivated apple trees across 24 orchards in central Belgium. We aimed at identifying the factors (soil chemical variables, organic vs. conventional farming, and geographical location) that affect AMF diversity and community composition. In total, 110 AMF OTUs were detected, of which the majority belonged to the Glomeraceae (73%) and the Claroideoglomeraceae (19%). We show that soil characteristics and farming system, rather than the geographical location of the orchards, shape AMF communities on apple trees. Particularly, plant‐available P content of the soil was associated with lower AMF diversity. In orchards with a lower plant‐available P content of the soil (P < 100 mg/kg soil), we also found a significantly higher AMF diversity in organically managed orchards as compared to conventionally managed orchards. Finally, the degree of nestedness of the AMF communities was related to plant‐available P and N content of the soil, pointing at a progressive loss of AMF taxa with increasing fertilization. Overall, we conclude that a combination of organic orchard management and moderate fertilization may preserve diverse AMF communities on apple trees and that AMF in the roots of apple trees appear not to be dispersal limited at the scale of central Belgium.     

Changes in arbuscular mycorrhizal fungal communities along a river delta island in northeastern Brazil

Arbuscular mycorrhizal fungi (AMF) play a key role in the maintenance of the balance of terrestrial ecosystems, but little is known about the biogeography of these fungi, especially on tropical islands. This study aims to compare AMF community structure along a transect crossing a fluvial-marine island and relate these communities with soil and vegetation parameters to shed light on the forces driving AMF community structure on a local scale. We tested the hypothesis that the composition of AMF communities changes across the island, even within short distances among sites, in response to differences in edaphic characteristics and vegetation physiognomies. We sampled roots and soils in five different natural and degraded habitats: preserved mangrove forest (MF), degraded mangrove forest (MD), natural Restinga forest (RF), and two regeneration Restinga forests (RR1 and RR2) on Ilha da Restinga, northeastern Brazil. We determined the mycorrhizal colonization rate and AMF community structure based on morphological spore identification. The island soils were sandy with pH varying from acid to neutral; higher levels of organic matter were registered in RF and lower in MF; other chemical and physical soil attributes differed along the habitat types on the island. In total, 22 AMF species were identified, without any difference in species richness. However, the diversity and composition of AMF communities, spore abundance per families, and mycorrhizal colonization were statistically different among the habitats. The composition of AMF communities was strongly related to soil characteristics, especially the sum of exchangeable bases. Our results indicate that the different habitat types have diverse AMF communities even within short distances among habitats. In conclusion, islands with high spatial heterogeneity in soil parameters and diverse vegetation are potential refuges for the diversity conservation of AM fungi.     

An arbuscular mycorrhizal fungus significantly modifies the soil bacterial community and nitrogen cycling during litter decomposition

Arbuscular mycorrhizal fungi (AMF) perform an important ecosystem service by improving plant nutrient capture from soil, yet little is known about how AMF influence soil microbial communities during nutrient uptake. We tested whether an AMF modifies the soil microbial community and nitrogen cycling during litter decomposition. A two‐chamber microcosm system was employed to create a root‐free soil environment to control AMF access to ¹³C‐ and ¹⁵N‐labelled root litter. Using a 16S rRNA gene microarray, we documented that approximately 10% of the bacterial community responded to the AMF, Glomus hoi. Taxa from the Firmicutes responded positively to AMF, while taxa from the Actinobacteria and Comamonadaceae responded negatively to AMF. Phylogenetic analyses indicate that AMF may influence bacterial community assembly processes. Using nanometre‐scale secondary ion mass spectrometry (NanoSIMS) we visualized the location of AMF‐transported ¹³C and ¹⁵N in plant roots. Bulk isotope ratio mass spectrometry revealed that the AMF exported 4.9% of the litter ¹⁵N to the host plant (Plantago lanceolata L.), and litter‐derived ¹⁵N was preferentially exported relative to litter‐derived ¹³C. Our results suggest that the AMF primarily took up N in the inorganic form, and N export is one mechanism by which AMF could modify the soil microbial community and decomposition processes.     

Microbial inoculation influences arbuscular mycorrhizal fungi community structure and nutrient dynamics in temperate tree restoration

Soil microbial communities have a profound influence on soil chemical processes and subsequently influence tree nutrition and growth. This study examined how the addition of a commercial inoculum or forest‐collected soils influenced nitrogen (N) and phosphorus (P) dynamics, soil microbial community structure, and growth in Liriodendron tulipifera and Prunus serotina tree saplings. Inoculation method was an important determinant of arbuscular mycorrhizal fungi (AMF) community structure in both species and altered soil N dynamics in Prunus and soil P dynamics in Liriodendron. Prunus saplings receiving whole forest soil transfers had a higher rhizosphere soil carbon/nitrogen ratio and ammonia content at the end of the first growing season when compared to unmanipulated control saplings. Inoculation with whole forest soil transfers resulted in increased inorganic phosphorus in Liriodendron rhizosphere soils. The number of AMF terminal restriction fragments was significantly greater in rhizosphere soils of Liriodendron saplings inoculated with whole forest soil transfers and Prunus saplings receiving either inoculum source than control saplings. Forest soil inoculation also increased AMF colonization and suppressed stem elongation in Liriodendron after 16 months; conversely, Prunus AMF colonization was unchanged and stem elongation was significantly greater when saplings were inoculated with whole forest soil transfers. Longer term monitoring of tree response to inoculation will be essential to assess whether early costs of AMF colonization may provide long‐term benefits. This study provides insight into how practitioners can use microbial inoculation to alter AMF community structure and functioning, subsequently influencing tree growth and nutrient cycling during the restoration of degraded lands.     

Edaphic and host plant factors are linked to the composition of arbuscular mycorrhizal fungal communities in the root zone of endangered Ulmus chenmoui Cheng in China

Despite the importance of arbuscular mycorrhizal fungi (AMF) within deciduous forest ecosystems, we know little about how natural AMF communities are structured in the root zone of the endangered elm species Ulmus chenmoui. In this study, three U. chenmoui sampling sites, differing with respect to plant health, age, and growth status, were selected in Anhui Province, China. AMF biodiversity in the root zones of individual U. chenmoui trees was investigated using high‐throughput sequencing. In total, 61 AMF operational taxonomic units were detected. Five genera, namely Glomus (62.82%), Paraglomus (17.82%), Rhizophagus (4.29%), Septoglomus (4.06%) and Funneliformis (2.35%), and 29 species of AMF were identified. Correlation analysis indicated that available soil phosphorus and potassium concentrations were the main edaphic factors influencing AMF community structure. There was a difference in AMF species richness among the three U. chenmoui stands. Our study showed that soil nutrient concentrations and plant health, age, and growth status can exert a selective effect on the composition of the AMF population in the soil in the root zones of U. chenmoui trees.     

Differences in the AMF diversity in soil and roots between two annual and perennial gramineous plants co-occurring in a Mediterranean, semiarid degraded area

Aims

In the present study, we analysed the diversity of indigenous arbuscular mycorrhizal fungi (AMF) colonising both the roots and rhizosphere soil of an annual herbaceous species, Bromus rubens, and a perennial herbaceous species, Brachypodium retusum, co-occurring in the same Mediterranean, semiarid degraded area. The intention was to study whether these two species promoted the diversity of AM fungi in their rhizospheres differently and to ascertain whether the AMF community harboured by an annual plant species differed from that harboured by a perennial species when both grew in the same place.

Methods

The AMF large subunit ribosomal RNA genes (LSU) were subjected to nested PCR, cloning, sequencing and phylogenetic analysis.

Results

Twenty AMF sequence types belonging to Glomus group A, Glomus group B and Diversispora were identified. The two plant species differed in the AMF community composition in their roots, B. rubens showing a higher diversity of AMF than B. retusum. However the composition of the AMF communities associated with the two rhizosphere soils was similar.

Conclusions

These results suggest that the management of these Mediterranean, semiarid degraded areas should include the promotion of annual herbaceous plant communities in order to maintain the sustainability and productivity of these ecosystems.     

A method for assessing arbuscular mycorrhizal fungi group distribution in tree roots by intergenic transcribed sequence variation

We identified five taxonomic groups of arbuscular mycorrhizal fungi (AMF) inside roots of young trees of six species of legumes and six species of non-legumes from a field site in southern Costa Rica using an AMF group-specific PCR assay of the intergenic transcribed sequence and 18S rRNA gene fragment. Assay specificity was verified by cloning and sequencing representatives from four of the five AMF groups. We found no difference in overall AMF diversity levels between legumes and non-legumes or between plant species. Some groups of AMF may associate more frequently with legumes than others, as Glomus Group A (Glomus mosseae/intradices group) representatives were detected more frequently in legumes than non-legumes relative to Glomus Group B (Glomus etunicatum/claroideum) representatives.     

Arbuscular mycorrhizal fungal communities along a pedo-hydrological gradient in a Central Amazonian terra firme forest

Little attention has been paid to plant mutualistic interactions in the Amazon rainforest, and the general pattern of occurrence and diversity of arbuscular mycorrhizal fungi (AMF) in these ecosystems is largely unknown. This study investigated AMF communities through their spores in soil in a ‘terra firme forest’ in Central Amazonia. The contribution played by abiotic factors and plant host species identity in regulating the composition, abundance and diversity of such communities along a topographic gradient with different soils and hydrology was also evaluated. Forty-one spore morphotypes were observed with species belonging to the genera Glomus and Acaulospora, representing 44 % of the total taxa. Soil texture and moisture, together with host identity, were predominant factors responsible for shaping AMF communities along the pedo-hydrological gradient. However, the variability within AMF communities was largely associated with shifts in the relative abundance of spores rather than changes in species composition, confirming that common AMF species are widely distributed in plant communities and all plants recruited into the forest are likely to be exposed to the dominant sporulating AMF species.     

Bare soil cover and arbuscular mycorrhizal community in the first montane forest restoration in Central Argentina

Soil erosion affects extensive areas worldwide and must be urgently reduced promoting plant cover and beneficial microorganisms associated with plants, including arbuscular mycorrhizal fungi (AMF). In mountain environments, plant cover is difficult to enhance due to harsh conditions during the dry season and steep slopes. Our objective was to evaluate the percentage of the soil surface covered by plants and the AMF community associated with trees 12.5 years after planting during forest restoration efforts in microsites at different levels of soil degradation. The study was performed in the first montane forest restoration initiative of Central Argentina, where one of the trials consisted of planting Polylepis australis saplings at microsites with different levels of soil degradation: high, intermediate, and low. After 12.5 years, percentage of bare soil cover was significantly reduced by 36 and 37% in the high and intermediate degradation microsites, respectively. Low degradation microsites were initially very low in bare soil and did not significantly change. Mycorrhizal colonization, hyphae, vesicles, arbuscules, AMF diversity, and community structure were similar among microsite types. Percentage of hyphal entry points was higher at microsites with low degradation, number of spores was higher in high and intermediate degradation, and species richness was higher in high degradation. Acaulospora and Glomus were the most abundant genera in all microsites. We conclude that even in the most degraded microsites around 2.8% of the bare soil is covered by vegetation each year and that the arbuscular mycorrhizal community is highly tolerant and adapted to soils with different disturbance types.     

模拟N沉降对太岳山油松人工林和天然林草本群落的影响

由于人类活动氮沉降呈逐年增加的趋势,进而增加了陆地生态系统氮的输入,从而影响陆地生态系统多样性、物种组成和功能。为揭示氮沉降增加对油松林草本群落的影响,于2009年7月在太岳山油松人工林和天然林,设计4个施氮水平:对照(CK,0 kg N hm-2a-1),低氮(LN,50 kg N hm-2a-1),中氮(MN,100 kg N hm-2a-1)和高氮(HN,150 kg N hm-2a-1),研究草本群落的生物多样性、生物量以及草本元素含量对模拟N沉降的响应。研究结果表明:模拟N沉降未能显著影响人工林草本群落的生物多样性(P0.05),而中氮、高氮显著降低了天然林草本群落的生物多样性(P0.05);从Jaccard指数和Sorensen指数分析得出人工林不同氮水平之间草本群落差异性较小,而天然林不同氮水平之间草本群落差异性较大。模拟N沉降没有显著改变人工林草本群落生物量(P0.05),而高氮明显促进天然林草本群落生物量的增加(P0.05)。与对照相比,模拟N沉降提高了人工林和天然林羊胡子苔草叶根中的全N含量(P0.05),而降低了全Mg的含量(P0.05),并且根部元素含量变化与土壤养分含量变化较为一致。施氮提高了N/K、N/Ca、N/Mg(P0.05)的比值。说明油松林下草本群落对氮沉降的响应因林分土壤N饱和程度以及林地利用历史的不同而产生差异,其中天然林响应最为敏感。     

Differences of arbuscular mycorrhizal fungal diversity and community between a cultivated land,an old field,and a never-cultivated field in a hot and arid ecosystem of southwest China

We investigated the spore density, species composition, and diversity of arbuscular mycorrhizal fungi (AMF) in a cultivated land (CL), an old field (OF), and a never-cultivated field (NCF), which are located adjacently in a slope in the hot and arid ecosystem of southwest China. AMF spores in the rhizosphere soils of representative plants in the three habitats were extracted by wet-sieving and decanting. A total of 47 taxa of AMF including 31 taxa from the genus Glomus, 8 from Acaulospora, 6 from Scutellospora, 1 from Entrophospora, and 1 from Gigaspora were extracted and identified morphologically. The highest spore density occurred in NCF, slightly lower in OF and lowest in CL, and the Shannon–Wiener index of species diversity was reversed. The dominant species of AMF were different in the three habitats. OF resembled NCF more than CL in AMF spore density, species richness, and community composition, which means that AMF community in the OF has been developing from cultivated land to natural habitat. Cluster analysis based on the similarity in AMF community composition indicated that the distribution of AMF was not random over space and that AMF community composition associated with a given plant species was greatly habitat-convergence. Following the cluster analysis, we hypothesized that the effect of habitats on AMF communities were greater than that of the host preference to AMF. L-F. Li and T. Li contributed equally to this work.