2017. Pitfall trap sampling bias depends on body mass, temperature, and trap number: insights fro... more 2017. Pitfall trap sampling bias depends on body mass, temperature, and trap number: insights from an individual-based model. Ecosphere 8(4): Abstract. The diversity and community composition of ground arthropods is routinely analyzed by pitfall trap sampling, which is a cost-and time-effective method to gather large numbers of replicates but also known to generate data that are biased by species-specific differences in locomotory activity. Previous studies have looked at factors that influence the sampling bias. These studies, however, were limited to one or few species and did rarely quantify how the species-specific sampling bias shapes community-level diversity metrics. In this study, we systematically quantify the species-specific and community-level sampling bias with an allometric individual-based model that simulates movement and pitfall sampling of 10 generic ground arthropod species differing in body mass. We perform multiple simulation experiments covering different scenarios of pitfall trap number, spatial trap arrangement, temperature, and population density. We show that the sampling bias decreased strongly with increasing body mass, temperature, and pitfall trap number, while population density had no effect and trap arrangement only had little effect. The average movement speed of a species in the field integrates body mass and temperature effects and could be used to derive reliable estimates of absolute species abundance. We demonstrate how unbiased relative species abundance can be derived using correction factors that need only information on species body mass. We find that community-level diversity metrics are sensitive to the particular community structure, namely the relation between body mass and relative abundance across species. Generally, pitfall trap sampling flattens the rank-abundance distribution and leads to overestimations of ground arthropod Shannon diversity. We conclude that the correction of the species-specific pitfall trap sampling bias is necessary for the reliability of conclusions drawn from ground arthropod field studies. We propose bias correction is a manageable task using either body mass to derive unbiased relative abundance or the average speed to derive reliable estimates of absolute abundance from pitfall trap sampling.
Ecosystem responses to changes in species diversity are often studied individually. However, chan... more Ecosystem responses to changes in species diversity are often studied individually. However, changes in species diversity can simultaneously influence multiple interdependent ecosystem functions. Therefore, an important challenge is to determine when and how changes in species diversity that influence one function will also drive changes in other functions. By providing the underlying structure of species interactions, ecological networks can quantify connections between biodiversity and multiple ecosystem functions. Here, we review parallels in the conceptual development of biodiversity–ecosystem functioning (BEF) and food web theory (FWT) research. Subsequently, we evaluate three common principles that unite these two research areas by explaining the patterns, concentrations, and direction of the flux of nutrients and energy through the species in diverse interaction webs. We give examples of combined BEF–FWT approaches that can be used to identify vulnerable species and habitats and to evaluate links that drive trade-offs between multiple ecosystems functions. These combined approaches reflect promising trends towards better management of biodiversity in landscapes that provide essential ecosystem services supporting human well-being
1 2 Microcosms, Substrate, and Soil Communities 3 Grassland microcosms were established under ste... more 1 2 Microcosms, Substrate, and Soil Communities 3 Grassland microcosms were established under sterile conditions in closed growth 4 chambers (1). To avoid any outside greenhouse-borne microbial contamination, 5 incoming air was filtered through a hydrophobic filter with a pore size of 0.2 µm 6 (Millex®-FG 50 ; Millipore Corporation, Billerica, USA) and water was filtered through a 7 hydrophilic filter with a 0.22 µm pore size (Millex®-GP 50 ; Millipore Corporation, 8 Billerica, USA). Microcosms were assembled, inoculated, and planted within a laminar 9 flow hood. All parts used for the microcosms were sterilized by autoclaving for 30 min 10 at 121 °C, with the exception of the Plexiglas tops and the PVC microcosm bottoms. 11 The bottom and top of the microcosms were sterilized by submersing in 0.5% sodium 12 hypochlorite for 20-30 minutes, then in 70% Ethanol with a few drops of Tween 20 for 13 a few minutes and air-dried within the Laminar flow hood. 14 Each microcosm had a 1-cm deep layer of 1 cm diameter sterilized (90 min at 15 121 °C) quartz stones at the bottom with a 0.5 mm propyltex mesh (Sefar AG, Heiden, 16 Switzerland) to aid in the collection of leachate (see below). Each microcosm was filled 17 with 6 kg (dry mass) of a 1:1 quartz sand:field soil mix that was sterilized by 18 autoclaving for 90 min at 121 °C. The field soil used was collected from a grassland 19 located at the Agroscope Reckenholz research station in Zürich, Switzerland (47° 25' 20 38.71'' N, 8° 31' 3.91'' E) and was sieved through a 5 mm mesh before mixing. This 21 same field soil was used for creating the gradient of soil communities via sieving out 22 soil communities based on size. In experiment 1 there were five soil community 23 treatments and in experiment 2 there were six, each being replicated 8 times with the 24 32 analyser (Skalar, Breda, NL) after extraction with 0.0125M CaCl 2 . Plant available P 2 O 5 33 and K 2 O, extracted by CO 2 -saturated water, was 1.25 (SEM = 0.01) mg·kg -1 and 0.61 34 (SEM = 0.003) mg·kg -1 respectively. The ammonium acetate-EDTA (pH 4.65) 35 extracted amounts of Ca, P, K and Mg in mg·kg -1 were 6.51 x 10 3 (SEM = 0.04 x10 3 ), 36 21.8 (SEM= 0.32), 15.7 (SEM = 0.11), and 4.88 (SEM = 0.03), respectively. In all cases 37 no soil characteristic listed above varied greatly among treatments (all F 4,5 < 2.05 and P 38 > 0.20). 39 40 Plant Community and Growing Conditions. Seeds of each plant species (Trifolium 41 pratense, Lotus corniculatus, Lolium multiflorum, Poa annua, Festuca pratensis, 42 Prunella vulgaris, Senecio jacobea, Plantago lanceolata, Achillea milleflorum, and 43
Background/Question/Methods Soil organisms play a key role in ecosystems by regulating nutrient u... more Background/Question/Methods Soil organisms play a key role in ecosystems by regulating nutrient uptake, plant productivity and by influencing plant diversity. The importance of soil biota for the sustainability of ecosystems is still unresolved. Moreover, it is unclear how multiple ecosystem functions are simultaneously affected by changes in soil biodiversity and community composition. We manipulated soil biodiversity in outdoor lysimeters filled with 230 kg soil and planted with an agricultural crop rotation. In addition to this we manipulated soil biodiversity and soil community composition in microcososm with experimental grassland. Subsequently we tested how changes in soil biodiversity and soil community composition influenced a number of ecosystem functions including nutrient leaching losses, greenhouse gas (N2O) production, plant productivity, nutrient uptake and plant diversity. Results/Conclusions Here we show that soil organisms and soil biodiversity can enhance the susta...
Background/Question/Methods Soil microbes, although for the most part unseen, represent the large... more Background/Question/Methods Soil microbes, although for the most part unseen, represent the largest portion of life on this planet and are crucial for the functioning of terrestrial ecosystems. But, soil community composition is dependent on soil history and may consequently alter the sensitivity of soil communities to biodiversity loss. Increased biodiversity supports ecosystem functioning as different organisms perform dissimilarly when abiotic conditions fluctuate over space and time. However, the ability of diverse soil communities to maintain multiple ecosystem functions in the face of a changing climate is not well known. We focused on understanding the link between soil community composition and diversity as a mechanism for stabilizing multiple ecosystem functions. To do this, soil was collected from three sites with varying soil histories. Within each we created a soil community diversity gradient based on species body size. Multiple ecosystem functions were traced over a on...
ABSTRACT Interactions between plant and soil communities are known to play an integral role in sh... more ABSTRACT Interactions between plant and soil communities are known to play an integral role in shaping ecosystems. Plants influence the composition of soil communities and soil communities in turn influence plant performance. Such a plant–soil feedback may incur selection pressure on plants and the associating soil community. However, the evolutionary consequences of these above-belowground feedback interactions remain largely speculative. Here we assess whether plant–soil feedback effects differ between intraspecific plant populations and between generations within the same plant population. We used two populations of Trifolium pratense and assessed their performance when grown in association with their home versus away soil biota. Both populations were colonized by distinct microbial communities and performed better with their own home soil communities than with the soil community from the other intraspecific population, demonstrating intraspecific positive feedback effects of home soil. In one of the two populations, we found that plant performance and the root associated microbiota community differed between parental and progeny plants when inoculated with their own home soil. Differences in root associated community characteristics could explain more than 80% of the variation in performance among the progeny and parental plants. Our results highlight that intraspecific differences in both plant and associated soil communities shape plant–soil feedback effects, and consequently indicate that plant–soil feedback can influence the direction of selection between intraspecific plant populations.
Sub-alpine environments consist of altitudinal gradients associated with dramatic changes in plan... more Sub-alpine environments consist of altitudinal gradients associated with dramatic changes in plant growth and community composition, but the role of soil feedbacks and microbe interactions is largely unknown. Here, we examine the influence of the overall soil microbial community, with a focus on ectomycorrhizal
Although roots of species in the Pinaceae are usually colonized by ectomycorrhizal (EM) fungi, th... more Although roots of species in the Pinaceae are usually colonized by ectomycorrhizal (EM) fungi, there are increasing reports of the presence of arbuscular mycorrhizal (AM) and dark septate endophytic (DSE) fungi in these species. The objective of this study was to determine the colonization patterns in seedlings of three Pinus (pine) species (Pinus banksiana, Pinus strobus, Pinus contorta) and Picea glauca x Picea engelmannii (hybrid spruce) grown in soil collected from a disturbed forest site. Seedlings of all three pine species and hybrid spruce became colonized by EM, AM, and DSE fungi. The dominant EM morphotype belonged to the E-strain category; limited colonization by a Tuber sp. was found on roots of Pinus strobus and an unknown morphotype (cf. Suillus-Rhizopogon group) with thick, cottony white mycelium was present on short roots of all species. The three fungal categories tended to occupy different niches in a single root system. No correlation was found between the percent root colonized by EM and percent colonization by either AM or DSE, although there was a positive correlation between percent root length colonized by AM and DSE. Hyphae and vesicles were the only AM intracellular structures found in roots of all species; arbuscules were not observed in any roots.
Lotus japonicus har1 mutants respond to inoculation with Mesorhizobium loti by forming an excessi... more Lotus japonicus har1 mutants respond to inoculation with Mesorhizobium loti by forming an excessive number of nodules due to genetic lesions in the HAR1 autoregulatory receptor kinase gene. In order to expand the repertoire of mutants available for the genetic dissection of the root nodule symbiosis (RNS), a screen for suppressors of the L. japonicus har1-1 hypernodulation phenotype was performed. Of 150,000 M2 plants analyzed, 61 stable L. japonicus double-mutant lines were isolated. In the context of the har1-1 mutation, 26 mutant lines were unable to form RNS, whereas the remaining 35 mutant lines carried more subtle symbiotic phenotypes, either forming white ineffective nodules or showing reduced nodulation capacity. When challenged with Glomus intraradices, 18 of the 61 suppressor lines were unable to establish a symbiosis with this arbuscular mycorrhiza fungus. Using a combined approach of genetic mapping, targeting induced local lesions in genomics, and sequencing, all non-nodulating mutant lines were characterized and shown to represent new alleles of at least nine independent symbiotic loci. The class of mutants with reduced nodulation capacity was of particular interest because some of them may specify novel plant functions that regulate nodule development in L. japonicus. To facilitate mapping of the latter class of mutants, an introgression line, in which the har1-1 allele was introduced into a polymorphic background of L. japonicus ecotype MG20, was constructed.
ABSTRACT Mutant lines of Lotus japonicus (Regel) Larsen that show defects in nodulation as well a... more ABSTRACT Mutant lines of Lotus japonicus (Regel) Larsen that show defects in nodulation as well as in mycorrhiza formation are valuable resources for studying the events required for the establishment of functional symbioses. In this study, 11 mutant lines derived from a screen for genetic suppressors of har1-1 hypernodulation were assessed quantitatively for their ability to form arbuscular mycorrhizal (AM) symbiosis. The presence of extraradicalmycelia, appressoria, intraradical hyphae, arbuscules and vesicles were scored. Roots of the har1-1 parental line were heavily colonised by six weeks after inoculation with the AM fungus Glomus intraradices showing the typical Arum-type colonisation pattern. Five mutants lacked internal root colonisation with blocks either at the surface of epidermal cells or at the outer tangential wall of cortical cells. These AM-lines showed some differences in relation to the amount of extraradical hyphae, the number of appressoria, and the degree of abnormal appressorium morphology. Four mutants had internal root colonisation but at a lower level than the parental line. Two mutants showed no difference from the parental line. Results of this study provide additional genetic resources for studying the mechanism of root colonisation by AM fungi.
There is a great interest in ecology in understanding the role of soil microbial diversity for pl... more There is a great interest in ecology in understanding the role of soil microbial diversity for plant productivity and coexistence. Recent research has shown increases in species richness of mutualistic soil fungi, the arbuscular mycorrhizal fungi (AMF), to be related to increases in aboveground productivity of plant communities. However, the impact of AMF richness on plant-plant interactions has not been determined. Moreover, it is unknown whether species-rich AMF communities can act as insurance to maintain productivity in a fluctuating environment (e.g., upon changing soil conditions).
Current Opinion in Environmental Sustainability, 2012
ABSTRACT Soil biodiversity vastly exceeds aboveground biodiversity, and is prerequisite for ecosy... more ABSTRACT Soil biodiversity vastly exceeds aboveground biodiversity, and is prerequisite for ecosystem stability and services. This review presents recent findings in soil biodiversity research focused on interrelations with agricultural soil management. Richness and community structure of soil biota depend on plant biodiversity and vice versa. Soil biota govern nutrient cycling and storage, soil organic matter (SOM) formation and turnover. Agriculture manipulates plants, soils and SOM. With intensification, regulation of functions through biodiversity is replaced by regulation through agricultural measures. Fertilizers and agrochemicals exert strong effects on soil biodiversity and functioning. Resulting community shifts feed back on soil functions such as carbon and nutrient cycling and pest control. Therefore, agricultural systems with less inputs may promote self-regulating systems and higher biodiversity.
Roots encounter a plethora of microorganisms in the soil environment that are either deleterious,... more Roots encounter a plethora of microorganisms in the soil environment that are either deleterious, neutral, or beneficial to plant growth. Root endophytic fungi are ubiquitous. These include dark septate endophytes whose role in plant growth and the maintenance of plant communities is largely unknown. The objectives of this review were to assess the structural features of the interactions between dark septate endophytic fungi and the roots of both angiopsperms and conifers, and to suggest avenues for further research. Several light microscopy studies of endophyte-root interactions have revealed a variety of structural features, depending on host species and plant growth conditions. In some cases, when fungal hyphae enter roots they cause cell breakdown, whereas in other situations there is little noticeable effect. In some tree species, associations with these endophytes may mimic ectomycorrhizas or ectendomycorrhizas. The few ultrastructural studies indicate that intracellular hyphae lack a host-derived perifungal membrane and interfacial matrix material, features typical of biotrophic fungus -plant cell interactions. This raises questions concerning nutrient exchange between these fungi and plant cells. Further research in this area is needed. New approaches that include molecular cytology and livecell imaging are needed to determine early changes in plant cells when challenged with these fungi.
Communities of arbuscular mycorrhizal fungi (AMF) are crucial for promoting plant productivity in... more Communities of arbuscular mycorrhizal fungi (AMF) are crucial for promoting plant productivity in most terrestrial systems, including anthropogenically managed ecosystems. Application of AMF inocula has therefore become a widespread practice. It is, however, pertinent to understand the mechanisms that govern AMF community composition and their performance in order to design successful manipulations. Here we assess whether the composition and plant growth-promotional effects of a synthetic AMF community can be altered by inoculum additions of the isolates forming the community. This was determined by following the effects of three AMF isolates, each inoculated in two propagule densities into a preestablished AMF community. Fungal abundance in roots and plant growth were evaluated in three sequential harvests. We found a transient positive response in AMF abundance to the intraspecific inoculation only in the competitively weakest isolate. The other two isolates responded negatively to intra-and interspecific inoculations, and in some cases plant growth was also reduced. Our results suggest that increasing the AMF density may lead to increased competition among fungi and a trade-off with their ability to promote plant productivity. This is a key ecological aspect to consider when introducing AMF into soils.
2017. Pitfall trap sampling bias depends on body mass, temperature, and trap number: insights fro... more 2017. Pitfall trap sampling bias depends on body mass, temperature, and trap number: insights from an individual-based model. Ecosphere 8(4): Abstract. The diversity and community composition of ground arthropods is routinely analyzed by pitfall trap sampling, which is a cost-and time-effective method to gather large numbers of replicates but also known to generate data that are biased by species-specific differences in locomotory activity. Previous studies have looked at factors that influence the sampling bias. These studies, however, were limited to one or few species and did rarely quantify how the species-specific sampling bias shapes community-level diversity metrics. In this study, we systematically quantify the species-specific and community-level sampling bias with an allometric individual-based model that simulates movement and pitfall sampling of 10 generic ground arthropod species differing in body mass. We perform multiple simulation experiments covering different scenarios of pitfall trap number, spatial trap arrangement, temperature, and population density. We show that the sampling bias decreased strongly with increasing body mass, temperature, and pitfall trap number, while population density had no effect and trap arrangement only had little effect. The average movement speed of a species in the field integrates body mass and temperature effects and could be used to derive reliable estimates of absolute species abundance. We demonstrate how unbiased relative species abundance can be derived using correction factors that need only information on species body mass. We find that community-level diversity metrics are sensitive to the particular community structure, namely the relation between body mass and relative abundance across species. Generally, pitfall trap sampling flattens the rank-abundance distribution and leads to overestimations of ground arthropod Shannon diversity. We conclude that the correction of the species-specific pitfall trap sampling bias is necessary for the reliability of conclusions drawn from ground arthropod field studies. We propose bias correction is a manageable task using either body mass to derive unbiased relative abundance or the average speed to derive reliable estimates of absolute abundance from pitfall trap sampling.
Ecosystem responses to changes in species diversity are often studied individually. However, chan... more Ecosystem responses to changes in species diversity are often studied individually. However, changes in species diversity can simultaneously influence multiple interdependent ecosystem functions. Therefore, an important challenge is to determine when and how changes in species diversity that influence one function will also drive changes in other functions. By providing the underlying structure of species interactions, ecological networks can quantify connections between biodiversity and multiple ecosystem functions. Here, we review parallels in the conceptual development of biodiversity–ecosystem functioning (BEF) and food web theory (FWT) research. Subsequently, we evaluate three common principles that unite these two research areas by explaining the patterns, concentrations, and direction of the flux of nutrients and energy through the species in diverse interaction webs. We give examples of combined BEF–FWT approaches that can be used to identify vulnerable species and habitats and to evaluate links that drive trade-offs between multiple ecosystems functions. These combined approaches reflect promising trends towards better management of biodiversity in landscapes that provide essential ecosystem services supporting human well-being
1 2 Microcosms, Substrate, and Soil Communities 3 Grassland microcosms were established under ste... more 1 2 Microcosms, Substrate, and Soil Communities 3 Grassland microcosms were established under sterile conditions in closed growth 4 chambers (1). To avoid any outside greenhouse-borne microbial contamination, 5 incoming air was filtered through a hydrophobic filter with a pore size of 0.2 µm 6 (Millex®-FG 50 ; Millipore Corporation, Billerica, USA) and water was filtered through a 7 hydrophilic filter with a 0.22 µm pore size (Millex®-GP 50 ; Millipore Corporation, 8 Billerica, USA). Microcosms were assembled, inoculated, and planted within a laminar 9 flow hood. All parts used for the microcosms were sterilized by autoclaving for 30 min 10 at 121 °C, with the exception of the Plexiglas tops and the PVC microcosm bottoms. 11 The bottom and top of the microcosms were sterilized by submersing in 0.5% sodium 12 hypochlorite for 20-30 minutes, then in 70% Ethanol with a few drops of Tween 20 for 13 a few minutes and air-dried within the Laminar flow hood. 14 Each microcosm had a 1-cm deep layer of 1 cm diameter sterilized (90 min at 15 121 °C) quartz stones at the bottom with a 0.5 mm propyltex mesh (Sefar AG, Heiden, 16 Switzerland) to aid in the collection of leachate (see below). Each microcosm was filled 17 with 6 kg (dry mass) of a 1:1 quartz sand:field soil mix that was sterilized by 18 autoclaving for 90 min at 121 °C. The field soil used was collected from a grassland 19 located at the Agroscope Reckenholz research station in Zürich, Switzerland (47° 25' 20 38.71'' N, 8° 31' 3.91'' E) and was sieved through a 5 mm mesh before mixing. This 21 same field soil was used for creating the gradient of soil communities via sieving out 22 soil communities based on size. In experiment 1 there were five soil community 23 treatments and in experiment 2 there were six, each being replicated 8 times with the 24 32 analyser (Skalar, Breda, NL) after extraction with 0.0125M CaCl 2 . Plant available P 2 O 5 33 and K 2 O, extracted by CO 2 -saturated water, was 1.25 (SEM = 0.01) mg·kg -1 and 0.61 34 (SEM = 0.003) mg·kg -1 respectively. The ammonium acetate-EDTA (pH 4.65) 35 extracted amounts of Ca, P, K and Mg in mg·kg -1 were 6.51 x 10 3 (SEM = 0.04 x10 3 ), 36 21.8 (SEM= 0.32), 15.7 (SEM = 0.11), and 4.88 (SEM = 0.03), respectively. In all cases 37 no soil characteristic listed above varied greatly among treatments (all F 4,5 < 2.05 and P 38 > 0.20). 39 40 Plant Community and Growing Conditions. Seeds of each plant species (Trifolium 41 pratense, Lotus corniculatus, Lolium multiflorum, Poa annua, Festuca pratensis, 42 Prunella vulgaris, Senecio jacobea, Plantago lanceolata, Achillea milleflorum, and 43
Background/Question/Methods Soil organisms play a key role in ecosystems by regulating nutrient u... more Background/Question/Methods Soil organisms play a key role in ecosystems by regulating nutrient uptake, plant productivity and by influencing plant diversity. The importance of soil biota for the sustainability of ecosystems is still unresolved. Moreover, it is unclear how multiple ecosystem functions are simultaneously affected by changes in soil biodiversity and community composition. We manipulated soil biodiversity in outdoor lysimeters filled with 230 kg soil and planted with an agricultural crop rotation. In addition to this we manipulated soil biodiversity and soil community composition in microcososm with experimental grassland. Subsequently we tested how changes in soil biodiversity and soil community composition influenced a number of ecosystem functions including nutrient leaching losses, greenhouse gas (N2O) production, plant productivity, nutrient uptake and plant diversity. Results/Conclusions Here we show that soil organisms and soil biodiversity can enhance the susta...
Background/Question/Methods Soil microbes, although for the most part unseen, represent the large... more Background/Question/Methods Soil microbes, although for the most part unseen, represent the largest portion of life on this planet and are crucial for the functioning of terrestrial ecosystems. But, soil community composition is dependent on soil history and may consequently alter the sensitivity of soil communities to biodiversity loss. Increased biodiversity supports ecosystem functioning as different organisms perform dissimilarly when abiotic conditions fluctuate over space and time. However, the ability of diverse soil communities to maintain multiple ecosystem functions in the face of a changing climate is not well known. We focused on understanding the link between soil community composition and diversity as a mechanism for stabilizing multiple ecosystem functions. To do this, soil was collected from three sites with varying soil histories. Within each we created a soil community diversity gradient based on species body size. Multiple ecosystem functions were traced over a on...
ABSTRACT Interactions between plant and soil communities are known to play an integral role in sh... more ABSTRACT Interactions between plant and soil communities are known to play an integral role in shaping ecosystems. Plants influence the composition of soil communities and soil communities in turn influence plant performance. Such a plant–soil feedback may incur selection pressure on plants and the associating soil community. However, the evolutionary consequences of these above-belowground feedback interactions remain largely speculative. Here we assess whether plant–soil feedback effects differ between intraspecific plant populations and between generations within the same plant population. We used two populations of Trifolium pratense and assessed their performance when grown in association with their home versus away soil biota. Both populations were colonized by distinct microbial communities and performed better with their own home soil communities than with the soil community from the other intraspecific population, demonstrating intraspecific positive feedback effects of home soil. In one of the two populations, we found that plant performance and the root associated microbiota community differed between parental and progeny plants when inoculated with their own home soil. Differences in root associated community characteristics could explain more than 80% of the variation in performance among the progeny and parental plants. Our results highlight that intraspecific differences in both plant and associated soil communities shape plant–soil feedback effects, and consequently indicate that plant–soil feedback can influence the direction of selection between intraspecific plant populations.
Sub-alpine environments consist of altitudinal gradients associated with dramatic changes in plan... more Sub-alpine environments consist of altitudinal gradients associated with dramatic changes in plant growth and community composition, but the role of soil feedbacks and microbe interactions is largely unknown. Here, we examine the influence of the overall soil microbial community, with a focus on ectomycorrhizal
Although roots of species in the Pinaceae are usually colonized by ectomycorrhizal (EM) fungi, th... more Although roots of species in the Pinaceae are usually colonized by ectomycorrhizal (EM) fungi, there are increasing reports of the presence of arbuscular mycorrhizal (AM) and dark septate endophytic (DSE) fungi in these species. The objective of this study was to determine the colonization patterns in seedlings of three Pinus (pine) species (Pinus banksiana, Pinus strobus, Pinus contorta) and Picea glauca x Picea engelmannii (hybrid spruce) grown in soil collected from a disturbed forest site. Seedlings of all three pine species and hybrid spruce became colonized by EM, AM, and DSE fungi. The dominant EM morphotype belonged to the E-strain category; limited colonization by a Tuber sp. was found on roots of Pinus strobus and an unknown morphotype (cf. Suillus-Rhizopogon group) with thick, cottony white mycelium was present on short roots of all species. The three fungal categories tended to occupy different niches in a single root system. No correlation was found between the percent root colonized by EM and percent colonization by either AM or DSE, although there was a positive correlation between percent root length colonized by AM and DSE. Hyphae and vesicles were the only AM intracellular structures found in roots of all species; arbuscules were not observed in any roots.
Lotus japonicus har1 mutants respond to inoculation with Mesorhizobium loti by forming an excessi... more Lotus japonicus har1 mutants respond to inoculation with Mesorhizobium loti by forming an excessive number of nodules due to genetic lesions in the HAR1 autoregulatory receptor kinase gene. In order to expand the repertoire of mutants available for the genetic dissection of the root nodule symbiosis (RNS), a screen for suppressors of the L. japonicus har1-1 hypernodulation phenotype was performed. Of 150,000 M2 plants analyzed, 61 stable L. japonicus double-mutant lines were isolated. In the context of the har1-1 mutation, 26 mutant lines were unable to form RNS, whereas the remaining 35 mutant lines carried more subtle symbiotic phenotypes, either forming white ineffective nodules or showing reduced nodulation capacity. When challenged with Glomus intraradices, 18 of the 61 suppressor lines were unable to establish a symbiosis with this arbuscular mycorrhiza fungus. Using a combined approach of genetic mapping, targeting induced local lesions in genomics, and sequencing, all non-nodulating mutant lines were characterized and shown to represent new alleles of at least nine independent symbiotic loci. The class of mutants with reduced nodulation capacity was of particular interest because some of them may specify novel plant functions that regulate nodule development in L. japonicus. To facilitate mapping of the latter class of mutants, an introgression line, in which the har1-1 allele was introduced into a polymorphic background of L. japonicus ecotype MG20, was constructed.
ABSTRACT Mutant lines of Lotus japonicus (Regel) Larsen that show defects in nodulation as well a... more ABSTRACT Mutant lines of Lotus japonicus (Regel) Larsen that show defects in nodulation as well as in mycorrhiza formation are valuable resources for studying the events required for the establishment of functional symbioses. In this study, 11 mutant lines derived from a screen for genetic suppressors of har1-1 hypernodulation were assessed quantitatively for their ability to form arbuscular mycorrhizal (AM) symbiosis. The presence of extraradicalmycelia, appressoria, intraradical hyphae, arbuscules and vesicles were scored. Roots of the har1-1 parental line were heavily colonised by six weeks after inoculation with the AM fungus Glomus intraradices showing the typical Arum-type colonisation pattern. Five mutants lacked internal root colonisation with blocks either at the surface of epidermal cells or at the outer tangential wall of cortical cells. These AM-lines showed some differences in relation to the amount of extraradical hyphae, the number of appressoria, and the degree of abnormal appressorium morphology. Four mutants had internal root colonisation but at a lower level than the parental line. Two mutants showed no difference from the parental line. Results of this study provide additional genetic resources for studying the mechanism of root colonisation by AM fungi.
There is a great interest in ecology in understanding the role of soil microbial diversity for pl... more There is a great interest in ecology in understanding the role of soil microbial diversity for plant productivity and coexistence. Recent research has shown increases in species richness of mutualistic soil fungi, the arbuscular mycorrhizal fungi (AMF), to be related to increases in aboveground productivity of plant communities. However, the impact of AMF richness on plant-plant interactions has not been determined. Moreover, it is unknown whether species-rich AMF communities can act as insurance to maintain productivity in a fluctuating environment (e.g., upon changing soil conditions).
Current Opinion in Environmental Sustainability, 2012
ABSTRACT Soil biodiversity vastly exceeds aboveground biodiversity, and is prerequisite for ecosy... more ABSTRACT Soil biodiversity vastly exceeds aboveground biodiversity, and is prerequisite for ecosystem stability and services. This review presents recent findings in soil biodiversity research focused on interrelations with agricultural soil management. Richness and community structure of soil biota depend on plant biodiversity and vice versa. Soil biota govern nutrient cycling and storage, soil organic matter (SOM) formation and turnover. Agriculture manipulates plants, soils and SOM. With intensification, regulation of functions through biodiversity is replaced by regulation through agricultural measures. Fertilizers and agrochemicals exert strong effects on soil biodiversity and functioning. Resulting community shifts feed back on soil functions such as carbon and nutrient cycling and pest control. Therefore, agricultural systems with less inputs may promote self-regulating systems and higher biodiversity.
Roots encounter a plethora of microorganisms in the soil environment that are either deleterious,... more Roots encounter a plethora of microorganisms in the soil environment that are either deleterious, neutral, or beneficial to plant growth. Root endophytic fungi are ubiquitous. These include dark septate endophytes whose role in plant growth and the maintenance of plant communities is largely unknown. The objectives of this review were to assess the structural features of the interactions between dark septate endophytic fungi and the roots of both angiopsperms and conifers, and to suggest avenues for further research. Several light microscopy studies of endophyte-root interactions have revealed a variety of structural features, depending on host species and plant growth conditions. In some cases, when fungal hyphae enter roots they cause cell breakdown, whereas in other situations there is little noticeable effect. In some tree species, associations with these endophytes may mimic ectomycorrhizas or ectendomycorrhizas. The few ultrastructural studies indicate that intracellular hyphae lack a host-derived perifungal membrane and interfacial matrix material, features typical of biotrophic fungus -plant cell interactions. This raises questions concerning nutrient exchange between these fungi and plant cells. Further research in this area is needed. New approaches that include molecular cytology and livecell imaging are needed to determine early changes in plant cells when challenged with these fungi.
Communities of arbuscular mycorrhizal fungi (AMF) are crucial for promoting plant productivity in... more Communities of arbuscular mycorrhizal fungi (AMF) are crucial for promoting plant productivity in most terrestrial systems, including anthropogenically managed ecosystems. Application of AMF inocula has therefore become a widespread practice. It is, however, pertinent to understand the mechanisms that govern AMF community composition and their performance in order to design successful manipulations. Here we assess whether the composition and plant growth-promotional effects of a synthetic AMF community can be altered by inoculum additions of the isolates forming the community. This was determined by following the effects of three AMF isolates, each inoculated in two propagule densities into a preestablished AMF community. Fungal abundance in roots and plant growth were evaluated in three sequential harvests. We found a transient positive response in AMF abundance to the intraspecific inoculation only in the competitively weakest isolate. The other two isolates responded negatively to intra-and interspecific inoculations, and in some cases plant growth was also reduced. Our results suggest that increasing the AMF density may lead to increased competition among fungi and a trade-off with their ability to promote plant productivity. This is a key ecological aspect to consider when introducing AMF into soils.
Uploads
Papers by Cameron Wagg