Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Variation in phosphorus acquisition efficiency among maize varieties as related to mycorrhizal functioning
    Wang, X.X. - \ 2016
    Wageningen University. Promotor(en): Thomas Kuijper; Ellis Hoffland, co-promotor(en): G. Feng. - Wageningen : Wageningen University - ISBN 9789462577985 - 168
    zea mays - mycorrhizas - maize - phosphorus - nutrient use efficiency - vesicular arbuscular mycorrhizas - nutrient uptake - varieties - zea mays - mycorrhizae - maïs - fosfor - nutriëntengebruiksefficiëntie - vesiculair-arbusculaire mycorrhizae - voedingsstoffenopname (planten) - rassen (planten)

    Phosphorus (P) is a main limiting factor for agricultural production, but overusing P fertilizer has brought serious environmental damages in China. Improving P acquisition efficiency of agricultural crops is an urgent topic. It has been proven repeatedly that arbuscular mycorrhizal fungi (AMF) and genetic diversity within one crop plant can play important roles in P uptake by crops. The main objective of this thesis was to understand the role of the arbuscular mycorrhizal symbiosis in P acquisition efficiency of different maize varieties. The specific objectives were to test: 1) how P uptake by maize varieties responds to colonization by the native AMF community in the field; and 2) whether AMF hyphae take up P for plants from phytate which is the most abundant organic P form in soil; 3) whether mixing maize cultivars can improve maize productivity and whether AMF can play a role in this system; and 4) how AMF species (or community) legacy affects successional maize growth. In this thesis, I combined field experiments and greenhouse experiments and made use of maize genetic diversity and (native) AMF to improve P (including inorganic and organic P) acquisition.

    The effects of one single AMF species on maize growth and nutrient uptake have been well studied, but how maize varieties respond to the native AMF community has been insufficiently studied. In Chapter 2, I focused on how maize varieties responded to the native AMF community by using rotated cores in the field, to compare mycorrhizal responsiveness among 20 maize varieties and the difference of the AMF native community of four maize varieties (two old landraces and two modern hybrids). The results indicated that, 1) increased P fertilizer significantly reduced mycorrhizal responsiveness in the field; 2) a complicated relationship exists between mycorrhizal responsiveness in the field and pot experiment; 3) there was no significant difference between old and modern maize varieties in terms of mycorrhizal responsiveness and colonization; 4) there were only small differences in AMF community composition among the four maize varieties. By comparing mycorrhizal responsiveness of maize varieties between in the pot experiment and in the field experiment (with in-growth cores), I found mycorrhizal responsiveness of maize varieties in the pot experiment was significantly larger than that in the field experiment. Thus, mycorrhizal responsiveness of varieties within one cereal plant species tested classically in pots may not present their realistically mycorrhizal responsiveness in field.

    Phytate is the most abundant form of organic P in soil. To explore the potential of phytate utilization by plants is agriculturally and environmentally essential. Increased P nutrition of mycorrhizal plants derived from phytate has been reported, indicating that phytate can be a potential P source. However, earlier studies assessed phytate use by using acid phosphatase rather than phytase, and did not consider that phytate adsorption could lead to phosphate release. Thus, I investigated the effect of mycorrhizal hyphae-mediated phytase activity on P uptake by maize in Chapter 3. I conducted a rhizobox experiment to explore phytate use by mycorrhizal hyphae for two maize varieties. The results showed that: 1) phytate addition increased phytase and acid phosphatase activity, and resulted in increased P uptake and plant biomass; 2) the increase in P uptake and biomass were correlated with the increase of phytase activity but not with the increase of acid phosphatase activity; 3) lower phytate addition rate increased, but higher addition rates decreased hyphal length density. I conclude that P from phytate can be used by mycorrhizal plants, but that the phytate contribution to plant nutrition is likely limited. Phytase activity is a more relevant indicator to assess phytate use. In addition, there was a significant interaction between maize varieties and AMF species in taking up P from phytate, which implies there is a possibility to combine different maize varieties to increase total yield using phytate. Besides, I used an empirical relationship to assess phosphate release due to phytate addition. My calculation implies that phosphate desorption cannot be ignored when assessing phytate use, particularly when a large amount of phytate is applied as a P source.

    In multispecies natural ecosystems, AMF can play a key role in enhancing plant productivity. However, their role in enhancing crop productivity in mixed cropping systems is still poorly understood. In Chapter 4, I conducted both greenhouse and field experiments to investigate whether mixing maize varieties with different P acquisition strategies could lead to overyielding, and what roles AMF play in this system with two maize varieties. The results showed that mixing maize varieties resulted in overyielding, both in P uptake and shoot biomass, but only when plants were mycorrhizal. At the same time, I found higher hyphal length density and higher AMF diversity in mixtures compared to the monocultures in the field experiment, and higher colonization rate and higher hyphal length density in mixtures in the pot experiment. Thus, I propose that overyielding by mixing maize varieties might be due to increased mycorrhizal performance leading to more P uptake. I also used the partitioning formula to calculate the contribution through the selection effect and complementarity effect to overyielding. I found that the increase of the total yield and P uptake in mixtures was largely due to complementarity effect, implying that relative overyielding and enhanced P uptake were not due to enhanced competitive ability by the larger variety. The results of Chapter 4 suggest that mixing mycorrhizal maize varieties might be beneficial for enhancing productivity and P uptake efficiency.

    Plant - soil feedback experiments have shown that AMF can play a crucial role in determining the direction and magnitude of that feedback. Most studies investigated plant - soil feedback dynamics between different plant species. However, it is unknown to what extent one variety of an agricultural crop can affect the performance of another variety of that same crop through plant - soil feedback. In Chapter 5, I carried out a two-phase experiment in a greenhouse, including conditioning phase and test phase to determine plant - soil feedbacks in the absence and presence of AMF species or community, to test the effects of AMF on feedback dynamics. The results in Chapter 5 showed that: 1) in the conditioning phase, both maize varieties were differentially influenced by different AMF species compared to non-mycorrhizal control; 2) in the feedback phase, non-mycorrhizal maize exhibited negative feedback dynamics for biomass and P-uptake; 3) on the feedback phase, mycorrhizal maize generally exhibited positive feedback dynamics for biomass and P-uptake. The interaction coefficient was largest with the mixture of three different AMF species. The interaction coefficient for shoot and P uptake were significantly correlated with the coefficient for mycorrhizal colonization. These results imply that different maize varieties are affected differently by different AMF species, thereby influencing the productivity of the subsequent maize variety. The results also raise questions how AMF influence rhizosphere biota and how maize varieties may select more beneficial AMF.

    In Chapter 6, I integrate the results from previous chapters. I discuss possible relationships between (negative) plant - soil feedback effect (due to pathogen) and the mycorrhizal effect on overyielding and improved P uptake due to mixing maize varieties (compared to the monoculture). I also discuss the linkage between phosphorus acquisition efficiency and mycorrhizal responsiveness within one crop species, and the relationship between plant genetic diversity and plant - soil feedback effects, and try to come up with a conceptual model how mixing maize varieties in the presence of AMF could be beneficial.

    Soil and plant responses to pyrogenic organic matter: carbon stability and symbiotic patterns
    Sagrilo, E. - \ 2014
    Wageningen University. Promotor(en): Thomas Kuijper; Ellis Hoffland. - Wageningen : Wageningen University - ISBN 9789462571679 - 128
    organisch bodemmateriaal - grondverbeteraars - koolstofvastlegging in de bodem - vesiculair-arbusculaire mycorrhizae - bodemvruchtbaarheid - glycine max - biochar - stikstoffixatie - kooldioxide - emissie - brazilië - soil organic matter - soil amendments - soil carbon sequestration - vesicular arbuscular mycorrhizas - soil fertility - glycine max - biochar - nitrogen fixation - carbon dioxide - emission - brazil

    Soil and plant responses to pyrogenic organic matter: carbon stability and symbiotic patterns

    Edvaldo Sagrilo

    Summary

    Pyrogenic organic matter (PyOM), also known as biochar, is the product of biomass combustion under low oxygen concentration. There is currently a growing interest in research on the use of PyOM as a soil amendment, inspired by the existence of highly fertile, PyOM-rich anthropogenic soils in the Amazon basin. The presence of PyOM in these so-called Amazonian Dark Earths (ADE) in quantities larger than in the non-anthropogenic surrounding soils is considered one of the main reasons for their high fertility.

    Soil additions of PyOM have been suggested to increase soil fertility and crop yields, simultaneously providing additional important environmental services. The offset of CO2 emissions through sequestration of a larger pool of recalcitrant soil organic carbon (SOC) is one of these services. This would at the same time sustain soil microbial activity, which is directly associated to soil quality, for instance, nutrient cycles and plant growth. This multiple win scenario suggests that the addition of PyOM to the soil would be the solution for the “carbon dilemma”. The dilemma states that the main biological benefits from soil organic matter are a consequence of its decay. Therefore, it is unlikely that increased C sequestration and the benefits from its decay can be simultaneously maximized. Rather than win-win, PyOM would then also be subjected to inevitable trade-offs.

    Additions of PyOM can modify the turnover rate of native SOC by either accelerating or decelerating its decomposition through a mechanism known as priming. Although positive priming by PyOM has been reported, negative priming has also been found. The higher amount of non-pyrogenic C in ADE, compared to non-anthropogenic surrounding soils has been considered evidence that PyOM can stabilize SOC in the long-term. A complicating issue in studies is that short-term increases in CO2 emission can be due to decomposition of labile PyOM fractions, erroneously suggesting positive priming of SOC. Addition of PyOM can also lead to modifications in the microbial activity and assemblages. Changes in microbial populations can have impacts on their functionality, favouring mutualistic root symbioses such as the arbuscular mycorrhizal fungal (AMF) symbiosis and the rhizobial symbiosis with legumes that is responsible for biological nitrogen fixation (BNF). Although soil amendments with PyOM can stimulate AMF and BNF, results are contrasting and mechanisms are not clear. Most studies of PyOM effects on SOC and on mutualistic root symbioses are from short-term experiments, often conducted in greenhouse or laboratory. Although such studies provide insights in potential factors driving changes in SOC and symbiotic relationships in PyOM-amended soils, they do not assess changes under realistic conditions over periods of time longer that one or a few cropping cycles. Therefore, there is still a gap in our understanding regarding the duration and magnitude of effects over time under field conditions and possible mechanisms involved. This thesis addresses these gaps.

    The aim of this research was to provide a better understanding of interactions between PyOM and SOC and the factors controlling symbiotic patterns in a tropical soil amended with PyOM. To reach this aim, I combined greenhouse and field studies. I also used meta-analytic methods in order to quantitatively synthesize data in literature.

    In Chapter 2, I combined the results of 46 studies in a meta-analysis. I investigated changes in CO2 emission patterns from an array of PyOM-amended soils and identified the causes of these changes and the possible factors involved. I showed an overall increase of 29% in CO2 emission from PyOM-amended soils. Such increases were only evident in soils amended with a PyOM-C (PyC):SOC ratio >2. These data are consistent with the hypothesis that increased CO2 emission after PyOM addition is additive and mainly derived from PyOM’s labile C fractions rather than from SOC. Therefore, positive priming is not a main driver of increases in CO2 emission in PyOM-amended soils. This PyC:SOC ratio provided the best predictor of increases in CO2 production after PyOM addition to soil. This meta-analysis indicates (i) the importance of taking into account the amount of applied PyC in relation to SOC for designing future decomposition experiments and that (ii) the recalcitrance of PyOM in soil-PyOM mixtures may be less than usually assumed.

    A technical problem of separating PyOM-induced priming on SOC from other non-additive interactions is the uncertainty regarding the origin of the respired CO2 (whether from SOC or PyOM). This issue can only be solved with the use of isotopes. In a field study (Chapter 3), I quantified changes in the PyOM and SOC stocks over four soybean cropping cycles (CC) in a sandy Ferralsol, previously supporting a vegetation with C4 plants, amended with different rates of PyOM (0, 5, 10, 20 and 40 Mg ha-1). The PyOM was produced from C3 woody species using traditional pyrolysis methods employed in Northeast Brazil. I used 13C isotopic analysis to discriminate the origin of the C in the soil and quantify the decomposition rates of native SOC and PyOM. I showed that decomposition of traditionally produced PyOM is faster (25-60% within first year) than normally assumed (10-20% within 5-10 years), which was higher than that of native SOC (5-14%). The data indicate preferential decomposition of PyOM compared to native SOC. The intensity of that effect depends on the rate of PyOM applied to the soil. Only on the longer term (>1 yr) addition of PyOM seems to stabilize SOC.

    In Chapter 4 I explored mechanisms controlling AMF activity and crop yield in PyOM-amended soils through the use of path analysis. I tested the effects of PyOM rates and P fertilization on soybean root colonization by AMF, soil P and plant performance over four cropping cycles (CCs). Data showed a major effect of CC and P, as well an interaction effect of PyOM x CC on mycorrhizal colonization. There was a linear decrease in root colonization by AMF in CC1 with increasing PyOM rates in contrast to a consistent linear increase in CC4. Plant performance was mainly affected by CC, but a significant interactive effect of PyOM x P was also observed on grain yield. Grain yield was highest at high PyOM rates (20 and 40 Mg ha-1) in the P-fertilized treatments in CC4. Soil pH increased in CC1 with increasing PyOM rates, but no effects were observed in CC4. Path analysis indicated that PyOM effects on root colonization by AMF were not mediated by changes in soil pH or P content. My data are consistent with the hypothesis that interference of PyOM in signalling processes is an important driver of change in AMF activity and that positive effects of PyOM on AMF and crop yield develop with time.

    In Chapter 5, I assessed the effects of PyOM application rates and P fertilization on BNF in soybean inoculated with Bradyrhizobium japonicum over four cropping cycles. Again I observed that CC had a significant main effect on most dependent variables, while PyOM was not a significant source of variation. There was a significant PyOM × CC interaction effect on shoot N concentration. In CC1 shoot N concentration after application of 5 Mg PyOM was significantly lower than that of plants grown on plots to which 10 or 20 Mg PyOM was applied. In CC4 shoot N concentration was not affected by PyOM. The major effect of CC was explained through changes in nutrient management, more specifically the addition of micronutrients in CC3 and CC4. Alleviation of micronutrient deficiency increased BNF and also resulted in a positive effect of P on BNF. I conclude that under conditions of adequate management, PyOM application does not improve BNF in soybean.

    In Chapter 6 (General Discussion) I synthesize the findings of the previous chapters and use data from additional greenhouse and litterbag field experiments to integrate the results. Data from Chapters 2 and 3 show that if any positive priming occurs due to PyOM addition, it is a small short-term event and does not lead to significant losses of native SOC in the long-term. This was confirmed by data from a 2 yr litterbag experiment, which showed no interaction between decomposition of PyOM and fresh organic matter.

    Stability of SOC has been considered an ecosystem property rather than a consequence of recalcitrance, but this definition has not yet been extended to PyOM. In this thesis I demonstrated that stability of PyOM can also be influenced by the soil environment. In order to link PyOM effects to SOC and on root symbioses, I performed path analysis integrating root colonization by AMF, SOC content and Ndfa in one model. We found no significant path coefficients linking AMF and BNF. The model indicated a significant positive path coefficient linking AMF root colonization and SOC in CC4, but not in CC1. The data suggest that PyOM may increase SOC stability through increased AMF activity. Soil aggregation and C sequestration are tightly correlated with abundance of AMF in the soil. I propose that the same mechanism through which AMF stabilizes native SOC may also positively influence PyOM stabilization in the long-term.

    In conclusion, I have shown that main beneficial effects of PyOM on AMF and crop yield develop with time, but in well-managed soils increased crop yield is not a direct consequence of increased AMF due to PyOM addition. Finally, although PyOM additions represent an effective form of sequestering C, positive effects of PyOM on crop yield are likely to occur after partial decomposition of PyOM. Therefore, although some benefits of adding PyOM can be simultaneously obtained (C sequestration and increased crop yield), they cannot be simultaneously maximized. This means that the carbon dilemma can only be partially solved by adding PyOM to the soil.

    Influences of agricultural management practices on Arbuscular Mycorrhiza Fungal symbioses in Kenyan agro-ecosystems
    Muriithi-Muchane, M.N. - \ 2013
    Wageningen University. Promotor(en): Thomas Kuijper, co-promotor(en): B. Vanlauwe; J. Jefwa. - S.l. : s.n. - ISBN 9789461735133 - 201
    vesiculair-arbusculaire mycorrhizae - mycorrhizae - agro-ecosystemen - organische verbeteraars - stikstofmeststoffen - kunstmeststoffen - schimmels - plantenvoeding - bodemvruchtbaarheid - bodembiologie - gewasproductie - bodemstructuur - bodemkwaliteit - kenya - vesicular arbuscular mycorrhizas - mycorrhizas - agroecosystems - organic amendments - nitrogen fertilizers - fertilizers - fungi - plant nutrition - soil fertility - soil biology - crop production - soil structure - soil quality - kenya

    Conservation agriculture (CA) and integrated soil fertility management (ISFM) practices are receiving increased attention as pathways to sustainable high-production agriculture in sub-Saharan Africa. However, little is known about the effects of these practices on arbuscular mycorrhizal fungi (AMF). The study aimed at understanding the long-term effects of (i) ISFM and CA on AMF communities and functioning, and on glomalin concentrations. The study also aimed at understanding the (ii) role of AMF in soil aggregation, plant nutrition and crop yield under field conditions and (iii) combined effect of AMF and earthworms on soil aggregation, plant nutrition and crop yield under greenhouse conditions. The study was conducted in two long-term field trials. The ISFM trial was in Kabete (central Kenya) and compared fertilization (nitrogen and phosphorus) and organic amendments (farmyard manure, crop residue) for 32 years, while the CA trial was in Nyabeda (western Kenya) and compared effect of tillage (conventional versus no-tillage), residue application, cropping system (monocropping versus rotation) and N-fertilization for 5 years. Long-term use of mineral fertilizer and organic amendments, as well as tillage and N fertilization altered AMF species composition, but the changes were relatively minor. Organic amendments alone or in combination with NP fertilization increased AMF incidence, whereas no-tillage in the presence of residue increased spore abundance and root colonization. N fertilization increased root colonization but had a negative effect on spore abundance and species richness. Crop rotation had no effect on AMF. Glomalin was also sensitive to management, but the response was site-specific. Glomalin responded more to CA in Nyabeda than ISFM in Kabete. N fertilization and residue increased glomalin, especially under conventional tillage. Path analysis indicated that AMF symbiosis and glomalin enhanced soil aggregation and crop nutrition and yield in both sites. The positive role of AMF on crop nutrition was stronger in Kabete than Nyabeda. However, yield and nutrient use efficiency were (very) low in Kabete. There was no interaction between AMF and earthworms on soil aggregation, but AMF enhanced soil aggregation. AMF interacted positively with the epigeic earthworm to enhance nutrient uptake and biomass production, but the endogeic earthworm negatively affected AMF symbiosis and function. The study highlights the potential of ISFM and CA practices in enhancing AMF diversity and activity, and indicates factors limiting AMF functioning under ISFM and CA systems. While AMF are important for agro-ecosystem functioning, remedying the non-responsive character of soils, especially Kabete, through judicious management of nitrogen and organic amendments remains a first priority.

    Mycorrhizal symbiosis and seedling performance of the frankincense tree (Boswellia papyrifera)
    Hizikias, E.B. - \ 2011
    Wageningen University. Promotor(en): Frans Bongers; Thomas Kuijper, co-promotor(en): Frank Sterck. - [S.l.] : S.n. - ISBN 9789085859635 - 141
    boswellia - mycorrhizae - symbiose - zaailingen - vesiculair-arbusculaire mycorrhizae - waterbeschikbaarheid - waterstress - tropen - ethiopië - boswellia - mycorrhizas - symbiosis - seedlings - vesicular arbuscular mycorrhizas - water availability - water stress - tropics - ethiopia

    Arid areas are characterized by a seasonal climate with a long dry period. In such stressful

    environment, resource availability is driven by longterm and shorterm rainfall pulses.

    Arbuscular Mycorrhizal (AM) fungi enhance access to moisture and nutrients and thereby

    influence plant performance. In this dissertation I applied field observations and

    greenhouse experiments to address four questions: 1) What are the major environmental

    factors influencing AM incidence in the Boswellia-dominated dry deciduous woodlands?

    2) How do Boswellia seedlings respond when they are exposed to AM fungi and water

    pulses? 3) How do AM fungi, water deficit and soil fertility influence the growth and gas

    exchange of Boswellia and Acacia seedlings? 4) Does the AM symbiosis influence

    competition between Acacia and Boswellia seedlings at different water pulse levels?

    The present study showed that almost all woodland plants in northern Ethiopia are

    colonized by AM fungi. Root colonization levels in dry and wet seasons demonstrated that

    in the sites with the harshest conditions, AM plants and fungi respond to pulsed resource

    availability by temporally disconnecting carbon gain by the plant and carbon expenditure

    by the fungus. Consequently, we studied below-ground processes in conferring adaptation

    to highly pulsed resources in Boswellia seedlings. The strong interactive AM fungi and

    water pulse showed that mycorrhizal Boswellia benefits from drought pulses during the

    short rainy season. Boswellia acquires carbon and water after rain events and store

    probably carbon and water in coarse roots, suggesting conservative strategy. From this

    observation we carried out an experiment to test whether other trees (Acacias) than

    Boswellia in this habitat also show this conservative acquisition strategy, or whether more

    acquisitive strategies may also be beneficial under such climates.

    My study show that acquisitive and conservative species both benefit from the AM

    symbiosis, but that the acquisitive Acacias mainly benefit at higher water availability,

    whereas the conservative Boswellia benefits at water or nutrient-stressed conditions. I also

    investigate on how mycorrhiza and water availability affect competition between plants

    with different resource acquisition strategies in these drylands. Seedlings of Boswellia are

    competitively inferior to seedlings of Acacia, and neither the presence of AM fungi nor a

    stronger water limitation (through pulsing) affected this outcome.

    Resistance to Fusarium basal rot and response to arbuscular mycorrhizal fungi in Allium
    Galvan Vivero, G.A. - \ 2009
    Wageningen University. Promotor(en): Rolf Hoekstra; Thomas Kuijper, co-promotor(en): Olga Scholten; Chris Kik. - [S.l. : S.n. - ISBN 9789085854760 - 160
    allium cepa - allium - fusarium oxysporum f.sp. cepae - fusarium proliferatum - glomus intraradices - ziekteresistentie - genetische analyse - vesiculair-arbusculaire mycorrhizae - symbiose - plantenveredeling - resistentieveredeling - allium cepa - allium - fusarium oxysporum f.sp. cepae - fusarium proliferatum - glomus intraradices - disease resistance - genetic analysis - vesicular arbuscular mycorrhizas - symbiosis - plant breeding - resistance breeding
    Onion (Allium cepa L.) cultivation in low input and organic farming systems is hampered by Fusarium basal rot (FBR) and the limited ability of onion to take up nutrients like phosphorus. The symbiosis with arbuscular mycorrhizal fungi (AMF) contributes to plant acquisition of phosphorus, among other benefits. This PhD research studied the potential contributions from A. fistulosum and A. roylei to breed onion cultivars with resistance to FBR and enhanced benefit from the symbiosis with AMF. The genetic basis of these traits was studied in an A. cepa x (A. roylei x A. fistulosum) population. A collection of Fusarium isolates was analysed using AFLP markers. The most abundant species was F. oxysporum (with isolates clustered in two clades) followed by F. proliferatum. The Allium species were screened for FBR resistance using one F. oxysporum isolate from each clade, and one F. proliferatum isolate. Allium fistulosum showed high levels of resistance to these three isolates and A. roylei intermediate levels of resistance. High level of resistance from A. fistulosum was dominantly expressed in the A. roylei x A. fistulosum hybrid and the tri-hybrid population. A molecular linkage map based on AFLP markers was developed for the A. roylei x A. fistulosum hybrid. A QTL for FBR resistance from A. roylei was mapped on chromosome 2, and a QTL from A. fistulosum on chromosome 8. Each QTL separately had significant effect on FBR but did not confer complete resistance, thus more QTLs from A. fistulosum remain to be discovered. Regarding Allium-AMF relationship, a first step of research studied genetic diversity and colonization levels of naturally occurring AMF, comparing organic and conventional onion farming in the Netherlands. All plants were colonized with 60% average arbuscular colonization. Onion yields were positively correlated with colonization. AMF phylotypes were identified by rDNA sequencing. The number of phylotypes per field ranged from one to six. Two Glomus-A phylotypes were the most abundant, whereas other phylotypes were infrequently found. Organic and conventional fields had similar number of phylotypes and Shannon diversity indices. A few organic and conventional fields had larger number of phylotypes, which suggested that specific environmental conditions or agricultural practices influence AMF diversity. The genetic basis for the response to AMF in the tri-hybrid Allium population was evaluated in two independent greenhouse experiments. The weights of mycorrhizal plants were significantly larger than the non-mycorrhizal plants. Mycorrhizal Responsiveness (MR) was negatively correlated with plant weight in the non-mycorrhizal condition and was therefore considered unsuitable as an index for plant breeding purposes. Two new indices were proposed: mycorrhizal benefit (MB) and mycorrhizal breeding value (MV). Tri-hybrid genotypes showed transgressive segregation for plant weight, MB, and MV. Two QTLs from A. roylei for these traits were detected on chromosomes 2 and 3. A QTL from A. fistulosum for MV (but not MB), plant weight and the number of stem-borne roots was found on linkage group 9. Positive correlations between plant weight, rooting system and benefit from mycorrhiza were observed, which open prospects to combine these traits in the development of more robust onion cultivars.


    Soil fungi and nitrogen cycling : causes and consequences of changing fungal biomass in grasslands
    Vries, F.T. de - \ 2009
    Wageningen University. Promotor(en): Lijbert Brussaard, co-promotor(en): Jaap Bloem; Ellis Hoffland. - [S.l. : S.n. - ISBN 9789085853251 - 126
    bodemschimmels - stikstof - stikstofkringloop - graslanden - kunstmeststoffen - vesiculair-arbusculaire mycorrhizae - uitspoelen - peulgewassen - stikstofverliezen - soil fungi - nitrogen - nitrogen cycle - grasslands - fertilizers - vesicular arbuscular mycorrhizas - leaching - legumes - nitrogen losses
    This thesis focuses on the interaction between fungi and the nitrogen cycle in grassland soils, and attempts to unravel causes and consequences of changing fungal biomass.
    Bioavailability of zinc to aerobic rice
    Gao, X. - \ 2007
    Wageningen University. Promotor(en): Sjoerd van der Zee; F.S. Zhang, co-promotor(en): Ellis Hoffland. - [S.l.] : S.n. - ISBN 9789085046462 - 147
    oryza sativa - rijst - zink - biologische beschikbaarheid - vesiculair-arbusculaire mycorrhizae - rizosfeer - bodem - voedingsstoffentekorten - oryza sativa - rice - zinc - bioavailability - vesicular arbuscular mycorrhizas - rhizosphere - soil - nutrient deficiencies
    Keywords:Arbuscular mycorrhiza, Exudation, Oryza sativa , Rhizosphere, Rice, Soil, Zinc

    Zinc deficiency is a wide-spread constraint for crop production and human health. This thesis should contribute to alleviation of Zn deficiency problems and aimed at identifying soil and plant factors affecting Zn bioavailability in rice ( Oryza sativa L.). Two main research questions were: 1) what is the consequence of a cultivation shift from flooded to aerobic rice on Zn bioavailability and 2) which mechanisms control Zn mobilization by aerobic rice? Field experiments demonstrated that the cultivation shift from flooded to aerobic may increase Zn deficiency problems. Lower Zn uptake and mass fraction in shoot and brown rice were observed in aerobic fields. Results of a soil incubation experiment and modeling showed that the difference found in plant Zn uptake between the two cultivation systems was orders of magnitude lower compared to what can be expected based on chemical equilibria in the bulk soil. This discrepancy suggests that soil chemical properties such as pH, DOC level and redox conditions in rhizosphere need consideration. We observed considerable variation among aerobic rice genotypes in tolerance to Zn deficiency under both field and pot conditions. In a pot experiment we found that variation in tolerance was mainly associated with Zn uptake. Plant Zn uptake from low Zn soils can be increased by both Zn-mobilizing rhizosphere processes and inoculation with arbuscular mycorrhizal fungi. We demonstrated that mycorrhizal inoculation significantly increased Zn uptake, but only in genotypes with a low inherent Zn uptake. High Zn mobilization by a combination of chemical rhizosphere and mycorrhizal effects seems impossible and may not be feasible as a target for breeders. In a rhizotron experiment and a nutrient solution experiment, aerobic rice genotypes responded to Zn deficiency with increased root exudation of malate.Genotypes with a higher Zn uptake showed a stronger increase in malate exudation in response to Zn deficiency.These results confirm our hypothesis that genotypic variation in Zn uptake of aerobic rice can partly be explained by root exudation of malate.
    Mycorrhizaschimmels: een rol in gewasbescherming?; thema bodemweerbaarheid
    Baar, J. - \ 2005
    Gewasbescherming 36 (2005)5. - ISSN 0166-6495 - p. 222 - 224.
    gewasbescherming - mycorrhizaschimmels - ectomycorrhiza - vesiculair-arbusculaire mycorrhizae - wortels - bodemschimmels - symbiose - worteloppervlak - plantenziekteverwekkers - entstof - plant protection - mycorrhizal fungi - ectomycorrhizas - vesicular arbuscular mycorrhizas - roots - soil fungi - symbiosis - rhizoplane - plant pathogens - inoculum
    In de grond kunnen bij planten specifieke bodemschimmels voorkomen. Dit zijn de zogeheten mycorrhizaschimmels. Kenmerkend voor mycorrhizaschimmels is dat deze schimmels met planten in een gebalanceerde symbiose leven. Van zo'n symbiose hebben zowel de planten als de schimmels profijt. In dit artikel wordt ingegaan op de achtergrond van de twee belangrijkste groepen mycorrhizaschimmels, de ecto- en arbusculaire mycorrhizaschimmels, en hun mogelijke rol in de gewasbescherming
    Diversity and dynamics of mycorrhizal associations in tropical rain forests with different disturbance regimes in South Cameroon
    Onguene, N.A. - \ 2000
    Agricultural University. Promotor(en): L. Brussaard; T.W. Kuyper. - S.l. : S.n. - ISBN 9789058082930 - 167
    mycorrhizae - mycorrhizaschimmels - ectomycorrhiza - vesiculair-arbusculaire mycorrhizae - symbiose - bosecologie - regenbossen - tropische regenbossen - bosbedrijfsvoering - bosschade - entstofdichtheid - kameroen - mycorrhizas - mycorrhizal fungi - ectomycorrhizas - vesicular arbuscular mycorrhizas - symbiosis - forest ecology - rain forests - tropical rain forests - forest management - forest damage - inoculum density - cameroon

    The present study documents the occurrence of mycorrhizal associations in the rain forests of south Cameroon. All species investigated are mycorrhizal. Most timber species form arbuscular mycorrhiza, but some timber species, which usually occur in clumps, form ectomycorrhiza. Species diversity of ectomycorrhizal fungi in the undisturbed rain forest is substantial, with more than 125 species having been recorded. Inoculum potential of arbuscular mycorrhizal and ectomycorrhizal fungi is high in the undisturbed rain forest. The shifting cultivation cycle increases inoculum potential of arbuscular mycorrhizal fungi, but lowers inoculum potential of ectomycorrhizal fungi to various extent.

    On sites of forestry practices (skid trails, landings) inoculum potential of arbuscular mycorrhizal and ectomycorrhizal fungi is very substantially reduced and recovery rates are low. Mycorrhizal colonisation and seedling growth are positively correlated with mycorrhiza inoculum potential. Inoculum potential of arbuscular mycorrhizal fungi and performance of seedlings of arbuscular mycorrhizal trees can be boosted after inoculum addition. Both inoculum quantity and inoculum quality are important criteria for inoculation practices. Ectomycorrhizal inoculum potential cannot be increased through inoculum addition and management of the intact ectomycorrhizal network is necessary for maintenance of the ectomycorrhizal tree species.

    Key words : Arbuscular mycorrhiza, ectomycorrhiza, disturbance, rain forest, diversity, inoculum potential, Cameroon, forestry practices

    The development and significance of vesicular-arbuscular mycorrhizas as influenced by agricultural practices
    Ruissen, M.A. - \ 1982
    Landbouwhogeschool Wageningen. Promotor(en): J. Dekker, co-promotor(en): T. Limonard. - Wageningen : Ruissen - 111
    agronomie - vesiculair-arbusculaire mycorrhizae - agronomy - vesicular arbuscular mycorrhizas
    The development and significance of vesicular- arbuscular mycorrhizas (VAM) in wheat and potatoes have been studied in relation to various farming systems and agricultural practices. The effects of farming systems on VAM have been observed on three neighbouring experimental farms in the vicinity of Nagele, in the North East Polder, The Netherlands. It appeared that varying amounts of organic matter used during a period of 26 years had little effect on the presence of VAM fungal spores. The results of a new project started on these farms in 1979 showed that nitrogen deficiency greatly stimulated the development of VAM in wheat. In potatoes, however, no such results were found. After winter wheat the number of spores of Glomus mosseae dominated the number of spores of the other species in the soil. After potatoes spores of Glomus macrocarpus were found more frequently.

    The influence of various agricultural practices on the development of VAM has been studied in long-term field experiments on the Lovink-farm, another experimental farm in the North East Polder. The relation between VAM and the amounts of nitrogen fertilizers applied has also been assessed in these experiments. From the results it can be concluded that the effect of various agricultural practices on VAM is based primarily on the effect of these practices on the growth of the plants and the inoculum potential of VAM in the soil. in addition, it appears that the effect of nitrogen on the development of VAM depends on the host plant species involved. This is in accordance with the results obtained on the farms at Nagele.

    Greenhouse experiments with wheat showed a strong interaction between the application of nitrogen and phosphorus fertilizers in relation to the development of VAM. When sufficient phosphorus was applied, the effect of nitrogen on VAM development depended on the way in which the VAM inoculum was applied.

    The significance of VAM fungi for the growth of plants depends largely on the environmental conditions in which the plants grow, particularly the nutrition of the plants, plant density and inoculum potential of VAM. These factors largely determine whether the symbiosis results in a positive or even a negative effect on the growth of plants.

    In spite of the fact that VAM fungi occur in the relatively rich arable soils in these polders, and that VAM fungi isolated from these soils greatly stimulate the growth of red clover in a poor soil, VAM does not appear as yet to be important for Dutch agriculture. Favourable conditions for the development of these mycorrhizas and conditions under which they have the greatest effect on the growth of plants are, in general, not present. Nevertheless, in circumstances in which little or no additional plant nutrients are used, or nutrients are not readily available for the plants, the importance of these fungi for the growth of plants increases.

    Protection given by VAM to plants against root pathogens seems to be limited. It is predominantly based on improved nutrition of poorly-fed plants and in a few special cases on competition for a site inside or outside the mycorrhizal root.

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