•Mycorrhizae stimulate plant growth and N acquisition in faba bean but not in wheat.•AM hyphal density is higher under intercropping than in sole cropping.•Mycorrhizal network enhances the transfer ...of fixed N from faba bean to wheat.•Transfer of fixed N is not correlated with proportion or total amount of fixed N.
In Morocco, the use of seed legumes is limited because significant water deficits and the low availability of soil phosphorus (P) limit nitrogen fixation. However, little is known about the ability of faba bean-rhizobium symbiosis to fix nitrogen in P-deficient soils and to transfer fixed nitrogen (N) to intercropped wheat. Arbuscular mycorrhizal fungi (AM) and their extraradical hyphae networks play an important role in the facilitation process by promoting interconnectivity and the transfer of nutrients, such as N and P, between associated plants. The aim of this study was to analyse the impact of AM inoculation on N2 fixation and the transfer of fixed N from faba bean to intercropped wheat. Germinated faba bean and wheat seeds were transferred into 1–l pots filled with a P-deficient soil that was collected from the Haouz valley near Marrakech (Morocco). Plants from the two species were grown in pots in either pure or mixed stands under greenhouse conditions, and each cropping system was subjected to three mycorrhizal inoculation treatments with a non-inoculated (AM0) and two concentrations of Rhizophagus irregularis inoculants containing 1000 (AM1) or 2000 (AM2) spores pot−1. The 15N isotope dilution method was used to determine the amount and proportion of atmospheric N fixed by faba bean (Ndfa%) and the fixed N that was transferred to wheat. Mycorrhizal inoculation had a significantly positive effect on the shoot dry weights and total shoot N in faba bean, but not in wheat. The cropping system had no significant effect on the plant growth and total shoot N in both faba bean and wheat. The Ndfa percentage was very high in all of the treatments, varying from 86 to 91%. The total N fixed by faba bean was 27% significantly higher in the AM2 treatment compared with the AM1 and AM0 treatments for both cropping systems combined. The estimated proportions of fixed N that were transferred from faba bean to wheat were far higher in AM1 (50%) and AM2 (32%) treatments than in AM0 (15%) treatment as well as for the total transferred fixed N. As corroborated by a parallel observation of root mycorrhizal colonization, these results suggest that the development of mycorrhizal networks stimulates the transfer of fixed N from faba bean to wheat, which could significantly contribute to the facilitation process under intercropping conditions.
This study aimed to investigate the role of arbuscular mycorrhizal (AM) fungi on biological N fixation in
Vachellia seyal
and transfer of fixed N
2
from
V. seyal
to intercropped
Sporobolus robustus
...under greenhouse conditions. Both plants were grown individually in pots to prevent root contact (“Solid barrier” treatment) or together in two-compartment containers delimited by a plexiglass plate with holes either covered with a 30 μm nylon mesh allowing only hyphal connections between plant roots (“Mesh barrier” treatment), or without nylon mesh allowing hyphae and roots to intermingle (“No barrier” treatment) in a low-nutrient soil. Both plant species were inoculated with the AM fungal
Rhizophagus irregularis
IR27 strain (“Myc+” treatment) or not inoculated (“Myc-” treatment), whereas all
V. seyal
seedlings were inoculated with a rhizobial strain
Ensifer
sp. LCM 4579 (“Nod+” treatment). The
15
N isotope dilution method was used to determine the amount and proportion of atmospheric N fixed by
V. seyal
(%Ndfa) and the total fixed N that was transferred to intercropped
S. robustus
. Mycorrhizal inoculation factor had a significantly effect on plant growth parameters and shoot N concentration in
V. seyal
, but not in
S. robustus
. The estimated proportions of N fixed by
V. seyal
was higher in Myc + treatment (65%) than in Myc- treatment (42%) as well as for the amount of fixed N. About 14% of fixed N were transferred to
S. robustus
from AM fungal links, whereas N transfer via exudation plus transfer through mycorrhizal network reached 19.5%. The implications of these results are discussed.
Cropping systems based on carefully designed species mixtures reveal many potential advantages in terms of enhancing crop productivity, reducing pest and diseases, and enhancing ecological services. ...Associating cereals and legume production either through intercropping or rotations might be a relevant strategy of producing both type of culture, while benefiting from combined nitrogen fixed by the legume through its symbiotic association with nitrogen-fixing bacteria, and from a better use of P and water through mycorrhizal associations. These practices also participate to the diversification of agricultural productions, enabling to secure the regularity of income returns across the seasonal and climatic uncertainties. In this context, we designed a field experiment aiming to estimate the 2 years impact of these practices on wheat yield and on soil microbial activities as estimated through Substrate Induced Respiration method and mycorrhizal soil infectivity (MSI) measurement. It is expected that understanding soil microbial functionalities in response to these agricultural practices might allows to target the best type of combination, in regard to crop productivity. We found that the tested cropping systems largely impacted soil microbial functionalities and MSI. Intercropping gave better results in terms of crop productivity than the rotation practice after two cropping seasons. Benefits resulting from intercrop should be highly linked with changes recorded on soil microbial functionalities.
(Jacq.) is a leguminous forestry tree species endemic to Caribbean swamp forests. In Guadeloupe, smallholder farmers traditionally cultivate flooded taro (
) cultures under the canopy of
stands. The ...role of arbuscular mycorrhizal (AM) fungi in the sustainability of this traditional agroforestry system has been suggested but the composition and distribution of AM fungi colonizing the leguminous tree and/or taro are poorly characterized. An in-depth characterization of root-associated AM fungal communities from
adult trees and seedlings and taro cultures, sampled in two localities of Guadeloupe, was performed by pyrosequencing (GS FLX+) of partial 18S rRNA gene. The AM fungal community was composed of 215 operational taxonomic units (OTUs), belonging to eight fungal families dominated by Glomeraceae, Acaulosporaceae, and Gigasporaceae. Results revealed a low AM fungal community membership between
and
. However, certain AM fungal community taxa (10% of total community) overlapped between
and
, notably predominant
OTUs. These findings provide new perspectives in deciphering the significance of
in nutrient exchange between
and
by forming a potential mycorrhizal network.
The diversity of ectomycorrhizal (ECM) fungi on adult trees and seedlings of five species, Anthonotha fragrans, Anthonotha macrophylla, Cryptosepalum tetraphyllum, Paramacrolobium coeruleum and ...Uapaca esculenta, was determined in a tropical rain forest of Guinea. Ectomycorrhizae were sampled within a surface area of 1600 m², and fungal taxa were identified by sequencing the rDNA Internal Transcribed Spacer region. Thirty-nine ECM fungal taxa were determined, of which 19 multi-hosts, 9 single-hosts and 11 singletons. The multi-host fungi represented 92% (89% when including the singletons in the analysis) of the total abundance. Except for A. fragrans, the adults of the host species displayed significant differentiation for their fungal communities, but their seedlings harboured a similar fungal community. These findings suggest that there was a potential for the formation of common mycorrhizal networks in close vicinity. However, no significant difference was detected for the δ¹³C and δ¹⁵N values between seedlings and adults of each ECM plant, and no ECM species exhibited signatures of mixotrophy. Our results revealed (i) variation in ECM fungal diversity according to the seedling versus adult development stage of trees and (ii) low host specificity of ECM fungi, and indicated that multi-host fungi are more abundant than single-host fungi in this forest stand.
Background and Aim: In Guadeloupe’s swamp forests, smallholder farmers traditionally cultivate flooded Colocasia esculenta (taro) monocultures under the canopy of Pterocarpus officinalis stands, ...without the use of pesticides and fertilizers. To better understand functioning of this traditional agroforestry system, we estimated the ability of the tree legume P. officinalis to fix atmospheric nitrogen (N) and to transfer fixed N to C. esculenta under natural and controlled conditions.Methods: We use the 15N natural abundance and the 15N isotope dilution methods to determine the ability of P. officinalis to fix atmospheric N and to transfer fixed N to C. esculenta under three natural sites and controlled conditions via arbuscular mycorrhizal (AM) inoculation, respectively.Results: The proportions of fixed N (%Ndfa) in P. officinalis in swamp forest varied from 72 to 95% in mature trees, from 52 to 81% in seedlings associated with C. esculenta, and from 78 to 84% in seedlings not associated with C. esculenta. The proportion of fixed N transferred from P. officinalis seedlings to C. esculenta neighboring plants was estimated to 27%. The AM inoculation had a significantly positive effect on N2 fixation in P. officinalis, leaf dry weight and leaf P concentration in both P. officinalis and C. esculenta plants in cropping systems. The proportion of fixed N transferred from P. officinalis to C. esculenta in the AM inoculated plants reached 18%.Conclusion: The development of AM mycorrhizal networks may have facilitated the transfer of fixed N from P. officinalis to C. esculenta in field and pot experiments.
• Despite the abundance and diversity of timber tree legumes in the West African rainforest, their ability to form nitrogen-fixing nodules in symbiosis with rhizobia, and their response to rhizobial ...inoculation, remain poorly documented. • In the first part of this study the occurrence of nodulation was determined in 156 leguminous species growing in six natural forest areas in Guinea, mostly mature trees. In the second part, an in situ experiment of rhizobial inoculation was performed on eight selected tree species belonging to three genera: Albizia, Erythrophleum and Millettia. • Of the 97 plant species and 14 genera that had never been examined before this study, 31 species and four genera were reported to be nodulated. After 4 months of growing in a nursery and a further 11 months after transplantation of plants to the field, we observed a highly significant (P < 0.001) and positive effect of inoculation with Bradyrhizobium sp. strains on the growth of the eight tree species tested. • The importance of determining the nodulation ability of unexplored local trees and subsequently using this information for inoculation in reforestation programmes was demonstrated.
Five species of Acacia (Acacia ehrenbergiana Hayne, A. nilotica (L.) Delile, A. seyal Delile, A. tortilis(Forssk.) Hayne and A. laeta Delile) indigenous to Tamanrasset (Algeria) were investigated for ...theirnodulation status and nodular endophytic diversity. A. ehrenbergiana showed the highest nodulationability across the different sites in this region, indicating the widespread occurrence of compatiblerhizobia in the soils. Altogether 81 strains were purified. Among this endophytic strain collection, onlyfour bacterial endophytes nodulated their respective host plants. On the basis of partial 16S rDNAsequencing, they were affiliated to Ensifer sp., Ensifer teranga, Mesorhizobium sp. and Rhizobium sp.Among the 79 non- symbiotic endophytes, 24 representative strains on the basis of PCR-RFLP profileobtained with MSPI enzyme digestion were characterized. They belonged to nine genera, namely: Paenibacillus, Ochrobactrum, Stenotrophomonas, Pseudomonas, Microbacterium, Rhizobium,Agrobacterium, Brevibacillus and Advenella. The isolated nodular endophytes in this study revealed astrong tolerance profile to salinity and high temperature. Principal component analysis confirmed thatno correlation was found between bacterial tolerance to a maximum temperature of growth and soildepth of sampling. This tolerance profile was distributed over the three levels of soil depth sampling:20, 40 and 60 cm. On the other hand, there was no relationship between in vitro tolerances of rhizobialstrains to NaCl and high temperature and corresponding edaphoclimatic characteristics of the samplingsites. This study is a contribution to nodular bacterial diversity knowledge of desert African Acaciaspecies growing in preserved ecosystems.
Some rare leguminous plants of the genus Crotalaria are specifically nodulated by the methylotrophic bacterium Methylobacterium nodulans. In this study, the expression and role of bacterial ...methylotrophy were investigated during symbiosis between M. nodulans, strain ORS 2060T, and its host legume, Crotalaria podocarpa. Using lacZ fusion to the mxaF gene, we showed that the methylotroph genes are expressed in the root nodules, suggesting methylotrophic activity during symbiosis. In addition, loss of the bacterial methylotrophic function significantly affected plant development. Indeed, inoculation of M. nodulans nonmethylotroph mutants in C. podocarpa decreased the total root nodule number per plant up to 60%, decreased the whole-plant nitrogen fixation capacity up to 42%, and reduced the total dry plant biomass up to 46% compared with the wild-type strain. In contrast, inoculation of the legume C. podocarpa with nonmethylotrophic mutants complemented with functional mxa genes restored the symbiotic wild phenotype. These results demonstrate the key role of methylotrophy during symbiosis between M. nodulans and C. podocarpa.
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