Contrasting effects of cover crops on ‘hot spot’ arbuscular mycorrhizal fungal communities in organic tomato

Abstract

Arbuscular mycorrhizal fungal (AMF) communities are fundamental in organic cropping systems where they provide essential agro-ecosystem services, improving soil fertility and sustaining crop production. They are affected by agronomic practices, but still, scanty information is available about the role of specific crops, crop rotations and the use of winter cover crops on the AMF community compositions at the field sites. A field experiment was conducted to elucidate the role of diversified cover crops and AMF inoculation on AMF diversity in organic tomato. Tomato, pre-inoculated at nursery with two AMF isolates, was grown following four cover crop treatments: Indian mustard, hairy vetch, a mixture of seven species and a fallow. Tomato root colonization at flowering was more affected by AMF pre-transplant inoculation than by the cover crop treatments. An enormous species richness was found by morphological spore identification: 58 AMF species belonging to 14 genera, with 46 and 53 species retrieved at the end of cover crop cycle and at tomato harvest, respectively. At both sampling times, AMF spore abundance was highest in hairy vetch, but after tomato harvest, AMF species richness and diversity were lower in hairy vetch than in the cover crop mixture and in the mustard treatments. A higher AMF diversity was found at tomato harvest, compared with the end of the cover crop cycle, independent of the cover crop and pre-transplant AMF inoculation. Our findings suggest that seasonal and environmental factors play a major role on AMF abundance and diversity than short-term agronomic practices, including AMF inoculation. The huge AMF diversity is explained by the field history and the Mediterranean environment, where species characteristic of temperate and sub-tropical climates co-occur.

Changes in the composition of native root arbuscular mycorrhizal fungal communities during a short-term cover crop-maize succession

“…A higher species richness than in our study was detected in Mediterranean semi-arid environments (Torrecillas et al 2012). Using a morphological approach, a previous study on the occurrence of AMF spores in an organic field located in the same area detected a very high number of AMF species (58), never reported from a single site (Njeru et al 2015). The lower number of species detected in the present work, compared with such a study, may be a consequence of the specific environment of the Bhot spot area^, the methodology used (morphological vs molecular) or the material analysed (spores vs roots).…”

“…Phylotypes affiliated to Archaeospora trappei, D. epigaea and Paraglomus sp. were also detected, although rarely and associated to single plant species, confirming their occurrence in the area (Njeru et al 2015).…”

“…Little is known about the effects of diversified cover crop treatments on AMF diversity. A previous work, based on morphological identification of spores, showed increases of AMF species richness in plots with high plant diversity (Njeru et al 2015). Other studies reported that a mixture of cover crops had a positive effect on AMF propagules and biomass (Lehman et al 2012) and on mycorrhizal colonization (Njeru et al 2014), compared to monocultures.…”

Invasive plants affect arbuscular mycorrhizal fungi abundance and species richness as well as the performance of native plants grown in invaded soils

“…We could have overlooked AMF species that produce spores rarely or seasonally (Njeru et al 2015). Moreover, by sampling to the depth of 20 cm, some part of spore diversity that exclusively occurred in the subsoils might have been missed (Oehl et al 2005).…”

Arbuscular mycorrhizal fungi biodiversity: prospecting in Southern-Central zone of Chile. A review

“…For example, a low AMF species richness (only 5) was found in the rhizospheric soils associated to pioneer plant species growing at the mouth of lake Budi, Chile (Medina et al, 2015); nevertheless, one of these corresponds to a new specie Corymbiglomus pacificum (Medina et al, 2014). On the contrary, enormous species richness was found in organic tomato in a Mediterranean site with 58 AMF species belonging to 14 genera (Njeru et al, 2015). Maurer et al (2014) reported 38 AMF species under no-till and in temperate grasslands Oehl et al (2010) found between 34-39 AMF species and Saito et al (2004) in Japan reported least amount with 24 taxa at two sites.…”