Arbuscular mycorrhizal fungi (AMF) play a central role in enhancing nutrient uptake by plants, increasing resilience to biotic and abiotic stresses, and supporting proper functioning of tropical agroecosystems, such as cacao plantations. However, little is known about diversity and capacity of native strains in rhizospheres, as well as soil factors shaping AMF communities. This study aimed to assess (i) AMF diversity and abundance in cocoa rhizospheres and the relationship with soil chemical properties and climatic variables at seven distinct areas in Côte d’Ivoire, i.e., Adzope, Agnibilekrou, Azaguie, Biankouma, Ble, Bonon and Soubre; (ii) in-situ capacity of strains from these rhizospheres. Soil samples were collected in 66 cocoa plots and AMF spores were extracted and identified based on morphometric criteria. Part of soils was used for trap cultures, while another part was used for determination of chemical properties. Our findings indicate that fungal communities associated with cacao are dominated by families Glomeraceae and Acaulosporaceae. Before establishment of trap cultures, cacao rhizospheres showed highest spore abundance at Ble (103 ± 47 spores/100 g soil) and lowest abundance at Biankouma (47.3 ± 21.6 spores/100 g soil). AMF strains from Agnibilekrou and Biankouma soils showed highest quantitative sporulation capacity, whereas strains from Soubré soils exhibited strongest infective capacity. 18.49% of variance in AMF community is explained by soil chemical variables, whereas 5.32% is explained by climatic variables, with Mn, Zn, Cr, and precipitation as main drivers. This study highlighted that a clear understanding of AMF communities in cocoa rhizospheres is essential to facilitate the design of efficient soil and plant conservation strategies, thus ensuring the sustainability and long-term productivity of cocoa agroecosystems in Côte d’Ivoire.
Tag: soil biology
Monitoring Soil Health in Agroforestry Systems: A Guide to Assessment
One output of the project is a study of methods for determining and accounting for soil health and greenhouse gas emissions within agroforestry systems (den Herder et al., 2026). The first half of that report describes the measurement and reporting of soil health across seven sites in Czechia, Finland, Italy, Portugal, Spain, the Netherlands, and the United Kingdom. The report that you are reading now was initially developed as an Annex to that report. The objective of this Annex report is to provide a harmonised guide that covers (i) sampling design in spatially heterogeneous agroforestry systems (isolated trees, row-based alley cropping, and areabased systems), (ii) field measurement protocols for a core indicator set spanning chemical, physical, and biological soil health dimensions, and (iii) laboratory analysis, calculation, and reporting steps. The core soil health indicators prioritised within WP3 include soil organic carbon (SOC) and soil pH (chemical), bulk density (physical), and earthworm abundance as a practical soil fauna indicator (biological), consistent with a previous produced Milestone report on DigitAF Methods for Carbon and Soil Health Assessments. Where resources allow, the guide also provides options to extend monitoring to microbial indicators such as bacteria and fungi, improving the completeness of soil biological assessment.
Agroforestry and the TSBF programme
Three aspects are discussed: (1) the relevance of the objectives and concepts of the Tropical Soil Biology and Fertility (TSBF) Programme to the design and development of agroforestry systems; (2) the potential role of agroforestry (in terms of practical management options) in fulfilment of the aims of the TSBF; and (3) ways of integrating the TSBF programme with agroforestry research (specifically, that of ICRAF).
Soil biological dynamics in slash-and-burn agriculture
Studies of shifting cultivation and other slash-and-burn systems over the past 30 years have basically confirmed the conceptual model of carbon and nutrient cycling put forth by Nye and Greenland. The model stresses that soil biological processes should not be viewed in isolation but as an integral part of the system. There has been some progress in refining certain aspects of the model but most studies have merely provided more numbers for specific fluxes or pools in the cycle rather than the entire cycle. While these studies have reinforced the model of Nye and Greenland, they have not added much to understanding the controls or improving the predictive capacity that would allow improved management of slash-and-burn systems. Future studies should concentrate on controlling and manipulating certain components in the system and looking at the resulting changes in the other pools and processes in the system. Results from these types of studies can be combined with system models for simulating and comparing different management strategies.
Belowground biodiversity and sustainability of complex agroecosystems
Diversity of components and interactions distinguishes complex agro-ecosystems from the simple agroecosystems which have replaced them in most of the temperate zone. In the tropics farmer decisions on agro-ecosystems have retained more similarity with natural ecosystems, but a strong trend toward specialization exists. As part of a re-appreciation of agro-ecosystem complexity, functional aspects of belowground diversity deserve more attention.
Conversion of rainforest to rubber plantations impacts rhizosphere soil mycobiome and alters soil biological activity
In Asia, large swathes of rainforest have been converted to rubber plantations, with major consequences for biodiversity and ecosystem services. However, the impact of this land use conversion on rhizosphere soil mycobiome has not yet been addressed. This study aims to investigate how rhizosphere soil fungal communities and their associated biological activity (soil respiration, soil methane (CH4) and potential soil enzyme production) are impacted by the conversion of rainforest to rubber plantations. Fungal richness and community composition in rhizosphere soils collected from natural rainforests, immature rubber, and mature rubber plantations were analyzed using paired-end Illumina sequencing. The conversion of natural rainforest to rubber plantations significantly altered fungal community composition of specific functional groups (saprotrophs, pathogens and mycorrhiza). We observed significant loss of saprotrophic and ectomycorrhizal fungi in natural rainforests, but enrichment of plant pathogenic fungi in immature rubber plantations. The mechanism underlying the effects of forest conversion on changes of fungal communities is related to reductions in soil pH, total nitrogen (N) and ammonium (NH4) in rubber plantations. Conversion to rubber plantation also resulted in decline of soil respiration rates and less potential for cellulase and chitinase productions. The significant negative correlations between fungal richness and soil respiration in mature rubber plantations indicated high competition among fungi and low nutrient availability in this system. We demonstrate the negative consequences of the conversion of rainforest to rubber plantations on soil biological activity and significant changes in fungal community composition that could threaten long-term ecosystem functions.