Abstract
Little is known to what extent soil biota, in particular, the mycorrhizae are altered through different fallow durations/types in tropical soils. We found that soil-N, -C, -Al, -K and -Ca contents significantly differed due to the fallow durations/types. Subsequently, the effects of fallow types and soil depths on the diversity, species richness and community structure of arbuscular mycorrhizal (AM) fungi were examined. A higher AM species richness was identified in the cropping than in forest fallow fields, suggesting a positive cropping feedback on the AM community composition. Distribution of the AM species was positively related to soil properties, specifically soil-pH, and soil-Pi, -Ca and -Mg contents. The soil properties conjointly accounted for 78.5% of explained variation in the AM community composition, signifying that the main factors altering the community structure under different fallow and cropping systems were the soil properties. Among the soil chemical characteristics, the soil-pH disclosed a significant explained variation in the AM community composition in the topsoil layer under the short fallow. Structural modeling equation to understand multiple predictive pathways that connect soil properties, fallow practices and AM community structures indicated that soil-C, -N and -Ca contents were highlighted as important factors influencing the AM community compositions.
Highlights
Shifting cultivation is a predominant and traditional farming practice, alternating cropping sequences and fallow phases in tropical forest, in the humid zone in the south of Cameroon[1,2]
Results of the structural equation modeling (SEM) using the data of analyzed soil properties under the different F, S and D conditions as a single group supported our previous observations obtained from the redundancy analysis (RDA), and further indicated the different pathways and effects in which each predictor exercised its influence on the arbuscular mycorrhizal (AM) community composition (Fig. 4c)
When the models were constructed separately using the datasets obtained from the two soil depths, we found that the fallow practices and soil characteristics disclosed direct effects on each other, and the soil-Ca variable exhibited relatively strong relationships to fallow practices under both sampling depths (Fig. 4c)
Summary
Shifting cultivation is a predominant and traditional farming practice, alternating cropping sequences and fallow phases in tropical forest, in the humid zone in the south of Cameroon[1,2]. The beneficial associations between plant roots and arbuscular mycorrhizal (AM) fungi support uptake and translocation of immobile nutrients, largely N, inorganic phosphate (Pi), carbon (C) and water to host plants in exchange for fixed C source to AM fungi[22,23] Because of their novel functions in mineral uptake and alleviation of water deprivation-related stresses, the contribution of AM fungi to smallholder agriculture in tropical areas has been recently considered the most important compared with that of other groups of the soil biota[24]. AM diversity and species richness are in turn largely influenced by the composition of associated plant communities, soil geography, and various agricultural management practices, mainly fertilizer applications, crop rotation, monocropping and tillage practices with selection of soil depths being an important part of tillage practices[32]. We could gain a better insight into the factors driving the AM community composition and structure in the context of farming systems under the humid tropical soil conditions
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