Plant communities affect the soil subsystem and vice-versa. Anthropogenic management activities impact both plants and soil, thereby interfering with the co-dependence between plant, soil, and microbial components. Land management practices are known to interfere with both above and belowground components of terrestrial ecosystems, but we still know very little about how land management impacts the combination of aboveground and belowground sub-systems and their linkages with each other. In this thesis, I focus on identifying potential land uses that induce or increase the co-dependence between plants and soil microorganisms by evaluating (1) successional changes in plant community assemblages in both taxonomic and functional composition; and (2) the effects of anthropogenic management on above- and belowground interactions between plant biomass and soil communities in two types of land-use systems in the Amazon forest: natural fallow after slash-and-burn agriculture and agroforestry systems. In this thesis, I took advantage of many different approaches (plant spatial arrangement, estimation of aboveground biomass, analysis of soil physico-chemical properties, and soil metagenomics) to investigate the influence of land use and anthropogenic management on aboveground and belowground communities and their interactions. With respect to plant-plant interactions (Chapter 2), I investigated successional dynamics using a chronosequence approach covering 2-25 years of regeneration after first-cycle shifting cultivation and compare these with mature rainforests. Additionally, I considered the impact of land use intensification with three second-cycle slash-and-burn forests (‘degraded’ sites). The results revealed that land-use intensification (2nd-cycle regrowth) strongly affected all aspects of the spatial organization of secondary vegetation, increasing clustering, co-occurrences of functionally distinct plants, and systematic increase in focal species’ negative impacts on surrounding legume diversity. Thus, land-use intensification affects spatial organization of self-regenerative vegetation far more than first-cycle secondary succession does. Therefore, a second-cycle of slash-and-burn agriculture is enough to induce a stronger clustering of leguminous plants at both univariate and bivariate interactions. When looking into plant-soil relationships (Chapter 3), I evaluated three types of rainforests (young, old, and mature rainforest) and three different agroforestry systems (enriched fallow, commercial plantation, and homegardens). I found a strong impact of agroforestry systems on both soil factors and aboveground biomass. Interestingly, I observed an increasing co-dependence between soil factors and plant biomass in successional systems, but not in the agroforests. These results suggested that agricultural practices in the agroforests disrupt the co-dependence between aboveground-belowground interactions. Finally, I added the soil microbiome to the picture of aboveground-belowground interactions by taking advantage of advanced statistical methods (reviewed in Chapters 4). The results revealed a fungal-driven relationship along succession and in mature forest (Chapter 5). On the other hand, agroforestry systems exhibited a weaker co-dependence between plant biomass and soil factors, and their soil microbiomes appear to promote more specific bacterial populations as opposed to fungal taxa. In conclusion, integrating high-resolution genomic data with complex environmental data in observational studies is an important step towards identifying ecological differentiation and shifts in aboveground-belowground interactions.
|Award date||09 Mar 2022|
|Place of Publication||Utrecht|
|Publication status||Published - 2022|