Intensive tropical land use massively shifts soil fungal communities

Abstract

soil fungi are key players in nutrient cycles as decomposers, mutualists and pathogens, but the impact of tropical rain forest transformation into rubber or oil palm plantations on fungal community structures and their ecological functions are unknown. We hypothesized that increasing land use intensity and habitat loss due to the replacement of the hyperdiverse forest flora by nonendemic cash crops drives a drastic loss of diversity of soil fungal taxa and impairs the ecological soil functions. Unexpectedly, rain forest conversion was not associated with strong diversity loss but with massive shifts in soil fungal community composition. Fungal communities clustered according to land use system and loss of plant species. Network analysis revealed characteristic fungal genera significantly associated with different land use systems. Shifts in soil fungal community structure were particularly distinct among different trophic groups, with substantial decreases in symbiotrophic fungi and increases in saprotrophic and pathotrophic fungi in oil palm and rubber plantations in comparison with rain forests. In conclusion, conversion of rain forests and current land use systems restructure soil fungal communities towards enhanced pathogen pressure and, thus, threaten ecosystem health functions.Tropical rain forests are the planet's most species-rich biomes 1 . In the past two decades, tropical rain forests in many parts of the world have been rapidly converted to monospecific plantations 2 . As a result, deforestation and human land use have irretrievably destroyed large areas of unique rain forests and enforced biodiversity loss 3,4 . High plant diversities are associated with active, abundant and diverse fungal communities 5-7 . Plant diversity was, therefore, predicted to be a strong driver of fungal species richness in soils of tropical rain forests 7-9 . However, the consequences of rain forest transformation into agricultural land for soil fungal diversity and the ecological functions of these fungi are not well understood.Soil fungi are integral components of ecosystems, driving nutrient cycling as decomposers 10-13 , regulating species composition as pathogens 14 and providing mutualistic benefits as symbiotrophs, thereby playing a key role in biogeochemical processes 15,16 and in soil health 17,18 . Because of their important functions, the impact of deforestation and land use intensification on soil fungal communities in the tropics is receiving increasing attention. To date, only a few studies have used next-generation sequencing methods to characterize soil fungal communities after the conversion of rain forests into agricultural land [19][20][21][22] . Those studies focused mainly on distinct fungal groups such as mycorrhizae and the turnover of their community structure in response to distinct land use systems such as the conversion of rain forest into pasture or cash crop plantations with oil palms or rubber trees [19][20][21][22] . However, approaches linking land use systems or aboveground vegetation divers...

Unravelling the effects of tropical land use conversion on the soil microbiome

“…The correlation of abiotic factors LUI, pH, C:N ratio and Fe to the entire community as well as to bacteria is not surprising as the communities and correspondingly our dataset were dominated by bacterial sequences. These results are in accordance with other taxonomic marker gene analysis-based studies targeting bacteria, archaea [15,16] and fungi [9] in the same study area. Management-related applications (e.g.…”

“…The soil microbial community composition changed in the converted land use systems compared to rainforest with similar trends as in previous studies targeting these sampling sites [9,15,16]. Proteobacteria were negatively and Acidobacteria positively affected by rainforest conversion.…”

“…Although we did not find hints for functional importance in these systems, we cannot rule out the possibility of important archaeal activity due to the limitations of the DNAbased study design. Our results showed that the fungal community composition in the studied land use systems was similar to an ITS-based analysis [9]. Eurotiales and Hypocreales are described as endophytes [50,51], further supporting the assumption that the reduction of plant diversity also reduces endophyte occurrence.…”

“…In addition, microorganisms play a key role in decomposing soil organic matter and mineralizing nutrients in soil [7]. It has been shown that rainforest conversion to plantations has negative effects on the biodiversity of fungi [8,9], protists [10], vertebrates [11], insects and plants [12][13][14], archaea [15], but not on bacterial diversity which increased [15,16]. Additionally, the microbial community composition was severely affected by these conversion processes with a high impact on Proteobacteria which showed an abundance decrease and Actinobacteria, which showed an abundance increase with increasing land use intensity [15,16].…”

“…We linked functional results with their corresponding taxonomic background. Based on our previous studies analysing the 16S rRNA marker gene sequences in the same sampling sites and studies on similar systems in Southeast Asia [9,10,15,16,18,33], we formulated three hypotheses. We assume that diversity will decrease for soilborne archaea, Eukaryotes and increase for bacteria with increasing land use intensity (H1).…”