Soil Edaphic Properties Research Articles

Exploring viral particle, soil, and extraction buffer physicochemical characteristics and their impacts on extractable viral communities

Viruses are expected to be pivotal members of soil ecosystems, and recent advances in viral size fraction metagenomic (viromic) approaches have improved our ability to interrogate soil viral ecology. However, viromics relies on extraction buffers to effectively desorb viral particles from the soil matrix for downstream analysis, and viral extraction efficiency could be affected by the interplay between viral particles, soils, and extraction buffer chemistry. Here, we investigated whether extraction buffer chemistry affected extractable viral community composition measured by viromics from different soil types, for both biological (samples collected 1 m apart) and technical (subsamples from the same soil homogenate) replicates. We investigated pH manipulation of protein-supplemented phosphate-buffered saline buffer (PPBS, pHs 4.5, 5.5, 6.5, and 7.5) on forest, grassland and wetland soils that exhibited different soil edaphic properties, and we tested different buffer chemistries (PPBS, Carbonated Buffer, Glycine, and Saline Magnesium) on just the wetland soil. Spatial distance (i.e., biological replicate) was the primary driver of extractable viral community composition across all buffers and soils tested. Differences in viral community composition according to extraction buffer properties were only observed in the grassland technical replicates at PPBS buffer pH 4.5, and in both the wetland technical and biological replicates treated with different buffer chemistries, but the effects of buffer chemistry were secondary to spatial distance in the biological replicates. The lack of buffering capacity in the grassland soil technical replicates likely increased sorption of viral particles at pH 4.5, but neither protein composition nor isoelectric point explained this phenomenon. Given that most soil viral ecological studies to date include sample collection over distances much farther apart than the 1-m distances considered here, results suggest that extraction buffer chemistry is likely of much lower importance than ecological considerations, such as spatial distance, in the design of future soil viral ecological investigations.

Soil edaphic factors and climate seasonality explain the turnover of methanotrophic communities in riparian wetlands

Aerobic CH4-oxidizing bacteria (methanotrophs) represent a biological model system for the removal of atmospheric CH4, which is sensitive to the dynamics of water tables. However, little attention has been given to the turnover of methanotrophic communities across wet and dry periods in riparian wetlands. Here, by sequencing the pmoA gene, we investigated the turnover of soil methanotrophic communities across wet and dry periods in typical riparian wetlands that experience intensive agricultural practices. The results demonstrated that the methanotrophic abundance and diversity were significantly higher in the wet period than in the dry period, probably owing to the climatic seasonal succession and associated variation in soil edaphic factors. The co-occurrence patterns of the interspecies association analysis demonstrated that the key ecological clusters (i.e., Mod#1, Mod#2, Mod#4, Mod#5) showed contrasting correlations with soil edaphic properties between wet and dry periods. The linear regression slope of the relationships between the relative abundance of Mod#1 and the carbon to nitrogen ratio was higher in the wet period than in the dry period, whereas the linear regression slope of the relationships between the relative abundance of Mod#2 and soil nitrogen content (i.e., dissolved organic nitrogen, nitrate, and total nitrogen) was higher in the dry period than in the wet period. Moreover, Stegen's null model combined with phylogenetic group-based assembly analysis demonstrated that the methanotrophic community exhibited a higher proportion of drift (55.0%) and a lower contribution of dispersal limitation (24.5%) in the wet period than in the dry period (43.8% and 35.7%, respectively). Overall, these findings demonstrate that the turnover of methanotrophic communities across wet and dry periods were soil edaphic factors and climate dependent.

Topographic attributes override impacts of agronomic practices on prokaryotic community structure

While topography can infer erosion potential, the practice of conventional agronomic management can trigger accelerated erosion and pose major threats to soil assets such as biodiversity. The majority of farmlands in Upper-Eastern Ghana are moderately hilly and highly susceptible to erosion. This study pioneered the comparative and interactive effects of topography and conventional versus conservation agriculture practices (reduced tillage, main crop and cover crop, crop residue retention vs. removal) in treatments amended with 0, 40, and 80 kg ha−1 N on soil physicochemical properties and microbiota. Topography imposed profound shifts in soil physiochemical properties and prokaryotic community structure. Foot-slope soils harbored higher prokaryotic richness and diversity compared to the up-slope. Bacillaceae (28.95%) and anaerobic bacteria increased in relative abundance in foot-slope soils, while Micrococcaceae (25.79%) gained prominence in up-slope soils. The effect of tillage was significant in foot-slope while crop rotation was influential in up-slope soils on structuring the prokaryotic community. The interactive effect of slope × tillage was significant in altering soil physiochemical properties, but not prokaryotic community structure. Variation in prokaryotic community composition was explained by soil physiochemical properties (14.5%), elevation as a proxy for topography (11.3%), and spatial distance (10.8%), but rather weakly overall by agronomic practices. Among the soil physicochemical properties, pH, clay content, total C%, volumetric water content, temperature, cation exchange capacity, and NO3−-N were relevant factors influencing the soil microbiota. Geomorphic and soil edaphic properties appeared to interact and were the primary triggers of variation in soil microbiota and their responses to the range of agronomic practices that incorporated conservation management outcomes.

Trends in Microbial Community Composition and Function by Soil Depth.

Microbial communities play important roles in soil health, contributing to processes such as the turnover of organic matter and nutrient cycling. As soil edaphic properties such as chemical composition and physical structure change from surface layers to deeper ones, the soil microbiome similarly exhibits substantial variability with depth, with respect to both community composition and functional profiles. However, soil microbiome studies often neglect deeper soils, instead focusing on the top layer of soil. Here, we provide a synthesis on how the soil and its resident microbiome change with depth. We touch upon soil physicochemical properties, microbial diversity, composition, and functional profiles, with a special emphasis on carbon cycling. In doing so, we seek to highlight the importance of incorporating analyses of deeper soils in soil studies.

Temperature sensitivity of organic matter mineralization as affected by soil edaphic properties and substrate quality

Warming in ecosystems simultaneously changes soil temperatures and inputs of organic matter into soils. Soil chemical properties and exogenous substrate inputs both have significant effects on the temperature sensitivity (Q10) of mineralization. In this study, three soil types (Cambisol, Chernozem and Luvisol) were collected from natural forests at three latitudes in temperate China, whereas the vegetation types are mixed broadleaf-conifer, broadleaf and conifer respectively. The soils differed in soil organic carbon (SOC) contents in the order Chernozem (8.5%), Luvisol (6%), Cambisol (3.6%). The soils were incubated for 40 days at three temperatures (5, 15, and 25 °C). Glucose and maize leaf powder were added as exogenous substrates. To add the same amounts of soluble carbon glucose and maize leaf powder were added at the rate of 2 and 4 mg C g−1 soil, respectively. Independent of substrate addition, the Chernozem had the highest cumulative CO2 efflux under all temperature treatments. Maize addition accelerated cumulative CO2 efflux more than glucose in most treatments. The Q10 value was higher (P < 0.05) in the Chernozem (1.29 ∼ 1.49) than the Cambisol (1.17 ∼ 1.28) and the Luvisol (1.10 ∼ 1.29), both in the treatments and the control. Soil Q10 was positively correlated (P < 0.001) with DOC and mineral N content, but negatively correlated (P < 0.001) with the MBC/MBN ratio. However, the effect of exogenous substrate addition on Q10 varied between the different soil types. Addition of both substrates reduced Q10 by 8.7 ∼ 13.4% in the Chernozem and by 10 ∼ 14.0% in the Luvisol, whereas maize input increased (P < 0.05) Q10 by 7.6% in the Cambisol. These results suggested that DOC, mineral N and MBC/MBN ratio significantly influenced Q10, whereas the effects of exogenous substrates on soil respiration and Q10 were highly dependent on SOC content and substrate type.

Environmental and management drivers of soil health indicators on Michigan field crop farms

Maintaining soil health is critical for sustainable field crop production. This on-farm study used participatory monitoring and employed a Bayesian linear regression model to investigate the impact of various drivers (i.e., climate, soil edaphic properties, management practices, cropping diversity, and tillage intensity) on soil health indicators. Over two years, we sampled 242 focal points in soybean fields on thirty-five farms across three regions in Michigan differing in climate, edaphic properties and management practices. Soils ranged from loam to sandy loam. Soil health indicators assessed included soil organic carbon (SOC), total soil nitrogen (TSN), permanganate oxidizable carbon (POXC), C mineralization (Cmin), potentially mineralizable nitrogen (PMN), phosphorus, calcium, soil surface and subsurface resistance, and wet aggregate stability (WAS). We observed location effects, with each of the three regions differing in their climate, soil edaphic properties, and management practices. We found that aridity and clay content are primary drivers of most soil health indicators. Specifically, crop diversity, irrespective of composition, was positively associated with Cmin and WAS. Tillage intensity was positively associated with PMN but negatively influenced POXC. Overall, we conclude that although climate and soil edaphic properties are the dominant drivers of soil health, management practices also play a critical role, especially when considering soil biological indicators.

Associations among the communities of soil-borne pathogens, soil edaphic properties and disease incidence in the field pea root rot complex

Background and aimsField pea production is greatly impacted by multiple soil-borne fungal and oomycete pathogens in a complex. The objectives of this research were to 1) identify the soil-borne pathogens associated with field pea in North Dakota and; 2) develop prediction models incorporating the occurrence of the soil-borne pathogen communities, soil edaphic properties and disease incidence.MethodsSoil and plants were sampled from 60 field pea fields in North Dakota during 2014 and 2015. Plants (1500 across two years) were rated for both root rot and soil-borne pathogens isolated from roots. Soils were analyzed for edaphic properties. Indicator species analysis was used to identify soil-borne pathogen communities. Logistic regression was used to determine associations and develop prediction models.ResultsSurvey results from 2014 and 2015 indicated that the most prevalent soil-borne pathogens identified in field pea fields were Fusarium spp. and Aphanomyces euteiches. Five soil-borne pathogen communities were identified; three of which had statistically significant associations characterized by (1) Fusarium acuminatum, (3) A. euteiches, and (4) Fusarium sporotrichioides. The occurrence of the three communities were associated with clay content, soil pH, Fe2+, and K+. Disease incidence was associated with the presence of either community 1 or 3 and K+.ConclusionsThe results generated from this research will contribute to the development of management strategies by providing a soil-borne pathogen community prediction tool.

Cover crop diversity improves multiple soil properties via altering root architectural traits

Cover crops may influence soil health and functioning. However, little is known about the role of belowground root architectural traits in linking cover crop diversity with rhizosphere soil ecosystem properties. We hypothesize that cover crop diversity may improve root traits, which in return, could influence its effects on essential indicators of soil physicochemical heterogeneity, such as the composition of soil aggregate-size classes and nutrients, and the soil organic matter (SOM) and soil organic carbon (SOC) contents. We studied the impact of plant diversity on root traits and soil properties. The four soil aggregate-size classes, such as large macro- (>2000 μm), small macro- (<2000-500 μm), meso- (<500-250 μm), and micro-aggregates (<250 μm) were separated by the dry sieving. Root traits such as surface area (cm2) and length (cm) were quantified by image analysis using Winrhizo. The soil nutrient, SOM, and SOC contents were determined by standard methods. We used Fox's (2005) method for partitioning the selection and complementarity effects on plant productivity. Plant diversity improved productivity, root architectural traits, root coverage, the composition of soil aggregate-size classes and nutrients, SOM and SOC contents across the soil depth. It increased and decreased the relative abundance of meso- and micro-aggregates, respectively. Both root architectural traits and SOC contents positively correlated with several soil edaphic properties essential for physicochemical heterogeneity, health, and functioning. Our results suggest that competition among plant roots in species-rich than poor communities may improve rhizosphere soil carbon storage, the composition of soil aggregate-size classes, and nutrients.

Microbial Communities Associated With Long-Term Tillage and Fertility Treatments in a Corn-Soybean Cropping System.

Tillage and fertilization are common practices used to enhance soil fertility and increase yield. Changes in soil edaphic properties associated with different tillage and fertility regimes have been widely examined, yet, the microbially mediated pathways and ecological niches involved in enhancing soil fertility are poorly understood. The effects of long-term conventional tillage and no-till in parallel with three fertility treatments (No fertilization, N-only, and NPK) on soil microbial communities were investigated in a long-term field study that was established in the 1970’s. Here, we used high-throughput sequencing of bacterial, fungal and oomycetes markers, followed by community-level functional and ecological assembly to discern principles governing tillage and fertility practices’ influence on associated soil microbiomes. Both tillage and fertilizer significantly altered microbial community structure, but the tillage effect was more prominent than the fertilizer effect. Tillage significantly affected bacteria, fungi, fusaria, and oomycete beta-diversity, whereas fertilizer only affected bacteria and fungi beta-diversity. In our study different tillage and fertilizer regimes favored specific networks of metabolic pathways and distinct ecological guilds. No-till selected for beneficial microbes that translocate nutrients and resources and protect the host against pathogens. Notably, ecological guilds featuring arbuscular mycorrhizae, mycoparasites, and nematophagous fungi were favored in no-till soils, while fungal saprotrophs and plant pathogens dominated in tilled soils. Conventional till and fertilizer management shifted the communities toward fast growing competitors. Copiotrophic bacteria and fusarium species were favored under conventional tillage and in the presence of fertilizers. The analysis of the metagenomes revealed a higher abundance of predicted pathways associated with energy metabolism, translation, metabolism of cofactors and vitamins, glycan biosynthesis and nucleotide metabolism in no-till. Furthermore, no specific pathways were found to be enriched under the investigated fertilization regimes. Understanding how tillage and fertilizer management shift microbial diversity, structure and ecological niches, such as presented here, can assist with designing farming systems that can maintain high crop yield, while reducing soil erosion and nutrient losses.

Disentangling abiotic and biotic controls of aerobic methane oxidation during re-colonization

Aerobic methane oxidation is driven by both abiotic and biotic factors, which are often confounded in the soil environment. Using a laboratory-scale reciprocal inoculation experiment with two native soils (paddy and upland agricultural soils) and the gamma-irradiated fraction of these soils, we aim to disentangle and determine the relative contribution of abiotic (i.e., soil edaphic properties) and biotic (i.e., initial methanotrophic community composition) controls of methane oxidation during re-colonization. Methane uptake was appreciably higher in incubations containing gamma-irradiated paddy than upland soil despite the initial difference in the methanotrophic community composition. This suggested an overriding effect of the soil edaphic properties, which positively regulated methane oxidation. Community composition was similar in incubations with the same starting inoculum, based on quantitative and qualitative pmoA gene analyses. Thus, results suggested that the initial community composition affects the trajectory of community succession to an extent, but not at the expense of the methanotrophic activity under high methane availability. Still, methane oxidation was affected more by soil edaphic properties than by the initial composition of the methanotrophic community.

Multiple, Compounding Disturbances in a Forest Ecosystem: Fire Increases Susceptibility of Soil Edaphic Properties, Bacterial Community Structure, and Function to Change with Extreme Precipitation Event

The intensity and frequency of ecosystem disturbances are shifting with climate change, and multiple disturbances in close succession have the potential to compound their independent effects and strongly alter ecosystem structure and function. In this paper, we examine the effects of an extreme precipitation event on a montane forest landscape that was previously decimated by wildfire (37 months prior) relative to an unburned site in the same ecosystem. We assessed responses in soil edaphic properties, bacterial community composition and assembly, and soil enzyme activities involved in carbon (C) and nitrogen (N) acquisition. Our research reveals that previously burned landscapes are susceptible to a subsequent extreme precipitation event via significant increases in soil pH where unburned soils are not. Beta- and Delta-proteobacteria associated with early succession increased and shifts were observed in N- vs. C-acquiring extracellular enzymes within burned soils after the extreme precipitation event. Finally, we connected variation in ecological selective pressures on bacterial communities associated with pH change to these differences in microbial mediated soil enzyme activity. Thus, this research demonstrates how multiple, compounding disturbances drive distinct changes relative to systems experiencing a single disturbance and suggests that changes in bacterial community assembly process with disturbance may underlie this response.

Changes in bacterial community composition across natural grassland and pine forests in the Bunya Mountains in subtropical Australia

Tree and grass species coexist in many ecosystems worldwide and support multiple ecosystem functions and services. However, the distribution of bacterial communities and factors driving coexistence in tree–grass associations and their ecosystem functions remain poorly understood. In this study, the distribution of soil bacteria and their link to changes in abiotic factors were investigated in adjacent montane grassland (C4 plants) and pine forest (bunya pine and hoop pine; C3 plants) sites in the Bunya Mountains, subtropical Australia. Different vegetation (grassy balds and forest) had a substantial effect on terrestrial ecosystem properties, with higher levels of soil nutrients (e.g. total nitrogen (N), total phosphorus (P)) and electrical conductivity (EC), and lower δ13C values and pH under forests compared with grassland. Bacterial α-diversity (total species per operational taxonomic unit richness) did not differ between grassland and pine forest sites, whereas strong shifts in the bacterial community composition and structure were evident. Patterns in bacterial community structure were strongly associated with changes in soil pH, EC, total P and δ13C. Different bacterial groups associated with pine forest (Gammaproteobacteria and Alphaproteobacteria) and grassland (Acidobacteria and Verrucomicrobia) were identified as key groups contributing to the segregation of these two ecosystems in the Bunya Mountains. These findings suggest that heterogeneity in soil edaphic properties (e.g. key nutrients) likely contributed to variation in bacterial β-diversity of grassland and pine forest, which has potential implications for species coexistence and ecosystem function in montane eastern Australia.

Soil Macrofauna and Edaphic Properties in Coffee Production Systems in Southern Colombia

ABSTRACT The objective of this study was to evaluate the occurrence of the soil macrofauna in coffee production systems, as well as their relationship with edaphic properties. Therefore, two coffee production systems were selected: coffee plantations at full-sun with conventional management (Intensive) and shaded coffee plantations with organic management (Traditional). In each crop system, three soil samples were collected randomly, in the form of blocks (25 × 25 cm), to a soil depth of 10 cm. In total, 17,109 individuals were recorded in this study being the Oligochaeta group the most representative, regardless of the coffee production system. The average density of soil macrofauna was higher in traditional coffee plantations (p < 0.05) due to the higher density of Oligochaeta, Diplopoda and Blattodea. The traditional coffee plantations provided a better soil chemical fertility reflected in the principal component analysis. Furthermore, these chemical attributes probably could affect the occurrence of the soil macrofauna groups.

Bulk soil bacterial community structure and function respond to long-term organic and conventional agricultural management.

Understanding how soil microbiomes respond to management is essential to maximizing soil health. We contrasted microbiomes in bulk soil under long-term organic and conventional management in a grain production setting. Management category significantly impacted the relative abundances of 17% of the most abundant taxa. Both conventional and organic management favored particular taxa, but these effects were not reflected in summary richness and diversity indices. Management systems also lead to differences in soil edaphic properties, including pH and nutrient status; this may have been the mechanism by which change in the prokaryote community was enacted. Community change between years of sampling was less pronounced, with only 6 taxa differentially abundant among years. Management category also impacted the abundance of functional genes related to the production and consumption of greenhouse gases. Particulate methane monooxygenase genes were more frequent in soil under organic management, while soluble methane monooxygenase genes were more frequent in soil under conventional management in 1 of 2 years. Nitrous oxide reductase genes were significantly less abundant in soils under second-year alfalfa than in soils under corn. This work highlights the ability of agricultural management to enact broad rearrangements to the structure of bulk soil bacterial communities.

Subterranean Desert Rodents (Genus Ctenomys) Create Soil Patches Enriched in Root Endophytic Fungal Propagules.

Subterranean rodents are considered major soil engineers, as they can locally modify soil properties by their burrowing activities. In this study, the effect of a subterranean rodent of the genus Ctenomys on soil properties and root endophytic fungal propagules in a shrub desert of northwest Argentina was examined. Our main goal was to include among root endophytic fungi not only arbuscular mycorrhiza but also the dark septate endophytes. We compared the abundance of fungal propagules as well as several microbiological and physicochemical parameters between soils from burrows and those from the surrounding landscape. Our results show that food haulage, the deposition of excretions, and soil mixing by rodents' burrowing promote soil patchiness by (1) the enrichment in both types of root endophytic fungal propagules; (2) the increase in organic matter and nutrients; and (3) changes in soil edaphic properties including moisture, field capacity, and texture. These patches may play a critical role as a source of soil heterogeneity in desert ecosystems, where burrows constructed in interpatches of bare soil can act, once abandoned, as "islands of fertility," promoting the establishment of plants in an otherwise hostile environment.

Soil microbial communities under cacao agroforestry and cover crop systems in Peru

Cacao (Theobroma cacao) trees are grown in tropical regions worldwide for chocolate production. We studied the effects of agroforestry management systems and cover cropping on soil microbial communities under cacao in two different replicated field experiments in Peru. In the first experiment, two agroforestry systems, Improved Traditional Agroforestry System (ITAS) and Improved Natural Agroforestry System (INAS), were compared. ITAS was a ‘slash and burn’ system in which all native vegetation was removed prior to replanting with cacao and other trees while INAS used selective removal of uneconomical trees followed by cacao planting. Soil microbial communities were analyzed by phospholipid fatty acid (PLFA) analysis and terminal restriction fragment length polymorphism (TRFLP) analysis. Soils in the ITAS system had altered microbial community structure and a lower Gram-negative to Gram-positive ratio when compared to soils in the INAS system. However, soil microbial community structure was also affected by a large soil pH gradient (three pH units) across this experiment. In the cover crop experiment, five cover crops, Arachis pintoi (perennial peanut), Calopogonium mucunoides (calopo), Canavalia ensiformis (jackbean), Centrosema macrocarpum (centro), and Callisia repens (callisia), and two controls (one with and one without nitrogen fertilization), were compared. Cover cropping with centro or perennial peanut increased the Gram-negative to Gram-positive ratio, while centro reduced the fungal biomass. Microbial community structure was significantly affected by cover cropping. Our results indicate that management systems and cover cropping can affect soil microbial community structure in tropical agroforestry systems, but the effects of soil edaphic properties must be considered as well.

Effects of ecological restoration on soil microbial diversity in a temperate grassy woodland

Soil microbial communities are often overlooked in the context of ecological restoration. Given their central role in a broad range of ecosystem processes, however, understanding their response to restoration activities is critical to predicting restoration trajectories. In this study, we quantified the response of soil bacterial and fungal communities to restoration treatments, variation in microhabitat elements and vegetation in a critically endangered Australian box-gum grassy woodland ecosystem. Restoration treatments included the addition of coarse woody debris (CWD) and reduced grazing pressure. Four years after applying restoration treatments, we found no significant effect of CWD addition on soil microbial diversity, while reduced grazing significantly affected composition of the fungal, but not the bacterial, communities. Both bacterial and fungal communities responded to microhabitat element (open ground vs. old logs and trees), overlying vegetation and soil edaphic properties, and strong aboveground-belowground linkages were observed. Plant alpha diversity was positively correlated to soil bacterial, but not fungal, alpha diversity and plant community composition was a good predictor of both soil bacterial and fungal beta diversity. Co-occurrence network analysis identified numerous complex, non-linear associations between soil bacteria, fungi, edaphic properties and overlying plants. Soil microbes affected by restoration treatments included fungal saprotrophs and Actinobacteria, likely involved in litter breakdown, as well as bacteria likely involved in soil N cycling. Although the directions of the observed plant-microbe relationships remain unclear, we demonstrated the possibility of inducing changes to soil microbial communities to enhance restoration outcomes in box-gum grassy woodland ecosystems.

Effect of soil edaphic factors on Rhizoctonia solani mediated diseases in major vegetable brassica growing districts of West Bengal

Gangetic alluvial region is the most fertile part of West Bengal where majority of farmers' livelihood is commercial vegetable production. Vegetable brassica such as cabbage, cauliflower and radish occupies 18 per cent of total vegetable cultivation in West Bengal and mainly cultivated in Nadia, Mursidabad, Purulia, North 24 praganas and South 24 praganas districts. Damping off, wire stem and root rot are the major diseases caused by Rhizoctonia solani in these districts. Different soil edaphic factors like soil temperature, soil pH, available carbon, available nitrogen etc. play a major role in survival and spread of Rhizoctonia solani and hence, this study was undertaken. The survey reveals that among different soil edaphic properties; soil pH, organic C and available N (kg/ha) are the important determinants of disease conduciveness and suppressiveness. Soil pH is the most important determining factor for disease development. The disease incidence is negatively correlated with the pH.

Driving forces of soil bacterial community structure, diversity, and function in temperate grasslands and forests.

Soil bacteria provide a large range of ecosystem services such as nutrient cycling. Despite their important role in soil systems, compositional and functional responses of bacterial communities to different land use and management regimes are not fully understood. Here, we assessed soil bacterial communities in 150 forest and 150 grassland soils derived from three German regions by pyrotag sequencing of 16S rRNA genes. Land use type (forest and grassland) and soil edaphic properties strongly affected bacterial community structure and function, whereas management regime had a minor effect. In addition, a separation of soil bacterial communities by sampling region was encountered. Soil pH was the best predictor for bacterial community structure, diversity and function. The application of multinomial log-linear models revealed distinct responses of abundant bacterial groups towards pH. Predicted functional profiles revealed that differences in land use not only select for distinct bacterial populations but also for specific functional traits. The combination of 16S rRNA data and corresponding functional profiles provided comprehensive insights into compositional and functional adaptations to changing environmental conditions associated with differences in land use and management.

Edaphic and Topographic Constraints on Exploitation of the Central Kenya Rift by Large Mammals and Early Hominins

Our aim in this paper is to create a palaeoenvironmental and spatio-temporal framework for interpreting human land use and exploitation of large mammals in the Central Kenya Rift over the past 2 million years, with particular reference to the Nakuru-Elmenteita-Naivasha basin and its adjacent rift flanks on the Kinangop Plateau and Mau escarpment. We pay particular attention to the tectonic and volcanic history of the region, and to the system of lakes that have undergone periodic expansion and contraction during the Pleistocene in response to climatic and tectonic controls. We use this information to reconstruct topographic features as they would have existed at different periods of the past and their likely influence on patterns of large-mammal movements. In addition we present a systematic mapping of variations in the mineral nutrients of soils – soil edaphics – based on 150 analyses of trace elements in modern soil and vegetation samples. Soil edaphics play an important role in animal and human health today, with serious deficiencies in some areas, and would have exerted an important constraint on animal distributions and movements in the past. We show how soil-edaphic properties vary across the region and demonstrate a close relationship between them and the underlying geology and sediments, which allows us to project patterns back into the past and extrapolate them over larger areas. Using this combination of variables, we construct maps that help to place archaeological sites into their wider regional setting. We focus in particular on the Acheulean site of Kariandusi and show that it occupied a unique window of opportunity in place and time for trapping mammals constrained to move through a narrowly defined topographic bottleneck between edaphically-rich areas. We infer that the site was used for a simple form of ambush hunting and briefly explore the implications for differential site use, formation, preservation and visibility.