Sebacinoids within rhizospheric fungal communities associated with subsistence farming in the Congo Basin: a needle in each haystack

The unique ecosystem of the Congolese rainforest has only scarcely been explored for its plant-fungal interactions. Here, we characterized the root fungal communities of field-grown maize and of Panicum from adjacent borders in the Congo Basin and assessed parameters that could shape them. The soil properties indicated that comparable poor soil conditions prevailed in fields and borders, illustrating the low input character of local subsistence farming. The rhizosphere fungal communities, dominated by ascomycetous members, were structured by plant species, slash-and-burn practices and soil P, pH and C/N ratio. Examining fungi with potential plant growth-promoting abilities, the glomeromycotan communities appeared to be affected by the same parameters, whereas the inconspicuous symbionts of the order Sebacinales seemed less susceptible to environmental and anthropogenic factors. Notwithstanding the low abundances at which they were detected, sebacinoids occurred in 87% of the field samples, implying that they represent a consistent taxon within indigenous fungal populations across smallholder farm sites. Pending further insight into their ecosystem functionality, these data suggest that Sebacinales are robust root inhabitants that might be relevant for on-farm inoculum development within sustainable soil fertility management in the Sub-Saharan region.

Congolese Rhizospheric Soils as a Rich Source of New Plant Growth-Promoting Endophytic Piriformospora Isolates

In the last decade, there has been an increasing focus on the implementation of plant growth-promoting (PGP) organisms as a sustainable option to compensate for poor soil fertility conditions in developing countries. Trap systems were used in an effort to isolate PGP fungi from rhizospheric soil samples collected in the region around Kisangani in the Democratic Republic of Congo. With sudangrass as a host, a highly conducive environment was created for sebacinalean chlamydospore formation inside the plant roots resulting in a collection of 51 axenically cultured isolates of the elusive genus Piriformospora (recently transferred to the genus Serendipita). Based on morphological data, ISSR fingerprinting profiles and marker gene sequences, we propose that these isolates together with Piriformospora williamsii constitute a species complex designated Piriformospora (= Serendipita) 'williamsii.' A selection of isolates strongly promoted plant growth of in vitro inoculated Arabidopsis seedlings, which was evidenced by an increase in shoot fresh weight and a strong stimulation of lateral root formation. This isolate collection provides unprecedented opportunities for fundamental as well as translational research on the Serendipitaceae, a family of fungal endophytes in full expansion.

Functional community structure of African monodominant Gilbertiodendron dewevrei forest influenced by local environmental filtering

Monodominant patches of forest dominated by Gilbertiodendron dewevrei are commonly found in central African tropical forests, alongside forests with high species diversity. Although these forests are generally found sparsely distributed along rivers, their occurrence is not thought to be (clearly) driven by edaphic conditions but rather by trait combinations of G. dewevrei that aid in achieving monodominance. Functional community structure between these monodominant and mixed forests has, however, not yet been compared. Additionally, little is known about nondominant species in the monodominant forest community. These two topics are addressed in this study. We investigate the functional community structure of 10 one-hectare plots of monodominant and mixed forests in a central region of the Congo basin, in DR Congo. Thirteen leaf and wood traits are measured, covering 95% (basal area weighted) of all species present in the plots, including leaf nutrient contents, leaf isotopic compositions, specific leaf area, wood density, and vessel anatomy. The trait-based assessment of G. dewevrei shows an ensemble of traits related to water use and transport that could be favorable for its location near forest rivers. Moreover, indications have been found for N and P limitations in the monodominant forest, possibly related to ectomycorrhizal associations formed with G. dewevrei. Reduced leaf N and P contents are found at the community level for the monodominant forest and for different nondominant groups, as compared to those in the mixed forest. In summary, this work shows that environmental filtering does prevail in the monodominant G. dewevrei forest, leading to lower functional diversity in this forest type, with the dominant species showing beneficial traits related to its common riverine locations and with reduced soil N and P availability found in this environment, both coregulating the tree community assembly.

Aboveground vs. Belowground Carbon Stocks in African Tropical Lowland Rainforest: Drivers and Implications

Background

African tropical rainforests are one of the most important hotspots to look for changes in the upcoming decades when it comes to C storage and release. The focus of studying C dynamics in these systems lies traditionally on living aboveground biomass. Belowground soil organic carbon stocks have received little attention and estimates of the size, controls and distribution of soil organic carbon stocks are highly uncertain. In our study on lowland rainforest in the central Congo basin, we combine both an assessment of the aboveground C stock with an assessment of the belowground C stock and analyze the latter in terms of functional pools and controlling factors.

Principal Findings

Our study shows that despite similar vegetation, soil and climatic conditions, soil organic carbon stocks in an area with greater tree height (= larger aboveground carbon stock) were only half compared to an area with lower tree height (= smaller aboveground carbon stock). This suggests that substantial variability in the aboveground vs. belowground C allocation strategy and/or C turnover in two similar tropical forest systems can lead to significant differences in total soil organic C content and C fractions with important consequences for the assessment of the total C stock of the system.

Conclusions/Significance

We suggest nutrient limitation, especially potassium, as the driver for aboveground versus belowground C allocation. However, other drivers such as C turnover, tree functional traits or demographic considerations cannot be excluded. We argue that large and unaccounted variability in C stocks is to be expected in African tropical rain-forests. Currently, these differences in aboveground and belowground C stocks are not adequately verified and implemented mechanistically into Earth System Models. This will, hence, introduce additional uncertainty to models and predictions of the response of C storage of the Congo basin forest to climate change and its contribution to the terrestrial C budget.

Compact extracorporeal circulation: reducing the surface of cardiopulmonary bypass to improve outcomes

We have introduced a number of modifications to minimize the deleterious effects of cardiopulmonary bypass (CPB) by reducing the surface of the extracorporeal circulation (ECC), the length of the ECC circuit, the contact surface of the oxygenator, and the volume of priming solution, in addition to employing biocompatible systems and isolation of excess blood volumes of venous reservoirs in transfusion bags very early in CPB. Encouraged by the results of our initial "Compact ECC," we have decided to improve it by implementing other techniques such as controlled hemodilution of the patient by reducing the diameter of ECC venous tubing (from 1/2 in. to 3/8 in.), limiting contact surface of the oxygenator and venous reservoir, positioning the oxygenator and venous reservoir at the level of the patient's shoulder, and employing venous cannulae adapted to vacuum assisted venous drainage (VAVD) to replace venous drainage by gravity. The purpose of this study is to evaluate postoperative outcomes of Compact ECC. Three groups of patients undergoing coronary artery bypass graft (CABG) are compared. Our new Compact ECC shows improved outcomes through reduced postoperative ventilation time, blood loss, intensive care stay, need for blood transfusion, and levels of lactate dehydrogenase despite the patients' pathologies and surgeries being more complex.