Heidy Schimann

Global sampling of plant roots expands the described molecular diversity of arbuscular mycorrhizal fungi.

We aimed to enhance understanding of the molecular diversity of arbuscular mycorrhizal fungi (AMF) by building a new global dataset targeting previously unstudied geographical areas. In total, we sampled 96 plant species from 25 sites that encompassed all continents except Antarctica. AMF in plant roots were detected by sequencing the nuclear SSU rRNA gene fragment using either cloning followed by Sanger sequencing or 454-sequencing. A total of 204 AMF phylogroups (virtual taxa, VT) were recorded, increasing the described number of Glomeromycota VT from 308 to 341 globally. Novel VT were detected from 21 sites; three novel but nevertheless widespread VT (Glomus spp. MO-G52, MO-G53, MO-G57) were recorded from six continents. The largest increases in regional VT number were recorded in previously little-studied Oceania and in the boreal and polar climatic zones — this study providing the first molecular data from the latter. Ordination revealed differences in AM fungal communities between different continents and climatic zones, suggesting that both biogeographic history and environmental conditions underlie the global variation of those communities. Our results show that a considerable proportion of Glomeromycota diversity has been recorded in many regions, though further large increases in richness can be expected in remaining unstudied areas.

Assessing foliar chlorophyll contents with the SPAD-502 chlorophyll meter: a calibration test with thirteen tree species of tropical rainforest in French Guiana

Abstract• Chlorophyll meters such as the SPAD-502 offer a simple, inexpensive and rapid method to estimate foliar chlorophyll content. However, values provided by SPAD-502 are unitless and require empirical calibrations between SPAD units and extracted chlorophyll values.• Leaves of 13 tree species from the tropical rain forest in French Guiana were sampled to select the most appropriate calibration model among the often-used linear, polynomial and exponential models, in addition to a novel homographic model that has a natural asymptote.• The homographic model best accurately predicted total chlorophyll content (μg cm−2) from SPAD units (R2 = 0.89). Interspecific differences in the homographic model parameters explain less than 7% of the variation in chlorophyll content in our data set.• The utility of the general homographic model for a variety of research and management applications clearly outweighs the slight loss of model accuracy due to the abandon of the species’ effect.

Interactive effects of C, N and P fertilization on soil microbial community structure and function in an Amazonian rain forest

Summary1. Resource control over abundance, structure and functional diversity of soil microbial com-munities is a key determinant of soil processes and related ecosystem functioning. Copiotroph-ic organisms tend to be found in environments which are rich in nutrients, particularly carbon,in contrast to oligotrophs, which survive in much lower carbon concentrations.2. We hypothesized that microbial biomass, activity and community structure in nutrient-poorsoils of an Amazonian rain forest are limited by multiple elements in interaction. We testedthis hypothesis with a fertilization experiment by adding C (as cellulose), N (as urea) and P (asphosphate) in all possible combinations to a total of 40 plots of an undisturbed tropical forestin French Guiana.3. After 2 years of fertilization, we measured a 47% higher biomass, a 21% increase in sub-strate-induced respiration rate and a 5-fold higher rate of decomposition of cellulose paperdiscs of soil microbial communities that grew in P-fertilized plots compared to plots without Pfertilization. These responses were amplified with a simultaneous C fertilization suggesting Pand C colimitation of soil micro-organisms at our study site.4. Moreover, P fertilization modified microbial community structure (PLFAs) to a morecopiotrophic bacterial community indicated by a significant decrease in the Gram-positive : Gram-negative ratio. The Fungi : Bacteria ratio increased in N fertilized plots,suggesting that fungi are relatively more limited by N than bacteria. Changes in microbialcommunity structure did not affect rates of general processes such as glucose mineralizationand cellulose paper decomposition. In contrast, community level physiological profiles under Pfertilization combined with either C or N fertilization or both differed strongly from all othertreatments, indicating functionally different microbial communities.5. While P appears to be the most critical from the three major elements we manipulated, thestrongest effects were observed in combination with either supplementary C or N addition insupport of multiple element control on soil microbial functioning and community structure.6. We conclude that the soil microbial community in the studied tropical rain forest and the pro-cessesitdrivesisfinelytunedbytherelativeavailabilityinC,NandP.Anyshiftsintherelativeabun-dance of these key elements may affect spatial and temporal heterogeneity in microbial communitystructure,theirassociatedfunctionsandthedynamicsofCandnutrientsintropicalecosystems.Key-words: ecosystem functioning, functional significance, microbial community structure,multiple resource limitation, phospholipid fatty acids (PLFA), phosphorus, soil functioning,tropical forest

Distinct Microbial Limitations in Litter and Underlying Soil Revealed by Carbon and Nutrient Fertilization in a Tropical Rainforest

Human-caused alterations of the carbon and nutrient cycles are expected to impact tropical ecosystems in the near future. Here we evaluated how a combined change in carbon (C), nitrogen (N) and phosphorus (P) availability affects soil and litter microbial respiration and litter decomposition in an undisturbed Amazonian rainforest in French Guiana. In a fully factorial C (as cellulose), N (as urea), and P (as phosphate) fertilization experiment we analyzed a total of 540 litterbag-soil pairs after a 158-day exposure in the field. Rates of substrate-induced respiration (SIR) measured in litter and litter mass loss were similarly affected by fertilization showing the strongest stimulation when N and P were added simultaneously. The stimulating NP effect on litter SIR increased considerably with increasing initial dissolved organic carbon (DOC) concentrations in litter, suggesting that the combined availability of N, P, and a labile C source has a particularly strong effect on microbial activity. Cellulose fertilization, however, did not further stimulate the NP effect. In contrast to litter SIR and litter mass loss, soil SIR was reduced with N fertilization and showed only a positive effect in response to P fertilization that was further enhanced with additional C fertilization. Our data suggest that increased nutrient enrichment in the studied Amazonian rainforest can considerably change microbial activity and litter decomposition, and that these effects differ between the litter layer and the underlying soil. Any resulting change in relative C and nutrient fluxes between the litter layer and the soil can have important consequences for biogeochemical cycles in tropical forest ecosystems.

Cantharellaceae of Guyana II: New species of Craterellus, new South American distribution records for Cantharellus guyanensis and Craterellus excelsus, and a key to the Neotropical taxa

Craterellus olivaceoluteus sp. nov. and Craterellus cinereofimbriatus sp. nov. are described as new to science. These fungi were collected from Guyana in association with ectomycorrhizal host trees in the genera Dicymbe (Fabaceae subfam. Caesalpinioideae) and Pakaraimaea (Dipterocarpaceae). Cantharellus guyanensis Mont., originally described from French Guiana, is redescribed from recent collections from Guyana, with additional range extensions for the species provided based on material examined from French Guiana, Venezuela, and north central, northeastern and southern Brazil, circumscribing nearly the entire Guiana Shield region and beyond. A new distribution record from French Guiana is provided for Craterellus excelsus T.W. Henkel & Aime. Macromorphological, micromorphological and habitat data are provided for the new species and C. guyanensis as well as DNA sequence data from the nuclear ribosomal regions of the internal transcribed spacer (ITS) and 28S large subunit (LSU); additional sequence data is provided for C. guyanensis and C. excelsus specimens collected outside Guyana. The relationships of these taxa within the Cantharellaceae were evaluated with phylogenetic analyses of ITS and LSU sequence data. This work brings the total number of Cantharellaceae species known from Guyana to eight. A key to the Cantharellus and Craterellus species known from the lowland Neotropics and extralimital montane Central and South America is provided.

Soil community assembly varies across body sizes in a tropical forest

The relative influence of deterministic niche-based (i.e. abiotic conditions, biotic interactions) and stochastic-distance dependent neutral processes (i.e. demography, dispersal) in shaping communities has been extensively studied for various organisms, but is far less explored jointly across the tree of life, in particular in soil environments. Here, using a thorough DNA-based census of the whole soil biota in a large tropical forest plot, we show that soil aluminium, topography, and plant species identity are all important drivers of soil richness and community composition. Body size emerges as an important feature of the comparative ecology of the different taxa at the studied spatial scale, with microorganisms being more importantly controlled by environmental factors, while soil mesofauna rather display random spatial distribution. We infer that niche-based processes contribute differently to community assembly across trophic levels due to spatial scaling. Body size could hence help better quantifying important properties of multitrophic assemblages.

The Genus Resinicium in French Guiana and the West Indies: a Morphological and Molecular Survey, Revealing Resinicium grandisporum sp. nov.

Abstract A revision of Resinicium collections (Basidiomycota, Hymenochaetales) from French Guiana and French West Indies is provided, and a new species, Resinicium grandisporum sp. nov., supported by morphological as well as phylogenetic analyses based on ITS rDNA sequences, is described and illustrated. An updated key of the genus Resinicium is also provided, which includes species previously described from outside of the studied area.