Etude à long terme de la biogéochimie des écosystèmes forestiers

Plan quinquennal de Recherches forestières 2019-202

Effect of tree species mixture on earthworm communities on a continental scale

The belowground food web represents a major part of associated biodiversity in forest ecosystems, and plays a significant role in the ecosystem processes of litter decomposition and nutrient turnover. Past research has demonstrated overwhelming evidence of strong tree species identity effects on earthworm communities. It has been proposed that increased plant community diversity would be beneficial to the abundance and diversity of the belowground food web, but effects of tree species diversity on earthworm communities have seldom been reported, and are inconclusive. In this study at continental scale we evaluated whether tree species diversity positively affects earthworm biomass and diversity. For this purpose the FunDivEUROPE Exploratory Platform was used with 209 plots in 6 regions well spread over Europe with a low within-region site variability, but a within-region tree species diversity gradient from monocultures to 3 or 4 species plots. In every plot earthworms were sampled using a combined method of mustard extraction and hand sorting of litter and a soil monolith. Data are being analysed with multivariate tools and mixed effects models. First results suggest only limited influence of tree diversity on the biomass of earthworm communities at continental scale. Tree diversity effects are weak, context specific and interacting with tree identity. In nutrient poor soils we found a negative tree diversity effect on earthworm biomass when deciduous monocultures are enriched with coniferous species, while in rich soils we found a positive tree diversity effect which could be related with the food security this provides to the earthworm community.FUNDIVEUROPE - Functional significance of forest biodiversity in Europ

Soil properties and microbial processes in response to land-use change in agricultural highlands of the Central Andes

peer reviewedAbstract Understanding changes in soil functions in response to land-use change is important for guiding agricultural practices towards sustainable soil management. We evaluated the differences in soil properties (soil organic matter, water extractable carbon (C) and nitrogen (N), microbial biomass, pHKCL and exchangeable cations) and microbial processes (respiration potential, net N mineralization, net nitrification and metabolic potential of soil bacteria), as well as the relative importance of soil properties in explaining changes in processes under three land uses (potato crops, fallow fields and eucalyptus plantations) in the agricultural highlands of the Central Andes. Soils under potato crops were characterized by the highest net N mineralization and net nitrification rates, and extractable phophorus (P), and the lowest microbial biomass P. Conversion to eucalyptus plantations led to an increase in soil organic matter, water extractable C and microbial biomass, and a decrease in extractable P and metabolic diversity of soil bacteria. Higher exchangeable aluminium (Al) indicated soil acidification under eucalyptus. Fallow practices did not lead to major changes in soil properties and microbial processes, indicating that fallow practices for up to 6 years were too short to substantially contribute to soil fertility restoration. Hot water extractable carbon (HWC) showed the best relationship with soil processes (respiration potential, net N mineralization and net nitrification). Our results highlight the necessity of alternative management practices for maintaining soil fertility under potato crops, the drastic modification of soil properties and processes under eucalyptus plantations, and the potential of HWC as a proxy for monitoring land-use-induced changes in soil functions related to C and N cycling. Highlights Effects of conversion from potato crops to eucalyptus and fallow on soil properties and processes were assessed. Under eucalyptus, soil respiration increased; metabolic diversity and N transformations decreased. Short fallow periods did not result in soil fertility restoration. Hot water extractable C was the best indicator of changes in soil processes

Soil microbial biomass and oxy-hydroxides contribute to aggregate stability and size distribution under different land uses in the Central Andes

peer reviewedContext: Agricultural intensification leads to land use changes with potential consequences for soil aggregate stability and size distribution, affecting nutrient and water retention capacity, aeration, sequestration of soil organic carbon, and biogeochemical cycling. Aims: This study evaluated soil aggregate stability and size distribution under potato, fallow and Eucalyptus globulus L. land uses in Cambisols of the eastern branch of the Central Andes, Bolivia. We also investigated the relation between aggregates and total C, extractable C, oxy-hydroxides, microbial biomass and activity. Methods: Aggregate stability, size distribution and oxy-hydroxides were measured in soil samples from eight plots of each land use. Key results: Compared to fields cultivated with potato (Solanum tuberosum L.), Eucalyptus increased aggregate stability, megaaggregate content, and C and N in the free silt + clay fraction. Fallow did not lead to significant changes in soil structure. Soil aggregate stability was related to both microbial biomass and oxy-hydroxides. Microbial biomass C, microbial activity and dithionite extractable Fe were positively related to megaaggregates and aggregate stability. Oxalate extractable Fe and Mn were related to microaggregates. Conclusions: The plantation of Eucalyptus is suitable for soil structural amelioration and C sequestration, but its introduction to cultivated areas should be carefully evaluated due to its effects on soil chemistry and microbiology. Short-term fallowing did not contribute to the maintenance of soil structure. Implications: In a context of land uses change, modifications of microbial biomass and activity would affect megaaggregate formation and stability. Alternative management practices are required to maintain soil structure and optimize sustainable land use of cultivated and fallow fields.2. Zero hunger15. Life on lan

Long-Term Effects of Forest Plantation Species on Chemical Soil Properties in Southern Rwanda

peer reviewedUnderstanding the long-term effects of tree species on soil properties is crucial for the development of forest restoration policies in relation to the choice of species that meet both environmental and local livelihood needs. This study was performed in the Arboretum of Ruhande, Southern Rwanda, where monocultures of 148 deciduous and 56 conifer species have been established in 0.25 ha replicated plots from 1933 onwards. We investigated the effects of six exotic and two native tree species planted in monoculture plots and native species mixed within one self-regenerated plot on soil properties in two layers (0–5 cm and 5–10 cm depth). We measured general soil properties (pH, SOM, exchangeable base cations) and water-soluble C and N as a proxy for soil functioning. Changes in soil properties were observed in the upper soil layer for all tree species. Planting Eucalyptus species caused soil acidification, whereas soil exchangeable cations and pH were higher under native species (Entandrophragma excelsum and Polyschias fulva) and mixed native species. The effects of tree species were more pronounced for hot water-extractable C and N than for other soil properties. Their analyses could be used for detecting changes in soil functioning linked to vegetation types

Effects of forest restoration tree species on soil properties in Southern Rwanda

Abstract Effects of forest restoration tree species on soil properties in Southern Rwanda 1,2 Peter Rwibasira*, 2Francois Xavier Naramabuye, 2Donat Nsabimana, and 1Monique Carnol 1University of Liège, Belgium – Plant and Microbial Ecology; 2University of Rwanda, Rwanda. *Corresponding Author: [email protected] Understanding the effects of tree species on soil properties is primordial for the development of forest restoration policies regarding the choice of species that will meet both environmental and local livelihood needs. We investigated the effects of exotic and native tree species, planted in 27 plots (31-82 years old), on selected soil properties (pH, SOM, water-extractable C and N) and soil exchangeable base cations (EBC) at two soil layers (0-5 cm and 5-10 cm) in the arboretum of Ruhande, Southern Rwanda. Given that trees were planted on one site with similar land-use history, climatic conditions, parent material, and soil type, we expect current differences in soil characteristics to reflect the influence of the tree species. The effects of tree species were most apparent in the upper thin layer (0-5 cm) and the values of parameters were higher in this layer compared to the lower soil layer. The influence of tree species at 5-10 cm depth, was less marked and the values were lower for all measured parameters except for Al3+ and Fe2+ concentration. Eucalyptus species stands had the lowest soil pH (3.7) and mixed native species had the highest soil pH (5.8) as well as the highest exchangeable base cations (EBC) at both 0-5 cm depth (63±1.4 cmol (+)/kg) and 5-10 cm depth (9.3±0.2 cmol (+)/kg). Water extractable C and N fractions were higher at the upper soil layer compared to the lower layer. At 0-5cm, hot and cold water-extractable C and N fractions were positively correlated to soil organic matter (SOM) and negatively correlated to pH, but no significant correlation was observed at 5-10 cm. Our results showed that: (i) the two soil layers (0-5 cm and 5-10 cm depths) which were visibly undistinguishable under most of the species significantly differed in soil properties. This highlights the importance of the upper thin layer (0-5 cm depth) in tropical soils, which are generally poor and rely heavily on internal nutrient cycling through rapid decomposition of above-and belowground litter from vegetation (ii) Eucalyptus had negative consequences on soil pH and EBC, whereas soil under mixed natives had higher pH and EBC (iii) The sensitivity of water-extractable C and N fractions to detect tree species effects and their correlation with SOM indicates that these fractions could be used as substitutes to SOM analysis. Keywords: Eucalyptus; organic matter; water-extractable C and N; exotic tree species; soil nutrients; soil quality; Ruhande ArboretumARES - Rwanda (Result1

Homology modeling and in vivo functional characterization of the zinc permeation pathway in a heavy metal P-type ATPase

The P1B ATPase Heavy Metal ATPase 4 (HMA4) is responsible for zinc and cadmium translocation from roots to shoots in the plant Arabidopsis thaliana. It couples ATP hydrolysis to cytosolic domain movements enabling metal transport across the membrane. Thanks to high conservation level within the P-type ATPase family, the role of the HMA4 cytoplasmic catalytic domains can be inferred from well characterized pumps. In contrast, the function of its terminal cytosolic extensions as well as the metal permeation mechanism through the membrane remains elusive. Here, homology modeling of the HMA4 transmembrane region was conducted based on the crystal structure of a ZntA bacterial homolog. The analysis highlighted amino acids forming a metal permeation pathway, whose importance was subsequently investigated functionally through mutagenesis and complementation experiments in plants. Although the zinc pathway displayed overall conservation among the two proteins, significant differences were observed, especially in the entrance area with altered electronegativity and the presence of a salt bridge/H-bond network. The analysis also newly identified amino acids whose mutation results in total or partial loss of the protein function. In addition, comparison of zinc and cadmium accumulation in shoots of A. thaliana complemented lines revealed a number of HMA4 mutants exhibiting different abilities in zinc and cadmium translocation. These observations could be instrumental to design low cadmium accumulating crops, hence decreasing human cadmium exposure

Biotic predictors complement models of bat and bird responses to climate and tree diversity in European forests

Bats and birds are key providers of ecosystem services in forests. How climate and habitat jointly shape their communities is well studied, but whether biotic predictors from other trophic levels may improve bird and bat diversity models is less known, especially across large bioclimatic gradients. Here, we achieved multi-taxa surveys in 209 mature forests replicated in six European countries from Spain to Finland, to investigate the importance of biotic predictors (i.e., the abundance or activity of defoliating insects, spiders, earthworms and wild ungulates) for bat and bird taxonomic and functional diversity. We found that 9 out of 12 bird and bat diversity metrics were best explained when biotic factors were added to models including climate and habitat variables, with a mean gain in explained variance of 38% for birds and 15% for bats. Tree functional diversity was the most important habitat predictor for birds, while bats responded more to understorey structure. The best biotic predictors for birds were spider abundance and defoliating insect activity, while only bat functional evenness responded positively to insect activity. Accounting for potential biotic interactions between bats, birds and other taxa of lower trophic levels will help to understand how environmental changes along large biogeographical gradients affect higher-level predator diversity in forest ecosystems

Jack-of-all-trades effects drive biodiversity-ecosystem multifunctionality relationships in European forests.

There is considerable evidence that biodiversity promotes multiple ecosystem functions (multifunctionality), thus ensuring the delivery of ecosystem services important for human well-being. However, the mechanisms underlying this relationship are poorly understood, especially in natural ecosystems. We develop a novel approach to partition biodiversity effects on multifunctionality into three mechanisms and apply this to European forest data. We show that throughout Europe, tree diversity is positively related with multifunctionality when moderate levels of functioning are required, but negatively when very high function levels are desired. For two well-known mechanisms, 'complementarity' and 'selection', we detect only minor effects on multifunctionality. Instead a third, so far overlooked mechanism, the 'jack-of-all-trades' effect, caused by the averaging of individual species effects on function, drives observed patterns. Simulations demonstrate that jack-of-all-trades effects occur whenever species effects on different functions are not perfectly correlated, meaning they may contribute to diversity-multifunctionality relationships in many of the world's ecosystems.The research leading to these results received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement no. 265171.This is the final version of the article. It first appeared from Nature Publishing Group via http://dx.doi.org/10.1038/ncomms1110