Productivité herbacée des savanes de la Cuvette congolaise (Congo-Brazzaville)

La savane à Hyparrhenia diplandra Stapfet celle à Loudetia simplex C.E. Hubbard ont été étudiées dans la Cuvette congolaise (Nord du Congo-Brazzaville), sur le plan de la production herbacée. Les sites retenus pour l’étude sont Ollombo, Owando et Makoua. L’étude a démarré à partir des feux de la saison « sèche ». L’objectif de cette étude était d’évaluer la phytomasse aérienne herbacée et sa productivité, en vue d’aider à la prise de décision sur le choix des espaces à occuper pour des activités agricoles et pastorales. Laphytomasse aérienne herbacée a été mesurée par la méthode de la récolte et sa productivité primaire nette réelle par la méthode de la différence entre le moment où la phytomasse est maximale et le moment où elle est minimale dans un cycle annuel. Les échantillons de sols ont été prélevés sous ces deux types de savanes. Leurs analyses granulométrique et chimiques révèlent que ces sols sont dans l’ensemble très sableux, acides et pauvres en matière organique. Le taux en argiles est légèrement supérieur dans le sol sous savane à H. diplandra (jusqu’à 14%) que dans celui sous savane à L. simplex (1% au maximum). La phytomasse aérienne totale maximale est enregistré à dix mois après les feux, en mai : 9,48 – 10,44 t MS ha-1 pour la savane à H. diplandra et 3,43 – 4,52 t MS ha-1 pour la savane à L. simplex. La productivité de la phytomasse varie de 9,29 – 10,04 t MS ha-1an-1 pour la savane à H. diplandra et de 3,09 – 4,64 t MS ha-1an-1 pour la savane à L. simplex. La savane à H. diplandra serait donc à recommander pour des activitésagricoles et pastorales que celle à L. simplex.Mots-clés : savanes, sols, phytomasse, strate aérienne herbacée, productivité, cuvette congolaise.Productivity of Congolese Basin savannas (Congo-Brazzaville)The Hyparrhenia diplandra Stapf and the Loudetia simplex C.E. Hubbard savannas have been studied in the Cuvette congolaise (the North of Congo-Brazzaville) on the herbaceous production level. The selected sites for this research are: Ollombo, Owando and Makoua. The study started with the fires of the dry season. The objective of this survey was to evaluate the aerial herbaceous phytomass and its productivity, in order to help the decision taking concerning the choice of the areas for agricultural and pastoral activities. Theherbaceous aerial phytomass has been examined within the harvesting framework and the net primary productivity of the phytomass is determined by the method of difference between the time when the phytomass is maximal and when it is minimal in an annual cycle. The soil samples have been taken from these two types of savannas. The granulometric and chemical analyses of soils reveal that the soils of the studied savannas are generally very sandy (79, 94-98, 38 %), acidic and poor in organic materials. The clay rate is slightly superior in the soil of the H. diplandra savanna (up to 14%) than in that of L. simplex (1% maxi). The maximal total aerial phytomass is recorded ten months after the fires, in may: 9, 48-10, 44 t MS ha-1 for H. diplandra savanna and 3, 43-4, 52 t MS ha-1 for L. simplex savanna (Figures 1 and 2). The phytomass productivity varies from 9, 29-10, 04 t MS ha-1an-1 for H. diplandra and from 3, 09-4, 64 t MS ha-1 an-1 for L. simplex. The H. diplandra savanna is more productive than the L. simplex savanna. The former should be recommended for agricultural and pastoral activities than the latter.Keywords : savannas, soils, phytomass, herbaceous aerial stratum, productivity, congolese cuvette

Évaluation de la diversité floristique en herbacées des savanes de la cuvette congolaise (République du Congo)

Les savanes de la République du Congo sont exploitées pour des fins agricoles et pastorales. Dans la Cuvette congolaise (nord du Congo), les savanes sont encore peu étudiées. La gestion durable de ces savanes nécessite leur connaissance sur le plan floristique. C’est ainsi qu’une étude floristique a été menée dans les savanes de la zone. Elle avait pour objectif d’évaluer l’intérêt pastoral des savanes de cette cuvette. A cet effet, des relevés floristiques ont été réalisés par la méthode des points quadrats alignés, afin d’inventorier la diversité floristique et les principales espèces fourragères. Ainsi, 37 espèces réparties en 33 genres et 10 familles ont été recensées dans la savane à Hyparrhenia diplandra (Hack.) Stapf , et 27 espèces réparties en 22 genres et 8 familles dans la savane à Loudetia simplex (Nees) C.E. Hubbard. Dans l’ensemble, les familles les plus riches en espèces étaient les Poaceae, les Fabaceae et les Cyperaceae. L’indice de diversité de Shannon et l’équitabilité de Piélou avaient des valeurs moyennes de 2,23 bits et 0,57 pour la savane à H. diplandra, et entre 2,1bits et 0,61 pour la savane à L. simplex. Il y a donc une diversité floristique non négligeable, dans ces savanes. Elle varie en fonction des stations d’étude et des phytocénoses. Une gestion planifiée de ces formations permettrait d’assurer une meilleure planification pour des fins pastorales.Mots-clés : savanes, phytodiversité, herbacée, pastoralisme, cuvette congolaise.Evaluation of herbaceous floristic diversity of Congolese basin savannahs (Republic of Congo)The savannas of the Republic of Congo are exploited for agricultural and pastoral. In the Congolese Basin (northern Congo), savannas are still poorly studied. Sustainable management of these savannas requires knowledge in terms of flora. Thus, a floristic study was conducted in the savannah area. It aimed to assess the value of pastoral savannas of the basin. To this end, the floristic surveys were conducted by the method of quadrat points aligned to inventory plant diversity and major forage species. Thus, 37 species, 33 kinds and 10 families were identified in the savannah of Hyparrhenia diplandra (Hack.) Stapf and 27 species, 22 kinds and 8 families in the savannah of Loudetia simplex (Nees) CE Hubbard. Overall, the richest families in species were Poaceae, Fabaceae and the Cyperaceae. The Shannon diversity index and equitability of Pielou had average values of 2.23 bits and 0.57 for the savannah of H. diplandra, and between 2.1 bits and 0.61 for the savannah of L. simplex. So there is substantial plant diversity in these savannas. It varies from study sites and phytocenoses. Planned management of such training would ensure better planning for pastoral purposes.Keywords : savannas, plant diversity, herbaceous, pastoralism, congolese basin

The production and turnover of extramatrical mycelium of ectomycorrhizal fungi in forest soils : role in carbon cycling

Peer reviewedPublisher PD

Effects of experimental warming on carbon sink function of a temperate pristine mire : the PEATWARM project.

communication oraleInternational audienceWithin the PEATWARM project, we use Sphagnum peatlands as a model to analyse their vulnerability to climate change using an experimental system (ITEX) that simulates in situ an increase in average temperature. We aim to determine the effects of temperature increase on the vegetation, the balance of above- and belowground gas fluxes (CO2 and CH4), the microbial diversity and activity in Sphagnum mosses and in peat, and the dynamics of labile and recalcitrant organic matter of peat. The ultimate objective is the creation of a biogeochemical model of C coupled with N and S cycles that includes interactions between these key compartments

Root trenching: a useful tool to estimate autotrophic soil respiration? A case study in an Austrian mountain forest

We conducted a trenching experiment in a mountain forest in order to assess the contribution of theautotrophic respiration to total soil respiration and evaluate trenching as a technique to achieve it. We hypothesised that the trenching experiment would alter both microbial biomass and microbial community structure and that Wne roots (less than 2 mm diameter) would be decomposed within one growing season. Soil CO2 eZux was measured roughlybiweekly over two growing seasons. Root presence and morphology parameters, as well as the soil microbial community were measured prior to trenching, 5 and 15 months after trenching. The trenched plots emitted about 20 and 30% less CO2 than the control plots in the Wrst and secondgrowing season, respectively. Roots died in trenched plots, but root decay was slow. After 5 and 15 months, Wne root biomass was decreased by 9% (not statistically diferent)and 30%, (statistically diVerent) respectively. When wecorrected for the additional trenched-plot CO2 eZux due to Wne root decomposition, the autotrophic soil respiration rose to »26% of the total soil respiration for the Wrst growing season, and to »44% for the second growing season.Soil microbial biomass and community structure was not altered by the end of the second growing season. We conclude that trenching can give accurate estimates of the autotrophic and heterotrophic components of soil respiration, ifmethodological side eVects are accounted for, only

Soil respiration at mean annual temperature predicts annual total across vegetation types and biomes

Soil respiration (SR) constitutes the largest flux of CO₂ from terrestrial ecosystems to the atmosphere. However, there still exist considerable uncertainties as to its actual magnitude, as well as its spatial and interannual variability. Based on a reanalysis and synthesis of 80 site-years for 57 forests, plantations, savannas, shrublands and grasslands from boreal to tropical climates we present evidence that total annual SR is closely related to SR at mean annual soil temperature (〖SR〗_MAT), irrespective of the type of ecosystem and biome. This is theoretically expected for non water-limited ecosystems within most of the globally occurring range of annual temperature variability and sensitivity (Q₁₀). We further show that for seasonally dry sites where annual precipitation (P) is lower than potential evapotranspiration (PET), annual SR can be predicted from wet season SRMAT corrected for a factor related to P/PET. Our finding indicates that it can be sufficient to measure 〖SR〗_MAT for obtaining a well constrained estimate of its annual total. This should substantially increase our capacity for assessing the spatial distribution of soil CO₂ emissions across ecosystems, landscapes and regions, and thereby contribute to improving the spatial resolution of a major component of the global carbon cycle

The moisture response of soil heterotrophic respiration: Interaction with soil properties

Soil moisture is of primary importance for predicting the evolution of soil carbon stocks and fluxes, both because it strongly controls organic matter decomposition and because it is predicted to change at global scales in the following decades. However, the soil functions used to model the heterotrophic respiration response to moisture have limited empirical support and introduce an uncertainty of at least 4% in global soil carbon stock predictions by 2100. The necessity of improving the representation of this relationship in models has been highlighted in recent studies. Here we present a data-driven analysis of soil moisture-respiration relations based on 90 soils. With the use of linear models we show how the relationship between soil heterotrophic respiration and different measures of soil moisture is consistently affected by soil properties. The empirical models derived include main effects and moisture interaction effects of soil texture, organic carbon content and bulk density. When compared to other functions currently used in different soil biogeochemical models, we observe that our results can correct biases and reconcile differences within and between such functions. Ultimately, accurate predictions of the response of soil carbon to future climate scenarios will require the integration of soil-dependent moisture-respiration functions coupled with realistic representations of soil water dynamic

Impacts of changed litter inputs on soil CO2 efflux in three forest types in central south China

We have defined Neutrosophic Over-/Under-/Off-Set and Logic for the first time in 1995 and published in 2007. During 1995-2016 we presented them to various national and international conferences and seminars. These new notions are totally different from other sets/logics/probabilities. We extended the neutrosophic set respectively to Neutrosophic Overset {when some neutrosophic component is > 1}, to Neutrosophic Underset {when some neutrosophic component is < 0}, and to Neutrosophic Offset {when some neutrosophic components are off the interval [0, 1], i.e. some neutrosophic component > 1 and other neutrosophic component < 0}. This is no surprise since our real-world has numerous examples and applications of over-/under-/off-neutrosophic components