AOBPreview originally published online on January 28, 2004
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Annals of Botany 93: 249-261, 2004
© 2004 Annals of Botany Company
The Function of the Superficial Root Mat in the Biogeochemical Cycles of Nutrients in Congolese Eucalyptus Plantations
1 CIRAD/UR2PI, Département Forêt, Programme Arbres et Plantations, TA 10/C, 34398 Montpellier cedex 5, France, 2 CNRS Limos, CNRS FRE 2440, 17, rue ND des Pauvres, BP 5, 54501 Vandoeuvre-les-Nancy cedex, France, 3 UR2PI, Pointe Noire, BP 1291, Republic of Congo, 4 CIRAD-Tera, Programme Ere, TA 60/15, 34398 Montpellier cedex 5, France, 5 CEFE-CNRS, 1919 route de Mende, 34293 Montpellier cedex 5, France and 6 INRA, Centre de Nancy, Unité Biogéochimie des Ecosystèmes Forestiers, 54280 Champenoux, France
* For correspondence. CIRAD/ESALQ, IPEF, Av. Pádua Dias 11, Caixa Postal 530, CEP 13·400–970, Piracicaba-SP, Brazil. Fax 55 19 3436 8666, e-mail laclau{at}cirad.fr
Received: 26 March 2003;; Returned for revision: 18 July 2003; Accepted: 24 October 2003, Published electronically: 28 January 2004
• Background and Aims The importance of superficial root mats inside the forest floor for the nutrition of Amazonian rain forests has been extensively investigated. The present study was aimed at assessing the function of a root mat adherent to decomposing organic material observed in Eucalyptus plantations.
• Methods The development of the root mat was studied through micromorphological observations of thin litter sections, and the influence of soil microtopography and soil water repellency on root mat biomass was assessed in situ on an area of 5 m2. In addition, input–output budgets of nutrients within the forest floor were established from measurements of litterfall, dissolved nutrients in gravitational solutions, and forest floor nutrient contents.
• Key Findings The amounts of nutrients released during litter decay in this ecosystem during the period of study were, on average, 46, 3, 4, 19 and 17 kg ha–1 year–1 for N, P, K, Ca and Mg, respectively. The simultaneous measurements of the chemical composition of throughfall solutions and leachates beneath the forest floor showed a very quick uptake of nutrients by the root mat during the decomposition processes. Indeed, the solutions did not become noticeably enriched in nutrients during their passage through the holorganic layer, despite large amounts of elements being released during litter decay. The root mat biomass decreased significantly during the dry season, and a preferential development in microdepressions at the soil surface was observed. A strong water repellency observed in these depressions might enhance the ability of the roots to take up water and nutrients during the dry periods.
• Conclusions The root mat was active throughout the year to catch the flux of nutrients from the biodegradation of the forest floor, preventing the transfer of dissolved nutrients toward deeper soil horizons. This mechanism is involved in the successful adaptation of this Eucalyptus hybrid in areas covered by ‘climacic’ savannas in Congo.
Key words: Root mat, Eucalyptus, nutrition, Africa, soil solution, water repellency, biogeochemistry, tropical soil, tropical forest, plantation.
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