Laclau Jean-Paul, Toutain François, M'bou Armel Thongo, Arnaud Michel, Joffre Richard, Ranger Jacques
CIRAD/UR2PI, Département Forêt, Programme Arbres et Plantations, TA 10/C, 34398 Montpellier cedex 5, France.
Ann Bot. 2004 Mar;93(3):249-61. doi: 10.1093/aob/mch035. Epub 2004 Jan 28.
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.
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.
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.
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.
森林地表内浅根垫对亚马逊雨林养分供应的重要性已得到广泛研究。本研究旨在评估在桉树林中观察到的附着于分解有机物质的根垫的功能。
通过对薄凋落物切片的微观形态观察研究根垫的发育，并在5平方米的区域内原位评估土壤微地形和土壤斥水性对根垫生物量的影响。此外，根据凋落物、重力溶液中溶解养分以及森林地表养分含量的测量结果，建立了森林地表内养分的输入 - 输出预算。
在研究期间，该生态系统中凋落物分解过程中释放的养分数量平均分别为：氮46千克·公顷⁻¹·年⁻¹、磷3千克·公顷⁻¹·年⁻¹、钾4千克·公顷⁻¹·年⁻¹、钙19千克·公顷⁻¹·年⁻¹和镁17千克·公顷⁻¹·年⁻¹。对森林地表穿透水和渗滤液化学成分的同步测量表明，在分解过程中根垫对养分的吸收非常迅速。实际上，尽管凋落物分解过程中释放了大量元素，但溶液在通过全有机层时并未显著富集养分。根垫生物量在旱季显著下降，并且观察到在土壤表面的微凹陷处有优先发育现象。在这些凹陷处观察到的强斥水性可能会增强根系在干旱时期吸收水分和养分的能力。
根垫全年都很活跃，能够捕获森林地表生物降解产生的养分通量，防止溶解养分向更深的土壤层转移。这种机制参与了这种杂交桉在刚果“气候性”稀树草原覆盖地区的成功适应。
