Nutrient Cycling in Agroecosystems

, Volume 92, Issue 1, pp 51–65 | Cite as

Leaf and root litter of a legume tree as nitrogen sources for cacaos with different root colonisation by arbuscular mycorrhizae

  • Anna-Kaisa Kähkölä
  • Pekka NygrenEmail author
  • Humberto A. Leblanc
  • Taina Pennanen
  • Janna Pietikäinen
Original Article


Traditionally cacao (Theobroma cacao L.) is cultivated under legume shade trees, which produce N-rich litter that improves soil organic matter content, microbial activity, and recycles N to the crop. Arbuscular mycorrhiza forming fungi (AMF) are known to play an important role in plant nutrient uptake, yet their role in plant N uptake from organic residues in tropical agroforestry systems is not clear. We studied root and leaf litter of the legume shade tree Inga edulis Mart. as a source of N for cacao and the importance of AMF colonisation in the uptake of litter N under controlled conditions. Leaf and root litter of I. edulis enriched with 15N was added to cacao pots filled with field soil. Half of the cacao saplings were AMF-inoculated and the soil of non-inoculated saplings was treated with fungicide to suppress AMF. During the 10-week experiment, young cacao leaves were sampled for 15N analyses and at the end of the experiment whole plants were harvested. Microbial populations in the soil were determined using phospholipid fatty acid (PLFA) analysis, and AMF structures in the roots were quantified. Fungicide treatment decreased AMF structures in roots and increased bacterial populations, but did not affect the decomposition rate of either litter type. Inoculated and non-inoculated cacao saplings used 2.6 and 2.1%, respectively, of N added to the pots in leaf litter and 12.1 and 7.1% of N available in root litter indicating that root litter of I. edulis may be a more efficient N source than leaf litter for cacao. Although the fungicide treatment did not completely suppress AMF in non-inoculated pots, it created sufficient contrast in root AMF colonisation for concluding that AMF significantly enhanced cacao N use from both litter types. The role of root litter of shade trees as a N source in agroforestry should not be neglected.


Theobroma cacao Inga edulis Agroforestry Litter quality Mycorrhizal inoculation 15N-labelling 



We thank Ms Riina Jalonen for assistance in designing and setting up the experiment, Mr Ricardo Palacios for logistics with the greenhouse work, Dr. Hannu Fritze for help with the PLFA analyses, and Ms Pirjo Kähkölä for language corrections. The study was funded by the Academy of Finland (grant 129166).


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Copyright information

© Springer Science+Business Media B.V. 2011

Authors and Affiliations

  • Anna-Kaisa Kähkölä
    • 1
  • Pekka Nygren
    • 1
    • 4
    Email author
  • Humberto A. Leblanc
    • 2
  • Taina Pennanen
    • 3
  • Janna Pietikäinen
    • 1
  1. 1.Department of Forest SciencesUniversity of HelsinkiFinland
  2. 2.EARTH UniversitySan JoséCosta Rica
  3. 3.Vantaa Research CentreFinnish Forest Research InstituteVantaaFinland
  4. 4.Finnish Society of Forest ScienceVantaaFinland

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