Photosynthesis limitations in cacao leaves under different agroforestry systems in the Colombian Amazon

PLoS One. 2018 Nov 1;13(11):e0206149. doi: 10.1371/journal.pone.0206149. eCollection 2018.

Abstract

Cacao (Theobroma cacao L.) has traditionally been considered a crop that requires shade, and consequently it is implemented under agroforestry systems (AFs) in order to regulate the level of incident solar radiation. However, optimal shade levels for this tree crop may vary depending on the climate conditions of where it is grown. Here we analyzed the physiological performance of cacao under three different AFs in the Colombian Amazon that differed in solar radiation patterns: high (HPAR), medium (MPAR), or low (LPAR) mean daily incident radiation. The physiological performance was characterized using photosynthetic variables in leaves such as light- and CO2-response curves, chlorophyll a fluorescence parameters, and total chlorophyll and carotenoid contents, in conjunction with other leaf functional traits. Cacao trees exposed to HPAR showed an improved physiological performance as compared to those from the other two AFs. Compared to MPAR and LPAR, cacao trees in HPAR doubled the rate of net carbon assimilation and reached higher maximum rates of RuBisCO carboxylation and RuBP regeneration. Moreover, cacao trees in HPAR presented photoprotection mechanisms that avoided photoinhibition, which was accompanied by a greater non-photochemical quenching coefficient and biochemical and morphological adjustments (low chlorophyll but higher carotenoid contents and low specific leaf area) compared to cacao trees from the other AFs. Overall, our results show that, due to the high cloud cover in the Colombian Amazon, cacao plantations under conditions of sparse shade maximized their carbon use, showing an improved physiological performance as a result of higher photosynthetic rates and energy dissipation mechanisms. If the crop were managed with sparse shade, the paradigm that favors the cultivation of cacao under shade would be called into question in the Colombian Amazon and other regions with similar climatic conditions.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cacao / growth & development*
  • Carbon Dioxide / chemistry
  • Chlorophyll A / chemistry
  • Colombia
  • Conservation of Natural Resources*
  • Forestry
  • Photosynthesis / physiology*
  • Plant Leaves / growth & development*
  • Sunlight

Substances

  • Carbon Dioxide
  • Chlorophyll A

Grants and funding

This study was conducted with the financial collaboration of COLCIENCIAS (http://www.colciencias.gov.co/) using BID funds (Inter-American Development Bank) under the framework of the project "Characterization and typification of traditional plantations of Theobroma cacao L. as a strategy for the design and implementation of agroforestry systems in the Bajo Caguan (Cartagena del Chaira)," implemented by Universidad de la Amazonía (Colombia) under the special contract 590 of 2010 to JCSS, as well as using Doctoral Training funds from Amazon University under the stamp "Pro-development of Amazon University" Law No. 1301 of 2009. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.