Coffee Genotypes and Improper Scientific Experimental Design

Posted by on Oct 8, 2015 in Blog, Science Times | No Comments

The article “Low Temperature Impact on Photosynthetic Parameters of Coffee Genotypes”, written by Fábio Luiz Partelli provides data regarding an experiment that tests the effect of temperature on the efficiency of photosynthetic processes. Partelli believed that the exposure of coffee genotypes to lower temperatures should slow down photosynthesis within the plant structures. Although the results justify a negative correlation between temperature and photosynthetic efficiency there aren’t many reasons to believe that the information gained from this experiment will make great contributions to this field of science.

Partelli’s goal was to analyze the response of coffee genotypes to lower temperatures with the hope to understand how these plants would acclimate to changing temperature. This is evident through Partelli’s emphasis on the “recovery period” of the plant throughout the experiment. From his results, he concluded that gas exchange, along with other internal processes, had a better performance as the recovery period went on. This led him to believe that gradual exposure to lower temperatures will facilitate acclimation and therefore keep photosynthetic processes as efficient as possible.

Several aspects of Partelli’s experimental design were questionable and, therefore, could lead to skepticism regarding the validity of the results. To start off, Partelli does a good job at explaining the reasons for which photosynthetic efficiency decreased. In particular, when he discussed the maximum quantum efficiency (the ratio between a plant’s stress and the amount of reaction centers that are available), he states that photosynthetic efficiency may have decreased because of an accumulation of zeaxanthin, a chemical that controls the overproduction of chlorophyll. As the zeathanin increases, the rate of photosynthesis decreased as well. Partelli also provided an clear, accurate, alternative explanation that demonstrated the thoroughness of his research. Despite his efforts, the overall experimental design raised many questions regarding its validity. In particular, the methods called for a rather small sample size when analyzing the photosynthetic rates of Coffea Canephora and Coffea arabica genotypes prior to lower temperature exposure. How is it that he expects to generalize the idea that gradual temperature decrease will allow a majority of coffee genotypes to maintain internal processes stabilized, if he is unable to provided the appropriate data for it? While I do believe the impact of this matter will have a large impact to the scientific field, I feel its impact would greater if the experiment analyzed the changes to photosynthetic rates in higher temperatures. This adjustment to the experiment would be more beneficial because the global increase of temperature due to climate change is more relevant nowadays.

Partelli’s experiment led him to conclude that there was a negative correlation between temperature and photosynthetic efficiency. While I do believe that Partelli drew accurate conclusions from the data he collected, I do not believe the conclusions can be applied in a larger sense because of the unreliability of the data. This was, however, a step in the right direction since we will need to understand the adaptations that coffee plants will need to make, especially as climate change carries on.


  1. Partelli, Fábio Luiz. 2009. Low temperature impact on photosynthetic parameters of coffee genotypes. Pesq. agropec. bras. [online]. 2009, vol.44, n.11, pp. 1404-1415.

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