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Plant microbial fuel cell (PMFC) is an intriguing and sustainable technology which can spontaneously generate electricity from biodegradable materials excreted through plant roots in rhizosphere by electroactive microbes. In this study, experiments were conducted to determine the effects of soil water contents, temperature fluctuations, and circadian rhythm on current and power densities of PMFCs using Purple guinea grass. Three PMFC systems were investigated including dry-soil, wet-soil, and waterlog PMFC under greenhouse temperature of 27 - 47 degrees C. Plants cultivation in waterlog were found to deliver a better performance as compared to the others with power density of 10.13 mW/m(2) of anode area. Wet soil and arid soil provided power densities of 6.7 and 2.3 mW/m(2), respectively. Soil water contents and temperature were found to have a substantial role in controlling the system performance. In account for temperature variations during the period of study, average power densities of 4.4, 5.9, and 6.0 mW/m(2) were obtained at a high temperature range between 41 degrees C to 47 degrees C for dry-, wet- and waterlog-soil, respectively. Within the intermediate temperature range of 34 degrees C to 41 degrees C, the obtained power densities were 1.0, 1.7, and 1.9 mW/m(2) while 0.3, 0.4, and 0.6 mW/m(2) were attained for a low temperature range of 27 degrees C - 34 degrees C for dry-, wet-and waterlog soil, respectively. The lower performance during low temperature were attributed to the electroactive bacteria activities in anode and the carbohydrate metabolism of plants. The power and current outputs during photo-period were much higher than at night. These outcomes authenticated that PMFCs are significantly affected by soil water contents, ambient temperatures, and photosynthesis.