Effect of Nitrogen and Periphyton Extract on the Growth of Nostoc sphaericum in Cultures

Nostoc sphaericum shows marked growth differences in two Mexican wetland ecosystems consisting of rain forest and tropical deciduous forest, respectively. The amount of nitrogen and periphyton extract dominated by other Cyanoprokaryota had been identified as the most obvious differences between these two ecosystems. We studied the impact of these variables on the physiology and morphology of N. sphaericum. that is, the chlorophyll-a content of the thalli and the changes in the size of the trichomes as well as the cell division rate. Our results combined with a statistical verification indicate that the cell division rate of N. sphaericum with solid media is neither stimulated by nitrogen nor by accompanying cyanoprokaryotes and therefore is assumed to have no impact on the thalli observed in situ. However, these two variables are affecting the size of both the trichomes and the thalli, thus suggested to cause the observed growth differences between the two wetlands. 1. Introduction Previous studies in the El Edén Ecological Reserve (EER) revealed that the periphyton is able to store large quantities of nutrients [1]. These findings suggested that the periphyton could be a potential fertilizer for widespread use like other organic fertilizers as, for example, chicken litter manure or compost [2]. Greenhouse experiments showed an outstanding concentration of nutrients in periphyton [3], and most of the periphyton doses that were applied to tomato and maize plants were as efficient as—or sometimes even superior to—modern organic fertilizers such as ammonium sulphate. It was also shown that periphyton acts as a natural source of micronutrients in the ecosystem that improves the indigenous arbuscular mycorrhizal symbiosis [2–4]. As illustrated in Figure 1(b), the intense periphyton production in these wetlands covers the entire substrate. However, the growth is the result of a long-time process as these wetlands are pristine and ancient ecosystems [5]. According to several observations [6], the periphyton recovery rate remains low once it has been removed. This underlines the necessity to study the growth characteristics of this life form before considering the idea of exploiting it as a fertilizer. Figure 1: The El Edén ecological reserve (EER) located in the state of Quintana Roo, northeast of the Yucatan peninsula, Mexico. The stars in the EER scheme indicate collection sites in the rainforest (a) and in the tropical deciduous forest (c). (b) Shows the periphyton biofilms over the entire substrate of the wetland rainforest. The periphyton biofilm attached