Sciente, Vol. 1, No. 1, [Article Under Review] (March 13, 2009) Research Report
sciente.upra.edu University of Puerto Rico at Arecibo 7
PLANETARY HABITABILITY: GROWTH TEMPERATURES AND THE GLOBAL DISTRIBUTION OF PRIMARY PRODUCERS Norberto González,1* Abel Méndez2 1Department of Biology, University of Puerto Rico at Arecibo 2Department of Physics and Chemistry, University of Puerto Rico at Arecibo P.O. Box 4010, Arecibo, PR, 00614 Abstract (English) — Vascular plants on land and phytoplankton on the ocean are the most important primary producers on Earth. They play the major role in the production of biomass at the base of the trophic levels. The global distribution of primary producers is controlled by a complex interaction of environmental variables where temperature is one of the most important factors defining their productivity and distribution. Although there are many laboratory studies about the effects of temperature in selected primary producers, little is known about the relation between their growth temperature and global distribution. Here we collected and analyzed data from the scientific literature for growth temperature of many cyanobacteria and algae. Our results shows that photoautotrophic metabolisms, among very diverse primary producers, have similar temperature requirements. We suggest that this is an intrinsic property of phototrophic organisms, which strongly controls their global distribution. The data is being used to model the habitability of land and ocean areas. Our future plans are to compare the relations of other environmental variables in primary production. The main goal of this type of work is to provide input data for planetary habitability models. Abstract (Spanish) — Las plantas vasculares en la tierra y el fitoplancton en los océanos son los productores primarios más importantes en el Planeta. Estos desempeñan el papel principal en la producción de materia orgánica en la base de la cadena alimenticia. La distribución mundial de los productores primarios está controlada por una compleja interacción de variables ambientales donde la temperatura es uno de los factores más importantes que definen su productividad y su distribución. Aunque hay muchos estudios en el laboratorio sobre los efectos de la temperatura en determinados productores primarios, poco se sabe sobre la relación entre la temperatura de crecimiento y su distribución global. En este trabajo se extrajeron y analizaron datos de la literatura científica sobre las temperaturas de crecimiento de cianobacterias y de algas. Nuestros resultados muestran que el metabolismo fotoautotrófico, entre una diversidad de productores primarios, presentan requisitos de temperatura similares. Sugerimos que esto se debe a una propiedad intrínseca de los organismos fotoautotróficos, la cual controla su distribución global. Los datos están siendo utilizados para modelar la habitabilidad de la tierra y las zonas oceánicas. Nuestros planes para el futuro son comparar otras variables ambientales en la producción primaria. El objetivo principal de este tipo de trabajo es proporcionar datos para modelos de habitabilidad planetaria. * Contact author E-mail: [norberto.gonzalez@upr.edu] Primary production is the production of organic compounds from atmospheric or aquatic carbon dioxide using the photosynthesis process. All life forms on planet earth depend directly or indirectly on primary production (Nicklish, 2008). The organisms responsible for primary production are known as primary producers. These producers can be divided in several groups based on their growth environments. Land producers can be defined as vascular plants and ocean producers as phytoplankton (Marra et al., 2002). The plankton can also be divided as algae and cyanobacteria (prokaryotes). Gross primary production (GPP) is the rate at which an ecosystem's producers capture and store an amount of chemical energy as biomass in a given length of time. Some fraction of this fixed energy is used by primary producers for cell respiration and maintenance of existing tissues. The remaining fixed energy is referred to as net primary production (NPP). Net primary production is the rate at which all the plants in an ecosystem produce net useful chemical energy; it is equal to the difference between the rate at which the plants in an ecosystem produce useful chemical energy (GPP) and the rate at which they use some of that energy through cellular respiration. The NPP is difficult to measure at global scales because it usually requires in situ observations. However, many computer models can estimate terrestrial NPP from climatology data from surface or satellites measurements (Cramer, 1999). The Primary Habitability (PH) of an environment can be defined as the ratio of the net primary production (NPP) and the maximum net primary production (NPPmax). PH can be modeled from the temperature and relative humidity (or water activity) of an environment (Méndez, 2009). A fit of the PH from land NPP and from global surface temperature and relative humidity shows that plants requires temperatures between -3°C to 53°C for physiological activity, with an optimum at 21°C.
The objective of this work is to collect and analyze data from the scientific literature for growth temperature of many phytoplankton and vascular plants. Our inquiry was to determinate if other primary producers such as phytoplankton can be compared with land primary producers in terms of growth/activity temperatures. This information is essential to understand and create habitability models about the global distribution of primary producers. We searched the scientific literature for data on the optimal growth temperature (Topt) and the specific growth rate (µmax) of cyanobacteria or blue-green algae. These organisms are prokaryotes that can carry out the process of photosynthesis (Konopka and Brock, 1978). We wanted to search for relations in these photosynthetic organisms and to compare them with other primary producers. We used gnuplot (a graph making computational program) to analyze and create distribution plots of the collected data. In the Topt and the µmax for 42 cyanobacteria we found that their optimum growth temperatures was between 20°C and 30°C. Their mean µmax was 1.01 d-1 and the Topt was 24 °C (Figure 1 and 2). This is very similar to the optimum growth temperature for terrestrial vascular plants obtained from PH models. The second phase of our research was to find data detailing the optimum growth temperature in algae. We collected data for 44 species of algae from the scientific literature. A distribution of the algae Topt shows an optimum between 15°C and 30°C (Figure 3). The mean Topt for the algae species was 18°C. Once again, very similar to the values for vascular plants and cyanobacteria. Optimun growth temperatures for many other simple and complex species are usually much higher (~37°C).