The workshop examined the potential application of molecular 

 biological approaches to help systems ecologists quantify and 

 identify limiting factors, energetic constraints, and community 

 structure and stability. Here, we briefly discuss some of the 

 issues faced in understanding how these themes affect the dynamics 

 of global biogeochemical cycles, especially those affected by 

 energy-related activities. 



Limiting Factors 



In nature, population density and the growth rate of organisms 

 may be significantly less than the maximum rate under optimal 

 conditions. Environmental constraints, or limitations, directly 

 affect biogeochemical cycles. For example, photosynthetic 

 organisms, which reduce inorganic carbon to organic materials, may 

 be limited by the availability of nitrogen, phosphorous, carbon, or 

 iron, and by the presence of natural or anthropogenic toxins, or by 

 physical factors, such as light, temperature, and salinity. 

 Heterotrophic organisms, which oxidize organic carbon compounds and 

 contribute to the production of COp, may be limited by the 

 availability of organic carbon, nitrogen, or temperature, or by 

 physical factors. Fundamental understanding of ecosystems requires 

 the identification of the factors limiting key biogeochemical 

 processes. Ecologists have traditionally identified limiting 

 factors by experimentally manipulating the organisms or small 

 portions of ecosystems, or by correlative inference. Often these 

 approaches are extremely tedious, expensive, ambiguous, and 

 contentious, and provide little predictive capability; at present, 

 there are few alternative in situ techniques. Thus, there would be 

 a major breakthrough in understanding ecosystem dynamics and 

 biogeochemical cycles if we could identify and understand the rate- 

 limiting factors for key biogeochemical processes in specific 

 ecosystems. 



The research would entail the following two elements: 



(a) identification of specific diagnostic genes or gene 

 products indicative of a limiting factor; and 



(b) identification of the mechanisms or regulatory motifs by 

 which organisms perceive the environment and transduce that signal 

 to modify the expression of specific genes or gene products. 



