Productivity, nutrient imbalance and fragility in coupled producer–decomposer systems

Ecosystem development is mediated by coupled synthesis–decomposition cycles that capture, store and release energy necessary for maintenance and growth. I present a minimal ecosystem model with explicit energy and matter conservation. Energy is captured and stored via synthesis and release through decomposition. This energy is used for biomass production and maintenance. I examine materially closed systems where growth is limited by nutrient availability. I present two key findings. First, maximum biomass production does not occur under conditions of equal nutrient concentrations. Instead, production is maximized when the initial environmental concentration of the energy carrying substrate is increased. Second, the system is characterized by an abrupt collapse when the concentration of the energy carrying substrate is increased above a threshold. This model indicates that in the region of maximum biomass production, ecosystems are fragile rather than resilient.