Nutrient cycling plays a key role in most of the problems currently pursued by grassland ecologists.
Because many of these research areas, including the loss or restoration of soil organic matter and N inputs and losses from grasslands, are now global in scale, the traditional division between agronomic studies of managed forage systems and ecological studies of native grasslands hinders our progress. In particular, an understanding of the N cycle is critical to both approaches. Plant tissue chemistry and physiology play a role in regulating the N cycle quite unlike their role in other nutrient cycles. The positive feedback between the physiological response of plants to N limitation and the response of microbial decomposers to plant tissue chemistry reinforces the tendency towards N limitation found in most grasslands. The potential for N immobilization created by plant detritus and associated soil organic matter may be as important as the uptake potential of living plants in regulating soil NO 3 - concentrations and N leaching losses in many grasslands.