CARBON STARVATION - A KEY TO REED DECLINE IN EUTROPHIC LAKES

This review paper deals with the carbon balance in reed plants, its response to environmental factors and implications for reed vitality. It is suggested that excessive nitrogen supply, anaerobiosis in the root surroundings, disturbance and high water levels all affect reed vitality through changes in the carbon budget. Excessive nitrogen supply, which reduces the accumulation of carbohydrate reserves and carbon allocation to structural tissues, acts as the main predisposing factor for reed decline. Anaerobiosis in the root medium acts as an additional predisposing factor, by making the use of carbohydrates less efficient. The predisposing factors do not harm plants directly, but increase their susceptibility to episodic stresses, such as disturbance and shoot flooding. These stresses, which create a large additional demand for carbohydrates, act as the inciting factor. They will not harm a stand with a balanced carbon budget, but will threaten with collapse stands that are starved for carbon. The hypothesis is considered taking the available evidence into account, gaps in knowledge and shortcomings in experimental design are identified and implications for reed management are indicated.