Catastrophic dieback of Cyperus papyrus in response to geochemical changes in an East Mediterranean altered wetland

Catastrophic vegetation dieback is a common phenomenon that has occurred in many wetland habitats worldwide. Different mechanisms have been proposed to explain these occurrences. We tested two published models proposed as potential mechanisms for the catastrophic dieback of Cyperus papyrus in the Hula Nature Reserve (HNR), Israel. Sulfide toxicity and P limitation models were tested using lysimeters. The sulfide toxicity was tested by redox-suppression simulation, while the P deficiency was evaluated using N/P ratio index. The sulfide toxicity model was not accepted as a viable mechanism because papyrus stands did not show any sign of stress, even when growing with sulfide concentration threefold that reported during the cattail dieback in a nearby wetland or values reported in the literature. The P limitation model was not supported by the N/P index that indicated N limitation rather than P limitation. Next, we tested two alternative mechanisms that link the dieback to N cycles and depletion in the HNR system or to a sequential stressor cascade that caused major N limitation. We concluded that the N deficiency hypothesis is a better explanation for the observed dieback and the current health status of C. papyrus in this East Mediterranean ecosystem.