The social-ecological ladder of restoration ambition.

Expanding in both scope and scale, ecosystem restoration needs to embrace complex social-ecological dynamics. To help scientists and practitioners navigate ever new demands on restoration, we propose the "social-ecological ladder of restoration ambition" as a conceptual model to approach dynamically shifting social and ecological restoration goals. The model focuses on three dynamic aspects of restoration, namely degrading processes, restoration goals and remedial actions. As these three change through time, new reinforcing and balancing feedback mechanisms characterize the restoration process. We illustrate our model through case studies in which restoration has become increasingly ambitious through time, namely forest landscape restoration in Rwanda and grassland restoration in Germany. The ladder of restoration ambition offers a new way of applying social-ecological systems thinking to ecosystem restoration. Additionally, it raises awareness of social-ecological trade-offs, power imbalances and conflicting goals in restoration projects, thereby laying an important foundation for finding more practicable and fairer solutions.

Two-way NxP fertilisation experiment on barley (Hordeum vulgare) reveals shift from additive to synergistic N-P interactions at critical phosphorus fertilisation level.

In a pot experiment, we investigated synergistic interaction of N and P fertilisation on barley biomass (Hordeum vulgare) on both shoot and root level with the aim to determine whether N-P interaction would be the same for all levels of N and P fertilisation. We further aimed to determine whether there was a critical level of N and/or P fertilisation rate, above which, a decrease in resource allocation to roots (as nutrient availability increased) could be demonstrated. Barley plants were grown from seed on a nutrient poor substrate and subjected to a two-way NxP fertilisation gradient using a modified Hoagland fertilisation solution. We observed N-P interactions in shoot and root biomass, and N and P use-efficiencies. A synergistic response in biomass was observed only above a critical level of P fertilisation when P was not limiting growth. Furthermore, we found that the same incremental increase in N:P ratio of applied fertiliser elicited different responses in shoot and root biomass depending on P treatment and concluded that barley plants were less able to cope with increasing stoichiometric imbalance when P was deficient. We provide, for the first time, stoichiometric evidence that critical levels for synergistic interactions between N-P may exist in crop plants.