Plant trait networks reveal adaptation strategies of a temperate steppe to alternations of nitrogen input

Plant trait network (PTN) has been used to elucidate plant adaptations to environmental changes. Enhanced anthropogenic nitrogen (N) deposition has had marked impacts on grassland ecosystems. A decline in atmospheric N deposition occurs in many regions across the globe in recent decades. However, no studies have evaluated whether and how PTN are involved in resource–use strategies of grassland community in response to disturbance of N input. We investigated the responses of architecture and hub traits within PTN of a grassland community to cessation of N addition for 5 years after consecutive N addition for 15 years in a temperate grassland of Inner Mongolia. We found that three functional modules (nutrient utilization, water maintenance, and light acquisition) operated independently under N addition. However, a 3-fold reduction in PTN modularity was found in response to cessation of N input by enhancing the integration of water maintenance and light acquisition module. Moreover, traits associated with water maintenance were strongly coupled with the nutrient–utilization traits. Cessation of N addition shifted PTN hub traits from phosphorus–(P) to N–related traits by alleviating P limitation. The traits of key drivers for ecosystem functions remained the most sensitive and robust responders to changes in soil nutrients. These traits may function as “meta–traits”, and drive coordinated responses of other traits to environmental variation. We applied PTN for the first time to examine multi-trait structure and functional integration, and highlight the necessity of integration of PTN with other analyses to understand how plants shift their strategies in adaptation to nutrient enrichment.