Previous research had shown that compared to species with conservative strategies, species with acquisitive strategies have higher N uptake when there is ample N in the soil, but also trigger N mineralization when soil N is limiting. Therefore, we hypothesized that compared to conservative species, species with acquisitive traits would reduce N2O emissions after a high N addition; and that species with conservative traits would have lower N2O emissions than acquisitive plants if there is no high N addition. This was tested in a greenhouse experiment using monocultures of six grass species with differing above- and below-ground traits, growing across a gradient of soil N availability. We found that acquisitive species reduced N2O emissions at all levels of N availability, produced higher biomass and showed larger N uptake. As such, acquisitive species had almost 90% lower N2O emissions per unit of N uptake than conservative species. Further analyses revealed that specific leaf area and root length density were key traits regulating the effects of plants on N2O emission and biomass productivity.
In a subsequent 2-year field experiment we translated our findings into realistic conditions, covering interactions between plants and including legume species due to their importance to improve fodder quality and their particular role in N cycling. The results of this experiment are been analysed and will be made public soon. One of the most pertinent questions this experiment will answer is how the role of plants in N-cycling is mediated by changes in soil microbial communities, and whether such changes can be linked to plant functional traits. We will also show if plant community effects on several soil biotic factors represent indirect and little studied mechanisms through which plants may modify soil N cycling in intensive grasslands.
In a greenhouse study using intact monoliths from the field experiment, we are currently evaluating the effect of a climate change-induced disturbance (flooding) on the N2O emissions and productivity of intensively managed grasslands across a plant diversity gradient. We are testing the hypothesis that the negative effects of flooding could be mitigated with increasing plant diversity due to a greater functional diversity in traits related to nutrient acquisition (lowering N2O emissions), and a greater resilience of the plant community to flooding (maximizing productivity under unfavourable conditions).
A review study is been conducted, in which we argue that combining plants based on their functional traits may provide an overlooked opportunity to improve the amount of N retained by plants in intensive agroecosystems. Then we illustrate associated benefits of this approach for yield stability, resilience, and agroecosystem multifunctionality. Finally, we will propose optimum plant combinations for enhanced N-cycling following a trait-based approach.
