Across the globe, grasslands face ongoing degradation, and reestablishing biodiversity is a key conservation priority. Highly diverse grassland plant communities are more productive and nutrient-efficient compared to grasslands with less diversity. To facilitate successful restoration, we must discover how to mimic ecological relationships found in native ecosystems. Numerous experiments suggest niche complementarity and positive interspecific interactions drive beneficial diversity effects. However, in intensively managed grasslands, we do not fully understand the influence of different plant functional groups, especially across a range of soil fertility. This constrains our ability to design and manage sustainable, highly diverse systems. We conducted a 4-year field experiment in reestablished grasslands, using a split-plot design at the Forage and Grass Research System in Yinchuan, China. We altered seeding proportions of two N2-fixing legumes (Medicago sativa and Onobrychis viciaefolia) and two grasses (Dactylis glomerate and Festuca arundinacea) to investigate effects of legume and grass ratios (L:G ratios, 5:5, 4:6, 3:7, 6:4, 7:3) on productivity under a gradient of phosphorus fertilization (0, 40, 80 or 120 kg ha-1 year-1) applied the first two years of establishment. Our investigation examines potential strategies to achieve sustainable grassland productivity and restoration.
Results/Conclusions
Total plant community production of all mixtures exceeded the average of any monoculture control (enhancing yield up to 69.48%), likely driven by legume and grass complementarities. Across multiple years, grasslands fertilized with 80 kg ha−1 P during establishment were more productive, presumably due to improved P availability in a P-limited system. During all four years, a 3:7 mixture of legumes:grasses consistently showed greater productivity, compared to the most productive monoculture. However, benefits in productivity due to increased species diversity were weakened by excessive P fertilization of 120 kg ha-1. When grown together, M. sativa and D. glomerate typically outcompeted O. viciifolia and F. arundinacea. Productivity was significantly increased by diversity, regardless of legume:grass ratio (r = 0.816, p <0.001). Both trait-independent complementarity effects (r = 0.708, p <0.001) and dominance effects (r = 0.369, p <0.001) positively contributed to increased productivity in species mixtures, while trait-dependent complementarity effects were minor but also significant (r = 0.802, p <0.001). Plant community diversity and moderate P fertilization contributed to greater production in an intensively managed grassland. Our results demonstrate diversity and effective nutrient management are critical for both grassland reestablishment, productivity, and sustainable utilization.