5 CONCLUSIONS
Seed production of the dominant species in the temperate steppe was enhanced by N addition, but a high level of N addition stimulated seed production more than a low N addition. Whereas seed production was unchanged by P addition alone, it was increased when the latter was in the presence of N addition. Seed production was enhanced mainly through an increasing of tiller and inflorescence numbers under N addition, and by decreased plant density stimulating plant height growth and enabling seed number per inflorescence under P addition. Our results indicate that N availability is the main factor limiting seed production, but seed production can become limited by P availability as N enrichment increases in the temperate steppe. These timely findings can facilitate better understanding of grassland seed banks and plant community structure responses to simultaneous multiple nutrient enrichment under future nutrient enrichment scenarios.