Interactive effects of elevated CO(2) and precipitation change on leaf nitrogen of dominant Stipa L. species

Nitrogen (N) serves as an important mineral element affecting plant productivity and nutritional quality. However, few studies have addressed the interactive effects of elevated CO(2) and precipitation change on leaf N of dominant grassland genera such as Stipa L. This has restricted our understanding of the responses of grassland to climate change. We simulated the interactive effects of elevated CO(2) concentration and varied precipitation on leaf N concentration (N(mass)) of four Stipa species (Stipa baicalensis, Stipa bungeana, Stipa grandis, and Stipa breviflora; the most dominant species in arid and semiarid grassland) using open-top chambers (OTCs). The relationship between the N(mass) of these four Stipa species and precipitation well fits a logarithmic function. The sensitivity of these four species to precipitation change was ranked as follows: S. bungeana > S. breviflora > S. baicalensis > S. grandis. The N(mass) of S. bungeana was the most sensitive to precipitation change, while S. grandis was the least sensitive among these Stipa species. Elevated CO(2) exacerbated the effect of precipitation on N(mass). N(mass) decreased under elevated CO(2) due to growth dilution and a direct negative effect on N assimilation. Elevated CO(2) reduced N(mass) only in a certain precipitation range for S. baicalensis (163–343 mm), S. bungeana (164–355 mm), S. grandis (148–286 mm), and S. breviflora (130–316 mm); severe drought or excessive rainfall would be expected to result in a reduced impact of elevated CO(2). Elevated CO(2) affected the N(mass) of S. grandis only in a narrow precipitation range. The effect of elevated CO(2) reached a maximum when the amount of precipitation was 253, 260, 217, and 222 mm for S. baicalensis, S. bungeana, S. grandis, and S. breviflora, respectively. The N(mass) of S. grandis was the least sensitive to elevated CO(2). The N(mass) of S. breviflora was more sensitive to elevated CO(2) under a drought condition compared with the other Stipa species.