Abstract: Plant phenology is a sensitive bioindicator of plant response to climate change. Under the context of climate warming accompanied by atmospheric nitrogen deposition, phenological shift is an important process in the adaptation of plant community to environmental changes. We conducted an experiment in a Stipa breviflora dominated desert steppe in Inner Mongolia to study the impacts of climate warming, nitrogen deposition and their interaction on plant phenology. Warming and nitrogen deposition were mimicked by using the infrared heaters and nitrogen addition respectively. We examined the plant reproductive phenology (flowering time, fruiting time and reproductive duration) of four perennial species (S. breviflora, Kochia prostrata, Convolvulus ammannii and Allium tenuissimum) during three consecutive growing seasons from 2008 to 2010. The reproductive phenology phases of each marked individual plant were estimated through fitting the phenological scores to the Richards function. We calculated the flowering time, fruiting time and the reproductive duration for each plant species in each year. The results showed that warming significantly advanced flowering and fruiting time by 2.28 and 1.88 d·a^-1， respectively across all the species and years. Nitrogen addition showed little effect on the flowering or fruiting time of any species. Combination of warming and nitrogen addition advanced flowering and fruiting time by 1.75 and 1.53 d·a^-1, respectively, but there was no interaction between the two treatments. Warming significantly elongated the average reproductive duration of S. breviflora and K. prostrata by 1.20 and 3.25 d·a^-1, respectively, while nitrogen addition significantly shortened the reproductive duration of A. tenuissimum by 1.52 d·a^-1. Our results provided the empirical evidence for the specie-specific response of plant phenology to climate warming and increasing nitrogen deposition. The findings in this study improved our understanding of the interspecific competition and succession dynamics of plant community in temperate desert steppe under global environmental changes.

Key words: completely autotrophic nitrogen removal over nitrite (CANON), COD/TN (C/N), denitrification, tidal flow constructed wetland (TFCW), anammox.