Abstract: Seasonality of available soil nutrient has an important effect on plant life history,plant growth and interspecies relations.It can be confirmed that the seasonal variation of soil nitrogen affects the process of flowering phenology,plant growth and biomass allocation of Malcolmia scorpioides and its interspecies relations with Descuminia sophia.In this study,the seasonal variation of available soil nitrogen was tested and simulated under three nitrogen treatments,i.e.the uniform,spring and summer nitrogen application modes,and the values of flowering phenology,plant height,biomass allocation and leaf nutrient content of M.scorpioides under three nitrogen treatments were measured.The growth situations of M.scorpioides plants potted alone and planted in a mixed way with D.sophia were compared,and the effects of different nitrogen application modes on the interspecies relations were analyzed.The main results are as follows:① The process of flowering phenology of M.scorpioides was significantly affected by the nitrogen application modes,and the curves of flowering amplitude of M.scorpioides plants potted alone were unimodal under uniform and spring nitrogen application modes but bimodal under summer nitrogen application mode.Cultivation ways affected significantly the process of flowering phenology of M.scorpioides.The flowering peak of M.scorpioides plants planted in a mixed way was 4-5 days earlier under the uniform nitrogen allocation mode,and the flowering proportion at flowering peak was 16% higher that of plants potted alone; ② There was no a significant interaction effect of nitrogen treatments and cultivation ways on the growth of M.scorpioides.The height of M.scorpioides plants potted alone was higher under spring nitrogen application mode than that under the uniform and autumn nitrogen application modes.Under the mixed environment,there was no significant effect of different nitrogen treatments on the plant height,aboveground biomass,underground biomass,total biomass of individual plants and root-shoot ratio of M.scorpioides; ③ There was no significant effect of nitrogen application mods and cultivation ways on the TN,TP and TN∶TP ratio in leaves of M.scorpioides.The competitiveness of M.scorpioides was higher than that of D.sophia when these two plant species were planted in a mixed way.The study results revealed that the seasonality of available soil nitrogen affected the phenological process,growth and community composition of desert herbs.

Key words: annual plant, Malcolmia scorpioides, Descuminia sophia, seasonal variation, flowering phenology, nitrogen