| The effect of warming and N addition on sexual reproduction of Stipa breviflora was researched in the desert steppe. The mimic 4-year temperature increased and N addition experiment showed that:(1) Warming increased the temperature and humidity in each soil layer significantly.(2) Warming and N addition significant delayed reproduce phenophase of Stipa breviflora. N addition delayed flowering stage, whereas the interaction of warming and N addition delayed productive. Warming and the interaction of warming and N addition extended reproductive growth respectively.(3) Warming significant reduced seed setting rate, the weight of 100-seed weight significant decreased and germination was also reduced, whereas significant higher were observed in N addition treatment, and germination was also significant increased by interaction of warming and N addition.(4) During reproductive growth, warming significant increased energy value in vegetative stage, but C content was significant lower in warming than interaction of warming and N addition. The interaction of warming and N addition significant raised energy value. The energy value of fertile tillers was higher in warming than in N addition and interaction of warming and N addition during productive stage, but the energy value of fertile tillers was lower in interaction of warming and N addition during productive stage than CK, and compared with warming and CK, C content was higher in interaction of warming and N addition.(5) The reproductive growth Pn of Stipa breviflora showed a bimodal pattern under diurnal variation, and the two peak have significant different in different treatment. Compared with CK, N addition significant increased Pn. In all environmental factors, PAR is an important environment factor to photosynthesis.
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