Effects of defoliation on growth and reproduction in the short-lived annual plant Bromus japonicas

Bromus japonicas is a high-quality forage grass that is typically short-lived and found in the Junggar desert in early spring. This study involved phenological observations based on natural populations. Experimental treatments involved plant clippings at two heights, 2.5 cm (short, S) and 7.6 cm (tall, T) at the jointing stage to study the effects of different defoliation intensities on the growth and reproduction of B. japonicas. The results showed: 1) Clipping had decreased the height, length of flag leaf, biomass and total biomass of the plants. Compared with the control, the plant height of T and S treatments decreased by 28.2% and 40.1%, and the biomass decreased by 29.9% and 60.6%, respectively. 2) Defoliation significantly reduced the fruit ear length, number of spikelets, number of fruits and weight of fruits. With the increase of clipping intensity, the length of spikelet, number of fruits and fruit weight decreased significantly. The length of fruit ear in T and S treatments compared to the control were reduced by 29.1% and 41.6%, and the number of fruits was reduced by 54.5% and 71.7%, respectively. 3) The compensation index of fruit weight, fruit number, biomass and total biomass after clipping was significantly less than 1, and the compensation growth pattern of B. japonicas was inadequate. The compensatory growth ability of S treatment was significantly lower than that of T treatment. The results provided scientific basis for revealing the compensatory growth pattern of short-lived plants and rational utilization of brome resources.