Irrigation and Nitrogen Application Promote Population Density through Altered Bud Bank Size and Components in Leymus chinensis

Abstract

The bud bank of perennial grasses is a controlling factor in population dynamics and is estrongly affected by soil water and nitrogen status. To explore how the bud bank size and its components affect shoot population density under different soil moisture and nitrogen contents in spring and autumn. A three-full-factorial field experiment with factors of treatment timing (spring and autumn), nitrogen rate (control and 10 g N m−2 yr−1) and irrigation rate (control and +40 mm rainfall) was conducted in Leymus chinensis (a C3 plant) in the northeast of China. The number of two types of buds (axillary shoot bud and rhizome bud), shoot population density, soil properties and rhizome traits (rhizome length and rhizome number) were determined to explore what and how changes in bud bank composition influences shoot population density in spring and autumn. The results showed that: (1) Regardless of the irrigation and nitrogen application timing, the simultaneous irrigation and nitrogen application significantly increased the number of two types of buds and promoted the shoot population density in spring and autumn by 56.75% and 47.74%, respectively. (2) The bud bank was dominated by rhizome buds in spring under control and dominated by axillary shoot buds under the combined irrigation and nitrogen treatment in autumn. Axillary shoot bud was the determining component in the population density increases in both spring and autumn, which were significantly associated with soil available phosphorus, available nitrogen and rhizome length and number. In summary, the number of different buds was strongly impacted by irrigation and nitrogen application at the crucial bud-bank formation stage. Agronomically, the forage yield could be largely increased through the increase in the axillary shoot bud density by using irrigation and nitrogen application in L. chinensis and other rhizomatous perennial grasses.