Different regrowth patterns after repeated clipping in two Mongolian pasture species.

We investigated changes in the regrowth patterns of two grass species on the Mongolian steppe, Agropyron cristatum and Stipa krylovii, in response to repeated clipping and used a growth analysis to identify the factors responsible for differences in their regrowth patterns. Plants grown in pots were clipped every 3 weeks, and leaf area, dry mass, and N and crude fiber contents were measured. Aboveground biomass recovered to the same level as that before clipping in both species even after 3 clipping–regrowth cycles, but their regrowth patterns differed. In A. cristatum, a decrease in biomass allocation to aboveground parts with repeated clipping was fully compensated by the positive effect derived from the increase in growth rate due to increased leaf area expansion associated with an increase in specific leaf area (SLA). In S. krylovii, a decrease in SLA reduced leaf area but at the same time increased N content per unit leaf area and consequently photosynthetic ability, leaving the growth rate unchanged. The values of growth parameters involved in regrowth after clipping changed with repeated clipping and those changes differed between species. In particular, the difference in the response of SLA to repeated clipping contributed greatly to the difference in regrowth patterns. As SLA reflects leaf toughness and grazing tolerance as well as leaf thickness and density, our results imply that the leaf morphological change at regrowth as plant strategies against grazing contribute to plants' regrowth patterns. [ABSTRACT FROM AUTHOR]