Root longevity and phenology differences between two co‐occurring savanna bunchgrasses with different leaf habits

Publisher Website
Google Scholar
Abstract
Summary: Aristida strictaandSchizachyrium scopariumare C4perennial bunchgrass species native toPinus palustrissavannas in the south‐eastern USA. Species differences in growth rate, tissue nutrient content and distribution suggest thatA. strictais more stress‐tolerant (sensuGrime) thanS. scoparium. In addition,A. strictaretains leaves all year, whereasS. scopariumis winter deciduous. Based on these observations, we wanted to determine (1) whether root longevity was higher forA. strictaas compared toS. scoparium; and (2) whether the leaf habits of these species had consequences for seasonal patterns of root production and death. Usingin siturhizotrons, we recorded root number and length of these species over the course of 2·5 years on flat, transparent 50 × 50 cm windows. Kaplan–Meier (product‐limit) analysis was used to produce survival functions and to estimate median lifespans for the right‐censored root longevity data. These survival functions were compared using log‐rank χ2statistics, and a proportional hazards model was used to examine the effects of season and species on the survival of each cohort. Final demographic variables were analysed usinganova. The median lifespan ofA. strictawas 777 days whereas that ofS. scopariumwas 374 days. This significant difference in median lifespan was consistent between species for all cohorts in both years. Also, coincident with winter leaf senescence, root production nearly stopped forS. scopariumwhereasA. strictaproduced roots all year. This is probably due to the winter photosynthetic capacity ofA. stricta. Root death did not exhibit any seasonal pattern in either species. A pulse of roots produced in apparent response to the 2000 drought was evident forS. scopariumbut not forA. stricta. This cohort, however, rapidly died during the dormant season, probably due to the lack of winter photosynthesis in that species. Aristida strictaandS. scopariumexhibited root production, death and longevity patterns that were predicted on the basis of ecological and leaf habit differences between them. These findings suggest species‐specific differences in performance and element cycling in these nutrient‐poor soils.