Lignotuber carbohydrate storage differs between different life history types in chaparral shrubs (Rosaceae)

Background/Question/Methods

The purpose of this project was to evaluate nonstructural carbohydrates (NC), including glucose, sucrose, and starch, within plant tissue of chaparral shrubs that differ in their life history type.  We analyzed the NC in lignotubers after fire of two confamilial chaparral species, Adenostoma fasciculatum and Heteromeles arbutifolia (Rosaceae) that differ in life history type.  A. fasciculatum is a facultative sprouter (FS) after fire meaning that it resprouts and recruits seedlings from fire-cured dormant seeds.  H. arbutifolia is an obligate sprouter (OS) that recruits no post-fire seedlings and instead relies exclusively on resprouting to reestablish.  An enzyme based protocol was developed to measure NC.  Measurements were taken for one year following initial resprouting in August 2007 at a post-fire site in the Santa Monica Mountains in southern California that burned in July 2006.  Burned and unburned mature plants were compared, and measurements were made seasonally.  We hypothesized that life history type would differ in NC such that OS species, reliant on post-fire resprouting, would have greater NC content than FS species.  Moreover, we expected that burned shrubs would have lower NC and that NC would be lower in the growing season than during the summer rainless season. 

Results/Conclusions

Results showed that burned plants had lower levels of NC (especially starch) than unburned plants. NC was higher in the OS, H. arbutifolia, than the FS, A. fasciculatum, in both burned and unburned plants (e.g. the mean ± 1SE seasonal high for starch was 16.68± 2.06 for the burned OS and 4.07± 1.30 for the burned FS, and 68.28 ± 8.02 for the unburned OS and 26.25 ± 3.81 for the unburned FS).   Seasonal changes in NC were greatest in H. arbutifolia and not different in A. fasciculatum.  Lignotubers appear to be important storage organs of NC that support resprouting in chaparral. Species differed in their storage capacity of NC, which may be linked to their ability to resprout post-fire. By contrast, seasonal growth was not supported by stored resources in A. fasciculatum, but it was in H. arbutifolia suggesting possible divergence in lignotuber function between confamilial FS and OS species.