Allelopathic Effects of Ceratiola Ericoides (Empetraceae) on Germination and Survival of Six Florida Scrub Species
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Plant Ecol (2008) 198:47–59 DOI 10.1007/s11258-007-9384-8 Allelopathic effects of Ceratiola ericoides (Empetraceae) on germination and survival of six Florida scrub species Rebecca E. Hewitt Æ Eric S. Menges Received: 14 August 2007 / Accepted: 7 November 2007 / Published online: 23 November 2007 Ó Springer Science+Business Media B.V. 2007 Abstract Allelopathic inhibition of germination by Keywords Gap specialist Á Leachates Á Florida scrub plants has been demonstrated in the Fire Á Seedling survival Á Rosemary scrub Á greenhouse and lab, but not in the field. We studied the Allelopathy allelopathic effects of Florida rosemary (Ceratiola ericoides) roots, leaves, and litter leachates on field germination and three-month survival of six Florida Introduction scrub species, three habitat generalists (Lechea deckertii, Palafoxia feayi, and Polygonella robusta), and three In 300 B.C., Theophrastus made the first known rosemary scrub specialists (Hypericum cumulicola, observation of allelopathy (Rice 1984). Since then Lechea cernua,andPolygonella basiramia). We used allelopathy, the direct or indirect harmful or stimula- AIC and model averaging to evaluate support for a tory effect of one plant on another through the series of non-exclusive hypotheses. Species varied in production and release of chemical compounds, has germination (2.7–24.6%) and survival (39.2–71%) been noted as an important form of plant-to-plant percentages, and in their sensitivity to leachates. interference in natural and agricultural settings (Rice Germination of scrub species was most negatively 1984). Allelochemicals, secondary compounds pro- affected by leaf [ root [ litter leachates, although not duced by plants, occur in leaves and stems, though all species followed the overall trend. Additional roots also have some allelopathic toxins (Harborne germination suppression by leachate combinations (rel- 1988). These chemicals are released into the environ- ative to single leachates) was minimal. Sites did not vary ment by plants through volatilization, root exudation, in germination, but seedling survival did differ among leaching, and decomposition of plant materials (Rice sites. This study further documents the negative impact 1984; Putnam 1985; Putnam and Tang 1986). Allelo- of Florida rosemary leachates on the germination of chemicals can negatively influence neighboring plants co-occurring plant species. Allelopathy may be partly by inhibition of the microbial symbionts (Putnam responsible for bare sand gaps in Florida rosemary 1985; Einhellig 1995), fungal-root colonization, and scrub, and therefore be one of the forces structuring free-living nitrogen-fixing bacteria (Einhellig 1995). Florida rosemary scrub ecosystems. There have been several studies in Florida scrub and sandhill documenting the release of allelochem- icals and their significant inhibition of germination & R. E. Hewitt ( ) Á E. S. Menges and radicle growth (Fischer et al. 1989; Williamson Archbold Biological Station, P. O. Box 2057, Lake Placid, FL 33862, USA 1992b; Fischer et al. 1994), and root and shoot e-mail: [email protected] biomass of sandhill grasses (Richard and Williamson 123 48 Plant Ecol (2008) 198:47–59 1988; Williamson 1992a). Most of these have been lab Hunter and Menges (2002), who examined allelopathy experiments, including analysis of ceratiolin, pro- and competition by Florida rosemary. They looked at posed as the primary allelopathic compound released the effect of leaf and litter leachates from FL rosemary from Florida rosemary, Ceratiola ericoides Michx., on germination of seven scrub species and the field and its derivative hydrocinnamic acid (Tanrisever distribution of litter and roots. They found that litter et al. 1987; Williamson et al. 1992a). These studies leachates limited germination more than leaf leachates, evaluated whether allelochemicals can inhibit the and that Florida rosemary roots extended into gaps invasion of rosemary scrub by grasses from adjacent while litter was found directly beneath shrub canopies. sandhill habitat (Richardson and Williamson 1988; To extend the study of allelopathy into in situ rosemary Fischer et al. 1989; Williamson et al. 1992b; Fischer scrub sites and to add the potential chemical effects of 1994). Germination percentage was the primary roots, we looked at the leachates of Florida rosemary dependent variable in these studies (Richardson and roots, litter, and leaves on the germination and survival Williamson 1988; Weidenhamer and Romeo 1989; of six scrub species in the field. Williamson et al. 1992a, b; Fischer et al. 1994). We examined the effect of leaf, litter, and root Washes of Ceratiola ericoides leaves have been leachates on the germination and early seedling shown to release ceratiolin, a phenolic compound. survival of six Florida scrub species. Most studies Phenolic compounds interfere with critical plant focus on the negative effect of allelochemicals on processes such as cell division (Einhellig 1995), germination and growth (Tanrisever et al. 1987; mineral and nutrient uptake (Einhellig 1995; Chaves Richardson and Williamson 1988; Fischer et al. and Escudero 1997), stomatal function, water balance, respiration, photosynthesis, protein and chlorophyll synthesis, and phytohormone activity (Einhellig 1995). In aqueous solution, ceratiolin degrades into hydrocinnamic acid when exposed to heat and light (Tanrisever et al. 1987; Obara et al. 1989; William- son et al. 1992a;). Hydrocinnamic acid degrades further into acetophenone, another allelopathic com- pound (Williamson et al. 1992a), when exposed to microbial degradation (Fischer et al. 1994). More recent studies have looked at the effects of leachates on germination of rosemary scrub species (Hunter and Menges 2002; Calabrese and Menges 2007). Germination is especially important for scrub species which do not resprout after fire (Hawkes and Menges 1995; Menges and Kohfeldt 1995; Hawkes 2004). Rosemary scrub supports many endemic species in gaps within the shrub matrix (Menges and Hawkes 1998). These gaps stay open long after fire, and allelochemicals from Florida rosemary may keep these gaps open (Hunter and Menges 2002). Field studies are necessary to evaluate the relevance of laboratory results on species interactions in nature. When greenhouse and laboratory studies indicate allelopathic interactions, field experiments are necessary to show that the significant effect of allelochemicals indoors under simplified conditions is still important in the field where there are many factors influencing plant success. This article uses a Fig. 1 Map of Archbold Biological Station, Lake Placid, FL field experiment to follow up a greenhouse study by showing the location of six study sites 123 Plant Ecol (2008) 198:47–59 Table 1 Characteristics of six target species used in germination experiment Species Hypericum Lechea Lechea Palafoxia Polygonella Polygonella cumulicola cernua deckertii feayi basiramia robusta Family Hypericaceae Cistaceae Cistaceae Asteraceae Polygonaceae Polygonaceae Common name Scrub Hypericum Nodding Pinweed Woody Pineweed Palafoxia Hairy Wireweed Sandhill Wireweed Guild habitat specialistsa habitat specialistsb habitat generalistsa,b habitat generalistsa,b,c habitat specialistsb habitat generalistsb Range endemic to the Lake endemic to Lake coastal plain of Georgia endemic to FLd endemic to Lake Wales endemic to Wales Ridge in Polk Wales Ridge and the south to peninsular FLd and Bombing Range peninsular FLd and Highlands Countiesd east coast of Ridgesd peninsular FLd Local distribution found in rosemary locally common common in rosemary common in scrubby common in scrubby locally common scrub and oak scrubd in rosemary scrub and scrubby flatwoods and gaps in flatwoods and rosemary in rosemary scrubd flatwoodsd oak scrubd scrub especially scrubd in open sandd a Hunter and Menges (2002) b Maliakal-Witt et al. (2005) c Petru and Menges (2003) d Weekley et al. (2006) assessed onCeratiola six ericoides targetscrub species, (Fischer et al. is a locallyFlorida rosemary, dominant endemic species ofStudy Florida species and a recorded fire withinvegetation, the the last absence 8 years. (Abrahamson of et mature al. rosemarythis shrubs, study (Fig. (Menges and Hawkes herbs living in the gapsand is of characterized the by rosemary areas of shrub open matrix sand ( ( sand pine scrub is dominated by Florida rosemary (Abrahamson et al. ABS include scrub,Lake flatwoods, Wales and Ridge. Predominant seasonalHighlands vegetation County, ponds Florida types at at Station the southern end (ABS), ofWe the 13 km conducted south this study ofStudy at Lake sites Archbold Placid Biological in Methods • • • • • • • • following hypotheses: survival is affected.1989 In this study, we posited the Ceratiola ericoides will differ in survivalSelected of sites germinants. will notsensitive differ to leachates. in germination,Germination but ofsensitivity gap to leachates. specialistsSpecies’ will germination be percentagesSpecies will most will vary in varygermination germination and and in survival. survival. Combinations willand have survival. differentRoots will effects haveand the on survival. least effectLitter on will have germination the greatestgermination. effect on germination Roots, leaves, and litter leachates will decrease , 1994 ) with little attention given to whether 1 ); all designated as rosemary scrub Ceratiola ericoides 1984 ) and sand pine ( 1989 1984 roots, leaves, and litter were 1998 ). We chose sites based on ). Allelopathic properties of ). The rosemary phase