Synergistic Effect of Herbivory and Mycorrhizal Interactions on Plant Invasiveness
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African Journal of Microbiology Research Vol. 6(19), pp. 4107-4112, 23 May, 2012 Available online at http://www.academicjournals.org/AJMR DOI: 10.5897/AJMR11.1278 ISSN 1996-0808 ©2012 Academic Journals Full Length Research Paper Synergistic effect of herbivory and mycorrhizal interactions on plant invasiveness Manzoor A. Shah1*, Z. A. Reshi and I. Rashid2 1Department of Botany, University of Kashmir, Srinagar-190006, Jammu and Kashmir, India. 2Government Degree College (Boys), Baramulla, Kashmir, India. Accepted 9 December, 2011 Amongst many novel interactions that alien plants forge with their new associates in the introduced range, the role of Arbuscular mycorrhizal (AM) mutualism and herbivory has been hitherto studied separately. Since these associations operate concurrently in nature to influence plant performance, we attempted to investigate their interactive effect on invasiveness of Mayweed Chamomile (Anthemis cotula L.), a highly invasive species in the Kashmir Himalaya, India. Survey of some field populations of A. cotula in native (European) and introduced (Kashmir Himalayan) regions revealed high incidence of phytophagous parasites on the species in native range, in contrast to almost enemy-free populations in the introduced range. However, occasional association of an aphid herbivore with some individuals of A. cotula in the introduced range was found to have positive influence on traits contributing to invasiveness of the species. We subsequently established a pot experiment in which A. cotula was grown with and without mycorrhizas and herbivores, both in isolation and combination. Results revealed that mycorrhizal inoculation and herbivory, both in isolation and in combination, influenced significantly growth and fitness, hence invasiveness, of A. cotula. While our simple study point towards likely synergistic influence of below- and above-ground interactions on plant invasiveness, we stress for the need of comprehensive multifactor interaction analysis while dealing with plant invasions. Key words: Anthemis cotula, arbuscular mycorrhizal fungi, alien invasive species, herbivory, overcompensatory growth. INTRODUCTION Introduced plant populations often lose interactions with and spread (Richardson et al., 2000). However invader enemies and mutualist from their native ranges and gain success may be better understood by considering the interactions with new species, under new abiotic joint effects of enemies and mutualist, including conditions. Many of the current hypotheses on the role of interactions between them, on introduced populations; biotic interactions in plant invasions focus exclusively on because alien plants, upon their introduction in the non- enemies, mutualist or competitors. For instance the native range, inevitably interact with multitude of enemy release hypothesis argues that the loss of organisms, such as competitors, predators, pathogens, interactions with natural enemies allows introduced and mutualist which can both positively and negatively populations to attain greater abundances (Colautti et al., affect their growth (Seifert et al., 2009). Herbivores, for 2004; Torchin and Mitchell, 2004), while the mutualisms example, can reduce photosynthetic area, plant fitness, facilitation hypothesis posits that the replacement of lost alter plant allocation patterns, increase plant defences, mutualist from plants native ranges with new mutualist in and even lead to plant death, while mutualists, such as their introduced ranges is key to invaders establishment mycorrhizal fungi can form symbiotic associations that often improve plant growth and survival (Bennett et al., 2009). Moreover, plants usually interact with herbivores or mutualists at the same time. Individual plants, for *Corresponding author. E-mail: [email protected]. Tel: example, may associate with many species of +9596191292. Fax: 0194-2424735. mycorrhizal fungi which differ greatly in their effect on 4108 Afr. J. Microbiol. Res. plant growth (Bever, 2002). For instance, Vannette and neighbour identity on its invasiveness ( Shah et al., 2008 Hunter (2011) revealed that while one species of AM a, b) and the over compensatory response of this species fungus (Scutellospora pellucid) has positive effect on host after herbivore damage (Rashid et al., 2006). The simple plant species, another species (Glomus etunicatum) study was designed to compare the extent of enemies appeared to act as a parasite on the same host species, associated with A. cotula in its native and invaded thereby indicating variability in the costs and benefits of regions and investigate the effect of AM fungi and resource mutualisms. herbivory, both in isolation and combination, on Aboveground foliage consumers may reduce invasiveness of this species. photosynthate translocation to the root system and The specific questions asked in the present study, decrease its availability to mycorrhizal fungi, resulting in carried out from 2008 to 2010, were (a) whether A. cotula reduction of mycorrhizal colonization and reduced has been released from native enemies in the introduced development of the symbiosis (Gehring et al., 1997; range, and (b) how herbivores interact with this species Hetrick et al., 1990; Trent et al., 1988). Mycorrhizas, in viz-a-viz mycorrhizal associates to influence its turn, may affect herbivores through alteration of plant invasiveness. growth or foliar chemistry (Goverde et al., 2000), and they may have large effects on plant responses to MATERIALS AND METHODS herbivores by influencing anti-herbivore defences and/or herbivory tolerance (re-growth capacity). However, Study species recently mycorrhizal colonization has been shown not to affect tolerance to defoliation of an annual herb in Mayweed Chamomile (Anthemis cotula L.), which is a member of different light availability and soil fertility treatments Asteraceae, is an annual herbaceous plant native to southern (Aguilar-Chama and Guevara, 2011). Garrido et al. Europe-west Siberia (Erneberg, 1999) where its most important (2010) reports that variation in AMF colonization modifies herbivores are aphids (Aphidae), spittlebugs (Cercopidae), bugs the expression of tolerance to above-ground defoliation (Heteroptera), moths, slugs and snails. In its native range the species is attacked by about 68 herbivores, mainly insects, of which and that a negative interaction between AMF 13 specifically use it as their host (Shah and Reshi, 2007). In concentration and plant tolerance to defoliation does addition, a stem mining agromyzid fly (Napomyza sp.) and two exist. It is important to note that the grazing tolerance and insect species, namely Cochylidia implicitana (Tortricidae) and mycorrhizal colonization of plants are linked to resource Homeosoma nimbella (Pyralidae) are also reported to feed on its manipulation and plant size, as shown for a biennial plant shoots, flowers, fruits and seeds (Shah and Reshi, 2007) keeping the species under check. However, no such bio-control is available species, Gentianella campestris, by Piippo et al. (2011). in its invaded region that is, Kashmir Himalaya. The role of mycorrhizas in plant invasions has been In the Himalayan valley of Kashmir, this fast spreading species reviewed by Shah et al. (2009) to highlight the paradoxi- is emerging as a major threat to native biodiversity and ecosystem cally conflicting observations in the context of mutualism- processes. commensalism-parasitism gradient that characterizes the Large-scale invasion of the ruderal habitats facilitated by AM relationship between AM fungi and their alien vs. native mutualists (Shah and Reshi, 2007) of this species has been attributed to its extended recruitment pattern aided by habitat hosts. In the said review authors have dealt with tripartite disturbance, high population size even after seedling mortality AMF-host plant-herbivore interactions also.While both (Allaie et al., 2005), allelopathic activity of its aqueous leaf leachate mycorrhizas and herbivores have been shown to (Allaie et al., 2006), herbivore induced over-compensatory growth influence plant invasions, their effects have been hitherto (Rashid et al., 2006) and profuse production and synchrony studied independently. This is so despite the likely between germination of achenes and favourable environmental interactions between herbivores and arbuscular conditions (Rashid et al., 2007). mycorrhizal (hereafter AM) fungi because both depend upon and influence important plant resources. The Field observations response of arbuscular mycorrhizal fungi to stimulate herbivory is reported to be species specific and is also Intensive surveys were carried out during the present study in relatively difficult to generalize even when dealing with different parts of the Kashmir Valley for observing any herbivores the same plant species (Klironomos et al., 2004). Gehring associated with this species. In order to assess whether or not A. and Witham (1991) showed herbivore driven mycorrhizal cotula was released from its native enemies, information was mutualism in insect-susceptible pinyon pine but did not previously obtained about the enemies associated with this species in its native range from Dr. S. Benvenuti, Agricultural Research know what drives such an interaction in resistant trees. Institute, National Resource and Environment, University of Pisa, Notwithstanding these sporadic attempts, the dynamics Italy. Moreover, 5 European populations of A. cotula were surveyed of tripartite (herbivore-plant-AM) interaction with respect in Gothenburg,