South African Journal of Botany 93 (2014) 14–18

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South African Journal of Botany

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Phytotoxicity of volatiles from fresh and dry leaves of two shrubs: Evaluation of seasonal effects

E.R. Silva a,b,⁎, G.E. Overbeck a,c, G.L.G. Soares a,b a Programa de Pós-Graduação em Ecologia, Instituto de Biociências, Universidade Federal do Rio Grande do Sul (UFRGS), b Laboratório de Ecologia Química e Quimiotaxonomia (LEQTAX), Departamento de Botânica, Instituto de Biociências, Universidade Federal do Rio Grande do Sul, Brazil c Laboratório de Estudos em Vegetação Campestre, Departamento de Botânica, Instituto de Biociências, Universidade Federal do Rio Grande do Sul, Brazil article info abstract

Article history: In South Brazilian grasslands, the shrubs Heterothalamus psiadioides Less and patens Baker show a dom- Received 23 August 2013 inance pattern that may be a consequence of allelopathy. In this study, the phytotoxic effects of H. psiadioides and Received in revised form 16 February 2014 B. patens and the seasonal variation in these effects were assessed. The effects of the volatiles released directly from Accepted 13 March 2014 fresh and dry leaves of the both species were evaluated on germination and growth of the target lettuce and Available online xxxx onion in four seasons. The volatiles from H. psiadioides and B. patens inhibited the germination rate and speed of Edited by TR Marks germination and reduced the shoot and root length of the target plants, with fresh leaves showing greater phyto- toxicity. These parameters were more affected by H. psiadioides than by B. patens in all seasons and both plants Keywords: showed a decrease in phytotoxicity in summer. It can be concluded that both shrubs possess allelopathic potential, Allelopathy with H. psiadioides showing stronger effects. Interseasonal variation of phytotoxicity should be taken into account Baccharis patens in studies of potentially allelopathic plants. Germination © 2014 SAAB. Published by Elsevier B.V. All rights reserved. Growth Heterothalamus psiadioides Seasonality

1. Introduction release (Ibáñez and Zoppolo, 2011; Muller et al., 1964). Besides, recent studies revealed that the volatile essential oil of H. psiadioides is able Allelopathy can be defined as any direct or indirect harmful effect by to affect cell division in target species (Schmidt-Silva et al., 2011). To one on another through production and release of chemical com- better assess allelopathic potential of plants, it is advantageous to pounds (allelochemicals), usually secondary metabolites (Andel, 2006; use methods where emission of volatiles occurs in a way similar to Rice, 1974). In many ecosystems, some plants form dominant stands processes actually taking place in the plant community. In this sense, and this pattern may be related to the release of allelochemicals, reduc- volatiles from senescent leaves of plants may affect germination and de- ing or preventing the establishment of other species near them. The velopment of other species when they are on the soil or incorporated shrubs Heterothalamus psiadioides Less and Baccharis patens Baker into it (Huang et al., 2013); therefore, to evaluate volatiles released di- (Asteraceae) grow in grasslands and shrublands in southern Brazil rectly from dry leaves of plants seems to be an interesting approach. and in Uruguay (Deble et al., 2005), where they often establish in Nevertheless, the development of neighboring species may be also dense populations, forming shrublands (Setubal and Boldrini, 2010), affected by volatiles from leaves that are still on the plant (Muller thus indicating the possibility of allelopathic interactions with nearby et al., 1964). The use of fresh leaves thus could be better to characterize species. However, it has not been investigated which factors are respon- potentially phytotoxic plants, as studies reported that the release of sible for these patterns, and almost nothing is known about the allelo- phytotoxic substances decreases during the decomposing process pathic potential of these species; there is only a study reporting the (Huang et al., 2013; Wilt et al., 1993). phytotoxic effects of H. psiadioides essential oil (Schmidt-Silva, 2012). The majority of studies consider only one point of time for testing the The most promising way to assess the phytotoxicity of H. psiadioides allelopathic potential of a plant. However, the production of secondary and B. patens should be to evaluate their volatiles, as the phytotoxic ef- metabolites may vary during the year (Frizzo et al., 2008; Helmig et al., fects of other aromatic shrubs have been mainly related to volatiles 2013) and this should be reflected by seasonal changes in plant phyto- toxicity. This seasonal variation in defensive chemistry is mainly related to the environmental conditions that plants are growing in: biotic and ⁎ Corresponding author at: Programa de Pós-Graduação em Ecologia, Universidade abiotic factors such as the presence of herbivores (Karban, 2007) and Federal do Rio Grande do Sul, Av. Bento Gonçalves 9500, 91501970 Porto Alegre, RS, Brazil. Tel.: +55 51 3308 7576; fax: +55 51 3308 7755. pathogens (Heil and Bostock, 2002), temperature (Lur et al., 2009)and E-mail address: [email protected] (E.R. Silva). precipitation (Gray et al., 2003) vary during the year, and are able to

http://dx.doi.org/10.1016/j.sajb.2014.03.006 0254-6299/© 2014 SAAB. Published by Elsevier B.V. All rights reserved. E.R. Silva et al. / South African Journal of Botany 93 (2014) 14–18 15 change secondary metabolites synthesis. Assessing this variation is cumulative numbers of seeds that germinate by times 1, 2, …,n required to characterize the potential phytotoxicity of a plant species (Anjum and Bajwa, 2005). The final germination percentage of the and to interpret its effects. diaspores (germination rate) was calculated after 96 h (lettuce) In this study, we aimed to evaluate the phytotoxic effects of and 240 h (onion). For growth experiments, the lettuce and onion di- H. psiadioides and B. patens and the seasonal variation of these effects, aspores were previously germinated (24 h for lettuce and 96 h for through a method that assesses the activity of volatiles released directly onion) and the treatments were added. The seedlings remained ex- from fresh and dry leaves of the plants. We tested the following posed to the volatiles for 72 h. After this period, the length of shoot hypotheses: (1) Considering that both species form dense stands, both and root (cm) of 20 seedlings per repetition was measured. H. psiadioides and B. patens present phytotoxicity, affecting germination The experiment on differences of effects of the volatiles on germina- and growth of other plants; (2) as the release of phytotoxic volatiles tion and growth of the two target species across seasons was conducted must decrease with leaves senescence, the fresh leaves of the plants at four different times of the year, in winter, spring, summer and autumn show stronger effects than the dry leaves; and (3) as allelochemicals (from June 2012 to May 2013), with fresh leaves of H. psiadioides and production may vary during the year, the phytotoxic effects of B. patens. Only fresh leaves of the plants were used because they were H. psiadioides and B. patens change seasonally. hypothesized to show stronger effects than dry leaves and should allow for a better characterization in the variation in phytotoxic effects 2. Material and methods of the plants. Methods followed those described above for the first experiment. 2.1. Plant collection 2.3. Statistical analysis Leaves of H. psiadioides and B. patens were collected in natural grass- land vegetation at Morro Santana (30° 03′ S, 51° 07′ W), a hill in the city The parameters analyzed (germination rate, speed of germination, of Porto Alegre, Rio Grande do Sul State, Brazil, where they occur with length of shoot and length of root) in the experiment with fresh and high frequency and abundance values (details on the grassland vegeta- dry leaves of H. psiadioides and B. patens were submitted to one-way tion on Santana hill: Overbeck et al., 2006). Voucher specimens of PERMANOVA univariate analysis, comparing all the treatments by ran- H. psiadioides (register number 175007) and B. patens (register number domization tests with 10,000 permutations and including pairwise 192266) were deposited in the herbarium ICN of the Federal University comparison. In the second experiment, the seasonal variation in these ofRioGrandedoSul. parameters was evaluated, through two-way PERMANOVA that tested the interaction between treatments and seasons, also using randomiza- 2.2. Germination and growth assays tion tests. Still, to test for differences between treatments specifically in each season, groups were compared through one-way PERMANOVA, in- The effect of the volatiles from H. psiadioides and B. patens was eval- cluding pairwise comparison. PERMANOVA enabled a conventional uated on the germination and growth of the target species lettuce ANOVA approach to be conducted without transformation on the raw (Lactuca sativa L. cv. Grand Rapids) and onion (Allium cepa L. cv. Baia data, since it is not based on assumptions of normality and homogeneity Periforme). Both target plants were used in the assays because of the of variances (Anderson, 2001). The analysis used Euclidean distances relevance of determining the potential selectivity of the phytotoxic and considered a significance level of p b 0.05. The tests were per- compounds on dicotyledons and monocotyledons (Lotina-Hennsen formed using the software MULTIV (Pillar, 2009). et al., 2006). Two separate experiments were conducted: the first exper- iment was designed to test for differences between effects of fresh 3. Results leaves and dry leaves of both species and the second experiment to eval- uate the difference in magnitude of the effects across different seasons. In the germination bioassays with fresh and dry leaves of the plants, For the first experiment, dry leaves of H. psiadioides and B. patens the volatiles from fresh leaves of H. psiadioides caused a significant, were obtained by collecting fresh leaves and leaving them exposed to though not always very strong, reduction on the speed of germination natural temperature conditions in the laboratory until they were and germination rate of lettuce (37% and 7%, respectively, when com- dried, for about ten days. For the treatment with fresh material, leaves pared to germination rate of the control treatment) and of onion (37% were collected and immediately used in the assays. The control group and 47%, respectively). The dry leaves of H. psiadioides only reduced consisted of absence of leaves. the speed of germination of lettuce (39%). Fresh and dry leaves of The treatments were arranged in a completely random design B. patens did not cause any significant effect on lettuce and onion germi- with four repetitions. Each repetition corresponded to 50 diaspores nation (Fig. 1AandB). of lettuce or onion, obtained from commercial dealers and sown in The effects of the volatiles from H. psiadioides and B. patens on seed- alayeroffilter paper (11 cm2, 0.16 mm thick) moistened with 7 mL lings growth are shown in Fig. 1C and D. The dry leaves of both shrubs of distilled water, inside germination boxes of 11 cm × 11 cm × caused lower inhibition on growth of the target plants in relation to 4cm.Heterothalamus psiadioides and B. patens leaves (5 g) were slightly the fresh leaves, as shown in the germination assays. The fresh leaves chopped, wrapped in cloth (tulle) and attached with double-sided tape of H. psiadioides caused the greatest reduction on shoot and root length to the inner face of the box lid without direct contact with the seeds, of the target plants (21% and 52% for lettuce and 43% and 46% for onion, but allowing the compounds to volatilize into the airspace within the respectively). The dry leaves of H. psiadioides reduced shoot and root box. The leaves were attached in the corners of the box lid to avoid inter- length of lettuce (13% and 28%) and shoot length of onion (28%). fering in light supply for the seeds. The boxes were sealed with plastic film B. patens fresh leaves also caused negative effects on the shoot and to minimize loss of the volatiles and were incubated in a germination root length of lettuce (11% and 32% of reduction) and shoot of onion room at an average temperature of 21 °C, with a daily light/dark cycle (13% of reduction). The dry leaves of B. patens only reduced lettuce of 12 h/12 h. The illumination was provided by white fluorescent lamps root (15%) and onion shoot length (14%). (20 W), with an irradiance of 48 μmol m−2 s−1. In relation to the experiment on differences of effects of the plants For the germination assay, the diaspores were sown and the volatiles across seasons, the interaction between treatment and season treatments were added. The germinated diaspores were recorded was significant in almost all the parameters evaluated, except for the every 12 and 24 h, for lettuce and onion, respectively. Speed of accu- speed of germination and the root length of onion, i.e. differences mulated germination (AS) was calculated using the following formu- among treatments vary according to the season (Table 1). In winter, la: AS = [N1/1 + N2/2 + … + Nn / n], where N1, N2, and Nn are the H. psiadioides caused a pronounced inhibition in all the parameters 16 E.R. Silva et al. / South African Journal of Botany 93 (2014) 14–18 B A Dry leaves Dry leaves a a ab ab a b Fresh leaves 40 a Fresh leaves 90 35 a 75 a a 30 a 25 b b 60 ab 45 b 20 15 30 10 a a ab ab 15 b Germination (%) 5

0 Speed of germination 0 Co Bp Hp Co Bp Hp Co Bp Hp Co Bp Hp Lettuce Onion Lettuce Onion C Dry leaves D Dry leaves 3.5 Fresh leaves 2.4 Fresh leaves a a 3 b 2.1 bcd 1.8 abc 2.5 c b bcd 1.5 2 d d 1.2 a abb 1.5 c c a a 0.9 1 a a b 0.6

Root length (cm) 0.5

Shoot length (cm) 0.3 0 0 Co Bp Hp Co Bp Hp Co Bp Hp Co Bp Hp Lettuce Onion Lettuce Onion

Fig. 1. Germination rate (A), speed of germination (B), root length (C) and shoot length (D) of lettuce and onion exposed to the volatiles from B. patens (Bp) and H. psiadioides (Hp) and control group (Co). Data presented as mean and standard deviation. Treatments sharing the same letter do not differ significantly according to one-way PERMANOVA for the same target species, at p b 0.05 level.

and in spring and autumn almost all the parameters were also substan- 4. Discussion tially affected by the plant volatiles. In summer, however, only the pa- rameters related to seedling growth were considerably inhibited by The results of the assays confirmed our hypothesis that both H. psiadioides volatiles. The seasonal pattern in the effects of B. patens H. psiadioides and B. patens present phytotoxicity, affecting germination on the target plants was similar to the pattern observed for and growth of seedlings. A greater phytotoxic effect of H. psiadioides H. psiadioides: the inhibition by B. patens volatiles was pronounced in compared to B. patens was observed. The volatiles released from some parameters in winter, spring and autumn. Nevertheless, almost H. psiadioides negatively affected all the parameters evaluated in the only the parameters related to seedling growth were considerably af- germination and growth assays. Baccharis patens affected only the pa- fected by the plant. In summer, the inhibition by B. patens was not pro- rameters related to growth (shoot and root length), which are usually nounced for any parameter. Besides, the inhibition in almost all the more sensitive to phytotoxic effects than parameters related to germi- parameters was greater when the target plants were exposed to nation (speed of germination and germination rate) (Chon and H. psiadioides; the reduction by B. patens was only slightly greater on Nelson, 2010). Besides, the inhibition on the target plants was stronger the speed of germination of lettuce in spring and summer, but in these when they were exposed to H. psiadioides leaves. The differences in the cases the inhibition was not substantial and does not consist in consid- effects of H. psiadioides and B. patens are likely associated to the amount erable difference between the treatments. of phytotoxic volatiles released by them and to differences in their

Table 1 Inhibition (%) of germination rate, speed of germination, root length and shoot length of lettuce and onion exposed to the volatiles from fresh leaves of H. psiadioides (Hp) and B. patens (Bp) in the four seasons of the year.

Season Treatment Germination assays — inhibition (%) Growth assays — inhibition (%)

Germination rate Speed of germination Shoot length Root length

Lettuce Onion Lettuce Onion Lettuce Onion Lettuce Onion

Winter Hp 7a 47a 37a 37a 21a 23a 52a 20a Bp 0 1502 0811 13a 32a 14 Spring Hp 2 25a 04 31a 32a 43a 42a 46a Bp 0 0810 1524 19a 19a 10 Summer Hp 0 10 01 10 03 21a 30a 21a Bp 0 0409 0300 0815 06 Autumn Hp 6 12 25a 07 11a 19a 33a 26a Bp 2 11 21a 07 00 11a 23 14 Treatment P-value 0.009 b0.001 b0.001 b0.001 b0.001 b0.001 b0.001 b0.001 Season 0.04 b0.001 b0.001 b0.001 b0.001 b0.001 0.02 b0.001 Treatment ∗ season 0.01 b0.001 b0.001 0.5 b0.001 b0.001 b0.001 0.18

a Significant differences in relation to control (no treatment), according to PERMANOVA, with p b 0.05. E.R. Silva et al. / South African Journal of Botany 93 (2014) 14–18 17 chemical composition. Most of the volatiles in these plants are in the es- such as interactions with pathogens (Heil and Bostock, 2002)andherbi- sential oil of their leaves, which showed 1.92% and 0.2% yield for vores (Karban, 2007)orwater(Gray et al., 2003)andnutrients H. psiadioides and B. patens, respectively (unpublished data). Therefore, (Tharayil et al., 2009) availability are also able to change secondary me- H. psiadioides is able to release a larger amount of volatiles than tabolite production and consequently the plants phytotoxicity. The var- B. patens.ThemajorcompoundsofH. psiadioides essential oil, obtained iation in the phytotoxic effects of H. psiadioides and B. patens evidences from the same population studied in this article, are monoterpenes hy- the importance of conducting allelopathy studies along different sea- drocarbons (77.31%), mainly β-pinene (43.17%), Δ3-carene (13.73%) sons; if this variation is not considered, the results may not reflect the and limonene (6.32%) and although this oil affected germination and potential phytotoxicity of a plant species correctly or, on the other growth of other plants, β-pinene, the major compound, did not show hand, the phytotoxic effects may be overestimated. phytotoxicity (Schmidt-Silva, 2012). Therefore, the phytotoxic effects The method used in this study was effective to determine volatiles of H. psiadioides must result from interactive effects of several phytotoxicity even though only a small amount of plants leaves was compounds, as assumed for the effects of plants allelochemicals in used. The similar pattern of phytotoxicity observed for both shrubs at field conditions (Inderjit et al., 2011). The essential oils of several all times when the assays were conducted, i.e. H. psiadioides showing Baccharis species have already been characterized (Frizzo et al., 2008; stronger effects than B. patens, indicates the efficacy of the technique. Simões-Pires et al., 2005), and although the species share most of the Besides, an advantage of the method is that it allows carrying out phy- compounds, the major ones vary among them: while monoterpene totoxicity studies without interferences, as shown in other methods fre- hydrocarbons are the predominant fraction in some species, in others quently used: extracts, for example, can inhibit test species through oxygenated sesquiterpenes or oxygenated monoterpenes are more sig- altering pH and osmotic potential (Wardle et al., 1998), masking the nificant. The chemical composition of B. patens has not been described true phytotoxic effects of a plant. Assays with essential oils, one of the up to now. Thus, further studies characterizing the volatile compounds most used ways to characterize volatiles phytotoxicity (e.g. Pawlowski of B. patens essential oil will shed light on the phytotoxic activity of this et al., 2012; Zahed et al., 2010), also show a constraint: the concentra- species. tion of these substances is much greater than what would be naturally The action of allelochemicals on germination and growth of plants is volatilized by plants. However, even though we can assume that our diverse and affects different physiological functions, as cell division, method should be more similar to natural emission of volatiles, it must metabolic processes, photosynthesis and respiration. A mechanism re- be considered that the interactions between plants and allelochemicals lated to modification in cell division was already reported for in the plant community occur in a more dynamic ecological situation H. psiadioides: the essential oil of this plant caused a decrease in mitotic and that phytotoxic effects observed in laboratory conditions may not activity and an increase of chromosomal abnormalities in target plants be relevant in nature. Many plants release compounds into the surround- (Schmidt-Silva et al., 2011). Besides, effects of allelochemicals on seed ing environment with minor consequences in their native habitat due to germination appear to be mediated mainly through a disruption of nor- a long coevolutionary history with other plants (Thorpe et al., 2009). Be- mal cellular metabolism. One of the effects can be in reserve mobiliza- sides, there are several biotic and abiotic factors that are able to change tion, a process that usually takes place rapidly during early stages of allelopathic activity (Inderjit et al., 2011). seed germination and seems to be delayed or decreased by phytotoxic- ity (Gniazdowska and Bogatek, 2005). Seedlings growth is usually 5. Conclusions affected by disturbances of photosynthesis (Qian et al., 2009)andrespi- ration (Hejl and Koster, 2004; Mushtaq et al., 2013), which are some of The shrubs H. psiadioides and B. patens show phytotoxicity, which is the most observed physiological effects of many allelochemicals. greater for H. psiadioides. The phytotoxic effects of both species differ in Considering the differences on the phytotoxicity of fresh and dry magnitude across seasons, evidencing the relevance of considering this leaves of H. psiadioides and B. patens, our hypothesis that the fresh leaves variation in allelopathy studies. The strong effects of the fresh leaves of of the plants present stronger effects than the dry leaves was confirmed. these shrubs indicate that the volatiles may affect the development of This indicates that in natural ecosystems the phytotoxicity of the shrubs other neighboring species when the leaves are still on the plants; thus, leaves must decrease until they are incorporated into the soil. Besides, allelopathy is a possible mechanism involved in the dominance pattern due to the low phytotoxicity of the dry leaves of H. psiadioides and shown by H. psiadioides and B. patens. However, additional studies B. patens, they would need to drop large amounts of leaves on the soil under field conditions are needed to evaluate if these shrubs, through to affect germination of other species; as these plants are not deciduous, allelopathic interactions, are effectively able to affect other species in this is unlikely to occur. Thus, it seems difficult that the volatiles from plant communities. these shrubs are able to affect the germination of other species in plant communities. On the other hand, the strong effects of the fresh Acknowledgments leaves of the shrubs, mainly H. psiadioides, on growth of the target plants suggest that the volatiles may affect the development of other neighbor- We thank the Coordenação de Aperfeiçoamento de Pessoal de Nível ing species when the leaves are still on the plants, as assumed for other Superior (CAPES) for the MSc scholarship granted to the first author. We fi aromatic shrubs which were reported to affect nearby species in eld also thank MSc. Ângela Pawlowski, Diana Carla Lazarotto and two anon- conditions (Ibáñez and Zoppolo, 2011; Muller et al., 1964). ymous reviewers for their valuable suggestions on the manuscript. The variation in magnitude in the phytotoxic effects of B. patens and H. psiadioides according to the period that they were collected con- References firmed our hypothesis that the plants phytotoxicity changes seasonally. The plants showed generally lower phytotoxicity in summer than in the Andel, J.V., 2006. Species interactions structuring plant communities. In: Van der Maarel, – other seasons — a pattern that must be related to seasonal fluctuations E. (Ed.), Vegetation Ecology. Blackwell Publishing, Oxford, pp. 238 264. Anderson, M., 2001. A new method for non-parametric multivariate analysis of variance. of environmental parameters and trade-offs between primary and sec- Austral Ecology 26, 32–46. ondary metabolism. In summer, plants are exposed to higher tempera- Anjum, T., Bajwa, R., 2005. Importance of germination indices in interpretation of – tures and solar radiation, which were reported to have an inverse allelochemical effects. International Journal of Agriculture and Biology 7, 417 419. Chon, S.U., Nelson, C.J., 2010. Allelopathy in Compositae plants. A review. Agronomy for relation with secondary metabolite accumulation in plant tissues (Lur Sustainable Development 30, 349–358. et al., 2009; Yu et al., 2003). Besides, plants growth increases in summer; Deble, L.P., Oliveira, A.S., Marchiori, J.N.C., 2005. O gênero Heterothalamus Lessing e studies revealed trade-offs between primary biological functions of táxones afins. Balduinia 1, 1–20. Donaldson, J.R., Kruger, E.L., Lindroth, R.L., 2006. Competition- and resource-mediated plants, as growth, and resources allocation for chemical defense tradeoffs between growth and defensive chemistry in trembling aspen (Populus (Donaldson et al., 2006; Züst et al., 2011). However, other factors, tremuloides). New Phytologist 169, 561–570. 18 E.R. Silva et al. / South African Journal of Botany 93 (2014) 14–18

Frizzo, C.D., Atti-Serafini, L., Laguna, S.E., Cassel, E., Lorenzo, D., Dellacassa, E., 2008. Essential aneugenic inducers in onion and lettuce root meristems. South African Journal of oil variability in Baccharis uncinella DC and Baccharis dracunculifolia DC growing wild in Botany 80, 96–103. southern Brazil, Bolivia and Uruguay. Flavour and Fragrance Journal 23, 99–106. Pillar, V.D., 2009. MULTIV, software for multivariate exploratory analysis, randomization Gniazdowska, A., Bogatek, R., 2005. Allelopathic interactions between plants. Multi site testing and bootstrap resampling. Version Beta 2.6.8 Departmento de Ecologia, action of allelochemicals. Acta Physiologiae Plantarum 27, 395–407. UFRGS, Porto Alegre, RS, Brazil (URL: http://ecoqua.ecologia.ufrgs.br). Gray, D.E., Pallardy, S.G., Garrett, H.E., Rottinghaus, G.E., 2003. Effect of acute drought Qian, H., Xu, X., Chen, W., Jiang, H., Jin, Y., Liu, W., Fu, Z., 2009. Allelochemical stress causes stress and time of harvest on phytochemistry and dry weight of St. John's wort leaves oxidative damage and inhibition of photosynthesis in Chlorella vulgaris.Chemosphere and flowers. Planta Medica 69, 1024–1030. 75, 368–375. Heil, M., Bostock, R.M., 2002. Induced systemic resistance (ISR) against pathogens in the Rice, E.L., 1974. Allelopathy. Academic Publishers, New York. context of induced plant defences. Annals of Botany 89, 503–512. Schmidt-Silva, V., 2012. Potencial alelopático do óleo essencial de espécies de Hejl, A.M., Koster, K.L., 2004. Juglone disrupts root plasma membrane H+-ATPase activity Heterothalamus nativas do Rio Grande do Sul. PhD Thesis Universidade Federal do and impairs water uptake, root respiration, and growth in soybean (Glycine max)and Rio Grande do Sul, Brazil. corn (Zea mays). Journal of Chemical Ecology 30, 453–471. Schmidt-Silva, V., Pawlowski, A., Santos, E.K., Zini, C.A., Soares, G.L.G., 2011. Cytotoxicity of Helmig, D., Daly, R.W., Milford, J., Guenther, A., 2013. Seasonal trends of biogenic terpene essential oils from two species of Heterothalamus (Asteraceae). Australian Journal of emissions. Chemosphere 93, 35–46. Botany 59, 681–690. Huang, W., Hu, T., Chen, H., Wang, Q., Hu, H., Tu, L., Jing, L., 2013. Impact of decomposing Setubal, R.B., Boldrini, I.I., 2010. Floristic and characterization of grassland vegetation at a Cinnamomum septentrionale leaf litter on the growth of Eucalyptus grandis saplings. granitic hill in Southern Brazil. Revista Brasileira de Biociências 8, 85–111. Plant Physiology and Biochemistry 70, 411–417. Simões-Pires, C.A., Debenedetti, S., Spegazzini, E., Mentz, L.A., Matzenbacher, N.I., Ibáñez, F., Zoppolo, R., 2011. Assessment of allelopathic properties of Baccharis Limberger, R.P., Henriques, A.T., 2005. Investigation of the essential oil from eight spe- dracunculifolia DC in laboratory and field conditions. Allelopathy Journal 28, 77–86. cies of Baccharis belonging to sect. Caulopterae (Asteraceae, ): a taxonomic Inderjit, Wardle, D.A., Karban, R., Callaway, R.M., 2011. The ecosystem and evolutionary approach. Plant Systematics and Evolution 253, 23–32. contexts of allelopathy. Trends in Ecology and Evolution 26, 655–662. Tharayil, N., Bhowmik, P., Alpert, P., Walker, E., Amarasiriwardena, D., Xing, B., 2009. Dual Karban, R., 2007. Experimental clipping of sagebrush inhibits seed germination of neigh- purpose secondary compounds: phytotoxin of Centaurea diffusa also facilitates bours. Ecological Letters 10, 791–797. nutrient uptake. New Phytologist 181, 424–434. Lotina-Hennsen, B., King-Diaz, B., Aguilar, M.I., Terrones, M.G.H., 2006. Plant secondary Thorpe, A.S., Thele, G.C., Diaconu, A., Callaway, R.M., 2009. Root exudate is allelopathic in metabolites. Targets and mechanisms of allelopathy. In: Reigosa, M.J., Pedrol, N., invaded community but not in native community: field evidence for the novel González, L. (Eds.), Allelopathy: A Physiological Process with Ecological Implications. weapons hypothesis. Journal of Ecology 97, 641–645. Springer, Netherlands, pp. 229–265. Wardle, D.A., Nilsson, M.C., Gallet, C., Zackrisson, O., 1998. An ecosystem level perspective Lur, H.S., Hsu, C.L., Wu, C.W., Lee, C.Y., Lao, C.L., Wu, Y.C., Chang, S.J., Wang, C.Y., Kondo, M., of allelopathy. Biological Reviews 73, 305–319. 2009. Changes in temperature, cultivation timing and grain quality of rice in Taiwan Wilt, F.M., Miller, G.C., Everett, R., Hackett, M., 1993. Monoterpene concentrations in fresh, in recent years. Crop, Environment & Bioinformatics 6, 175–182. senescent, and decaying foliage of single-leaf pinyon (Pinus monophylla Torr. & Frem.: Muller, C.H., Muller, W.H., Haines, B.L., 1964. Volatile growth inhibitors produced by aro- Pinaceae) from the western great basin. Journal of Chemical Ecology 19, 185–194. matic shrubs. Science 143, 471–473. Yu, L., Perett, J., Harris, M., Wilson, J., Haley, S., 2003. Antioxidant properties of bran ex- Mushtaq, N.M., Sunohara, Y., Matsumoto, H., 2013. Allelochemical L-DOPA induces tracts from “Akron” wheat grown at different locations. Journal of Agricultural and quinoprotein adducts and inhibits NADH dehydrogenase activity and root growth Food Chemistry 51, 1566–1570. of cucumber. Plant Physiology and Biochemistry 70, 374–378. Zahed, N., Hosni, K., Brahim, N.B., Kallel, M., Sebei, H., 2010. Allelopathic effect of Schinus Overbeck, G.E., Müller, S.C., Pillar, V.C., Pfadenhauer, J., 2006. Floristic composition, molle essential oils on wheat germination. Acta Physiologiae Plantarum 32, environmental variation and species distribution patterns in burned grassland in 1221–1227. southern Brazil. Brazilian Journal of Biology 66, 1073–1090. Züst, T., Joseph, B., Shimizu, K.K., Kliebenstein, D.J., Turnbull, L.A., 2011. Using knockout Pawlowski, A., Kaltchuk-Santos, E., Zini, C.A., Caramão, E.B., Soares, G.L.G., 2012. Essential mutants to reveal the growth costs of defensive traits. Proceedings of the Royal oils of Schinus terebinthifolius and S. molle (Anacardiaceae): mitodepressive and Society B 278, 2598–2603.