METHODS

1. Phenol Content Reduce Leaf Decomposition in a Mountain Cloud Forest Randall A. Montoya-Solano, German Vargas, Jairo E. Hidalgo-Mora, José Miguel Chávez and Roberto A. Cordero S. Laboratorio de Ecología Funcional y Ecosistemas Tropicales, Escuela de Ciencias Biológicas, Universidad Nacional de Costa Rica Leaf decomposition works as the resource turnover mechanism in tropical ecosystems, which happens through lixiviation, fragmentation and chemical transformation processes, having CO2 as the final product of leaf decomposition, remarking its importance in ecosystem carbon balance, which influences carbon global cycle (Chapin et al. 2002, Lamberset al. 2008).This process cannot be explained as a single factor response, because climatic conditions influence leaf decomposition rates (K). For example, in a global context precipitation increases K and the release period (Álvarez-Sánchez & Becerra 1996). Locally leaf tissue structure properties, such as specific leaf area (SLA), has been proof as main factor determining K (Lamberset al. 2008). Also, but not least important, nutrients and secondary metabolites affects K positively or negatively respectively (Álvarez-Sánchez & Becerra 1996, Lang et al 2009). Although leaf decomposition is a really important and seldom studied process, in tropical montane ecosystems data related to that matter are still scant (Aerts 1997). We studied how SLA (structural trait) and polyphenol content (chemical composition trait) of several important plant species affects K in a tropical montane cloud forest of Costa Rica. D. arboreuspresented the higher K value, and the lowest PC, however its SLA was close to the mean. On the other side M. laxiflora showed the lower K, SLA and the highest Pc (Table 1). We found that Pc works as a main factor determining K, having a negative effect on it (Fig. 1), with a significant correlation between (r2=0.56, p=0.02) Moreover SLA did not show any effect on K, resulting in non significant correlation between both variables (r2 =0.02, p=0.66). (a) (b) Specific Leaf Area cm2/g Polyphenol mg/mL Fig.1. Correlation analysis between studied variables. Where (a) shows the significant relationship between the polyphenol content (PC) and the leaf decomposition rates (K), and (b) the non significant relationship between the specific leaf area (SLA) and leaf decomposition rates (K). DISCUSSION It had been showed that leaf nutrient concentration increases decomposition processes (Álvarez-Sánchez & Becerra 1996, Pérez-Harguindeguy 2000, Lang et al 2009). On the other side, leaf secondary metabolites content could have an effect on K (Cornelissen 1996); but few or none tropical ecology studies has considered this variable. Kazakouet al (2006) found no effect found of the leaf secondary metabolites content on K in temperate and subtropical zones as the Mediterranean coast of Europe. However we found that in tropical montane forests species with higher polyphenol content had lower rates of decomposition. Although SLA has previously reported as main factor influencing leaf decomposition (Cornelissen 1996), in this study we showed that in neotropicalmontane forests SLA does not affect K. As evidenced in M. laxiflora, which presented the lower SLA and at the same time the lower K. It is important to know the ecological implications of polyphenols as many other secondary metabolites. Because, leaf litter accumulation could protect soil, conserving an stable humus stratum and the long-term potential importance in carbon sequestration. However, in a restoration approach, a thick litter layer could obstruct seedling recruitment (Celentano et al 2011). Also as a way to study forest succession functional changes, because in early successional stages the higher decomposition rates are commonly found (Kazakouet al. 2006). We remark the important of these results specially in the environmental services that a thick leaf litter layer may provide, such as helping to mitigate greenhouse gases effects by sequestering carbon, by protecting water resourcesand soil stabilization in landslide areas. As well, this study shows a way to easily assess ecosystems health as a management tool in the reforestation and restoration programs in tropical montane forests. METHODS Study site: The experiment was conducted between March and August 2012, in the 0.5 ha plot of the “EstaciónBiológica y Acuicultura Río Macho”, at Orosi, Cartago, located at 1650 m.a.s.l. (9º45’52’’ N, 83º51’45’’ W) in a tropical montane rain forest. Plant material: We collected fresh leaves of nine commonly found species (Table 1). Before the decomposition experiment starts, plant material was dried in an oven for 72 hours and then weighed. We placed approximately three grams in 3 mm plastic mesh bags, for a total of seven repetitions per species. We collected plant material after six months. Then we dried and weighed the material to determine the remnant mass. Polyphenol analysis: To determine polyphenol content (PC) we follow the Foling-Ciocalteu procedure to extract total polyphenols and then analyze each sample polyphenols content through a mass spectrophotometry. Data analysis: All the analysis were performed using StatGraphics Centurion XV statistical software. The regression analysis were performed using Sigma Plot 10.0 software. K was estimated according to Anderson & Ingram (1993), as follows: whereWtisremnantmass in a specific time t (t=1year) and Wo as theinitialmass. RESULTS • REFERENCES • Aerts, R. 1997. Climate, leaf litter chemistry and leaf litter decomposition in terrestrial ecosystems: a triangular relationship. Oikos 79: 439-449. • Álvarez-Sánchez, A. & R. Becerra. 1996. Leaf decomposition in a mexican tropical rain forest. Biotropica 28 (4): 657-667. • Anderson, J. M. & J. S. I. Ingram. 1993. Tropical soil biology and fertility a handbook of methods. 2 ed. CAB International. Wallingford, U.S.A. 36-40. • Celentano, D., R. A. Zahawi, B. Finegan, F. Casanoves, R. Ostertag, R.J. Cole & K.D. Holl. Restauraciónecológica de bosquestropicales en Costa Rica: efecto de variosmodelos en la producción, acumulación y descomposición de hojarasca. Rev. Biol. Trop. 59 (3): 1323-1336 • Chapin III, F.S., P.A. Matson & H.A. Mooney. 2002. Principles of terrestialecosistem ecology. Springer-Verlag. New York. USA. • Cornelissen, J.H.C. 1996. An experimental comparison of leaf decomposition rates in a widw range of temperate plant species and types. Journal of Ecology 84: 573-582. • Kazakou, E., D. Vile, B. Shipley, C. Gallet & E. Garnier. 2006. Variations in litter decomposition, leaf traits and plant growth in species from a Mediterranean old-field succesion. Functional Ecology 20: 21-30. • Lambers,H., F.S. Chapin II & T.L. Pons. 2008. Plant Physiological Ecology. Springer Science-Business Media. New York.USA. • Lang, S.I., J.H.C. Cornelissen, T. Klahn, R.S.P. van Logtestijn, R. Broekman, W. Schuseikert & R. Aerts. An experimental comparison of chemical traits and litter decomposition rates in a diverse range of subartic bryophyte, lichen and vascular plant species. Journal of Ecology 97: 886-900 • Pérez-Harguindeguy, N., S. Díaz, J.H.C. Cornelissen, F. Vendramini, M. Cabido & A. Castellanos. 2000. Chemistry and toughness predict leaf litter decomposition rates over a wide spectrum of functional types and taxa in central Argentina. Plant and Soil 218: 21–30. Table1. Arimethic mean of speciesdecompositionrates (K), polyphenolcontent (PC) and specificleafarea (SLA).