Selección temprana de clones de Gmelina arborea ROXB con base en su comportamiento fisiológico en vivero versus plantación, en el Pacífico Sur de Costa Rica
Ávila-Arias, Carlos Enrique
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Gmelina arborea Roxb. is an excellent choice to ensure supply of raw material for the forest industry (Kumar 2007, Adebisi et al. 2011, Wee et al. 2012). Its importance is due to a rapid initial growth and its easy adaptation to a variety of site conditions (Adebisi et al. 2011). The nursery phase is essential to evaluate a number of characteristics involved with plant productivity in different conditions, obtaining valuable information to determinate the potential of the selected genotypes. The plant physiology knowledge plays an important role in the understanding the plants - environment interactions (El- Sharkawy 2006, da Matta 2007), and the conditions must be provide to the different genotypes in the nursery to express their best photosynthetic performance (Triono 2004), thereby achieving more plants prepared to deal with adverse field conditions. Once past the nursery stage, the establishment of trees in open terrain is a critical period where adaptation strategies are implemented to the soil and climatic conditions of the site. Here changes occur in the morphological and physiological characteristics, which directly influence growth rates. The study of physiological characteristics must be considered a priority by their genetic content and its relationship with productivity in forest plantations. Photosynthesis is the most important process associated with growth; their relationship is not simple and has been discussed for many years (Flood et al. 2011). Photosynthetic rate is considered an important criterion with potential for early selection (Lapido et al. 1984). 8 The development of superior genetic material points out the need to identify parameters for early selection of genotypes with superior growth. To Zas et al. (2005), comparing the juvenile behavior in nursery and adult behavior of genotypes in field through retrospective trials, becomes the main alternative in the search for appropriate juvenile parameters that maximize genetic correlation nursery - field. However, beforehand it is noted that the correlation between morphological and physiological parameters and growth in the field are generally poor ( Blake and Bevilacqua 1990), primarily in young trees, since the genotype has not yet expressed some of its characteristics is a result of genotype -environment interaction at early ages (Adams et al. 2001, Codesido et al. 2012). Therefore, the question of interest is: what is the magnitude of nursery - field, or juvenile –adult, correlation to expect and wich parameters are best suited to perform a retrospective analysis? The aim of this investigation was to determine the physiological performance of five clones of both stage rooted cuttings in nursery and planting at 15 months of age, and with this information to identify possible juvenile - adult correlations, to finally determine its potential for early selection of Gmelina arborea genotypes. The physiological evaluation of 1, 2, 5, 6 and 12 Gmelina arborea clones in rooted cuttings condition was conducted in the nursery of the Institute of Research and Forestry Services (INISEFOR) located at La Palma, Puerto Jimenez, Golfito, and Puntarenas. Physiological measurements were made when cuttings had rooted, which is when they were ready to leave the mini-tunnels to acclimation condition in semi - open nursery. The light curve response and gas exchange performance of the clones was evaluated both. For the evaluation of both processes a portable photosynthesis system (CIRAS-2, PP Systems) was used. To obtain photosynthetic parameters was used a CO2 average of 360 ppm ± 16.05 ppm and an air temperature of 30 within the trough. Response curves to light was evaluated for 14 levels of density photosynthetic photon flux incident (0, 50, 100, 150, 200, 250, 300, 350, 400, 600, 800, 1000, 1200, 1400 μmol photons m - 2 s- 1). Evaluation of gas exchange was 9 performed to a PAR of 1000 μmol photons m-2 s -1 ± 4.57 μmol photons m-2 s -1, the physiological parameters obtained were: net photosynthesis (An), stomatal conductance (Gs) , transpiration (E) and water use efficiency (WUE ) . Physiological evaluation of the five clones in 15 months plantation was made in a six randomized complete blocks clonal trial. Individual clones 1, 2, 5, 6 and 12 in each of the blocks 1 to 5 was evaluated, for a total of 25 evaluated trees in this condition. The response to the light curve of the clones and its gas exchange performance was investigated both. For the evaluation of both processes a portable photosynthesis system (CIRAS-2, PP Systems) was used , in a clear day. To obtain photosynthetic parameters was used a CO2 average of 360 ppm ± 16.05 ppm and an air temperature of 30 within the trough. Measurements were made on fully developed, expanded and illuminated leaves, located in the upper layer of the crown. Response curves to light was evaluated for 17 levels of density photosynthetic photon flux incident ( 0 , 50 , 100, 150 , 200, 250 , 300 , 350, 400 , 600, 800 , 1000 , 1200, 1400 , 1600, 1800 2000 μmol photons m-2 s -1). Evaluation of gas exchange was performed to a PAR of 1000 μmol photons m-2 s -1 ± 4.57 μmol photons m-2 s -1, the physiological parameters obtained were: net photosynthesis (An) , stomatal conductance (Gs) , transpiration (E) and water use efficiency (WUE). Statistical analysis of both conditions was performed by InfoStat (2012) software. Also an analysis of variance was performed on each stage , and a comparison of means using the Tukey test (p < 0.05 ) to determine differences between the five genotypes for each physiological parameter investigated. Finally, the average value of each clone for each physiological parameters assessed, we proceeded to construct a matrix of correlations juvenile (rooted cuttings) - adult (plantation of 15 months age), to calculate the Pearson correlation coefficient between the means of the parameters evaluated. 10 No statistically significant differences between genotypes were recorded for any of the investigated parameters obtained from the light curves in rooted cuttings stage in nursery (convex curve, apparent quantum yield, maximum photosynthetic rate and light saturation point). The maximum photosynthetic rate at light saturation (Anmax) ranged from 6.99 μmol m -2 s -1 and 8.58 μmol m-2 s -1, with a mean of 7.89 μmol m -2 s -1. The light saturation point (LSP) varied between 336.75 μmol m-2 s -1 and 394 μmmol m -2 s -1, with an average for the species 366.04 μmol m-2 s -1. The light saturation point average for the species rooted miniestaquilla condition (366.04 μmol m -2 s -1) suggests that the mini - tunnels rooting could be exposed to higher values of incident radiation, to obtain higher biomass production . No statistically significant differences were recorded between the five genotypes investigated for the physiological parameters obtained from the evaluation of gas exchange in stage of rooted cuttings, neither. Net photosynthesis (An) showed a variation from 8.14 to 10.45 μmol m -2 s -1 between clones, with an average of 9.63 μmol m -2 s -1 for the species. Stomatal conductance (Gs) reported variability from 120.97 to 154.40 mmol m-2 s -1, with an average of 142.83 mmol m-2 s -1. Transpiration (E) varied from 1.7 to 3.2 μmol m-2 s - 1, 2.40 in average. High efficiency in water use (WUE) among clones was recorded, which is a competitive advantage - adaptive, with values from 3.82 μmol m-2 s - 1 to 4.53 μmol m-2 s -1 with an average of 4.16 μmol m - 2 s-1. Although no statistically significant differences between the clones were presented, clone number six showed the most desirable values in most physiological parameters evaluated. Therefore, it is identified as the highest photosynthetic capacity investigated genotypes. No statistically significant differences were recorded between the five genotypes investigated for any of the parameters obtained from the response curves to light in the plantation at 15 months age stage. The maximum photosynthetic rate at light saturation (Anmax) ranged from 22.36 μmol CO2 m- 2s- 1 and 30.08 μmol CO2 m- 2s -1, with an average of 25.23 μmol CO2 m- 2s- 1. The light saturation point (LSP) 11 average recorded was 1499.95 μmol CO2 m -2s-1 , ranging from 1158.26 μmol m-2 s -1 and 2110.26 μmol m-2 s -1. Moreover, no statistically significant difference among the five clones for any of the physiological parameters obtained from the evaluation of the process of gas exchange was detected. Net photosynthesis (An) ranged from 19.47 μmol m- 2s- 1 to 22.62 μmol m -2s-1 , with an average of 20.87 μmol m- 2s- 1. Stomatal conductance (Gs) ranged from 185.53 mmol m- 2s- 1 to 289.53 mmol m- 2s- 1. The average transpiration of the investigated genotypes was 4.38 μmol m-2 s -1. Efficiency in water use among the five genotypes averaged 5.03 μmol m-2 s - 1, was varying from 5.76 μmol m-2 s – 1 to 4.31 μmol m-2 s -1. Although no statistically significant differences between the clones were submitted, clone 2 showed the most desirable values for the parameters of net photosynthesis (An) and water use efficiency (WUE) also presented the second best value in terms of transpiration (E) and stomatal conductance (Gs). As becomes the clone having the most efficient photosynthetic capacity in plantation condition at 15 months of age. The analysis of correlations nursery - field intended to increase the accuracy of the information supporting silvicultural production packages. The nursery net photosynthesis (Pn- V) was direct and slightly correlated with stomatal conductance (Gs-C) and transpiration (E-C) both in the field ( r = 0.27 and r = 0.32 respectively). Transpiration nursery (E-V) showed an inverse correlation with net photosynthesis (Pn -C), water use efficiency (WUE -C) and total tree height (Ht-C), all in the field. This suggests preliminarily that genotypes recorded lower transpiration in the nursery could be linked with higher values of Pn- C, WUE-C and Ht-C. The efficient use of water in the nursery (WUE - V) recorded a moderate direct correlation (r = 0.45) with field photosynthesis (Pn-C). The efficient use of water in nursery (WUE-V) reported positive correlations, from moderate to strong for all genotypes, with Pn-C and WUE-C. Chlorophyll content in the leaves of rooted cuttings in nursery (Cloro-V) was directly correlated with Pn-C, suggesting that measuring the chlorophyll content in the leaves of rooted cuttings using a SPAD -502, could 12 discriminate the genotypes with higher net photosynthesis in field. The total height of the plants in the nursery (Ht- V) should not be used for early selection bearing no consistent correlation with dasometric parameters in field. These results keep latent the hypothesis that is possible to find physiological variables that can be carried out early selection of the most desirable genotypes. Caution must to be tacked when trying to select using information at such young ages, until genotypes are fully expressed phenotype through interaction with environmental conditions. Furthermore, the study of a single parameter does not guarantee selection. It´s necessary to determine whether physiological variables are heritable through genetic analysis, for which a larger experimental sample is needed.
Proyecto de Graduación (Maestría en Gestión de Recursos Naturales y Tecnologías de Producción) Instituto Tecnológico de Costa Rica. Escuela de Ingeniería Agroforestal, 2013.