*Dirección para correspondencia:

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]]> Abstract

Alibertia patinoi (Rubiaceae). Alibertia patinoi (Rubiaceae) is of  economic and cultural importance for communities in the Colombian Pacific and Amazon regions, where it is cultivated and mature fruits are highly ]]> Alibertia patinoi, and relate them to its habitat. Fruits were collected from a mixed food crop and a commercial plantation in Guaimía village, Buenaventura, Colombia, a tropical rain forest area. We measured length, width, thickness, mass (n=1 400), and moisture content of seeds (n=252). Primary dormancy tests were conducted (n=200), followed by imbibition (n=252) and germination dynamics, under different conditions of light ]]> A. patinoi is adapted to conditions of mature tropical rain forests.

Key words: climax species, far-red ]]>

Resumen

La germinación y ]]> Alibertia patinoi se describen y se relacionan con el hábitat de la especie, el Bosque Pluvial Tropical Americano. Se midió la longitud, ancho, grosor, peso y contenido de humedad de las semillas. Se realizaron pruebas de latencia, imbibición y dinámica de  la germinación con diferentes condiciones de luz y temperatura específicas de claros y de sotobosque cubierto por un dosel denso. Además, se estableció el comportamiento de almacenamiento de las semillas. El tamaño y  peso de las ]]> A. patinoi está adaptada a las condiciones del bosque lluvioso tropical maduro y se comporta como una especie que no es pionera.

Palabras  clave: luz rojo-lejano, bosque  pluvial  tropical maduro, especie no pionera, semillas sin latencia, estrategia de germinación rápida, semilla recalcitrante.

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Seed  biology  constitutes  a  key  element in clarifying the distribution and abundance patterns of species, and seed ecologists seek to understand how seed characteristics affect dispersal, colonization, and establishment of seedlings, and ultimately succession ]]>
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The establishment and survival of plant species in the rain forest are better known than germination and they vary with light condition (Paz et al. 1999). Seed morphology and shade tolerance  seem  to  organize  the  community of seedlings and saplings. In general, recruitment of both small and large-seeded species is more frequent in lighter parts of the understory than  in  shaded  understory  ]]>

However,  in  the  closed-canopied  rain  forest the establishment of large-seeded species is favored, and seedlings of about half of the seed species come from fruits produced in the forest, and half from fruiting trees from outside the forest (Martínez-Ramos & Soto-Castro 1993). Large seeds are slowly removed by mammals from their sites (Paine & Beck 2007), their germination is not regulated by ]]> et al. 1999, Svenning & Wright 2005). For instance, a low ratio between red (R) and far-red light (FR) occurs in understory and determines germination and establishment of plants in the canopied forest (Orozco-Segovia et al. ]]>

Although the abiotic conditions of the tropical  rainforest  are  highly  variable,  there are two groups of environmental conditions defined by the vegetation. A first group is found in open areas and forest clearings, where the temperature fluctuates widely and the amount of radiant energy from the sun is high and has a high ratio of red/far red. The other group is found on the floor of dense canopy ]]>

According to the shade tolerance of seeds and  seedlings,  species  can  be  classified  as non-pioneer or pioneer. Following Swaine & Whitmore  (1988),  seeds  of  pioneer  species can only germinate in forest clearings or open areas, where the ]]>

Rubiaceae is one of the plant ]]> et al. 2004). In Colombia it is one of the most diverse and abundant families in the Andean region, not the least in the rain forests of the Amazonian and Chocó biogeographic regions (Mendoza et al. 2004). Alibertia patinoi (Cuatrec.) Delprete & C. Pers- son is a Rubiaceae of economic and cultural importance  for  communities  in  the  Colombian Pacific and Amazon regions where this is ]]> A. patinoi seeds, and this study aimed to investigate and describe the physiological and morphological traits of the seeds of A. patinoi and to relate them to its habitat.
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Materials and methods

Collection site: The fruits were collected from a mixed plantation of about 2ha in the village of Guaimía (3°43’6.97” N - 76°57’47.11” W), located in the ]]>
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Reproductive phenology and geographic distribution: To establish the distribution of the species and the reproductive phenology, we consulted the data bases of the herbaria of the Missouri Botanical Garden (MO), Universidad del  Valle  (CUVC),  Universidad  del  Chocó (CHOCO), Herbario Nacional Colombiano (COL), and the Colombian Instituto Amazónico de Investigaciones Científicas ]]>

Seed morphometrics: We collected and weighed 10 ripe fruits using a Mettler Toledo PL1501S scale. The seeds from each fruit were disinfected with 2% sodium hypochlorite solution for five min, and then were dried indoors under shade and with aeration for 24h at ambient temperature (ca. 25°C). The morphological variables of the seeds measured were length, width, ]]>

Seed moisture content: Eighteen ]]>

Primary dormancy: The germination tests were conducted with four replications of 50 recently extracted seeds (n=200), randomly selected from 30 ripe fruits. These seeds were submitted  to  dormancy  breaking  treatments: (1) Intact seeds pre-treated with distilled water for  24h  (wet  control);  (2)  Seeds  mechanically scarified with a scalpel; (3) Intact seeds (dry control).

After treatments, ]]> size with two layers of wet paper to germinate in a Kryoven incubator (irradiance 142.7μmol/m2.s) at constant temperature (31°C) and a 12/12h photoperiod. The test lasted 23 days. Germination was assessed every 48h from the seventh day. Petri dishes of 90mm size were used for this and all germination tests.

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Germination dynamics and determination of the ecological group: To measure the response of seeds to their natural environmental  conditions,  the  experimental  conditions of temperature were established according to climatic data (mean-minimum/mean-maximum annual; mean/mean-maximum annual) reported for Buenaventura from 1961 to 1990 (IDEAM 2001). The day/night temperature regimes used (20/30 vs. 25/30°C) had ]]>

A factorial experiment (2x5) was ]]>

The far-red lighting was obtained by filtering the light produced by two incandescent 60W bulbs (Osram perla) through two layers of Lee 26 filter and one layer of Lee 120 filter (Benvenuti et al. 2001). The red light was generated by two 20W white fluorescent light tubes (Sylvania F20T12/D). Total darkness was achieved by storing the Petri dishes in double high-density black ]]>

To describe the germination behavior (distribution of germination in time) and under- stand how temperature fluctuation affects this behavior, we used seeds treated to 12/12h photoperiod only at alternate temperatures 20/30 and 25/30°C.

The germination test ]]>

Behavior of seeds in storage: Seed behavior was determined by following the Hong & Ellis (1996) ]]>

Analysis of physiological variables: The emergence of the radicle was the criterion of germination. Germination percentages were transformed with the arc-sine function to stabilize the variances of the observations (Kuehl 2001). The mean germination time was calculated as the mean time to achieve maximum germination of a seed lot. Meanwhile, mean germination rate was ]]>

The synchrony of germination was determined  by  the  Z  index,  which  measures  the synchrony of germination of a seed with another seed included in the same repetition of a treatment. Z varies between zero and one; it is one when the seeds germinate at the same time and zero when at least two seeds can germinate at distinct times (Ranal & ]]>

Depending on the behaviour of the data regarding normality and variance, we applied parametric tests for comparison of measurements  (ANOVA, Tukey,  Student´s  t-test  and Dunnett) or non-parametric tests (Mann-Whitney). Data were analyzed with the Minitab Statistical Software program version 16. Differences were considered significant at α=0.05.
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Results

Reproductive phenology and geographic distribution: According to the herbaria consulted, which ]]> A. patinoi specimens collected  between  1944  and  2008,  this  species is distributed along the American Tropical rainforest (sensu Primack & Corlett 2005) from Costa Rica to Northern Ecuador, crossing the Chocó biogeographic region and reappearing in the Colombian Amazon, separated from the Chocó biogeographic by the Andean Mountains (Fig. 1). In 90% of the records, this species was registered between 0 and 330m, although ]]>
Seed morphometrics: The seeds collected in Guaimía, Buenaventura, measured 8.8±1mm length; 6.3±0.8mm width; 3.6±0.6mm thick; and a mass ]]> A. patinoi, with low variation coefficients within and among fruits. However, these features varied slightly according to the variation of fruit mass. Thus, the linear regression of the relationship between fruit mass and seed length, and between fruit mass and seed mass were very close to zero (Fig. 2). The first relationship was substantially linear (sensu Davis 1971) and statistically significant (p=0.021), ]]> sensu Davis 1971) and was not  statistically  significant  (p=0.08)  for  the 10 fruits used.

The size and mass of the seeds of A. patinoi varied slightly within and among fruits, while seed ]]> sensu Davis 1971), and statistically significant (p=0.012) (Fig. 3).

Seed moisture content: A. patinoi seeds were released from the mother plant with high seed moisture content (44.3±0.8%). In consequence, seeds presented continuous metabolism characteristic of recalcitrant species; these traits are typical of non-pioneer seeds of tropical rain forest (Hong & Ellis 1996, Baskin & Baskin1998).

Dormancy: The germination of ]]> sensu Baskin & Baskin 1998).

]]> Determination of the ecological group and germination dynamics: The seed germination under both alternating temperature regimes (20/30 vs. 25/30) and under all lighting conditions, including continuous darkness, was  very  high  (96.7-99.0%).  Further,  there was no difference in percentage germination among treatments with respect to quality of light (ANOVA, p=0.773). Nor was there an interaction between lighting condition and temperature  (Two  way ANOVA,  p=0.609). This means that A. patinoi ]]>

On the other hand, temperature did affect germination (ANOVA, p=0.016); the percent- age germination of seeds incubated at 25/30°C was greater than those incubated at 20/30°C. Mean germination time was less at 25/30°C than at 20/30°C (13.1d or 14.6d, respectively; Student’s  t-test,  p<0.001).  Germination  rate was greater for ]]>

The pattern of germination distribution over time (Fig. 4) allows us to understand the low synchrony of germination under both temperature regimes, since seeds ]]>

The seeds began to germinate on day seven and ended on day 25th. Germination occurred intermittently with two pulses of germination, on days 11th and 16th, one of rapid germination and one of late germination. When seeds were incubated at 20/30°C, the higher proportion of germination was on day 16th, ]]>

Behavior  of  seeds  in  storage:  A.  patinoi  seeds  were  sensitive  to  desiccation  and had recalcitrant storage behavior. When seed moisture content was high (40.3%), the viability of the seeds was high (98.8%), but when seed moisture content was below or ]]>


]]> Discussion

Size and mass of seeds are relatively constant in the population of A. patinoi studied with slight variation within a fruit and between fruits of different mass. According to Baker (1972) and Foster & Janson (1985), each ]]> A. patinoi seeds are within the range of size and mass of the tree species of mature tropical rainforest (Ng 1978, Foster & Janson1985).

A. patinoi seeds are released from the mother plant with high moisture content (ca. 44%), continuous metabolism, and have recalcitrant behavior. Therefore, A. patinoi would be restricted to constantly humid locations, where its seeds are protected from desiccation by a thick layer of leaf litter or by a dense canopy. The high seed moisture content and continuous metabolism favor rapid germination, given that the seeds are released ready to germinate.
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Percent germination is high (>96%) and does not differ under the light conditions tested, nor do temperature and light interact to affect germination. That is, seeds germinate equally well in light or darkness, and they germinate at high percentages under conditions of alternate temperatures with an amplitude of 5 or 10°C. Therefore, the seeds can germinate under conditions of dense canopies and thick layers of leaf litter (low red/far-red ratio and low temperature fluctuation) or buried (darkness ]]> A. patinoi a typical member of the ecological group “non-pioneer species” in the sense of Swaine & Whitmore (1988), and the requirements of the seeds to germinate are easily fulfilled under the specific conditions in the mature tropical rainforest, favoring rapid germination.

The low germination ]]> A. patinoi  germinates more efficiently in shady forests than in clearings and forest gaps, confirming that the species is a non-pioneer.

The physiological characteristics of A. patinoi seeds are ]]>

The  rapid  ]]> sensu  Ng 1978) is the establishment strategy of A. patinoi, and this behaviour is favored by seed physiological traits such as: (1) lack of primary dormancy; (2) ability to germinate over a range of light conditions; and (3) recalcitrant behavior,  seeds  with  high  moisture  content, and continuous metabolism. However, ability to germinate rapidly depends on seeds being exposed to the high temperatures characteristic of the shady tropical rainforest floor. This ]]>

In the mature tropical rainforest, ]]>
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One trait of seed survival is rapid germination, as it diminishes seed death by pathogenesis and predation because it reduces the time spent as a seed, given that the nutritional reservoir is greater for seeds than for seedlings. Besides,  seedlings  are  usually  less  susceptible to parasitism and depredation, especially when the seedlings grow slowly because their cell walls thicken rapidly (Augspurger 1984). In addition, rapid germination increases the concentration of seedlings ]]>

In conclusion, the seed physiological traits (i.e.,  rapid  germination  rate,  low  germination requirements, non-primary dormancy, ]]> A. patinoi, as well as seed size and mass, suggest that this species  is  well  adapted  to  its  mature  tropical rain forest habitat. In addition, this species is a typical member of the ecological group of “non-pioneer species” in the sense of Swaine & Whitmore (1988).


Acknowledgments

We wish to thank the community of Guaimía, Philip A. Silverstone Sopkin, Director of the CUVC herbarium, Yan A. Ramos, director of the CHOCO herbarium, Mercedes Andrade for her statistical advice, John Miles for reading the manuscript, Jorge Rubiano for the mapping, the Group of Research on Quantum Optics at the Universidad del Valle for the technical support, ]]>

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*Correspondencia:
Diego Fernando Escobar Escobar: Departamento de Biología, Universidad del Valle, Ciudad Universitaria Meléndez, A.A.  25360, Cali, Colombia. barescoesco@gmail.com
Alba Marina Torres G: Departamento de Biología, Universidad del Valle, Ciudad Universitaria Meléndez, A.A. 25360, Cali, Colombia. alba.torres@correounivalle.edu.com
1. Departamento de Biología, Universidad del Valle, Ciudad Universitaria Meléndez, A.A.  25360, Cali, Colombia; barescoesco@gmail.com
2. Departamento de Biología, Universidad del Valle, Ciudad Universitaria Meléndez, A.A. 25360, Cali, Colombia; alba.torres@correounivalle.edu.com

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