Effect of seed burial in different soils on the germination of three

Effect of seed burial in different soils on the germination of three specially
protected cactus species
Author(s): Gisela Muro-Pérez, Enrique Jurado, Joel Flores, and Jaime Sánchez-Salas
Source: The Southwestern Naturalist, 59(3):344-348.
Published By: Southwestern Association of Naturalists
DOI: http://dx.doi.org/10.1894/MLA-06.1
URL: http://www.bioone.org/doi/full/10.1894/MLA-06.1
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THE SOUTHWESTERN NATURALIST 59(3): 344–348
SEPTEMBER 2014
EFFECT OF SEED BURIAL IN DIFFERENT SOILS ON THE
GERMINATION OF THREE SPECIALLY PROTECTED CACTUS SPECIES
GISELA MURO-PÉREZ, ENRIQUE JURADO,* JOEL FLORES,
AND JAIME
SÁNCHEZ-SALAS
Facultad de Ciencias Forestales, Universidad Autónoma de Nuevo León, A.P. 41. Carretera Nacional km. 145, Linares,
N.L. 67700, México (GM, EJ, JS)
Instituto Potosino de Investigación Cientı́fica y Tecnológica, A.C., División de Ciencias Ambientales.
Camino a la Presa San José No. 2055, Lomas 4ª Sección, San Luis Potosı́, 78216, S.L.P., México (JF)
Facultad de Ciencias Biológicas-UJED, Av. Universidad s/n, Fracc. Filadelfia, Gómez Palacio 35010, Dgo., México (JS)
*Correspondent: enrique_jurado@hotmail.com
ABSTRACT—Seedling establishment of many cactus species appears to be more frequent under canopies of
nurse plants, which provide a less stressful microenvironment. Under these nurse plants, nutrient levels in the
soil could be higher than in surrounding areas; these higher nutrient levels could promote higher seed
germination. Seed burial under nurse plants may occur by seeds falling in the litter or in soil cracks; however,
buried seeds are in the dark, which has been shown to inhibit seed germination for some cactus species. We
measured germination percentage on nutrient-rich soil from under nurse mesquites and in soil from open
spaces, and the effect of seed burial (buried and unburied seeds) on seed germination of three cactus species
(Coryphantha durangensis, Peniocereus greggii, and Echinocereus longisetus) that grow under nurse plants in the
Chihuahuan Desert. Echinocereus longisetus had very low germination across substrates. Coryphantha durangensis
had higher germination on mesquite soil than on poor soil, and its buried seeds had lower germination than
seeds on the soil surface. Germination of P. greggii seeds was higher on mesquite soil than on poor soil, and its
buried seeds had lower germination than seeds on the soil surface.
RESUMEN—El establecimiento de muchas especies de cactus parece ser más frecuente bajo la copa de plantas
nodriza, la cual provee un microambiente menos estresante. Bajo estas plantas nodrizas, los niveles de
nutrientes en el suelo podrı́an ser más altos que en los alrededores, ası́ que estos nutrientes podrı́an promover
la germinación más alta de semillas. Bajo plantas nodriza puede ocurrir enterramiento de semillas, ya que las
semillas caen en la hojarasca o en las grietas del suelo; sin embargo, las semillas enterradas están en la
oscuridad, y se ha encontrado que esta condición inhibe la germinación de semillas de algunas especies de
cactus. Se evaluó el porcentaje de germinación en suelo rico en nutrientes bajo mezquites nodrizos y en suelo
de espacios abiertos y el efecto del enterramiento de las semillas (enterradas y no enterradas) en la
germinación de semillas de tres especies de cactus (Coryphantha durangensis, Peniocereus greggii y Echinocereus
longisetus) que crecen bajo plantas nodriza en el desierto Chihuahuense. Echinocereus longisetus tuvo muy baja
germinación en ambos tipos de suelo. Coryphantha durangensis presentó mayor germinación en suelo de
mezquite que en suelo pobre, y sus semillas enterradas tuvieron menor germinación que las de la superficie
del suelo. La germinación de P. greggii fue más alta en suelo de mesquite que en suelo pobre, y sus semillas
enterradas tuvieron menor germinación que las semillas que estuvieron en la superficie del suelo.
Favorable conditions for recruitment in arid systems
are rare because of prevailing harsh conditions (Flores
and Jurado, 2003; Zhang et al., 2011). Seedling establishment of many species appears to be more frequent under
canopies of adult plants of other species that provide a
less stressful microenvironment (Ellner and Shmida,
1981). This association of emergent seedlings and adult
plants has been called ‘‘nurse plant syndrome’’ (Niering et
al., 1963) or ‘‘nurse–protégé’’ interaction (Cody, 1993;
Flores and Jurado, 2003).
The causes of nurse–seedling relationships can vary
between species and environments, and it is possible that
multiple causes account for this association (Flores and
Jurado, 2003). For example, a larger number of seeds can
be recruited under shrubs compared with bare soil (seed
trapping); more water is available under established
shrubs than on bare soil (moisture safe site); more
nutrients are available in the soil under established
shrubs than under surrounding soil (nutrient safe site);
greater protection of protégé species from grazing and
trampling is available under shrubs (safe site from
herbivores), or greater physical support for protégé
species is available, at least in the early stages of their
life cycle (physical support safe site).
September 2014
Muro-Pérez et al.—Seed burial effect on cactus germination
Nutrient levels in the soil could be higher under the
canopies of established shrubs than in surrounding soil as
a result of nutrient concentration from vertical and
horizontal root uptake, accumulation of litter, increased
bird and insect droppings, and, in some cases, nitrogen
fixation (Flores and Jurado, 2003). These higher nutrient
levels in the soil could promote higher seed germination
(Godı́nez-Álvarez and Valiente-Banuet, 1998; Baskin and
Baskin, 2001).
Many cactus species grow under nurse plants (Flores
and Jurado, 2003). Soil characteristics have been found to
affect seed germination of several cacti, like Carnegiea
gigantea and Stenocereus thurberi (McDonough, 1964),
Ferocactus histrix (Del Castillo, 1986), Mammillaria heyderi
(Trejo-Hernández and Garza-Castillo, 1993), Turbinicarpus
polaskii, T. schwarzii, and Echinocereus morricallii (Jolly and
Lockert, 1996). The soil under mesquite plants has been
found to have more organic matter and nutrients than
soil from open areas (Muro-Pérez et al., 2012); however,
there are no studies evaluating whether the soil under
nurse plants, likely to have more nutrients, results in
higher seed germination than soil from open spaces.
Nutrients in the soil are important for germination of
some species (i.e., biological soil crusts) that have higher
nutrients than soils without them, and have a positive
effect on the seed germination of the cactus Myrtillocactus
geometrizans (Rivera-Aguilar et al., 2005).
Another factor influencing germination and seedling
emergence is the depth of seed burial in the soil (Fuchs et
al., 2000; Traba et al., 2004; Flores-Cano et al., 2012). Seed
burial may be promoted by abiotic-driven soil disturbances, such as those caused by water and wind, as well as by
biotic factors, including the foraging behavior of seed
dispersers and earthworm activity (Vander-Wall 1990,
1993; Chambers and MacMahon, 1994; Renard et al.,
2010). Seed burial helps seeds escape from postdispersal
predation and prevents death of the embryo by desiccation or exposure to extreme temperatures during an
unfavorable season (Borchert et al., 1989; Vander-Wall,
1990; Seiwa et al., 2002; Cheng et al., 2007). Burial may
occur by seeds falling in the litter or in soil cracks, and is
important for germination, because it may provide
benefits such as reduction of air exposure, maintenance
of high humidity levels, and protection against extreme
temperatures and foraging granivores (Everitt, 1983;
Seiwa et al., 2002; Li et al., 2012). However, buried seeds
are in the dark, which has been shown to inhibit seed
germination for some cactus species (Benı́tez-Rodrı́guez
et al., 2004; Flores et al., 2006, 2011).
We evaluated germination percentage on nutrient-rich
soil under nurse plants and poor soil from open spaces,
and the effect of seed burial (buried and unburied seeds)
on seed germination of three cactus species: Coryphantha
durangensis, Peniocereus greggii, and E. longisetus, that grow
under nurse plants (Muro-Pérez et al., 2012). The three
345
studied species are under special protection status (Hunt,
1992; SEMARNAT, 2010).
MATERIALS AND METHODS—Study Area and Studied Species—
Coryphantha durangnesis, P. greggii, and E. longisetus are
distributed in a canyon in Cañón de Fernández State Park
(25827 0 N, 103846 0 W) within the Chihuahuan Desert in México at
an elevation of 1,200 m above sea level. Temperature ranges
from 1.68C (in January) to 37.48C (in June), with an annual
rainfall of 200–350 mm. The main plant communities are
thornscrub dominated by either small-leaved, rosette, or
hemisucculent and succulent plants (Muro-Pérez et al., 2012).
Coryphantha durangensis grows 10–15 cm high and 4–6 cm wide
as isolated individuals or in small clumps (Bravo-Hollis, 1978;
Bravo-Hollis and Sánchez-Mejorada, 1989). Echinocereus longisetus
is cylindrical, 15–30 cm high and 5–7 cm wide (Bravo-Hollis and
Sánchez-Mejorada, 1989). Peniocereus greggii has an erect curved
stem 20–60 cm high and 3 cm in diameter (Bravo-Hollis and
Sánchez-Mejorada, 1989).
Area of Species Distribution—Coryphantha durangensis grows in
Coahuila and Durango, México; P. greggii is distributed in
Chihuahua, Coahuila, Durango, Nuevo León, Sonora, and
Zacatecas, México (Guzmán et al., 2003) as well as in Texas,
New Mexico, and Arizona, USA (Sánchez-Salas et al., 2009).
Echinocereus longisetus is found in Coahuila and Nuevo León
(Guzmán et al., 2003). Seeds from these species were collected
in the Cañón de Fernández, an area with high cactus richness in
the southern Chihuahuan Desert (Valencia-Castro, 2005).
Seed Collection—Fruits from the three cactus species were
collected in April 2009 at Cañón de Fernández State Park from
at least 10 mother plants. Fruits were placed in paper bags and
set to dry at room temperature for a month to prevent any
moisture development that might prompt germination or
decomposition (Moreno et al., 1992).
Experimental Design—Germination was recorded daily for 1
month as the emergence of the radicle or any part of the
embryo, as recommended for arid-zone plants (Baskin and
Baskin, 2001). The experimental design was complete random
factorial 3 · 4 · 5. There were 20 seeds per plot and five plots
per line, with a total of 100 seeds per treatment. There were four
treatments: 1) seeds placed on mesquite soil, 2) seeds placed on
poor soil, 3) seeds buried at 0.5 cm under mesquite soil, and 4)
seeds buried 0.5 cm under poor soil.
Statistical Analyses—Treatment and species were used as
factors for the analysis of variance. Percentage germination
data were arcsine transformed before analysis to comply with
analysis of variance requirements.
RESULTS AND DISCUSSION—Previous studies have shown
that nutrient levels in the soil are higher under the
canopies of established shrubs than in the surrounding
soil (Flores and Jurado, 2003; Muro-Pérez et al., 2012).
We hypothesized that higher nutrient levels in the soil
could promote higher seed germination (Godı́nezÁlvarez and Valiente-Banuet, 1998; Baskin and Baskin,
2001). Echinocereus longisetus had very low germination
(4% – 1.2%) across substrates, and there were no
significant differences among treatments (F = 2.66; P =
0.08). Coryphanta durangensis (Fig. 1) had higher germination on mesquite soil (96% – 0.024%) than on poor
346
vol. 59, no. 3
The Southwestern Naturalist
FIG. 1—Germination of Coryphanta durangensis. Different
lowercase letters represent differences between means (a =
0.05).
soil (56% – 0.605%; F = 21.09, P < 0.0001). A similar
result was found for P. greggii seeds (Fig. 2), which had
higher germination on mesquite soil (85% – 0.076%)
than on poor soil (69% – 0.55%; F = 7.67, P < 0.0001).
The results for these two species are in agreement with
the proposed hypothesis, in that more seeds of C.
durangensis and P. greggii germinated on mesquite soil
than on poor soil. For these species, germination on poor
soil was also high; suggesting that seed distribution and
seedling establishment may differ under both conditions
for other reasons besides soil quality, such as hydraulic
uplift or protection from trampling (Flores and Jurado,
2003). These results should be considered in conservation programs for these protected species.
We also hypothesized that cactus seeds would not
germinate when buried, because they would be in total
darkness and require light to germinate (Flores et al.,
2006, 2011). Accordingly, we found very low germination
for buried seeds of C. durangensis (Fig. 1) and P. greggii
(Fig. 2). Coryphantha durangensis buried seeds had lower
germination (2% for seeds buried in mesquite soil and no
germination for seeds buried in poor soil) than seeds on
the soil surface (F = 21.09, P < 0.0001). Germination of P.
greggii buried seeds had lower germination (F = 7.67, P <
0.0001) than seeds on the soil surface (6% – 0.604%
under mesquite soil and 8% – 0.152% under poor soil).
Most cactus seeds need light to germinate (Flores et al.,
2011); hence it is possible that ungerminated buried
seeds in our study were dormant, because burial is an
essential prelude to dormancy in several species (Thompson et al., 1993; Grime, 2001). Burial may also provide
safe sites from harsh conditions for seeds until germination occurs, although other processes such as seed
predation and fungal attack could also be operating
FIG. 2—Germination of Peniocereus greggii. Different lowercase
letters represent differences between means (a = 0.05).
(Borchert et al., 1989; Vander-Wall, 1993; Seiwa et al.,
2002).
Seeds of E. longisetus appear to exhibit seed dormancy
even under light conditions. In arid and semiarid
environments, seed germination and seedling establishment are infrequent because of extreme temperatures
and low water availability (Flores and Jurado, 2003; Flores
et al., 2004). Thus, a common plant strategy in these
environments is seed dormancy, which is found in several
plant families (Baskin and Baskin, 2001; Jurado and
Moles, 2003; including Cactaceae (Rojas-Aréchiga and
Vázquez-Yanes, 2000; Flores et al., 2005, 2006, 2008,
2011).
CONCLUSIONS—Echinocereus longisetus had very low germination across substrates. Seeds of C. durangensis and P.
greggii had higher germination on soil from under nurse
mesquites than on poor soil. Buried seeds of both species
had lower germination than seeds on the soil surface.
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