Factors Affecting Regeneration Potential of Quercus semecarpifolia, Smith: A Poor Regenerated Oak of Himalayan Timberline
Quercus semecarpifolia is a multipurpose tree species but facing the problem of poor regeneration in natural habitat. The seeds of Q. semecarpifolia shows the recalcitrant behavior as the seeds shed at high moisture content, short viable, desiccation and chilling sensitive and skip the maturation drying stage. To understand the regeneration potential of the species, seeds were examined under different temperature and light/dark conditions in intact form and after scarification and stratification. The finding indicates that the light, temperature, scarification and stratification have considerable effect on regeneration of Q. semecarpifolia when tested for radicle emergence and seedling recruitment under laboratory conditions. Higher (35°C) as well as lower (5°C) temperature did not favour radicle emergence, its growth and seedling establishment; however 15°C is best suited temperature to emerge radicle and root shoot development at which around 91% seeds resulted into seedlings. Scarification of seeds hardly matters for enhancement of radicle growth and seedling production significantly but light matters a lot. Light exhibits highest (90%) and fastest radicle growth (within 10 days) as well as shoot emergence (within 30 days) and survival percentage if compared with the germination in dark. Prechilling treatment at 0°C lost total viability even within 24 h.
November 02, 2011; Accepted: February 06, 2012;
Published: February 24, 2012
Quercus semecarpifolia, a high level Himalayan oak species forms timberline
in many of the Western Himalayan regions. The species has wider distribution
range from 1800 to 3500 m and phytosociological studies declare Q. semecarpifolia
as the single abundant species or less associated species in the study area
(Bisht, 2001). The species has a potential as a multipurpose
tree for the production of fodder, tannin, fuel wood and wood for agricultural
implements in the mountain areas, so the settlements in nearby areas highly
dependent on the species for their livelihood. The species is considered as
most older and overexploited plant of sub-alpine zones (Singh
et al., 2010). Low regeneration, short viability, failure of a good
seed crop every year, climate change, regular anthropogenic exploitation and
the high magnitude of human pressure on the species could be dangerous to the
existence of the species and in very near future the species may disappear from
the subjected regions. Some of the studies were conducted on phytosociology
and ecology of the species (Singh et al., 2010;
Singh and Rawat, 2010; Bhatt and
Ram, 2005; Shrestha, 2003) but the studies are limited
on regeneration and factors affecting it particularly in the Western Himalayan
perspective. The species need immediate attention for conservation of its genetic
resources because of great role of this tree in the economy as well as ecology
The seeds of Q. semecarpifolia behave as a recalcitrant seeds like many
other oak species (Bisht, 2001). Similar to all recalcitrant
seeds Q. semecarpifolia seeds shed at very high moisture content, undergo
a biphasic seed development and lack maturation drying, short viable, very big
in size, short storable, desiccation as well as chilling sensitive too (Bisht,
2001). Moreover the process of germination in these seeds was found to progress
very slowly and was interesting as well as different than other oaks and associated
species. In this species sprouting takes place immediately after shedding like
white oaks (Tilki, 2010). After emergence radicle first
grew to a length varying from 12-20 cm and subsequently began to grow in diameter.
Shoot and root later emerged from thick portion of the radicle and the remaining
portion of the radicle, towards seed gradually degenerated and seed was automatically
detached from the radicle (Bisht, 2001). All these characteristics
and low regeneration status of the species in nature make the seed interesting
and initiate us to propose the study to determine the regeneration potential
and impact of different factors on seedling establishment to develop conservation
strategies for Q. semecarpifolia. Regeneration studies are very acceptable
approach to understand the seed behavior and its requirement for germination
(Chauhan et al., 2006) and seedling recruitment,
for conservation (Sharma and Sharma, 2010; Srivastava
et al., 2011), reintroduction and mass propagation (Zaman
et al., 2011), technology development (Kumar
et al., 2011) and effective management studies (Wei
et al., 2009) of any of the species.
MATERIALS AND METHODS
Seeds (acorn sensu stricto) of Q. semecarpifolia (brown oak) were collected from the forest floor under the canopy of healthy tree, growing in the natural stand of Western Himalayan region near Duggalbitta (2590 masl) in district Rudraprayag, Uttarakhand, India. To collect the mature and immediately fallen fresh seeds, the forest floor was first swept to remove earlier fallen seeds and the seeds abscised within 24 h were collected for the regeneration studies. Natural shedding and easy sloughing out of cupule (a cup like structure by which approximately half of the seed enclosed) was considered as the maturity index of the seed.
To determine the effect of temperature on germination, mature seeds were kept at 5, 15, 25 and 35°C temperature in seed germinator. In addition to this, to determine the effect of light and dark, the seeds of Q. semecarpifolia were kept under light and dark conditions in the intact form and after removing the pericarp (scarified seeds) at 15°C temperature, which is the best suited temperature for germination. Mature intact seeds in light (IL), mature intact seeds in dark (ID) and mature scarified seeds in light (SL) and mature scarified seeds in dark (SD) were the conditions to analyze light/dark and scarification effect on regeneration.
Seeds were also sown after prechilling treatment for which, seeds were stored at 0°C in moist vermiculite and then sown to regenerate after 24 h to understand the behavior of seeds under the snow conditions in natural habitat during winter if the seeds not germinate early and lays as it is in situ.
For all the studies, the seeds were placed in styrofoam seedling trays filled
with the mixture of vermiculite and sand (3:1) in triplicate, each replicate
comprising 100 seeds. The sowing substratum (vermiculite and sand mixture) moistened
regularly with distilled water. Radicle emergence resulted shoot/root emergence
was noted as the criterion for germination because all the seeds of the Q.
semecarpifolia already emerges radicle immediately after shedding from tree
but all can not produce seedlings even after radicle emergence. Increase in
radicle length and expansion in radicle diameter in the crucial and important
stage resulted into seedlings. So, the observations were made for increase in
radicle length, expansion in radicle diameter leading shoot/root emergence resulting
successful seedling establishment in all these laboratory conditions. Statistical
analysis was carried out by using ANOVA.
Seed germination leading radicle emergence, its growth and seedling production
in Q. semecarpifolia showed disappointing results under natural condition
on the forest floor (Bisht, 2001) in contrast to laboratory
where not only the higher percentage of seeds resulted into germination but
also the seedlings establishment was high. As high as 92% seeds had radicle
emergence at laboratory within 16 days after sowing, resulting shoot emergence
in 90% seeds within a month and only 2% degenerated after radicle emergence
(Fig. 1, 2) but in situ only 5% seedlings
were recovered even after next growing season (Bisht, 2001).
||Percent seedling emergence in Q. semecarpifolia seed
sown at 5, 15, 25 and 35°C temperature under laboratory conditions
|| Percent radicle growth in intact and scarified seeds of Q.
semecarpifolia under laboratory conditions in light and dark
|| Percent seedling emergence from intact and scarified seeds
of Q. semecarpifolia under laboratory conditions in light and dark
Freshly collected seeds of Q. semecarpifolia when tested for the germinability under different temperatures revealed that the higher (35°C) as well as lower (5°C) temperature did not favour germination in these seeds. All the seeds emerge radicle irrespective of the conditions applied. Maximum percentage of seedling (90) was achieved at 15°C as compared to 86% at 5°C as well as 25°C (Fig. 1). Elevated temperature further reduced radicle growth of these seeds as only 66% seed achieved required length of radicle and later recovered as seedlings at 35°C. With temperature the days for onset of germination also varied. Germination under different temperature for 8 days had 80-99% correlation coefficient with significant variation with F = 4.22 (F critical = 3.00, p = 0.01) due to different temperature conditions, however, the variation was less pronounced. This is due to more or less similar germination percentage at different temperature conditions.
Seeds sown after removing the pericarp (scarified seeds) did not affect regeneration considerably but the scarified/intact seeds under light and dark conditions at room temperature exhibited significantly different results in respect of radicle growth and shoot emergence and has been depicted in Fig. 2. Highest and fastest radicle growth was recorded in the seeds sown in scarified state under the light (92%) within 10 days. Contrary to this, intact seeds in dark had lowest and slowest performance and took 16 days to reach upto maximum (50%). The results are highly significant (F = 30.44, F critical = 3 at p level<0.01) due to around 87-89% positive correlation coefficient between ID (mature intact seeds in dark) and SL (mature scarified seeds in light) as well as ID (mature intact seeds in dark) and SD (mature scarified seeds in dark) and maximum 99% positive correlation between SD and SL.
Percent seedling emergence from intact and scarified seeds of Q. semecarpifolia under laboratory conditions in light and dark has been depicted in Fig. 3. Shoot emergence also followed trend similar to that of radicle emergence and its growth wherein shoot emergence in light germinated excised seeds was earliest and in highest percentage (90% within 25 days) while dark germinated intact as well as excised seeds had lowest and slowest emergence of shoots (45 and 55%, respectively within 32 days). Although, removal of pericarp does not seem to be essential for the germination of the seeds of Q. semecarpifolia, it had promoting effect on germinability of these seeds. Emergence of shoots took place after 17 days in SL, 18 days in ID and IL and 25 days in SD conditions. Also, unlike the radicle emergence differences in the percentage of seeds resulting into shoot emergence in light germinated intact seeds and dark germinated excised seeds were considerably high and not only the final percentage varied in the two but even initially the differences were high.
Regeneration studies on natural regeneration status of Q. semecarpifolia
conducted previously by Thakuri (2010), Singh
and Rawat (2010), Tashi (2004), Shrestha
(2003), Bisht (2001) and Vetaas
(2000) and agreed on very low regeneration under different microclimatic
conditions. High percentage of seeds degenerated on the forest floor even after
sprouting, percentage of such seeds ranging from 74-96% depending on the condition
in which seeds were sown in-situ (Bisht, 2001).
Unlike in situ, 90% seedlings were recovered within one month in laboratory
conditions. This is due to promoting effect of light and temperature on germination
of the seeds in controlled laboratory condition which must have ecophysiological
implications. In natural conditions also, seeds must germinate immediately during
rainy season to avoid the desiccation thereafter and escape to harsh chilling
temperate environment as the seed of Q. semecarpifolia are chilling and
desiccation sensitive (Bisht, 2001). Light had significant
influence on radicle growth and seedling establishment of Q. semecarpifolia
seeds wherein a higher percentage of seeds germinated under light than in dark
like many other temperate tree species viz., Q. robur (Kuhne
and Bartsch, 2007) Betula papyrifera (Bevington
and Hoyle, 1981), Picea marina (Farmer et
al., 1984) and Pinus contorta (Li et
However, in most of these cases, stratification of the seeds resulted in identical
germination percentages in light as well as dark. Absolute darkness and 90 days
prechilling treatment ceased germination but alteration of light dark conditions
enhance germination in a woody species, Vaccinium arctostaphylos (Shahram,
2007). Evidences of seed germination enhancement in continuous dark and
reduction in continuous light were presented but in presence of growth regulators
in Digitaria exilis by Idu et al. (2008).
It is evident from these studies that even if light is not essential for germination
but it may have a promoting or retarding effect on germinability of seeds.
Studies reviewed by Baskin and Baskin (1998) indicate
that seeds of different temperate and sub-alpine species have different responses
to light and dark as well as varying temperature regimes. For example, a trans
Himalayan medicinal plant, Bunium persicum germinate only at 4°C
and shifting of seeds from 4-25°C ceased germination (Sharma
and Sharma, 2010) but Q. semecarpifolia respond well at 15°C
in presence of light however lower (>15°C) as well as higher (<30°C)
temperature did not favour the regeneration similar to the Campsis radicans
(Chachalis and Reddy, 2000). However, in crop plants
like Glycine max and Pisum sativum reduction in percentage and
rate of germination was noticed at high temperature (Beena and Jayaram, 2010).
But the germination in Brassica tournefortii does not affected by light
at optimum temperature but at low temperature, light inhibit germination (Chauhan
et al., 2006).
Regeneration process in this species in nature begins with radicle emergence
which takes place immediately after seed shedding during spring in the month
of July-August unlike most of the oak species viz., Q. leucotrichophora,
Q. robur, Q. glauca etc. in which seed shedding occurred during winter in
November-December. Radicle emergence followed by thickening of radicle and most
of the seeds remain in this condition over winter. Seedling emergence (roots
and shoot emergence) from this swollen portion takes place after a longitudinal
split only in the subsequent year in natural condition (Bisht,
2001) when light intensity and temperature conditions increase in the timberline
after snowmelt. It can be presumed that this thick portion of radicle requires
a chilling treatment for seedling emergence as an adaptive strategy to over-winter
under its natural conditions/habitat where such conditions prevail subsequent
to its germination (Bisht, 2001). However, the freshly
collected seeds of Q. semecarpifolia sown in the laboratory at high
temperature conditions (30°C) underwent normal course of events leading
to seedling emergence and did not require any chilling or low temperature cycle/condition
for the same. The process of regeneration in these seeds was found to progress
slow and low in nature but in favourable light and temperature conditions in
laboratory high as well as early seedling establishment occurred. This rules
out any such possibility of low temperature requirement in these seeds but probably
an adaptive strategy against typical temperate conditions. The seeds of some
other temperate plants viz., Quercus, Trillium, Viburnum, Convallaria and
Polygonatum species also exhibit epicotyle dormancy where seeds germinate
and put out a radicle in the autumn without prior chilling (Baskin
and Baskin, 1998). However, development of the epicotyle depends upon a
chilling treatment and this does not normally occur during the spring. Seedlings
of these species do not emerge above the ground before the second spring after
seed dispersal (Panneerselvam, 1998).
Moreover, scarification of the seeds in Q. semecarpifolia did not contribute
to enhance the regeneration but in other Himalayan oaks in Q. glauca and
Q. leucotrichophora, removal of pericarp improved germinability of the
seeds (Rawat et al., 1998). Pericarp in this
case posed as mechanical resistant for cotyledon expansion restricting water
uptake by the seed during radicle emergence. But in Q. semecarpifolia
scarification did not affect regeneration may be because of high moisture content
and non requirement of water for radicle emergence as the seed emerge radicle
immediately after shedding without water.
Q. semecarpifolia seeds lost their viability on prechilling treatment
at 0°C even within 24 h. This is because of ice crystal formation in the
cells at/below 0°C due to high moisture content of the seeds at shedding
(Bisht, 2001). Contrast to this, in Jasminus fruticans
seed germination enhances after 3 months cold stratification (Pipinis
et al., 2009) and seed dormancy in a temperate oak, Q. ilex,
broken by stratification of scarified seeds and seedling growth also positively
affected (Ghasemi and Khosh-Khui, 2007). Similar to
a deciduous Iranian mountain tree, Pistacia khinjuk (Baninasab
and Rahemi, 2008). Stratification of lower altitude plant, Pterocarya
fraxinifolia also maximize seed germination rate as well as percentage (Cicek
and Tilki, 2008). Scarification and stratification were efficient to promote
germination and seedling growth in many of the angiosperms and gymnosperms (Esen
et al., 2007) and also not only in herbaceous plant but in tree species
too viz. Rubia tinctorum (Sadeghi et al.,
2009), Solanum nigrum (Suthar et al.,
2009), Prunus scoparia and P. webbii (Heidari
et al., 2008), Parkia biglobosa (Okunlola
et al., 2011), Convolvulus oxyphyllus and Aeluropus lagopoides
(Zaman et al., 2011), Lupinus leptophyllus
(Alderete-Chavez et al., 2010). These observations
declare that the requirement/factors of seed germination vary individually irrespective
of the similarity in plant habit or habitat. So, the development, management
and implementation of strategies for conservation must be species specific and
also area specific.
It is evident from findings that although radicle emergence took place in a high percentage of seeds irrespective of the conditions, only a few could result in production of a seedling even after radicle emergence. Although, only a few seeds failed to emerge radicle, the deterioration of radicle caused maximum mortality. Scarification does not affect radicle growth as well as seedling emergence significantly but light and temperature contribute to enhance the seedling establishment in totality. Identification of responsible factors for poor regeneration even after radicle emergence and the mechanism associated with it would further help in understanding the ecophysiology of its regeneration and to develop conservational strategies of this species and restoration of timberline ecosystem.
We thank Ministry of Non-Conventional Energy Sources, Government of India and Council for Scientific and Industrial Research, New Delhi, India for the financial assistance during the study.
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