Xylogenesis of pinus heldreichii and pinus peuce in Pirin Mts

Abstract

Pinus heldreichii and Pinus peuce are tree species characterized by longevity. Previous studies have outlined the potential for constructing long tree ring chronologies, which may be used for studying the climatic variation in the past. A difficulty is the mixed climatic signal with negative effect of summer droughts, but also of extremely cold summers and the positive effect of warm winters. Therefore, for successful dendroclimatic analysis better understanding of the processes of tree ring production is necessary. Our aim within this project was to study the cambial activity and production of tracheids during the growth period. Old 100-250 years trees of P. heldreichii and P. peuce from natural forests in Pirin Mts. were chosen. Beginning from 2010 microcores was taken every 10 to 14 days. The samples were prepared with a sliding microtom GSL-1 and analyzed for the onset of cambial activity, the period of production of first cells and the period until cells were produced. In 2010 and 2011, the onset of cambial activity was delayed until the end of June - beginning of July. In 2012, it started at the beginning of June. The late start in 2010 and 2011 was probably due to cold periods in April and May. Despite this the trees produced tree rings with more rows of cells and higher width than all the rings in the period 2000-2009. This confirms our initial hypothesis that warmer winters promote the production of wider tree rings. The production of new cells continued until the end of September, while the differentiation - until the middle of October. In both years P. heldreichii trees produced more cells than P. peuce trees.

Full text

229
Bulgarian Journal of Agricultural Science, 19 (2) 2013, 229–232
Agricultural Academy
XYLOGENESIS OF PINUS HELDREICHII AND PINUS PEUCE IN PIRIN MTS.
A. IVANOVA*, Y. TODOROVA, P. RANGELOVA and M. PANAYOTOV
University of Forestry, Dendrology Department, BG – 1756 Sofi a, Bulgaria
Abstract
IVANOVA, A., Y. TODOROVA, P. RANGELOVA and M. PANAYOTOV, 2013. Xylogenesis of Pinus heldreichii and Pinus
peuce in Pirin Mts. Bulg. J. Agric. Sci., Supplement 2, 19: 229–232
Pinus heldreichii and Pinus peuce are tree species characterized by longevity. Previous studies have outlined the potential
for constructing long tree ring chronologies, which may be used for studying the climatic variation in the past. A diffi culty is
the mixed climatic signal with negative effect of summer droughts, but also of extremely cold summers and the positive effect
of warm winters. Therefore, for successful dendroclimatic analysis better understanding of the processes of tree ring produc-
tion is necessary. Our aim within this project was to study the cambial activity and production of tracheids during the growth
period. Old 100–250 years trees of P. heldreichii and P. peuce from natural forests in Pirin Mts. were chosen. Beginning from
2010 microcores was taken every 10 to 14 days. The samples were prepared with a sliding microtom GSL-1 and analyzed for
the onset of cambial activity, the period of production of fi rst cells and the period until cells were produced. In 2010 and 2011,
the onset of cambial activity was delayed until the end of June – beginning of July. In 2012, it started at the beginning of June.
The late start in 2010 and 2011 was probably due to cold periods in April and May. Despite this the trees produced tree rings
with more rows of cells and higher width than all the rings in the period 2000–2009. This confi rms our initial hypothesis that
warmer winters promote the production of wider tree rings. The production of new cells continued until the end of September,
while the differentiation – until the middle of October. In both years P. heldreichii trees produced more cells than P. peuce trees.
Key words: tree rings, xylogenesis, Pinus heldreichii, Pinus peuce, Pirin
*E-mail: albenabeti@gmail.com
Introduction
Annual tree-ring differentiation involves the production of
cells through the phases of division, expansion, secondary wall
thickening, lignifi cation’s and programmed cell death (Savidge,
1996; Plomion et al., 2001). Intra-annual radial growth rates
and durations in trees are reported to differ greatly in relation
to species, site and environmental conditions. Understanding
of the pattern of response mechanisms is critical for predict-
ing vegetation changes associated with projected future climate
change, and fundamental for adopting appropriate and timely
management measures. Radial patterns of wood structure re-
fl ect the changing demands placed upon woody plants as they
grow and experience changing environmental conditions. The
study of their variation over time offers the opportunity to eval-
uate how well plants will respond to predicted global changes.
Previous studies on tree ring width series of Pinus held-
reichii Christ (Panaytov et al., 2010) and Pinus peuce Griseb
(Panayotov and Yurukov, 2007) have shown strong inter-series
correlation, but mixed climatic signal. Tree ring growth was
found to be strongly dependent from both summer precipitation
and temperature, but from winter temperatures (P. heldreichii).
Thus, better knowledge of the relationship between tree-ring
development and climate is needed to improve dendroclimatic
studies. At the same time up to this moment, there are no de-
tailed studies for the cambial activity and tree ring production of
the Balkan endemic species P. peuce. The cambial activity of P.
heldreichii, which is also a species under global protection, was
studied only in a location in Italy (Rossi et al., 2006) but not for
the Balkan Peninsula. Climate differences are present between
these two regions (Panayotov et al., 2010) and this might be a
reason for differences in the cambial activity phases.

230 A. Ivanova, Y. Todorova, P. Rangelova and M. Panayotov
This paper presents the fi rst results from a study about
the timing of production of tracheids and tree ring formation
in P. peuce and P. heldreichii in the Pirin Mountains. Our
aim was to analyze the differences in the onset of cambial
activity, the duration of cell production and number of cells
produced between the two studied species and between sites
with different exposures.
Material and Methods
The study area is situated in the Bunderitsa valley in the
Pirin Mountains, Bulgaria. On the eastern slope of Vihren
peak, 5 trees from P. heldreichii and 2 trees P. peuce situated
from 1850 m to 2000 m a.s.l. were studied. On the north-
western slope of Todorka peak 4 P. peuce and 2 P. heldreichii
trees situated between 1750 and 1850 m a.s.l. were studied.
Wood microcores (1.2–2.4 mm in diameter) were collect-
ed at breast height (1. 3 m) using increment punchers (Forster
et al., 2000). The microcores were placed in ethanol-vinegar
based solution in Eppendorf microtubes. Samples usually
contain the previous fi ve to ten tree rings, newly developing
cambial zone and adjacent phloematic tissue. Micro sections
were cut with 10–15 μm thickness with sledge microtome
GSL-1 following procedures described by Schweingruber
(1990). Micro-sections were stained with Shafranin and
Astra-blue, observed with ZEISS Standart 20 microscope,
and captured with Progres-CT3 camera. The number of cells
each year was counted in fi ve lines of cell rows.
Results and Discussion
In 2010 started the collection of the fi rst data of this type
in Bulgaria and the fi rst for P. peuce worldwide. In 2010, the
cambial activity of P. peuce started in early June, the fi rst
formed cells being observed on June 11th (Figure 1). By mid-
November the cambial activity and formation of new cells
had completely stopped. In P. heldreichii trees from the same
slope and altitude similar start and end of cambial activity
was observed, but more cells were produced. That confi rmed
the data for total number of cells generated in the previous
years (Todorova et al., 2010), which were more in P. held-
reichii than P. peuce trees.
Although the data for cambial activity in 2010 were scarce,
it set an interesting trend. The beginning of cell formation was
in the middle of June, the most active period of cell formation
in August and the end of the formation of new cells till Octo-
ber. This was a surprising result in comparison with data from
other studies in the Alps (Rossi et al, 2003), showing the start
of the division at the beginning of June, the most active phase
in July and the end of the formation of new cells in September.
Probably this was because 2010 was special in several aspects.
First, excluding January and October, average monthly tem-
peratures throughout the year were higher than the long-term
average temperatures. With the exception of February the au-
tumn-winter period (November 2009 – March 2010) was very
dry and warm with lower than normal snowfalls. The relative-
ly warmer beginning of May was followed by a sharp cooling
in the second decade of the month followed by snow accumu-
lation even in lower mountain areas (i.e. Petrohan area, Stara
Planina Mts, aprox. 1300 m a.s.l.). Perhaps that played a role
in delaying the start of cambial activity. Meanwhile the sum-
mer could be characterized by high temperatures in the pres-
ence of normal rainfalls. The relatively warm autumn prob-
ably contributed for the observed prolonged cambial activity,
which lasted until the end of October, when there was a cold
period with heavy snowfalls (30 October 2010).
In 2011 the cambial activity also started at the end of June
(Figure 1). First formed cells (3 to 10 lines) were observed
01.Юни 01.Юли 01.Август 01.Септември 01.Октомври 01.Ноември 01.Декември
2010
2011
2012
Fig. 1. Duration of tracheid
production period in 2010-2012

231
Xylogenesis of Pinus heldreichii and Pinus peuce in Pirin Mts.
in the samples taken on July 2nd. This was also a surprising
result, because for a second consecutive year the start of cam-
bial activity was later than expected. In addition to literature
data (Rossi et al., 2003), analysis of observed frost rings (Pan-
ayotov, 2007; Panayotov and Yurukov, 2007 ) formed in years
with late frosts events in late May and early June in the studied
species gave additional evidence that in other years cambial
activity started earlier. It should be noted however that 2011
was also special in several aspects. The winter was unusually
warm, with less than normal snow. In mid-April most of the
eastern slope of Vihren peak, where most of the studied trees
are situated, was without snow cover. Then similarly, to 2010
there were long-lasting cold period in May. This is the most
likely reason for the delay in the start of cambial activity. Also
similarly, to 2010 the summer was warm without the presence
of long droughts. Autumn was extremely warm (September)
followed by heavy snowfalls and very strong cooling (-6 / -7 °
C at an altitude of 1700-2000 meters on October 16th).
It is interesting, that despite the late start of cambial ac-
tivity in 2011- 2012, the number of cells generated in all
trees was higher than those in previous 5 to 10 years.
Although these data should be interpreted with caution
as they are based on different samples, they clearly outline
the trends that during those three years were formed larger
than usual number of cells. Thus our fi ndings for the cam-
bial activity in 2010 and 2011 confi rm conclusions from the
analysis of the correlations of chronologies from tree rings
widths in P. heldreihii that in years with warmer winters and
summers without long lasting droughts, wide annual rings
were formed, which in turn contain larger number of cells
(Panayotov et al., 2010; Todorova et al., 2010).
In 2012, cambial activity started at the beginning of June
(Figure 1). First cells were formed shortly before 10th of June.
In comparing with the observed previous years, winter of
2012 was much colder, with heavy snowfalls and long last-
ing snow cover. This is the main difference in winter climate
conditions between these years. Yet, the spring was normal,
without any cold spells and late snowfalls. Perhaps this con-
tributes for start of cell formation in the expected period in
2012. The summer and autumn were extreme hot and dry.
Despite this, the cambial activity in 2012 ended at the end of
October as in earlier years. Perhaps this is an indication of
lack of dependence of the termination of cell division on the
temperature regime, but rather on light conditions In general,
plants synchronize their preparation for the winter season
with the decreased light and reduced average temperatures.
Comparing the number of produced cells also showed
that P. heldreichii trees generally produce more cells than
those of P. peuce (Figure 2). Those fi nding must be verifi ed
by testing more P. peuce trees.
0
10
20
30
40
50
60
70
80
2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012
Year
Number of cells
BTH1
BTH2
P1
P2
VH1
VH2
VH3
VH4
VH5
Fig. 2. Number of produced cells in Pinus heldreichii and Pinus peuce for the period 2000–2012, from the eastern
slope of Vihren peak and the northwestern slope of Todorka peak in Pirin Mts.

232 A. Ivanova, Y. Todorova, P. Rangelova and M. Panayotov
Conclusions
Our data shows that the hypothesis based on the anal-
ysis of variation in tree rings widths that warmer winters
contribute to the formation of wider annual rings is con-
firmed. This study suggests that this is due to the greater
number of formed cells. Even late start of the cambial
activity caused by spring frosts did not change the ob-
served production of more cells in such years. Thus, our
data confirm that chronologies of P. helldreichii can be
used to analyze past climate extremes and outline unusu-
ally warm or cold winters for periods without available
instrumental climate measurements.
Acknowledgements
The current study was supported financially by proj-
ect 115/2008 of the University of Forestry and DTK
02/02/2010 of the National Science Fund of Bulgaria. We
are grateful to Dr. Valerie Trouet from the WSL in Swit-
zerland for providing the sliding microtome, dr. Melissa
Dawes (SLF, Switzerland) for providing trephor tool for
extraction of cores and Holger Gratner (WSL, Switzer-
land), Schweingruber F. (WSL, Switzerland) for practi-
cal training and advices in the micro-slices preparation
technique and MedCLEVAR for providing financial sup-
port for training course at the WSL (Switzerland). We
would also like to thank Blagoy Stoyanov for assistance
in the collection of the micro cores.
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