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6Journal of Siberian Federal University. Biology 2018 11(3): 206-217
УДК 581.5+581.134.5:581.824+582.475+551.510.534
Cyclic Variation of Residual (CO2 + H2O) and Total Pressure in Conifer Stem and Woody Root Tree Rings
Boris G. Ageeva,
Aleksandr N. Gruzdevb and Valeria A. Sapozhnikova*a
aV.E. Zuev Institute of Atmospheric Optics SB RAS 1 Academician Zuev square, Tomsk, 634055, Russia bA.M. Obukhov Institute of Atmospheric Physics RAS 3 Pyzhevskii Lane, Moscow, 119017, Russia
Received 07.04.2018, received in revised form 16.06.2018, accepted 27.07.2018 Tree-ring chronologies of stem discs and core samples have been widely used to reconstruct the climatic conditions of tree growth. However, insufficient attention has been given to the fact that root and stem wood accumulate biogenic gases, whose distribution in annual rings can also be related to the climate-dependent features of tree growth. The study of chronologies of gas samples extracted under vacuum from the wood of tree-ring discs of the Siberian stone pine (Pinus sibirica Du Tour), Scots pine (Pinus sylvestris L.), Siberian larch (Larix sibirica Ledeb.) and Siberian spruce (Picea obovata Ledeb.) suggests that annual distributions of CO2 and H2O in the rings and pressure variation in extracted samples follow a cyclic pattern. It was found that the sample pressure and the content of CO2 and H2O in the annual rings in stems and roots of the Siberian stone pine and Scots pine from Tomsk (Russia) area are characterized by varied time cycles, including periods of about 4 and 11 years, the latter corresponding to the period of the solar activity cycle. The four-year cycle in the above chronologies is explained by the presence of similar cycles in temperature and precipitation chronologies, where cyclic variations of CO2 in the rings can be interpreted as a response of the plant to the change in the climatic conditions. The established cyclic variation of the pressure and CO2 content in tree rings in stems and roots indicates that CO2 release into the atmosphere should also follow a cyclic pattern. Therefore, to estimate correctly the release of CO2 by tree stems and large roots, long-term measurements are required.
Keywords: (CO2 + H2O), total pressure, stem, woody roots, cyclicity.
Citation: Ageev B.G., Gruzgev A.N., Sapozhnikova V.A. Cyclic variation of residual (CO2 + H2O) and total pressure in conifer stem and woody root tree rings. J. Sib. Fed. Univ. Biol., 2018, 11(3), 206-217. DOI: 10.17516/1997-1389-0066.
© Siberian Federal University. All rights reserved
This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License (CC BY-NC 4.0). Corresponding author E-mail address: [email protected]
Циклические вариации остаточного (СО2 + Н2О) и полного давления в древесине колец ствола и корня хвойных деревьев
Б.Г. Агеева, А.Н. Груздев6, В.А. Сапожниковаа
аИнститут оптики атмосферы им. В.Е. Зуева СО РАН Россия, 634055, Томск, площадь Академика Зуева, 1 бИнститут физики атмосферы им. А.М. Обухова РАН Россия, 119017, Москва, Пыжевский пер., 3
Древесно-кольцевые хронологии спилов и кернов деревьев широко используются для реконструкций климатических условий роста дерева. Однако остается в стороне тот факт, что древесина корней и стволов сохраняет внутри себя биогенные газы, распределение которых по годичным кольцам также может отражать климатические особенности роста дерева. Исследование хронологий газовых проб, извлекаемых под вакуумом из древесины годичных колец спилов кедра (Pinus sibirica Du Tour), сосны (Pinus sylvestris L.), лиственницы (Larix sibirica Ledeb.), ели (Picea obovata Ledeb), указывает на то, что погодичные распределения сохранившихся в кольцах СО2, Н2О и вариации давления извлекаемой пробы носят циклический характер. Обнаружено, что давление пробы, содержание СО2 и Н2О в годичных кольцах стволов и корней кедра и сосны из района Томска (Россия) испытывают вариации различных временных масштабов, в том числе вариации с периодами около 4 и 11 лет, последний соответствует периоду цикла солнечной активности. Появление цикла с периодом 4 года в найденных хронологиях объясняется существованием подобных циклов в хронологиях температур и осадков, а циклические вариации регистрируемого в кольцах СО2 можно считать реакцией растения на изменение климатических условий. Из обнаруженной циклической вариации давления и СО2 в кольцах спилов стволов и корней деревьев следует, что выделение в атмосферу СО2 должно носить также циклический характер, поэтому для корректной оценки выделения СО2 стволами и крупными корнями следует проводить длительные измерения.
Ключевые слова: (CO2 + H2O), полное давление, ствол, древесные корни, цикличность.
Stem CO2 occurs both in gaseous and aqueous phases (dissolved CO2). It can be released to the atmosphere by diffusion, transported to tree branches and leaves by transpiration flow, or re-fixed in green stem parts (Saveyn, 2007; Teskey et al., 2008). CO2 is transported by transpiration flow to the parts where its concentration is low, being further transformed from the aqueous to the gaseous phase again (Angert et al., 2012). CO2 stem diffusion (stem respiration) is known - 207 -
Introduction
It is well known that gases fill a considerable part of tree stems. Stem CO2 concentrations were found to vary within < 1-26%, which is much higher than the amounts detected in the atmosphere (0.04%) (Bloemen et al., 2013). Stem CO2 pressure would amount to 22-69 Torr (Levy et al., 1999), exceeding atmospheric CO2 concentration by several orders of magnitude (Teskey et al., 2002; Mcguire et al., 2002).
to exhibit daily and seasonal dynamics (see, for example, (Etzold et al., 2013)). The main source of stem CO2 is the respiration of living inner bark cells, cambium, and xylem; even though the experiments on C13 addition to transpiration flow show that the major part of CO2 arrives from the root system (Bloemen et al., 2013).
A great deal of effort was made to perform extensive long-term investigations into stem tissue respiration, i.e. stem CO2 efflux, as stem respiration varies widely from one tree to the other. This variety is due to the fact that physiological processes involved and physical factors controlling the CO2 efflux and/ or influencing radial diffusion of stem CO2 to the atmosphere are very complicated and hard to understand (Saveyn, 2007). That is why it is difficult to estimate CO2 balance for a forest as a whole. It is not surprising, then, that a considerable attention is given to the study of CO2 behavior in tree stems, as carbon dioxide is the main component of the forest carbon balance, and the problem of correct measurements of the stem CO2 efflux is still high on the agenda (Angert et al., 2012).
There is more information published about water content than about tree stem gas concentration (Gartner et al., 2001; Gartner et al., 2004). In natural tree wood, there are only two kinds of water: free water (e.g. in cell lumens), and non-freezing bound water in cell walls. The main stem wood-water interaction occurs by means of hydroxyl groups of wood polymers (Engelund et al., 2013). The interaction appears to be complicated due to non-linearity of bulk flow, capillary condensation of water vapor, gas dissolution and diffusion, migration of bound water through cell walls, etc. (Khazaei, 2008).
Most research on the behavior of CO2 and H2O in tree wood, however, leaves aside the problems of the residual CO2 and H2O content in stems and interannual pressure variations in disc tree
rings. Using a photoacoustic spectrometer with a tunable CO2 laser it is possible both to trace CO2 in discs, and to characterize H2O distribution over tree rings. The water content in the discs of living trees has been studied using different methods (e.g. x-ray computer tomography (Fromm et al., 2001)). However, we are not aware of any attempts to describe annual water distribution over rings in dry discs. Laser photoacoustic analysis has been successfully used in many applications for a long time (Meyer et al., 1990; Sigrist, 1994; Harren et al., 2000; Webber et al., 2005; Sigrist et al., 2008; Cernat et al., 2010; Lima et al., 2011; Popa, 2014; Popa et al., 2015), but we were the first to apply this approach to measuring annual CO2 and H2O distribution in disc wood.
Our findings have shown that a porous wood structure is capable of annual sorption of stem gas components, including water vapor and plant-respired CO2. Thus, for better understanding ofthe behavior of stem gases, additional chronologies are of special importance. In this paper, we present the main results of our investigations into the chronologies of (CO2 + H2O) vacuum-extracted from stem discs of the Siberian stone pine (Pinus sibirica Du Tour), Scots pine (Pinus sylvestris L.), Siberian larch (Larix sibirica Ledeb.), Siberian spruce (Picea obovata Ledeb.) as well as root discs of the Siberian stone pine and Scots pine. An analysis of certain features inherent in the behavior of CO2 chronologies (Sapozhnikova et al., 2013; Ageev et al., 2015) has revealed, among other things: 1) a high correlation between CO2 and H2O chronologies, 2) a statistically significant correlation between the 4-year pressure variations in vacuum-extracted gas samples and the CO2 content, 3) a clearly pronounced cyclicity in chronologies. We put forward the hypothesis that the stem chronology cyclicity is the result of the root chronology cyclicity and studied the (CO2 + H2O) and the pressure distribution in tree-ring wood of large roots.
The results obtained can be used by dendrochronologists, dendroecologists and experts dealing with the carbon budget and carbon dioxide flux estimations between terrestrial ecosystems and the atmosphere.
Materials and methods
Tree-ring samples
The (CO2 + H2O) content and the total pressure in gas samples vacuum-extracted from the disc stem rings of the Siberian stone pine (P. sibirica), Scots pine (P. sylvestris), Siberian larch (L. sibirica), spruce (P. obovata) and disc root rings of the Scots pine and Siberian stone pine that grew at 56°26'N and 85°03'E in Tomsk Oblast (West Siberia, Russia) were studied. All discs were taken from different study sites near Tomsk.
A part of the Scots pine root was separated from a pine sawn in 2013. The root was taken in 2014 from the depth of ~20 cm, its diameter and length were ~8 cm and ~22 cm, respectively; 47 wood rings (of 59) were studied. A sample of the Siberian stone pine root was taken in May 2016 from the root system of the Siberian stone pine sawn in the summer of 2015. The root diameter and length were ~11 cm and ~30 cm, respectively; 21 wood rings (of 28) were studied. Before the measurements, discs and roots were stored under laboratory conditions from 12 weeks to several years, so the wood material can be considered to be room-dried. The method employed allows even very old discs to be used, since tree-ring wood saves bound water with dissolved CO2 regardless to the conditions of disc storage.
The experimental procedure and data processing techniques
The analysis of vacuum-extracted gas samples of root-ring wood was performed on a laser photoacoustic (PA) spectrometer with a computer-controlled tunable CO2 laser
(Sapozhnikova et al., 2013; Ageev et al., 2015; Ageev et al., 2017). Every root-ring wood sample was planed down with chisels, so that the root material was almost completely utilized. Weighted root-ring wood samples were placed in exposure chambers, and short-term vacuum was created. The pressure of the desorbed gas samples in each exposure chamber was measured with a manometer. The data for gas samples vacuum-extracted from tree-ring wood (desorbed gases) were stored in a file containing recorded PA signals of the gas sample absorption in four laser lines: 10 P (20, 16, 14) which coincided with the CO2 absorption lines, and 10 R (20) which coincided with the absorption line of CO2 and water-vapor. The measurements in the R (20) line allowed to detect the signal from the sum of the gas components (CO2 + H2O). Preliminary calibration of the PA detector allowed the partial pressure of studied gases to be determined.
An isotope analysis of carbon CO2 desorbed from several wood root-rings was performed. CO2 was desorbed from root-ring wood in a stream of gaseous nitrogen at T = 80°C and then was precipitated in the form of BaCO3. Carbon dioxide was produced in the reaction of BaCO3 with orthophosphoric acid and was then frozen and injected into ampoules. In addition, a standard sample was prepared, and carbon isotope composition (513C) of the resultant CO2 was measured against the standard sample. The isotope composition was expressed in terms of deviations from internationally accepted standards Vienna Pee Dee Belemnite (VPDB). The composition of stable carbon isotope (513C) of wood CO2 was measured to ±0.5 in the Laboratory of Isotope Methods (Tomsk, Russia), using the DELTA V Advantage mass spectrometer with a probability confidence interval of 0.95.
When dealing with the root wood, it was difficult to separate the current year's wood because of either narrow rings (pine roots) or
weakly colored latewood (stone pine roots). For this reason, the error in root ring dating was estimated to be 1 year.
To estimate the periodic and temporal variations in the obtained chronologies, we used high-resolution spectral and cross-spectral analyses based on the maximum entropy and wavelet techniques and digital filtration of time series (Jones, 1978; Kay et al., 1981). Long-term trends were eliminated from the data analyzed. Fourier analysis (Fast Fourier Transform, FFT) using the ORIGIN software was also employed for testing periodic signals.
Results
Analysis of the desorbed CO2 carbon isotope composition (S13Q
By now the carbon isotope composition of samples desorbed from Siberian stone pine, Scots pine, Siberian larch, and spruce tree ring disc wood has been investigated. The results obtained showed that the gas samples desorbed from
several stem discs of the Siberian stone pine, Scots pine, Siberian larch, spruce were enriched in light isotope 12C up to (513C) = -25.3%o for spruce, varying between -25%o (1894) and -36.4%o (1986) for the Siberian stone pine, from (513C) ~ -25 % up to (513C) ~ -30% for the larch, from (513C) ~ -25 % to (513C) ~ -34% for the Scots pine (Tomsk Oblast, Russia) (Fig. 1) (Ageev et al., 2016). (513C) = - 27% for the Siberian stone pine root, and (513C ) = -33.5% for the Scots pine root.
It is evident that CO2 is produced by the stem and root itself but not supplied from the atmosphere, as the carbon isotope composition of CO2 in the atmosphere is on average -8.5% (Rubino et al., 2013).
Special features inherent in the behavior of tree ring (CO2 + H2O)
The absorption by two gas components (CO2+H2O) in R(20) CO2 laser line was recorded for the Siberian stone pine stem disc, as CO2 and H2O absorption lines coincide (Fig. 2a). The
-30-
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1800 1850 1900 1950 2000 Year
a)
-45 -40 O -35
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1920 1960 Year
b)
1980 Year
c)
d)
Fig. 1. Annual variations in carbon isotope composition of vacuum-desorbed CO2 (S13C, %) from the tree-ring gas samples of the 300 year old larch (a), Siberian stone pine (b), spruce (c), and Scots pine (d) (Ageev et al., 2016)
1990
chronology of residual (CO2 + H2O) vacuum-desorbed from the tree rings of the Siberian stone pine is characterized by distinct short-and long-term cyclic variations (Fig. 2a). The results of Fourier analysis of the PA signals from (CO 2 + H2O) in the Siberian stone pine stem tree rings using the ORIGIN software
confirmed the existence of 2- and 4-year cycles (Fig. 2b). Fourier analysis (FFT) also revealed weak spectral maxima with a period approaching that of the 11-year solar cycles (near 10-year cycle in Fig. 2b).
Figure 3 shows the results of FFT analysis of the tree-ring (CO2 + H2O) chronologies for
iear Period (year)
a) b)
Fig. 2. Interannual variations in PA signals accounting for the behavior of (CO2 + H2O) vacuum-desorbed from stem tree-rings of the Siberian stone pine (N=117, 1878-1994) (a) and results of Fourier analysis of (CO2 + H2O) distribution in annual tree rings (b) (without trend)
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4 6 8 10 12 14 16
Period (year)
b)
14-A.
4 6 8 10 12 14 16 Period (year)
d)
Fig. 3. Results of Fourier analysis of (CO2 + H2O) chronologies for spruce discs: (a) N=96 rings (1919-2004); (b) N=67 rings (1938-2004); for Scots pine discs (c): N=128 rings (1878-2005); and larch disc (d): N=285 rings (1724-2008)
2
spruce, Scots pine and larch discs the same way it was done for the CO2 chronologies (Ageev et al., 2017).
The disc tree-ring (CO2+H2O) chronologies of conifers which grew in the same region (West Siberia, Russia) exhibited distinct 2-,4- year and approximately 11-year cycles (Figs. 2, 3).
Total pressure variations in a larch stem disc
Total pressure variations in a 300-year-old larch stem disc were studied in the exposure chambere. As a result, we obtained (CO2 + H2O) and total pressure variation chronologies, which he0.0005 to reveal a 4-year cycle of the (CO2 + H2O) (Fig. 3d) variations associated with a 4-year period of the total pressure variations in gas samples. Figure 4a demonstrates the trend for the variations (polynomial approximation) in the total pressure of the gas samples in the exposure chambers of the 300 year old larch. We analyze d the results obtained for total pressure of the vacuum-extracted gas samples from tree rings to 0.005 out whether the measurements showed cydic variations. The results of Fourier analysis of the variations in tree ring pressure are presented in Fig. 4b: in addition to the 2-year variations, well-defined 4-year cycles can be clearly seen.
Root characteristics
In this section, we present the results of the analysis of (CO2 + H2O) and total pressure variations of the vacuum-desorbed root-ring wood samples of the Scots pine and Siberian stone pine. Figure 5 shows the results of the PA signal measurements for (CO2 + H2O) absorption (a); variation of CO2 concentration (b); total pressure variation in the gas samples (c) and pressure power spectra (d) in Scots pine root-rings. It should be noted that the concentration of the residual CO2 (ppm) varied in pine woody root-rings up to 1200 ppm (atmospheric CO2 now is ~400 ppm).
A lmear correlation coefficient between CO2 and (CO°+H 2O) chronologies, as we might expect, was fou nd to be quite high: R = 0.79 (N = 49, level of statistical significance P < 0.0001), but there was no C0rrelati0n b etween the se chronologies and the pressure chronology. An examination of CO2 and pressure chronologies of pine root by spect0al and cross-spectral analyses (Fig. 5d; Ageev et al., 2017) showed that they have common features - spectral maxima within ~4.5 and 11 year ac0.03 (the latter period correlates with the 11-year so!ar activity cycle).
Figure 6 shows the PA signal variation for (CO2+H2O) absorption ani pressure chronologies of the vacuum-extracted samples of the Siberian stone pine wood. The analysis of the examined chronologies showed that the concentrations of
1750 1800 1850 1900 1950 2000
Year
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Fig. 4. Total pressure variations of gas samples in the exposure chambers (a) and results of Fourier analysis of total pressure chronology for wood of larch tree rings (b)
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Fig. 5. The PA signal variations for (CO2 + H2O) absorption (a), the variation of the CO2 concentration (b), the total pressure variation (c), and the power spectra of pressure (d) in the Scots pine root-rings
6
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Fig. 6. The PA signal variations for (CO2 + H2O) absorption (a), the variation of the CO2 concentration (b), the total pressure variation in the vacuum-extracted gas samples (c), and the power spectra of pressure (the black curve -the lower resolution, the gray curve - the higher resolution) (d) in the Siberian stone pine root-rings
the residual CO2 in the wood of both roots are of the same order of magnitude (400-2000 ppm), but the pattern of annual distribution of CO2 concentration is different. As in the previous case, a linear correlation between CO2 and (CO2 H2O) was found to be high: R = 0.95 (N = 21), P < 0.0001, but there was no correlation between CO2 and pressure chronologies. The chronologies obtained were also examined by spectral and cross-spectral techniques. The spectra of the pressure chronologies for two spectral resolutions are shown in Fig. 6d: the black curve illustrates the lower resolution, and the gray curve illustrates the higher resolution. It can be seen that all parameters undergo variations with a period in the vicinity of 4 years. The cross-spectral analysis shows that the (CO2+H2O) variations with this period are coherent with the pressure variation and are observed approximately in antiphase with
them.
The climatic chronology cyclicity
The experimental results showed a stable cyclicity for the established pressure chronologies of the vacuum-extracted samples and (CO2 H2O) for tree-ring discs. To explain this phenomenon, we analyzed the temperature and precipitation chronologies for the region of the tree growth. Earlier we had established a relationship
between CO2 in the tree-ring discs and climatic parameters (Sapozhnikova et al., 2013). Figure 7a, b demonstrates the results of Fourier analysis of the temperature and precipitation chronologies (weather station data, Tomsk). The graph shows that the chronologies contain cycles with periods close to 4 years.
Discussion
We suggest that a porous wood structure is capable of annual accumulation (sorption) of stem gas components that include H2O vapor and plant cell-respired CO2. A vacuum extraction and laser photoacoustic analysis provide long (CO 2 + H2O) and total pressure chronologies and enable us to reveal a number of features inherent in the time series examined. We have obtained annual total pressure and (CO2 + H2O) distribution in the wood of stem tree rings of the Siberian stone pine (P. sibirica), Scots pine (P. sylvestris), Siberian larch (L. sibirica), spruce (P. obovata) and disc root rings of the Scots pine and Siberian stone pine. The stable cyclicity in the obtained results can be explained by the influence of the climatic conditions in which similar cyclicity is observed.
Apparently, a periodic increase in summer precipitation increases root pressure which in its turn affects stem pressure, as it was observed in
3000
2000
1000-
Precipitation
2 4 6 8 10 12 14 16 Period(year)
a)
4 5 6 Period (year)
b)
Fig. 7. The result of FFT analysis of the chronologies of summer precipitation (a) and temperatures (b) of the region of tree growth
0
our experiment. Plant response to this increase may result in the increase of cell respiration, i.e. an increase of CO2 release. A classic example of such response was observed in the Siberian stone pine (see Fig. 1).
A cyclic pressure variation in roots and stems must lead to a cyclic CO2 diffusion into the atmosphere. The data on additional periodic variations of the background CO2 were acquired from the measurements of the CO2 concentrations in the air samples using Fourier spectros-copy (Aref'ev et al., 2014), and it was concluded that the background CO2 was formed for the most part due to equilibrium CO2 exchange between the atmosphere and biosphere and exhibited variations with the outer (generally periodic) heliogeophysical conditions. Apparently, the background CO2 concentrations found in (Aref'ev et al., 2014) to vary within the periods ranging between 2 and 126 months (1.7, 4, 5.2, 6.4, and 10.5 years) account for the cyclic variations of the plant-extracted CO2 in the region under study.
Conclusions
We have undertaken a study of the (CO2 + H2O) and total pressure variations in stem wood rings of the Siberian stone pine (P. sibirica), Scots pine (P. sylvestris), Siberian larch (L. sibirica), spruce (P. obovata) and disc root rings of the Scots pine and Siberian stone pine. The results obtained from this work allow to make the following conclusions:
1. The measured carbon isotope composition of vacuum-extracted stem and root CO2 was 513C ~ (-25) - (-36)%«. This means that CO2 belongs to the tree itself and is not supplied from the atmosphere.
2. The (CO2 + H2O) and total pressure variations in the gas samples vacuum-extracted from conifer stem and root wood exhibit two- and four-year cycles.
3. Similar cycles in the precipitation and temperatures can explain the observed cyclicity in the chronologies of residual (CO2 + H2O) and in the pressure chronologies in tree rings of the stems and roots of some conifers.
4. The observed cycle that is close to the 11-year period can be related to the 11-year solar activity cycle.
5. The cyclic pressure variation in roots and stems should lead to the cyclic CO2 diffusion into the atmosphere.
To sum up, the results obtained show that tree ring discs contain valuable information for estimating residual CO2 related to respired CO2 and may contribute to better understanding of the role of the gases present in the tree. We believe, (CO2 + H2O) measurements in trees will allow to reveal the mechanism involved in the forest adaptation to environmental and climatic changes. Practical significance of the investigation could be much higher if portable instruments for taking CO2, (CO2 + H2O) cores had been used. An instrument for online tree-ring CO2, (CO2 + H2O) monitoring could be a means to investigate tree adaptation to climate changes and provide useful data about tree health in ecological risk areas.
Acknowledgments
This work was performed in the framework of a Basic Research Program (Project VIII.80.1.3) of the Russian Academy of Sciences. We would like to thank the staff of the Laboratory of Isotope Methods (Tomsk, Russia) for performing the isotope analysis.
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