Stem Respiration of a Larch (Larix gmelini ...

植　　物　　学　　报 Acta Botanica Sinica 2003, 45 (12): 1387－1397

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Stem Respiration of a Larch (Larix gmelini) Plantation in Northeast China WANG Wen-Jie1, YANG Feng-Jian1, ZU Yuan-Gang1, WANG Hui-Mei1, TAKAGI Kentaro2, SASA Kaichiro2, KOIKE Takayoshi2 (1. Key Laboratory of Forest Plant Ecology, Ministry of Education, Northeast Forestry University, Harbin 150040, China; 2. Hokkaido University Forests, FSC, Sapporo 060-0809, Japan)

Abstract: Stem respiration is an important part of the activity of a tree and is an important source of CO2 evolution from a forest ecosystem. Presently, no standard methods are available for the accurate estimation of total stem CO2 efflux from a forest. In the current study, a 33-year-old (by the year 2001) larch (Larix gmelini Rupr.) plantation was measured throughout 2001-2002 to analyze its monthly and seasonal patterns of stem respiration. Stem respiration rate was also measured at different heights, at different daily intervals and any variation in the larch plantation was recorded. The relationship between stem temperature, growth status and respiration rate was analyzed. Higher respiration rates were recorded in upper reaches of the larch tree throughout the season and these were affected partially by temperature difference. Midday depression was found in the diurnal changes in stem respiration. In the morning, but not in the afternoon, stem respiration was positively correlated with stem temperature. The reason for this variation may be attributed to water deficit, which was stronger in the afternoon. In the larch plantation, a maximum 7-fold variation in stem respiration was found. The growth status (such as mean growth rate of stem and canopy projection area) instead of stem temperature difference was positively correlated with this large variation. An S-model (sigmoid curve) or Power model shows the greatest regression of the field data. In the courses of seasonal and annual changes of stem respiration, peak values were observed in July of both years, but substantial interannual differences in magnitude were observed. An exponential model can clearly show this regression of the temperature-respiration relationship. In our results, Q10 values ranged from 2.22 in 2001 to 3.53 in 2002. Therefore, estimation of total stem CO2 efflux only by a constant Q10 value may give biased results. More parameters of growth status and water status should be considered for more accurate estimation. Key words: Larix gmelini ; stem respiration; growth status; growth rate; canopy projection area; Q10 The CO2 sequestration capacity of forest ecosystems has recently become a primary focus for satisfying the commitment of COP3 (Schulze et al., 1999;Valentini et al., 2000). In particular, respiration from non-photosynthetic organs (stem and soil) has gained attention since forest CO2 flux is mainly determined by respiration of the ecosystem instead of total photosynthesis by green organs (Valentini et al., 2000; Janssens et al., 2001). The Northern Hemisphere has been recognized as an important CO2 sink owing to the broad distribution and high productivity of coniferous forest ecosystems (Fan et al., 1998; Schulze et al., 1999). Larch, characterized by its high biomass productivity, only occurs in this hemisphere (Gower and Richards, 1990). The high photosynthetic capacities may make larch forest ecosystems an important CO2 sink of this region (Koike et al., 2000). However, the respiration cost of stem in larch forest still remains uncertain although the stem biomass has taken the most important percentage of total forest ecosystem (Waring and Running, 1995).

Respiration of total tree commonly depletes from 30% to more than 80% of the daily production of photosynthates (Negisi, 1977; Kozlowski et al., 1997). Respiration depletion of daily photosynthates by branches, trunk and roots of trees ranges from 25% to 50% (Landsberg and Gower, 1997) and may amount to greater than 65% in the tropics (Kira, 1975; Sprugel and Benecke, 1991). The cost of stem respiration is estimated to be at least 5% or more of the total photosynthetic production (Iqbal, 1990; Edwards et al., 2002). This part of stem CO2 efflux should be taken into account in estimating total CO2 efflux capacity from a forest ecosystem (Law et al., 1999). Therefore, more intensive research such as in spatial and temporal changes of stem respiration is necessary for the understanding and estimating of total CO2 flux from a forest ecosystem. The carbon sequestration capacity of larch species has also been of interest to scientists (Schulze et al., 1999; Koike et al., 2000). Whilst few documents record data on stem respiration in this species (Wang et al., 2001a; 2001b)

Received: 2003-05-22 Accepted: 2003-09-03 Supported by the National Natural Science Foundation of China (30300271). * Author for correspondence. E-mail: .

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several studies have been conducted to provide data on other species. These include stem respiration in contrasting sites, unstable temperature coefficient (Q10) and possible correlation with growth status (Linder and Troeng, 1981a;1981b; Paembonan et al., 1992; Ryan and Waring, 1992; Ryan et al., 1994; 1995) and diurnal and seasonal changes (Negisi, 1972; Negisi, 1978; Xu et al., 2000; Edwards et al., 2002). In a Japanese larch forest it has been reported that stem respiration ranged from 0.9 µmol.m－2.s－1 to 6.2 µmol.m－2.s－1 and peaked around July or August, and its magnitude being similar to that of soil respiration observed in the same plantation. Seasonal Q10 variation of larch stem respiration was also observed (Wang et al., 2001a; 2001b). Furthermore, the complexity of trunk space (from forest floor to the lowest part of canopy) including the spatial difference has been investigated by meteorological methods (Green et al., 1995), although studies about their possible effects on stem respiration are limited. To date, little research has been conducted into the spatial difference of stem respiration in other species (Araki et al., 2001). In larch species, it is still not clear whether there are spatial and diurnal changes of stem respiration and variation of stem respiration in even-aged forests. This would be important for the precise estimation of annual stem CO2 efflux. The present study was conducted in order to better understand the larch stem respiration characteristics. A larch plantation, equipped with a monitoring tower system (Shi et al., 2001) located in the Laoshan experimental station of Northeast Forestry University, was selected to study the patterns of spatial (vertical changes at different stem height, horizontal changes of individual trees in the same forests) differences and temporal (diurnal seasonal and interannual) changes and their possible correlation with temperature difference and growth status.

gmelini and invaded canopy species include Franxinus mandshurica and Betula platyphylla. Succeeding species also include Acer mono, Pinus koraiensis and Quercus mongolica. The height of L. gmelini is approximately 18 m and the diameter at breast height (DBH) is (17.2 ±4.5) cm. The frequency distribution of DBH of total material trees used in the present study are shown in Fig.1. 1.2 Stem respiration measurement Respiration rates of stem were measured by a LI-6400 portable photosynthesis system with a null balance chamber for soil respiration rates (LiCor, NE, USA). To measure the respiration of stem, a soft plasticine was used to close the space between the chamber and the stem (the so-called Horizontally Oriented Soil Chamber (HOSC) proposed by Xu et al.(2000)). The long-term recording of stem temperature at the depth of ca. 1 cm was automatically measured by a mini-thermometer system (RTW-30s, Espec Mic Corp. Aichi, Japan). The frequency of data recording was twice per hour. Stem temperature was concurrently measured by the thermometer of the LI-6400 system when respiration was measured in order to estimate the relationship between stem temperature and respiration. To avoid the influence of diurnal changes to stem respiration, measurements of seasonal changes and variations in the even-aged forest were taken in the afternoon. Four trees were taken as samples for the measurements of seasonal changes and interannual differences in stem respiration. All measurements were taken once a month. Three trees were measured for the determination of diurnal course pattern. Forty-two and 83 individual trees were measured to assess the possible relationship between stem

1 Materials and Methods 1.1 Study sites and plant materials A larch stand (33-year-old as of 2001) at Laoshan station (45°20' N, 127°34' E) in Northeast China was selected as our study site. The altitude is approximately 340 m above sea level. The mean annual precipitation is 723 mm. The frost-free period is 120－140 d. The annual mean air temperature is 2.8 ℃. The mean potential evapotranspiration is 1 094 mm. The mean air humidity is 70%. This region is characterized by a typical continental climate with precipitation less than adequate precipitation and a short growing period. Spring and autumn are usually short, summer is hot and humid, and winter is long and cold. Soil is characterized as dark brown forest soil. The main tree species is L.

Fig.1. Frequency distribution of the diameter at breast height (DBH) of total material trees measured in present study.

WANG Wen-Jie et al.: Stem Respiration of a Larch (Larix gmelini) Plantation in Northeast China

respiration and mean growth rate and canopy projection area, respectively . A steel tower (20 m with an 8 m mast ), together with wooden platforms, was used to measure stem respiration at different heights. Two heights (1.3 m and 12 m, just below the lowest branch) were chosen for measurements. Three replicates were made in May and July of 2002 and one tree was measured in August 2001. 1.3 Measurement and calculation of other parameters Differences in water status were given as soil water content, relative air humidity, xylem water potential of branch tips formed in the last year, leaf transpiration and stomatal conductance. Water potential of branch tip was measured once every two hours from morning (6:00 am) to evening (6:00 pm) by a ZLZ-5 plant water status system (Lanzhou University, China). Four replicates were measured at each timepoint. Soil water content and relative air humidity were automatically recorded twice per hour by a CS615 water content reflectometer (Campbell, Logan,USA) and HMP45D humidity temperature probes (Vaisala Helsinki, Finland), respectively. The transpiration rate and stomatal conductance of leaf were measured once every two hours from morning (6:00 am) to evening (6:00 pm) by the LI-6400 portable photosynthesis system (LiCor, NE, USA). Canopy projection area (Acanopy) was estimated as the quadrangle area of canopy branch from the east, south, west and north directions. The equation is: π Acanopy= (a+b) (c+d) (1) 4 where, a, b, c and d are the lengths between the stem and the outermost projected point of branch to the east, south, west and northerly directions, respectively. The mean growth rate of tree were calculated by DBH divided by the age of tree. The measured area enclosed in the chamber was not the default area 71.6 cm2 since the tree stem is cylindrical in form. When the stem diameter was larger than the diameter of the chamber, the measured stem area was taken as the projected area (Anew) of the chamber on the stem. The new area was calculated according to the ellipse area formula: Anew=π r1 r2 arcsin (r1/r2) (2) where, r1 is the radial diameter of the chamber (4.77 cm) and r2 is the stem diameter at the place of measurement. Also, r1 is the short radial diameter of the projected ellipse of the chamber and r2 arcsin (r1/r2) is the long radial diameter of the projected ellipse of the chamber on the stem (Fig.2a). When the stem diameter was smaller than the diameter of the chamber, the new area is calculated according

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Fig.2. Sketch map of area enclosed in the chamber for stem respiration measurement. (a) when stem diameter is larger than chamber diameter (r2>r1).The projected area of chamber on the stem is the ellipse area with r2, and arc length of AB as long and short radial diameter, respectively. AB=r2 arcsin(r1/r2). (b) when stem diameter is smaller than chamber diameter (r2