Journal of Integrative Plant Biology http://www.blackwell-synergy.com Formerly Acta Botanica Sinica 2005, 47 (12): 1459−1469 http://www.chineseplantscience.com Seasonal Variation of δ13C of Four Tree Species: A Biological Integrator of Environmental Variables Hai-Tao LI1*, Jun XIA1, 2, Le XIANG1, Tao LIANG1 and Qi-Jing LIU1 (1. Institute of Geographic Sciences and Natural Resources Research, the Chinese Academy of Sciences, Beijing 100101, China; 2. Key Laboratory of Water Cycle and Related Land Surface Processes, Institute of Geographic Sciences and Natural Resources Research, the Chinese Academy of Sciences, Beijing 100101, China) Abstract: Foliar δ13C values, an indicator of long-term intercellular carbon dioxide concentration and, thus, of long-term water use efficiency (WUE) in plants, were measured for Pinus massoniana Lamb., P. elliottii Engelm., Cunninghamia laceolata (Lamb.) Hook., and Schima superba Gardn. et Champ. in a restored forest ecosystem in the Jiazhu River Basin. Seasonal variation and the relationship between the foliar δ13C values of the four species and environmental factors (monthly total precipitation, monthly average air temperature, relative humidity, atmospheric pressure, and monthly total solar radiation and evaporation) were investigated. The monthly δ13C values and WUE of the four species increased with increasing precipitation, air temperature, solar radiation, and evaporation, whereas δ13C values of the four species decreased with increasing relative humidity and atmospheric pressure. Despite significant differences in δ13C seasonal means for the four species, our results demonstrate a significant convergence in the re- sponses of δ13C values and WUE to seasonal variations in environmental factors among the species inves- tigated and that the δ13C signature for each species gives a strong indication of environmental variables. Key words: δ13C; Cunninghamia laceolata; Pinus elliottii; Pinus massoniana; Schima superba; water use efficiency (WUE). During the past few decades, there has been a grow- between photosynthesis (A) and transpiration (E) of ing awareness of the importance of land-surface hy- vegetation crown in homogeneous models using the drological processes in global climate modeling (US big leaf approach (Friend 2001). Global Change Research Program (USGCRP) 2001). WUE is conventionally determined either as the ra- Models are very sensitive to changes in many surface tio of A/E in the short term or as the ratio of dry matter parameters and, in particular, to the partitioning of en- accumulation to water consumption over a longer time ergy between carbon fixation and water loss (Houghton interval, such as, for example, a growing season. The et al. 2001; IPCC Working Group 1 2004). Therefore, former (A/E) gives instantaneous estimates of WUE an increased understanding of the interactions between and the latter gives a long-term WUE. The long-term the vegetation and the hydrological cycle is of great method cannot be determined easily because it possi- importance. More recently, water use efficiency bly requires a large amount of labor in addition to the (WUE), that is, the amount of carbon biomass pro- actual difficulties involved in the simultaneous and ac- duced per unit water transpired by the plant leaf, has curate measurement of transpiration and biomass in been used as a tool to measure the coupling process the field (Wright et al. 1988). The instantaneous method, Received 9 Dec. 2004 Accepted 12 Jun. 2005 Supported by the Frontier Project (CX10G-E01-08-02) and the Backbone Project (CX10G-E01-02-01) of the Knowledge Innovation Program of the Institute of Geographic Sciences and Natural Resources Research, the Chinese Academy of Sciences. *Author for correspondence. Tel.: +86 (0)10 6488 8996; Fax: +86 (0)10 6485 9781; E-mail: <[email protected]>. 1460 Journal of Integrative Plant Biology (Formerly Acta Botanica Sinica) Vol. 47 No. 12 2005 although it can be performed easily, may not necessar- coupling process between carbon assimilation and wa- ily correlate with long-term plant performance (Martin ter transpiration of vegetation in a subtropical watershed, and Thorstenson 1998) and, thus, the WUE calculated we investigated the seasonal changes of foliar δ13C using this method is not suitable to the time scales of values and WUE during the whole growing year, from many hydrological models. Therefore, new and reli- May 2002 to May 2003, and focused on differences in able methods for measuring the WUE of plants need to physiological responses, as indicated by δ13C values be used. and WUE, to meteorological factors for the species A significant positive correlation has been shown investigated under common environmental conditions. between δ13C and WUE both theoretically and empiri- We expect to use monthly integrated data collected from cally (Farquhar et al. 1982a, 1982b, 1989). Since then, the routine weather stations to predict seasonal δ13C δ13C has been gradually developed as an indicator to values and WUE of the species studied to yield useful measure WUE by many authors (Ehleringer and information for the parameterization of WUE for fu- Osmond 1989; Gower and Richards 1990; Smedley et ture modeling considerations. al. 1991; Dawson and Ehleringer 1993; Knight 1994). 13 1 Materials and Methods In part, δ C is partly by Ci/Ca, the ratio of CO2 con- centrations in leaf intercellular spaces (Ci) to that in the 1.1 Study site atmosphere (Ca; Farquhar et al. 1982, 1989; Farquhar The study was performed at the Qianyanzhou Eco- and Richards 1984). This ratio can be used as a proxy logical Research Station, which is located in the Jiazhu of a plant’s long-term WUE because, under water watershed (115°03'01'' E–115°04'22'' E, 26°44'12'' N– 13 stress, plants discriminate less against C during CO2 26°45'28'' N, altitude 80–110 m), Taihe County, Jiangxi uptake, resulting in an increase in integrated WUE. Province. The area is characteristic of a typical sub- Thus, the δ13C value of plant leaves provides an inte- tropical monsoon climate. Annual air temperature av- grated measurement of internal plant physiological and erages 17.8 °C (–5.1 °C in January and 31.3 °C in external environmental traits affecting photosynthetic July). Total solar radiation is 4 349 MJ/m2 and annual gas exchange over the period while the carbon was precipitation amounts to 1 461 mm. Approximately 70% assimilated (Ewe et al. 2003) and it can also be re- of the annual rainfall occurs from March to June and garded as an index of physiological coupling of carbon 30% occurs from July to September. The soil is typi- fixation and water loss in plants. cal red earth generally less than 80 cm in depth. The application of the δ13C method to ecological The Jiazhu watershed belongs to the red soil hilly studies has not been widespread in China (Sun et al. region of subtropical southern China. Originally, there 1993; Lin et al. 1994, 1995;Yan et al. 1998; Liang et was a large area of evergreen broad-leaved forest dis- al. 2000; Su et al. 2000; Qu et al. 2001; Chen 2002). tributed in this region. However, because of anthropo- Most of the research using δ13C in China has focused genic activities or clear-cutting for cultivation, espe- mainly on deciduous forests and grasslands in the tem- cially in the 1950–1960s, the original forest was totally perate zone of northern China, whereas studies on the destroyed at the end of 1970s. Later, the Chinese Acad- conifer and evergreen forests in subtropical zones of emy of Sciences (CAS) established Qianyanzhou Eco- southern China are rare (Lin et al. 1994, 1995). In logical Pilot Station, targeting the restoration of veg- particular, there has been no study investigating the etation and the conservation of soil and water in the seasonal variation of δ13C and the WUE of trees and area. After nearly 20 years forestation by the CAS, the their responses to changes in environmental factors in present forest patch was constructed mainly by the the subtropical region of China. coniferous species Pinus massoniana Lamb., P. elliottii As part of a larger study seeking to model the Engelm., and Cunninghamia laceolata (Lamb.) Hook., Hai-Tao LI et al.: Seasonal Variation of δ13C of Four Tree Species: A Biological Integrator of Environmental Variables 1461 as well as the evergreen broad-leaved species Schima laboratory for stable isotope analysis. superba Gardn. et Champ. In total, 270 carbon isotopic samples were analyzed 1.2 Species selected on a Finnigan MAT253 gas mass spectrometer (Thermo All species investigated are C3 plants. They were Electron Corporation, FL, USA) to a precision of ± 0. located in three plots (Table 1). The conifers P. 01‰, in the Stable Isotope Laboratory, Institute of massoniana, P. elliottii, and C. laceolata and the ev- Geology and Geophysics, the Chinese Academy of ergreen broad-leaved species S. superba were all planted Sciences. Carbon isotopic abundance, in per mil units in 1984. Of them, P. elliottii is the most widely planted (‰) was determined using the following equation: 13 exotic species in the subtropical region of southern δ C=((Rsample/Rstandard)–1)×1000 13 12 China. Imported from southeastern America over 50 where Rsample is the C/ C ratio of the sample and 13 12 years ago, this exotic is now the main timber species in Rstandard is the C/ C of the Pee-Dee Belemnite the region because of its high productivity. The other standard. three co-occurring species are all native species. P. 1.4 Meteorological variables massoniana is a typical pioneer species that used to be Routine meteorological data, including precipitation, planted in completely open ground with harsh habitat air temperature, solar radiation, relative humidity, at- conditions. C. laceolata is a widely distributed timber mospheric pressure, and evaporation (Fig. 1), were species with a long history in southern China. The only collected using an AMRS-1 weather station (Changchun, broad-leaved tree species, S.