Δ13c Values of C3 Herbaceous Plants and Their Relationships With
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Research Journal of Chemistry and Environment___________________________________ Vol.17 (4) April (2013) Res. J. Chem. Environ. 13 δ C Values of C3 herbaceous plants and their relationships with humidity indexes in arid and humid climatic regions in northern China Liu X. Z.1, 2, 3* and Wang C. Z.3 1. State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau,Institute of Water and Soil Conservation, Chinese Academy of Sciences, Yangling 712100, CHINA 2. College of Architecture and Urban Planning, Hunan University of Science and Technology, Xiangtan 411201, CHINA 3. College of Geography and Planning,Ludong University,Yantai 264025,CHINA *[email protected] Abstract Keywords: Arid and humid climate zones, C3 herbaceous By measuring the stable carbon isotopes of C3 plants, carbon isotope, humidity index, northern China. herbaceous plants and collecting the carbon isotope data of vegetation in northern China, such data as the Introduction geographic locations and climate factors of 47 Global warming and CO2 concentration enrichment exerted sampling sites (33 of which were measured in this a deep influence to the physiology and ecological process of plants1-2. The complicated relationships between plants study) and carbon isotope of 325 plant samples (217 and climatic environmental factors can be reflected by the of which were measured in this study) were obtained. stable carbon isotope (δ13C) in plant tissues, as the carbon In addition, the humidity indexes in different climatic isotope carried a lot of information reflecting the plants’ zones in northern China were calculated and environmental changes in the past, which was consequently 13 moreover the spatial features of δ C values of C3 used to extract the climatic change information such as herbaceous plants and their relationships with temperature, humidity and precipitation or to reconstruct environmental factors such as humidity indexes were the paleoclimate and paleoenvironment3-6. Currently, 13 analyzed. Within the research scope, the δ13C values relationships between δ C compositions of vegetations and environmental factors in northern China have been studied of C3 herbaceous plants in northern China ranged 7-15 from –29.9 ‰ to –25.4 ‰, with the average value of – by researchers at home and abroad ; however, most studies are limited to a certain single climatic or 27.3‰. The average δ13C value of C herbaceous 3 environmental factor, such as air temperature, precipitation plants increased notably from the semi-humid zone to (soil moisture), or altitude and few studies have been the semi-arid zone to the arid zone; the variation conducted on the relationships between δ13C values of 13 ranges of δ C values of C3 plants in the above three plants and humidity indexes in northern China which can climatic zones were –29.9‰ to –26.7‰ (semi-humid comprehensively reflect the water heat balance. area), –28.4 ‰ to –25.6‰ (semiarid area) and –28.0 ‰ to –25.4 ‰ (arid area), respectively. Temperature and precipitation are two decisive factors affecting plant growth and vegetation distribution and Simple regression analysis showed that differences hence affect the stable carbon isotope compositions of 13 plants. As for plants, temperature can affect their carbon existed in the relationship between δ C values of C3 herbaceous plants and humidity indexes. In the semi- isotope fractionation via the change in biochemical reaction speed during the photosynthesis process (such as the arid zone, semi-humid zone and overall northern 13 activity of enzymes participating in photosynthesis) and the area, δ C values of C3 herbaceous plants showed stomatal conductance of leaves. There are some studies obvious linear negative correlation to humidity showing that carbon isotope values of C3 plants were indexes (P < 0.05). With the increase of humidity negatively correlated to temperature rise16-20 while there are 13 indexes, the average δ C value of C3 herbaceous even more studies indicating that positive correlation plants tended to decrease to different extents. In the existed between carbon isotope and temperature21-24. Still, arid zone, however, linear positive correlation existed there are some other studies suggesting that the above two 13 25 between the δ C values of C3 herbaceous plants and factors were not remarkably correlated . the humidity indexes (P < 0.05). With every 0.1 increase in the humidity index, the average δ13C value In addition to differences in ecological and physiological processes of different plant species and genetic increased significantly by 1.3 ‰. Annual average characteristics, the uncertainty regarding the relationship temperature may be the main reason for the 13 between δ C values of C3 plants and temperature may differences in humidity indexes of the sampling sites relate to the difficulty in distinguishing the influence and 13 and for the C fractionation abilities of C3 degree of influence of environmental factors such as herbaceous plants in arid area. precipitation and lighting to the δ13C values, as well as the *Author for Correspondence interaction of various factors. Besides being controlled by (2) Research Journal of Chemistry and Environment___________________________________ Vol.17 (4) April (2013) Res. J. Chem. Environ. the carbon physiological metabolism process by itself, δ13C and 2009. All the sampling sites chosen were flat, broad, values of plants are also greatly affected due to the bright and distant from villages to avoid human activity and combined effects of various environmental factors. micro relief influence on plant isotopes. The collected samples were all from growing plants. They were either the Farquhar et al26 stated that precipitation, as an important dominant species in the local area or plants collected in the environmental factor, cannot be ignored regarding its three climatic zones to obtain spatial variations of carbon influence on the δ13C values of plants. For example, carbon isotope compositions of the same plant species. Upon isotope values often decrease with the increase of sampling, the number of the same plant species collected in precipitation26-28; no doubt that there are also some studies a sampling site could not be less than 5 to 7 plants. obtaining results opposite to such changing law29. Depending on the number of leaves of each species, the Therefore, if the interference of precipitation cannot be same number of leaves were collected from each plant and eliminated, uncertainties would exist in the relationship then mixed together as a sample for this species. between δ13C values and environmental factors such as precipitation and temperature, resulting in unreliable After the samples were washed with water and air dried reconstruction of paleoclimate, extraction of paleoecology naturally, they were oven-dried at 70°C for 48 hours and information and explanation of stable carbon isotopic were then ground and screened through the 80 mesh sieve composition30. From the above, it is important to establish into samples. Finally, 3-5 mg of the samples was put into a rational relationships between the δ13C values of plants and vacuum combustion tube with catalysts and oxidants added compound humidity and temperature indexes which can and were then fired at a temperature of 1020°C while CO2 comprehensively reflect air temperature and precipitation was produced. After being transformed by an element and apply the results to the inversion of paleoclimate, analyzer (Flash EA1112), the samples were placed on a paleoenvironment and prediction of future trends. Delta Plus XP in College of Resources and Environment, China Agricultural University to measure the plant carbon The humidity index comprehensively describes the water isotope value. Each sample was measured 3-5 times as heat balance conditions and quantitatively reflects the above. The measurement error was ±0.15‰ and the 13 influences of meteorological factors such as air temperature analysis results were expressed by δ CPDB. and precipitation to the dry and wet features in a certain area which not only includes water balance, but also the In addition, the corresponding latitude, longitude and variation of ground energy based on temperature and hence altitude of the sampling sites were all measured by the reflects the interactive action of water heat balance. So far, global positioning system (Magellan GPS Field PRO however, there are rare reports which combined climatic VTM,California). The meteorological data were obtained 13 humidity indexes and δ C values. from meteorological stations near the sampling sites or from the Natural Resource Database of the Institute of Northern China is a region with a fragile ecological Geographical Sciences and Resource (http://www.natural environment and serious land desertification. The resources csdb.cn/index.asp), the Meteorological Science vegetative ecosystem is an obvious indicator of climatic Data Sharing Service Network (http://cdc.cma. gov.cn/ changes. Based on the stable carbon isotope results of shishi/ climate.jsp) and the Meteorological Reference plants in northern China reported at home and abroad, Office of National Meteorological Information Centre. The through field survey, sampling and laboratory test, the meteorological data obtained from the above sources humidity indexes of different sampling sites were included the annual average temperature and annual 13 calculated and the spatial features of δ C compositions of average precipitation from 1971 to 2008 and the average air C3 herbaceous