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An evaluation of biological and climatic effects on plant n-alkane distributions and δ2Halk in a field experiment conducted in central Tibet

Author:
Bai, Yan, Azamdzhon, Murodov, Wang, Shiping, Fang, Xiaomin, Guo, Haichao, Zhou, Pengchao, Chen, Chihao, Liu, Xiaomin, Jia, Shugang, Wang, Qi
Source:
Organic geochemistry 2019 v.135 pp. 53-63
ISSN:
0146-6380
Subject:
Angiospermae, alkanes, carbon, field experimentation, herbaceous plants, hydrogen, isotopes, paleoclimatology, temperature, China
Abstract:
The distributions of long chain n-alkanes and their hydrogen isotope values (δ2Halk) can be used to investigate paleoclimatic changes, but, as yet, the degree to which plant types, temperature and/or hydrology may drive such variations, cannot be discriminated. Seven co-occurring herbaceous plants (angiosperms) were studied in climate-controlled growing conditions in an open-top chamber located in Naqu, Tibet, in 2015 and 2017, using generalized n-alkane parameters, viz. n-alkane concentrations (Concalk), the carbon preference index (CPI) and the average chain length (ACL), and δ2Halk values. These plants were subjected to warming (W, spanning a < 4 °C mean annual temperature (MAT) gradient) and the amount of water that plants received (100% precipitation differences) conditions in 2015 and 2017, respectively. Growth experiments showed that: (1) No significant relationships were found between n-alkane parameters (Concalk, ACL and CPI) and temperature (a 4 °C difference) or precipitation (100% precipitation differences); (2) The δ2Halk increased ca. 10–30‰ during W 4 °C conditions, with differences in the sensitivity of responses to W between different species. During P treatments, the variability in δ2Halk values was close to that caused by a W 4 °C response; and 3) the interspecies variability in n-alkane distributions and δ2Halk (ca. 30–50‰) was higher than that caused by these P and W responses. These results highlight the importance of the potential impact of any changes in the floral assemblage when interpreting sedimentary n-alkane distributions and δ2Halk records.
Agid:
6474547