TITLE	A reexamination of the relationships among phenological complementarity, species diversity, and ecosystem function
AUTHOR	Guanglian Qin State Key Laboratory of Arid Agroecology, Lanzhou University, Lanzhou 730000, Gansu Province, P.R. China Guozhen Du State Key Laboratory of Arid Agroecology, Lanzhou University, Lanzhou 730000, Gansu Province, P.R. China Yanjiang Luo State Key Laboratory of Arid Agroecology, Lanzhou University, Lanzhou 730000, Gansu Province, P.R. China Gaosheng Dong Grassland Workgroup of Maqu County, Maqu 747000, Gansu Province, P.R. China Jianyun Ma Grassland Workgroup of Maqu County, Maqu 747000, Gansu Province, P.R. China
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ABSTRACT	Interest in the effects of species diversity on ecosystem function has been rapidly increasing, and many studies have concluded that increasing species diversity improves ecosystem function. Theories predict that phenological complementarity, the asynchrony of species resource use and growth, may explain how species diversity enhances ecosystem function but it remains largely untested. In this paper, we tried to determine: (i) whether, in a species-rich natural assemblage, increasing species diversity enhances ecosystem function by increasing phenological complementarity, and (ii) how phenological complementarity was related to the scales of alpha-diversity. Over a three-year period, we conducted the experiment in 55 permanent plots with a relatively homogeneous environment in natural alpine grasslands, and estimated percent cover of each plant species present in each plot three times in each growing season. Species diversity in each permanent plot was quantified in two ways, the total number of species, and the evenness of species abundance. Phenological complementarity was quantified as the negative logarithm of the variance ratio. Ecosystem function was measured as total annual cover (i.e. the sum of maximum cover values recorded for each species in a growing season). Statistical analysis of the relationships between total annual cover, species diversity, and phenological complementarity found that total annual cover increased with species diversity, and phenological complementarity was responsible for the positive effects of species diversity on total annual cover. Phenological complementarity, however, was not significantly related to species diversity. These results indicate that phenological complementarity was critical to the maintenance of total annual cover in our studied alpine plant communities. However, considering different mechanisms of species coexistence (e.g. local similarity), phenological complementarity is not necessarily linearly correlated with the scales of alpha-diversity in species-rich plant assemblages. In addition, other mechanisms, for example, the sampling effect for phenological complementarity, may simultaneously act on how phenological complementarity enhances ecosystem function. Therefore, greater understanding of how diversity and phenological complementarity influence ecosystem function will require more extensive experiments that control the effects of composition.
KEYWORD	Alpine grassland; Ecosystem function; Evenness; Phenological complementarity; Species diversity; Variance ratio;
ARTICLE INFO	Botanical Bulletin of Academia Sinica, Volume 44 Number 3 July 2003, page 239-244, 6 pages
PUBLISHER	Institute of Plant and Microbial Biology, Academia Sinica, Taipei, Taiwan, Republic of China