Changes in foliar litter decomposition of woody plants with elevation across an alpine forest–tundra ecotone in eastern Tibet Plateau

Plant Ecol DOI 10.1007/s11258-016-0594-9 Changes in foliar litter decomposition of woody plants with elevation across an alpine forest–tundra ecotone in eastern Tibet Plateau Yang Liu . Yamei Chen . Jian Zhang . Wanqin Yang . Zhu Peng . Xinhua He . Changchun Deng . Runlian He Received: 6 July 2015 / Accepted: 25 March 2016 Ó The Author(s) 2016. This article is published with open access at Springerlink.com Abstract To determine litter decomposition rates at different elevations in the alpine forest–tundra ecotone under climate change scenarios in which woody plants shift their ranges upward, litterbags containing foliar litter were incubated on the surface of forest, tree line, and alpine meadow soils (3900, 4000, and 4200 m above sea level, respectively) in the eastern Tibet Plateau of China in October 2012. The selected woody plant species were Abies faxoniana, Betula albosinensis, Sorbus rufopilosa, Rhododendron taliense, Communicated by Karen Harper. Y. Liu  Y. Chen  J. Zhang  W. Yang (&)  Z. Peng  C. Deng  R. He Long-term Research Station of Alpine Forest Ecosystems, Institute of Ecology and Forestry, Sichuan Agricultural University, 211 Huimin Road, Wenjiang District, Chengdu 611130, China e-mail: Y. Liu  J. Zhang  W. Yang Collaborative Innovation Center of Ecological Security in the Upper Reaches of Yangtze River, Chengdu 611130, China X. He Centre of Excellence for Soil Biology, College of Resources and Environment, Southwest University, Chongqing 400715, China X. He School of Plant Biology, University of Western Australia, Crawley 6009, Australia Lonicera lanceolata, and L. myrtillus. Mass loss, carbon (C), nitrogen (N), and phosphorus (P) release, and cellulose and lignin degradation in litter were examined from retrieved litterbags over a 6 month period at the end of one snow-covered season. The results showed that the mass loss of A. faxoniana, L. lanceolata, and S. rufopilosa litter, but not that of the other species, was accelerated at higher elevations. Abies faxoniana, B. albosinensis, and S. rufopilosa C release, A. faxoniana and S. rufopilosa N release, L. myrtillus, L. lanceolata, and S. rufopilosa P release, B. albosinensis, S. rufopilosa, and R. taliense cellulose degradation, and L. myrtillus lignin degradation significantly increased with increasing elevation. These results imply that changes in foliar litter decomposition with elevation, although species-specific, could indicate a possible shift in woody plant composition in the alpine forest–tundra ecotone under climate change scenarios. Thus, further studies regarding how elevation shifts could alter litter decomposition and ecosystem sustainability are warranted. Keywords Alpine forest–tundra ecotone  Climate change  Elevation  Litter decomposition  Woody plants Introduction Global warming has strong impacts on high-elevation ecosystems (Stocker et al. 2013), as it leads to upward 123 Plant Ecol shifts of alpine plants (Pauli et al. 2007; Lenoir et al. 2008), as well as the tree line (Theurillat and Guisan 2001; Grace et al. 2002; Wipf and Rixen 2010). For example, graminoids and herbs have been gradually replaced by shrubs in alpine ecosystems (Cornelissen et al. 2007; Baptist et al. 2010), leading to alterations of plant community structure and species composition (Lenoir et al. 2008), as well as plant litter decomposition (Gavazov 2010). The process of litter decomposition is controlled by environmental conditions, litter quality, and soil organisms (Berg and McClaugherty 2008). Climate change will directly alter environmental factors, such as soil temperature and moisture, snow cover, and soil freezing depth, which in turn affect litter decomposition (Sturm et al. 2005). Additionally, it will alter plant species composition and community structure, leading to changes in plant litter quality and nutrient cycling (Gavazov 2010). For example, shifts in plant communities could affect nutrient release (Santonja et al. 2015). However, whether this process could slow or accelerate litter decomposition is still uncertain. Litter decomposition in alpine ecosystems is generally determined by low-temperature conditions (Baptist et al. 2010; Gavazov 2010). The pattern of foliar litter decomposition and its related releases of carbon (C) and nutrients at high elevations and latitudes are complicated during the long, snowcovered season (Baptist et al. 2010). It has been demonstrated that the first-year decomposition largely accounts for litter decomposition in subalpine forests in winter (Wu et al. 2010; Zhu et al. 2012), and that the role of environmental factors seems to be the most important for winter decomposition in cold biomes (Taylor and Jones 1990; Hobbie and Chapin III 1996). The alpine forest–tundra transition from coniferous forests to shrublands and alpine meadows is sensitive to global climate change (Körner and Paulsen 2004). In such sensitive areas, different vegetations may give rise to dramatic variations in snow depth, snowmelt timing, soil temperature, and soil freezing depth, which, in combination, affect litter decomposition processes (Sjögersten and Wookey 2004; Xu et al. 2010). In addition, shifts in plant species along an elevational gradient could also be related to the availability of nutrients resulting from litter decomposition. In this study, we hypothesized that the litter decomposition of woody plants in an alpine forest– tundra ecotone would increase with increasing 123 elevation because of changes in temperature and the number of freeze–thaw cycles. To test this hypothesis, a short-term, wintertime, litter decomposition experiment was performed during one snow-covered season (from November 2012 to April 2013) in an alpine forest–tundra ecotone located on the eastern Tibetan Plateau, China. The objective of this study was to understand how the foliar litter decomposition of woody plants changes with elevation across an alpine forest–tundra ecotone over one winter season. Materials and methods Site description This study was conducted on Zhegu Mountain (31°510 42800 N, 102°410 23000 E, at approximately 3200–4800 m above sea level (a.s.l.), with a remarkable vertical zonality), which is located in Li County, Sichuan, southwest China. This region is within a transitional area between the Tibetan Plateau and the Sichuan Basin, where the watersheds of the Dadu River and Minjiang River are distributed. There are mixed coniferous broadleaved forests, dark coniferous forests, alpine shrub woodlands, successive alpine meadows from the valley to the ridge, and a snow belt above 4500 m a.s.l. The weather is cool in summer and cold in winter. The annual mean air temperature ranges from approximately 6–12 °C . The coldest month is January (-8 °C), and the warmest month is July (12.6 °C). The mean annual precipitation ranges from 600 to 1100 mm. The snow-covered season starts in November and lasts until the end of April (about 6 or 7 months) in the alpine (...truncated)