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Root Biomass Distribution in Alpine Ecosystems of the Northern Tibetan Plateau

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Root Biomass Distribution in Alpine Ecosystems of the Northern Tibetan Plateau Environ Earth Sci (2011) 64:1911–1919 DOI 10.1007/s12665-011-1004-1 ORIGINAL ARTICLE Root biomass distribution in alpine ecosystems of the northern Tibetan Plateau Xiaojia Li • Xianzhou Zhang • Jianshuang Wu • Zhenxi Shen • Yangjian Zhang • Xingliang Xu • Yuzhi Fan • Yuping Zhao • Wei Yan Received: 26 May 2010 / Accepted: 8 March 2011 / Published online: 29 March 2011 Ó Springer-Verlag 2011 Abstract The root biomass distribution in alpine eco- Introduction systems (alpine meadow, alpine steppe, desert grassland and alpine desert) was investigated along a transect on the Plant root is a critical component of ecosystems (Norby northern Tibetan Plateau in 2009. The results showed that and Jackson 2000). Root production represents the pri- roots were mainly concentrated in the 0–20 cm layer, and mary input source of organic carbon for soils and plant root biomass decreased exponentially with increasing soil carbon stocks in terrestrial ecosystems can be measured depth. Root biomass was estimated to be 1,381.41 ± based on root production (Eswaran et al. 1993; Jackson 245.29 g m-2 in the top 20 cm soil, accounting for 85% of et al. 1996; Scurlock and Hall 1998; Mokany et al. 2006). the total root biomass. The distribution pattern of the root For grassland ecosystems, the root systems represent a biomass proportion along the soil profile was similar in more important carbon storage mechanism than forests different alpine ecosystems. The root biomass density because root/shoot ratios are higher for grasslands (Jack- varied with different alpine ecosystems and the total son et al. 1996). The proportion of root biomass can be average root biomass was 1,626.08 ± 301.76 g m-2. Root greater than 80% of the total plant biomass in some biomass was significantly correlated with average relative grassland ecosystems (Caldwell and Richards 1986; humidity, annual precipitation and soil organic matter. This Mokany et al. 2006). In Tibet Plateau, the proportion of indicates that precipitation and soil organic matter might be root/shoot can reach up to 5.8 (Yang et al. 2009b). crucial for plant growth in the study area, while tempera- Moreover, root biomass constitutes the core portion of a ture is not an important factor controlling root growth. plant’s total primary productivity in grassland ecosystem (Yan et al. 2005). The primary productivity of roots often Keywords Alpine ecosystem Á Environmental factors Á accounts for 60–80% of total net primary production in Northern Tibetan Plateau Á Root biomass grassland ecosystem (Coleman 1976; Agren et al. 1980). Thus, it is vitally important to study the distribution of root biomass in grasslands. Relative to the aboveground biomass, investigation of root biomass distribution and belowground processes are much more challenging due to the high requirement of X. Li Á X. Zhang (&) Á J. Wu Á Z. Shen Á Y. Zhang Á X. Xu Á intensive labor and high cost (Vogt et al. 1995; Hu et al. Y. Fan Á Y. Zhao Á W. Yan 2005; Hendricks et al. 2006; Metcalfe et al. 2007). In Key Laboratory of Ecosystem Network Observation and addition, environmental factors, including climate, soil Modeling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, physical, chemical and biological characteristics, and plant Beijing 100101, China properties can all affect the distribution of root biomass e-mail: [email protected] (Zhang et al. 1996; Rodrı´guez et al. 2007a; Macinnis-Ng et al. 2010). It is important to understand the effects of X. Li Á J. Wu Á Y. Fan Á Y. Zhao Á W. Yan Graduate University of Chinese Academy of Sciences, environmental factors on root biomass distribution in var- Beijing 100049, China ious regions. 123 1912 Environ Earth Sci (2011) 64:1911–1919 Current studies about root system in Chinese grass- Materials and methods lands have been mainly carried out on temperate grass- lands in Inner Mongolia (Ma et al. 2008), alpine Study area grasslands in the Tianshan Mountains (Wang et al. 2008; Li et al. 2008), and alpine meadows on the Tibetan The study was carried out on northern Tibetan Plateau, Plateau (Wang et al. 2007a). Studies on the vast northern where the mean elevation is 4,500 m above sea level, being Tibetan grassland are still limited. Field data about root high in the north and south and low in the middle. The biomass has been collected along the south–north transect plateau’s surface is characterized by quite integrated, transiting from forest to alpine grassland in the eastern hummocky uneven terrain. The strath and basin are widely Tibetan Plateau (Luo et al. 2005). Yang et al. (2009a) distributed. It features a typical continental highland cli- reported the root biomass distribution around Beiluhe mate, being cold, dry and arid or semi-arid in most regions station (34°51.2360N, 92°56.3950E, 4,628 m asl) of of the Plateau and has low annual precipitation and high Tibetan Plateau. Wu et al. (2011) studied root biomass annual evaporation. There are large annual and daily and root turnover rate in a Kobresia humilis meadow changes in air temperature. The mean air temperature is (37°29–450N, 101°12–230E) at Haibei alpine meadow 6–10°C in the warmest month and below -10°C in the ecosystem research station at the northeast edge of coldest month. Annual precipitation ranges from 100 to Tibetan Plateau. These studies involved only a small 300 mm and decreases from southeast to northwest (Yang portion of the northern Tibetan Plateau. and Zheng 2002). It exhibits no obvious four seasons, and it The Tibetan Plateau is known as the third pole of the has only a cold season (long, cold and dry) and a warm world, and the grassland ecosystem occupies approxi- season (short, wet and cool). The growing season is only mately 2.5 9 106 km2 of area. The alpine ecosystems of 90–150 days. This area has strong winds in winter and the northern Tibetan Plateau, southwest China, are in the spring, and the annual wind velocity averages 3.4 m s-1. central part of Tibetan Plateau (Li 2000). With its unique The representative vegetation types are alpine meadow geographical environment, the northern Tibetan Plateau is mainly consisting of S. subsessiliflora var. basiplumosa or a region particularly sensitive to global change, especially Festuca ovina, alpine steppe typically composed of Stipa warming. It has been reported that global warming has purpurea, Carex moorcroftii and compact ceratoides, and been more severe on northern Tibetan Plateau than other desert grassland principally consisting of Stipa glareosa and region in northern hemisphere (IPCC 2007). Due to the alpine desert predominated by Ceratoides laten. The soil combined effects of global change and anthropogenic layer is thin with a high gravel content. The most widely activities (i.e., grazing), the ecological conditions have distributed soil type is cold frozen calcium (alpine steppe deteriorated in the past decades (Zhou et al. 2005; Duan soil) under the alpine steppe, followed by alpine desert et al. 2006). A clear understanding of grassland root dis- grassland soil and alpine desert soil, which developed under tribution in northern Tibet is critical to reserving and plants of the alpine semi-desert and desert (Li 2000). recovering grassland of northern Tibet. In addition, the northern Tibetan Plateau is an ideal place to study root Sampling biomass distribution and the relationships between root biomass and environmental factors due to the low popu- Thirty-seven sampling sites were set up along a transect lation density and relatively less frequent human activities from Anduo County of Naqu district (31°36.432 N0, in the region. 91°42.2970E) in the east to Risong county of Ali district The objectives of the present study were to investigate (33°21.0550N, 79°42.6440E) in the west (Fig. 1). The the root distribution pattern and its relationship with transect covers latitudes from 30°Nto34°N and longitudes environmental factors on the northern Tibetan Plateau of from 79°Eto92°E across an area approximately 1,200 km China. Specifically, the study was aimed (1) to analyze long and 400 km wide. The transect traversed four vege- the vertical distribution of root biomass density in four tation zones, including an alpine meadow zone, alpine alpine ecosystems and (2) to measure total soil nitrogen, steppe zone, desert grassland zone and alpine desert zone, total soil phosphorus, pH and soil organic matter to from east to west on the northern Tibetan Plateau. analyze their potential influence on root biomass. In Soil data were collected using soil core in May 2009 this study, the hypothesis that root distribution may (Table 1). A global positioning system was used to locate be limited by precipitation or temperature was tested. It longitude, latitude and altitude. Belowground biomass was was hoped that this study would provide a scientific measured on each sampling site to the visible root depth, reference for the restoration of degraded alpine grassland with the deepest measurements being 1.3 m (depth inter- ecosystems. vals of 0–5, 5–10, 10–20, 20–30, 30–50, 50–70, 70–100 123 Environ Earth Sci (2011) 64:1911–1919 1913 Fig. 1 Location of study area and sampling sites on the northern Tibetan Plateau of China and 100–130 cm). A soil core (5 cm inner diameter) was root biomass decreased exponentially with increasing soil utilized to sample roots. Three soil samples were collected depth. The exponentially fit equation between the root from each soil layer in each site and then washed through a biomass proportion in each layer to the total and the soil sieve to obtain roots. All root samples were oven-dried in a depth in all alpine ecosystems was: forced-air oven at 85°C for 48 h to a constant weight, and ÀÁ 2 their weights were recorded.
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