Trace metals of needles and litter in timberline forests in the Eastern of Tibetan Plateau, China

Ecological Indicators 45 (2014) 669–676

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Trace metals of needles and litter in timberline forests in the Eastern of Tibetan Plateau, China Ronggui Tang a,b , Ji Luo a,∗ , Peijun Yang c , Jia She a,b , Youchao Chen a,b , Yiwen Gong a , Jun Zhou a a Key Laboratory of Mountain Surface Processes and Ecological Regulation, Institute of Mountain Hazards and Environment, Chinese Academy of Sciences & Ministry of Water Conservancy, Chengdu, China b University of the Chinese Academy of Sciences, Beijing, China c School of Biological Sciences and Engineering, Shaanxi University of Technology, Hanzhong, Shaanxi 723000, China

a r t i c l e

i n f o

Article history: Received 29 November 2013 Received in revised form 8 May 2014 Accepted 1 June 2014 Keywords: Trace metals Timberline needles Geostatistical analysis Bio-monitor

a b s t r a c t Concentrations of six trace elements (Cr, Pb, Cd, Co, V and Ni) in needles and litter of the fir (Picea spinulosa) and spruce (Abies georgei var. smithii) collected respectively at 42 sites and 18 sites in timberline forests in Heng Duan mountains, China, are reported in the present study. Mean concentrations of trace metals (Cr, Co, Ni, V, Cd and Pb) were 3.07 mg kg−1 , 2.48 mg kg−1 , 39.81 mg kg−1 , 8.12 mg kg−1 , 0.13 mg kg−1 , 4.26 mg kg−1 respectively in litter and 0.89 mg kg−1 , 0.38 mg kg−1 , 7.33 mg kg−1 , 0.38 mg kg−1 , 0.92 mg kg−1 and 0.92 mg kg−1 in needles. In contrast to needles, all of elements in both parts were significantly enriched in the litter. Translocation of trace metals in the needles senescence before falling off may be confirmed, but additional investigations should be performed. Geostatistical analysis of Arcgis 10.0 was carried out in order to present the spacial distribution of trace metals in needles. The mine areas had relatively high levels of trace metals according to our original data. Trace metal concentrations of three belt transects, which could be the results of responding to the effects of the monsoon, were different. We deduced that mineral resources and climatic factor (southeasterly and southwesterly monsoon) could be possible contributions regarding the distribution of trace metals in needles. Depending on the results, we proposed a simple and novel way of the biomonitor of trace metal. This method maybe used as a preliminary judgment to the possible source of trace metals. This study also is the first report on the spatial distribution of needle trace metals in the timberline forests by geostatistical analysis. Such biological monitoring is needed to provide databases which will facilitate the next step of this kind of studies which would be to evaluate levels of trace metal accumulation. In order to better understand trace metals of our study area, more sampling sites, climate data, soil data of trace metal, back trajectory studies of air mass and the continuous monitor should be good choices. © 2014 Elsevier Ltd. All rights reserved.

1. Introduction Trace metals may create adverse effects on the environment and human health depending upon their bioavailability and toxicity in various environmental compartments (Pacyna and Pacyna, 2001). Many trace metals are ubiquitous in various raw materials, such as

∗ Corresponding author at: Institute of Mountain Hazards and Environment, Chinese Academy of Sciences & Ministry of Water Conservancy, #9, Block 4, Renminnan Road, Chengdu 610041, China. Tel.: +86 13548109631; fax: +86 028 85222258. E-mail address: [email protected] (J. Luo). http://dx.doi.org/10.1016/j.ecolind.2014.06.003 1470-160X/© 2014 Elsevier Ltd. All rights reserved.

fossil fuels and metal ores, as well as in industrial products (Pacyna and Pacyna, 2001). Some elements, such as Co, Ni and Zn are essential for various metabolic processes with trace amounts in organisms but can also be toxic to these organisms at high concentrations (Clemens, 2006; Gandois and Probst, 2012). Some other elements, especially toxic metallic elements (Pb, Cd, Cr) have been reported to reduce plant growth and development at high concentrations, causing death of plants in extreme cases (Kuang et al., 2007). Previous studies of trace metal in needles mainly are limited to the region which is located in the nearby zone of smelters, urban and industrial areas (Gratton et al., 2000). Pinus pinea L. is suitable to assess the pollution of trace metal in industrial areas

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and pine needles could be considered as a suitable bio-monitor for atmospheric pollution (Aksoy and Öztürk, 1997; Mingorance et al., 2007; Mingorance et al., 2005; Oliva and Mingorance, 2004; Rossini Oliva and Mingorance, 2006; Sawidis et al., 1995). High concentrations of trace metals (Pb, Cr, and Cd) in needles of Masson Pine growing near industrial sources are reported, which indicate that industrial activities heavily influence the contents of trace metals in needles (Sun et al., 2010). Moreover, needles could be used as a bio-monitor of airborne trace element polluˇ tion (Aboal et al., 2004; Al-Alawi and Mandiwana, 2007; Ceburnis and Steinnes, 2000; Holoubek et al., 2000; Trimbacher and Weiss, 2004). Although a few studies focus on the trace metal in the soil under natural plants (Sheng et al., 2012; Wang et al., 2009; Wu et al., 2011), little attention has been paid to trace metals of fragile ecology timberline areas. There are not any perceptible anthropogenic activities and human intrusion is very rare. However, human population, urbanization and industrialization continue to expand. The emission of trace metals into the atmosphere and the resultant hazards to human life are growing up to be a matter of great concern (Sun et al., 2010, 2011). Trace metal pollutants are brought to remote mountain areas by long-range atmospheric transport and accumulate in the soil and plants by wet or dry deposition (Gandois and Probst, 2012; Migon et al., 1997; Wu et al., 2011). The majority of trace metals from the atmosphere, which are intercepted by plant canopies, are the main source of natural forest areas. On step further, trace metals could be trapped in the epicuticular waxes on the needles surface following atmospheric particulate deposition because of large surface area (Gandois and Probst, 2012). Furthermore, trace metal concentration levels in needles rarely are assessed in low contamination environment (Gandois and Probst, 2012). Kuang et al. report that trace metals (Pb, Cd, etc.) may threaten the health of Masson pine (Kuang et al., 2007). Apparently, the determination of trace metals in needle samples is extremely important for monitoring environmental pollution. Under global climate warming and metabolic changing (Dillon et al., 2010), in addition to the fact that timberline forests are very sensitive to input of pollutants, also the enhanced photosynthesis or respiration is likely to boost the absorption, transfer, and accumulation of many trace metals. 30–40 years ago, forest’s health received a major concern from scientists and the general public in Europe, and two levels of the forest monitoring system have been established successfully (Shparyk and Parpan, 2004). However, health study of timberline forests in the Eastern of the Tibetan Plateau is rare. The eastern Tibetan Plateau is just an isolated region and remote from anthropogenic activities. Due to global change and regional economic development, a large amount of fossil fuel combustion and smelting produce different kinds of pollution. Because these mountain areas are the head water of many large rivers such as the Salween River, Lancang River, Jinsha River, long-term and extensive pollution can be a severe threat to its ecosystem stability (especially to the fragile timberline forest) and downstream (Luo et al., 2013a). As a result, bio-monitor of trace metals in timberline forests becomes increasingly significant. In this present study, the fir (Picea spinulosa) and spruce (Abies georgei var. smithii) are selected as a bio-monitor of trace metals for several reasons; (1) the similarity of nutrient uptake between spruce and fir, data from the two species are comparable (Yanai et al., 2009); (2) they grow abundantly in timberline; have a widely geographical range in the mountains of southwest, China; and (3) sampling, identification is easy (C¸elik et al., 2005). The aim of the present study is (1) to investigate the current regional levels and distributional characterization of Cr, Co, Ni, V, Cd and Pb using needles of fir and spruce in timberline forests in Hengduan mountains, Eastern Tibetan Plateau, China; (2) to explore possible sources and influence factors of trace metal in needle.

2. Materials and method 2.1. Study sites Needles samples were separately collected from July to August, 2012, in timberline forests of the middle of the Hengduan Mountains, eastern Tibetan Plateau, China. The Hengduan mountains are situated in western Sichuan and Yunnan provinces in China and eastern Tibetan Autonomous Region, China. It is a series of mountain ranges that stretch in the north-south direction, with nearly 900 km long, 4000–5000 m above sea level, and commonly 1000 m or more elevation difference between mountain valleys. The climate of Hengduan mountain is affected by westerly circulation (south branch), Indian Ocean monsoon and Pacific Ocean monsoon. It is also the only region containing both the Pacific and Indian Ocean water system (Yao et al., 2013). Pacific and Indian Ocean water system produced southeasterly and southwesterly monsoon respectively in the summer. The southwesterly monsoon was landed and developed northward from India and Myanmar in May each year. The air mass southeasterly monsoon from Pacific Ocean passed though Sichuan province and was northwestard taken to our study area (Wang et al., 1983). There are for two seasons: the dry season and the wet season, with a deposition ranging 903–2595 mm. Most of (∼85%)precipitation is concentrated in June, July and August. In the dry season, the region is mainly dominated by westerly circulation, with scarce rainfall and dry air (Cong et al., 2010). The annual mean temperature ranges from 14–16 ◦ C and the mean temperature in the coldest month was 6–9 ◦ C. Needle materials were collected at 42 sites and litter samples were collected at 18 sites (Fig. 1) in Heng Duan mountains, where mentioned vegetation species were abundant. In order to understand the influence of further large scale of air mass, differences of trace metal concentrations were analyzed among three belt transects, which were divided into TA, TB and TC due to the climatic factor (Figs. 1 and 5). TA included S29, S30, S31, S42, S25, S40, S41, S19, S20, S21, S22, S23, S18, S24, S39, S28 and S26; TB included S35, S36, S27 and S37; and TC included S2, S32, S33, S3, S4, S38, S1, S6, S7, S8, S5, S12, S13, S16, S17, S9, S10, S11, S14, S15 and S34. “S” stood for the sample site. TA was more influenced by the southwesterly monsoon, while TB was mainly influenced by southeasterly monsoon. As for TC, there was scarcely any influence of southeasterly and southwesterly monsoon compared with TA and TB. 2.2. Sampling At each sample point, three 20 m × 30 m sample plots were established as replicates (Fig. 2). Each sample plot was composed of twenty-four 5 m × 5 m quadrants (Pouyat and McDonnell, 1991). Twelve quadrants in each sample plot were randomly selected for sampling like the cell A (Luo et al., 2013b). Needles were collected from 1 to 2 trees in each quadrant. From those trees, the age of needles, which were gathered from three years or older branches 2 m ˇ and Steinnes, 2000), above the ground in all directions (Ceburnis should be one or two years. Needle samples from different trees and litter samples from the latest deciduous needles (just including needles with rare decomposing) under the corresponding conifer tree were homogeneously mixed respectively. The latest litter was judged by an experienced specialist who worked on the study of decomposition of litter many years. All samples were kept in plastic bags in a cold room. After transferred to laboratory, the samples were rinsed with distilled water for about 1 min to remove materials deposited on needle and litter surfaces so that the results of chemical analysis of samples collected in various locations could be compared (Dmuchowski and Bytnerowicz, 1995; Karweta and Poborski, 1988). After the attachments of litter surface were eliminated, we would easily prove the transfer of trace metals between

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Fig. 1. Sampling sites of conifer needles and litter (fir, spruce) in the Eastern of the Tibetan Plateau, China.

Fig. 2. Sketch map of sampling plan. The outline border stands for sampling point in the “a”. Three big cells (A–C) stand for sample plots (20 m × 30 m). The small green cell stands for one quadrat (5 m × 5 m). The tree is presented to fir and spruce. In the “b”, alphabets stand for the direction of sampling, and numbers stand for the ages of branches and needles. Needles on the dotted line circle are our samples.

needles and litter in a more reliable way. In other word, the effect of atmospheric deposition could be removed in litter. In addition, trace metal concentration in needles became less affected by washing (Sun et al., 2010). After washing, all samples were oven-dried at 60 ◦ C for 24 h, milled in agate mortar and passed through a 0.2mm sieve. Then, needles and litter samples were stored in clean self-sealing plastic bags until chemically analyzed. 2.3. Element analysis All plant samples which were prepared for analysis have gone through the same procedure. After being wet digested with nitric acid–hydrogenperoxide–hydrofluoric acid, the solutions were analyzed using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) (7700x, Agilent Technologies, America) for Cr, Cd, Co, V, Ni and Pb. For analysis Method referred to Inductively Coupled Plasma Mass Spectrometry (ICP-MS), USA EPA Method 6020a (Revision 1, February 2007). The detection limits were: Cr (0.01 mg L−1 ),

Cd (0.001 mg L−1 ), Co (0.001 mg L−1 ), V (0.01 mg L−1 ), Ni (0.005 mg L−1 ), and Pb (0.002 mg L−1 ).Quality control was ensured through the analysis of duplicate reference materials according to the National Quality and Technology Supervision Agency of China (GBW07603 and GBW07604). Accuracy was accessed by measuring reference materials and the measurement errors were lower than 5% for ICP-MS analysis. Recoveries of trace metals were located between 110% and 99% of reference materials. Geostatistical analysis and Descriptive statistics and Anova test were carried out by arcgis 10.0 and SPSS 16.0 statistical program respectively. 3. Result and discussion 3.1. Concentrations of trace metals in the needles and litter Concentrations (range, mean value and SD) of Cr, Co, Ni, V, Cd and Pb were given in Table 1. All these sampling data were from natural timberline forests. We had not removed

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Table 1 Concentrations of trace metals in needles (n = 126) and litter (n = 54).

Cr Co Ni V Cd Pb

Table 3 The result of statistical analysis (ANOVA).

Trace element concentrations (mg kg−1 )

Parameters

F

P

n

Needles (n = 126)

Cr Co Ni V Cd Pb

40.059 66.319 14.734 72.223 10.677 11.380

<0.001 <0.001 <0.001 <0.001 0.002 <0.001

174 174 174 174 180 180

Litter (n = 54)

Min

Max

Mean

SD

Min

Max

Mean

SD

0.16 0.04 0.29 0.05 0.00 0.00

3.98 1.73 58.95 3.05 0.57 8.30

0.89 0.38 7.33 0.38 0.05 0.92

0.57 0.30 9.04 0.49 0.09 1.94

0.94 0.20 3.55 0.80 0.02 0.66

8.64 5.34 186.40 21.41 0.43 13.17

3.07 2.48 39.81 8.12 0.14 4.26

2.06 1.62 53.60 5.93 0.13 3.29

Table 4 The ratio between litter and needle concentrations.

the possible outliers. Concentration of different metals in litter and needles varied widely. Mean concentrations of trace metals (Cr, Co, Ni, V, Cd and Pb) were 3.07 mg kg−1 , 2.48 mg kg−1 , 39.81 mg kg−1 , 8.12 mg kg−1 , 0.14 mg kg−1 , 4.26 mg kg−1 in litter respectively and 0.89 mg kg−1 , 0.38 mg kg−1 , 7.33 mg kg−1 , 0.38 mg kg−1 , 0.05 mg kg−1 and 0.92 mg kg−1 in needles respectively. Other studies of trace metal in needles were compared (Table 2). All these concentrations in needles came from control sites of their study areas. From Table 2, in contrast to other studies, Ni concentration of our result was high. On the other hand, concentration of Ni in plants was generally not more than 5 mg kg−1 (Adriano, 2001). It could be drawn a preliminary conclusion that Ni concentration of needles in our study area was singularly high. Further studies of Ni concentration would be done in order to find the cause of high Ni concentrations in needles. Ni concentration of other organs and soil samples should be good choices. Cr concentration in plants were in the <1 mg kg−1 range and seldom exceed 5 mg kg−1 (CHAPMAN, 1966). Pb concentrations in needles are 0.04–1.67 mg kg−1 (Adriano, 2001; Berthelsen et al., 1995). Cadmium concentrations in needles were 0.1–0.9 mg kg−1 in normal areas (Adriano, 2001). Co concentration of tissues of higher plants were generally reported less than 1 mg kg−1 (Waldron, 1980). V concentration was not unreasonable to fall in the range of 0.5–2 mg kg−1 in noncontaminated areas (Bengtsson and Germund, 1976). Some of trace metals in our sampling sites extended above the range of trace metals. This showed our study area existed high concentration of trace elements.

Parameter

Litter/needles

Cr Co Ni V Cd Pb

3.4 6.5 4.6 6.6 21.2 2.6

It was reported that exceed trace metal might be toxic to vegetation and vegetation used them as defense processes in order to keep normal metabolic activity. For example, toxic elements were transferred, excluded or accumulated in non-essential or senescent plant part before needle fell (Aznar et al., 2009; Gandois and Probst, 2012; Mingorance et al., 2007; Probst et al., 2009). According to our result, translocation of trace metal in needles senescence before falling may be proved. However, we could not know the ages of these deciduous needles when they fell, even if it is a fact that we collected the freshly fallen litter. Maybe the litter was mixture of more than one-year needles. Because there were higher concentration of trace metal in needles from more than one-year sample (Kuang et al., 2007). Therefore, the problem, either trace metal transferred from needle to litter or the litter was from the mixture of many years of needles, also should be further studied. In general, litter had a significantly high concentration of trace metal. More investigations should be done so that the sources of trace metal in litter can be found. Under the most recent conditions, any signs of damage of spruce and fir were never seen in our study area due to the toxicity of trace metal. Concentration of trace metal may be not high, but potential risk should be realized. The next step work, technology of the cell level should be used to explain toxicological effect, because pollutants influence firstly reflect hurt of the molecular and biochemical characteristics (Ma et al., 2001). Therefore, in order to better understand the behavior of trace metals from needles to litter, 1–5 years old needles should be collected and detected respectively. In addition, different valence forms of trace metal should also be taken into account to explore the pathways of translocation and accumulation between needles and litter.

3.2. Comparison of trace metal in needles and litter Fig. 3 showed that trace metal (Cr, Co, Ni, V, Cd and Pb) concentration of litter was significantly higher (Table 3). The litter’s trace metal (Cr, Co, Ni, V, Cd and Pb) concentrations were as 3.4, 6.5, 4.6, 6.6, 21.2, 2.6 times as needles’ trace metal concentrations respectively (Table 4). Table 2 The mean concentrations of trace metal in other needles. Species

1 2 3 4 5 6 7 8 9 10 11

Pinus Eldarica Medw. Pinus banksiana Picea abies Pinus massoniana Lamb Spruce Pinus sylvestris L. Pinus pinaster Pinus sylvestris L. White fir Pinus halepensis L. Spruce and fir

Concentration (mg kg−1 ) n

Site

Cr

Co

Ni

V

Cd

Pb

Reference

8 10 22 6 6 35 44 36 17 12 126

Tehran city Ontario Lithuania Mount. Xiaoqiao Carpathians Bialowieza Galicia Kampinos national park Pyrénées Mountains Amman city Tibet Plateau

0.39 – 0.24 0.91 – – 0.13 0.83 – – 0.89

– 0.18 – – 1.1 – – – 0.09 – 0.38

1.86 3.3 – 0.53 – – 2.52 – 4.66 – 7.33

– – 0.42 – 0.55 – – – – – 0.38

– 0.05 0.09 0.26 0.65 0.25 0.05 0.23 0.09 0.12 0.05

14.1 0.6 0.77 0.12 6.8 1.29 0.05 2.1 0.20 11.0 0.92

Kord et al. (2010) Gratton et al. (2000) ˇ and Steinnes (2000) Ceburnis Kuang et al. (2007) Shparyk and Parpan (2004) Dmuchowski and Bytnerowicz, (1995) Aboal et al. (2004) ´ Kurczynska et al. (1997) Gandois and Probst (2012) Al-Alawi and Mandiwana (2007) This study

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Fig. 3. Comparison of trace metal in needles and litter

3.3. Spacial distribution maps of trace metals in needles According to mean concentration of trace metal in each site, geostatistical analysis using spatial interpolation method of IDW (Inverse Distance Weighted) was carried out and spatial distribution of trace metals was presented in Fig. 4. Similar spatial distribution patterns were found for Cr, Co and Ni. Relatively high concentration sites with red and orange color were shown along northwest–southeast direction of map. Pb and V concentration was relatively high (>0.77 mg kg−1 and >0.28 mg kg−1 respectively) in the southeast and relatively low in the northwest (<0.02 mg kg−1 and <0.05 mg kg−1 respectively). Cd mean concentration was relatively high (>0.06 mg kg−1 ) in north, south and east, while low concentration (<0.01 mg kg−1 ) of Cd was in west. It was noteworthy that the high and low concentration of trace metal were a relative value based on the data in our study area. From Fig. 4(a), relatively high concentration (>0.82 mg kg−1 )of Cr within the vicinity of chromium mine in the southeast direction was seen. In northwest direction, there was a little high Cr concentration (0.87–2.75 mg kg−1 ) and possible reason was the contribution of vehicle traffic, because the distance between sample sites and roads was no more than 0.5 km. Map (b) also told us relatively high concentration (>0.30 mg kg−1 ) of Co is near cobalt mines. However, because no sample sites in the northeast direction were performed, which had a cobalt ore in map (b), there was no high Co concentration (<0.14 mg kg−1 ) in needles. Unexpectedly, although relatively high Ni concentration (>5.77 mg kg−1 ) was found near a Ni mine, Ni concentration of sample sites within the vicinity of other Ni mines was low, whereas, Ni concentration away from Ni mines was a little higher. Mineral resources could be no longer a sole influencing factor regard to Ni concentration in needles. From the distributional trend of Ni concentration, climatic factor (southwesterly and southeasterly monsoon) could be a likely contribution. From map (d), there were only two V mines inside our studies area and V concentration of needles near V mines was relatively high (>0.48 mg kg−1 ) compared to that of sites without V mine. In map (e) where relatively high concentration (>0.06 mg kg−1 ) of Cd was

presented close to cadmium mine area. There was relatively low Cd (<0.01 mg kg−1 ) concentration in the west of our study area, where no cadmium mine was found, because Cd belonged to an element of long-range transport family (Breckle and Kahle, 1992). It was possible that contaminants of mining process, which were carried by the air mass or aerosol, were trapped and adsorbed by needles. Final map (f) presented Pb concentration in needles near lead mines was relatively high (>0.77 mg kg−1 ), while Pb concentration near other lead mines where we had not sampling sites was relatively low (<0.23 mg kg−1 ). In general, the relationships between concentrations of trace metal and mineral distribution were recognized, and it was deduced that the corresponding nearby mineral resources could be an important contribution to distribution of trace metal in needles. The climatic factor could also be a possible contribution as to distribution of trace metals in needles. However, in order to confirm the inference, more sites around the mine areas and climatic data should be included into future study. 3.4. Comparison of trace metal in needles between three belt transects Although atmospheric deposition may be the main source of some trace metals (Pb, Cd) in forests (Adriano, 2001), part elements concentration like Cd, Ni and Co what were observed in plant samples may be also from soil uptake. In order to explore source and influence factors of trace metal in needles, trace metal in soil, mining process and atmospheric deposition were mainly taken into account. Regrettably, we did not collect soil samples and just cite other studies. Fig. 5(a) showed that mean concentration of Cr was TA > TC > TB. According to a study of Sheng et al., concentration of Cr in soil was lower in TA (60–80 mg kg−1 ) than in TC (150–500 mg kg−1 ) (Sheng et al., 2012). However, Cr was translocated poorly from soil to shoots (Shanker et al., 2005). So Cr of soil could have little contribution to needles’ Cr concentration. The relatively high Cr concentration of TA may be caused by southerly monsoon with Cr contamination from northeast India and mining area of southwest China (Luo

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Fig. 4. Spatial distribution map of trace metal (Cr, Co, Ni, V, Cd, and Pb) in needles. Red circle points in each small map represented the sketch map of mineral distribution of the corresponding trace metal. Big red points represented large mines and small ones represented small mines. Maps just present the inner and nearby mining areas of our studies. Red circle points of (a), (b), (d), (e) and (f) came from http://baidu.comandhttp://google.com, while red circle points of (c) rooted in Yuan et al. (2012) (Shanshan et al., 2012). Red and orange colors on the each small map represented a relatively high concentration of trace metal, while green and reseda colors represented relatively low concentration of trace metals. Buff color represented the middle value of trace metals.

et al., 2013b). However, in the southeast direction of our study area there existed an abnormally high areas of Cr distribution in soil (Xuejin et al., 2008). Limited Cr substances may be taken to the TB by southeasterly monsoon. Similar pattern was found between Cr and Ni: TA > TC ≥ TB. Soil of TC had high concentration of Ni (100–200 mg kg−1 ) (Sheng et al., 2012) and TA was close to mining areas. Ni was easily absorbed by root and transported with xylem as organic complexes and was highly mobile in plants, with leaves being the major sink in the shoot during vegetative growth (Adriano, 2001). Ni in soil of TC could make a significant

contribution to needles. However, mining process could influence concentration of needle in TA. To some extent, soil and mining process jointly influenced Ni in needles in our study area. Mean concentration of Co was TA = TC > TB, the adjacent areas between TA and TC had high Co concentration (20–40 mg kg−1 ) in soil (Sheng et al., 2012). Co could be absorbed by roots and translocated to foliage (Adriano, 2001). This indicated that Co in soil could be an important contribution to Co in needles. Cd mean concentration of needle was TA > TB = TC, the soil of adjacent area in TC and TA had high Cd concentration 0.2–0.6 mg kg−1 and 0.2–0.4 mg kg−1

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Fig. 5. Comparison of trace metals between three belt transects.

respectively, and the TA was close to Cd mine. And Cd was rather readily translocated throughout the plant following its uptake by roots (Adriano, 2001; Luo et al., 2013a). Maybe relatively high Cd concentration of needles in TA was attributed to both high Cd concentration (0.2–0.4 mg kg−1 ) of soil and atmospheric absorption of needle from fine particle of mine pollutants. Compared to TA and TC, although TB was closer to developed city, Cd coming from polluted areas far away by long distance atmosphere transport was a limited contribution under southeasterly monsoon. However, V concentration was TB > TA > TC, we easily associated V concentration to “the capital of Vanadium and Titanium in the world” – Panzhihua city (near TB), which was located in Sichuan province, China. More than hundreds of billions tons V mines had been explored. Smelters of V mine could be a significant contribution to V concentration in needles in TB due to long distance pollutant transport by southeasterly monsoon. Under southwesterly monsoon, the nearby tiny V mines could influence V concentration of needles in TA. Lead concentration was TA > TB > TC. TA and TB were surrounded by numerous lead mines. Southwesterly and southeasterly monsoon can expand and impact the area. Both of them could lead to high concentration of Pb in needles in TA and TB compared to TC. In general, according to these original data, soil, mine distribution and climatic factor (southwesterly and southeasterly monsoon) could influence the distribution of trace metals in needles in our study areas. In order to better understand distribution of trace metal in our study areas, more sample sites inside the three belt transects and climatic data (dry deposition and precipitation) should be added. Soil properties (pH, TOC, texture, trace metals etc.) of sample sites should also be measured. More investigations should be done to explore source of trace metals. For example, back trajectory studies of air mass that had transboundary contributions to our studies could be a good program. 4. Conclusion According to our results, concentrations of different trace metals in needles and litter have varied widely. The mean

concentrations of trace metals (Cr, Co, Ni, Cd, V and Pb) in litter were 3.07 mg kg−1 , 2.48 mg kg−1 , 39.81 mg kg−1 , 0.13 mg kg−1 , 8.12 mg kg−1 , 4.26 mg kg−1 respectively and in needles 0.89 mg kg−1 , 0.38 mg kg−1 , 7.33 mg kg−1 ,0.92 mg kg−1 , 0.38 mg kg−1 and 0.92 mg kg−1 . In contrast to needles, all of the elements are significantly enriched in the litter. The proof as for translocation of trace metals in needles senescence before falling off could be proved. Compared to other studies, Ni concentration of needles was singularly high. According to the geostatistical analysis, mineral resources and climatic factor (southeasterly and southwesterly monsoon) could be possible contributions regarding to the distribution of trace metals in needles. Co, Cd and Ni of needles may partly come from soil. A way of bio-monitor which could preliminarily detect the possible source of trace metals was proposed. The next step of work, in order to better understanding the behavior of trace metals from needles to litter, 1–5 years old needles should be collected and detected respectively. In addition, different valence forms of trace metals should also be considered to explore the pathways of translocation and accumulation between needles and litter. Furthermore, more sample sites inside the three belt transects and climatic data (precipitation) should be added. Soil properties (pH, TOC, texture, trace metals, etc.) of sample sites should also be measured. Back trajectory studies of air mass had transboundary contributions to our studies shall be included into the program.

Acknowledgements This work was funded by the Knowledge Innovation Project of the Chinese Academy of Science (grant KZCX2-EW-309) and the National Natural Science Foundation of China (grants to 41272200 and 40871042). We thank Zijiang, Yang, Jianhong, Liang and Dong, Yan, Institute of Mountain Hazards and Environment, Chinese Academy of Sciences & Ministry of Water Conservancy, Chengdu, for allowing many kindnesses in the use of software.

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