The Thousand Buddha Grottoes of Tuyoq, Turpan, Xinjiang, China were once a famous Buddhist temple along the ancient Silk Road which was first constructed in the Fifth Century (A.D.). Although archaeological researches about the Grottoes have been undertaken for over a century, the ancient environment has remained enigmatic. Based on seven clay samples from the Grottoes’ adobes, pollen and leaf epidermis were analyzed to decipher the vegetation and climate of Fifth Century Turpan, and the environmental landscape was reconstructed in three dimensions. The results suggest that temperate steppe vegetation dominated the Tuyoq region under a warmer and wetter environment with more moderate seasonality than today, as the ancient mean annual temperature was 15.3°C, the mean annual precipitation was approximately 1000 mm and the temperature difference between coldest and warmest months was 24°C using Co-existence Approach. Taken in the context of wheat and grape cultivation as shown by pollen of Vitis and leaf epidermis of Triticum, we infer that the Tuyoq region was an oasis with booming Buddhism in the Fifth Century, which was probably encouraged by a 1°C warmer temperature with an abundant water supply compared to the coeval world that experienced the 1.4 k BP cooling event.
Citation: Tang Y-N, Li X, Yao Y-F, Ferguson DK, Li C-S (2014) Environmental Reconstruction of Tuyoq in the Fifth Century and Its Bearing on Buddhism in Turpan, Xinjiang, China. PLoS ONE 9(1): e86363. doi:10.1371/journal.pone.0086363
Editor: Michael D. Petraglia, University of Oxford, United Kingdom
Received: September 3, 2013; Accepted: December 2, 2013; Published: January 27, 2014
Copyright: © 2014 Tang et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: This research was supported by China National Key Basic Research Program (2014CB954201). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: The authors have declared that no competing interests exist.
The Xinjiang Uygur Autonomous Region in China is located in the heart of Central Eurasia (Fig. 1), where it has been governed by an arid, temperate continental climate since the uplift of the Tibetan Plateau , . In particular, the Turpan Basin is an extremely arid region of Xinjiang, with only 16.4 mm mean annual precipitation , but 3000 mm evaporation . However, Turpan was once an important stop on the overland trade route ‘Silk Road’ linking China with Central Asia. The investigation of the historical vegetation and climate may provide a key to understand the people’s lifestyle in the Turpan oasis in ancient time.
(A) Location of Turpan in Eurasia, (B) Location of Tuyoq Grottoes in Turpan.
Turpan has been generally characterized by an arid climate with expanding temperate desert and steppe vegetation throughout the Holocene , . In recent years, there have been a series of archaeobotanical discoveries from the Turpan area, including Cannabis sativa , Capparis spinosa , Lithospermum officinale , Vitis vinifera from the Yanghai Tombs (2.5 kyrs BP) , Sesamum indicum from Boziklik Thousand Buddha Grottoes (700 yrs BP) , most of which were plants utilized by indigenous people for medicine, oil, spice etc. Moreover, six species of cereals including Triticum aestivum and Setaria italica from the Astana Cemeteries were recognized as food for local people in 3rd to 9th centuries . Furthermore, Jiang et al.  and Yao et al.  reported the ancient Yanghai people of Turpan were living in an oasis with some swamps 2700 yrs BP ago based on an archaeological environmental study. However, there is still a shortage of research on the ancient climate and environmental reconstruction of Turpan.
The Tuyoq Grottoes of Turpan, first constructed in the Fifth Century and abandoned during the Fifteenth Century, were once a notable Buddhist pilgrimage site, even for the Tang royal family between the seventh to eighth centuries . Since they were discovered by the Russian botanist E. A. Regel in the early 1870s, there have been continuous reports on the archaeological findings such as Buddhist frescoes, silk paintings, wood and pottery utensils and so on –. In 2010, approximately 2500 square meters of caves were excavated by a joint team of the Research Center for Frontier Archaeology of the Institute of Archaeology, Chinese Academy of Social Sciences and Academia Turfanica and Kizil Research Institute .
In the present study, we employ pollen and epidermis analyses to reconstruct the ancient vegetation, climate and environment of the archaeological site ‘The Thousand Buddha Grottoes of Tuyoq’ in Turpan in the Fifth Century, as well as to probe the possible historical signatures of the environment-human interaction there.
Materials and Methods
All necessary permits were obtained for the described field studies and were granted by the Academia Turfanica of Xinjiang Uygur Autonomous Region, China.
Turpan (41°12′–43°40′N, 87°16′–91°55′E) is located in an intermontane basin enclosed by high mountains in Xinjiang, NW China. The basin covers 50,140 km2 including a 7.8 km2 oasis , with the highest Bogeda Peak (5445 m) in the north and the second lowest lake on the planet Aydingkol Lake (−154 m) in the central basin (Fig. 1). The basin is governed by an arid, temperate continental climate, and water resources in the basin come mainly from glacial melt in the Tian and Bogeda Mountains channeled by karez irrigation systems . Modern plants in the basin include camel thorn (Alhagi sparsifolia), sea-buckthorn (Hippophae rhamnoides), tamarisk (Tamarix chinensis), artemisia (Artemisia ordosica), sand ilex (Ammopiptanthus mongolicus) and some cultivated grape (Vitis vinifera), cotton (Gossypium hirsutum), sweet melon (Cucumis melo), poplar (Populus tomentosa), mulberry (Morus alba) etc. .
The Thousand Buddha Grottoes of Tuyoq, comprising 94 caves, are situated in the eastern and western cliff faces of Tuyoq Valley cutting through the Flaming Mountains, Shanshan County near Turpan (Fig. 1). The Grottoes lie fifteen kilometers east of the Gaochang ruins, which are regarded as the earliest example of a combined central Asiatic and Chinese style of Buddhism . The Tuyoq Valley is about eight kilometers in length, with Subeixi Cemeteries in the north and Yanghai Tombs in the south. About one kilometer from the Tuyoq Grottoes, an ancient, small Uighur village called ‘Mazar Village’ is located at the southern mouth of the valley, where yellow clay was the main source of material for local building.
Studied Materials and Methods
Seven soil samples from intact yellow-clay adobes in the northern portion of the eastern Tuyoq Grottoes (42°51.9′N, 89°41.7′E) were selected for this study. There were diverse plant stems and leaves mixed in the clay as architectural strengthening materials (Fig. 2). Samples nos.1 to 5 were collected from Grotto K18, the central Buddhist prayer room in the eastern grottoes. Samples no.6 and no.7 collected from Grotto K38, a cave with a Buddha niche in the center (Fig. 2). According to Chinese Bodhisattva frescoes classification and archaeological research, the grottoes must have been constructed in the Fifth Century , .
(A) Sampling Grottoes K18 and K38, (B) Buddha fresco in the Grotto K18, (C) Picture showing plants fragments mixed in the clay adobe as strengthening materials.
Based on the technique of Heavy Liquid Separation (density: 2.0 g mL−1,) , , 20 g soil samples were analyzed for pollen, which were preserved in glycerin, observed under a Leica DM 2500 light microscope and photographed at 200× or 400× magnifications. The single-grain technique of Ferguson et al.  was applied for pollen observation under a Hitachi S-4800 scanning electron microscope (SEM). 3500 pollen grains from the Tuyoq Grottoes were counted in all, 500 grains from each sample. Pollen identification was based on the monographs ‘Pollen Flora of China’, ‘Pollen morphology of plants from dry and semi-arid areas in China’ and other published literature –, and compared to the pollen of modern plants from the Chinese National Herbarium (PE) if necessary. Simultaneously, pollen of nine common Poaceae species from the modern Tuyoq region were observed under SEM to assist ancient Poaceae pollen identification. The relative abundance (RA) of a pollen taxon is calculated by the equation: RA = N/Nt (N: pollen/spore number of a taxon, Nt: total pollen/spore number in the sample).
Leaf epidermis analysis was carried out by washing plant remains from the ancient clay adobe, then preparing the epidermis in a 1∶1 mixture of 30% hydrogen peroxide (H2O2) and 99% glacial acetic acid (CH3COOH) at 60°C in a water bath for one or two days . Finally, the epidermides were cleaned with a fine brush and washed again in distilled water until the epidermis textures were clearly visible under a stereo microscope. The epidermides were mounted on microscopical slides with glycerin for observation and measurement, followed by the same procedure as pollen observation and photography. 35 blades of leaf epidermides were analyzed from the Tuyoq Grottoes, 5 blades from each sample. The epidermides were mainly identified using the monograph ‘Micromorphological Atlas of Leaf Epidermis in Gramineae’ and other published literature –, and compared to the epidermides of modern plants from PE if necessary. Eight structural features were employed for leaf epidermis taxonomy, including the long cells, short cells, stomatal complexes and subsidiary cell shape, prickle-hairs, macro- and micro-hairs, and silica bodies. The terminology used to describe the leaf epidermis follows Ellis (1979)  and Chen (1993) .
The ancient climate of the Tuyoq Grottoes was reconstructed following the Coexistence Approach (CA) , whereby the following five climatic parameters were calculated: the mean annual temperature (MAT), the mean warmest monthly temperature (MWMT), the mean coldest monthly temperature (MCMT), the temperature difference between coldest and warmest months (DT) and the mean annual precipitation (MAP). On the assumption that the climatic tolerance of an ancient taxon was similar to its nearest living relatives (NLRs), the principle of CA is to estimate the ancient climatic parameters by using the modern climatic parameters of NLRs distribution . In this work, each ancient pollen taxon in the assemblage is identified to a NLR. Modern distribution of NLRs in China follows Wu & Ding (1999) , and the climatic tolerances of NLRs were obtained from the modern meteorological data (1951–1980) recorded at various meteorological stations in China , –. The 3D reconstruction of the Tuyoq landscape in the Fifth Century was completed using software of ‘3D Studio Max’ and ‘Adobe Photoshop’.
44 palynomorphs were extracted from the samples of Tuyoq Grottoes, consisting of 38 angiosperms (85.45%), 3 gymnosperms (13.83%), 1 pteridophyte (0.43%) and 2 unknowns (0.29%) (Table 1, Figs. 3–4). The angiosperms were assigned to 31 families and the gymnosperms to 2 families.
1. Poaceae 2. Ranunculaceae 3. Lamiaceae 4. Castanea 5. Alhagi 6. Apiaceae 7. Chenopodiaceae 8. Picea 9. Betula 10. Artemisia 11. Ephedra 12. Moraceae 13. Caryophyllaceae 14. Fabaceae 15. Pinus 16. Ulmus 17. Salix 18. Vitis 19. Typha 20. Potamogetonaceae 21. Malvaceae 22. Convolvulaceae 23. Elaeagnaceae 24. Polypodiaceae; Scale bar = 20 µm.
1. Ephedra 2. Artemisia 3. Chenopodiaceae 4. Alhagi 5. Castanea 6. Ranunculaceae 7. Vitis 8. Elaeagnaceae 9. Malvaceae 10. Picea; Scale bar in light microscope (LM) and scanning electron microscopic (SEM) overview 10 µm, in SEM close-up 2.5 µm.
In the spermatophytes, terrestrial plants comprised 93.02%, of which 70.11% were herbs (Poaceae 26.11% , Artemisia 19.83%, Chenopodiaceae 10.71%), 15.20% shrubs (Ephedra 10.69%, Alhagi 3.83%, Rosaceae 0.34%), 7.54% trees (Pinus 1.89%, Moraceae 1.80%, Picea 1.26%), 0.17% vines (Vitis), swamp plants (Phragmites australis) comprised 4.00%, aquatic plants only comprised 2.26% (Typha 0.97%, Alisma 0.91%, Potamogetonaceae 0.37%) (Fig. 5).
1,3: Unearthed lower leaf epidermis of wheat (Triticum sp.) from Tuyoq Grottoes, 2,4: Lower leaf epidermis of modern wheat (Triticum aestivum), 5,7: Unearthed lower leaf epidermis of Agropyron mongolicum from Tuyoq Grottoes, 6,8: Lower leaf epidermis of modern Agropyron mongolicum; Scale bar in1,2,5,6 = 30 µm; in 3,4,7,8 = 20 µm.
1,3: Unearthed lower leaf epidermis of reed (Phragmites sp.) from Tuyoq Grottoes, 2,4: Lower leaf epidermis of modern reed (Phragmites australis); Scale bar in 1,2 = 20 µm; in 3,4 = 5 µm.
- 1. Triticum sp. (Family: Poaceae, subfamily: Pooideae).
Lower leaf epidermis composed of long cells, short cells, and stomatal complexes. Long cells narrowly oblong, 37–127 µm long (Xn = 78 µm, n = 20), 7–18 µm wide (Xn = 13 µm, n = 20), with wavy and thick walls, regularly or irregularly interspersed with short cells, non-papillate. Short cells present, paired. Stomatal complexes 19–39 µm long (Xn = 33 µm, n = 20), 9–25 µm wide (Xn = 20 µm, n = 20), subsidiary cells usually low dome-shaped or parallel-sided. Macro-hairs absent, micro-hairs present occasionally.
Unearthed epidermis of wheat (Triticum sp.) was identified by comparison with illustrations in Chen et al. (1993) , and Cai & Guo (1995) , and epidermis from modern wheat (Triticum aestivum) (specimen no. 01941718). The thick cell-walls with constant width, remarkable and large stomatal complexes are characteristic features of Triticum epidermis (Fig. 6).
- 2. Agropyron mongolicum (Family: Poaceae, subfamily: Pooideae).
Lower leaf epidermis composed of long cells, short cells with pitted-cells, and stomatal complexes. Long cells narrowly oblong, 34–85 µm long (Xn = 62 µm, n = 10), 8–25 µm wide (Xn = 16 µm, n = 10), with wavy walls, irregularly interspersed with short cells, non-papillate. Short cells present, solitary or occasionally paired, pitted-cells distinctive with round shape having a diameter of 10–24 µm (Xn = 17 µm, n = 10). Stomatal complexes 18–32 µm long (Xn = 28 µm, n = 10), 15–27 µm wide (Xn = 23 µm, n = 10), subsidiary cells usually low dome-shaped or parallel-sided. Macro-hairs absent, micro-hairs present occasionally.
Unearthed epidermis of Agropyron mongolicum was identified by comparison with illustrations in Chen et al. (1993)  and Xie & Yang (1994) , and an epidermis from a modern plant (specimen no. 01821117). There are five species in the genus Agropyron, Agropyron mongolicum is characterized by pitted-cells, as well as paired short cells present occasionally (Fig. 6).
- 3. Phragmites sp. (Family: Poaceae, subfamily: Arundinoideae).
Lower epidermis composed of long cells, short cells, stomatal complexes, and prickle-hairs. Long cells narrowly oblong with coarse wavy walls, non-papillate, 51–97 µm long (Xn = 61 µm, n = 20), 5–12 µm wide (Xn = 8 µm, n = 20), irregularly interspersed with short cells. Short cells single or paired, silica short cells usually saddle-shaped. Stomatal complexes 12–18 µm long (Xn = 15 µm, n = 20), 3–8 µm wide (Xn = 5 µm, n = 20), subsidiary cells usually parallel-sided, occasionally low dome-shaped. Prickle-hairs and micro-hairs present occasionally.
Unearthed epidermis of reed (Phragmites sp.) was identified by comparison with illustrations in Chen et al. (1993) , Cai & Guo (1995)  and Lin (2008) , and an epidermis from modern reed (Phragmites australis) (specimen no. 0595279). Arundinoideae are distinct from other subfamilies of the Poaceae in having micro-hairs, no papillae, and saddle-shaped silica cells. Phragmites is characterized by the coarse wavy wall of the lower epidermis (Fig. 7).
As a whole, the pollen assemblage of Tuyoq Grottoes is dominated by herbs (70.11%), whereas shrubs and trees are only represented by 15.20% and 7.54% respectively. Apart from widespread Poaceae and Artemisia, almost all palynotaxa with the greatest relative abundance are herbs and shrubs mainly found in arid or semiarid areas of the temperate zones: Artemisia, Chenopodiaceae, Ephedra, Alhagi. The leaf epidermis of Agropyron mongolicum also indicates arid steppe or sandy land. The few trees such as Moraceae, Ulmus and Populus in the palynoassemblage indicate the local presence of some deciduous broad-leaved plants. The coniferous pollen of Pinus and Picea was probably transported to the Turpan Basin by wind . Based on the occurrence of aquatic plants (2.26%) such as Typha and Potamogetonaceae, swamp plants (4.00%) as Phragmites australis and the presence of Polypodiaceae (0.43%), the Tuyoq Valley is suggested to have represented a moist microenvironment with flowing water while the Turpan Basin was generally arid in the Fifth Century. At the same time, wheat and grape were cultivated in this region as pollen of Vitis and leaf epidermis of Triticum were found.
The A/C ratio (A: Artemisia, C: Chenopodiaceae) has been widely used in distinguishing different vegetation of arid areas –. Based on Luo et al.’s (2007)  study on surface soil pollen of Xinjiang, the A/C ratio (median value) of coniferous forest was 3.47, steppes 1.26, desert 0.57, thus an A/C ratio of 1.8 at the Tuyoq Grottoes is indicative of steppe. Furthermore, Artemisia, Ephedra and Chenopodiaceae are the most widespread pollen taxa throughout unforested areas of Xinjiang. When these taxa occurred with Asteraceae, Poaceae, Cyperaceae and Brassicaceae as the dominant pollen group, they suggest a meadow-steppe vegetation, whereas an alpine-steppe is indicated when they were found alongside Caryophyllaceae, Rosaceae, Ranunculaceae and Apiaceae . Clearly, the dominant pollen group of Tuyoq Grottoes (Poaceae Artemisia, Ephedra, Chenopodiaceae, Ephedra and Alhagi) points to a temperate vegetation of meadow-steppe (Table 3).
Based on the 41 identified palynomorphs of spermatophytes, five ancient climatic parameters of the Tuyoq Grottoes were reconstructed by CA as follows: MAT = 8.5–22.1°C (15.3°C median value), delimited by Castanea and Alhagi; MWMT = 23.2–27.5°C (25.4°C), delimited by Alhagi and Betula; MCMT = −9.4–5.9°C (−1.8°C), delimited by Castanea and Ephedra; DT = 13.8–34.2°C (24°C), delimited by Alhagi and Castanea; MAP = 618.9–1389.4 mm (1004 mm), delimited by Castanea and Ephedra (Fig. 8). Compared with the current meteorologic data (Table 4), the median value of the MAP was much higher 1500 years ago, the MAT, MCMT were respectively 1.4°C and 7.7°C higher 1500 years ago, whereas MWMT and DT were lower than today by 7.3°C and 18.2°C, which indicates that in the Tuyoq region the climate was warmer and wetter with weaker seasonality during the Fifth Century.
1. Alhagi 2. Alisma 3. Apiaceae 4. Artemisia 5. Asteraceae 6. Betula 7. Boraginaceae 8. Brassicaceae 9. Caryophyllaceae 10. Castanea 11. Celastraceae 12. Chenopodiaceae 13. Convolvulaceae 14. Corylus 15. Elaeagnaceae 16. Ephedra 17. Euphorbiaceae 18. Fabaceae 19. Fagaceae 20. Juglandaceae 21. Lamiaceae 22. Liliaceae 23. Malvaceae 24. Medicago 25. Moraceae 26. Phragmites australis 27. Picea 28. Pinus 29. Plantaginaceae 30. Poaceae 31. Polygonum 32. Potamogetonaceae 33. Quercus 34. Ranunculaceae 35. Rosaceae 36. Rubiaceae 37. Rutaceae 38. Salix 39. Typha 40. Ulmus 41. Vitis.
3D Reconstruction of Ancient Environment
The environment of Turpan in the Fifth Century was reconstructed and visualized in a 3D presentation based on the investigation of ancient vegetation and climate at the Tuyoq Grottoes (Fig. 9). In the Fifth Century, the landscape of the Tuyoq region was composed of valley, village, mountains and distant desert. Temperate vegetation of meadow-steppe predominated in this area with widespread herbs of Artemisia, Chenopodiaceae and numerous shrubs of Ephedra and Alhagi. The Tuyoq Grottoes were constructed in the cliffs on the sides of the valley. A river flowed through the valley, the village and on to the distant desert. Phragmites australis, Typha and other aquatic plants grew luxuriantly in the Tuyoq Valley. People lived in the basin oasis nourished by the river, wheat fields and vineyards around the village, along with a few deciduous trees such as Ulmus, Betula, Moraceae, Salix and Populus. In the distance, the river is seen vanishing into the desert, while the conifers Picea and Pinus lived in the surrounding mountains.
Ancient Pollen of Reed (Phragmites australis) Identified by SEM and its Archeological Significance
Poaceae pollen have never been used as a diagnostic trait for distinguishing between genera or species since they share the same characteristics (stenopalynous) under light microscopy . In recent years, the scanning electron microscope (SEM) has been increasingly used in pollen identification of cereals and other grasses –. In the Tuyoq Grottoes pollen assemblage, the content of Poaceae pollen reached 26.11%. In order to improve the accuracy of pollen identification, pollen of nine common Poaceae species from the modern Tuyoq region were observed under a SEM, namely Agropyron cristatum, Agropyron mongolicum, Festuca arundinacea subsp. orientalis, Festuca ovina, Sorghum bicolor, Stipa sareptana, Triticum aestivum, Zea mays. In the sample from 1500 years ago, pollen which has the same characteristics as modern reed (Phragmites australis) was identified (Fig. 10). Although the identification of a wide range of grasses by their pollen remains a problem, our results are a useful reminder that there is a very real possibility of determining fossil or ancient grass palynotaxa under SEM observation when only a limited number of species is involved. This is promising and practicable for a higher resolution of crop pollen in archaeological research.
1. Unearthed pollen of reed (Phragmites australis) from Tuyoq Grottoes, 2. Pollen of modern reed (Phragmites australis); Scale bar in light microscope (LM) and scanning electron microscopic (SEM) overview = 10 µm, in SEM close-up = 1 µm.
MAP and Water Supplied by Glacial Melt and Underground Water
We noticed that the reconstructed MAP of the Fifth Century was apparently more than sixty times higher than the current precipitation. Actually, in the arid Turpan Basin, most water is supplied by glacial melt from the Tian and Bogeda Mountains and underground water at present. We suppose that the actual rainfall in the Fifth Century could have either been higher than or similar to that of today. If it was similar to today, the reconstructed 1000 mm MAP may not only have consisted of the actual rainfall, but also incorporated glacial melt or underground water, since plants can utilize any source of available water. Although the meteorological precipitation 1500 years ago is hard to evaluate, it is clear that the Tuyoq region had an abundant water supply as a river flowed in the Tuyoq Valley, which was crucial for the oasis development. At the same time, it indicates that a water source such as glacial melt and underground water have to be taken into account when the ancient MAP of an arid area such as Xinjiang is reconstructed using CA.
Oasis and Buddhism Nourished by Amicable Environment in Turpan
According to the epidermis analysis (Table 2), wheat (Triticum sp.) and reed (Phragmites sp.) were the most used materials mixed in the clay to strengthen the adobe, whereas Agropyron mongolicum and other plants were probably weeds for only a few of them were found. During the early period of the Subeixi Culture (around 700 BC), wheat (Triticum aestivum) was a supplemental crop of oases in Turpan . Until the Fifth Century, the frequent occurrence of wheat (Triticum sp.) in the Tuyoq Grottoes suggests that it was cultivated on a certain scale,and it became one of the major crops during the Gaochang Period . The development of wheat cultivation and the discovery of grape (Vitis sp.) pollen witnessed the blooming of oasis agriculture in this period.
In the Fifth Century, the Xinjiang area experienced a warming climatic tendency ,  whereas the global temperature was undergoing a cooling event around 1.4k BP , . The reconstructed MAT of Turpan 15.3°C was 1.1°C warmer than that of the northern hemisphere  and 7.4°C warmer than the winter half-year-mean temperature of eastern China  in the Fifth Century (Fig. 11), as well as 1.4°C warmer than the current temperature of Turpan 13.9°C . Li (1985) believed that the MAT of the whole of Xinjiang in the Fifth Century was 1–2°C warmer than today ; our result is consistent with this conclusion. Since glacial melt was the main water source for the Turpan Basin , the alteration of water resources caused by climatic change was the crucial factor for oases development . In the Fifth Century, the warmer climate at the Tuyoq Grottoes supplied abundant glacial meltwater to the valley, which enabled the oasis agriculture to flourish.
(A) Temperature reconstruction of Northern Hemisphere from 133 to 1925 A.D., the mean temperature of fifth century (401–500 A.D.) was 14.20°C , (B) Winter half-year-mean temperature reconstruction of eastern China during the past 2000 years, the mean temperature of Fifth Century was 7.9°C .
The Tuyoq Grottoes, included 94 caves along half a kilometer of cliff face in the Tuyoq Valley, were initiated during the Fifth Century. Construction continued until the Seventh Century . If the oases were not well enough developed to furnish financial and material support, such large scale Buddhist grotto construction would have been impossible.
However, in the same period with a similar warm climate in the Taklamakan Desert , , Niya and a series of ancient cities with Buddhist temples were abandoned (Fig. 12, Table 5). Possible reasons for the abandonment may include: 1) River diversion , . As glacial melt increased, increased flow of rivers in the desert basin was prone to cause river diversion but not in an enclosed mountain valley like Tuyoq. 2) River desiccation. When rivers flow across a desert, any increase in temperature would have strengthened evaporation, causing the lower part of the river to dry up. This is considered a possible reason for Niya abandonment , , . 3) Desertification caused by an expansion of the Taklimakan Desert could explain the abandonment of Kaladun city . 4) War or plague. Based on archaeological observations, we speculate that the abandonment of Niya was probably associated with a war threat or plague, since the unearthed Kharoshthi tablets repeatedly mentioned invasions by the Supis (probably Sump Kingdom of northern Tibet).
We thank Dr. Yun-Jun Bai, Institute of Botany, CAS, Beijing, China, for his kind help in identifying the leaf epidermides.
Conceived and designed the experiments: YNT YFY CSL. Performed the experiments: YNT YFY. Analyzed the data: YNT YFY DKF CSL. Contributed reagents/materials/analysis tools: XL CSL. Wrote the paper: YNT.
- 1. Li JJ, Fang XM (1999) Uplift of the Tibetan Plateau and environmental changes. Chin Sci Bull 44: 2117–2124 doi:10.1007/BF03182692.
- 2. Zhang DF, Fengquan L, Jianmin B (2000) Eco-environmental effects of the Qinghai-Tibet Plateau uplift during the Quaternary in China. Environ Geol 39: 1352–1358 doi:10.1007/s002540000174.
- 3. IDBMC (Information Department of Beijing Meteorological Center) (1983c) Land Climate Data of China (1951–1980) (Part VI). Beijing: China Meteorological Press. 4–6, 126–128 p.
- 4. Li X, Yin JY (1993) Arid and dry characteristics of Turpan Basin. Arid Land Geogr 16: 63–69.
- 5. Pan W, Cheng J, Wang SH (2003) Quaternary climate change in Turpan basin and its significance to sandstone-type uranium mineralization. Uranium Geol 19: 332–338.
- 6. Cheng J, Zan LH, Zhang XW (2006) The Holocene vegetation and climate changes in the Turpan Basin of Xinjiang, China Beijing: China Ocean Press. 283–294.
- 7. Jiang HE, Li X, Zhao YX, Ferguson DK, Hueber F, et al. (2006) A new insight into Cannabis sativa (Cannabaceae) utilization from 2500-year-old Yanghai Tombs, Xinjiang, China. J Ethnopharmacol 108: 414–422 doi:10.1016/j.jep.2006.05.034.
- 8. Jiang HE, Li X, Ferguson DK, Wang YF, Liu CJ, et al. (2007) The discovery of Capparis spinosa L. (Capparidaceae) in the Yanghai Tombs (2800 years b.p.), NW China, and its medicinal implications. J Ethnopharmacol 113: 409–420 doi:10.1016/j.jep.2007.06.020.
- 9. Jiang HE, Li X, Liu CJ, Wang YF, Li CS (2007) Fruits of Lithospermum officinale L. (Boraginaceae) used as an early plant decoration (2500 years BP) in Xinjiang, China. J Archaeol Sci 34: 167–170 doi:10.1016/j.jas.2006.04.003.
- 10. Jiang HE, Zhang YB, Li X, Yao YF, Ferguson DK, et al. (2009) Evidence for early viticulture in China: proof of a grapevine (Vitis vinifera L., Vitaceae) in the Yanghai Tombs, Xinjiang. J Archaeol Sci 36: 1458–1465 doi:10.1016/j.jas.2009.02.010.
- 11. Qiu Z, Zhang Y, Bedigian D, Li X, Wang C, et al. (2012) Sesame Utilization in China: New Archaeobotanical Evidence from Xinjiang. Econ Bot 66: 255–263 doi:10.1007/s12231-012-9204-5.
- 12. Chen T, Wu Y, Zhang YB, Wang B, Hu YW, et al. (2012) Archaeobotanical Study of Ancient Food and Cereal Remains at the Astana Cemeteries, Xinjiang, China. PLoS ONE 7: e45137 doi:10.1371/journal.pone.0045137.
- 13. Jiang HE, Li X, Li CS (2007) Cereal remains from Yanghai Tomb in Turpan, Xinjiang and their pelaeoenvrionmental significance. J Palaeogeogr 9: 551–558.
- 14. Yao YF, Li X, Jiang HE, Ferguson DK, Hueber F, et al. (2012) Pollen and Phytoliths from Fired Ancient Potsherds as Potential Indicators for Deciphering Past Vegetation and Climate in Turpan, Xinjiang, NW China. PLoS ONE 7: e39780 doi:10.1371/journal.pone.0039780.
- 15. Editorial office (2007) Thousand Buddha Grottoes of Tuyoq-the earliest confluence of Buddhist from Central Plains and the Western Regions. Chin Cult Herit: 80–82.
- 16. Klementz DA (1899) Nachrichten uber die von der Kaiserlichen Akademie der Wissenschaften zu St. Petersburg in Jahre 1898 ausgerustete Expedition nach Trufan, St. Petersburg.
- 17. Le Coq VA (1913) Chostscho.
- 18. Mokushiki K (1999) Xiyu kao gu tu pu. Beijing: Xuanyuan Press.
- 19. JAT (Joint Archaeological Team of Research Center for Frontier Archaeology of the Institute of Archaeology, Chinese Academy of Social Sciences and Academia Turfanica and Kizil Research Institute) (2011) The Excavation of Tuyoq Grottoes in Shanshan County, Xinjian. Archaeology 7: 27–32.
- 20. Abdirahman H, Bian ZF, Wahap H (2009) Discussion on the Water Resources and Their Rational Development and Utilization in Turpan Basin. J China Hydrol 29: 50–54.
- 21. The editorial board of Chinese Frescoes Corpus (1995) Corpus of Chinese Art Classification-Corpus of Xinjiang Frescoes (6) Tuyoq, Bezeklik. Liaoning Province Art Press.
- 22. JAT (Joint Archaeological Team of Research Center for Frontier Archaeology of the Institute of Archaeology, Chinese Academy of Social Sciences and Academia Turfanica and Kizil Research Institute) (2012) The Excavation of the North Portion of the East Zone of Tuyoq Grottoes in Shanshan(Piqan) County,Xinjiang. Archaeology: 7–16.
- 23. Moore PD, Webb JA, Collinson ME (1991) Pollen Analysis, 2nd edn. Oxford: Blackwell scientific publications.
- 24. Li XQ, Du NQ (1999) The Acid-alkali-free analysis of Quaternary pollen. Acta Bot Sin 41: 782–784.
- 25. Ferguson DK, Zetter R, Paudayal KN (2007) The need for the SEM in palaeopalynology. Comptes Rendus Palevol 6: 423–430 doi:10.1016/j.crpv.2007.09.018.
- 26. IBCAS (Institute of Botany, the Chinese Academy of Sciences) (1976) Sporae Pterido-phytorum Sinicorum. Beijing: Science Press.
- 27. Xi YZ, Ning JC (1994) Pollen morphology of plants from dry and semidry area in China. Yushania 11: 119–191.
- 28. Wang FX, Chien NF, Zhang YL, Yang HQ (1995) Pollen Flora of China,2nd edn. Beijing: Science Press.
- 29. Ma QW, Zhang XS, Li FL (2005) Method of maceration and microscopical analysis on cuticle. Bull Bot Res 25: 307–310.
- 30. Chen SL, Jin YX, Wu ZJ (1993) Micromorphological atlas of leaf epidermis in Gramineae. Nanjing: Jiangsu Science Technology Press. 1–193 p.
- 31. Xie XM, Yang XL (1994) Taxonomic Values of the Leaf Anatomical Characters of Agropyron J.Gaertn.. J Inn Mong Norm Univ Nat Sci Ed 1: 53–58.
- 32. Cai LB, Guo YP (1995) study on constitute cells of leaf epidermis, systematic and phylogenetic path of the family Poaceae. Acta Bot Boreal- Occident Sin 15: 323–335.
- 33. Cai LB, Guo YP (1996) continue study on constitute cells of leaf epidermis, systematic and phylogenetic path of the family Poaceae. Acta Bot Boreal- Occident Sin 16: 65–72.
- 34. Ellis RP (1979) A procedure for standardizing comparative leaf anatomy in the Poaceae II: the epidermis as seen in surface view. Bothalia 12: 641–671.
- 35. Mosbrugger V, Utescher T (1997) The coexistence approach – a method for quantitative reconstructions of Tertiary terrestrial palaeoclimate data using plant fossils. Palaeogeogr Palaeoclimatol Palaeoecol 134: 61–86 doi:10.1016/S0031-0182(96)00154-X.
- 36. Wu ZY, Ding TY (1999) Seed Plants of China. Kunming: Yunnan Science and Technology Press.
- 37. IDBMC (Information Department of Beijing Meteorological Center) (1983a) Land Climate Data of China (1951–1980) (Part I). Beijing: China Meteorological Press. 4–6, 86–87 p.
- 38. IDBMC (Information Department of Beijing Meteorological Center) (1983b) Land Climate Data of China (1951–1980) (Part II). Beijing: China Meteorological Press. 4–5, 72–73 p.
- 39. IDBMC (Information Department of Beijing Meteorological Center) (1984a) Land Climate Data of China (1951–1980) (Part III). Beijing: China Meteorological Press. 4–6, 107–109 p.
- 40. IDBMC (Information Department of Beijing Meteorological Center) (1984b) Land Climate Data of China (1951–1980) (Part IV). Beijing: China Meteorological Press. 4–6, 99–101 p.
- 41. IDBMC (Information Department of Beijing Meteorological Center) (1984c) Land Climate Data of China (1951–1980) (Part V). Beijing: China Meteorological Press. 4–6, 108–110 p.
- 42. Lin XL (2008) Systematic Studies of the Cleistogenes(Poaceae) in China [Master Thesis]. Shandong Normal University.
- 43. Li WY (1998) Quaternary Vegetation and Environment of China. Beijing: Science Press. 1–253 p.
- 44. Yan S, Xu YQ (1989) Spore-pollen association in surface soils in the Altay Mountains, Xinjiang. Arid ZoneResearch 6: 26–33.
- 45. Yan S (1991) Quaternary pollen and spore assemblages and vegetation succession in Xinjiang. Arid Land Geogr 14: 1–9.
- 46. Weng CY, Sun XJ, Chen YS (1993) Numerical characteristics of pollen assemblages of surface samples from the West Kunlun mountains. Acta Bot Sin 35: 69–79.
- 47. Zhao Y, Liu HY, Li FR, Huang XZ, Sun JH, et al. (2012) Application and limitations of the Artemisia/Chenopodiaceae pollen ratio in arid and semi-arid China. The Holocene 22: 1385–1392 doi:10.1177/0959683612449762.
- 48. Luo CX, Zheng Z, Pan AD, An FZ, Beaudouin C, et al. (2007) Distribution of surface soil spore-pollen and its relationship with vegetation in X injiang, China. Arid Land Geogr 30: 536–543.
- 49. Luo CX, Zheng Z, Pan AD, An FZ, Beaudouin C, et al. (2008) Spatial Distribution of Modern Pollen in Xinjiang Region. Arid Land Geogr 28: 272–275.
- 50. Driessen MNBM, Willemse MTM, Van Luijn JAG (1989) Grass Pollen Grain Determination by Light- and UV-microscopy. Grana 28: 115–122 doi:10.1080/00173138909429962.
- 51. Andersen TS, Bertelsen F (1972) Scanning Electron Microscope Studies of Pollen of Cereals and other Grasses. Grana 12: 79–86 doi:10.1080/00173137209428830.
- 52. Page JS (1978) A Scanning Electron Microscope Survey of Grass Pollen. Kew Bull 32: 313–319 doi:10.2307/4117102.
- 53. Ma YX, Li Q, Cui DL (2004) Studies on the pollen morphology of nineteen species Poaceae from Northeast China. Bull Bot Res 24.
- 54. Perveen A (2006) A Contribution to the Pollen Morphology of Family Gramineae. World Appl Sci J 1: 60–65.
- 55. Mao LM, Yang XL (2011) Comparative poolen morphology of 7 species in Stipeae of Poaceae. Acta Micropalaeontologica Sin 28: 169–180.
- 56. Wang S (2000) Gaochang history: Transportation. Beijing: Cultural Relics Press. 85–102 p.
- 57. Li JF (1985) Climatic variation of Xinjiang in recent 3000 years. Proceeding of Quaternary Xinjiang Arid Area. Urumqi: Xinjiang people’s publishing house. 1–7.
- 58. Zhong W, Shu Q, Xiong HG, Tashplati T (2001) Historic paleoenvironmental changes reflected by susceptibility in the sediment, southern margin of Tarim basin. Arid Land Geogr 24: 212–216.
- 59. Bond G, Showers W, Cheseby M, Lotti R, Almasi P, et al. (1997) A Pervasive Millennial-Scale Cycle in North Atlantic Holocene and Glacial Climates. Science 278: 1257–1266 doi:10.1126/science.278.5341.1257.
- 60. Moberg A, Sonechkin DM, Holmgren K, Datsenko NM, Karlén W (2005) Highly variable Northern Hemisphere temperatures reconstructed from low- and high-resolution proxy data. Nature 433: 613–617 doi:10.1038/nature03265.
- 61. Ge QS, Zheng JY, Fang XQ, Man ZM, Zhang XQ, et al. (2002) Temperature changes of winter-half-year in eastern China during the past 2000 years. Quat Sci 22: 166–173.
- 62. Zhang H, Wu JW, Zheng QH, Yu YJ (2003) A preliminary study of oasis evolution in the Tarim Basin, Xinjiang, China. J Arid Environ 55: 545–553 doi:10.1016/S0140-1963(02)00283-5.
- 63. Editorial office (2012) Witness Buddhist cultural confluence -The Tuyoq Grottoes Ruins of Shanshan County, Xinjiang. Hist Ref 22: 24–27.
- 64. Shu Q, Zhong W, Li C (2007) Distribution feature of ancient ruins in south edge of Tarim Basin and relationship with environmental changes and human activities. J Arid Land Resour Environ 21: 95–100.
- 65. Zhou XJ (1989) Probe into the historical period of Tarim Basin desertification. J Arid Reg Res 1: 9–17.
- 66. Fan ZL (1995) Study on the causes of formation and abandonment of ancient oasis in Taklimakan desert. Arid Zone Res Supp 12: 308–317.
- 67. Lin M (1996) Jingjue kingdom and ruins of Niya. Cult Relic 12: 54–55.