Neolithic millet farmers contributed to the permanent settlement of the Tibetan Plateau by adopting barley agriculture.

The permanent human settlement of the Tibetan Plateau (TP) has been suggested to have been facilitated by the introduction of barley agriculture ∼3.6 kilo-years ago (ka). However, how barley agriculture spread onto the TP remains unknown. Given that the lower altitudes in the northeastern TP were occupied by millet cultivators from 5.2 ka, who also adopted barley farming ∼4 ka, it is highly possible that it was millet farmers who brought barley agriculture onto the TP ∼3.6 ka. To test this hypothesis, we analyzed mitochondrial DNA (mtDNA) from 8277 Tibetans and 58 514 individuals from surrounding populations, including 682 newly sequenced whole mitogenomes. Multiple lines of evidence, together with radiocarbon dating of cereal remains at different elevations, supports the scenario that two haplogroups (M9a1a1c1b1a and A11a1a), which are common in contemporary Tibetans (20.9%) and were probably even more common (40-50%) in early Tibetans prior to historical immigrations to the TP, represent the genetic legacy of the Neolithic millet farmers. Both haplogroups originated in northern China between 10.0-6.0 ka and differentiated in the ancestors of modern Tibetans ∼5.2-4.0 ka, matching the dispersal history of millet farming. By showing that substantial genetic components in contemporary Tibetans can trace their ancestry back to the Neolithic millet farmers, our study reveals that millet farmers adopted and brought barley agriculture to the TP ∼3.6-3.3 ka, and made an important contribution to the Tibetan gene pool.

Variation in the stable carbon and nitrogen isotope composition of plants and soil along a precipitation gradient in northern China.

Water availability is the most influential factor affecting plant carbon (δ(13)C) and nitrogen (δ(15)N) isotope composition in arid and semi-arid environments. However, there are potential differences among locations and/or species in the sensitivity of plant δ(13)C and δ(15)N to variation in precipitation, which are important for using stable isotope signatures to extract paleo-vegetation and paleo-climate information. We measured δ(13)C and δ(15)N of plant and soil organic matter (SOM) samples collected from 64 locations across a precipitation gradient with an isotherm in northern China. δ(13)C and δ(15)N for both C(3) and C(4) plants decreased significantly with increasing mean annual precipitation (MAP). The sensitivity of δ(13)C to MAP in C(3) plants (-0.6 ± 0.07‰/100 mm) was twice as high as that in C(4) plants (-0.3 ± 0.08‰/100 mm). Species differences in the sensitivity of plant δ(13)C and δ(15)N to MAP were not observed among three main dominant plants. SOM became depleted in (13)C with increasing MAP, while no significant correlations existed between δ(15)N of SOM and MAP. We conclude that water availability is the primary environmental factor controlling the variability of plant δ(13)C and δ(15)N and soil δ(13)C in the studied arid and semi-arid regions. Carbon isotope composition is useful for tracing environmental precipitation changes. Plant nitrogen isotope composition can reflect relative openness of ecosystem nitrogen cycling.

Agricultural origins and the isotopic identity of domestication in northern China.

Stable isotope biochemistry (delta(13)C and delta(15)N) and radiocarbon dating of ancient human and animal bone document 2 distinct phases of plant and animal domestication at the Dadiwan site in northwest China. The first was brief and nonintensive: at various times between 7900 and 7200 calendar years before present (calBP) people harvested and stored enough broomcorn millet (Panicum miliaceum) to provision themselves and their hunting dogs (Canis sp.) throughout the year. The second, much more intensive phase was in place by 5900 calBP: during this time both broomcorn and foxtail (Setaria viridis spp. italica) millets were cultivated and made significant contributions to the diets of people, dogs, and pigs (Sus sp.). The systems represented in both phases developed elsewhere: the earlier, low-intensity domestic relationship emerged with hunter-gatherers in the arid north, while the more intensive, later one evolved further east and arrived at Dadiwan with the Yangshao Neolithic. The stable isotope methodology used here is probably the best means of detecting the symbiotic human-plant-animal linkages that develop during the very earliest phases of domestication and is thus applicable to the areas where these connections first emerged and are critical to explaining how and why agriculture began in East Asia.

[Correlations between leaf delta13C and physiological parameters of desert plant Reaumuria soongorica].

Reaumuria soongorica is a dominant species in the desert shrubbery vegetation in arid regions of northwestern China, playing an important role in the maintenance of the stability and continuity of desert ecosystem. In this paper, a total of 407 individuals in 21 natural populations of R. soongorica were selected from its main distribution areas to measure the leaf stable carbon isotope composition (delta13C) and nitrogen, phosphorus, potassium, water, proline and chlorophyll contents, with the correlations between the delta13C value and the test physiological parameters analyzed. The results showed that leaf delta13C value was significantly correlated with the contents of leaf potassium, water, and proline (P <0.001), and the correlation with leaf potassium content was most profound (r = 0.793), followed by that with leaf water content (r = -0.786), indicating that the variation of leaf delta13C value could reflect the nutritional status of the plants, and also, their water-deficient degree. The different distribution trends in leaf delta13C value of R. soongorica were likely caused by stomatal conductance, rather than by nutrient-related changes in photosynthetic efficiency under extremely low available water conditions.

[Magnetic characteristics of street dust in Lanzhou and its environmental significance].

Lanzhou has been one of the most seriously polluted cities in the world due to its special geographical location and weather conditions, which make it an ideal place for urban pollution studies. A set of environmental magnetic parameters (chi lf, chi fd%, chi ARM, chi HIRM, SOFT and back field IRM) of the street dust sampled in Lanzhou during spring and summer 2005 were analyzed. These samples were collected along a main street across the urban area and a mountain route from foot to the top. Results demonstrate that the main magnetic minerals in the street dust are magnetite, maghaemite and haematite with some paramagnetic minerals. Plots of Mrs/Ms vs. Bcr/Bc and chi fd% vs. chi ARM/SIRM indicate that the main grain size of magnetic minerals in the street dust are pseudo single domain (PSD). The results reveal that the Lanzhou city is more polluted in spring than in summer. The main pollution sources are anthropogenic activities (81.9%) and natural dust (18.1%), especially the former. The spatial distribution of pollution is controlled by the topography and weather conditions.