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Water stress and nutrient deficiency are considered to be the main environmental factors limiting plant growth and species interaction in semiarid regions. However, less is known about the interactive effects of soil water, nitrogen and phosphorus on native species growth and relative competitive ability. A replacement series design method was used with 12 mixed plants of Bothriochloa ischaemum and Lespedeza davurica grown in a pot experiment under three water regimes and four fertility treatments. Intercropping systems were assessed on the basis of indices such as biomass production and allocation, relative competitive ability, aggressivity, relative yield total and water use efficiency (WUE). Water stress decreased significantly the total biomass production for each species, either in monoculture or in mixtures. N, P, or NP application can significantly improve biomass production of the two species in their mixtures. There was no obvious change trend in root/shoot ratio of B. ischaemum or L. davurica in different mixture proportions. Relative yield total (RYT) values ranged from 0.98 to 1.39. Aggressivity values of B. ischaemum to L. davurica were positive in all water regimes and fertilizations, implying that B. ischaemum was the dominant species. Relative competition intensity values of B. ischaemum (i.e., RCI) were less than zero, while greater than zero for L. davurica (i.e., RCI), indicating that the effects of intraspecific competition with L. davurica were stronger for B. ischaemum, and the opposite for L. davurica. WUE increased gradually as the proportion of B. ischaemum increased in mixtures, and a 10:2 B. ischaemum: L. davurica mixture proportion had significantly higher WUE. Results suggest that it is advantageous to grow the two species together to maximize biomass production and the recommended mixture ratio was 10:2 of B. ischaemum to L. davurica because it gave higher RYT and significantly higher WUE under conditions of water deficit. [ABSTRACT FROM AUTHOR]

Abstract: A better understanding of the growth and interspecific competition of native dominant species under water stress should aid in prediction of succession in plant communities. In addition, such research would guide the selection of appropriate conservation and agricultural utilization of plants in semiarid environments that have not been very well characterized. Biomass production and allocation, relative competitive ability and water use efficiency of one C4 herbaceous grass (Bothriochloa ischaemum) and one C3 leguminous subshrub (Lespedeza davurica), both important species from the semiarid Loess Plateau of China, were investigated in a pot-cultivation experiment. The experiment was conducted using a replacement series design in which B. ischaemum and L. davurica were grown with twelve plants per pot, in seven combinations of the two species (12:0, 10:2, 8:4, 6:6, 4:8, 2:10, and 0:12). Three levels of water treatments included sufficient water supply (HW), moderate water stress (MW) and severe water stress (LW). These treatments were applied after seedling establishment and remained until the end of the experiment. Biomass production and its partitioning, and transpiration water use efficiency (TWUE) were determined at the end of the experiment. Interspecific competitive indices (competitive ratio (CR), aggressiveness (A) and relative yield total (RYT)) were calculated from the dry weight for shoots, roots and total biomass. Water stress decreased biomass production of both species in monoculture and mixture. The growth of L. davurica was restrained in their mixtures for each water treatment. L. davurica had significantly (P <0.05) greater root:shoot allocation than B. ischaemum for each water treatment and proportion within the replacement series. Aggressiveness (A) values for B. ischaemum with respect to L. davurica were negative only at the proportions of B. ischaemum to L. davurica being 8:4 and 10:2 in LW treatment. B. ischaemum had a significantly (P <0.05) higher CR value under each water treatment, and water stress considerably reduced its relative CR while increased that of L. davurica. RYT values of the two species indicated some degree of resource complimentarity under both water sufficient and deficit conditions. The results suggest that it is advantageous for growing the two species together to maximize biomass production, and the suggested ratio was 10:2 of B. ischaemum to L. davurica because of significantly higher (P <0.05) RYT and TWUE under low water availability condition. [Copyright &y& Elsevier]

Abstract: The provenance of middle Pleistocene loess in the middle and lower reaches of the Yangtze River, the most intensively investigated loess deposits outside the Loess Plateau region in China, remains controversial. Identification of the provenance will provide crucial insight into the environmental implications of this valuable sedimentary archive, and into the potential role of the East Asian winter monsoon in transporting the dust from deserts in the Asian interior. In this study, geochemistry was used to compare the provenance of loess in the lower reaches of the Yangtze River in southern China with that inferred for loess deposits on the Loess Plateau in northern China. Compared with samples from the Loess Plateau, the <20 μm fraction in the loess deposits of southern China has higher TiO2/Al2O3, Zr/Nb, Zr/Al, Zr/Ti, Zr/Hf, Y/Al and LaN/SmN ratios, and lower Eu/Eu*, Th/Nb, Y/Nb and Al/Nb ratios. The clear distinction in immobile element ratios between samples from the two regions indicates that the loess deposits in the two regions have different provenances. The inferred difference in source area is also supported by variations in the major element composition of bulk samples obtained in this study and collected from published data. These lines of evidence indicate that the deserts in the Asian interior are not the primary provenance for the southern loess. It is suggested that the adjacent floodplains to the north of Yangtze River are the dominant dust sources, and the occurrence of sustained loess deposits in the lower reaches of the Yangtze River, currently an area of northern subtropical climate, is an indication of local aridification and strengthened winter monsoon activity during glacial periods as a regional response to the Middle Pleistocene climate transition around 0.8 Ma. The role of the East Asian winter monsoon in transporting the dust from northern deserts to southern China has been overestimated in previous studies. [Copyright &y& Elsevier]