Leaf δ13C values were measured in fifteen plant species along the grassland zone of the Northeast China Transect (NECT). The responses of δ13C values and long-term water use efficiency (WUE) as indicated by δ13C value of these species to environmental factors (annual average precipitation, annual average air temperature and altitude) were investigated. The δ13C value and WUE of many plant species decreased with increasing annual average precipitation and air temperature. Examples of such species include :Leymus chinensis (Trin.) Tzvel. , Ulmus pumila L. , Caragana microphylla Lam. , Astragalus adsurgens Pall. , Sanguisorba officinalis L. and Potentila tanacetifolia Willd. ex Schlecht. Other species show an increase in δ13C and WUE with increasing altitude (Melissitus ruthenicus (L.) Peschkova, Leymus chinensis (Trin.) Tzvel. , Ulmus pumila L. , Caragana microphylla Lam. , Astragalus adsurgens Pall. and Sanguisorba officinalis L. , for instance). By contrast, a few plant species (Lespedeza davurica(Laxm. ) Schindl. and Serratula centauroides L. ) showed an opposite trend. Finally several species showed no change in δ13C value or WUE with these environmental factors (e. g. Astragalus dahuricus (Pall.) DC. , Caragana intermedia Kuang et H. C. Fu, Caragana stenophylla Pojark. , Artemisia frigida Willd. , Astragalus scaberrimus Bunge, Glycyrrhiza uralensis Fisch .). These results demonstrate strong differences in the responses of water use status to environmental gradients among different plant species and that each species has its own adaptive strategy to environmental change. When considering restoration of degraded grassland it is important to consider variation between plant species in their potential to adapt to dry habitats.

We assessed the potential impact of global warming on rates of net ammonification, net nitrification and net mineralization of soil nitrogen by transferring intact soil cores (0-15 cm) from 1469 m higher-elevation meadow steppe to 1187 m and 960 m lower-elevation sites respectively in the Xilin River Basin of Inner Mongolia. After incubation for one growing season, ammonium nitrogen and nitrate nitrogen (including nitrite nitrogen) of the soil samples were determined. The annual mean air temperature at the three selected study sites during the field study was, from higher-to lower-elevation, -0.5℃, 2.2℃ and 4.4℃ respectively. Affected by these different air temperature regimes, the net ammonification rate was 0.05 mgN·kg-1·m-1, 0.13 mgN·kg-1·m-1, 1.09mgN·kg-1·m-1. Correspondingly,the net nitrification rate was respectively 0.05mgN·kg-1·m-1, 0.76 mgN·kg-1·m-1 and 0.26mgN·kg-1·m-1,and the net mineralization rate was 0.10mgN·kg-1·m-1, 0.89mgN ·kg-1·m-1 and 1.35 mg N·kg-1·m-1 in the soil transferred to the three sites. Hence we conclude that increasing air temperature will enhance soil N mineralization.

Spatial and temporal changes in vegetation patterns of the Yinma River Basin were reconstructed using analysis of modern pollen-vegetation type relationships and a pollen core. This 4. 6 m alluvial section was collected Yanshen Port in Lulong county, Hebei province. Forest coverage in 11000-9000 aBP was about 10% and this increased to 20%-40% in 9000-4000 aBP. During 3000～2500 aBP the forest coverage decreased to 10%～20%. The large quantity of Picea and Abies pollen found about 9000 aBP, indicates that movement in the altitudinal zonation of vegetation occurred in Yinma River Basin at around this time.