Analysis of Canopy Structure of Plant Communities in Mongolian Grasslands

We studied the nitrogen use efficiency(NUE)and water use efficiency(WUE)of species growing in a humidity gradient in Mongolian grasslands to examine if there is a trade-off between the two efficiencies.Total131 species were collected from7sites。WUE was evaluated by the compositional deviation of I D 113 I D 1C(δI D 113 I D 1C)。NUE was evaluated as a reciprocal of leaf nitrogen concentration(LNC)。Species in drier habitats tended to have higher WUE，but there was no such trend in NUE。No trade-off was found between WUE and NUE across species distributed in different climates.However，when the values for WUE and NUE were standardized against their means for species found more than three sites，WUE increased and NUE decreased with increasing aridity，indicating the trade-off between NUE and WUE within species.Only two(Cleistogenes Squarrosa And Salsola Passerina)out of 131 species were found to have the C4 metabolism.Effects of climate and grazing intensities on the structure of grassland vegetation were studied。We have established three exclosures in different climates：Partizan(Mesic Steppe)，Tumentsogt(Typical Steppe)and Bayan-Unjuul(Dry Steppe)。First year vegetation survey gave45species(Including7grasses)in Partizan，46species(8grasses)in Tumentsogt and 18species(4grasses)in Bayan-Unjuul。Aboveground biomass was 122g dw m I D2-2个D 2 at Parizan，122 at Tumentsogt，and 53 at Bayan-Unjuul。Difference between exclosure and grazing plots was small，probably because of the short time since establishment of the exclosure and an unusually dry summer in1999。

We studied the nitrogen use efficiency (NUE) and water use efficiency (WUE) of species growing in a humidity gradient in Mongolian grasslands to examine if there is a trade-off between the two efficiencies. Total 131 species were collected from 7 sites. WUE was evaluated by the compositional deviation of ィイD113ィエD1C(δィイD113ィエD1C). NUE was evaluated as a reciprocal of leaf nitrogen concentration (LNC). Species in drier habitats tended to have higher WUE, but there was no such trend in NUE. No trade-off was found between WUE and NUE across species distributed in different climates. However, when the values for WUE and NUE were standardized against their means for species found more than three sites, WUE increased and NUE decreased with increasing aridity, indicating the trade-off between NUE and WUE within species. Only two (Cleistogenes squarrosa and Salsola passerina) out of 131 species were found to have the C4 metabolism.Effects of climate and grazing intensities on the structure of grassland vegetation were studied. We have established three exclosures in different climates : Partizan (mesic steppe), Tumentsogt (typical steppe) and Bayan-Unjuul (dry steppe). First year vegetation survey gave 45 species (including 7 grasses) in Partizan, 46 species (8 grasses) in Tumentsogt and 18 species (4 grasses) in Bayan-Unjuul. Aboveground biomass was 122 g dw mィイD2-2ィエD2 at Parizan, 122 at Tumentsogt, and 53 at Bayan-Unjuul. Difference between exclosure and grazing plots was small, probably because of the short time since establishment of the exclosure and an unusually dry summer in 1999.