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In arid and semi-arid ecosystems, shrubs have an important effect on neighboring plants. However, little is known about the interaction of herb growth stages and shrub location on herb performance. We selected Reaumuria soongorica, (Pall.) Maxim a shrub dominant in the semiarid region of northwest China, to determine whether (1) shrubs facilitate or have negative effects on neighbouring herbaceous vegetation, and (2) such effects vary with herb growth stage and with shrub orientation relative to herbs. The presence of herbaceous plant species, plant density, plant height, and percent cover were determined along 2 m long transects spreading in four directions from the base of shrub – east (transect E), west (transect W), south (transect S), and north (transect N); this was repeated for three growth stages (in May, June and July). Results indicated that the effects of R. soongorica on neighboring herbs in different growth stages were similar. Species number of herb-layer plants tended to increase from beneath the canopy to the opening, but plant density, cover and plant height decreased with distance away from shrub base. The presence of R. soongorica had positive effects on density, cover, and plant height, and negative on the number of herbaceous species during the entire growing season. Herbaceous plants growing on transect N under the shrub canopy had significantly higher density and percent cover than those growing in other directions. Biomass of herbs on transect N grown under the shrub canopy was higher than that of herbs on other transects. We concluded that shrub effects on neighbouring herbaceous vegetation were closely related to the shrub orientation relative to the herbs. Therefore, using shrubs as nurse plants for grass-growing must consider the relative placement of shrubs.
Content available remote Middle Jurassic flora from Turpan-Hami Basin, Xinjiang, Northwest China
A flora of 88 species belonging to 42 genera has been recorded from the Xishanyao Formation of Turpan-Hami Basin, Xinjiang, Northwestern China. The list of the species include: bryophyte - Thallites clarus Zhang et Zheng, T. sp.; lycopod - Lycopodites falcatus Lindley et Hutton; Sphenopsida - Equisetites lateralis Phillips, Equisetites sp., Neocalamites hoerensis (Schimper) Halle, N. carcinoides Harris, N. carrerei (Zeiller) Halle, Radicites sp. and Annulariopsis simpsoni (Phillips); ferns - Todites williamsoni (Brongniart) Seward, Coniopteris bella Harris, C. burejensis (Zalessky) Seward, C. hymenophylloides (Brongniart) Seward, C. murrayana (Brongniart) Harris, C. spectabilis Brick, C. tatungensis Sze, C. sp., Eboracia lobifolia (Phillips) Thomas, Clathropteris cf. obovata Oishi, Dictyophyllum sp., Cladophlebis asiatica Chow et Yeh, Cl. argutula (Heer) Fontaine, Cl. haiburnensis (L. et H.) Brongniart, Cl. hirta Moeller, Cl. fangtzuensis Sze, Cl. magnifica Brick, Cl. ulanensis Li et Wu, Cl. sp. 1, Cl. sp. 2, Cl. sp. 3, Raphaelia diamensis Seward and Sphenopteris sp.; Cycadales and Bennettitales - Pterophyllum mentougouensis Chen et Dou, P. sp., Anomozamites nilssoni (Phillips), A. major (Brongnart), A. sp., Nilssonia cf. acuminata Presl, Nilssonia sp., Nilssoniopteris pristis Harris, N. vittata (Brongniart) Florin, N. cf. uwatakoi (Oishi) Li, Williamsoniella cf. karataviensis Turiket., Williamsonia(?) sp., Taeniopteris sp. and Deltolepis sp.; Ginkgopsida - Ginkgo longifolius Harris, G. digitata (Brongniart) Heer, Ginkgoites sibiricus (Heer) Seward, G. obrutschewi Seward, G. yimaensis Zhou et Zhang, G. sp., Baiera gracilis (Benan MS) Bunbury, B. furcata (L. et H.) Braun, B. setacea Zhang, B. sp., Sphenobaiera longifolia (Pomer) Florin, Sph. setacea Zhang, Sph. sp., Eretmophyllum cf. saighanense (Seward) Seward, E. sp., Phoenicopsis angustifolia Heer, Ph. speciosa Heer, Ph. sp., Czekanowskia rigida Heer, C. setacea Heer, Vittifoliolum cf. segregatum Zhou and Ixostrobus lepidus (Heer) Harris; Coniferopsida - Pityophyllum lindstroemi Nathorst, P. longifolium (Nathorst) Moeller, P. nordenskioldi Heer, Pityocladus kobukensis Seward, P. sp., Pityostrobus sp., Elatocladus manchurica (Yokoyama) Yabe, E. sp., Schizolepis sp., Podozamites eichwaldi Schimper, P. lanceolatus (Lindley et Hutton) Braun, P. sp., Ferganiella sp., Storgaardia sp. and Elatides sp.; and some seeds - Conites sp., Carpolithus latizonus Li, C. retioformus Wu, C. strumatus Wu. The flora is chiefly composed of Filicopsida, Ginkgoposida and Cycadopsida. Among the Filicopsida, the Dicksoniaceae and Cladophlebis are the predominating groups. The former is represented by 8 species and the latter - about 10 species which are characterized by large pinnules. Ginkgopsida with 22 species are dominated by Ginko-like leaves and Phoenicopsis. Cycadopsida ranks the third position with 14 species, mostly assigned to Anomozamites, Nilssoniopteris and Nilssonia. Coniferopsida with 15 species makes up about 17% of the flora and are characterized by long or broad leaf types including Podozamites, Elatocladus and Pytyophyllum. Sphenopsida is a relative smaller group, but specimens of Neocalamites are abundant. The flora can be compared with the Middle Jurassic floras of Middle Asia, England, which indicates the age of the flora is the Middle Jurassic, possibly the Aalenian-Bajocian.
The Upper Triassic and Lower Jurassic deposits in Junggar Basin, Xinjiang, Northwest China represent continuous succession and are divided into the Haojiagou Formation, Badaowan Formation and Sangonghe Formation (from base to the top). The Sangonghe Formation is definitely of the Early Jurassic age as based on plant, spore-pollen, conchostracans and bivalves. The ages of the Haojiagou and Badaowan formations are less clear. The Triassic/Jurassic boundary runs somewhere in the uppermost part of the Haojiagou Formation or in the Badaowan Formation as indicated by flora assemblages. Organic carbonaceous isotopic measurement suggests the position of the boundary in question at the base of the Badaowan Formation. The flora of the Haojiagou and the Badaowan Formations may be subdivided into the following assemblages. 1. Danaeopsis fecunda - Cladophlebis ichunensis assemblage. This assemblage is from the lower part of the Haojiagou Formation. It consists of about 20 species, characterized by Danaeopsis fecunda and numerous Cladophlebis. The main species include Danaeopsis fecunda Halle, Todites cf. shensiensis Pan, Cladophlebis ichunensis Sze, Cl. nebbensis (Brongn.) Nathorst, Cl. paralobifolia Sze, Sphenopteris chowkiawanensis Sze, Rireticopteris sp. and Cycadocarpidium sp. It is definitely of the Late Triassic age. 2. Neocalamites - Hausmannia assemblage. This assemblage is from the upper part of the Haojiagou Formation. It is composed of about 10 species with marked dominance of Neocalamites horerensis and Hausmannia xinjiangensis sp. nov. The assemblage is possibly of the Late Triassic age. 3. Todites princeps - Clathropteris elegans, assemblage. This assemblage is from the lower part of the Badaowan Formation, with about 15 species. Todites princes and Clathropteris elegans are dominant in the assemblage. It may be of earliest Early Jurassic age. 4. Coniopteris gaojiatianensis - Cladophlebis denticulata assemblage. This assemblage is abundant and of higher specific diversity. The main elements are: Selaginellites drepanoformis Zheng, Todites williamsoni (Brongniart) Seward, Coniopteris gaojiatianensis Zhang, Cladophlebis denticulata (Brongniart) Fontaine, Cl. gracilis Sze, Cl. hirta Moeller, Cl. cf. shansiensis Sze, Raphaelia diamensis Seward, Ginkgoites sp., Sphenobaiera sp., Czekanowskia rigida Heer, Samaropsis parvula Heer, S. rotundata Heer. It is noticeable that Coniopteris is recorded commonly. The assemblage occurs in the upper part of the Badaowan Formation and is of Early Jurassic age.
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