关键词: 高寒草甸, 禾本科植物, 种子萌发

Abstract:

Background and Aims The study area is located on the eastern Qinghai-Tibetan Plateau (101°-103° E, 34°-35°70' N). The altitude ranges from 2 900 m to 4 000 m, and the climate is cold and humid with an annual rainfall of 450-780 mm, which is mainly distributed in July, August and September. Mean annual air temperature is 1.8 ℃ with -10.7 ℃ in January and 11.7 ℃ in July, and average annual frost days are no less than 270 d. The grassland types include mainly alpine meadow (59.32%), brushy meadow (33.39%), woodland meadow (0.32%), saline meadow (0.15%), swampy meadow (5.61%) and upland grass (1.21%). The vegetation belongs to typical alpine meadows, and the species composition of the plant community is dominated by many monocotyledons and various dicotyledons. The capacity of seed germination and seedling establishment determines partially the regeneration of plant communities of the grassland. However, there is few germination data. Accordingly, we have undertaken a major study of the gramineous species of the alpine meadow. A comparison of the germination biology of many species will provide an ecological context for subsequent studies of field distribution.
Methods Seeds were collected from as many sources as possible to get an adequate representation of the whole community from July to October in 2003. Enveloped seeds were spread on tables at room temperatures(about 15 ℃)until dried and threshed by hand through screens. The experiment of germination started on March 3, 2004. For each species 50 seeds were placed in Petri-dishes on filter paper moistened with distilled water in a growth chamber with a 12-h day at 25 ℃ and a 12-h night at 5 ℃. This temperature regime has relevance to field conditions: it approximates the mean daily maximum and minimum temperature in 5 cm deep soil from May to August. The percentage of seeds germinated was recorded every day. Newly emerged seedlings were removed from the Petri-dishes and seeds were regularly watered with distilled water. A seed was considered germinated when the length of the emerged radicle was equal to the length of seed. Germination was judged to be complete when no further germination occurred for five successive days. The remaining ungerminated seeds were checked for viability by soaking in water at 30 ℃ for 2 h, removing the seed coats and sliting open the seeds, then soaking the embryos in 0.1% tetrazomium chloride for 4 h at 30 ℃. In viable seeds embryos were stained pink. The amount of germination was then calculated as a percentage of the total number of viable seeds and rate of seed germination as the number of seeds germinating each day expressed as a percentage of the final germination. In this study, we make use of 4 indices: percent germination, days to first germination, germination period and days to 50% germination.
Key Results Of the 54 species examined, the following 26 species exceeded 80% germination: Achnatherum inebrians, Agrostis alba, A. sp1., A. stolonifera, Aneurolepidium dasystachys, Arundinella anomala, Bromus tectorum, Deschampsia caespitosa, Deyeuxia scabrescens, D. sp., Elymus dahuricus, E. tangutorum, Festuca sinensis ,Helictotrichon leianthum, Mellica scabrosa , Orinus kokonorica, Poa schoenites, P. sinattenuata, P. botryoides, P. poophagorum, P. pratensis, Ptilagrostis dichotoma, P. mongholica, P. roshevitsiana, Roegneria nutans and R. stricta. The following 11 species had 60%-80% germination: Achnatherum sibiricum, A. splendens, Brachypodium sylvaticum, Bromus magnus, B. sinensis, Deyeuxia arundinacea, Gramineae sp., Helictotrichon tibeticum, Ptilagrostis junatovii, Stipa capillacea and S. przewalskyi. The following 8 species had 40%-60% germination: Agrostis hugoniana, Brachypodium sp., Festuca ovina, F. rubra, Helictotrichon sp2., Poa declinata, Roegneria kokonorica and Stipa aliena. The following 5 species had 20%-40%germination: Aristida triseta, Helictotrichon schellianum, H. sp1., Koeleria cristata and Oryzopsis munroi and the following 4 species had values of less than 20%: Stipa purpurea, Agrostis sp2., Stipa penicillata var. hirsuta and A. trinii; 14 species, Achnatherum inebrians, A. splendens, Agrostis alba, Aneurolepidium dasystachys, Arundinella anomala, Brachypodium sp., Bromus tectorum, Elymus dahuricus, E. tangutorum, Mellica scabrosa, Orinus kokonorica, Poa sinattenuata, Ptilagrostis mongholica and Roegneria nutansbegan, began to germinate within 3-5 days; 29 species, Poa schoenites, Achnatherum sibiricum, Agrostis sp2., A. stolonifera, Brachypodium sylvaticum, Bromus magnus, B. sinensis, Deschampsia caespitosa, Deyeuxia arundinacea, D. sp., Festuca ovina, F. rubra, F. sinensis, Gramineae sp., Helictotrichon sp2., H. tibeticum, Koeleria cristata, Oryzopsis munroi, Poa botryoides, P. declinata, P. poophagorum, P. pratensis, Ptilagrostis junatovii, P. roshevitsiana, Roegneria kokonorica, R. stricta, Stipa aliena, S. capillacea and Stipa penicillata var. hirsuta, began to germinate within 6-8 days; 10 species, Agrostis hugoniana, A. sp1., A. trinii, Aristida triseta, Deyeuxia scabrescens, Helictotrichon leianthum, H. schellianum, H. sp1., Ptilagrostis dichotoma and Stipa przewalskyi, began to germinate within 9-10 d; and only Stipa purpurea exceeded 10 d. For species such as Stipa purpurea, Achnatherum inebrians, Agrostis alba, A. sp1., A. sp2., A. stolonifera, Aneurolepidium dasystachys, Aristida triseta, Arundinella anomala, Elymus dahuricus, E. tangutorum, Helictotrichon schellianum, H. sp1., Mellica scabrosa, Poa poophagorum and P. sinattenuat (16 species), the germination period was short (1-7 d); 28 species, Poa schoenites, Achnatherum splendens, Agrostis hugoniana, A. trinii, Brachypodium sp., Bromus magnus, B. sinensis, B. tectorum, Deschampsia caespitosa, Deyeuxia arundinacea, D. scabrescens, D. sp., Festuca ovina, F. rubra, F. sinensis, Gramineae sp., Helictotrichon leianthum, H. tibeticum, Koeleria cristata, Orinus kokonorica, Oryzopsis munroi, Poa botryoides, P. declinata, P. pratensis, Roegneria kokonorica, R. nutans, Stipa capillacea and Stipa penicillata var. hirsuta, had the germination period of 8-14 d; and 10 species, Achnatherum sibiricum, Brachypodium sylvaticum, Helictotrichon sp2., Ptilagrostis dichotoma, P. junatovii, P. mongholica, P. roshevitsiana, Roegneria stricta, Stipa aliena and S. przewalskyi, germinated over a longer period (15-21 d);for species such as Poa sinattenuata, Achnatherum inebrians, Agrostis alba, Aneurolepidium dasystachys, Arundinella anomala, Brachypodium sp., Bromus tectorum, Elymus dahuricus, E. tangutorum, Mellica scabrosa and Roegneria nutans (11 species), germinated 50% within 1-7 d, while Poa schoenites, Achnatherum splendens, Agrostis hugoniana, A. sp1, A. stolonifera, Bromus magnus, B. sinensis, Deschampsia caespitosa, Deyeuxia arundinacea, D. scabrescens, D. sp., Festuca ovina, F. rubra, F. sinensis, Gramineae sp., Helictotrichon leianthum, H. tibeticum, Orinus kokonorica, Poa botryoides, P. declinata, P. poophagorum, P. pratensis, Ptilagrostis mongholica, P. roshevitsiana, Roegneria kokonorica, R. stricta and Stipa capillacea (27 species) germinated 50% within 8-14 d; and the time to 50% germination of Achnatherum sibiricum, Brachypodium sylvaticum, Ptilagrostis dichotoma, P. junatovii and Stipa przewalskyi exceeded 14 d, but 11 species, Agrostis sp2., A. trinii, Aristida triseta, Helictotrichon schellianum, H. sp1., H. sp2., Koeleria cristata, Oryzopsis munroi, Stipa aliena, S. purpurea and Stipa penicillata var. hirsuta, failed to germinate 50% after the experiment.
Conclusions These species showed four germination patterns: rapid (e.g. Achnatherum inebrians and Agrostis alba), slow (e.g. Achnatherum sibiricum and Stipa przewalskyi), intermediate (e.g. Deschampsia caespitosa and Orinus kokonorica) (percent germination >50%) and low germination (e.g. Oryzopsis munroi and Stipa purpurea) (percent germination <50%).The experiment illustrated that the gramineous species of the alpine meadow on the eastern Qinghai-Tibetan Plateau are heterogeneous in their germination characteristics. Nevertheless, knowledge of other factors (e.g. light, temperature and storage methods) influencing germination is needed before we can fully understand the relationships between germination characteristics and field distribution.

Key words: Alpine meadow, Gramineous plants, Seed germination