内蒙古典型草原群落实生苗动态对刈割和放牧干扰的响应(英文)

SEEDLING DYNAMICS IN RESPONSE TO MOWING AND GRAZING IN A TYPICAL STEPPE COMMUNITY IN INNER MONGOLIA,CHINA

该文通过刈割和放牧样地的实生苗动态观测,试图揭示刈割和放牧干扰对冰草（Agropyron cristatum）、克氏针茅（Stipa krylovii）和糙隐子草（Cleistogenes squarrosa）等3种禾草实生苗出生、存活和死亡季节动态的影响,以及这种效应是如何受气温和降水影响的。利用有重复测量的方差分析,比较了不同刈割留茬高度（0、5和15cm）与放牧处理之间在实生苗密度、死亡率和出现率的时间动态方面的差异。结果表明：3种禾草的实生苗密度自5月下旬至8月中旬一直呈增加态势。刈割在一定程度上抑制了克氏针茅的实生苗出现率,原因可能是相对高大的克氏针茅在前一年刈割时会被去掉相当多的生殖部分,其种子数量必然受到影响,导致实生苗出现率的降低。同时,刈割对相对低矮的糙隐子草实生苗有正向效应,即促进其实生苗的出现,可能的原因是刈割使植被高度降低、植被稀疏,植被冠层以下至地面的光照较好、地温较高,同时位于下层的糙隐子草受到的高大植株的竞争压力减小。生长季早期和晚期实生苗死亡率较高,这与这两个时期的干旱和低温有关,而自6月中旬至7月初之间的死亡率小高峰也是先前的干旱少雨导致的。3种禾草实生苗的大规模出现几乎都在5-7月,这与该时期相对适宜的气温、地温和水分条件有关。对实生苗更新相关过程（如种子萌发、休眠、种子库存量等）进行更加深入细致的研究,将进一步揭示种子生产和有性繁殖在群落过程中的作用。

Aims Seedlings are central to population maintenance, community structure and succession, but the dynamics of seedling recruitment at the community level and responses of seedling dynamics to different disturbances in typical steppe are unclear. Our aims are to uncover the effects of mowing and/or grazing on the seasonal dynamics of seedling emergence, survival and mortality in three common grass species （Agropyron cristatum, Stipa krylovii and Cleistogenes squarrosa ） in typical steppe communities, and to determine how dynamics are affected by temporal variation in air temperature and precipitation. Methods Four treatments were used in five 10 m × 20 m replicate blocks： control, mowing to 15 cm height, mowing to 5 cm height, and grazing （also annually mown by farmers）. Seedlings were censused from May 20 to September 28. Plant species composition of each block was surveyed with conventional methods and dominance values were calculated for the three grass species. Differences in seedling density, mortality and emergence among treatments were tested using repeated measures define factor ANOVA in the SPSS package, but the mortality and emergence data were extracted and then arcsine-transformed before ANOVA analysis. One-Way ANOVA was adopted to compare the overall coverage of the community and the dominance of the three grass species among different treatments. Important findings Seedling densities of all three species increased from late May to mid-August. Mowing suppressed seedling emergence of tall-growing S. krylovii possibly by affecting seed availability due to removal of reproductive parts in the previous year. Mowing had a positive effect on low-growing C. squarrosa probably as a result of increased light availability and less competitive pressure from adult individuals as mowing lowered plant heights and densities. Relatively high seedling mortality during early and late growing season was thought to be associated with aridity and/or low air temperature, and a small peak from mid-June to early July probably was attributed to drought due to previous rainfall shortage. Seedling emergence in all species took place fairly synchronously from May to July, probably due to the relatively optimum environmental conditions in air temperature and water supply. More detailed and complex studies relating seedling recruitment to such processes as seed germination, seed dormancy and seed availability are required, especially under mowing and gazing prac- tices, to uncover the roles of seed reproduction in community processes.