科尔沁沙地植被恢复演替进程中群落土壤种子库研究

Soil seed bank of plant communities along restoring succession gradients in Horqin Sandy Land

研究了科尔沁沙地植被恢复演替进程中各群落土壤种子库种类组成、密度以及物种多样性等特征.主要结论是:①科尔沁沙地植被退化后的恢复演替是一种次生的中途恢复演替.演替各阶段土壤种子库密度为流动沙丘＜半流动沙丘＜固定沙丘,从流动到半流动沙丘阶段,土壤种子库密度平均增加了709%;从半流动到固定沙丘阶段,土壤种子库密度平均增加了393%.从流动到半流动沙丘阶段是土壤种子库密度的快速增长期.②植被恢复演替过程中,土壤种子库组成均以1年生草本植物为主(优势度为60.40%～91.83%),到演替中后期阶段,多年生草本植物的种类有所增加,但其所占比例仍很小.③演替各阶段群落种子库物种多样性指数分别为0.6616、0.7736、0.7281、1.0939、1.0648和0.9682,可见种子库物种多样性最高的群落并非是演替历史最大的群落.④恢复演替系列各阶段土壤种子库间的相似性系数都较大,在0.368～1.000范围之内,任一群落总是与其下一阶段最邻近的群落具有最高的相似性系数.

In the Horqin Sandy Land in Inner Mongolia of China, vegetation restoration usually occurs under proper management regimes in fragile environmental conditions, e. g. , enclosing and non-grazing. In restoring succession series, shifting, semi-shifting or semi-fixed and fixed sandy dunes correspond to early, middle and late succession phases. However, few information is available about the effects of community succession on the structure and performance of soil seed banks in the semi-arid desert environment. Therefore, a field experiment was cunducted in sandy dunes to examine the structure and performance of the soil seed banks in restoring succession series. In early April 2003, six types of communities respectively representing the succession time of 1, 3, 5, 12, 15 and 20 years, were selected as experimental sites. On each site, three parallel 200m line transects （20m apart） were established along the sandy dune （across windward slope, dune crest and leeward slope）. For each transect, 20 sampling points were set up at 10-m intervals, and a soil sample of depth of 5cm, dimension of 20cm× 20cm was collected from each sampling piont. All soil samples were transported to the laboratory in open plastic bags and chopped and sieved （mess width 2mm） soon. The sieved soil samples were placed in plastic germination pots （diameter 35cm and 12cm in depth） and spread evenly to form an approximately 2cm thick layer in individual pots. Pots were placed in an unheated greenhouse for seed germination. Pots were watered daily with a very fine nozzle in the afternoon. Emergent seedlings were identified to species and carefully removed from the pots. Seed germination and seedling identification were carried out continuely in the following three months. However, some unidentifiable seedlings remained longer in the pots until they were identified. The density of the existing seed bank was expressed as the number of viable seeds per square meter. At each site, the frequency of species in the soil seed bank was determined in terms of the 60 sampling points or the 60 quadrats. Some conclusions can be drawn from this study （1） The restoring succession of sandy vegetation was a kind of secondary and halfway seccession series. The total density of soil seed bank increased with the restoring series of succession, but there were differences in the rates of increase. Density of seed bank increased by 393% from the semi-shifting dune to the fixed dune and by 709% from the shifting dune to the seni-shifting dune, which was the greatest augment in the process of restoration. （2） In the restoring series of succession, annual herbaceous plants were dominant in the seed banks（60. 40-91.83% ）. Although perennials increased in the late stage of succession, the ratio was lower yet. （3） In the process of rstoration, the species diversity index were 0. 6616, 0. 7736, 0. 7281, 1. 0939, 1. 0648 and 0. 9682, respectively. We seggested that the community with the highest diversity index was not that of the longest succession time in scale. （4） There was high similarity between one community and the adjacent community, of which the similarity coefficients ranged from 0. 368 to 1. 000.