| The natural recovery and self-renewal of vegetation is the key to ecosystem restoration, regeneration and expansion. And seeds are the prerequisite and basis for vegetation restoration and regeneration. The dynamic changes of seed input and output determines soil seed bank size and species composition, which determine the complexity and potential of template that provided for vegetation restoration and natural regeneration. In this study, three abandoned slopes in Zhifanggou watershed in the typical loess hilly region were selected. Based on the investigation of seed production, seed rain, seed erosion, seedling and soil seed bank in the abandoned slopes, seed input and output characteristics, soil seed bank characteristics and their relationships were analyzed, and the influences of dynamic changes of seed input and output on vegetation restoration, regeneration, and succession were discussed, the main results were obtained as follows:(1) The seed yield of main species on the abandoned slopes was ordered as Artemisia scoparia>Setaira viridis>Bothriochloa ischaemum>Heteropappus altaicus>Stipa bungeana>Lespedezad avurica>Artemisia gmelinii, and there is a linear correlation between seed yield and important values. The average accumulative density of seed rain was6642.60seeds/m2, there were two seed rain density peaks in June-July and September-next January, and seed rain density reach a minimum value in April and August. The sum of seed rain of the above seven species accounted for about85%of total seed rain. The percentage of seed rain of the above seven species from the seed production was5.81%-82.65%, with an average of25.75%.(2) The total seed erosion within one year on the abandoned slope was240.39seeds/m2, the seed erosion was mainly concentrated in July to October, the highest value was58.44seeds/m2in August, the lowest value under the second erosive rainfall in May was8.44seeds/m2. Seed morphology and their distribution in soil seed bank and seed rain have an important influence on seed erosion. The relationship of soil erosion degree and total seed erosion was significant (p<0.05), i.e., the more serious soil erosion degree, the greater seed loss. While there was no obvious relationship between seed loss and soil erosion amount.(3) The density of seedling within one year on the abandoned slope averaged388.94 seeds/m2, the most seed germination were the species in the early succession stage like Artemisia scoparia and Setaira viridis, while the seed germination of Lespedezad avurica, Artemisia gmelinii, Bothriochloa ischaemum and other species in the late succession stage were less; the seedling time was mainly between July to October with concentrated rainfall, and the seedling accounted for83.04%of the total seed germination. Seed germination density is closely related to soil erosion degree, i.e., the more serious erosion degree, the smaller seed germination density; while seed germination density decreased as vegetation cover increased.(4) The density of soil seed bank on the abandoned slope averaged5945.74seeds/m2. The seed density of Artemisia scoparia in early succession stage was the largest, with an average proportion in the total soil seed bank of71.94%, while the seed density of the late-successional species like Bothriochloa ischaemum, Artemisia gmelinii, Lespedezad avurica and Stipa bungeana was relatively small. The soil seed bank density in the0-2cm soil layer was the largest, accounting for49.55-66.37%, while in2-5cm and in5-10cm soil layer accounted for21.35-32.12%and12.65-20.08%, respectively. The soil seed bank density in different erosion micro-environment was deposited area> under vegetation>bare area. Seeds moved and lost on the slopes as runoff wash and sediment transport, or trapped on the slope as sediment deposited.(5) With the seed input and output on the abonded slopes, the potential soil seed bank still had an increasing trend, while the seed density of different species in the potential soil seed bank show different trends, which can be divided into two categories:first, seed density of species in the potential soil seed bank maintained at a certain level, like Artemisia scoparia and Artemisia gmelinii; second, seed density of species in the potential soil seed bank increased sharply after the seed rain peak, like Heteropappus altaicus, Stipa bungeana, Setaira viridis, Lespedezad avurica and Bothriochloa ischaemum.(6) The seed rain input from March2011to March2012accounted for above60%of the soil seed bank, seed loss is only about4%of the soil seed bank. To a certain extent, seed loss reduced the seed density in the soil seed bank, but it was not the key factor to affect natural renewal of ground vegetation. Seed germination accounted for only about6%of the soil seed bank, and it indicted that the soil seed bank is fully capable of providing seed sources for vegetation regeneration... |
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