Morphological Characteristics And Availability Of Seed From Main Plantson The Hilly-Gullied Loess Plateau

Vegetation restoration is the key measure for soil erosion control on the hilly-gullied Loess Plateau. Seed is the base of revegetation, seed morphological characteristic and availability play an important role on seed dispersal, loss, dormancy, germination, seeding regeneration and estabilishment, thus affect vegetation recovery and succesion. Therefore, the experiment was designed to study seed morphological characteristics (seed weight, size, mode of dispersal, external traits, etc.), seed availability (yield, germination characteristics, and effect of burial on seed vitality, etc.), and characteristics of canopy seed bank and soil seed bank. The main results were obtained as follows:1) The morphological characteristics of seeds (fruits) of plants are diverse. The weight of seeds(fruits) have a widely range, about five order of magnitude, the smallest individual weight only 0.020mg, while the largest up to 357.428mg. The range of length, width, and height of seeds(fruits) is very wide, and the largest is 33times, 34times and 55times of the smallest, respectively. The fruit type are mainly achene, pod, grain, capsule. Shape are mainly oval, ellipse, round and kindy-shape. Colour are mainiy brown, snuff colour and blank. Emblazonry on surface are edge, coat, smooth, rough, strip, partical, lumpur. The seeds(fruits) of six plants(Artemisia scoparia, Artemisia gmelinii, Artemisia Giralaii, Artemisia mongolica, Herminium monorchis, Linum usitatissimum) have the characteristics of mucilage. 31.25 percent of the seeds(fruits) have different appendages. such as pappus, awns and hairs.2) The seed germination characteristics of 14 species (collected in current year) indicated that the germination rate of Periploca sepium, Artemisia gmelinii and Artemisia giraldii was over 80%, Bothriochloa ischaemum, Syringa oblata, Heteropappus altaicus, Stipa grandis, Hippophae rhamnoides and Artemisia scoparia was 60%-80%, Stipa bungeana was 37.3%, while Cleistogenes caespitosa, Robinia psendoacacia, Sophora viciifolia, Ostryopsis davidiana was less than 20%. The shortest days of these species began to germination was 2d, the longest was 8d, almost all the species with the day reaching 50% of the final germination amount was 7d; most of the species reached 90% of the final germination amount within 15 days. The germination period of 4 species including Robinia psendoacacia, Sophora viciifolia, Ostryopsis davidiana and Hippophae rhamnoides was shortest (6d), but the germination period of Artemisia scoparia was reaching 32d.3) Seed burial experiment showed that Artemisia gmelinii, Ostryopsis davidiana, Sophora davidii, Lespedeza davurica, Robinia psendoacacia and Heteropappus altaicus can be stored in soil at least one year, have the potential to form persistent seed bank, while Hippophae rhamnoides, Syringa oblata, Periploca sepium, Bothriochloa ischaemun easily decayed, Stipa grandis easily sprouted. Comparison of seed germination rate between seeds collected in current year and seeds after buried one year, we know that the germination rate of Lespedeza davurica increased, and the others decreased, and seed germination pattern have great changes after buried one year.4) The Investigation showed that the six species (Artemisia scoparia, Artemisia gmelinii, Artemisia giraldii, Sophora viciifolia, Periploca sepium and Rose xanthina) can keep seeds in plant canopy more or less. Artemisia scoparia, Artemisia gmelinii and Artemisia giraldii, Rose xanthina can make the seeds stay longer (more than 7 months) than Sophora viciifolia and Periploca sepium (5-7months). The time of seed storage correlated to the mechanism of seed shedding and environmental factors which the species faced.5) Seed yield of different species have greatly difference due to their different reproductive strategies. For example, seeds amount of Artemisia giralaii can up to 130 000 per plant, Artemisia gmelinii nearly 20 000 per plant, far greater than Periploca sepium, Sophora viciifolia and Rose xanthina (780, 202 and 250 seeds per plant, respectively). Based on the seed yield and seed germination characteristics of Artemisia scoparia, Artemisia gmelinii, Artemisia giralaii, Heteropappus altaicus, Bothriochloa ischaemun and Stipa bungeana under different soil erosion conditions, it was showed that the degree of soil erosion have a great impact on seed yield and seed germination rate, the more serious soil erosion, the lower yield and germination rate of seed.6) Different morphological characteristics of seeds showed significant differences in the process of soil erosion. There are about 46.25 percent of seeds(fruits) have the morphological characteristics to resist soil erosion. Seed morphological characteristics to resist soil erosion were seeds have large individual weight (e.g Ziziphus jujuba, Rose xanthina), seeds have wings and other structures to increase friction with the ground (e.g Raphanus raphanistrum, Patrinia heterophylla), seeds have greater FI, that is, the shape of seeds was slender (e.g Bidens tripartita, Stipa grandis), seeds have the mucilage that enchance the consolidation to the soil (e.g Dracocephalum moldavica, Artemisia scoparia), seeds have specific accessory to increase contact with the soil surface (e.g Stipa bungeana with the mount). While the seeds easy to loss by water erosion were less weights and do not have the special structure what we referenced above (e.g Bothriochloa ischaemun, Heteropappus altaicus), about 53.75 percent.7) Seed with the characteristics of smaller weight (individual weight less than 0.1mg), approximately spherical and spherical have larger numbers and a higher frequency in soil seed bank. This showed that pellet, nearly spherical seed storaged more in the soil seed bank, and have higher availability, e.g Artemisia scoparia, Eragrostis pilosa and so on.