The sandy-hilly region of northwest Shanxi is a typical fragile agro-pastoral ecotone in north China. With the artificial Caragana korshinskii at 0 (the uncultivated land), 6, 12, 18, 40 and 50 years-old in the typical sandy-hilly region of northwest Shanxi as the subjects, we investigated soil moisture, aboveground and belowground biomass, individual morphological characteristics, growth, reproduction, and photosynthetic physiological characteristics of different-aged C. korshinskii, with the aim to evaluate the long-term growth and reproductive dynamic characteristics of artificial C. korshinskii. The results showed that soil moisture was significantly affected by stand ages. Soil moisture was low under the 6-year-old C. korshinskii plantation. During 6-18 years-old, soil moisture increased due to the increased crown width and reduced the near-surface wind speed, solar radiation, and soil water evaporation. During 18-50 years-old, soil moisture decreased sharply due to higher biomass and plant transpiration of C. korshinskii, and soil moisture was reduced to the lowest level of 11.1%. C. korshinskii mainly developed underground root system during 6-18 years-old, and changed to the aboveground biomass accumulation in 18-40 years-old. At the 40-year-old stand, biomass reached to the highest level with the greatest crown width and plant height. During 40-50 years-old, crown width and plant height decreased significantly, while the growth began to degrade. Photosynthetic capacity (chlorophyll a, b, carotenoid and total chlorophyll content) gra-dually decreased with the increases of planting ages, especially after 18 years-old. The quantity and quality of C. korshinskii seeds increased from 6 to 40 years-old, reached the maximum at 40 years-old stand, and began to decrease after 50 years-old. In the later growth period (30-40 years-old), more seeds with small individual weight were produced compared with early period (6-12 years-old). The germination test showed that small seeds had higher germination rate than the large ones under the same stand age, suggesting a shift of reproduction strategy. After 50 years-old, both of the growth and reproduction of C. korshinskii degenerated, and the plantation began to degrade.
晋西北丘陵风沙区生态环境脆弱,是我国风沙活动危害最为严重的地区之一。本文以晋西北典型丘陵风沙区0(撂荒地)、6、12、18、40和50年生人工柠条为研究对象,分析了不同林龄柠条的土壤含水量、地上和地下生物量、个体形态特征、生长繁殖及光合生理特征,研究0～50年长时间序列人工柠条的生长和繁殖动态特征。结果表明: 人工柠条林土壤水分变化与柠条林龄密切相关。6年生柠条的土壤水分较低,6～18年生柠条由于冠幅增加,降低了近地表的风速和太阳辐射,减少了土壤水分的蒸发,土壤水分呈上升趋势,18～50年生柠条的生物量快速积累,植物蒸腾量和根系对水分的吸收量大幅度增加,土壤水分不断降低,到50 年则下降至最低水平(11.1%);6～18年生人工柠条以地下根系生长为主,18～40年生柠条以地上部生长为主,40年生柠条的生物量维持在较高水平,冠幅和株高达到最高,生长状态达到最佳,40～50年生柠条的冠幅和株高显著降低,生长进入衰退期;柠条的光合能力(叶绿素a、b,类胡萝卜素和总叶绿素含量)随着种植年限的增加逐渐下降,尤其在18年后显著下降;柠条种子的数量和质量从6年生到40年生不断上升,40年生达到最大;与 6～12年生柠条相比,30～40年生柠条能产生更多个体质量小的种子。萌发试验表明,在相同年限,柠条的小种子比大种子的萌发速率更高,表明柠条繁殖策略有从前期(6～12年生)K策略向后期(30～40年生)r策略转化的趋势,而从50年生开始,柠条种子数量和质量显著下降,人工柠条的生长和繁殖出现退化。.
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