高寒草甸土地退化及其恢复重建对植被碳、氮含量的影响

 以青海省达日县高寒草甸原生高寒嵩草（Kobresia）草甸封育系统为对照，研究了土地退化对植被生产力的影响，检验了不同人工重建措施（ 两个人工种植处理：混播（HB）、翻耕单播（DBF）和1个退化草地封育自然恢复处理（NR）及1个退化草地自然状态（SDL））对植被生产力的 相对影响程度。结果表明，原生植被封育处理（YF）地上总生物量为265.1 g•m^-2，混播(HB)和翻耕单播(DBF)处理中地上总生物量分别为原生 植被封育处理的116%和68%。退化草地封育自然恢复处理（NR）和重度退化自然状态下地上总生物量分别为原生植被封育的76%和53%。YF处理根 系生物量远大于其它处理。原生植被封育系统中植被地上部分碳储量为 110.14 g•m^－2，地下根系（0～30 cm）碳储量为2 957 g•m^－2，植被 总碳储量为 3 067.14 g•m^－2；重度退化草地系统中植被地上部分碳储量为 57.07 g•m^－2，地下根系（0～30 cm）碳储量为 357 g•m^－2，植 被总碳储量为 414.07 g•m^－2。由此可见， 高寒草甸严重退化后，通过植物组织流失的碳达到2 653.35 g•m^－2，即86.5%的碳损失；原生植被 封育系统植被总氮储量为 56.85 g•m^－2，而重度退化草地植被总氮储量为 18.02 g•m^－2，高寒草甸严重退化使植物组织68.30%氮损失。与重 度退化地相比，由于恢复重建措施增加了植物的生物量输入和群落组成，除翻耕单播处理外，其它恢复重建措施均能恢复系统植被的碳氮储量 。这些恢复重建措施将会逐步改善土壤的物理和化学特性，最终使这些生态系统逐步由碳源向碳汇方向的转变成为可能。

EFFECTS OF LAND DEGRADATION AND REHABILITATION ON VEGETATION CARBON AND NITROGEN CONTENT OF ALPINE MEADOW IN CHINA

Aims Our objectives were to compare vegetation biomass and total carbon and nitrogen content of severely degraded grassland and undisturbed Kobresia meadow, and to measure the relative influence of various rehabilitation practices on vegetation biomass and carbon and nitrogen content in early secondary succession.  Methods The research was conducted on alpine meadows in Dari County, Qinghai Province, China, using five treatments: undisturbed native meadow, severely degraded grassland, and three grasslands rehabilitated by different practices (mixed seeded , single seeded and natural recovery). In each treatment, vegetation C and N contents were calculated on an area and depth basis from biomass samples and plant concentration analyses.  Important findings In the undisturbed native meadow treatment, total aboveground biomass was 265.1 g•m^－2 and root biomass in the uppermost 30 cm averaged 6 982 g•m^－2. In the severely degraded grassland treatment, above ground biomass was only 139.9 g•m^－2 and root biomass was only 916 g•m^－2. Total aboveground biomass in the mixed seeded, single seeded and natural recovery treatments was 307.1, 179.9 and 200.4 g•m^－2, and root biomass was 1 323, 1 169 and 1 412 g•m^－2, respectively, after seven growing seasons. Total C content of vegetation in the undisturbed native meadow was 3 067.42 g•m^－2, while that of the severely degraded grassland treatment was only 414.07 g•m^－2. Therefore, land degradation leads to loss of 86.5% of the original plant tissue C. In addition, land degradation leads to loss of 68.3% of the original plant tissue N. Compared with the severely degraded land, mixed seeded and natural recovery treatments partly recover C and N content, indicating that they may be alternative approaches to sequestering C in former degraded alpine meadow.