水氮添加对内蒙古多伦县退耕还草地生物量、 生产力及其分配的影响

以内蒙古多伦县退耕还草地为研究对象,调查了施肥N10:10 g(N)?m?2?a?1]和加水(180 mm?a?1)对其植被生物量、生产力和分配方式的影响,并与围封草地作比较。结果发现:1)施肥使退耕还草地地上生物量增加近1倍;加水使退耕还草地地上生物量提高17%~37%,但未达到统计显著性;2)无论施肥还是加水都没有显著影响退耕还草地地下生物量,加水使其地下净初级生产力(BNPP)提高35%~90%;3)施肥降低了退耕还草地根冠比和地下、地上净初级生产力比(BNPP/ANPP),而降水增加对两个指标无显著影响;4)施肥使退耕还草地禾草类植物比例增加,生物量均匀度降低;加水处理后,退耕还草地的杂类草生物量提高128%,而优势种猪毛蒿(Artemisia scoparia)和蒙古冰草(Agropyron mongolicum)的地上生物量对加水处理不敏感;5)水肥处理后,退耕还草地总生产力、根冠比和生物量远小于围封草地。表明水氮添加对退耕还草地生物量的影响主要在地上部分,且与物种组成有关。

Responses of plant biomass and net primary production to nitrogen fertilization and increased precipitation in re-grassed croplands in Duolun County of Inner Mongolia, China

Biomass and NPP (net primary productivity) are the primary data which describe the structure and function of ecosystems. The allocations of biomass and NPP are related to nutrient, water use efficiencies and the ability to resist erosion of ecosystems. Excessive farming has intensified wind-erosion desertification in northern China, which has not only affected local economic development and ecological conditions, but also posed threat to the ecological state of the inland areas. Re-grassing abandoned croplands has been a common measure to prevent wind-erosion-caused desertification in the agro-pastoral ecotone of northern China. Grassland vegetation is very sensitive to nitrogen and water in arid and semiarid areas, but is unclear whether and how nitrogen (N) fertilization and increased precipitation affect the restoration of vegetation in re-grassed croplands. The responses of biomass and NPP to N fertilization N10: 10 g(N)·m-2·a-1] and irrigation (irrigation amount was 180 mm to simulate 50% increase in precipitation) were investigated in a re-grassed abandoned cropland in Duolun County of Inner Mongolia, China. The results showed that fertilization increased the aboveground biomass of re-grassed croplands by nearly 100% while irrigation increased aboveground biomass by only 17%-37%. Either fertilization or irrigation had no significant effect on belowground biomass in re-grassed croplands (P > 0.05) while irrigation enhanced belowground NPP (BNPP) by 35%-90%. Fertilization reduced root-to-shoot ratio (R︰S) and ratio of BNPP to aboveground NPP (ANPP) in re-grassed cropland but increased precipitation had no significant effect on the two indicators (P > 0.05). The dominant species (Agropyron mongolicum and Artemisia scoparia) had significant positive responses to fertilization, respectively with 130% and 70% increase in biomass in the second year. However, fertilization had no significant effect on biomass of forbs (P > 0.05). Asymmetric competition for fertilizer among plant species increased the proportion of perennial grass and decreased the proportion of forbs in vegetation community of re-grassed cropland. In contrast, forbs were very sensitive to irrigation, with 128% increase in biomass in the second year of treatments. Increased precipitation enhanced the proportion of forbs in the community by 13%. A. mongolicum and A. scoparia biomass was not affected by increased summer precipitation. Belowground biomass, BNPP, total NPP (TNPP) and R︰S ratio of treated or untreated re-grassed croplands were much lower than those of fenced grassland. The results indicated that fertilization significantly increased aboveground biomass and changed the proportions of biomass and NPP in re-grassed farmlands. The results also suggested that increased precipitation hastened vegetation restoration in abandoned croplands. This strongly depended on functional types of dominant species due to the distinct sensitivity of plant species to increased precipitation.