荒漠草原人工柠条林对冠下草本植物群落的保育作用

以宁夏盐池县荒漠草原人工柠条（Caragana intermedia）林为研究对象，分别选取柠条林冠下东侧（SE），冠下西侧（SW）及带间（Gap）为研究样地，从群落水平探讨柠条对冠下草本植物群落结构、物种多样性及功能群分布的影响。结果表明：（1）在3种微生境中均鉴定出12种植物，SW以蒙古冰草为优势种，SE以蒙古冰草和中亚白草为优势种，Gap则以蒙古冰草和牛枝子为优势种。（2）与Gap相比，SW和SE植物群落的平均高度分别增加了41.06%和81.75%，地上生物量分别增加了40.88%和38.73%。SW和SE中，禾本科植物地上生物量分别占地上总生物量的67.10%和58.40%，显著高于Gap （P<0.05）。（3）柠条冠层效应使得草本植物的物种丰富度指数增加，但Shannon-Winner指数、Simpson指数和Pielou指数显著差异（P>0.05），变化范围分别为1.620-1.756、0.701-0.730和0.775-0.878。（4）冗余分析表明：土壤温度、空气相对湿度及土壤有机碳是影响草本植物物种多样性及生物量的主要因子，解释量分别为42.70%，11.70%和8.80%。研究表明，柠条对冠下草本植物群落尤其是禾本科植物具有一定的保育作用，该效应的产生主要是由于柠条冠下微气候及土壤环境因子的改善为草本植物的生长发育提供了有利条件。柠条对草本植物的保育作用对荒漠草原生态环境的保护与恢复具有重要意义。

Nurse effects of artificial forest of Caragana intermedia on herbaceous plant communities under its canopies in desert steppe

The nurse effects are critical for maintaining biodiversity and ecosystem functions in arid and semiarid areas. However, whether promoting or competing interactions dominate in regions with high biotic and abiotic stress remains unclear. In order to investigate the effects of artificial Caragana intermedia forest on the community structure, species diversity and functional group distribution of herbaceous plant communities under its canopy in desert steppe in Yanchi County, Ningxia, the estern side under the canopies (SE), western side under the canopies (SW) and the gaps (Gap) were selected as the research plots. The vegetation characteristics, microclimate and soil factors were studied. The results showed that:(1) 12 plant species were identified in each of the 3 microhabitats. The dominant species in SW, SE and Gap were Agropyron mongolicum, A. mongolicum and Pennisetum centrasiaticum, A. mongolicum and Lespedeza potaninii, respectively, and the important values varied from 19.35 to 43.07. (2) Compared with Gap, the average height of plant communities for SW and SE increased by 41.06% and 81.75%, and the aboveground biomass increased by 40.88% and 38.73%, respectively. There were no significant differences in vegetation coverage among SW, SE and Gap (P>0.05). The aboveground biomass of the gramineous plants occupied 67.10% and 58.40% of the total aboveground biomass and the important values of the gramineous plants were 62.17 and 66.79 in SW and SE respectively, which were significantly higher than that in Gap(P<0.05). (3) The canopy effects of C. intermedia increased the richness index of herbaceous plants, the species richness index of SW was 8.8, which was significantly higher than that of Gap (P<0.05). There were no significant effects of C. intermedia on Shannon-Winner index, Simpson index and Pielou index of herbaceous plant communities, which ranged from 1.620 to1.756, 0.701 to 0.730 and 0.775 to 0.878 (P>0.05). (4) Redundancy analysis showed that soil temperature, relative air humidity and soil organic carbon were the main factors affecting herbaceous plant species diversities and biomass, and their explaining rates were 42.70%, 11.70% and 8.80% respectively. Based on the results of this study, the C. intermedia had a certain conservation effect on herbaceous plant communities under its canopies, especially Gramineae. This effect was mainly caused by the improvement of the microclimates such as relative air humidity, soil temperature and soil organic carbon under the canopies of C. intermedia, which provides favorable conditions for the growth and development of herbaceous plant. The nurse effect of C. intermedia on herbaceous plant is of great significance to the protection and restoration of the desert steppe ecological environment.