青藏高原筑路取土迹地恢复植物群落与土壤的碳氮磷化学计量特征

恢复筑路取土迹地植物群落是青藏高原退化高寒草地恢复的重要组分,而生态化学计量是揭示退化草地自然恢复过程中土壤和植物间养分互作的重要方法。通过调查青藏公路筑路取土迹地自然恢复群落和天然群落内植物和土壤C、N、P的含量及其比值,研究了恢复群落和天然群落的C、N、P生态化学计量特征。结果表明:经历18a自然恢复后,不同地点筑路取土迹地均已逐步实现植物群落的定居,但其恢复程度存在明显差异。恢复群落植物叶片N含量高于天然群落,导致其叶片C∶N较低,表明恢复群落植物的N利用效率较低,N含量较高的模式主要原因可能是豆科植物比例较高和土壤有效N的供应较充足所致。恢复样地在0—10 cm和10—20 cm的土层内的有机碳(SOC)都显著低于天然样地,恢复样地土壤全氮(STN)仍一定程度上低于天然样地但含量较接近,恢复样地在10—20 cm土层中土壤全磷(STP)含量较高,这说明恢复群落尽管在土壤恢复方面并未达到天然群落的水平,但已得到了明显改善,土壤肥力正发生着正向的演替。叶片N含量与土壤STN相关性不显著,叶片P含量与土壤STP含量显著地正相关,表明植物叶片P含量在一定程度上受到土壤环境中全磷的影响。综合N∶P判定阈值和叶片土壤养分相关分析结果表明研究地区草地植被主要受到P元素的限制,且工程迹地草地恢复群落比天然群落容易受到P元素的限制。

C, N, and P stoichiometry of plant and soil in the restorable plant communities distributed on the Land Used for Qinghai-Tibet Highway Construction in the Qinghai-Tibetan Plateau, China

The restoration of Land Used for Qinghai-Tibet Highway Construction is an important part to restore degraded alpine grassland in the Qinghai-Tibet Plateau, China. C, N, P stoichiometry is considered an effective tool to disclose the synergistic adaptation of plant growth and element availability in the process of plant restoration on Land Used for Qinghai-Tibet Highway Construction. A field survey was carried out to investigate whether the Land Used for Qinghai-Tibet Highway Construction contributes to shifts in the C, N, and P stoichiometry of the leaves and soil of the plant community, and to identify the N- or P- limitation status of plants in the natural community and restorable communities growing for nearly two decades as part of the natural regeneration of Land Used for Qinghai-Tibet Highway Construction. Seven survey sites were selected along the Qinghai-Tibet Highway, in which four groups of restorable and natural plots were arranged. Then, four subplots for each plot were randomly used to harvest community leaves and soil samples. Organic C, N, and P concentrations of plant leaves and soil samples were analyzed by using the external heating method, the Kjeldahl acid-digestion method, and the Mo-Sb-Ascorbic acid colorimetric method, respectively. The independent-sample t test and paired t test were used to analyze differences in leaf C, N, and P stoichiometric variables and differences in soil organic C, N, and P stoichiometric variables from restorable and natural plots, respectively. The relationship between leaf and soil C, N, and P stoichiometric variables was analyzed by Pearson correlation. This study showed that the plant communities had gradually established on the Land Used for Qinghai-Tibet Highway Construction at each study site, but that the plant composition was different between restorable communities and natural communities after 18 years natural restoration. The leaf N concentration of restorable communities was higher than that of natural communities;thus, inducing lower leaf C : N, which showed that the N nutrient-use efficiency of the restorable communities was lower than that of the natural communities. A high percentage legume plant and relatively adequate available N supplement may be the major reasons for lower leaf C : N in restorable communities. The soil organic carbon (SOC) of the restorable plots at both 0-10 cm and 10-20 cm soil depths were significantly lower than those of natural plots, and the soil total nitrogen (STN)shared the similar pattern with SOC. The soil total P of the restorable plots in the 10-20 cm soil layer was higher than that in natural plots. These results indicate that the soil fertility of restorable communities did not reach the level of natural communities, but that it had improved significantly. Leaf N and STN had no significant correlation;however, leaf P was significantly positively correlated with soil total phosphorus (STP), showing that leaf P is influenced by STP to some certain extent. Using the thresholds of N, P-limitation, and the results of the correlation between leaf elements and soil nutrients, this study shows that plants are probably P-limited in the study region, with plants in the restorable communities suffering from more intense P-limited conditions than those in the natural communities.