黄土高原退耕还草地植物群落动态对生态系统碳储量的影响

退化农地通过植被恢复能够提高生态系统的固碳能力，但是植被恢复中植物群落特征如何影响生态系统碳储量仍存在不确定性。以农田为对照，选取自然恢复8、15、25、35 a草地为对象，探讨退耕还草地植物群落特征对生态系统碳储量的影响。结果表明：群落盖度随着恢复年限的增加而显著增加，恢复35 a时达到最大值（64.0%），优势种从达乌里胡枝子、赖草、茵陈蒿演变为长芒草、铁杆蒿；禾草类、多年生草本和灌木逐渐成为优势种。Shannon-Weiner指数、Patrick指数均呈先上升后下降的趋势，均在第15年达到最大值。地上植被碳储量和地下植被碳储量在恢复期间呈直线增加的趋势，且均在35 a达最大值，分别为0.83 Mg C/hm²、1.49 Mg C/hm²，而凋落物碳储量在第25年达到最大值，为0.40 Mg C/hm²。土壤碳储量与有机碳含量总体呈先下降后上升的趋势，在第8年达到最低值，在第35年恢复到农田水平之上，占生态系统碳储量的93.3%-99.6%；表层0-10 cm土壤碳储量占0-30 cm碳储量的38.9%-50.3%，呈表聚现象。生态系统碳储量与土壤碳储量趋势一致，即恢复到第8年最低，为24.32 Mg C/hm²，恢复到第35年最高，为43.70 Mg C/hm²。群落盖度、地上生物量、凋落物生物量、禾草、豆科以及多年生植物的重要值与生态系统碳储量呈显著正相关（P<0.05），杂草和一年生植物重要值与生态系统碳储量呈显著负相关（P<0.05）。研究表明植被群落组成的动态变化通过增加植被碳储量和土壤碳储量实现生态系统碳储量的增加，而多年生植物、杂草与禾草的重要值和地下生物量与凋落物生物量是影响生态系统碳储量的重要植被因子。

Effects of plant community dynamics on ecosystem carbon stocks since returning farmlands to grasslands on the Loess Plateau

Global warming is an important problem faced by mankind at present. The increase in greenhouse gas emissions due to human activities is the main cause of global warming. The degraded agricultural land can reduce soil greenhouse gas emissions by improving the carbon sequestration capacity of ecosystems through vegetation restoration, but there is still uncertainty how plant community characteristics affect ecosystem carbon stocks following vegetation restoration. This paper selected a chronosequence of 0 (farmland), 8, 15, 25 and 35 years of grassland restoration since farmlands abandonment. We aimed to explore (1) how the plant community and ecosystem carbon stocks changed with the increase of restoration age; and (2) how the composition of the plant communities affected the changes of the ecosystem carbon stocks. The results showed that the community cover increased significantly with the increase of restoration age, and reached the maximum value (64.0%) in 35 years since farmlands abandonment. The advantage strains evolved from Lespedeza daurica, Leymus secalinus, Artemisia capillaris, to Stipa bungeana, Artemisia sacrorum; grasses, perennial herbs and shrubs gradually became the dominant species. The Shannon-Weiner index and the Patrick index both showed a trend of first increase and then decrease, reaching their highest level in the farmland abandonment for 15 years. The carbon stocks of aboveground vegetation and underground vegetation showed a linear increase during the restoration period. They both reached the maximum value in 35 years, which were 0.83 and 1.49 Mg C/hm², respectively. The carbon stocks of litters reached the maximum value of 0.40 Mg C/hm² in the 25 years. Soil carbon stocks and organic carbon content showed a trend of first decline and then increase, reaching the lowest value in 8 years and returning to the same level with farmland in 35 years, and soil carbon stocks accounted for 93.3%-99.6% of ecosystem carbon stocks in the grassland restoration ecosystems. Ecosystem carbon stocks were in line with soil carbon stocks, with a minimum of 24.32 Mg C/hm² in 8 years and 43.70 Mg C/hm² in 35 years. Community cover, above-ground biomass, litter, plant structure and function showed significantly positive correlation between carbon stocks (P<0.05), and the important values of forbs and annual herbs showed significantly negative correlation with ecosystem carbon stocks (P<0.05). The study suggested that vegetation community composition increased ecosystem carbon stocks by increasing vegetation and soil carbon stocks. The important values of perennials, forbs and grasses and underground biomasses and litters are important vegetation factors to affect the carbon stocks in the restoring grassland ecosystems.