沙化程度和林龄对湿地松叶片及林下土壤C、N、P化学计量特征影响

为阐明沙化程度和林龄对湿地松(Pinus elliottii)叶片及林下土壤碳(C)、氮(N)、磷(P)化学计量特征影响,探讨C、N、P化学计量比对沙山植被恢复的指示意义,在鄱阳湖多宝沙山沿沙化梯度测定了不同林龄湿地松叶片及林下土壤C、N、P含量。结果表明:1)在叶片C、N、P及其化学计量比中叶N与C∶N对沙化程度和林龄变化反应最为敏感。对于轻度与中度沙化区的5年生与10年生湿地松林,林龄、林龄与沙化程度的交互作用均对叶N及C∶N产生显著影响;对于中度与重度沙化区的2年生和10年生湿地松林,林龄和沙化程度均显著影响叶N与C∶N。2)叶片与土壤二者C、N、P及化学计量比对沙化程度与林龄变化的响应不完全一致。林龄、林龄与沙化程度的交互作用对轻度与中度沙化区5年生和10年生湿地松林土壤全N有显著影响;对于中度与重度沙化区2年生和10年生湿地松林,仅沙化程度对土壤全磷以及林龄对土壤有机碳影响显著。3)10年生湿地松叶片N∶P平均值为20.63,10年生以下湿地松叶片N∶P平均值为15.61,随着林龄的增加,湿地松生长由N、P共同限制逐渐转向更受P的限制。

Effects of desertification intensity and stand age on leaf and soil carbon, nitrogen and phosphorus stoichiometry in Pinus elliottii plantation

There are some sandy hills distributed along Poyang Lake, which belong to typical southern desertification. As located in subtropical climate zone, the sandy hills differed in vegetation and soil from northern deserts. During the past ten to twenty years, Pinus elliottii was introduced in sandy hills for vegetation restoration. Since carbon (C), nitrogen (N) and phosphorus (P) stoichiometry are critical indicators of biogeochemical coupling in terrestrial ecosystems, the nutrients stoichiometry has been successfully used in indicating community succession and vegetation restoration in recent years. However, our knowledge of the temporal variability of carbon, nitrogen and phosphorus stoichiometry is much less developed than its spatial pattern. Besides, it remains unknown whether there is consistent temporal pattern for various ecosystem components, such as plants and soil. In this study, leaf and soil organic carbon, total nitrogen and total phosphorus in Pinus elliottii plantation were measured along desertification gradient in a typical sandy hill close to Poyang Lake. The objectives were (1) to clarify effects of desertification intensity and stand age on leaf and soil carbon, nitrogen and phosphorus stoichiometry, as well as the role of nutrients stoichiometry in indicating vegetation restoration in sandy hills, and (2) to discuss the temporal variation pattern of leaf and soil nutrients stoichiometry during stand development. Results showed that mean concentrations of leaf carbon, nitrogen and phosphorus were (437.48±16.96) mg/g, (6.09±1.51) mg/g and (0.71±0.66) mg/g, respectively. The counterparts for top 0-10 cm soil were (3.48±0.63) mg/g, (0.117±0.032) mg/g and (0.050±0.012) mg/g, respectively. The mean ratio of C:N, C:P and N:P was 75.70, 1297.86 and 17.76 for leaf, and 32.45, 74.04 and 2.52 for soil, respectively. Leaf carbon, nitrogen and phosphorus concentrations were all lower than the means of global plants. However, the ratio of N:P was comparable to other researches. Leaf nitrogen and ratio of C:N were most sensitive to changes in desertification intensity and stand age. For 5-year and 10-year Pinus elliottii plantation distributed at low and medium desertification area, both leaf nitrogen and C:N ratio were significantly affected by stand age and interaction of stand age plus desertification intensity. By comparison, stand age and desertification intensity significantly influenced leaf nitrogen and C:N ratio for 2-year and 10-year Pinus elliottii plantation distributed at medium and high desertification area. Leaf nutrients stoichiometry differed from soil in response to changes of stand age and desertification intensity. For 5-year and 10-year Pinus elliottii plantation distributed at low and medium desertification area, stand age and interaction of stand age plus desertification intensity significantly affected soil total nitrogen. However, for 2-year and 10-year Pinus elliottii plantation distributed at medium and high desertification area, desertification intensity significantly affected soil total phosphorus, and stand age significantly affected soil organic carbon. Additionally, leaf N:P ratios were 20.63 and 15.61 for 10-year and less than10-year Pinus elliottii, respectively, which suggested growth of Pinus elliottii was firstly limited by both nitrogen and phosphorus, however, Pinus elliottii plantation would change to phosphorus limitation during stand development.