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土壤养分作为陆地植物养分的主要来源,除了养分含量之外,养分间的平衡关系也是调控植物生长和分布的关键因子之一[1]。生态化学计量学通过比较元素间的比例关系,为探究生态系统结构和功能的提供新的角度和方法[2]。由于土壤碳(C)、氮(N)是植物演替早期最主要的元素,因而碳氮化学计量特征是影响陆地植被生态系统的演化与恢复关键因素之一[3-4]。
九寨沟自然保护区作为世界自然遗产,是中国第一个以保护自然风景为主的自然保护区,也是全球生物多样性保护热点地区[5]。2017年8月的7.0级地震导致了该地大量的土壤流失和植被摧毁等一系列生态环境问题。如何恢复受损的生态系统对其生物多样性的保护及生态旅游至关重要。地震所造成的滑坡体上植被的恢复为认识植被演替的调控因子提供了较好的模式[6-7]。植被恢复主要通过自然恢复和人工恢复。一般而言,人工恢复模式因恢复时间快、景观效果好而受到欢迎,而在生物多样性保护和稳定性方面的价值却遭到了怀疑[8]。因此,通过比较自然恢复和人工恢复下土壤碳氮化学计量特征的差异,探讨不同植被恢复方式对植被恢复的影响机理,以期为该地植被快速恢复提供理论依据。
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通过调查震后人工恢复、自然恢复及邻近未受损坡体的典型区域植被后发现:在1年多的人工修复措施显著改变了坡体上的植被特征,尽管这些植被与地震未受损的植被显著不同。在人工恢复的坡体上有燕麦(Avena sativa)、悬钩子(Rubus spp.)等草灌植被,而自然恢复的坡体上偶有高山柳等。从总盖度来看,地震未受损的坡体(CK)、受损人工恢复坡体(AR)、受损自然恢复坡体(NR)的平均总盖度分别为0.79、0.33、0.10,且CK>AR>NR(见图1)。
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土壤pH值(CK、NR、AR的平均值分别为7.06、8.09、7.58),土壤有机碳含量(CK、NR、AR的平均值分别为23.55、8.73、14.70%)、总氮含量(CK、NR、AR的平均值分别为1.36、0.20、0.65%)、可利用氮含量(CK、NR、AR的平均值分别为590.17、168.89、337.58 mg·kg−1)及碳氮比(CK、NR、AR的平均值分别为17.32、56.61、29.96)均受土壤恢复方式显著影响(P<0.001),其中有机碳、总氮、可利用氮的含量均为CK>AR>NR,而pH值和碳氮比均为CK<AR<NR(见图2和表1)。此外,除pH值变异系数较小外(<10),其余各项指标的变异系数均较大(见表1)。
表 1 不同恢复方式下土壤养分状况
Table 1. Soil nutrient status under different restoration models
指标 恢复方式 均值 标准差 最大值 最小值 变异系数/% pH值 CK 7.06 0.53 5.83 7.99 7.47 NR 8.09 0.37 6.98 8.57 4.60 AR 7.58 0.61 6.52 8.39 8.00 有机碳/% CK 23.55 6.71 11.90 37.35 28.50 NR 8.73 2.66 4.65 15.00 30.51 AR 14.70 5.07 10.25 26.86 34.50 总氮/% CK 1.36 0.36 0.75 1.95 26.42 NR 0.20 0.14 0.08 0.60 68.89 AR 0.65 0.35 0.18 1.12 53.61 碳氮比 CK 17.32 2.30 12.16 21.84 13.28 NR 56.61 26.67 15.57 100.00 47.11 AR 29.96 17.05 12.27 67.61 56.93 碱解性氮 CK 590.17 156.38 193.40 889.15 26.50 /mg·kg−1 NR 168.89 81.23 43.86 394.81 48.10 AR 337.58 130.57 87.64 523.00 38.68 图 2 不同恢复方式对土壤养分及化学计量特征的影响差异
Figure 2. Effects of different restoration models on soil nutrients and stoichiometric characteristics
土壤养分与其化学计量特征之间存在一定相关性。土壤有机碳含量与pH值、C/N呈显著负相关,而与全氮或可利用氮含量呈显著正相关;全氮或可利用氮含量与pH值、C/N呈显著负相关(见表2)。
表 2 不同恢复方式下九寨沟土壤养分与其化学计量特征相关性分析
Table 2. Correlation analysis of soil nutrients and the stoichiometric characteristics under different restoration models in Jiuzhaigou country
pH值 Soil organic carbon Total nitrogen C/N Soil organic carbon −0.713*** Total nitrogen −0.784*** 0.916*** C/N 0.701*** −0.526*** −0.727*** Available nitrogen −0.772*** 0.896*** 0.958*** −0.688*** ***表示相关度达到极显著水平(P<0.001)
Effects of Different Restoration Models on Soil Carbon and Nitrogen Stoichiometry in Junzhaigou Earthquake-stricken Landslides
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摘要: 通过比较自然恢复、人为恢复及与自然植被的土壤碳氮化学计量特征,以期为九寨沟地震受损滑坡体快速恢复提供理论依据。结果表明:(1)与未受损植被的土壤相比,受损植被滑坡体的土壤有机碳、总氮、可利用氮含量均更低,但pH值和碳氮比均更高。(2)人为恢复下的植被总盖度、土壤有机碳、总氮、可利用氮含量均高于自然恢复。(3)土壤有机碳含量与总氮或可利用氮含量呈现正相关、而与pH值或碳氮比呈显著负相关。短期的结果表明人为恢复措施比自然恢复更有利于九寨沟震损坡体植被的快速恢复。此外,建议在未来植被恢复中注意栽植固氮植物。Abstract: According to the comparison of soil carbon and nitrogen stoichiometry characteristics between natural restoration after earthquake (NR), artificial restoration after earthquake (AR) and natural vegetation without earthquake (CK) in Jiuzhaigou country, it could provide theoretical basis for rapid restoration of landslide damaged by Jiuzhaigou earthquake. The results showed that: (1) Compared with the soil without earthquake damage, the contents of soil organic carbon (SOC), total nitrogen (TN), available nitrogen (AN) in landslides with earthquake-damaged vegetation were lower than that on CK, but the pH value and C/N were higher. (2) The total vegetation coverage, SOC, TN and AN contents under artificial restoration were higher than those under natural restoration. (3) SOC was positively correlated with TN or AN, but negatively correlated with pH or C/N. These short-term results indicated that artificial restoration was better for vegetation recovery of earthquake-stricken landslides than natural restoration. In addition, it is suggested that nitrogen-fixing plants should be planted in the future vegetation restoration.
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表 1 不同恢复方式下土壤养分状况
Tab. 1 Soil nutrient status under different restoration models
指标 恢复方式 均值 标准差 最大值 最小值 变异系数/% pH值 CK 7.06 0.53 5.83 7.99 7.47 NR 8.09 0.37 6.98 8.57 4.60 AR 7.58 0.61 6.52 8.39 8.00 有机碳/% CK 23.55 6.71 11.90 37.35 28.50 NR 8.73 2.66 4.65 15.00 30.51 AR 14.70 5.07 10.25 26.86 34.50 总氮/% CK 1.36 0.36 0.75 1.95 26.42 NR 0.20 0.14 0.08 0.60 68.89 AR 0.65 0.35 0.18 1.12 53.61 碳氮比 CK 17.32 2.30 12.16 21.84 13.28 NR 56.61 26.67 15.57 100.00 47.11 AR 29.96 17.05 12.27 67.61 56.93 碱解性氮 CK 590.17 156.38 193.40 889.15 26.50 /mg·kg−1 NR 168.89 81.23 43.86 394.81 48.10 AR 337.58 130.57 87.64 523.00 38.68 表 2 不同恢复方式下九寨沟土壤养分与其化学计量特征相关性分析
Tab. 2 Correlation analysis of soil nutrients and the stoichiometric characteristics under different restoration models in Jiuzhaigou country
pH值 Soil organic carbon Total nitrogen C/N Soil organic carbon −0.713*** Total nitrogen −0.784*** 0.916*** C/N 0.701*** −0.526*** −0.727*** Available nitrogen −0.772*** 0.896*** 0.958*** −0.688*** ***表示相关度达到极显著水平(P<0.001) -
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