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林业科学 ›› 2021, Vol. 57 ›› Issue (11): 13-23.doi: 10.11707/j.1001-7488.20211102

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黄土丘陵区不同退耕林地表土水溶性有机质含量及光谱特征差异

芦琛1,蒋小董2,吴冠宇3,郝爽敬1,丁宏博1,佟小刚1,*   

  1. 1. 西北农林科技大学资源环境学院 杨凌 712100
    2. 西北农林科技大学水土保持研究所 杨凌 712100
    3. 陕西省水利水电工程咨询中心 西安 710000
  • 收稿日期:2020-06-11 出版日期:2021-11-25 发布日期:2022-01-12
  • 通讯作者: 佟小刚
  • 基金资助:
    陕西省自然科学基金重点项目(2018JZ4002);陕西省水利科技计划项目(2018slkj-7);国家自然科学基金项目(41771308)

Content and Spectral Properties of Water Dissolved Organic Matters in Surface Soil of Various Cropland-Converted Forest in the Loess Hilly Region

Chen Lu1,Xiaodong Jiang2,Guanyu Wu3,Shuangjing Hao1,Hongbo Ding1,Xiaogang Tong1,*   

  1. 1. College of Natural Resources and Environment, Northwest A & F University Yangling 712100
    2. Institute of Soil and Water Conservation, Northwest A & F University Yangling 712100
    3. Shaanxi Provincial Water Conservancy and Hydropower Engineering Consulting Center Xi'an 710000
  • Received:2020-06-11 Online:2021-11-25 Published:2022-01-12
  • Contact: Xiaogang Tong

摘要:

目的: 研究黄土丘陵区不同退耕还林植被恢复对表层土壤碳氮、水溶性有机质含量及其有机组成和荧光特性的影响,以期揭示退耕林地土壤累积水溶性有机碳氮的效应和机理,为退耕还林类型选择及生态功能评估提供科学依据。方法: 选择人工退耕还林19年的山杏、沙棘、油松、杨树、刺槐纯林和刺槐×山桃混交林及对照撂荒地,对比分析表层土壤(0~20 cm)的有机碳(SOC)、全氮(TN)、水溶性有机碳(WDOC)和水溶性有机氮(WDON)含量差异;基于三维荧光光谱技术和平行因子法探究不同退耕林地土壤水溶性有机质(WDOM)的有机组分及其荧光指数(API)、自身生产力指数(BIX)、新鲜度指数(βα)和腐殖化指数(HI)的异同。结果: 除山杏林地外,其他林地土壤的SOC和TN含量相比撂荒地平均增加131.1%和106.0%;仅山杏林地未能提高WDOC含量,刺槐×山桃混交林地WDOC含量增幅最大,达108.9%;刺槐纯林和刺槐×山桃混交林地的WDON分别比撂荒地增加173.5%和105.8%(P<0.05)。各林地土壤的WDOC/SOC百分比为0.30%~0.37%,WDON/TN百分比为0.29%~0.64%,2种比例均比撂荒地小。所有林地土壤的SOC:TN为14.1~20.2,均显著高于WDOC:WDON的9.0~16.5(P<0.05),油松林地土壤的SOC:TN和WDOC:WDON最高,分别比撂荒地高44.1%和98.9%。三维荧光分析显示,退耕林地WDOM主要由稳定性强的大分子芳香性腐殖质(C1)、低分子量富里酸和腐殖酸(C2)、类色氨酸(C3)组成;所有样地均以C1组分占比最大,且除沙棘林地外,其他林地CI组分占比相比撂荒地平均增加45.1%(P<0.05),C3组分占比最低,且各林地均比撂荒地低。不同退耕林地土壤水溶性有机质的荧光指数(FI)、新鲜度指数(βα)和自身生产力指数(API)无显著差异(P<0.05),分别为1.60~1.69、0.57~0.62和0.56~0.61,腐殖化指数(HI)表现为杨树、山杏林地显著高于其他林地。进一步相关分析表明,WDOC和WDON分别与SOC、TN极显著正相关(P<0.01)和显著正相关(P<0.05),C2组分与WDOC和WDON显著负相关(P<0.05);WDOC:WDON与SOC:TN显著正相关(P<0.05),但与WDON/TN显著负相关(P<0.05)。结论: 相比自然恢复的撂荒地,退耕林地土壤均表现出总有机碳和全氮的累积效应,可显著提升土壤WDOC含量,特别是刺槐林和刺槐×山桃混交林地可同时提升WDOC和WDON含量;杨树、山杏林地土壤WDOM表现出相对较高的腐殖化程度;退耕还林亦使土壤水溶性有机质趋向组成复杂和结构稳定,抗分解性提高,有利于土壤碳氮累积。

关键词: 退耕还林, 土壤水溶性有机质, 三维荧光特征, 植被恢复, 黄土丘陵区

Abstract:

Objective: The effects of restoration of farmland to forests with different vegetation was analyzed in the Loess Hilly Region by assessing the soil carbon and nitrogen, dissolved organic matter contentand organic composition, fluorescence characteristics of the surface soil. This study was aimed to reveal the effect and mechanism of accumulation of water dissolved carbon and nitrogen in the soil of the farmland-converted forest, it will provide a scientific basis for the selection of types of returning farmland to forest and ecological function evaluation. Method: Armeniaca sibirica, Hippophae rhamnoides, Pinus tabulaeformis, Populus simonii, Robinia pseudoacacia, and R. pseudoacacia×Amygdalus davidiana mixed forest converted from cropland for 19 years and abandoned land as control were investigated by comparing the differences in the contents of soil organic carbon (SOC), total nitrogen (TN), water dissolved organic carbon (WDOC), and water dissolved organic nitrogen (WDON) in the surface soil (0-20 cm). Three-dimensional fluorescence spectroscopy technology and the parallel factor method was used to estimate the organic components, fluorescence index (FI), autotrophic productivity index (API), freshness index (β:α) and humification index (HI) of different soil water dissolved organic matters (WDOM). Result: Except for A. sibirica, the differences in SOC and TN contents of other forest types increased on average by 131.1% and 106.0%, respectively, over those of the abandoned land. Among the WDOC, the A. sibirica forest alone failed to increase the WDOC content, and the R. pseudoacacia×A. davidiana mixed mixed increased the most, reaching 108.9%. The WDON increased by 173.5% and 105.8% for R. pseudoacacia and the mixed forest land, respectively. The WDOC/SOC ratio of all forest soils was maintained at 0.30%-0.37%, and the WDON/TN percentage was 0.29%-0.64%. Both ratios were less than those of the abandoned land. The soil SOC: TN ratio of each forest type was 14.1-20.2, which was significantly higher than that of WDOC: WDON (9.0-16.5). The SOC: TN and WDOC: WDON of P. tabulaeformis forest are the highest, 44.1% and 98.9% higher than those of abandoned land. Three-dimensional fluorescence analysis showed that the WDOC of forest land reclaimed from farmland was mainly composed of stable macromolecular aromatic humus(C2), fulvic acid with a smaller molecular weight, humus acid(C2), and tryptophan-like(C3) compounds. Except for the H. rhamnoides forest macromolecular humus accounted for the largest proportion of all forest lands with an average increase of 45.1% when compared with abandoned land. There were no significant differences in FI, API and β:α indexes of the soil dissolved organic matters of different forest types, which ranged between 1.60-1.69, 0.57-0.62, and 0.56-0.61, respectively. The HI index of P. simonii and A. sibirica was significantly higher than that of the other forest types. Further correlation analysis showed that WDOC and WDON are extremely significantly positively correlated and significantly positively correlated with SOC and TN, respectively. C2 component is significantly negatively correlated with WDOC and WDON. WDOC: WDON is significantly positively correlated with SOC: TN, but is significantly negatively correlated with WDON/TN (P < 0.05). Conclusion: When compared with naturally restored abandoned land, farmland conversion to forests show the cumulative effect of total organic carbon and total nitrogen and it can significantly increase the WDOC content, especially for R. pseudoacacia mixed and single species that can simultaneously increase the dissolved carbon and nitrogen contents. At the same time, the soil WDOM of P. simonii and A. sibirica forests showed a relatively high degree of humification. This is because the farmland conversion to forests resulted in more stable and complex composition at the same time, the soil WDOM of P. simonii and A. sibirica forests showed a relatively high degree of humification, organic matters which increases the resistance to decomposition and is conducive to accumulation of soil carbon and nitrogen.

Key words: cropland conversion to forest, soil water dissolved organic matter, three-dimensional fluorescence properties, vegetation restoration, Loess Hilly Region

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