摘 要

氮是林木需求量最大的矿质元素，杨树（Populus L.）人工林地力的维持、生产力的提高与土壤氮的供应密切相关，虽然普遍认为林下植被在土壤氮转化方面起着一定作用，但其保留与否以及多样性和种类对土壤中氮转化和供应所起的作用及程度尚未清晰。本研究以不同林下植被处理的杨树人工林为对象，通过对现地土壤中无机氮（铵态氮和硝态氮）、土壤N转化相关酶活性（主要是芳基酰胺酶和L-天冬酰胺酶）、土壤微生物生物量（MBC和MBN）以及矿化一段时间后的土壤里的无机氮进行测定，研究杨树人工林林下植被的有无、多样性和种类对土壤氮转化的影响，为杨树人工林林下植被的科学管理提供一定的数据支撑。

研究结果表明，林下植被的存在在某种程度上会促进土壤氮转化，保留自然林下植被的5-10 cm土层硝态氮含量比清除林下植被的5-10 cm土层的硝态氮含量高4.87 mg/Kg；在0-5cm土层，保留自然林下植被MBC含量比清除林下植被的MBC含量值为178.69mg/Kg，MBN含量高13.15 mg/Kg；。此外，林下植被多样性越高越会促进土壤氮转化，保留自然林下植被的硝态氮含量比保留一种主要杂草（稗草）的5-10 cm土层的硝态氮含量高2.94 mg/Kg；在0-5cm土层，保留自然林下植被的MBC含量比保留一种主要杂草（稗草）的MBC含量高172.84mg/Kg，MBN含量比保留一种主要杂草（稗草）高9.94mg/Kg。种植固氮植物能有效提高土壤中的硝态氮含量，与保留一种主要杂草（稗草）相比，种植固氮植物土壤中的硝态氮含量比保留一种主要杂草（稗草）土壤中的硝态氮含量在0-5 cm土层高6.76 mg/Kg；在5-10 cm土层高7.97 mg/Kg；在10-20 cm土层高4.65 mg/Kg。保留一种主要杂草（稗草）的MBN含量比种植固氮植物（田菁）的MBN含量高11.91 mg/Kg。在0-5㎝土层，保留自然林下植被的矿化量最高，矿化量为12.97 mg/Kg，而在5-10cm和10-20cm的土层中，清除林下植被的矿化量最高，分别为11.75mg/Kg和11.58 mg/Kg。

关键词：杨树；林下植被；氮转化

Effects of understory vegetation on soil nitrogen transformation in poplar plantations

Abstract

Nitrogen is the most demanding mineral element in forests. The maintenance of soil fertility and productivity of poplar(Populus L.)plantations are closely related to the supply of soil nitrogen. Although it is generally believed that understory vegetation plays a role in soil nitrogen conversion, its retention or not The extent and extent to which diversity and species contribute to nitrogen conversion and supply in soil is not clear. In this study, the poplar plantations treated with different understory vegetations were used to investigate the activities of inorganic nitrogen (ammonium and nitrate nitrogen) and soil N conversion related enzymes (mainly aryl amidase and L- in the soil). Asparaginase, soil microbial biomass (MBC and MBN) and inorganic nitrogen in soil after mineralization for a period of time were studied to study the presence, diversity and species of understory vegetation in poplar plantations. The impact of this provides a certain data support for the scientific management of understory vegetation in poplar plantations.

The results show that the presence of understory vegetation promotes soil nitrogen conversion to a certain extent, retaining the nitrate content of 5-10 cm soil layer of natural understory vegetation and removing the nitrate of 5-10 cm soil layer of understory vegetation. The nitrogen content was 4.87 mg/Kg. In the 0-5 cm soil layer, the MBC content of the natural understory vegetation was 178.69 mg/Kg and the MBN content was 13.15mg/Kg. In addition, the higher the diversity of understory vegetation, the more the soil nitrogen transformation will be promoted. The nitrate nitrogen content of the natural understory vegetation is higher than that of the 5-10 cm soil layer retaining a major weed (Herb). 2.94 mg/Kg; in the 0-5 cm soil layer, the MBC content of the natural understory vegetation is 172.84 mg/Kg higher than the MBC content of a major weed (Herb), and the MBN content retains a major weed ( Valerian) is 9.94mg/Kg high. Planting nitrogen-fixing plants can effectively increase the content of nitrate nitrogen in the soil. Compared with retaining a main weed (grass), the nitrate-nitrogen content in the soil of nitrogen-fixing plants is better than that of retaining a major weed (grass) soil. The nitrate content in the 0-5 cm soil layer is 6.76 mg/Kg higher; in the 5-10 cm soil layer, it is 7.97 mg/Kg higher; in the 10-20 cm soil layer, it is 4.65 mg/Kg higher. The MBN content of a major weed (Herb) was 11.91 mg/Kg higher than that of the nitrogen-fixing plant (Tianjing). In the 0-5cm soil layer, the mineralization of the understory vegetation is the highest, and the mineralization is 12.97 mg/Kg. In the soil layers of 5-10cm and 10-20cm, the mineralization of the understory vegetation is removed. The highest was 11.75mg/Kg and 11.58mg/Kg, respectively.

Key words: poplar; undergrowth; nitrogen transformation

目录

1 前言 1

1.1立题依据及研究意义 1

1.2国内外研究进展 1

1.2.1杨树人工林研究概况 1

1.2.2林下植被及其功能 2

1.2.3森林土壤氮素转化的研究进展 5

2 主要研究内容 8

3 试验地概况 8

4 试验设计 9

5 调查内容与方法 10

5.1田间调查与样品采集、处理 10

5.2测定指标及分析测试方法 10

5.3数据统计与分析 12

6 结论与分析 13

6.1不同林下植被处理对土壤温、湿度的影响 13

6.2不同林下植被处理对林地土壤无机氮的影响 14

6.3不同林下植被处理对林地土壤微生物生物量的影响 16

6.4不同林下植被处理对林地土壤N转化相关酶活性的影响 18

6.5不同林下植被处理对林地土壤氮净矿化的影响 20

7 结论与讨论 22

7.1林下植被有无对土壤氮转化的影响 22

7.2林下植被多样性对土壤氮转化的影响 23

7.3林下植被种类对土壤氮转化的影响 24

致 谢 26

参考文献 27

1 前言

1.1立题依据及研究意义

杨树（Populus L.）是我国主要的短周期速生丰产用材林树种，适应性强、生长快、成材早、产量高、易于更新, 是用材林、防护林和进行林农复合经营的主要树种^[1]。在以往的经营管理中，杨树人工林多采用单一的纯林经营模式。在杨树人工林的传统管理过程中，人们认为林下植被可能会与杨树之间产生养分和水分的竞争，因此通常会通过去除林下植被的方式^[2]加以控制。然而越来越多的研究发现，林下植被在森林生态系统的物质循环、长期立地生产力维护以及生物多样性保护等方面均发挥重要作用。