摘 要

土壤磷的有效性是制约杨树人工林生长的重要因素，而不同的林下植被处理会对土壤磷的有效性产生一定的影响。本研究以不同林下植被处理的杨树人工林为对象，采用改良的Hedley土壤磷素分级法，研究杨树人工林林下植被的有无、多样性和种类对土壤磷素形态及其转化的影响，探讨不同的林下植被处理措施在杨树人工林土壤磷素形态及有效性方面的效应，从土壤磷素供应的角度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，林下植被消耗的磷素比其自身转化所产生的要多，所以导致清除林下植被处理的土壤磷素含量高于保留自然植被的处理。其中，清除林下植被处理的全磷含量在0-5cm土层中比保留自然植被处理的全磷含量高0.026g/Kg。

不同种类和多样性的林下植被可以形成不同的林下小生境，并提供不同种类的凋落物，从而改变林地环境和土壤理化特性和生化特征，进而改变并影响土壤中磷素形态特征和转化，供应水平及有效性。研究结果表明，林下植被越丰富对磷有效性的增加越显著。根据改良后的Hedley土壤磷素分级法，保留自然林下植被处理的树脂交换态磷和NaHCO₃-Pi、NaOH-Pi、D.HCl-Pi、conc.HCl-Pi和残留态磷组成的无机磷含量在0-5cm土层中比保留稗草处理高154mg/Kg。同时，不同林下植被的处理也会对土壤中全磷含量的增加有不同程度的促进作用。保留稗草处理的全磷含量在0-5cm土层中比种植田菁处理高0.0054g/Kg。

关键词：杨树人工林；林下植被；磷分级

Effects of Underground Vegetation on Soil Phosphorus Availability in Poplar Plantation

ABSTRACT

Soil phosphorus availability is an important factor restricting the growth of poplar plantations, and different understory vegetation treatments will have a certain impact on soil phosphorus availability. Taking poplar plantations with different undergrowth vegetation treatments as the object of this study, the effects of the presence, diversity and species of Undergrowth Vegetation on the forms and transformation of soil phosphorus in poplar plantations were studied by using the improved Hadley soil phosph- orus classification method, and the effects of different undergrowth vegetation treat- ments on the forms and availability of soil phosphorus in poplar plantations were di- scussed. The angle provides certain data support for scientific management of under- story vegetation of poplar plantation.

The results show that the phosphorus consumption of undergrowth vegetation is more than that of its own transformation, so the phosphorus content of soil in the treatment of clearing undergrowth vegetation is higher than that in the treatment of retaining natural vegetation. Among them, the total phosphorus content of the treatment of clearing undergrowth vegetation was 0.026 g/Kg higher than that of the treatment of retaining natural vegetation in 0-5 cm soil layer.

Different types and diversity of understory vegetation can form different understory niches and provide different types of litter, which can change the physical, chemical and biochemical characteristics of forest environment and soil, and then change and affect the morphological characteristics and transformation of phosphorus in soil, supply level and availability. The results showed that the more abundant undergrowth vegetation, the more significant the increase of phosphorus availability. According to the improved Hedley soil phosphorus classification method, the inorganic phosphorus content of resin exchangeable phosphorus and NaHCO3-Pi、NaOH-Pi、D.HCl-Pi、conc.HCl-Pi and residual phosphorus in the 0-5 cm soil layer was 154 mg/Kg higher than that in the barnyard grass treatment. At the same time, the treatment of different undergrowth vegetation can also promote the increase of total phosphorus content in soil to varying degrees. The total phosphorus content of barnyard grass treatment was 0.0054g/Kg higher than that of Sesbania treatment in 0-5cm soil layer.

Key words: Poplar plantation；Understory vegetation；Phosphorusclassification

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 2

1.2.1杨树人工林研究概况 2

1.2.2林下植被的作用 3

1.2.3 森林生态系统土壤磷素循环与供应 4

1.2.4 森林土壤形态及分级方法 5

1.2.4.1 土壤磷形态 5

1.2.4.2 土壤磷的分级方法 6

2 主要研究内容 8

3 研究区概况 9

4 研究方法与流程 10

4.1 试验调查及样品采集小区的设置 10

4.2 根际土壤和林地土壤的采集和处理 10

4.3 样品测定指标及方法 11

4.3.1 土壤全P的测定 11

4.3.2 Hedley磷素分级测定 11

5 结果与分析 13

5.1 不同林下植被杨树人工林土壤全磷含量比较 13

5.2 不同林下植被杨树人工林Hedley磷素分级比较与结果 13

5.3 不同林下植被杨树人工林土壤有机磷和无机磷变化特征 19

5.4不同林下植被处理下林地土壤磷的矿化量 21

6 结论与讨论 23

6.1 林下植被有无对杨树人工林土壤全磷含量影响 23

6.2 林下植被多样性对杨树人工林土壤磷素含量的影响不同 23

6.3 林下植被对土壤有机磷和无机磷变化特征...................................................................24

致 谢 27

参考文献 28

1 前言

1.1立题依据及研究意义

杨树具有生长快、成材早、产量高、易于更新的特点，是中纬度平原地区人工造林的主要树种。目前，我国杨树（Populus L.）人工林面积位居世界第一。截至2015年底，我国杨树人工林面积已达854万hm²，其中用材林面积309万hm²，仅占全国用材林面积的3.11%，而产出木材占全国木材总量的30%左右。在杨树人工林的传统管理过程中，林下自然生长的植被认为会与杨树产生养分和水分竞争，因此通常会被去除或进行林农复合经营加以控制。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着重要作用^[1-2]。

磷是杨树人工林生长所必需的大量营养元素之一，其供应程度在很大程度上制约着杨树人工林的生产力和可持续经营。磷在土壤中很容易受到土壤胶体和有机成分的吸附，其有效性受到含量、组分和和转化动态的影响，土壤磷素分级是评价土壤磷库大小和磷供应状况的有效指标。不同种类和多样性的林下植被可以形成不同的林下小生境，并提供不同种类的凋落物，从而改变林地环境和土壤理化特性和生化特征，进而改变土壤中磷素形态特征和转化，影响其有效性和供应水平^[3]。