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CAS Workshop on Ecosystem Succession Theory and Practice of Ecological Restoration 中国西北鄂尔多斯草地退化中3种土壤元素的小尺度异质化及其损失 程小莉
安树青 （南京大学生命科学学院，南京210093） 摘要：在中国西北鄂尔多斯高原毛乌素沙地调查了三种土壤元素的空间分布和流失的过程。选择了代表荒漠化过程中连续退化的5个群落，分别为本氏针（Stipa bungeana）茅群落（群落1）、本氏针茅+油蒿（Artemisia ordosia）群落（群落2）、油蒿群落（群落3）、油蒿+牛心朴子（Cynanchum komorovii）群落（群落4）和牛心朴子群落（群落5）。在这5个退化群落中，分别在根区和空白地测定土壤有机质（TOC）、
全氮（TN）、水解性氮（DN）、全磷（TP）和有效磷（AP）。 实验结果表明：在土壤元素异质化过程中首先表现为土壤有机质的异质化过程，其次为土壤全氮的异质化过程，全磷只有在群落3中才表现出异质化过程，在5个退化群落中有效磷没有表现出明显的异质化过程。在退化的开始阶段，灌丛油蒿的入侵，由于本氏针茅和油蒿对土壤元素的竞争使群落2出现了土壤资源的暂时的异质化。在群落3中，土壤元素开始出现了空间异质化过程，从而形成了“肥料岛”（islands
of fertility）。土壤元素（TOC,
TN 和
DN）的浓度在油蒿根系下最高。随着荒漠化过程的加深（从群落4到群落5），“肥料岛”开始崩溃，主要元素的浓度开始下降。在荒漠化过程中磷元素的变化机制不同其他元素，从群落1到群落5的退化过程中，全磷的浓度一直是下降的过程，而有效磷在中度荒漠化过程（从群落1到群落3）中没有变化，在严重荒漠化过程中（群落3到群落5）却是增长的过程。 关键词：荒漠化；土壤营养元素；空间异质化；异质化过程；土壤元素流失 Micro-scale spatial
heterogeneity and the loss of three soil elements in degraded
grassland in Ordos Plateau, north-western China Cheng Xiaoli An
Shuqing (School of Life Science, Nanjing University, Nanjing 210093, China) Abstract:
The micro-scale spatial distribution and loss of three soil elements
were examined in degraded grassland near Ordos, in the Mu Us
Sand-land, north-western China. Five communities that represented a
series of successionally degraded stages in desertification were
chosen for the work. The dominant plant of Community 1 was the steppe
grass Stipa bungeana; Community 2 was dominated by a mix of S.
bungeana and the shrub Artemisia
ordosia; Community 3 was A.
ordosia; Community 4 was a mix of
A. ordosia and the desert grass Cynanchum
komorovii; and Community 5 was C.
komorovii. The soils in root-spheres and
in the bare openings between plants in five successionally degraded
plant communities were analyzed for total
organic carbon (TOC), total nitrogen (TN), dissolved nitrogen (DN),
total phosphorus (TP), and available
phosphorus (AP). The results showed that the
heterogeneity process of the soil chemistry was characterized first by
TOC heterogeneity and later by TN heterogeneity. The heterogeneity
process of TP was only characterized in the community 3. No
significant heterogeneity was present for AP in the five community
stages. At the beginning of degradation, invasion
by the shrub A. ordosia of S. bungeana grassland
was found to lead to competition for soil elements between S. bungeana and
A. ordosia
and made the community 2 soil environment temporarily
homogeneous. In community 3, however, the
soil elements became spatially heterogeneous, and this led to
the development of ‘islands of fertility’. The concentrations of
soil elements (TOC, TN and DN) were greatest in the shrub
root-spheres. With further desertification (from community 4 to
community 5), the islands of fertility began to collapse, and the
concentrations of the main soil elements declined rapidly. The
dynamics of soil phosphorus under progressive desertification were
different from those of the other soil elements. TP decreased from
form community 1 to community 5, while the AP concentration did not
change in mid-level desertification (community 3), but increased with
serious desertification (community 5). Key words:
desertification; soil nutrients; spatial heterogeneity; heterogeneity
process; soil element loss
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