黄土丘陵区不同立地条件下猪毛蒿种内、种间竞争

INTRASPECFIC AND INTERSPECFIC COMPETITION OF ARTEMISIA SCOPARIA UNDER DIFFERENT SITE CONDITIONS IN THE HILLY REGION OF LOESS PLATEAU

猪毛蒿(Artemisiascoparia)通常是黄土丘陵区撂荒演替前期群落优势种,在无人为干扰的情况下,猪毛蒿群落通常会向冰草(Agropyroncristatum)群落或阿尔泰狗娃花(Heteropappusaltaicus)群落,或长芒草(Stipabungeana)群落等演替。该文通过河阶地和梁峁阴坡中猪毛蒿生长特征的调查和种内、种间竞争田间试验,从植物竞争角度对猪毛蒿群落的演替机制给予了解释。结果表明:1)两类样地中猪毛蒿的生长都趋于小型化,有少数大个体和多数小个体,都存在异速生长现象,说明两类样地存在竞争,且对猪毛蒿的生长形态具有塑造作用;2)由于单位地上生物量竞争效应排除了立地条件和个体大小的影响,因而比总竞争效应更能说明种对间的相对竞争能力。梁峁阴坡地和一、二级河阶地三种立地条件下,7种测试植物中对猪毛蒿的相对竞争能力以演替后期多年生植物较高,而演替前期一年生植物较低,说明演替后期种对前期种的竞争抑制是演替驱动力之一;3)以各测试植物对猪毛蒿单位重量竞争抑制程度平均值来看,以梁峁阴坡地最大,二级河阶地次之,一级河阶地最小,说明立地条件越差,土壤资源可利用水平越低,竞争越激烈;4)一级河阶地和梁峁阴坡地各测试植物对猪毛蒿的竞争等级发生了显著变化,说明环境条件差别较大时,植物的竞争等级会发生变化。

Background and Aims In hilly Loess region, Artemisia scoparia is always the dominator in the early abandoned field communities. It may be replaced by Agropyron cristatum or Heteropappus altaicus or Stipa bungeana in next succession stage when no disturbance occurs. In order to study the direction of Artemisia scoparia community succession under different standing conditions, we conducted transplant experiments to test the intraspecfic and interspecfic competition of Artemisia scoparia in river terrace and northern mound land and, at the same time, its morphological traits were investigated. Methods In the experiments, nine species （three coexisting species, five later sere species and Artemisia scoparia itself） were chosen and transplanted as test species, but due to the low survival of two species, only seven species were analyzed to test the relative competition ability to phytometer Artemisia scoparia under different standing conditions. Key Results The results show that the individuals tend to be miniaturized, i.e., its communities are composed mainly of small-sized individuals and competition can change the morphological traits. The unit biomass competition intensity is better than total competition intensity in explaining plants＇ relative competitive ability when local conditions and plant size are considered. Under the northern mound land and the lowest river terrace, late-successional and perennials species have higher competitative ability than early-successional and annual plants, suggesting that the competition of late- against early-successional species is one of the driving force to succession. Comparison of the competition between the seven test species and the unit biomass of Artemisia scoparia, the northern mound land ranks the first, lower river terrace the second and the lowest terrace the third, suggesting that intensive competition occurs more severely in poor growing conditions. There is significant difference in the ability of competition between the test species and Artemisia scoparia from the lowest river terrace to the northern mound land, suggesting that the ranks of the competition ability may vary depending on standing conditions. Conclusions As competition is one of the decisive factors in constructing plant community, the shift or variation of competition ability between coexisting species and sere species may result in different community structure and dynamics, so it changes the direction and pathway of succession under different standing conditions.