松嫩平原羊草草地植物功能群组成及多样性特征对水淹干扰的响应

THE RESPONSES OF FUNCTIONAL GROUP COMPOSITION AND SPECIES DIVERSITY OF ANEUROLEPIDIUM CHINENSE GRASSLAND TO FLOODING DISTURBANCE ON SONGNEN PLAIN, NORTHEASTERN CHINA

为研究草地植被对水淹干扰的响应 ,在松嫩平原羊草 (Aneurolepidiumchinense)草地 1998年部分遭受水淹的吉林省大安市三家甸子草场内设置了经历不同水淹强度的样带 ,并对这些样带的植被组成及物种多样性特征进行了比较研究。结果表明 :1)在植被的水分生态类型功能群组成中 ,随水淹干扰强度的增加 ,湿生、湿中生类植物功能群的优势度比例基本上是逐渐增加的 ,中生、中旱生类植物功能群的优势度比例则逐渐减小 ;2 )在植被的生活型功能群组成中 ,随水淹干扰强度的增加 ,一年生植物的优势度比例呈单峰型变化 ,地下芽植物比例增加 ,地面芽植物比例减小。某些单个物种优势度比例的不规则变化和功能群组成的规则变化表明 ,生态补偿作用不仅仅存在于植物群落的各个功能群之间 ,而且存在于同一功能群内部的不同物种之间 ;3)群落的物种丰富度、多样性在经历中等强度水淹干扰的样带上较高 ,而在未受干扰的对照样带和受干扰较为严重的样带都较低 ,这有力地支持了中度干扰假说。

Flooding disturbance has tremendous effects on a variety of vegetation types, but most related studies have focused on very limited vegetation types, such as floodplain forests, riverine and lakeshore grasslands, wetlands and swamps. Little effort has been made on the effect of flooding disturbance on the temperate meadow steppe, such as Songnen meadow steppe dominated by Aneurolepidium chinense in Northeastern China, a transitional type between forest in the east and Inner-Mongolian typical steppe in the west, and also the very eastern end of temperate steppe zone of Eurasian continent. To investigate the effects of flooding disturbance on such a vegetation type, a comparatively thorough study was conducted in August 1999 in Sanjiadian State-owned Pasture in the territory of Da'an city, Jilin province, which was partly flooded in August 1998. Along the flooding gradient (from un-flooded to heavily flooded) formed on an extensive mild slope taken as the study site, five flooded transects coded T_1, T_2, T_3, T_4 and T_5 respectively were designed, and also an un-flooded one coded T_0 was set as a control at relatively higher elevation, so as to make comparisons among the transects on such aspects as vegetation composition, species richness and diversity. Before the flood occurred in 1998, the slope had almost uniform soil and vegetation, mainly A. chinense dominated community. Each transect was 0.2 hm2 (100 m×20 m) in size and all the five flooded transects were almost parallel to one another, with the longer sides of them perpendicular to the retrieving direction of floodwater. In elevation, T_0>T_1>T_2>T_3>T_4>T_5, so T_0 was the highest and the only un-flooded transect among the six, and T_1, T_2, T_3, T_4 and T_5 were flooded transects, but subject to flooding of different durations: about 3, 5, 7, 9 and 11 months respectively. In each of the transects, twenty 1 m2 sized quadrates were randomly chosen to survey the community structure of the corresponding transect, and aboveground parts in five of them were harvested, taken to the labs, separated according to species, and dried under 80 ℃. To compare the species composition among the transects, the dominance values of most of the plant species present were calculated for all the transects, then the dominances were pooled and averaged according to functional groups both in sense of the hydro-ecological types and of life forms. Furthermore, the species richness (Gleason index and Margalef index) and diversity (Simpson index and Shannon-Weiner index) were also analyzed. The results were as follows: 1) Flooding disturbance had effects on species composition: for the functional group composition in sense of hydro-ecological types, with the elongation of the flooding durations or the increase of flooding severity, the ratio of hygric and hygro-mesic plants increase, while that of mesic and mesoxeric plants decrease; 2) For the functional group composition in sense of life forms, the ratio of Therophytes changed unimodally, of Geophytes increased, while the ratio of Hemicryptophytes decreased. The contingency of the irregular changes of the dominance of some individual species and of the regular changes of the summed dominance of functional groups revealed that the ecological compensation not only operated among functional groups in a community, but among individual species within a functional group; 3) The species richness and diversity of the communities were higher on the intermediately-flooded transect than on un-flooded (control) and heavily-flooded transects, which supported the Intermediate Disturbance Hypothesis. It could be concluded that the following three factors affected the species composition of the sites: The first was soil water status and concomitant oxygen pressure changes in the soil on the flooded sites, which had become a limiting factor for establishment, growth and reproduction of plants; The second was physiological endurance and adaptability; The third was the inter-plant ecological interactions, whose results would be modified by the si