高寒草甸种间性状差异和物种均匀度对物种多样性与功能多样性关系的影响

物种多样性(SD)与功能多样性(FD)之间存在多种关系,但由于生态系统功能主要由物种的功能属性决定,因而功能多样性对生态系统功能的影响大于物种多样性的影响。但在种间性状差异和物种均匀度这两个构成功能多样性的基本成分中,何者对功能多样性影响更大,并进而决定SD-FD关系尚不明确。通过在高寒矮嵩草(Kobresia humilis)草甸为期6a的刈割(留茬1 cm、3 cm及不刈割)和施肥(尿素7.5 g m~(-2)a~(-1)+磷酸二胺1.8 g m~(-2)a~(-1)、不施肥)控制实验,研究了种间性状差异(33个物种13个性状)和物种均匀度(所有物种)对物种多样性(所有物种)与功能多样性(33个物种13个性状)之间关系的影响。研究结果显示:(1)物种多样性与功能多样性正相关,它们与多性状种间差异负相关,而与物种均匀度正相关。物种均匀度是导致功能多样性变化的主要因素,也是导致SD-FD正相关的原因,这是因为随着物种多样性增加,物种均匀度的增加程度大于多性状种间差异的减少程度,因而功能多样性增加,SD-FD正相关;(2)功能多样性指数(FD_(Rao)和FDis)随物种多样性指数(H')减速递增,表明群落存在一定的功能冗余,且功能冗余随物种多样性的增大而增大,但尚未达到产生SD-FD无相关性的极限H'值;(3)功能多样性对高寒草甸生态系统地上净初级生产力(ANPP)的影响大于物种多样性的影响,二元线性回归显示在同时考虑二者对ANPP的影响时,可排除物种多样性的作用。但由于物种多样性下降或物种丧失引起的物种功能性状丢失或性状空间维度减小将导致功能多样性降低,表明它们之间存在一定互补性,在研究生物多样性与生态系统功能关系时,同时考虑物种多样性和功能多样性的影响仍十分必要。

Effects of interspecific trait dissimilarity and species evenness on the relationship between species diversity and functional diversity in an alpine meadow

Species diversity (SD) and functional diversity (FD) have previously been reported to be associated in a variety of ways, and identifying the relationship between these two parameters is important for our understanding the relationship between biodiversity and ecosystem functioning. Since ecosystem functioning is mainly influenced by plant functional attributes, it is widely held that functional diversity exerts a greater influence upon ecosystem functioning than does species diversity. However, it remains unclear which basic component of functional diversity (i.e., species evenness or trait dissimilarity among species) contributes more to functional diversity and thus determines or alters the SD-FD relationship. In this study, a field manipulation experiment was conducted in an alpine Kobresia humilis meadow at the Haibei Research Station of the Chinese Academy of Sciences from 2007 to 2012. The experiment employed a split-plot design, in which vegetation was clipped to one of two lengths (above ground stubble =1 cm or 3 cm) or left unclipped. Subplots were treated with fertilizer (urea 7.5 g m^-2 a^-1 + ammonium phosphate 1.8 g m^-2 a^-1) or remained unfertilized. Data analysis methods, e.g. general linear model univariate ANOVA, multivariate analysis, binary linear regression and curve fitting, were employed to analyze the effects of these treatments on trait dissimilarity among species (d_ij, 13 traits of 33 species), community species evenness (Pielou evenness index, J) and community species diversity (Shannon-Wiener index,H''), and functional diversity (Rao index, FD_Rao; Functional dispersion, FDis) (13 traits of 33 species), as well as potential relationships among these measures. 1) SD (H'') was significantly positively correlated with FD (FD_Rao, FDis), and J was positively correlated with SD (H'') and FD (FD_Rao, FDis), whereas d_ij (dissimilarity of 13 traits among 33 species) was negatively correlated with SD (H'') and FD (FD_Rao, FDis). J was more strongly correlated with SD (H'') than d_ij, and was also correlated with FD (FD_Rao, FDis). Thus, it can be concluded that species evenness is a major driving factor of both variation in FD and the positive correlation between SD and FD. 2) Curve fitting revealed that the increase in FD (FD_Rao, FDis) leveled off as SD (H'') increased, indicating that a certain degree of functional redundancy occurred in the community and that this increased with species diversity. As a result, species diversity (H'') failed to reach the limit that would result in a non-significant correlation between species diversity and functional diversity. 3) The effect of FD (FD_Rao, FDis) on aboveground net primary productivity (ANPP) of the alpine meadow ecosystem was greater than that of SD (H''). Binary linear regression showed that the effect of SD (H'') on ANPP was negligible compared with that of FD (FD_Rao,FDis).It should be noted that the loss of functional traits or a reduction in the number of trait space dimensions, such as results from the decline or loss of species diversity, would inevitably reduce the functional diversity of community, indicating a complementary relationship between species diversity and functional diversity. Thus, future studies on the relationship between biodiversity and ecosystem functioning should focus simultaneously on the effects of both species diversity and functional diversity on ecosystem functioning.