There has been a growing interest in understanding how biodiversity affects the functioning of ecosystems, while, it is still unclear how and to what extent different aspects of biodiversity are related to ecosystems function. We tested the relationship between aboveground biomass (AGB) and various aspects of functional diversity (functional richness (FRic), functional evenness (FEve) and functional divergence (FDiv)), functional β diversity and functional composition. Our study areas were located in four different bioclimatic regions including desert-steppe, steppe, semi-steppe, and Mediterranean rangelands extending along a productivity gradient created by the elevational-rainfall variations in the central Zagros Mountains of Iran.

The results showed that FDiv positively predicted AGB in more productive (i.e., Mediterranean) and negatively in less productive rangelands of desert-steppe, steppe and semi-steppe. Functional β diversity predicted AGB only in more productive regions in semi-steppe and Mediterranean rangelands. Functional β diversity decomposed into turnover and nestedness, with turnover being more important in more productive and nestedness being more important in less productive ecosystems. The results also showed that the effects of FD and functional β diversity on AGB are generally directed by animal grazing through homogenizing community-wide trait composition in less productive ecosystems and inducing shifting mosaics across locations in more productive ecosystem.

The results indicate that different components of FD were significantly related to AGB and the strength and direction of these effects vary with the different components studied and the bioclimatic regions under the study. In higher productive ecosystems, both functional diversity and functional β diversity are likely to contribute more to AGB through the complementary use of the resources. In less productive ecosystems, however, the functional identity of dominant species and traits would drive AGB.

人们越来越了解生物多样性如何影响生态系统的功能，而目前尚不清楚生物多样性的不同方面如何以及在何种程度上与生态系统功能相关。我们测试了地上生物量（AGB）与功能多样性（功能丰富度（FRic），功能均匀度（FEve）和功能差异（FDiv）），功能β多样性和功能组成的各个方面之间的关系。我们的研究区域位于四个不同的生物气候区域，包括沙漠草原，草原，半草原和地中海牧场，它们沿着由伊朗中部扎格罗斯山脉中的高程降雨形成的生产力梯度延伸。

结果表明，FDiv在沙漠草原，草原和半草原的生产力较高的地区（即地中海地区）积极预测AGB，而在生产力较低的牧场中进行负面预测。功能性β多样性仅在半草原和地中海牧场的高产地区预测AGB。功能性β多样性分解为周转率和嵌套度，其中周转率对生产力更高的环境更重要，而巢度对生产力较低的生态系统更重要。结果还表明，FD和AGB官能β多样性的效果是通过动物放牧通过均质化社会一般涉及-在更短的生产性的生态系统宽性状组合物和诱导更有生产力的生态系统移各地点马赛克。

结果表明，FD的不同成分与AGB显着相关，并且这些影响的强度和方向随所研究的不同成分和所研究的生物气候区域而变化。在生产力更高的生态系统中，功能多样性和功能β多样性都可能通过资源的补充利用为AGB做出更大贡献。然而，在生产力较低的生态系统中，优势物种和性状的功能特性将驱动AGB。