Abstract: The relationship between biomass and diversity is a hot topic in ecological research. Although studies have found that this relationship is influenced by environmental factors, no study has tested the congruence of biomass-diversity responses to changing soil pH obtained from studies using an observational approach and studies using manipulative experiments in grasslands. Here, we combined manipulative and observational approaches to investigate the biomass-diversity relationship response to soil pH in Inner Mongolian grasslands. We found: 1) Along a natural transect, soil pH was mainly affected by soil and grassland types, and aridity index. The relationship between aboveground biomass and soil pH showed a U-shaped curve. Species richness showed a significant U-shaped curve in relation to soil pH. Diversity was positively correlated to aboveground biomass. 2) In the acid/alkaline addition experiments, the relationship between aboveground biomass and soil pH was characterized by a one-peak curve. This was also true for species richness in relation to soil pH. The biomass-diversity relationship depended on grassland types: A positive correlation could be found in desert grasslands, but not in typical/meadow grasslands. Our study suggested that the relationships between biomass and diversity in temperate grasslands were dependent upon the variations in soil pH. The observation that results from manipulative experiments were opposite to those from observational studies might be attributed to the fact that the observations along transects reflect the results of long-term adaptation. In contrast, results from manipulative experiments reflect the short-term response to environmental changes.

Key words: manipulative experiments, observational studies, soil pH, temperate grasslands, biomass, diversity