Humped Relationship between Herbaceous Species Richness and Biomass Reveals a Potential for Increasing Productivity in a Temperate Desert in Central Asia

ABSTRACT Species richness-biomass relationship has become a primary focus in plant community ecology. The most commonly reported pattern of species richness and biomass is the humped relationship with a peak in richness at moderate biomass, although negative, positive, or no relationships exited in some cases. However, the richness-biomass relationship in the temperate deserts of Central Asia, where herbaceous species with different life forms are abundant, remains unclear. In this study, 21–214 plots with herbaceous richness and aboveground biomass for each of four plot sizes (0.25, 25, 100, and 400 m2) were surveyed in early summer and early autumn in the Gurbantunggut Desert, China. Linear and quadratic regressions were employed to examine the richness-biomass relationship and the location of the richness peak. Significantly unimodal species richness-biomass relationships were observed in all plot sizes and seasons (except for 0.25 m2 plot in summer). In most cases (9/11), the biomass at the richness peak was higher than half of the biomass range. Meanwhile, the percent of sampling plots where the biomass was less than the peak was considerably greater than 50% (72.7 to 100%) in all cases, and nine of them were more than 95%, indicating strong interspecific coexistence and weak interspecific competition. In conclusion, under the background of increasing precipitation and nitrogen deposition, the humped richness-biomass relationship and the high percent of sampling plots with low biomass jointly revealed a huge potential for increasing productivity, which is crucial for the carbon fixation and ecosystem stability in deserts of Central Asia.