Plant biomass in three subalpine grasslands on Qinghai-Tibetan Plateau

Aims: Multiple studies have addressed the relationship between plant biomass and species richness, often reporting a hump-shaped curve. However, such research in natural grassland was mostly conducted in temperate, arid and semiarid areas, with few studies focused on alpine regions. Moreover, in most cases, plant community biomass was the main variable of interest, with few studies considering also plant individual biomass, calculated by dividing plant community biomass by plant abundance.

Location: To explore the relationship between plant biomass and species richness in subalpine regions, a field survey was conducted in three locations with fenced subalpine grasslands on the Qinghai-Tibetan Plateau in China in 2020 and 2023.

Methods: Plant aboveground biomass and species richness were recorded along four transects in each location. Analyses were performed using both plant community biomass and plant individual biomass to test whether using a different biomass measure affected the plant biomass-species richness relationship.

Results: Location and year × location significantly affected species richness, plant community biomass and plant individual biomass. Curve estimations demonstrated a positive nonlinear relationship between plant community biomass and species richness, and a negative nonlinear relationship between plant individual biomass and species richness. These patterns were modified by the locations of the three grasslands. Competition can explain some of the different patterns between plant community biomass-species richness relationship and plant individual biomass-species richness relationship.

Conclusions: In general, the choice of biomass approach affected the relationship between plant biomass and species richness in subalpine grasslands, which indicates that plant abundance impacts plant biomass-species richness relationship. Future research should consider further modulators and drivers when exploring the plant biomass-species richness relationship in grasslands in a climate change context.

Methods
Transect sampling is assumed to be an effective method to incorporate variation between grassland communities. Accordingly, four transects were randomly set in each location. All transects had a length of 105 m, and quadrats with a size of 0.5 m × 0.5 m were laid out at 0, 5, 15, 30, 50, 75, and 105 m along each transect, with the quadrat size matching previous studies conducted in these locations. In each quadrat, species richness was quantified (i.e. the total number of different species), plant abundance (i.e. plant density in this case) was measured by counting the total individual number of each species, and dry biomass was determined after harvesting all plants in each quadrat and oven drying at 105 °C for 48 hours.