Responses of plant biomass allocation to changed precipitation timing in a semi-arid steppe

Precipitation changes can affect patterns of biomass allocation by altering species composition. However, how shifts in species with different growth forms under precipitation changes affect above- and belowground biomass allocation and the vertical root distribution remains unclear.

We conducted a 7-year experiment in a semi-arid grassland in northern China to explore how plant biomass allocation responds to changed precipitation during different periods of the growing season.

The results showed that both decreased precipitation during the late (DLP) and entire (DP) growing season significantly reduced forb ANPP. In contrast, increased precipitation during the early (IEP), late (ILP), and entire (IP) growing season significantly increased forb ANPP. Decreased precipitation during the early (DEP) growing season, DP, IEP, and ILP significantly reduced grass ANPP. Changes in the abundance of grasses and forbs with different growth forms altered biomass allocation patterns. DEP and DP augmented the proportion of BNPP, and DLP had little effect on BNPP. IP decreased the proportion of BNPP, whereas neither IEP nor ILP affected the proportion of BNPP. DP significantly decreased the proportion of BNPP_0-20 cm, and IEP and ILP increased the proportion of BNPP_0-20 cm.

Our findings indicate that precipitation during the early growing season determines the allocation of above- and belowground productivity and the distribution of shallow roots by altering soil moisture, and precipitation during the late growing season with large changes in water availability determines the deep root distribution by shifting the composition of plant species with different root distribution.