Divergent responses of plant biomass and its allocation to the altered precipitation regimes among different degraded grasslands in China

Purpose: Climate models predict shifts in precipitation patterns characterized by increased precipitation amount and decreased frequency for semi-arid grasslands in northeast China. However, under these novel climatic conditions, potential differences in plant biomass and its allocation among different degraded grasslands remain unclear. Methods: We conducted a mesocosm experiment to test the effects of higher precipitation amount (increased by 50% from the long-term mean) and lower frequency (decreased by 50%) on plant biomass and allocation in the lightly, moderately, and severely degraded grasslands. Results: Lower precipitation frequency promoted belowground biomass but reduced aboveground biomass through enhancing soil water variability. Higher precipitation amount enhanced aboveground biomass in the lightly and moderately degraded grasslands, but not in the severely degraded grassland due to lower soil nitrogen availability. Lower precipitation frequency weakened or ended the positive effects of higher precipitation amount on aboveground and belowground biomass, and higher precipitation amount suppressed the enhancement of lower precipitation frequency on belowground biomass, which could be attributed to temporary waterlogging. Plants in the moderately degraded grassland preferred to adjust root vertical distribution, which was impacted by the changes in plant community composition. However, adjustment of aboveground biomass vs. belowground biomass was the primary biomass allocation strategy in the other two grasslands. Conclusions: Our findings emphasized the importance of considering the degradation level of grasslands when predicting responses of ecosystem functions to the projected changes in precipitation regimes. These findings are critical for making feasible decisions for the sustainable management of degraded grasslands. Graphical abstract: [Figure not available: see fulltext.] Legend: + and − indicate positive and negative relationships, respectively LDG, MDG and SDG-lightly degraded, moderately degraded and severely degraded grasslands, respectively DPF-decreased precipitation frequency treatment, IPA-increased precipitation amount treatment SWC and CV_SWC-mean and variation of soil water content, respectively SINC-soil inorganic nitrogen content AGB and BGB-aboveground and belowground biomass, respectively f_AGB-AGB / total biomass BGB_0–10(%)-belowground biomass proportion in the 0–10 cm soil layer, BGB _{0 - 10}/ BGB _{0 - 30}× 100 RAGB-relative aboveground biomass.