Growth response of dominant species and companion species to grazing and precipitation addition in a typical steppe

Growth strategies of plant populations plays an important role in biodiversity and productivity of community while over half 77% of global terrestrial ecosystem is used for grazing and simultaneously 30%-40% is exposed to precipitation addition (PA). However, the combined effects of grazing and PA on plant population growth and their relationship with community characteristics remain poorly understood, largely due to the limited number and quality of field experiments. Hereby, a four-year PA experiment was conducted in long-term grazed paddocks in a typical steppe, which aimed to compare the effects of both grazing and PA on the growth, reproduction, and trade-offs between dominant and companion species. The interaction between grazing and PA prompted the dominant species to adopt a horizontal growth strategy and sexual reproduction, allocating 69 % of its resources to offspring production, whereas the companion species opted for a vertical growth strategy and asexual reproduction, allocating 87 % of its resources to individual survival and dispersal. This trade-off strategy increased the proportion of dominant species while companion species remained stable, and PA mitigated this trend while concurrently decreasing the proportion of other species within the community. The interaction between grazing and PA promotes the coupling of aboveground biomass and species riches in community by decreasing plant height of dominant and companion species and increasing canopy diameter of companion species. There were mainly four biotic response curves of dominant and companion species to grazing and PA interaction: full saturation, sufficient saturation, equal saturation, and deficit saturation. Correspondingly, there were three pairs of threshold values for three phases of each pattern. Our study reveals how communities improve their adaptability by regulating population growth, providing important insights for developing sustainable grazing management strategies under global climate change.