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The three principal fates of axillary meristem in flowering plants are growth (G), reproduction (R), and inactivity (I). The allocation relationships between each meristem and plant size in annual herbaceous plants tend to change with altered precipitation (P) patterns in arid and semiarid grasslands. Here, we examined the allometry and plasticity of meristem allocation in three dominant annual herbaceous plants: Setaria viridis, Corispermum macrocarpum, and Bassia dasyphylla in a semiarid sandy grassland in northern China. We determined the range of plant sizes for each of the three species in the following treatments: ambient environment (Amb), P increased by 30% (P[+]) and by 60% (P[++]), P decreased by 30% (P[−]) and by 60% (P[− −]), drought for 46 days from May 1st to June 15th (D1) and from July 1st to August 15th (D2). We found that meristem allocation to branching intensity increased while allocation to apical dominance decreased with increasing plant size under decreased precipitation and seasonal drought. Decreased precipitation and seasonal drought caused the slope of allometry of meristem allocation in the three species to be significantly different from 1. Plasticity of meristem allocation to G, R, and I in S. viridis tended to be significantly greater in August under P(+) and P(++) while in C. macrocarpum tended to be greater in July under P(−), P(− −), D1, and D2. Our findings are important components of an adaptive strategy in annual herbaceous plants throughout the development stage, which will contribute to predict their developmental dynamics in the semiarid sandy grassland under future climate change. [ABSTRACT FROM AUTHOR]

Overgrazing in semiarid grassland is a major cause of vegetation degradation. Understanding the changes in seedling patterns driven by grazing is crucial to unveiling mechanisms of plant community regeneration and succession in grazed grassland. However, the dynamics of seedling emergence and species diversity under grazing are rarely studied. This study used periodical field investigation to examine the variation in seedling emergence, plant diversity, species composition, and seedling survival of herbaceous plants under four grazing intensities, including light (LG), moderate (MG), heavy (HG), and non‐grazed (NG), in a semiarid sandy grassland. The results showed that seedling number and density were significantly higher in HG plots, while the seedling survival rate was significantly lower in HG, and that seedling emergence dynamics varied with grazing. Seventy‐five percent of the seedlings in HG emerged during early spring in April, while approximately 50% of the seedlings in LG, MG, and NG emerged in May. Differences in species richness and diversity varied with growth stages and the diversity was always higher in LG than in other grazing habitats during the main growing season. Annual forb seedlings increased while annual grass seedlings decreased after grazing with no perennial grass seedlings in HG. Our study suggests that high seedling emergence but low seedling survival rate, and simple species composition especially the disappearance of perennial plants caused by HG may be an important factor leading to vegetation degradation in the semiarid grazed grassland. [ABSTRACT FROM AUTHOR]