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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]

Seedlings are a crucial part of the plant community and the basis of vegetation restoration and regeneration. Grazing and climate change are two main factors contributing to vegetation changes in semiarid grasslands. However, the effects of grazing on seedling emergence with rainfall variation are not clearly understood. This study aimed to address how seedling abundance and the emergence dynamics of annuals respond to grazing with rainfall changes in different years. We conducted a seedling investigation experiment in a grassland along a grazing intensity gradient (light grazing—LG; moderate grazing—MG; heavy grazing—HG) in contrasting wet and dry years. The results showed that MG increased the seedling richness of grasses and forbs in the wet year, but increasing grazing resulted in a decline in forb richness in the dry year. Seedling abundance of grasses was enhanced under MG, while seedling abundance of forbs was higher under HG. The monthly emergence dynamics were generally in a single peak pattern, but the peak time of seedling emergence for forbs advanced under HG. Seedling abundance of whole annuals increased with grazing in the wet year but was much higher under MG in the dry year. Our results suggest that more judicious grazing management based on rainfall variation and functional composition of the plant community should be undertaken to facilitate grassland restoration. [ABSTRACT FROM AUTHOR]

Plant litter derived from the living biomass is the primary source of soil carbon (C). However, the contribution and the mechanism of plant litter production to soil C remains uncertain in aeolian regions. In this study, the relationship between plant biomass, litter mass, and soil C content was analyzed after a spatial field investigation in Horqin sandy land, northeast China. Long-term monitoring of wind speed and plant litter production was also conducted in three habitats (mobile dune, semi-fixed dune, and fenced grassland). The soil C content was significantly affected by belowground biomass and belowground litter mass but not aboveground biomass and aboveground litter. The litter production in the desertified habitat (mobile dune and semi-fixed dune) significantly differed with that of the undesertified habitat (fixed dune and fenced grassland). In mobile dune, 38% of the aboveground primary production was lost, while there was a distinct enrichment of plant litter in semi-fixed dune and fenced grassland. Wind events (wind speeds of 7 and 8 m s−1) at the end of the growing season significantly affected litter production rate, and wind was a major driver for litter transportation between habitats. In summary, plant litter production can be affected by wind events, and this influence differs among habitats in degraded grassland, leading to spatial heterogeneity of soil C accumulation. These results can strengthen the understanding of the relationship between soil properties and plant litter production in aeolian regions and furthermore, can provide information for ecological restoration of different types of desertified land, especially for the soil C accumulation. Plant litter is the major source for soil organic matter accumulation. In degraded sandy grasslands in semi-arid regions, wind is a visible factor which transported the aboveground litter from regions with lower vegetation coverage (e.g. mobile dune or semi-fixed dune) to regions with higher vegetation coverage (e.g. fixed dune or fenced grassland), which means that, wind is the driving force for the source-sink relationships of plant litters. There remains no clear description of the influence of wind events on litter production and litter distribution. The contribution of plant litter production to soil C remains uncertain in aeolian regions. The schematic diagram strengthened the understanding of the relationship between soil properties and plant litter production, and providing important information for ecological restoration in semi-arid sandy grasslands. [Display omitted] [ABSTRACT FROM AUTHOR]