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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]

Soil respiration is a major pathway by which carbon dioxide (CO2) fixed by terrestrial plants returns to the atmosphere. Studies of the dynamics of soil respiration in sandy land are rare and the contribution (Rc) of plant root respiration to the total soil respiration (Rt) is not well known. In this study, Rt in a semi-fixed dune planted with Artemisia halodendron was separated into autotrophic (root) respiration (Ra) and heterotrophic respiration (Rh) by the root-exclusion method. Rt and its two components were measured or calculated during 2013 on seven dates during the growing season when variation during the day was measured. Both Ra and Rh showed similar dynamics, with the maximum rates observed in July and with large daily variability observed on the earlier dates. Rc ranged from 39.3% to 53.1% during the growing season and exhibited a single peak in early August. Soil temperature at a depth of 20 cm was significantly correlated with soil respiration. Ra was more sensitive to soil temperature than Rh and the temperature sensitivity coefficients (Q10) were 3.39, 2.52, and 2.79 for Ra, Rh, and Rt, respectively. In summary, A. halodendron roots contributed an average of 46% to the total soil respiration, although this contribution varied during the growing season. [ABSTRACT FROM AUTHOR]