Effect of precipitation frequency on litter decomposition of three annual species (Setaria viridis, Artemisia sacrorum, and Chenopodium acuminatum) in a semi-arid sandy grassland of northeastern China

Annual total precipitation typically fails to predict litter decomposition rates, especially in semi-arid regions, where precipitation frequency (PF) significantly affects decomposition. We hypothesized that low PF would decrease decomposition rates. We performed a litterbag decomposition experiment with litter of three annual species at three depths (aboveground litter, litter at 0–10 and 10–20 cm below the surface). We used the same total amount (280 mm), but three precipitation frequencies (PF1, 10 mm every 5 days; PF2, 20 mm every 10 days; PF3, 40 mm every 20 days) during the growing season. We measured the remaining mass, carbon (C) content, nitrogen (N) content, C:N ratio, and C and N losses of each species at the three positions. Litter decomposition and the C and N dynamics were influenced by species, depth, and PF. Low PF significantly decreased litter decomposition (mass loss rates of 49.7, 49.1, and 41.2% for PF1, PF2, and PF3, respectively). This effect interacted with placement-depth but not with species. This interaction also existed for C and N dynamics except for the N loss rate. The influence of PF on C loss mainly resulted from its effect on mass loss, whereas N loss was not affected by PF. Our results highlight the importance of PF for litter decomposition in a semi-arid region. The relationship between PF and litter decomposition provides a theoretical basis for regional carbon-cycle models and carbon budget predictions. Our results also suggest that non-graminaceous species showed higher potential than grasses for improving soil carbon in semi-arid sandy grasslands due to faster decomposition rates, especially below ground.