Effects of nitrogen addition and watering on soil seed bank germination in a semiarid grassland on the Loess Plateau of China

Abstract

AbstractElevated atmospheric nitrogen (N) deposition has caused many adverse effects on ecosystem services. However, the impacts of N deposition and its interaction with soil moisture on soil seed bank remain largely unknown in semiarid grasslands. Here, we quantified the effects of two soil water regimes (HW: watered to field capacity every day; LW: watered to field capacity every 2 days) and two types of N addition (NO3−‐N and NH4+‐N) with different levels on seed bank germination in two separate trials in April and July 2015 in a semiarid grassland on the Loess Plateau, China. Results showed seed bank germination was remarkably inhibited under the LW soil water regime. Species composition of emerged seedlings significantly differed between the two soil water regimes. N addition promoted seed bank germination under the HW soil water regime. This promoting effect was less noticeable under the LW, while still significant in the high level of NH4+‐N in the July trial. N addition did not alter the species composition of emerged seedlings. Overall, this study suggests that soil moisture controls soil seed bank germination and species composition of emerged seedlings. Soil N addition, for example, by N deposition, greatly promotes soil seed bank germination when soil moisture is high (e.g., during seed germination season in July), and still marginally facilitates seed germination under low soil moisture conditions (e.g., at the beginning of the growing season in April). N deposition may therefore deplete the grassland soil seed bank if other processes (e.g., seed input) remain unchanged.