Influence of Simulated Nitrogen Deposition on the Soil Seed Bank of a Subtropical Evergreen Broadleaved Forest

Jun Wang,Qinfeng Guo,Hongfang Lu,Long Yang,Hai Ren,Yao Huang

doi:10.3390/f12111538

Abstract

Increased nitrogen (N) deposition may have profound effects on forest ecosystems. However, information on the impacts of elevated N deposition on belowground soil seed bank in forests is lacking. In a field experiment, we added N at 50 and 25 kg N ha−1 year−1 to the canopy (CAN50 and CAN25) and to the understory (UAN50 and UAN25), to determine the effects of N deposition on soil seed bank structure and composition in a subtropical evergreen broadleaved forest. A total of 1545 seedlings belonging to 37 species emerged from the 10 cm-depth soil samples. After 6 years of N addition, soil seed bank density significantly increased at the depth of 0–10 cm under CAN50 treatment relative to the control. N addition did not significantly affect species richness, the Simpson index, Shannon–Wiener index, or Pielou index of the soil seed banks. Seed bank density and species richness were positively correlated with soil organic matter content. For the whole 0–10 cm soil layer, the percentage of total seed abundance and total species richness represented by tree species among the N-addition treatments was ≤9.3% and ≤16.1%, respectively. Soil seed bank composition was similar among UAN25, UAN50, and the control, but canopy N addition and especially CAN50 altered the species composition of the seed bank. Overall, our results indicate that artificial canopy N deposition at 50 kg N ha−1 year−1 but not understory N addition tends to promote seed storage and to change species composition in the soil seed bank. Because of the dominance of shrubs and herbs in the soil seed bank, the potential to regenerate tree species from the soil seed bank is limited in the subtropical evergreen broadleaved forest.

Highlights

Anthropogenic activities resulting in reactive nitrogen (N) emission have greatly increased in the past several decades, leading to substantial increases in atmospheric N deposition worldwide [1,2]
We addressed the following questions: (1) How does N addition affect the density, species richness and diversity of the forest soil seed bank? (2) Does forest canopy and understory N addition differ in their effects on the structure and composition of forest soil seed bank?
A total of 1521 seedlings belonging to 37 species emerged from the 10 cm-depth soil samples (Table 1)

Summary

Introduction

Anthropogenic activities resulting in reactive nitrogen (N) emission have greatly increased in the past several decades, leading to substantial increases in atmospheric N deposition worldwide [1,2]. N deposition has emerged as a critical environmental factor of global change and has greatly affected global terrestrial ecosystems [3,4,5]. N deposition is recognized as an important factor influencing natural regeneration of plant communities and affecting future vegetation structure and ecosystem functioning [10,11]. The soil seed bank is often considered as an important source of seed for natural vegetation recovery and community regeneration [12,13,14]. Both the quantitative and qualitative characteristics of soil seed bank determine the results of plant replenishment through the soil seed bank. In the context of global change, understanding the effects of N deposition on soil seed banks could facilitate forest restoration and conservation

Methods

Results

Discussion

Conclusion