Grazing influences Stipa breviflora seed germination in desert grasslands of the Inner Mongolia Plateau.

Wenting Liu,Lijun Ding,Tianle Wang,Shuang Zhang,Zhijun Wei

doi:10.7717/peerj.4447

Abstract

Seed germination plays an important role in determining the composition and regeneration of plant populations (Stipa breviflora). However, the influencing factors and strategies employed for seed germination in desert grasslands under grazing remain unknown. Therefore, in this study, the reproductive allocation, seed density, seed properties, and corresponding seed germination rates of S. breviflora were examined. Possible situations encountered during dispersal were also simulated to determine their effects on seed germination. The results showed that reproductive individual density not subjected to grazing were significantly higher than those subjected to moderate and heavy grazing. For seed density and seed bank in soil, the highest values were observed for the no grazing treatment, followed by the moderate and heavy grazing treatments. The seed density for germination of soil seed banks was nearly one-fourth of seed density during the growing season. In addition, grazing treatments affected the phenotypic characteristics of seeds and reduced the lower limit of the weight of germinable seeds. Awn removal significantly increased germination. The longest germination time was observed for seeds that entered the soil at an angle of 0°. Our research demonstrated that grazing negatively affected the desert grassland edificator. Individual plants adopted different adaptation strategies under different grazing intensities; for example, a fixed proportion of the seed number and seed germination number of S. breviflora in the soil seed bank was maintained by exceeding the minimum weight of a seed for seed germination. During seed dispersion, the awn effectively prevented germination under unfavourable conditions and helped seeds enter the soil at an optimal angle for promoting germination.

Highlights

As a critical and the most basic process for completing the life cycle of a plant, propagation affects plant population dynamics, ensures population stability, and maintains grassland biodiversity and ecosystem health
For S. breviflora under different grazing treatments (Figs. 4A–4D), at a sample scale of 1 × 1 m, the reproductive and non-reproductive individual density were significantly higher in the no grazing treatment than those under moderate grazing (P < 0.05), with approximately 3-fold more reproductive individuals under the no grazing treatment than under grazing; values were not significantly different between moderate and heavy grazing
At the scale of the reproductive individual, the results showed that the weight of reproductive branches of S. breviflora under the moderate grazing treatment was significantly higher than that under the no and heavy grazing treatments (P < 0.05), with an increase of approximately 82.99%

Summary

Introduction

As a critical and the most basic process for completing the life cycle of a plant, propagation affects plant population dynamics, ensures population stability, and maintains grassland biodiversity and ecosystem health. The potential mechanisms of seed germination have been analysed with respect to temperature (Khan & Ungar, 1998), light (Yamaguchi & Kamiya, 2001), moisture (Foolad, Zhang & Subbiah, 2003), soil acidity and salinity (Khan & Ungar, 1997), chemical substances and burial depth (Okamoto et al, 2010; Hu, Wu & Wang, 2009) These studies have greatly enriched our understanding of factors that influence seed germination, they were performed under limited and controllable experimental conditions. In the wild state, the propagation process of plants is frequently threatened by the risk of falling prey to herbivores in addition to the abovementioned physical threats (Yagihashi, Hayashida & Miyamoto, 1998)

Methods

Results

Discussion

Conclusion