Seed size and germination strategy of Sophora davidii under drought stress

Sophora davidii is an important leguminous shrub that is widely used for revegetating areas experiencing karst rocky desertification in southwest China. Karst is a fragile environment that is very sensitive to environmental and climate change,and is often under considerable drought stress. Seed size is a prominent life history trait of plants. Experiments were conducted in the laboratory to evaluate the effect of osmotic potential and seed size on germination,dormancy and mortality. The effect of drought stress on seed germination was examined by using different concentrations of polyethylene glycol treatments( 0,5%,10%,15%,and 20%) to provide designated osmotic potentials. The results showed that S.davidii seeds had a similar germination process under different degrees of drought stress. Seed germination percentage under moderate drought stress( 10% PEG) was significantly higher than under non-stress and severe stress treatment( P 0.05). The initiation of seed germination under severe drought stress( 20% PEG) was slower than under non-stress and moderate stress. Seed size had a significant negative linear correlation with the initiation time for seed germination undernon-stress treatment and a negative curve correlation for treatments under severe stress treatments( 15% PEG,20% PEG),while there was no correlation for moderate drought stress( 5% PEG,10% PEG). The relationship between seed size and seed fate of S. davidii showed that non-stress conditions may beneficial to germination for large or small seeds and dormancy for small seeds; moderate drought stress can drive medium seed germination,large seed dormancy and small seed mortality,and severe drought stress( 15% PEG,20% PEG) can lead to large seed mortality,and medium and small seed dormancy.Seed size,germination behavior and seed fate were heavily dependent on environmental factors. The germination strategy had a diverse pattern,that is,the larger seed size,the earlier seeds germination; in non-stress conditions,but larger and smaller seeds germinate earlier than medium seeds in adversity. The seed fate of S. davidii showed that seed mortality increased in non-stress conditions,seed germination was facilitated under moderate stress,and that seed dormancy was expedited in adversity. The information in this study may help land managers develop effective and sustainable revegetation management strategies.