The allelopathy of the exotic invasive plant, Solidago canadensis L. was studied. S. canadensis leaves were extracted with water and partitioned against ethyl acetate and n-butanol sequentially. The two organic fractions, original water extract and the residual water after the organic solvent extraction were tested for inhibitory activity on seed germination and seedling growth of wheat (Triticum aestivum), setaria (Setaria viridis) and its own species. Germination rate, vigor and index were recorded as germination parameters, and radicle and plumule growth and fresh weight of seedlings were recorded as seedling growth parameters. Results showed that the water extracts of S. Canadensis leaves had significant impacts on the seed germination and seedling growth of the three tested plants. n-Butanol fraction showed the strongest allelopathic effect, while the residual water after the organic solvent extraction had no significant phytotoxic effect compared with the control. n-Butanol fraction at 0.5 mg•ml-1 could significantly inhibited the seed germination of the same species, and that at 5 mg•ml-1 could significantly inhibited the seedling growth of the same species. n-Butanol fraction at 1.5 mg•ml-1 could significantly inhibited the seed germination and seedling growth of wheat. n-Butanol fraction at 5 mg•ml-1 could significantly inhibited the seed germination and seedling growth of setaria. The allelochemicals were mainly contained in n-butanol fraction of water extracts from S. canadensis leaves.

For clarifying the relationship between a leaf-to-fruit ratio (LFR) and photosynthesis, LFR manipulation was performed with Juglans regia cv. Xinxin2 in order to test the photosynthesis response to LFR in source leaves. Results showed that LFR with one and two leaves was positively correlated with net photosynthetic rate (PN), chlorophyll content, and specific leaf mass, implying extremely low LFR inhibited the leaf development. However, LFR with five leaves was negatively correlated with PN, positively correlated with starch, but not related to intercellular CO2 concentration, indicating the high LFR caused the nonstomatal limitation and feedback inhibition of photosynthetic production. No significant differences in PN between LFRs (with three and four leaves) probably indicated a balanced state of coordinated supply and demand between the source leaf and sink fruit. The above results indicated that the response of photosynthesis in the source leaves to LFR depends on the variation range of LFR.Additional key words: gas exchange; leaf anatomical structure; leaf traits; nut; source-sink relationship. CO2 concentration; DAF -days after full bloom of female flowers; gs -stomatal conductance; FL -LFRs with five leaves; LFR -leaf-to-fruit ratio; LT -leaf thickness; OTL -LFRs with one and two leaves; PN -net photosynthetic rate; PN-PAR -photosynthetic rate response to PAR; PTT -palisade tissue thickness; SLM -specific leaf mass; Sta -starch; STT -spongy tissue thickness; TFL -LFRs with three and four leaves; TSS -total soluble sugar.