<正>通过对苏北海堤杉木杨树混交林及杉木纯林林木生长情况、土壤理化性质及酶活性的分析表明：混交林林木生长、林地土壤结构状况和养分含量均好于纯林；提高土壤酶活性及肥力水平，是有效防止杉木林多代连栽林地地力衰退的有效方法，可在海堤防护林更新过程中逐步推广。

Blend films of poly(L-lactic acid) (PLLA) and ethylcellulose (EC) with various compositions were prepared by casting from respective chloroform solution. The obtained blends were characterized with FT-IR, DSC, and X-ray diffraction. All results showed that PLLA and EC were liable to form interpolymer hydrogen bonds, and PLLA and EC were partially miscible. The crystal formation and crystal perfection of PLLA-EC blend relied on PLLA/EC ratios, which resulted from interpolymer hydrogen bonds of PLLA with EC. The degradation of blend in phosphoric buffer was great affected by PLLA-EC ratios. The degradation of PLLA-EC blend increased greatly with the ethylcellulose contents as PLLAEC being less than 70/30. Thus PLLA-EC blends with various properties may be used as biodegradable polymers.