保障蔬菜安全生产中十分重要的是研究推导出适用于蔬菜安全生产的土壤镉阈值。在高自然背景地区，可提取态镉的土壤阈值对于食品安全和环境管理显得尤为重要。本研究采用物种敏感性分布法，耦合土壤老化、生物有效性、以及土壤性质影响，推导土壤全量镉和可提取态镉的阈值。在5个文献数据库中，利用指定的关键字对已发表论文中的数据进行筛选，共筛选出90种符合条件的蔬菜品种。利用土壤-植物系统中镉迁移转化模型对生物积累数据进行归一化处理后，种内变异性降低18.3 ~ 84.4%。利用物种敏感性分布曲线推导出保护95%的物种不超标的土壤镉浓度，即HC5值。进而提出了基于外源添加法推导的土壤镉阈值，该阈值可以用基于土壤有机质和pH的连续性方程表示。全量镉和EDTA可提取态镉的阈值分别为0.23 ~ 0.61 mg kg^-1和0.09 ~ 0.25 mg kg^-1。利用田间试验数据对推导的阈值模型进行验证。大部分的预测值都小于由田间试验计算出的HC5值，说明本阈值是保守可行的。综上所述，本研究为建立蔬菜种植土壤镉阈值提供了以保障蔬菜产品质量安全的科学依据。

Leaf thickness is an important morphological trait in rice. Its association to the yield potential, as of now has not been documented because of the shortage of the equipment which could conveniently measure the leaf thickness in rice. In this study, the thickness of top three leaves of 208 cultivars had been determined by a nondestructive rice leaf thickness instrument for the research of the natural variation of leaves thickness and its association to yield traits in indica rice. The results showed that the flag leaf was the thickest, and the 2nd leaf was thicker than the 3rd leaf. Analysis of variance indicated the existence of wide genetic diversity of leaf thickness among the investigated indica rice genotypes. The tight correlation among the thicknesses of the top three leaves means that the leaf thickness traits share one genetic control system. Leaf thickness had a significant positive correlation with leaf length and a positive correlation with leaf width, indicated that thicker leaf was beneficial to increasing the single leaf area. The results of correlation analysis revealed that thicker leaf should be profitable to the leaf erection, higher numbers of grains per panicle and higher grains weight per panicle. However, the significantly negative correlation between leaf thickness and number of panicles per plant counteracted the profitability from increased grains weight per panicle, so that the correlations of the thicknesses of the top three leaves to yield and biomass were positive but not significantly. It has made great progress in the genetic improvement of leaves thickness in inbred indica rice breeding in Guangdong Province, China, since the 1990s.