Silicon sources for studies of rice plants in nutrient solutions

The objective of this work was to evaluate the effects of various Si sources currently used in studies of Si doses in nutrient solutions on dry matter yield and the accumulation of nutrients and Si in rice plants. Treatments of rice plants with three sources of Si (monossilicic acid, sodium metasilicate, potassium metasilicate) and a treatment without Si were allocated in a randomized block design with ten replications. After 39 days in the nutrient solution, the following traits were evaluated: leaf area, leaf specific mass, dry matter yield of roots and shoots, and levels of K, Na, and Si in leaves and roots. Si increased leaf area, leaf specific mass, and dry matter yield of shoots and roots regardless of the Si source. Levels of Si in leaves and roots were significantly higher in relation to the control treatment but no significant difference among Si sources was identified. It was also observed that K and Na were adequately balanced across the treatments. Thus, a cheaper and easier to obtain Si source, such as sodium metasilicate and potassium metasilicate, may be chosen to carry out studies of Si additions to nutrient solutions.

Gas exchange and leaf specific mass of different foliar cohorts of the wintergreen shrub Aristotelia chilensis (Mol.) stuntz (Eleocarpaceae) fifteen days before the flowering and the fall of the old cohort

In the beginning of the spring Aristotelia chilensis sheds the old cohort, forms a new one and flowers. Fifteen days before the flowering and the fall we measured net photosynthesis (A), transpiration (E), water use efficiency (WUE), specific leaf mass (SLM) and area and mass of leaves per branch in old and new cohorts. Under low irradiance the old cohort exhibited higher mean values of A and WUE on area bases (P<0.05). Under high irradiance A and WUE on mass bases were higher in new cohort due to its lower SLM (42.10 gm-2) in relation to old cohort (79.53 gm-2). Because old cohort showed 3.7 times more dry mass per branch it was able to counterbalance its lower performance on mass bases. It was concluded that old cohort was an important source of carbon during two powerful sink processes in the beginning of the spring: new leaves cohort construction and flowering.