Effects of applied rare earth elements lanthanum on the growth and some physiological characteristics of Digitaria smutsii

A pot experiment was conducted to study the effects of rare earth elements (REEs) lanthanum (La) on the growth of graminaceous grass Digitaria smutsii under the conditions of foliage and soil application. The results showed that by either foliage or soil application of REEs, the leaf superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6) and peroxidase (POD, EC 1.11.1.7) antioxidase activity were significantly increased, thus, leaf malondialdehyde (MDA) content was decreased, which alleviated reactive oxygen species (ROS) peroxidation injury to cell and chloroplast membrane and maintained leaf photosynthesis function. By application of REEs La, leaf chlorophyll content was evidently increased, and net photosynthesis rate (Pn) was increased accordingly, thus, D. smutsii growth was boosted, and leaf area was increased accordingly. Finally, the dry matter weight of D. smutsii was evidently increased. Compared with control, the final harvested shoot dry matter weight of D. smutsii was increased by 5.60%～14.45% with foliage application, and 4.00%～12.85% with soil application, and the difference between these application methods was significantly different. Compared with control, the final harvested root dry matter weight was increased by 6.28%～20.96% with foliage application, and increased by 7.01%～21.18% with soil application. At the same La application rate, the dry matter accumulation showed no significant difference between foliage and soil application. Furthermore, the highest dry matter accumulation also showed no significant difference between foliage and soil application. Based on these results, the reasonable soil application rate of REEs should be increased one or two times over foliage application rate. This rate can not only promote the growth of D. smutsii, but also avoid excessive accumulation of REEs in the soil and negative impact on the ecological environment.