Inhibitory Effects of Low Temperatures on the Rhizospheric Microorganisms and Apple Rootstock Growth

The contribution of nitrogen (N) supply is an essential source for the growth of apple trees from budding to fruiting. In new apple-producing regions of north China, such as the Shenyang area, air temperature rises rapidly, while in contrast, soil temperature rises very slowly. In such weather conditions, the amount of nitrogen absorbed by the roots is not sufficient for the growth and development of apple tree. In this research, the main attention has been paid to the effects of low soil temperature on rhizospheric microorganisms, soil enzyme activities, and the associated traits of seedlings such as nitrogen uptake and photosynthesis of Malus baccata Borkh. during early spring. Results showed that the bacteria and Actinomycetes activity decreased, while fungi activity in the rhizosphere increased. The bacterial ammonifiers and nitrogen-fixing bacteria activity increased, whereas nitrifying and denitrifying bacteria activity decreased in the seedling rhizosphere. Low temperature reduced protease activity but increased urease activity in the rhizosphere. No significant changes in phosphatase activity were observed. Nitrite reductase activity in the seedling roots decreased at low temperature, thereby reducing absorption of nitrogenous nutrients. Low temperature also reduced seedling chlorophyll content, thus reducing photosynthetic capacity. This finding implies that the low temperature of soil in early spring inhibited the metabolism of soil nitrogen in microorganisms and enzymes, and thus reduced the absorption ability and utilization of nitrogen in apple roots. As a result, physiological processes like photosynthesis were affected concomitantly. © 2017 Friends Science Publishers