Responses of Soil Microorganisms and Enzymatic Activities to Alkaline Stress in Sugar Beet Rhizosphere

The objective of this study was to evaluate the effects of alkaline stress (0, 5, 7 and 9 g/kg NaHCO3 and Na2CO3, identified as A0, A5, A7 and A9) on sugar beet seedlings root growth, rhizosphere soil microbial population, and soil enzyme activities to better understand their functions and relationships The present results total root length (TRL), total root surface area (TRSA) and root volume ( RV) with the increase of alkaline levels, whereas the above items were significantly improved in A7 at S2 and S3 stages. The root activity (RA), quantity of rhizosphere microorganisms (bacteria, fungi, actinomycete and total microbial) and soil enzyme (urease, alkaline phosphatase and catalase) activities were decreased at A0, A5, and A9 but significantly increasedat A7. Moreover, the value of all indexes except rhizosphere fungi quantity of tolerant cultivar under the same treatment was higher than sensitive cultivar. These results demonstrated that alkaline stress inhibited root growth and reduced whole plant biomass, however, the suitable concentration of alkaline could stimulate the growth of sugar beet seedlings and increase the activities of rhizosphere microorganisms and soil enzymes.