Objectives Premature senescence is often occurred in K-deficient soil, which seriously inhibites the yield of maize. In the study, the premature senescence of maize caused by K deficient stress was studied from root morphology, structure and activity after flowering stage.

Methods Pool experiment was conducted using maize inbred line of K-tolerant 90-21-3 and K-sensitive D937 as tested materials. Both maize lines were grown in K-deficient soil without applying K (–K) and applying K (+K). The root morphology, microscopic structure and activity of maize were measured after flowering stage.

Results Compared with +K controls, K contents in both maize lines were significantly decreased under –K stress; the crown number and weight of first layer root in line 90-21-3 were significantly decreased by 20.37% and 42.24%, and by 39.06% and 59.64% in line D937; the crown number and weight of second layer root in line 90-21-3 were significantly decreased by 23.40% and 39.30%, and by 36.67% and 59.86% in line D937. As maize grew, the root activity in line 90-21-3 and D937 were all decreased under-K stress, as well as the root length, surface area, volume and lateral length of first and second layer root, while root diameter was increased, more variation in D937 than in 90-21-3. Compared with controls, the anatomical structure of 90-21-3 root was intact and clearly visible, including complete cortex and endodermis, regular vessels. But the anatomical structure of D937 root was seriously damaged, including incomplete cortex and endodermis, irregular vessels. The diameter and area of large vessel in 90-21-3 root were decreased by 11.15% and 21.07%, and the diameter and area of small vessel were decreased by 14.37% and 30.21%. The diameter and area of large vessel in D937 root were significantly decreased by 33.99% and 56.43%, and the diameter and area of small vessel were significantly decreased by 22.86% and 40.55%.

Conclusions The growth and structural stability of maize roots are significantly reduced under K-deficit stress. Compared with K-tolerant inbred lines (90-21-3), K-sensitive inbred lines (D937) suffers severe damage in cortex tissue and endodermis, irregular vessels and plasma membrane permeability, which decreases efficiency in absorption and utilization of nutrients and water. The root of K-deficit tolerant line 90-21-3 shows larger root volume, activity and conducting tissue, which could enhance the capability of absorption and transportation for nutrient, and delayed root premature under K deficiency stress.