Enzymatic hotspots of root-detritus (dying or dead roots), the small soil volumes around the dead roots with intensive C input in which high enzyme activity occurs, are strongly affected by the C/P ratio of root-detritus. However, distribution and dynamics of enzyme activities in root-detritusphere under P-fertilization remain poorly understood.

To understand the role of root-detritus in nutrient cycling in paddy soil, scientists from the Institute of Subtropical Agriculture (ISA) of the Chinese Academy of Sciences (CAS) and their coworkers investigated how the C/P ratio affected the distribution and dynamics of enzyme activities in rice root-detritusphere.

They used Topsoil (0-20 cm) with limited P, and the soil was subject to phosphorus fertilization (P80) and non-fertilization control (P0). The soil was packaged in rhizoboxes with one side removable and 7-day-old rice seedlings were planted.

To allow the roots to grow along the removable side, the rhizoboxes were inclined by 45°. When roots were fully developed (after 45 days of rice growth) the shoots were cut.

Root-detritus in half rhizoboxes were sampled immediately and the residues were kept intact in the soil and allowed to decompose for 150 days. Distribution of enzyme activities in root-detritusphere was determined using direct soil zymography.

Root-detritus with lower C/P ratio was generated in P80 (59.0) than that in P0   (170.8).  Enzyme-specific responds to the C/P ratio of root-detritus were detected in their experiment. The distribution of C- acquiring enzyme activities was more associated with the root-detritus than P-acquiring enzymes. Hotspot areas of C-acquiring enzyme activities were increased by P-fertilization but their temporal dynamics were not affected. The effect of P fertilization on P- acquiring enzymes was time depended, and delayed the appearance of their hot moments. 

The study published in Biology and Fertility of Soils, was supported by the National Natural Science Foundation of China and the Youth Innovation Team Project of ISA, CAS.

Contact: GE Tida

E-mail: gtd@isa.ac.cn

Institute of Subtropical Agriculture, Chinese Academy of Sciences