Fine root functional group based estimates of fine root production and turnover rate in natural mangrove forests

It has been increasingly recognized that only distal lower order roots turn over actively within the < 2 mm fine root system of trees. This study aimed to estimate fine root production and turnover rate based on lower order fine roots and their relations to soil variables in mangroves. We conducted sequential coring in five natural mangrove forests at Dongzhai Bay, China. Annual fine root production and turnover rate were calculated based on the seasonal variations of the biomass and necromass of lower order roots or the whole fine root system. Annual fine root production and turnover rate ranged between 571 and 2838 g m(-2) and 1.46-5.96 yr(-1), respectively, estimated with lower order roots, and they were increased by 0-30 % and reduced by 13-48 %, respectively, estimated with the whole fine root system. Annual fine root production was 1-3.5 times higher than aboveground litter production and was positively related to soil carbon, nitrogen and phosphorus concentrations. Fine root turnover rate was negatively related to soil salinity. Mangrove fine root turnover plays a more important role than aboveground litter production in soil C accumulation. Sites with higher soil nutrients and lower salinity favor fine root production and turnover, and thus favor soil C accumulation.