VARIATION IN ROOT DIAMETER AMONG 45 COMMON TREE SPECIES IN TEMPERATE,SUBTROPICAL AND TROPICAL FORESTS IN CHINA

Aims Fine roots play an important role in plant functioning and ecosystem carbon and nutrient cycling. We studied root diameter across the first five branch orders of 45 tree species from three forest ecosystems in China, in order to: 1) examine fine root diameter distributions of various tree species in temperate, subtropical and tropical forests in China; 2) identify factors influencing the variations in root diameter; and 3) analyze the relationship between branch order and diameter. Methods Fine roots of 45 tree species were sampled by branch order in temperate, subtropical and tropical forests in summers of 2006 and 2007. Study sites included Beijing Baihua, Shanxi Guandi, Shanxi Zhongtiao and Guangdong Dinghu Mountains and Yunnan Xishuangbanna. We excavated soil blocks of 20 cm×20cm×10cm to sample intact fine root branches containing at least the first five branch orders, dissected these intact root branches by order and measured the diameters of individual roots of each order. Important findings Root diameter increases from first to fifth order, although the diameter of the same order varied markedly among species. On average, the diameter of tree species in the three forests is temperate subtropicaltropical. Variations in diameter among species were different for the three forests: temperate subtropical ≤tropical. Branch order can explain 52% of diameter variations, species 33%,ecosystem 7% and life form 2%.