ESTIMATING FINE ROOT PRODUCTION, MORTALITY AND TURNOVER WITH MINIRHIZOTRONS IN LARIX GMELINII AND FRAXINUS MANDSHURICA PLANTATIONS
落叶松和水曲柳人工林细根生长、死亡和周转

Aims Fine root turnover is a major pathway for carbon and nutrient cycling in forest ecosystems, but our understanding of fine root turnover is limited, because fine root dynamic processes associated with soil resource availability and climate factors are poorly understood. The objectives of this study were to: 1) examine patterns of fine root production and mortality in different seasons and soil depths in Larix gmelinii and Fraxinus mandshurica plantations, 2) analyze correlation of fine root production and mortality with environment factors such as air temperature, precipitation, soil temperature and available nitrogen, and 3) estimate fine root turnover. Methods We installed 36 minirhizotron tubes in six mono-specific plots of each species in September 2003 in Maoershan Experiment Forest Station. Minirhizotron sampling was conducted every two weeks from April 2004 to April 2005. We calculated average fine root length, annual fine root length production and mortality using the image data of minirhizotrons and estimated fine root turnover using three approaches. Important findings The average growth rate and mortality rate in L. gmelinii was markedly smaller than in F. mandshurica, and rates were highest in the surface soil and lowest in the deepest of four soil layers. Annual fine root production and mortality in F. mandshurica were significantly higher than in L. gmelinii and were highest in the surface layer. Fine root production in spring and summer accounted for 41.7% and 39.7% of total annual production in F. mandshurica and 24.0% and 51.2% in L. gmelinii. The majority of fine root mortality was in spring and summer for F. mandshurica and summer and autumn for L. gmelinii. Turnover rate was 3.1 a-1 for L. gmelinii and 2.7 a-1 for F. mandshurica. Multiple regression analysis indicated that climate and soil resource factors together explained 80% variation of fine root seasonal growth and 95% of seasonal mortality. This study showed that fine root production and mortality of L. gmelinii and F. mandshurica had different patterns in different seasons and at different soil depths, and air temperature, precipitation, soil temperature and soil available nitrogen controlled the dynamics of fine root production, mortality and turnover in both species.