Fine Root Production, Mortality And Turnover And Effects Of Nitrogen Addition In Fraxinus Mandshurica And Larix Gmelinii Plantations

Root production and turnover is an important component of the C and nutrient budget in the terrestrial ecosystems. N deposition continue increasing all over the world, which have an important effect on root dynamic and growth. So the relationship between root dynamic and soil available nitrogen is a major issue of ecologist. In the study, manchurican ash (Fraxinus mandshurica) and davurian larch (Larix gmelinii), two of the important forest trees in northeastern China, were used as the experimental materials. Fine root dynamic was monitored in situ by minirhizotron technique across five years. The main results were below:Root production and turnover showed obvious seasonal dynamic in control and N fertilization plots in the two plantations. Root production occurred in June and July primarily, root death occurred from August to October. Correlation analysis showed the change of atmosphere temperature accounted for 55% and 66% of root production in ash and larch plantation. The change of rainfall accounted for 28% and 27% of root production in ash and larch plantation. The relationship between root production and atmosphere temperature were increased by 14% by N fertilization in ash plantation. The relationship between root production and rainfall were increased by 21% by N fertilization in ash plantation. The changes is tiny in larch plantation. The environmental factors have little effect on root death. There were significant negative correlation between root mortality and the atmosphere temperature.Root production and mortality in ash plantation was higher than in larch plantation. Root production and mortality were declining year by year across five years. N fertilization increased mean root production of five years, and decreased the root mortality in ash plantation. N fertilization have no significant effect on root production and mortality in larch plantation. N fertilization decreased root production in 2004, and increased root production in 2005-2008 in the two plantations. The changes of root mortality were differ from root production. N fertilization decreased root mortality in 2004-2006 in the two plantations, increased root mortality in 2007-2008 in ash plantation and in 2007 in larch plantation. Root production and mortality were foucus in 0-20cm of the soil in the two plantations. Root production accounted for 62% in 0-20cm of the soil, root mortality accounted for 72% in ash plantation of the five years.Root production accounted for 65% in 0-20cm of the soil, root mortality accounted for 64% in larch plantation. N fertilization root production and mortality decreased in 0-20cm of the soil in ash plantation, while increased in 30-40cm of the soil. N fertilization root production and mortality decreased in 0-40cm of the soil in larch plantation. The percent of root production and mortality in 0-20cm of the soil decreased across fertilization time. Root turnover rate was higher in larch plantation than in ash plantation. N fertilization decreased root turnover rate in the two plantations. N fertilization increased root turnover rate in 2004 in ash plantation, while decreased in larch plantation. N fertilization decreased root turnover rate in 2006-2008 in the two plantations.Root diameter effect root production, death and turniver. Root production, death and turniver was higher of 0-0.5 mm diameter than 0.5-2.0 mm. N fertilization decreased root production and death of 0-0.5 mm in the two plantations, while 0.5-2.0mm increased. N fertilization increased root turniver rate of 0-0.5 mm, have no effect on 0.5-2.0 mm root in ash plantation. N fertilization decreased root turniver rate of 0-0.5 mm, increased 0.5-2.0 mm root in larch plantation.As a whole, root production, death and turnover were controled by intermediate factor and experimental factor.