落叶松和水曲柳人工林细根生长、死亡和周转

 细根周转是陆地生态系统碳分配格局与过程的核心环节，而细根周转估计的关键是了解细根的生长和死亡动态。该研究以18年生落叶松(Larix gmelinii)和水曲柳(Fraxi nus mandshurica)人工林为对象，采用微根管（Minirhizotron）技术对两树种0～40 cm深度的细根生长和死亡动态进行了为期1年的观测，研究了两树种细根在不同土层深度的生长与死亡动态、细根周转以及与土壤有效氮含量、土壤温度、大气温度和降水的关系。结果表明：1） 落叶松平均细根生长（Root length density production, RLDP）0.0045 mm•cm^－2•d^－1）明显低于水曲柳RLDP（0.0077 mm•cm^－2•d^－1）。两个树种细根平均RLDP在表层（0～10 cm）最大，而底层（30～40 cm）最小 ，两树种平均细根死亡（Root length density mortality, RLDM）也表现同样规律 。水曲柳春季生长的细根占41.7%，夏季占39.7%，而落叶松细根生长分别是24.0%和51.2%，水曲柳细根死亡主要发生在春季（34.3%） 和夏季（34.0%），而落叶松细根死亡主要发生在夏季和秋季（分别占28.5%和32.3%），两 树种细根生长与死亡在冬季均较小；2）落叶松细根年生长量（0.94 mm•cm^－2•a^－1）和年死亡量（0.72 mm•cm^－2•a^－1）明显低于水曲柳（1.52和1.21 mm•cm^－2•a^－1），两树种细根表层年生长量和年死亡量均最高，底层最低。落叶松细根年周转为3.1次•a^－1（按年生长量计算）和2.4次•a^－1（按年死亡量计算），相比较，水曲柳细根年周转分别为2.7次•a^－1和2.2次•a^－1；3）土壤有效氮含量、土壤温度、大气温度和降水综合作用影响细根生长和死亡动态，可以解释细根生长80%的变异和细根死亡95%以上的变异。

ESTIMATING FINE ROOT PRODUCTION, MORTALITY AND TURNOVER WITH MINIRHIZOTRONS IN LARIX GMELINII AND FRAXINUS MANDSHURICA PLANTATIONS

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.