Kern Christel C, Friend Alexander L, Johnson Jane M-F, Coleman Mark D
USDA Forest Service, North Central Research Station, 1831 Hwy 169 E, Grand Rapids, MN 55744, USA.
Tree Physiol. 2004 Jun;24(6):651-60. doi: 10.1093/treephys/24.6.651.
A closely spaced (1 x 1 m) cottonwood (Populus deltoides Bartr.) plantation was established to evaluate the effects of nutrient availability on fine root dynamics. Slow-release fertilizer (17:6:12 N,P,K plus micronutrients) was applied to 225-m(2) plots at 0, 50, 100 and 200 kg N ha(-1), and plots were monitored for two growing seasons. Fine root production, mortality, live root standing crop and life span were analyzed based on monthly minirhizotron observations. Fine root biomass was measured in soil cores. Fine root dynamics were controlled more by temporal, depth and root diameter factors than by fertilization. Cumulative fine root production and mortality showed strong seasonal patterns; production was greatest in the middle of the growing season and mortality was greatest after the growing season. Small diameter roots at shallow soil depths cycled more rapidly than larger or deeper roots. The strongest treatment effects were found in the most rapidly cycling roots. The standing crop of live roots increased with fertilizer treatment according to both minirhizotron and soil coring methods. However, production and mortality had unique treatment response patterns. Although cumulative mortality decreased in response to increased fertilization, cumulative production was intermediate at 0 kg N ha(-1), lowest with 50 kg N ha (-1), and highest with 200 kg N ha(-1). Aboveground growth responded positively to fertilization up to an application rate of 50 kg N ha(-1), but no further increases in growth were observed despite a threefold increase in application rate. Median fine root life span varied from 307 to over 700 days and increased with depth, diameter and nutrient availability.
建立了一个间距紧密（1×1米）的三角叶杨（Populus deltoides Bartr.）人工林，以评估养分有效性对细根动态的影响。在0、50、100和200千克氮/公顷的用量下，将缓释肥料（17:6:12氮、磷、钾加微量元素）施用于225平方米的地块，并对这些地块进行了两个生长季的监测。基于每月的微根窗观测数据，分析了细根的生产、死亡、活根存量和寿命。通过土芯测定细根生物量。细根动态更多地受时间、深度和根直径因素的控制，而非施肥。累积细根生产和死亡呈现出强烈的季节性模式；生产在生长季中期最高，死亡在生长季之后最高。浅层土壤中直径较小的根周转速度比更大或更深层的根更快。在周转最快的根中发现了最强的处理效应。根据微根窗和土芯法，活根存量随施肥处理而增加。然而，生产和死亡具有独特的处理响应模式。尽管随着施肥量增加累积死亡率降低，但累积生产量在0千克氮/公顷时处于中等水平，在50千克氮/公顷时最低，在200千克氮/公顷时最高。地上生长在施肥量达到50千克氮/公顷之前对施肥呈正向响应，但尽管施肥量增加了两倍，却未观察到生长进一步增加。细根寿命中位数从307天到超过700天不等，并随深度、直径和养分有效性增加。
