Burton A J, Pregitzer K S, Hendrick R L
School of Forestry and Wood Products, Michigan Technological University, Houghton, MI 49931, USA, USA.
D.B. Warnell School of Forest Resources, University of Georgia, Athens, GA 30602, USA, USA.
Oecologia. 2000 Nov;125(3):389-399. doi: 10.1007/s004420000455. Epub 2000 Nov 1.
Minirhizotrons were used to observe fine root (≤1 mm) production, mortality, and longevity over 2 years in four sugar-maple-dominated northern hardwood forests located along a latitudinal temperature gradient. The sites also differed in N availability, allowing us to assess the relative influences of soil temperature and N availability in controlling fine root lifespans. Root production and mortality occurred throughout the year, with most production occurring in the early portion of the growing season (by mid-July). Mortality was distributed much more evenly throughout the year. For surface fine roots (0-10 cm deep), significant differences in root longevity existed among the sites, with median root lifespans for root cohorts produced in 1994 ranging from 405 to 540 days. Estimates of fine root turnover, based on the average of annual root production and mortality as a proportion of standing crop, ranged from 0.50 to 0.68 year for roots in the upper 30 cm of soil. The patterns across sites in root longevity and turnover did not follow the north to south temperature gradient, but rather corresponded to site differences in N availability, with longer average root lifespans and lower root turnover occurring where N availability was greater. This suggests the possibility that roots are maintained as long as the benefit (nutrients) they provide outweighs the C cost of keeping them alive. Root N concentrations and respiration rates (at a given temperature) were also higher at sites where N availability was greater. It is proposed that greater metabolic activity for roots in nitrogen-rich zones leads to greater carbohydrate allocation to those roots, and that a reduction in root C sink strength when local nutrients are depleted provides a mechanism through which root lifespan is regulated in these forests.
微型根窗用于观察沿纬度温度梯度分布的四个以糖枫为主的北方硬木森林中细根（≤1毫米）的生长、死亡和寿命情况，为期两年。这些地点的氮有效性也存在差异，这使我们能够评估土壤温度和氮有效性对控制细根寿命的相对影响。根系的生长和死亡全年都有发生，大部分生长发生在生长季节的早期（到7月中旬）。死亡则在全年分布得更为均匀。对于表层细根（0 - 10厘米深），各地点的根寿命存在显著差异，1994年产生的根群的中位根寿命在405至540天之间。基于年根系生长和死亡的平均值占现存作物比例的细根周转率估计，土壤上部30厘米的根系周转率在0.68年之间。各地点根寿命和周转率的模式并不遵循从北到南的温度梯度，而是与氮有效性的地点差异相对应，在氮有效性较高的地方，平均根寿命更长，根周转率更低。这表明只要根系提供的益处（养分）超过维持其存活的碳成本，根系就会维持存活。在氮有效性较高的地点，根氮浓度和呼吸速率（在给定温度下）也更高。有人提出，富氮区域根系更高的代谢活性会导致更多的碳水化合物分配到这些根系，并且当局部养分耗尽时根碳汇强度的降低提供了一种调节这些森林中根寿命的机制。
