Relationships between fine root dynamics and nitrogen availability in Michigan northern hardwood forests
Relationships between fine root dynamics and nitrogen availability in Michigan northern hardwood forests
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DOI：
10.1007/s004420000455
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发表时间：
2000-11-01
期刊：
影响因子：
2.7
通讯作者：
Hendrick, RL
中科院分区：
文献类型：
--
作者：
Burton, AJ;Pregitzer, KS;Hendrick, RL
使用微型根管机对位于沿纬度温度梯度的四个以糖枫为主的北方硬木森林进行了两年多的细根（小于或等于 1 毫米）产量、死亡率和寿命的观察。这些地点的氮利用率也不同，使我们能够评估土壤温度和氮利用率在控制细根寿命方面的相对影响。根的生产和死亡发生在全年，其中大部分生产发生在生长季节的早期（七月中旬）。全年死亡率分布更加均匀。对于表面细根（0-10厘米深），不同地点之间的根寿命存在显着差异，1994年生产的根群的中位根寿命为405至540天。根据平均年根产量和死亡率占未收作物的比例，对土壤上部 30 厘米的根的细根周转率的估计范围为 0.50 至 0.68 年(-1)。不同地点的根系寿命和周转率的模式并不遵循从北到南的温度梯度，而是与氮素有效性的地点差异相对应，在氮素有效性较高的地方，平均根系寿命较长，根系周转率较低。这表明，只要根部提供的益处（养分）超过了维持根部生存所需的碳成本，根部就有可能得以维持。在氮利用率较高的地点，根氮浓度和呼吸速率（在给定温度下）也较高。有人提出，富氮地区根系的代谢活动更强，导致更多的碳水化合物分配给这些根系，并且当当地养分耗尽时，根系碳汇强度的降低提供了一种在这些森林中调节根系寿命的机制。
Minirhizotrons were used to observe fine root (less than or equal to1 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(-1) for roots in the upper 30 cm of soil. The pat terns 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.