Gallet-Budynek Anne, Brzostek Edward, Rodgers Vikki L, Talbot Jennifer M, Hyzy Sharon, Finzi Adrien C
Department of Biology, Boston University, Boston, MA 02215, USA.
Oecologia. 2009 May;160(1):129-38. doi: 10.1007/s00442-009-1284-2. Epub 2009 Feb 24.
Empirical and modeling studies of the N cycle in temperate forests of eastern North America have focused on the mechanisms regulating the production of inorganic N, and assumed that only inorganic forms of N are available for plant growth. Recent isotope studies in field conditions suggest that amino acid capture is a widespread ecological phenomenon, although northern temperate forests have yet to be studied. We quantified fine root biomass and applied tracer-level quantities of U-(13)C(2)-(15)N-glycine, (15)NH(4) (+) and (15)NO(3) (-) in two stands, one dominated by sugar maple and white ash, the other dominated by red oak, beech, and hemlock, to assess the importance of amino acids to the N nutrition of northeastern US forests. Significant enrichment of (13)C in fine roots 2 and 5 h following tracer application indicated intact glycine uptake in both stands. Glycine accounted for up to 77% of total N uptake in the oak-beech-hemlock stand, a stand that produces recalcitrant litter, cycles N slowly and has a thick, amino acid-rich organic horizon. By contrast, glycine accounted for only 20% of total N uptake in the sugar maple and white ash stand, a stand characterized by labile litter and rapid rates of amino acid production and turnover resulting in high rates of mineralization and nitrification. This study shows that amino acid uptake is an important process occurring in two widespread, northeastern US temperate forest types with widely differing rates of N cycling.
北美东部温带森林氮循环的实证研究和模型研究主要聚焦于调节无机氮产生的机制，并假定只有无机形态的氮可用于植物生长。近期的野外条件下的同位素研究表明，氨基酸捕获是一种广泛存在的生态现象，尽管北方温带森林尚未得到研究。我们在两个林分中对细根生物量进行了量化，并施用了示踪剂量的U-(13)C(2)-(15)N-甘氨酸、(15)NH(4) (+)和(15)NO(3) (-)，其中一个林分以糖枫和白蜡树为主，另一个林分以红橡树、山毛榉和铁杉为主，以评估氨基酸对美国东北部森林氮营养的重要性。施用示踪剂后2小时和5小时，细根中(13)C显著富集，表明两个林分均存在完整的甘氨酸吸收。在橡树-山毛榉-铁杉林分中，甘氨酸占总氮吸收量的比例高达77%，该林分产生难分解的凋落物，氮循环缓慢，且有一层厚厚的、富含氨基酸的有机层。相比之下，在糖枫和白蜡树林分中，甘氨酸仅占总氮吸收量的20%，该林分的特点是凋落物易分解，氨基酸产生和周转速度快，导致矿化和硝化速率较高。这项研究表明，氨基酸吸收是美国东北部两种广泛分布的温带森林类型中发生的一个重要过程，这两种森林类型的氮循环速率差异很大。
