Institute of Forest Botany and Tree Physiology, University of Freiburg, Freiburg, Germany.
Plant Biol (Stuttg). 2010 May 1;12(3):453-8. doi: 10.1111/j.1438-8677.2009.00225.x.
To investigate the short-term consequences of direct competition between beech and sycamore maple on root N uptake and N composition, mycorrhizal seedlings of both tree species were incubated for 4 days (i.e. beech only, sycamore maple only or both together) in an artificial nutrient solution with low N availability. On the fourth day, N uptake experiments were conducted to study the effects of competition on inorganic and organic N uptake. For this purpose, multiple N sources were applied with a single label. Furthermore, fine roots were sampled and analysed for total amino acids, soluble protein, total nitrogen, nitrate and ammonium content. Our results clearly show that both tree species were able to use inorganic and organic N sources. Uptake of inorganic and organic N by beech roots was negatively affected in the presence of the competing tree species. In contrast, the presence of beech stimulated inorganic N uptake by sycamore maple roots. Both the negative effect of sycamore maple on N uptake of beech and the positive effect of beech on N uptake of sycamore maple led to an increase in root soluble protein in beech, despite an overall decrease in total N concentration. Thus, beech compensated for the negative effects of the tree competitor on N uptake by incorporating less N into structural N components, but otherwise exhibited the same strategy as the competitor, namely, enhancing soluble protein levels in roots when grown under competition. It is speculated that enhanced enzyme activities of so far unknown nature are required in beech as a defence response to inter-specific competition.
为了研究山毛榉和三角枫之间直接竞争对根系氮吸收和氮组成的短期影响，将两种树种的菌根幼苗在低氮供应的人工营养液中培养 4 天（即仅山毛榉、仅三角枫或两者共同生长）。在第 4 天，进行氮吸收实验以研究竞争对无机和有机氮吸收的影响。为此，应用了单一标签的多种氮源。此外，还采集了细根并分析了总氨基酸、可溶性蛋白、总氮、硝酸盐和铵盐含量。我们的研究结果清楚地表明，两种树种都能够利用无机和有机氮源。在存在竞争树种的情况下，山毛榉根系对无机和有机氮的吸收受到抑制。相比之下，山毛榉的存在刺激了三角枫根系对无机氮的吸收。三角枫对山毛榉氮吸收的负影响和山毛榉对三角枫氮吸收的正影响导致了山毛榉根中可溶性蛋白的增加，尽管总氮浓度总体下降。因此，山毛榉通过将较少的氮纳入结构氮成分来补偿树竞争对氮吸收的负面影响，但在竞争条件下表现出与竞争树种相同的策略，即在根中增强可溶性蛋白水平。据推测，山毛榉需要增强目前未知性质的酶活性作为对种间竞争的防御反应。
