叶子的碳同位素组成(δ13C)通常用作植物性能的代表。然而,NO3的影响-vs.叶片代谢物和呼吸的CO2的δ13C上的NH4供应在很大程度上是未知的。我们为烟草植物提供了NO3-与NH4浓度比的梯度,并确定了气体交换变量,三羧酸(TCA)循环中间体的浓度和δ13C,暗呼吸CO2的δ13C和关键酶硝酸还原酶的活性,苹果酸酶和磷酸烯醇丙酮酸羧化酶。净同化率,干生物量以及有机酸和淀粉的浓度沿梯度下降。相比之下,呼吸率,细胞间CO2,可溶性糖和氨基酸的浓度增加。随着NO3-减少,所有测得的酶的活性均降低。CO2和有机酸的δ13C紧密共变,在NO3-供应下更正,表明有机酸是呼吸的潜在底物。连同分子内13C富集苹果酸的估计值,我们得出的结论是,在NO3供应下,TCA循环的回补反应的变化可能有助于有机酸中的13C富集和呼吸的CO2。因此,NO3的影响-vs.δ13C上的NH4+高度相关,特别是如果将叶片代谢物或呼吸作用的δ13C用作植物性能的代表。
The carbon isotopic composition (δ13C) of foliage is often used as proxy for plant performance. However, the effect of N O 3 - vs. N H 4 + supply on δ13C of leaf metabolites and respired CO2 is largely unknown. We supplied tobacco plants with a gradient of N O 3 - to N H 4 + concentration ratios and determined gas exchange variables, concentrations and δ13C of tricarboxylic acid (TCA) cycle intermediates, δ13C of dark-respired CO2, and activities of key enzymes nitrate reductase, malic enzyme and phosphoenolpyruvate
carboxylase. Net assimilation rate, dry biomass and concentrations of organic acids and starch decreased along the gradient. In contrast, respiration rates, concentrations of intercellular CO2, soluble sugars and amino acids increased. As N O 3 - decreased, activities of all measured enzymes decreased. δ13C of CO2 and organic acids closely co-varied and were more positive under N O 3 - supply, suggesting organic acids as potential substrates for respiration. Together with estimates of intra-molecular 13C enrichment in malate, we conclude that a change in the anaplerotic reaction of the TCA cycle possibly contributes to 13C enrichment in organic acids and respired CO2 under N O 3 - supply. Thus, the effect of N O 3 - vs. N H 4 + on δ13C is highly relevant, particularly if δ13C of leaf metabolites or respiration is used as proxy for plant performance.