Plant–microbe interactions in the rhizosphere influence rates of organic matter mineralization and nutrient cycling that are critical to sustainable agricultural productivity. Agricultural intensification, particularly the introduction of synthetic fertilizer in the USA, altered the abundance and dominant forms of nitrogen (N), a critical plant nutrient, potentially imposing selection pressure on plant traits and plant–microbe interactions regulating N cycling and acquisition. We hypothesized that maize adaptation to synthetic N fertilization altered root functional traits and rhizosphere microbial nutrient cycling, reducing maize ability to acquire N from organic sources. Six maize genotypes released pre-fertilizer (1936, 1939, 1942) or post-fertilizer (1984, 1994, 2015) were grown in rhizoboxes containing patches of ¹⁵N-labelled clover/vetch residue. Multivariate approaches did not identify architectural traits that strongly and consistently predicted rhizosphere processes, though metrics of root morphological plasticity were linked to carbon- and N-cycling enzyme activities. Root traits, potential activities of extracellular enzymes (BG, LAP, NAG, urease), abundances of N-cycling genes (amoA, narG, nirK, nirS, nosZ) and uptake of organic N did not differ between eras of release despite substantial variation among genotypes and replicates. Thus, agricultural intensification does not appear to have impaired N cycling and acquisition from organic sources by modern maize and its rhizobiome. Improved mechanistic understanding of rhizosphere processes and their response to selective pressures will contribute greatly to rhizosphere engineering for sustainable agriculture.

中文翻译：

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农业集约化是否影响了玉米根部性状以及与有机氮获取相关的根际相互作用？


根际植物与微生物的相互作用影响有机质矿化和养分循环的速率，这对可持续农业生产力至关重要。农业集约化，特别是在美国引入合成肥料，改变了氮（N）的丰度和主要形式，氮（N）是一种重要的植物养分，可能对植物性状和调节氮循环和获取的植物-微生物相互作用施加选择压力。我们假设玉米对合成氮肥的适应改变了根部功能性状和根际微生物养分循环，降低了玉米从有机来源获取氮的能力。施肥前（1936、1939、1942）或施肥后（1984、1994、2015）释放的六种玉米基因型在含有¹⁵ N 标记三叶草/野豌豆残留物斑块的根箱中生长。尽管根形态可塑性的指标与碳循环和氮循环酶活性相关，但多变量方法并未确定能够强烈且一致地预测根际过程的结构特征。根性状、细胞外酶（BG、LAP、NAG、脲酶）的潜在活性、氮循环基因（ amoA 、 narG 、 nirK 、 nirS 、 nosZ ）的丰度和有机氮的吸收在释放时期之间没有差异，尽管存在很大差异基因型和重复之间。因此，农业集约化似乎并没有损害现代玉米及其根瘤菌从有机来源获取氮的循环和获取。提高对根际过程及其对选择压力的响应的机械理解将极大地促进可持续农业的根际工程。