Spatial pattern of enzyme activities depends on root exudate composition
Spatial pattern of enzyme activities depends on root exudate composition
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DOI：
10.1016/j.soilbio.2019.02.010
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发表时间：
2019-06
影响因子：
9.7
通讯作者：
Xuechen Zhang;M. Dippold;Y. Kuzyakov;B. Razavi
中科院分区：
文献类型：
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作者：
Xuechen Zhang;M. Dippold;Y. Kuzyakov;B. Razavi
根根据分泌物组成，特别是糖、羧酸和氨基酸的比例，增加微生物活性，从而构建根际酶活性。我们引入了一种新方法，将土壤酶谱和Rhizon®采样器释放的模拟分泌物相结合，以刺激微生物活性，但避免活根直接释放酶。这使得可视化，定位和分析模拟根分泌物对参与碳（C）（β-葡萄糖苷酶，纤维二糖水解酶），氮（N）（亮氨酸氨肽酶），磷（P）（磷酸酶）和硫（S）（硫酸酯酶）循环的五种微生物酶活性的影响。我们测试的假设，1）人工分泌物刺激微生物酶的生产，并在根周围形成空间梯度，和2）在根际微生物酶活性的程度是组分特异性的。与这些假设一致，P-，N-和S-相关酶的活性较高的人工根附近，并逐渐降低，作为离根的函数。C-循环酶的模式是统一的，独立的渗出液组成。在所有组分中，丙氨酸增加根际范围的作用比其他物质强得多，而蛋氨酸对酶活性的空间分布没有影响。所有酶的Vmax随着丙氨酸的添加而增加，但在添加柠檬酸盐后降低。酶活性的比值表明，根际微生物释放更多的亮氨酸氨肽酶比其他酶，以满足他们的N需求。葡萄糖增加了纤维二糖水解酶和β-葡萄糖苷酶的Km，而丙氨酸对亮氨酸氨肽酶和硫酸酯酶的Km影响最大。磷酸酶是对根系分泌物组成最敏感的酶，因此，任何影响根系分泌物组成的因素都会强烈影响P循环。我们的结论是，根际微生物衍生的酶活性的程度是组件和酶的具体和这种程度取决于底物的化学计量和微生物的营养需求。
Roots increase microbial activities depending on exudate composition, especially on the ratios of sugars, carboxylic and amino acids, and thus structure enzyme activities in the rhizosphere. We introduce a new approach combining soil zymography and simulated exudates released from Rhizon®samplers to stimulate microbial activities but avoid the direct release of enzymes by living roots. This enabled visualizing, localizing and analyzing the effects of simulated root exudates on activity of five microbial enzymes involved in carbon (C) (β-glucosidase, cellobiohydrolase), nitrogen (N) (leucine aminopeptidase), phosphorus (P) (phosphatase) and sulfur (S) (sulfatase) cycles. We tested the hypotheses that 1) artificial exudates stimulate microorganisms for enzyme production and form spatial gradients around roots, and 2) the extent of microbial enzyme activities in the rhizosphere is component-specific. In line with these hypotheses, the activities of P-, N- and S-related enzymes were higher near the artificial root and gradually decreased as a function of distance from the root. The pattern for C-cycle enzymes was uniform and independent of the exudate composition. Among all components, alanine increased the rhizosphere extent much stronger than other substances, while methionine had no effect on the spatial distribution of enzyme activities. Vmaxof all enzymes increased with alanine addition, but decreased after adding citrate. The ratios of enzyme activities demonstrated that rhizosphere microorganisms release more leucine aminopeptidase than other enzymes to meet their N demand. Glucose increased the Kmof cellobiohydrolase and β-glucosidase, while alanine had the greatest effect on the Kmof leucine aminopeptidase and sulfatase. Phosphatase is the enzyme most sensitive to the composition of root exudates; consequently, any factor influencing root exudate composition can strongly affect the P cycle. We conclude that the rhizosphere extent of microbial-derived enzyme activities is component- and enzyme-specific and that this extent depends on the substrate stoichiometry and microbial nutrient demand.