Effects of soil type and composition of rhizodeposits on rhizosphere priming phenomena
Effects of soil type and composition of rhizodeposits on rhizosphere priming phenomena
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DOI：
10.1016/j.soilbio.2016.10.002
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发表时间：
2016-12
影响因子：
9.7
通讯作者：
D. Lloyd;K. Ritz;E. Paterson;G. Kirk
中科院分区：
文献类型：
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作者：
D. Lloyd;K. Ritz;E. Paterson;G. Kirk
新鲜植物源碳的输入可能会刺激根际土壤有机质（SOM）的微生物介导的周转。但是，对人工系统中这种“启动”效应的研究往往产生相互矛盾的结果，这取决于诸如底物添加速率、底物组成、是使用纯化合物还是底物混合物、添加是脉冲式的还是连续的等变量。对种植系统的研究不太常见，但也产生了明显相互矛盾的结果，而且对这些影响的机制知之甚少。为了增加这些问题的证据，我们在两种不同的土壤中种植了一种C4草61天，一种是酸性沙土，另一种是更肥沃的粘土壤土，这两种土壤以前只支持C3植物。我们测量了土壤总呼吸及其碳同位素组成，并利用后者来划分植物和土壤碳源之间的呼吸作用。我们发现，在两种土壤中，植物生长增强了SOM的周转（即正启动）。在剪草处理中，净生长量大大减少，启动效应相应较弱。未修剪处理的植株净生长、土壤总呼吸和som衍生呼吸均显著高于修剪处理。此外，som衍生的呼吸随着时间的推移与植物生长的增加平行增加，但增加在较不肥沃的土壤中被延迟。我们得出结论，微生物对氮的需求驱动了诱导效应，根系对碳基质的沉积和根系对氮的竞争促进了诱导效应，诱导程度取决于土壤类型和植物生长条件。在进一步的实验中，我们模拟了可溶性微生物基质在相同的两种土壤中的根沉积，在19 d内几乎连续添加c4标记的蔗糖（即简单的单一基质）或玉米根提取物（即相对多样化的基质），并测量了土壤呼吸及其C同位素特征。在较肥沃的土壤中，随着时间的推移，蔗糖诱导的启动效应越来越积极，而玉米根提取物的启动效应随着时间的推移而下降。我们认为这是因为氮和其他营养物质是由这种更多样化的基质的矿化提供的。在较不肥沃的土壤中，微生物对氮的需求可能从未被添加的基质和土壤有机质的联合矿化所满足。因此，随着时间的推移，启动效应几乎是恒定的。我们得出结论，假定的启动化合物的化学性质可以极大地影响启动现象。
Inputs of fresh plant-derived C may stimulate microbially-mediated turnover of soil organic matter (SOM) in the rhizosphere. But studies of such ‘priming’ effects in artificial systems often produce conflicting results, depending on such variables as rates of substrate addition, substrate composition, whether pure compounds or mixtures of substrates are used, and whether the addition is pulsed or continuous. Studies in planted systems are less common, but also produce apparently conflicting results, and the mechanisms of these effects are poorly understood.To add to the evidence on these matters, we grew a C4 grass for 61 d in two contrasting soils – an acid sandy soil and a more fertile clay-loam – which had previously only supported C3 vegetation. We measured total soil respiration and its C isotope composition, and used the latter to partition the respiration between plant- and soil-C sources. We found SOM turnover was enhanced (i.e. positive priming) by plant growth in both soils. In treatments in which the grass was clipped, net growth was greatly diminished, and priming effects were correspondingly weak. In treatments without clipping, net plant growth, total soil respiration and SOM-derived respiration were all much greater. Further, SOM-derived respiration increased over time in parallel with increases in plant growth, but the increase was delayed in the less fertile soil. We conclude the observed priming effects were driven by microbial demand for N, fuelled by deposition of C substrate from roots and competition with roots for N. The extent of priming depended on soil type and plant growing conditions.In a further experiment, we simulated rhizodeposition of soluble microbial substrates in the same two soils with near-continuous additions for 19 d of either C4-labelled sucrose (i.e. a simple single substrate) or a maize root extract (i.e. a relatively diverse substrate), and we measured soil respiration and its C isotope signature. In the more fertile soil, sucrose induced increasingly positive priming effects over time, whereas the maize root extract produced declining priming effects over time. We suggest this was because N and other nutrients were provided from the mineralization of this more diverse substrate. In the less-fertile soil, microbial N demand was probably never satisfied by the combined mineralization from added substrate and soil organic matter. Therefore priming effects were approximately constant over time. We conclude that the chemical nature of putative priming compounds can greatly influence priming phenomena.