Crop plant root effects on the soil environment for denitrification in agricultural soils

土壤中易降解的有机化合物，如作物残留物和土壤硝酸盐，是农业土壤微生物反硝化的关键驱动因素。反硝化微生物群落的活性和组成受多种环境因素的控制。该项目的重点是作物对反硝化的控制和影响。植物迅速吸收养分，尤其是硝酸盐，并通过蒸腾和光合作用消耗水分。这会导致硝酸盐有效性和土壤水分的变化，从而降低反硝化作用。同时，植物可以通过将同化物转移到根部来加速反硝化作用。在这里，这些碳化合物导致根呼吸消耗土壤氧气，并导致根沉积，为土壤微生物提供容易降解的碳化合物。因此，这些植物活动不仅改变了反硝化的非生物条件，而且还影响了土壤中的微生物群落，特别是根际群落。我们建议在受控条件下进行一系列实验，以评估通过工厂进行的反硝化控制，其中一项实验将扩展到田间条件。将使用15N和13C稳定同位素标记来追踪反硝化气体(N2O、NO和N2)的通量以及根际沉积对微生物群落的影响。其目的是评估作物及其根系以及作物残体效应对土壤反硝化速率的影响，为农业系统反硝化模型的参数化和验证提供植物效应的定量数据。在第一个项目阶段的方法和结果的基础上，将有三个主要的工作领域：i)影响组成，即植物地上部分和根部凋落物的质量对土壤有机碳有效性的影响，以及反硝化产物的化学计量。在这里，我们的活动与DASIM研究单位的项目P3密切相关，在该项目中，我们共同解决土壤有机质质量描述符的问题；ii)量化根部沉积和植物N吸收的动态及其对反硝化和气体产生率的影响。这构成了DASIM研究单位的联合实验13，稳定同位素标记将不仅用于气体通量分析，还将用于功能基因分析，并与P3合作评估微生物N循环群落的多样性；iii)在农业田间条件下，植物生长和N吸收对反硝化的影响以及不同气体反硝化产物的速率。这项研究还将使用P6开发的改进的实地方法进行15N稳定同位素标记，并将包括前面提到的一些定性评估，以提供数据，以便为景观DNDC模型的参数化和验证提供数据，该模型是P7项目的一个关键重点。

Easily degradable organic compounds in soil such as residues deposited by crop plants and soil nitrate are among the key drivers of microbial denitrification in agricultural soils. The activities and composition of denitrifying microbial communities are controlled by numerous environmental factors. This project focuses on the denitrification controls and effects exerted by crop plants. Plants take up nutrients and particularly nitrate rapidly and consume water by transpiration and photosynthesis. This leads to alteration of nitrate availability and soil moisture which may lower denitrification. At the same time plants may accelerate denitrification by translocating assimilates to their roots. Here these carbon compounds lead to root respiration consuming soil oxygen and to rhizodeposition providing easily degradable carbon compounds to soil microbes. Thus, these plant activities not only lead to changes in abiotic conditions for denitrification but they also influence microbial communities in soil and especially rhizosphere communities. We propose a series of experiments under controlled conditions for assessing denitrification controls through plants and one them will extend to field conditions. 15N and 13C stable isotope labelling will be employed to trace denitrification gas fluxes (N2O, NO and N2) as well as rhizodeposition effects on microbial communities. The objective is to assess the influence of crop plants and their roots as well as crop residue effects on soil denitrification rates to provide quantitative data on plant effects for parametrization and validation of denitrification modelling in agricultural systems. Building on methods and results of the first project phase there will be three major working fields: i) effects the composition, i.e. quality of plant shoot and root litter on soil organic carbon availability for denitrification and denitrification product stoichiometry. Here our activities are closely linked to project P3 of the DASIM research unit where we jointly address soil organic matter quality descriptors; ii) quantification of the dynamics of rhizodeposition and plant N uptake and their effects on denitrification and gaseous product rates. This makes up Associated Experiment 13 of the DASIM Research Unit and stable isotope labelling will be used not only for gas flux analysis but also for functional gene analysis and assessment of the diversity of microbial N cycling communities in cooperation with P3; iii) effects of growing plants and N uptake on denitrification and the rates of different gaseous denitrification products in an agricultural field situation. The study will also employ 15N stable isotope labelling using an improved field methodology developed by P6 and it will include a number of qualitative assessments mentioned before to provide data for parametrization and validation of the LandscapeDNDC model which is a key focus of project P7.