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首页> 外文学位 >Plant-soil-microbial nitrogen cycling across contrasting organic farms in an intensively-managed agricultural landscape.
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Plant-soil-microbial nitrogen cycling across contrasting organic farms in an intensively-managed agricultural landscape.

机译：在集约化管理的农业景观中，不同有机农场之间的植物-土壤-微生物氮循环。

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摘要

How farming systems supply sufficient nitrogen (N) for high yields but with reduced N losses is a central challenge for reducing the tradeoffs often associated with N cycling in agriculture. This dissertation consists of three studies that assess how variability in organic farms across an agricultural landscape may yield insights for improving N cycling and for evaluating novel indicators of N availability.;Pulses of N are common in agricultural systems and often result in N losses if N is not quickly captured by plants or soil microbes. But understanding of how root behavioral responses and microbial N dynamics interact following soil N pulses remains limited, especially in soil under field conditions relevant to actual agroecosystem processes. The first study examined rhizosphere responses to a soil N pulse in an organic farm soil. A novel combination of molecular and 15N isotopic techniques was used to investigate the response of tomato (Solanum lycopersicum L.) roots and soil N cycling to a pulse of inorganic N in an undisturbed soil patch on an organic farm. Tomato roots rapidly responded to and exploited the N pulse via upregulation of key N metabolism genes that comprise the core physiological response of roots to patchy soil N availability. The transient root gene expression response underscored the sensitivity of root N uptake to local N availability. Strong root activity limited accumulation of soil nitrate (NO3 -) despite high rates of gross nitrification and allowed roots to out-compete soil microbes for uptake of the inorganic N pulse, even on the short time scale of a few days. Root expression of genes such as cytosolic glutamine synthetase, a key gene in root N assimilation, could serve as a "plant's eye view" of N availability when plant-soil N cycling is rapid, complementing more typical measures of N availability like soil inorganic N pools and bioassays of N mineralization potential.;Much of the research geared toward improving N cycling takes place at research stations with fixed management factors and limited variation in soil characteristics. Better understanding of how the plant-soil-microbe interactions that underpin N availability, potential for N loss, and yields vary across working farms would help reveal how to simultaneously achieve high provisioning (yields) and regulating (low potential for N loss) ecosystem services in heterogeneous landscapes. A landscape approach was thus used in the second and third studies to assess crop yields, plant-soil N cycling, root gene expression, and soil microbial community activity and composition over the course of a tomato growing season on working organic farms in Yolo County, California, USA. The 13 selected fields were representative of organic tomato production in the local landscape and spanned a three-fold range of soil carbon (C) and N but had similar soil types, texture, and pH. Yields ranged from 22.9 to 120.1 Mg ha-1 with a mean similar to the county average (86.1 Mg ha-1), which included mostly conventionally-grown tomatoes. Substantial variability in soil inorganic N concentrations, tomato N, and root gene expression indicated a range of possible tradeoffs between yields and potential for N losses across the fields. Soil enzyme activities reflected distinct metabolic capacity in each field, such that soil C-cycling enzyme potential activities increased with inorganic N availability while those of soil N-cycling enzymes increased with soil C availability. Compared to potential enzyme activity, there was less variation in soil microbial community composition, likely reflecting the history of high soil disturbance and low ecological complexity in this landscape. The variation in potential activity of soil enzymes across the organic fields thus may be due to high plasticity of the resident microbial community to environmental conditions.;Those fields in the landscape that showed evidence of tightly-coupled plant-soil N cycling, a desirable scenario in which high crop yields are supported by adequate N availability but low potential for N loss, had the highest total and labile soil C and N and received diverse types of organic matter inputs with a range of N availability. In these fields, elevated expression of cytosolic glutamine synthetase in roots (as evaluated in the first study), confirmed that plant N assimilation was high even when soil inorganic N pools were low. The on-farm approach provided a wide range of farming practices and soil characteristics to reveal how microbially-derived ecosystem functions can be effectively manipulated to enhance nutrient cycling capacity. Novel combinations of N cycling indicators (i.e. inorganic N along with soil microbial activity and root gene expression for N assimilation) would support adaptive management for improved N cycling on organic as well as conventional farms, and could overcome the uncertainty of managing N inputs accurately, especially when plant-soil N cycling is rapid.
机译：农业系统如何提供足够的氮（N）以实现高产，但减少的N损失是减少农业中经常与氮循环相关的权衡的主要挑战。本论文包括三项研究，这些研究评估了整个农业景观中有机农场的变异性如何为改善氮素循环和评估氮素有效性的新指标提供了见识。氮素脉冲在农业系统中很常见，如果氮素不足，通常会​​导致氮素损失不能被植物或土壤微生物迅速捕获。但是，对于土壤氮脉冲后根系行为响应和微生物氮动力学如何相互作用的理解仍然有限，尤其是在土壤中与实际农业生态系统过程相关的田间条件下。第一项研究检验了有机农场土壤中根际对土壤氮脉冲的响应。分子和15N同位素技术的新颖组合用于研究番茄（Solanum lycopersicum L.）根和土壤氮对有机农场中未受干扰的土壤斑块中无机氮脉冲的响应。番茄的根系通过关键氮素代谢基因的上调快速响应并利用了氮素脉冲，这些基因包括根系对斑块土壤氮素有效性的核心生理反应。瞬时根基因表达反应强调了根氮吸收对局部氮有效性的敏感性。尽管总硝化率很高，但强大的根系活动限制了土壤硝态氮（NO3-）的积累，即使在短短几天内，根系也无法与土壤微生物竞争，从而吸收了无机氮脉冲。当植物-土壤氮循环快速时，诸如胞质谷氨酰胺合成酶（根氮同化的关键基因）之类的基因的根表达可作为氮素有效性的“植物眼”，补充了土壤无机氮等更典型的氮素有效性测量N矿化潜力的资源库和生物测定法。许多旨在改善N循环的研究都在管理因子固定且土壤特性变化有限的研究站进行。更好地了解在不同工作农场中构成氮素可用性，氮素损失潜力和产量变化基础的植物-土壤-微生物相互作用如何帮助揭示如何同时实现高配置（产量）和调节（氮素损失潜力低）生态系统服务在异质景观中。因此，在第二个和第三个研究中，采用了景观方法来评估Yolo县有工作的有机农场在番茄生长期期间的作物产量，植物-土壤氮循环，根基因表达以及土壤微生物群落活性和组成。美国加利福尼亚。选定的13个田地代表了当地景观中有机番茄的生产，覆盖了土壤碳（C）和氮的三倍范围，但土壤类型，质地和pH值相似。产量范围从22.9至120.1 Mg ha-1，平均水平与该县的平均水平（86.1 Mg ha-1）相近，其中包括大部分常规种植的番茄。土壤无机氮含量，番茄氮和根基因表达的显着差异表明，整个田间在产量和氮素损失潜力之间可能存在一定的权衡取舍。土壤酶活性反映了每个领域的独特代谢能力，因此，土壤C循环酶的潜在活性随无机氮的利用而增加，而土壤N循环酶的活性随土壤C的利用而增加。与潜在的酶活性相比，土壤微生物群落组成的变化较小，这很可能反映了该景观中高土壤扰动和低生态复杂性的历史。因此，土壤酶在整个有机田间潜在活性的变化可能是由于居民微生物群落对环境条件的高度可塑性所致；景观中的这些田间显示出植物-土壤氮循环紧密耦合的证据，这是理想的情况。在这种作物中，充足的氮素可提供较高的农作物产量，但氮素损失的可能性较低，土壤中的碳和氮素含量最高且不稳定，并接受了各种类型的有机物投入，且氮素的利用率也各不相同。在这些领域中，根中胞质谷氨酰胺合成酶的表达升高（在第一个研究中进行了评估），证实了即使土壤中的无机氮池较低，植物的氮吸收也很高。农场方式提供了广泛的耕作方法和土壤特性，以揭示如何有效地控制微生物来源的生态系统功能，以增强养分循环能力。氮素循环指标的新颖组合（即无机氮以及土壤微生物活性和氮同化的根基因表达）将支持适应性管理，以改善有机农场和常规农场的氮素循环，并可以克服准确管理氮素输入的不确定性，特别是当植物土壤氮素循环快速时。

著录项

  • 作者

    Bowles, Timothy M.;

  • 作者单位

    University of California, Davis.;

  • 授予单位 University of California, Davis.;
  • 学科 Ecology.;Agriculture.;Soil sciences.
  • 学位 Ph.D.
  • 年度 2015
  • 页码 158 p.
  • 总页数 158
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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