Soil Microorganisms Mediating Phosphorus Availability
Soil Microorganisms Mediating Phosphorus Availability
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DOI：
10.1104/pp.111.175448
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发表时间：
2011-07-01
期刊：
影响因子：
7.4
通讯作者：
Simpson, Richard J.
中科院分区：
文献类型：
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作者：
Richardson, Alan E.;Simpson, Richard J.
微生物是土壤磷 (P) 循环的组成部分，因此在调节植物磷的利用率方面发挥着重要作用。因此，几十年来，了解微生物对植物磷营养的贡献以及操纵特定微生物以提高土壤中磷的利用率的机会一直引起人们的极大兴趣。由于全球风化土壤和热带土壤中常见的缺磷现象、磷肥成本的上升以及植物从土壤和肥料来源利用磷的效率往往较低，尽管许多土壤含有相对大量的总磷，而植物只能少量利用，所以加剧了这种兴趣。世界上优质磷矿资源是有限的，这本身就证明需要开发磷效率更高的植物和/或农业系统。因此，利用微生物增加土壤中磷的利用率对于发展更可持续的农业来说是一个有吸引力的主张。这与发达国家的高投入生产系统有关，也与获得矿物肥料受到限制的发展中国家有关（Sánchez，2010）。微生物增强植物磷利用率的概念并不新鲜。 Gerretsen (1948) 表明，在受控条件下，土壤细菌的纯培养物可以通过溶解沉淀形式的磷酸钙 (Ca) 来增加植物的磷营养。自这项研究以来，已经报道了许多微生物介导的磷动员和不同微生物特征的例子（综述见 Richardson，2001；Gyaneshwar 等，2002；Khan 等，2007、2010；Harvey 等，2009；Richardson 等，2009a；Zaidi 等，2009）。然而，尽管用于磷动员的微生物产品前景广阔，但尚未在大面积农业系统中得到重大应用。一个例外是基于真菌的接种剂在北美以及最近在澳大利亚和欧洲的商业化。显然，土壤环境中微生物和植物之间的相互作用是复杂的，除了少数例外（例如根瘤菌，以及较小程度的菌根真菌），已证明难以管理，因此对接种剂的反应变化很大。此外，土壤中的磷会发生广泛的物理化学和生物反应，土壤总磷中只有一小部分以直接可供植物或微生物吸收的形式存在（图1）。从土壤溶液中吸收磷是通过高亲和力转运蛋白以正磷酸盐的形式发生的，转运蛋白在植物中位于根表皮，并通过与菌根真菌的相互作用响应磷缺乏而协调表达（Bucher，2007）。土壤中的磷主要以无机部分存在，它们要么被吸附到土壤矿物表面，要么以稀有的沉淀物形式存在，而有机形式要么被吸附、掺入生物量，要么与土壤有机质相关。这些形式的正磷酸盐的溶解（或动员）以及土壤溶液中磷的扩散速率是植物生长所需磷充足供应的主要限制。在本次更新中，我们总结了有关自由生活的非共生微生物在增加植物磷利用率方面的作用的最新证据。概述了阻碍我们理解根际微生物介导的磷动态的关键问题，并讨论了增强磷动员的机会。
Microorganisms are integral to the soil phosphorus (P) cycle and as such play an important role in mediating the availability of P to plants. Understanding the microbial contribution to plant P nutrition and opportunities for manipulating specific microorganisms to enhance P availability in soil has therefore been of considerable interest over many decades. This interest is accentuated by P deficiency being common in weathered and tropical soils throughout the world, by rising costs of P fertilizer, and because the efficiency of P use by plants from soil and fertilizer sources is often poor despite many soils containing a relatively large amount of total P that is only sparingly available to plants. The world’s high-quality sources of rock phosphate are finite and this itself justifies the need to develop plants and/or agricultural systems that are more P efficient. Utilization of microorganisms to increase the availability of P in soil therefore is an attractive proposition for developing a more sustainable agriculture. This is relevant to the high-input production systems of the developed world, and also to developing countries where access to mineral fertilizers is restricted (Sánchez, 2010). The concept of microbial enhancement of P availability to plants is not new. Gerretsen (1948) showed that pure cultures of soil bacteria could increase the P nutrition of plants under controlled conditions through solubilization of precipitated forms of calcium (Ca) phosphates. Since this study, many examples of microbially mediated P mobilization and characterization of different microorganisms have been reported (for review, see Richardson, 2001; Gyaneshwar et al., 2002; Khan et al., 2007, 2010; Harvey et al., 2009; Richardson et al., 2009a; Zaidi et al., 2009). However, despite considerable promise microbial products for P mobilization have not had major application to broad-acre farming systems. An exception to this is the commercialization of fungal-based inoculants in North America and more recently in Australia and Europe. Clearly, interactions between microorganisms and plants in soil environments are complex and with a few exceptions only (such as rhizobia, and to a much lesser extent mycorrhizal fungi), have proven difficult to manage and as a consequence responses to inoculants have been highly variable. In addition, P in soil is subject to extensive physicochemical and biological reactions with only a small component of total soil P being in a form directly available for plant or microbial uptake (Fig. 1). Uptake of P from soil solution occurs as orthophosphate via high-affinity transporters that in plants are localized to the root epidermis and are coordinately expressed in response to P deficiency and through interaction with mycorrhizal fungi (Bucher, 2007). P in soil exists predominantly in inorganic fractions that are either adsorbed to soil mineral surfaces or occur as sparingly available precipitates, and in organic forms that are either adsorbed, incorporated within biomass, or associated with soil organic matter. It is the dissolution (or mobilization) of orthophosphate from these forms, and rates of P diffusion within soil solution that represents the major limitation to adequate supply of P required for plant growth. In this Update we summarize current evidence concerning the role of free-living nonsymbiotic microorganisms in increasing the availability of P to plants. Critical issues that impede our understanding of microbially mediated P dynamics in the rhizosphere are outlined and opportunities for enhancing P mobilization are discussed.