Key message

The roles of root exudates are not to directly solubilize P bound to non-crystalline minerals but to increase organic-P and plant-available P through priming effects for microbes on volcanic soils.

Abstract

Volcanic soils are generally characterized by low phosphorus (P) availability for plants because the non-crystalline minerals produced during weathering process strongly combine P with ligand binding. How forest trees absorb such bound P in volcanic soils have not been well known. The aim of this study was to investigate the mechanisms of P acquisition by trees in three evergreen broadleaved forests on volcanic soils differing in the concentration of non-crystalline minerals with an emphasis on the role of low-molecular-weight organic acids (LMWOAs). LMWOAs released from tree fine roots were expected (1) to chemically release P bound to non-crystalline minerals, and/or (2) to biologically enhance P availability through priming effects by stimulating soil microbial activities and by increasing the concentration of organic P in the rhizosphere. Compositions of LMWOA exudates were phylogenetically determined but the flux of citric and malic acids tended to increase in soils where the concentration of non-crystalline minerals was higher. The concentration of P bound to non-crystalline minerals was lower in the rhizosphere than in non-rhizosphere soils, suggesting the solubilization of the bound P in the rhizosphere; however, this trend occurred only in one forest. In contrast, the concentrations of organic P, easily soluble P and total P were significantly greater in the rhizosphere than in non-rhizosphere soils in all sites. Our results suggested that LMWOAs exudates did not directly release P from non-crystalline minerals but increased organic P associated with soil microbial biomass in rhizosphere soils, which in turn enhanced plant-available P and total P.

中文翻译：

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树根分泌物对日本屋久岛根际火山土壤中非结晶矿物吸附磷的影响

关键信息

根系分泌物的作用不是直接溶解与非结晶矿物质结合的磷，而是通过对火山土壤上微生物的引发作用来增加有机磷和植物可利用的磷。

抽象的

火山土壤的特征通常是植物的磷 (P) 可用性低，因为风化过程中产生的非结晶矿物质将 P 与配体结合牢固地结合在一起。森林树木如何吸收火山土壤中的这种结合 P 尚不清楚。本研究的目的是研究火山土壤上三种常绿阔叶林中树木获取磷的机制，这些森林的非结晶矿物质浓度不同，重点是低分子量有机酸 (LMWOA) 的作用。预计从树木细根中释放的 LMWOA 会 (1) 以化学方式释放与非结晶矿物质结合的磷，和/或 (2) 通过刺激土壤微生物活动和增加有机磷浓度的启动效应，在生物学上提高磷的有效性。根际。LMWOA 渗出液的组成由系统发育决定，但柠檬酸和苹果酸的通量在非结晶矿物质浓度较高的土壤中趋于增加。与非晶态矿物结合的磷浓度在根际低于非根际土壤，表明结合磷在根际溶解；然而，这种趋势只发生在一个森林中。相比之下，所有地点的根际有机磷、易溶磷和总磷的浓度显着高于非根际土壤。我们的研究结果表明，LMWOAs 渗出物不会直接从非结晶矿物中释放磷，而是增加了与根际土壤中土壤微生物生物量相关的有机磷，从而提高了植物有效磷和总磷。