黄花苜蓿与蒺藜苜蓿对土壤低磷胁迫适应策略的比较研究

doi:10.3724/SP.J.1258.2011.00632

摘要/Abstract

摘要：

土壤有效磷(P)含量低是限制植物生长的主要因素之一。根形态变化和根系大量分泌以柠檬酸为主的有机酸是植物适应土壤P素缺乏的重要机制。以广泛分布于我国北方的重要豆科牧草黄花苜蓿(Medicago falcata)和豆科模式植物蒺藜苜蓿(M. truncatula)为材料, 采用砂培方法, 研究了低P胁迫对其植株生长、根系形态和柠檬酸分泌的影响, 对比了两种苜蓿适应低P胁迫的不同策略。结果表明: 1)低P处理显著抑制了蒺藜苜蓿与黄花苜蓿的地上部生长, 而对地下部生长影响较小, 从而导致根冠比增加。2)低P胁迫显著降低黄花苜蓿的总根长和侧根长, 而对蒺藜苜蓿的上述根系形态指标没有显著影响。3)低P胁迫促进两种苜蓿根系的柠檬酸分泌, 无论是在正常供P还是低P胁迫条件下, 黄花苜蓿根系分泌柠檬酸量显著高于蒺藜苜蓿根系。上述结果表明, 黄花苜蓿和蒺藜苜蓿对低P胁迫的适应策略不同, 低P胁迫下, 黄花苜蓿主要通过根系大量分泌柠檬酸, 活化根际难溶态P来提高对P的吸收, 而蒺藜苜蓿维持较大的根系是其适应低P胁迫的主要策略。

关键词: 柠檬酸分泌, 黄花苜蓿, 蒺藜苜蓿, 低P胁迫, 根构型

Abstract:

Aims Phosphorus (P) is an essential macronutrient for plant growth and development. Phosphorus deficiency is one of the major constraints limiting plant growth in many types of soils. To cope with P deficiency, plants have evolved numerous strategies including changes in root architecture and exudation of organic acids in general and citrate in particular to maximize P uptake and mobilize soil P. To unravel the adaptive strategies of Medicago falcata, a native legume species in temperate grassland in northern China, and M. truncatula, a legume model plant, to P deficiency, we compared biomass, root traits and exudation of citrate of the two species under two levels of P supply.

Methods Pot experiments were conducted to compare biomass, root traits and exudation of citrate in M. falcata and M. truncatula under two levels of P supply (500 and 5 µmol·L^-1).

Important findings Shoot biomass was reduced while root biomass was not affected in both M. falcata and M. truncatula when exposed to P-deficient medium, leading to an increase in root/shoot ratio. The lateral root length and total root length of M. falcata seedlings grown in P-deficient medium were markedly reduced compared to those grown in P-sufficient medium, while no significant effect of P deficiency on these parameters in M. truncatula seedlings was observed. A greater amount of citrate was exuded from M. falcata roots than M. truncatula roots under P-sufficient conditions. Citrate exudation from both species was stimulated in response to P deficiency with the stimulatory effect being much more evident in M. falcata than in M. truncatula. Taken together, these findings reveal that M. falcata and M. truncatula have developed different strategies to cope with P deficiency. Medicago falcata had a small root system and exuded large amount of citrate to mobilize soil P bound to soil particles. In contrast, M. truncatula had limited capacity to mobilize soil P by releasing citrate, but it maintained a large root system to more effectively explore sparse soil P and maximize P uptake by its large root surface area.

Key words: citrate exudation, Medicago falcata, Medicago truncatula, phosphorus deficiency, root architecture

高艳, 田秋英, 石凤翎, 李凌浩, 张文浩. 黄花苜蓿与蒺藜苜蓿对土壤低磷胁迫适应策略的比较研究. 植物生态学报, 2011, 35(6): 632-640. DOI: 10.3724/SP.J.1258.2011.00632

GAO Yan, TIAN Qiu-Ying, SHI Feng-Ling, LI Ling-Hao, ZHANG Wen-Hao. Comparative studies on adaptive strategies of Medicago falcata and M. truncatula to phosphorus deficiency in soil. Chinese Journal of Plant Ecology, 2011, 35(6): 632-640. DOI: 10.3724/SP.J.1258.2011.00632

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https://www.plant-ecology.com/CN/Y2011/V35/I6/632

图/表 5

图1 黄花苜蓿和蒺藜苜蓿在正常供磷(+P, 500 μmol·L-1)和低磷(-P, 5 μmol·L-1)条件下的地上、地下生物量和根冠比(平均值±标准误差, n = 4)。不同字母表示物种之间和处理间差异显著(p < 0.05)。

Fig. 1 Biomass of shoots and roots, and shoot/root ratio in Medicago falcata and M. truncatula under supply of normal (+P, 500 μmol·L-1) and low P (-P, 5 μmol·L-1) (mean ± SE, n = 4). Different letters indicate significant difference between species and treatments at p < 0.05.

表1 正常供磷(+P, 500 μmol·L-1)和低磷(-P, 5 μmol·L-1)条件下黄花苜蓿和蒺藜苜蓿地上、地下、整株P含量和P累积量的比较(平均值±标准误差, n = 4)

Table 1 P contents in shoots, roots, whole plants and accumulative amounts of P in Medicago falcata and M. truncatula under conditions of normal (+P, 500 μmol·L-1) and low P (-P, 5 μmol·L-1 ) supply (mean ± SE, n = 4)

植物种 Species	供P水平 P level	地上P含量 Shoot P concentration (mg·g^-1 DW)	地下P含量 Root P concentration (mg·g^-1 DW)	植株P含量 Plant P concentration (mg·g^-1 DW)	P累积量 Accumulative P (μg·plant^-1)
黄花苜蓿 M. falcata	+ P - P	4.837 ± 0.060^a 1.157 ± 0.067^b	5.679 ± 0.153^a 1.631 ± 0.043^c	5.43 ± 0.16^a 1.45 ± 0.05^c	97.72 ± 2.07^b 12.50 ± 0.77^d
蒺藜苜蓿 M. truncatula	+ P - P	4.260 ± 0.272^a 1.130 ± 0.023^b	3.909 ± 0.202^b 1.796 ± 0.021^c	4.02 ± 0.23^b 1.26 ± 0.02^c	124.11 ± 5.47^a 26.47 ± 0.56^c

图2 黄花苜蓿和蒺藜苜蓿在正常供磷(+P, 500 μmol·L-1)和低磷(-P, 5 μmol·L-1)条件下的主根长、侧根长、侧根密度和总根长(平均值±标准误差, n = 4)。不同字母表示物种之间和处理间差异显著(p < 0.05)。

Fig. 2 Primary root length, lateral root length, lateral root density and total root length of Medicago falcata and M. truncatula under supply of normal (+P, 500 μmol·L-1) and low P (- P, 5 μmol·L-1) (mean ± SE, n = 4). Different letters indicate significant difference between species and treatments at p < 0.05.

表2 正常供磷(+P, 500 μmol·L-1)和低磷(-P, 5 μmol·L-1)条件下黄花苜蓿和蒺藜苜蓿根表面积、根体积和比根长的比较(平均值±标准误差, n = 4)

Table 2 Root surface area, root volume and specific root length of Medicago falcata and M. truncatula under conditions of normal (+P, 500 μmol·L-1) and low P (-P, 5 μmol·L-1 ) supply (mean ± SE, n = 4)

植物种 Species	供磷水平 P level	根表面积 Root surface area (cm²)	根体积 Root volume (cm³)	比根长 Specific root length (cm·g^-1 DW)
黄花苜蓿 M. falcata	+P	13.74 ± 2.39^a	0.104 ± 0.012^b	32.36 ± 5.07^a
黄花苜蓿 M. falcata	-P	6.40 ± 0.67^b	0.053 ± 0.003^c	19.51 ± 2.52^b
蒺藜苜蓿 M. truncatula	+P	18.43 ± 2.61^a	0.148 ± 0.021^a	15.47 ± 2.80^b
蒺藜苜蓿 M. truncatula	-P	14.50 ± 1.43^a	0.116 ± 0.011^ab	13.39 ± 1.79^b

图3 黄花苜蓿和蒺藜苜蓿在正常供磷(+P, 500 μmol·L-1)和低磷(-P, 5 μmol·L-1)条件下的根系柠檬酸量(平均值±标准误差, n = 4)。不同字母表示物种之间和处理间差异显著(p < 0.05)。

Fig. 3 Exudation of citrate from roots of Medicago falcata and M. truncatula under supply of normal (+P, 500 μmol·L-1) and low (- P, 5 μmol·L-1) P (mean ± SE, n = 4). Different letters indicate significant difference between species and treatments at p < 0.05.

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