Comparative studies on adaptive strategies of Medicago falcata and M. truncatula to phosphorus deficiency in soil

doi:10.3724/SP.J.1258.2011.00632

Abstract

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

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[J]. Chin J Plant Ecol, 2011, 35(6): 632-640.

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URL: https://www.plant-ecology.com/EN/10.3724/SP.J.1258.2011.00632

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

Figures/Tables 5

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.

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

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.

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

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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