Research advances on trade-off relationships of plant fine root functional traits

doi:10.17521/cjpe.2022.0456

Abstract

Abstract:

Trade-offs among plant functional traits reflect the trade-off relationships between resource acquisition and conservation of different plants, which are of pivotal importance for understanding the mechanisms by which plants adapt to the environment. However, due to the heterogeneity of the soil environment and the limitations of technical means, the study of below-ground root functional traits and their interrelationships is currently lagging behind that of above-ground functional traits. Traditionally, fine roots have been defined as all roots ≤2 mm in diameter. The acquisition and utilization of soil resources by plants depends on architectural traits, morphological traits, chemical traits and biotic traits of fine roots and so on, including fine roots associations with mycorrhizal fungi. Recently, the root economics space has been proposed, which demonstrates the existence of trade-offs between the do-it-yourself strategy of plants increasing their own root surface area and the outsourcing strategy of investments into fungal symbionts for enhanced nutrient mobilization from hyphal expansion, in addition to the traditional trade-offs between fast (high nitrogen content and metabolic rate) and slow (high tissue density) investment return. It was found that thin-root species obtained soil resources mainly by increasing specific root length, whereas thick-root species relied more on mycorrhizal fungi. However, the carbon economy of resource acquisition through the root and mycorrhizal hyphal pathways remains unclear. In future research, the key issues of root functional traits were suggested as follows: 1) for research methods, it is urgent to establish a unified set of definitions and research methods for root classification, sampling, storage, functional traits and their research methods; 2) for research traits, the research of “hard” traits of fine roots should be strengthened; 3) for the trade-offs between functional traits of fine roots, it is of great significance to strengthen the study of the trade-offs between construction costs and resource benefits between plant roots and mycorrhizal fungi.

Key words: fine root, functional trait, mycorrhizae, trade-off strategy

SUN Jia-Hui, SHI Hai-Lan, CHEN Ke-Yu, JI Bao-Ming, ZHANG Jing. Research advances on trade-off relationships of plant fine root functional traits[J]. Chin J Plant Ecol, 2023, 47(8): 1055-1070.

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References 134

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分类方法 Approach	描述 Description	优点 Advantage	缺点 Disadvantage
传统分类方法 Traditional classification	直径≤2 mm的细根集合 Roots ≤2 mm in diameter grouped together	快速, 不需要事先了解采样地点和物种 Fast, requires no prior knowledge of site or species	根系性状和生物量数据很难跨物种和地点进行解释和比较, 不适用于多物种相同直径的根系比较 Root trait and biomass data are difficult to interpret and compare across species and sites, it is not applicable to the comparison of root systems with the same diameter of multiple species
根序分类方法 Order-based classification	直径≤2 mm的根按根序分类 Roots ≤2 mm in diameter separated into individual root orders	可以跨越物种和地点比较根性状 Consistent and accurate comparisons of root traits across species and sites	工作量较大且耗时 Labor-intensive and time-consuming
功能分类方法 Functional classification	根据根系分级与解剖特征, 将直径≤2 mm的细根分为具有吸收和运输作用的根 Roots ≤2 mm in diameter were separated into absorptive and transport fine roots according to root orders and anatomical traits	适用于功能相似的根之间进行比较, 比顺序分类方法快速 Enables comparisons among functionally similar roots, faster than order-based	需要事先了解根系解剖特征, 根据解剖特征来确定分支层次中的功能划分 Might require a prior assessment of root anatomical traits to determine functional divisions within branching hierarchy

分类方法 Approach	描述 Description	优点 Advantage	缺点 Disadvantage
传统分类方法 Traditional classification	直径≤2 mm的细根集合 Roots ≤2 mm in diameter grouped together	快速, 不需要事先了解采样地点和物种 Fast, requires no prior knowledge of site or species	根系性状和生物量数据很难跨物种和地点进行解释和比较, 不适用于多物种相同直径的根系比较 Root trait and biomass data are difficult to interpret and compare across species and sites, it is not applicable to the comparison of root systems with the same diameter of multiple species
根序分类方法 Order-based classification	直径≤2 mm的根按根序分类 Roots ≤2 mm in diameter separated into individual root orders	可以跨越物种和地点比较根性状 Consistent and accurate comparisons of root traits across species and sites	工作量较大且耗时 Labor-intensive and time-consuming
功能分类方法 Functional classification	根据根系分级与解剖特征, 将直径≤2 mm的细根分为具有吸收和运输作用的根 Roots ≤2 mm in diameter were separated into absorptive and transport fine roots according to root orders and anatomical traits	适用于功能相似的根之间进行比较, 比顺序分类方法快速 Enables comparisons among functionally similar roots, faster than order-based	需要事先了解根系解剖特征, 根据解剖特征来确定分支层次中的功能划分 Might require a prior assessment of root anatomical traits to determine functional divisions within branching hierarchy

性状类型 Type of trait	性状指标 Trait index	缩写(单位) Abbreviation (unit)	描述 Description
构型性状 Architectural trait	根长密度 Root length density	RLD (cm·cm^-3)	单位体积土壤中的根长, 反映根系对养分获取的能力 The length of roots per unit soil volume, reflects the ability of the roots to acquire nutrients
	根分支强度 Root branching intensity	RBI (cm^-1)	单位2级根长度上的1级根数量, 反映根系从土壤中获取水分和养分的能力 The number of laterals on a given length unit of parent root, reflects the ability of the root to explore the soil for water and nutrients
	根分布深度 Root depth	RD (cm)	反映植物吸收与利用土壤资源的能力 Reflects the ability of the plant to acquire soil resources
形态性状 Morphological trait	根直径 Root diameter	D (mm)	影响根资源获取、生理功能 Affects the root resource acquisition and physiological function
	比根长 Specific root length	SRL (m·g^-1)	单位生物量的根长度, 反映根系吸收水分和养分的能力, 衡量根系的消耗与效益 The length of root per unit dry mass, reflects the potential extent of soil exploration (for nutrients and water) per unit cost (in terms of plant biomass allocation) and measures the root consumption and benefits
	比根面积 Specific root area	SRA (g·cm^-2)	单位生物量的根面积, 反映根系对土壤资源的获取能力 The area of root per unit dry mass, reflects the ability of the root to acquire soil resources
	根组织密度 Root tissue density	RTD (g·cm^-3)	单位体积的根质量, 反映根系资源获取和防御能力 Root mass per unit volume, reflects the root resource acquisition and defense capability
	根干物质含量 Root dry matter content	RDMC (mg·g^-1)	单位鲜质量的根干质量, 反映根系的资源获取能力 The dry mass of root per unit fresh root mass, reflects the ability of root system to acquire soil resources
生理性状 Physiological trait	根寿命 Root lifespan	(d)	单位生物量的根系组织存活的时间, 决定根系养分和碳消耗与循环的速率, 属于硬性状 The survival time of root tissue per unit of biomass, determines the rate at which root nutrients and carbon are consumed and recycled, hard trait
	根系呼吸速率 Root respiration rate	Rr (μmol·g^-1·s^-1)	单位根质量和时间内CO₂通量, 属于硬性状 The flux rate of CO₂ per unit root mass and time, hard trait
	根系分泌速率 Root exudation rate	RER (mg·g^-1·h^-1)	单位根质量和时间内根系分泌碳通量, 属于硬性状 The flux rate of root exudates was calculated by dividing the total carbon content by incubation time and root dry mass, hard trait
	根系磷酸酶活性 Root phosphatase activity	RPA (μmol·g^-1·h^-1)	单位根质量和时间内磷酸单脂酶含量 The content of phosphomonoesterase in per unit root dry mass and time
生物性状 Biotic trait	菌根侵染率 Mycorrhizal fungal colonization	RLC (%)	菌根真菌的侵染比例 The proportion of mycorrhizal colonization
生物性状 Biotic trait	菌丝密度 Hyphal length density	HLD (m·g^-1)	单位土干质量的菌丝长度 The length of fungal hypha per unit of dry soil mass
化学性状 Chemical trait	根碳含量 Root carbon content	RC (mg·g^-1)	单位根干质量的碳含量, 影响根资源获取及代谢速率 The mass of carbon content per root dry mass, affects the root resource acquisition and metabolic rate
化学性状 Chemical trait	根氮含量 Root nitrogen content	RN (mg·g^-1)	单位根干质量的氮含量, 影响根资源获取及代谢速率 The mass of nitrogen content per root dry mass, affects the root resource acquisition and metabolic rate
解剖性状 Anatomical trait	皮层厚度 Cortical thickness	CT (mm)	反映根系对土壤资源的获取能力 Reflects the ability of the root to acquire soil resources
解剖性状 Anatomical trait	中柱直径 Stele diameter	SD (mm)	反映根系对土壤养分的运输能力 Reflects the ability of the root to transport soil resources

性状类型 Type of trait	性状指标 Trait index	缩写(单位) Abbreviation (unit)	描述 Description
构型性状 Architectural trait	根长密度 Root length density	RLD (cm·cm^-3)	单位体积土壤中的根长, 反映根系对养分获取的能力 The length of roots per unit soil volume, reflects the ability of the roots to acquire nutrients
	根分支强度 Root branching intensity	RBI (cm^-1)	单位2级根长度上的1级根数量, 反映根系从土壤中获取水分和养分的能力 The number of laterals on a given length unit of parent root, reflects the ability of the root to explore the soil for water and nutrients
	根分布深度 Root depth	RD (cm)	反映植物吸收与利用土壤资源的能力 Reflects the ability of the plant to acquire soil resources
形态性状 Morphological trait	根直径 Root diameter	D (mm)	影响根资源获取、生理功能 Affects the root resource acquisition and physiological function
	比根长 Specific root length	SRL (m·g^-1)	单位生物量的根长度, 反映根系吸收水分和养分的能力, 衡量根系的消耗与效益 The length of root per unit dry mass, reflects the potential extent of soil exploration (for nutrients and water) per unit cost (in terms of plant biomass allocation) and measures the root consumption and benefits
	比根面积 Specific root area	SRA (g·cm^-2)	单位生物量的根面积, 反映根系对土壤资源的获取能力 The area of root per unit dry mass, reflects the ability of the root to acquire soil resources
	根组织密度 Root tissue density	RTD (g·cm^-3)	单位体积的根质量, 反映根系资源获取和防御能力 Root mass per unit volume, reflects the root resource acquisition and defense capability
	根干物质含量 Root dry matter content	RDMC (mg·g^-1)	单位鲜质量的根干质量, 反映根系的资源获取能力 The dry mass of root per unit fresh root mass, reflects the ability of root system to acquire soil resources
生理性状 Physiological trait	根寿命 Root lifespan	(d)	单位生物量的根系组织存活的时间, 决定根系养分和碳消耗与循环的速率, 属于硬性状 The survival time of root tissue per unit of biomass, determines the rate at which root nutrients and carbon are consumed and recycled, hard trait
	根系呼吸速率 Root respiration rate	Rr (μmol·g^-1·s^-1)	单位根质量和时间内CO₂通量, 属于硬性状 The flux rate of CO₂ per unit root mass and time, hard trait
	根系分泌速率 Root exudation rate	RER (mg·g^-1·h^-1)	单位根质量和时间内根系分泌碳通量, 属于硬性状 The flux rate of root exudates was calculated by dividing the total carbon content by incubation time and root dry mass, hard trait
	根系磷酸酶活性 Root phosphatase activity	RPA (μmol·g^-1·h^-1)	单位根质量和时间内磷酸单脂酶含量 The content of phosphomonoesterase in per unit root dry mass and time
生物性状 Biotic trait	菌根侵染率 Mycorrhizal fungal colonization	RLC (%)	菌根真菌的侵染比例 The proportion of mycorrhizal colonization
生物性状 Biotic trait	菌丝密度 Hyphal length density	HLD (m·g^-1)	单位土干质量的菌丝长度 The length of fungal hypha per unit of dry soil mass
化学性状 Chemical trait	根碳含量 Root carbon content	RC (mg·g^-1)	单位根干质量的碳含量, 影响根资源获取及代谢速率 The mass of carbon content per root dry mass, affects the root resource acquisition and metabolic rate
化学性状 Chemical trait	根氮含量 Root nitrogen content	RN (mg·g^-1)	单位根干质量的氮含量, 影响根资源获取及代谢速率 The mass of nitrogen content per root dry mass, affects the root resource acquisition and metabolic rate
解剖性状 Anatomical trait	皮层厚度 Cortical thickness	CT (mm)	反映根系对土壤资源的获取能力 Reflects the ability of the root to acquire soil resources
解剖性状 Anatomical trait	中柱直径 Stele diameter	SD (mm)	反映根系对土壤养分的运输能力 Reflects the ability of the root to transport soil resources