Contrasting responses of root morphology and root-exuded organic acids to low phosphorus availability in three important food crops with divergent root traits

Early root traits and allometrics of wheat are important for competition and use of resources. They are under-utilized in research and un-explored in many ancient wheats. This is especially true for the rhizosheath emerging from root-soil interactions. We investigated root morphology, root/shoot relations and the amount of rhizosheath of four tetrapoid wheat seedlings (30 days after emergence): the italian landrace Saragolle Lucana and modern varieties Creso, Simeto and Ciclope, and tested the hypothesis that inoculation with Trichoderma harzianum T-22 (T-22) enhances rhizosheath formation and affects wheat varieties differently. Overall growth of non-inoculated plants showed different patterns in wheat varieties, with Saragolle and Ciclope at the two extremes: Saragolle invests in shoot rather than root mass, and in the occupation of space with highest (p < 0.05) shoot height to the uppermost internode (5.02 cm) and length-to-mass shoot (97.8 cm g−1) and root (more than 140 m g−1) ratios. This may be interpreted as maximizing competition for light but also as a compensation for low shoot efficiency due to the lowest (p < 0.05) recorded values of optically-measured chlorophyll content index (22.8). Ciclope invests in biomass with highest shoot (0.06 g) and root (0.04 g) mass and a thicker root system (average diameter 0.34 mm vs. 0.29 in Saragolle) as well as a highest root/shoot ratio (0.95 g g−1 vs. 0.54 in Saragolle). Rhizosheath mass ranged between 22.14 times that of shoot mass in Ciclope and 43.40 in Saragolle (different for p < 0.05). Inoculation with Trichoderma increased the amount of rhizosheath from 9.4% in Ciclope to 36.1% in Simeto and modified root architecture in this variety more than in others. Ours are the first data on roots and seedling shoot traits of Saragolle Lucana and of Trichoderma inoculation effects on rhizosheath. This opens to new unreported interpretations of effects of Trichoderma inoculation on improving plant growth.

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Potassium Improves Drought Stress Tolerance in Plants by Affecting Root Morphology, Root Exudates and Microbial Diversity

Metabolites ◽

10.3390/metabo11030131 ◽

2021 ◽

Vol 11 (3) ◽

pp. 131

Author(s):

Qiwen Xu ◽

Hao Fu ◽

Bo Zhu ◽

Hafiz Athar Hussain ◽

Kangping Zhang ◽

...

Keyword(s):

Microbial Community ◽

Drought Stress ◽

Organic Acids ◽

Microbial Diversity ◽

Root Exudates ◽

Root Morphology ◽

Diversity Index ◽

Equation Modeling ◽

Available Phosphorus ◽

Underground Part

Potassium (K) reduces the deleterious effects of drought stress on plants. However, this mitigation has been studied mainly in the aboveground plant pathways, while the effect of K on root-soil interactions in the underground part is still underexplored. Here, we conducted the experiments to investigate how K enhances plant resistance and tolerance to drought by controlling rhizosphere processes. Three culture methods (sand, water, and soil) evaluated two rapeseed cultivars’ root morphology, root exudates, soil nutrients, and microbial community structure under different K supply levels and water conditions to construct a defensive network of the underground part. We found that K supply increased the root length and density and the organic acids secretion. The organic acids were significantly associated with the available potassium decomposition, in order of formic acid > malonic acid > lactic acid > oxalic acid > citric acid. However, the mitigation had the hormesis effect, as the appropriate range of K facilitated the morphological characteristic and physiological function of the root system with increases of supply levels, while the excessive input of K could hinder the plant growth. The positive effect of K-fertilizer on soil pH, available phosphorus and available potassium content, and microbial diversity index was more significant under the water stress. The rhizosphere nutrients and pH further promoted the microbial community development by the structural equation modeling, while the non-rhizosphere nutrients had an indirect negative effect on microbes. In short, K application could alleviate drought stress on the growth and development of plants by regulating the morphology and secretion of roots and soil ecosystems.

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The contribution of lateral rooting to phosphorus acquisition efficiency in maize (Zea mays) seedlings

Functional Plant Biology ◽

10.1071/fp04046 ◽

2004 ◽

Vol 31 (10) ◽

pp. 949 ◽

Cited By ~ 136

Author(s):

Jinming Zhu ◽

Jonathan P. Lynch

Keyword(s):

Growth Rate ◽

Lateral Root ◽

Root Respiration ◽

Lateral Roots ◽

Biomass Accumulation ◽

Phosphorus Availability ◽

Phosphorus Acquisition ◽

Relative Growth ◽

Phosphorus Stress ◽

Low Phosphorus

Low soil phosphorus availability is a primary constraint for plant growth in many terrestrial ecosystems. Lateral root initiation and elongation may play an important role in the uptake of immobile nutrients, such as phosphorus, by increasing soil exploration and phosphorus solubilisation. The overall objective of this study was to assess the value of lateral rooting for phosphorus acquisition through assessment of the ‘benefit’ of lateral rooting for phosphorus uptake and the ‘cost’ of lateral roots in terms of root respiration and phosphorus investment at low and high phosphorus availability. Five recombinant inbred lines (RILs) of maize derived from a cross between B73 and Mo17 with contrasting lateral rooting were grown in sand culture in a controlled environment. Genotypes with enhanced or sustained lateral rooting at low phosphorus availability had greater phosphorus acquisition, biomass accumulation, and relative growth rate (RGR) than genotypes with reduced lateral rooting at low phosphorus availability. The association of lateral root development and plant biomass accumulation under phosphorus stress was not caused by allometry. Genotypes varied in the phosphorus investment required for lateral root elongation, owing to genetic differences in specific root length (SRL, which was correlated with root diameter) and phosphorus concentration of lateral roots. Lateral root extension required less biomass and phosphorus investment than the extension of other root types. Relative growth rate was negatively correlated with specific root respiration, supporting the hypothesis that root carbon costs are an important aspect of adaptation to low phosphorus availability. Two distinct cost–benefit analyses, one with phosphorus acquisition rate as a benefit and root respiration as a cost, the other with plant phosphorus accumulation as a benefit and phosphorus allocation to lateral roots as a cost, both showed that lateral rooting was advantageous under conditions of low phosphorus availability. Our data suggest that enhanced lateral rooting under phosphorus stress may be harnessed as a useful trait for the selection and breeding of more phosphorus-efficient maize genotypes.

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