Do plants use root-derived proteases to promote the uptake of soil organic nitrogen?

Abstract Aims The capacity of plant roots to directly acquire organic nitrogen (N) in the form of oligopeptides and amino acids from soil is well established. However, plants have poor access to protein, the central reservoir of soil organic N. Our question is: do plants actively secrete proteases to enhance the breakdown of soil protein or are they functionally reliant on soil microorganisms to undertake this role? Methods Growing maize and wheat under sterile hydroponic conditions with and without inorganic N, we measured protease activity on the root surface (root-bound proteases) or exogenously in the solution (free proteases). We compared root protease activities to the rhizosphere microbial community to estimate the ecological significance of root-derived proteases. Results We found little evidence for the secretion of free proteases, with almost all protease activity associated with the root surface. Root protease activity was not stimulated under N deficiency. Our findings suggest that cereal roots contribute one-fifth of rhizosphere protease activity. Conclusions Our results indicate that plant N uptake is only functionally significant when soil protein is in direct contact with root surfaces. The lack of protease upregulation under N deficiency suggests that root protease activity is unrelated to enhanced soil N capture.

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The Potential Availability of Organic Nitrogen Fractions in Some West Indian Soils

Experimental Agriculture ◽

10.1017/s0014479700004191 ◽

1968 ◽

Vol 4 (3) ◽

pp. 193-201 ◽

Cited By ~ 9

Author(s):

I. S. Cornforth

Keyword(s):

Organic Nitrogen ◽

N Uptake ◽

Acid Soils ◽

West Indian ◽

Greenhouse Experiment ◽

Organic N ◽

Available N ◽

Indian Soils ◽

Potential Availability ◽

Hydrolysable N

SummaryThe effect of four crops of maize on the distribution of organic nitrogen in ten West Indian soils, given either lime, P, K, Mg and trace elements or no fertilizers, was studied in a greenhouse experiment. The soils were also analysed for ‘available N’ by incubation and chemical methods. Variations in the redistribution of organic N fractions during the greenhouse experiment did not permit conclusions to be drawn on the source of N used by the maize, although the amount of hydrolysable N, particularly hexosamine, amino and hydroxy-amino N, in the initial samples was closely related to N uptake. Part of the chemically stable, non-hydrolysable organic N was broken down by soil organisms during the experiment; this was increased by liming acid soils.

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Soil as a potential source of nitrogen for mat-forming lichens

Canadian Journal of Botany ◽

10.1139/b03-144 ◽

2004 ◽

Vol 82 (1) ◽

pp. 145-149 ◽

Cited By ~ 15

Author(s):

Christopher J Ellis ◽

Peter D Crittenden ◽

Charles M Scrimgeour

Keyword(s):

Field Experiment ◽

Soil Nutrients ◽

Vascular Plants ◽

Organic Nitrogen ◽

N Uptake ◽

Soil Surface ◽

Organic N ◽

Soil N ◽

Potential Source ◽

Efficient Uptake

A field experiment is described, the aim of which was to assess the extent of nitrogen (N) movement from heathland soil upwards into terricolous mat-forming lichens. A molten agar solution of either 15N-labelled glycine or 15N-labelled ammonium (as NH4Cl) was injected onto the soil surface beneath undisturbed cushions of Cladonia por tentosa (Dufour) Coem. Lichen thalli were recovered after 9 months and analysed for 15N content. There was no evidence of 15N uptake by the lichen, though 15N was taken up by vascular plants rooted beneath the lichen cushions. The results suggest that C. portentosa does not compete effectively for soil N. This refutes the conclusions of previous studies, which inferred the efficient uptake of soil organic N by mat-forming lichens based on values of δ15N.Key words: ammonium, lichens, 15N, organic nitrogen, soil nutrients.

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Identification of Soil Organic Nitrogen Substance Acting as Indicator of Response of Cocoa Plants to Nitrogen Fertilizer

Pelita Perkebunan (a Coffee and Cocoa Research Journal) ◽

10.22302/iccri.jur.pelitaperkebunan.v24i2.98 ◽

2008 ◽

Vol 24 (2) ◽

Author(s):

John Bako Baon

Keyword(s):

Theobroma Cacao ◽

Organic Nitrogen ◽

Growth Parameters ◽

Dry Weight ◽

N Fertilizer ◽

Organic N ◽

Soil Organic Nitrogen ◽

Hydrolysable N ◽

Stem Leaf ◽

N Fractions

An indicator needed for estimating the presence of response of cocoa (Theobroma cacao) trees to nitrogen (N) fertilizer has been well understood, however there is still little progress on the work on identification of organic N fraction which regulates the response of cocoa to N fertilizer. The objective of this study is to identify a fraction of soil organic N which is very closely related with degree of cocoa response to N fertilizer. Hydrolyses were performed on soil samples derived from 23 sites of cocoa plantations distributed both in Banyuwangi district (12 sites) and in Jember district (11 sites). Analysis of organic N fractions consisted of total hydrolysable N, ammonium N, amino sugar N, amino acid N and combinations of those fractions. To investigate the level of cocoa plants response to N fertilizer, seedlings of cocoa were planted in plastic pots treated with and without urea as source of N. Degree of response of cocoa plants to N fertilizer was measured based on growth parameters, such as plant height, leaf number, stem girth, fresh weight of stem, leaf and shoot; and dry weight of stem, leaf and shoot. Results of this study showed that biggest response of cocoa was shown by dry weight of leaf at the level of 29,22% (in the range of -17,43% – 95,98%), whereas the smallest response was shown by stem dry weight at the level of -1,04 (in the range of -26,16 – 47,54). From those of organic N fractions analyzed, only N ammonium did not show any significant correlations with all the growth parameters observed. Leaf dry weight was the most closely related parameter with nearly all organic N fractions followed by shoot dry weight and stem girth. The soil organic N fraction which had very significant relation with cocoa plant response was total hydrolysable N. Using the method of Cate-Nelson, it was revealed that cocoa gardens contain total hydrolysable N less than 1273 mg/kg were classified as responsive to N fertilizer.Key words: plant response, Theobroma cacao, soil organic nitrogen, N fertilizer, soil testing, fertilization, soil variability, soil hydrolysis

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Ectomycorrhizal Fungal Protein Degradation Ability Predicted by Soil Organic Nitrogen Availability

Applied and Environmental Microbiology ◽

10.1128/aem.03191-15 ◽

2015 ◽

Vol 82 (5) ◽

pp. 1391-1400 ◽

Cited By ~ 13

Author(s):

Francois Rineau ◽

Jelle Stas ◽

Nhu H. Nguyen ◽

Thomas W. Kuyper ◽

Robert Carleer ◽

...

Keyword(s):

Organic Matter ◽

Protein Degradation ◽

Protease Activity ◽

Nitrogen Availability ◽

N Uptake ◽

Organic N ◽

Content Type ◽

N Source ◽

Ecm Fungi

ABSTRACTIn temperate and boreal forest ecosystems, nitrogen (N) limitation of tree metabolism is alleviated by ectomycorrhizal (ECM) fungi. As forest soils age, the primary source of N in soil switches from inorganic (NH4+and NO3−) to organic (mostly proteins). It has been hypothesized that ECM fungi adapt to the most common N source in their environment, which implies that fungi growing in older forests would have greater protein degradation abilities. Moreover, recent results for a model ECM fungal species suggest that organic N uptake requires a glucose supply. To test the generality of these hypotheses, we screened 55 strains of 13Suillusspecies with different ecological preferences for theirin vitroprotein degradation abilities.Suillusspecies preferentially occurring in mature forests, where soil contains more organic matter, had significantly higher protease activity than those from young forests with low-organic-matter soils or species indifferent to forest age. Within species, the protease activities of ecotypes from soils with high or low soil organic N content did not differ significantly, suggesting resource partitioning between mineral and organic soil layers. The secreted protease mixtures were strongly dominated by aspartic peptidases. Glucose addition had variable effects on secreted protease activity; in some species, it triggered activity, but in others, activity was repressed at high concentrations. Collectively, our results indicate that protease activity, a key ectomycorrhizal functional trait, is positively related to environmental N source availability but is also influenced by additional factors, such as carbon availability.

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Root-Derived Proteases as a Plant Tool to Access Soil Organic Nitrogen; Current Stage of Knowledge and Controversies

Plants ◽

10.3390/plants10040731 ◽

2021 ◽

Vol 10 (4) ◽

pp. 731

Author(s):

Bartosz Adamczyk

Keyword(s):

Cropping Systems ◽

N Uptake ◽

Organic N ◽

Inorganic N ◽

Available N ◽

Plant Nitrogen ◽

N Cycle ◽

Soil Organic Nitrogen ◽

Use Efficiency ◽

N Pool

Anthropogenic deterioration of the global nitrogen (N) cycle emerges mainly from overuse of inorganic N fertilizers in nutrient-limited cropping systems. To counteract a further dysregulation of the N cycle, we need to improve plant nitrogen use efficiency. This aim may be reached via unravelling all plant mechanisms to access soil N, with special attention to the dominating high-molecular-mass N pool. Traditionally, we believe that inorganic N is the only plant-available N pool, however, more recent studies point to acquisition of organic N compounds, i.e., amino acids, short peptides, and proteins. The least known mechanism of plants to increase the N uptake is a direct increase of soil proteolysis via root-derived proteases. This paper provides a review of the knowledge about root-derived proteases and also controversies behind this phenomenon.

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Growth, Mineral Nutrients, Photosynthesis and Related Physiological Parameters of Citrus in Response to Nitrogen Deficiency

Agronomy ◽

10.3390/agronomy11091859 ◽

2021 ◽

Vol 11 (9) ◽

pp. 1859

Author(s):

Wei-Tao Huang ◽

Yi-Zhi Xie ◽

Xu-Feng Chen ◽

Jiang Zhang ◽

Huan-Huan Chen ◽

...

Keyword(s):

N Uptake ◽

Nutrient Balance ◽

Photosynthetic Pigment ◽

Nitrogen Deficiency ◽

Photosynthetic Electron Transport ◽

Dry Weight ◽

Root Surface ◽

Co2 Assimilation ◽

N Concentration ◽

N Deficiency

Limited data are available on the physiological responses of Citrus to nitrogen (N) deficiency. ‘Xuegan’ (Citrus sinensis (L.) Osbeck) and ‘Shantian pummelo’ (Citrus grandis (L.) Osbeck) seedlings were fertilized with nutrient solution at a N concentration of 0, 5, 10, 15 or 20 mM for 10 weeks. N deficiency decreased N uptake and N concentration in leaves, stems and roots and disturbed nutrient balance and homeostasis in plants, thus inhibiting plant growth, as well as reducing photosynthetic pigment levels and impairing thylakoid structure and photosynthetic electron transport chain (PETC) in leaves, hence lowering CO2 assimilation. The imbalance of nutrients intensified N deficiency’s adverse impacts on biomass, PETC, CO2 assimilation and biosynthesis of photosynthetic pigments. Citrus displayed adaptive responses to N deficiency, including (a) elevating the distributions of N and other elements in roots, as well as root dry weight (DW)/shoot DW ratio and root-surface-per-unit volume and (b) improving photosynthetic N use efficiency (PNUE). In general, N deficiency had less impact on biomass and photosynthetic pigment levels in C. grandis than in C. sinensis seedlings, demonstrating that the tolerance of C. grandis seedlings to N deficiency was slightly higher than that of C. sinensis seedlings, which might be related to the higher PNUE of the former.

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Genotypic Difference in the Responses to Nitrogen Fertilizer Form in Tibetan Wild and Cultivated Barley

Plants ◽

10.3390/plants10030595 ◽

2021 ◽

Vol 10 (3) ◽

pp. 595

Author(s):

Shama Naz ◽

Qiufang Shen ◽

Jonas Lwalaba Wa Lwalaba ◽

Guoping Zhang

Keyword(s):

Wild Barley ◽

Growth Parameters ◽

Inorganic Nitrogen ◽

N Uptake ◽

Total Soluble Protein ◽

Organic N ◽

Genotypic Difference ◽

N Availability ◽

Tibetan Wild Barley ◽

Cultivated Barley

Nitrogen (N) availability and form have a dramatic effect on N uptake and assimilation in plants, affecting growth and development. In the previous studies, we found great differences in low-N tolerance between Tibetan wild barley accessions and cultivated barley varieties. We hypothesized that there are different responses to N forms between the two kinds of barleys. Accordingly, this study was carried out to determine the response of four barley genotypes (two wild, XZ16 and XZ179; and two cultivated, ZD9 andHua30) under 4Nforms (NO3−, NH4+, urea and glycine). The results showed significant reduction in growth parameters such as root/shoot length and biomass, as well as photosynthesis parameters and total soluble protein content under glycine treatment relative to other N treatments, for both wild and cultivated barley, however, XZ179 was least affected. Similarly, ammonium adversely affected growth parameters in both wild and cultivated barleys, with XZ179 being severely affected. On the other hand, both wild and cultivated genotypes showed higher biomass, net photosynthetic rate, chlorophyll and protein in NO3− treatment relative to other three N treatments. It may be concluded that barley undisputedly grows well under inorganic nitrogen (NO3−), however in response to the organic N wild barley prefer glycine more than cultivated barely.

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Tree species rather than type of mycorrhizal association drives inorganic and organic nitrogen acquisition in tree-tree interactions

Tree Physiology ◽

10.1093/treephys/tpab059 ◽

2021 ◽

Author(s):

Robert Reuter ◽

Olga Ferlian ◽

Mika Tarkka ◽

Nico Eisenhauer ◽

Karin Pritsch ◽

...

Keyword(s):

Tree Species ◽

Mycorrhizal Fungi ◽

Prunus Avium ◽

N Uptake ◽

Organic N ◽

Acer Pseudoplatanus ◽

N Sources ◽

Mycorrhizal Association ◽

N Acquisition ◽

Inorganic And Organic

Abstract Mycorrhizal fungi play an important role for the nitrogen (N) supply of trees. The influence of different mycorrhizal types on N acquisition in tree-tree interactions is, however, not well understood, particularly with regard to the competition for growth-limiting N. We studied the effect of competition between temperate forest tree species on their inorganic and organic N acquisition in relation to their mycorrhizal type (i.e., arbuscular mycorrhiza or ectomycorrhiza). In a field experiment, we quantified net N uptake capacity from inorganic and organic N sources using 15N/13C stable isotopes for arbuscular mycorrhizal tree species (i.e., Acer pseudoplatanus L., Fraxinus excelsior L., and Prunus avium L.) as well as ectomycorrhizal tree species (i.e., Carpinus betulus L., Fagus sylvatica L., and Tilia platyphyllos Scop.). All species were grown in intra- and interspecific competition (i.e., monoculture or mixture). Our results showed that N sources were not used complementarily depending on a species´ mycorrhizal association, but their uptake rather depended on the competitor indicating species-specific effects. Generally, ammonium was preferred over glutamine and glutamine over nitrate. In conclusion, our findings suggest that inorganic and organic N acquisition of the studied temperate tree species is less regulated by mycorrhizal association, but rather by the availability of specific N sources in the soil as well as the competitive environment of different tree species.

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