**7. Conclusions**

By conducting these experiments, several findings were obtained: (1) increase of NO3 – uptake by application of MAA, (2) different effect of MAA dictated by N status, (3) efficient NO3– removal by application of AAF, and (4) true role of MAA in process of NO3– uptake and assimilation.

Both for radish and red pepper, the application of MAA led to significant increase of NO3– uptake and activities of the three enzymes (NR, NiR and GS) of the NO3− assimilatory pathway in solution experiment. These results are different from other researches which inhibition was observed in most case. This difference was caused by two main reasons: (1) that effect of MAA was different to single amino acid, and (2) comparative high level NO3<sup>−</sup> was supplied in these experiments.

In pot experiments, responses to applied MAA were affected by plant species and NO3– level in soil. For radish, application of MAA led to increases of activities of three enzymes, growth, N utilization, and concentrations of proteins, and decrease of NO3– content in plant shoots, when the plants were planted in high NO3– soil. However, in the case that radish was planted in low NO3– soil, activities of the enzymes were decreased by using MAA, and growth, and concentrations of proteins, amino acids, total N and NO3– content were not affected. These phenomena indicate that the effect of MAA is dependent on NO3– level.

**(g m–2) (%)** 

was found in treatment A0, the most removed NO3– was leached (73.7%) and would lead to pollution for groundwater. The application of AAF can enhance NO3– removal rate by planting, and avoid N losses through leaching and runoff due to increases of N utilization

In conclusion, the results of the present experiment suggest that application of amino acid fertilizer can affect activities of three enzymes of N assimilation (NR, NiR and GS) and increase the growth and N assimilation in radish. However, the exact reason for this observation is not known and requires further investigation. The planting of radish proves very effective for nitrate removal in soil by its fast growth and very high biomass production (345.7~404.4 g DW m–2) and N utilization (9.33~14.48 g m–2) in short time (only 35 days in our experiment). Furthermore, the application of amino acid fertilizer can enhance biomass production, N utilization, and concentrations of proteins and amino acids,

By conducting these experiments, several findings were obtained: (1) increase of NO3– uptake by application of MAA, (2) different effect of MAA dictated by N status, (3) efficient NO3– removal by application of AAF, and (4) true role of MAA in process of NO3– uptake

Both for radish and red pepper, the application of MAA led to significant increase of NO3– uptake and activities of the three enzymes (NR, NiR and GS) of the NO3− assimilatory pathway in solution experiment. These results are different from other researches which inhibition was observed in most case. This difference was caused by two main reasons: (1) that effect of MAA was different to single amino acid, and (2) comparative high level NO3<sup>−</sup>

In pot experiments, responses to applied MAA were affected by plant species and NO3– level in soil. For radish, application of MAA led to increases of activities of three enzymes, growth, N utilization, and concentrations of proteins, and decrease of NO3– content in plant shoots, when the plants were planted in high NO3– soil. However, in the case that radish was planted in low NO3– soil, activities of the enzymes were decreased by using MAA, and growth, and concentrations of proteins, amino acids, total N and NO3– content were not affected. These phenomena indicate that the effect of MAA is dependent on

NP 25.2 – 100.0 A0 35.4 26.3 73.7 A1 32.6 44.4 55.6 A2 32.8 39.7 60.3 A3 30.7 41.8 58.2

**Removal rate by plant** 

– removal are showed in Table 23. Even though the highest NO3– removal

**Removal rate by leaching** 

**Treatments** 

The data of NO3

**7. Conclusions** 

and assimilation.

NO3– level.

was supplied in these experiments.

**NO3**

(Table 18) and vegetation cover (Table 19).

and it can reduce N losses through leaching and runoff.

**– removal (0~20cm)** 

Table 23. Effect of amino acid fertilizer on nitrate removal from the soil

With respect to red pepper which was planted in high NO3 – soil, foliar MAA sprays increased activities of the three enzymes, while reduced NO3– content, concentrations of proteins and amino acids, total N and N utilization. Partially different results were found in red pepper which was planted in low NO3– soil, including decreased activities of NiR and GS and increased of NO3 – content in plant shoots by the application of MAA. The reason for these differences is the same to that of radish.

In field experiment of radish, the foliar sprays of AAF increased NO3 – removal rate by planting, and avoid N losses through leaching and runoff due to increases of N utilization and vegetation cover. In addition, the application of AAF enhanced activities of three enzymes, biomass production, and concentrations of proteins and amino acids, reduced NO3 – content in plant shoots. Similarly, for red pepper, the use of AAF led to increase of N utilization. However, decrease of total N content in red pepper plants was found in AAF treatments.

These results of 15N labeled experiments and field experiments suggest that the main role of amino acids on nitrate uptake and assimilation might be relation with the regulation of NO3– uptake and assimilation, but not as sources of reduced nitrogen. In pot experiments, it was indicated that the N utilization of plants was depended on soil NO3 – uptake which was regulated by application of MAA. In field experiment of radish, the increase of N utilization is about 200 times more than N supplied by applying AAF, indicating application of AAF could enhance the ability of uptake and assimilation of inorganic N by plants.

Finally, the effect of amino acids on NO3 – uptake and assimilation was also influenced by stage of plant growth. For leaf radish, response of enzymes activity and yield was not affected by the stage of growth, while N accumulation (total N content) was more sensitive to applied amino acids in vegetative stage than that of young stage. With regard to red pepper, effects of amino acids on enzymes activity and N content in different growth stage were quite similar, while growth (dry biomass) showed to be increased significantly in vegetative stage.

A better understanding of effect of amino acid on process of NO3 – uptake and assimilation will undoubtedly help in developing an approach to improve the management of fertilizer nitrogen and to prevent N loss through leaching or runoff. In the further study, more detailed researches should be carried out to investigate the precise manner by which MAA influences NO3 – uptake and assimilation. The researches will focus on the effect of MAA on NR gene expression and relation between GDH and GS.

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**Section 4** 

**Crop Response to Temperature** 

