The studies discussed above showed that the physiological activity of humic substances is also manifested in the case where the plant receives part of the humic acid molecule that is part of its core. However, the simple statement of this fact in itself does not say anything about the changes in the plant's metabolic processes that lead to a positive agronomic effect, and, in essence, does not explain the nature of the physiological action of humic acids.
In order to establish in what direction the physiological action of humic acids manifests itself, we set the goal of tracking shifts in plant metabolism under the influence of these compounds. This is especially convenient to observe during the development of sprouts, since at the initial stages of plant development they most actively react to the physiological action of humic acids.
Experimental methodology
The first thing that seemed important to find out was whether the sprouting plants use the humic substances of the environment for their life activity and what is the nature of their impact on the body. It was most convenient to study this issue on potatoes, since the sprouts of this crop feed on the ready organic substances of the tuber for a long time and, it would seem, the need for their inflow from the outside to the sprouting eye is excluded.
For this purpose, a laboratory experiment was set up in an aquatic culture with potatoes. In order to avoid secondary processes of synthesis during the absorption of mineral substances by the roots, the experiment was carried out on distilled water. Thus, any deviations in development from the control plants had to be attributed only to those organic substances that were introduced into the aquatic environment.
In this experiment, potassium humate obtained from peat using the generally accepted method was tested. The tubers were germinated in the light from April 29 to June 3. By this time, well-formed sprouts 2-2.5 cm long had developed from the apical eyes. Further germination was carried out in vessels on water and on a 0.001% solution of potassium humate. For this, some of the tubers were placed on a honeycomb plate that was in contact with the surface of the water in the vessel. From the base of the eyes, filter paper wicks were lowered through the cells, through which water was supplied to the rudimentary root tubercles. After the roots reached the water, the wicks were removed. The same was done with the other part of the tubers, but instead of water, a solution of potassium humate was used for germination. In both cases, the tubers were exposed to air the entire time.
1 - control (water), 2 - potassium humate solution (0.001%)
Experiment results
Figure 2 shows experimental plants on the fifteenth day of germination. The stronger growth of buds and especially roots in the variant with potassium humate is noteworthy. The average weight of the bud and roots per tuber here was 6.66 and 1.52 g, while in the control it was 4.88 and 0.86 grams, respectively.
It is especially interesting to note the difference in the lifespan of the experimental plants. Thus, in the control variant, the growth of roots and buds stopped early, and on June 18, i.e. 15 days after setting up for germination, the experiment had to be liquidated due to the obvious necrotic state of the plants. In the variant with potassium humate, such signs appeared only on June 28, i.e. nine days later.
Biochemical changes
Biochemical studies have shown that, compared to the initial data (Table 4), hydrolytic processes predominate in the tubers of both variants during the germination period. They are accompanied by the movement of nutrients into the growing organs.
| Dry matter | Ash | Nitrogen | Phosphorus | Starch | Ascorbic acid, mg% | Peroxidase activity, mg Co | |
|---|---|---|---|---|---|---|---|
| Tuber | Peephole | ||||||
| 24.05 | 1.26 | 0.339 | 0.133 | 13.6 | 4.96 | 2.6 | 38 |
Thus, by the end of the experiment, the ash and dry matter reserves in the tubers had decreased by an average of 20%. The content of optically active substances, the products of carbohydrate hydrolysis, had increased sharply (by 23%). Peroxidase activity increased very quickly in the growing organs. In particular, in the eye of the original tuber, the peroxidase activity was 39 mg Co per 1 g of substance, a week after germination it was already equal to 86.6 mg Co, and a week later it reached 106 mg Co. At the same time, the enzyme activity in the tuber remained almost unchanged and was only 2.1 mg Co.
Distribution of nitrogen and phosphorus
The issue of tuber nitrogen and phosphorus mobilization under the influence of potassium humate was studied in more detail (Tables 5, 6, 7, 8). The analysis data show the distribution of elements among plant organs, as it developed by the end of the experiment (15 days after germination). These data show that during the germination period, the potato root system is greatly enriched with phosphorus and especially nitrogenous substances due to the influx of plastic substances from the mother tuber.
| Plant organs | Phosphorus content on a wet basis, % | Total phosphorus content, mg | Distribution of phosphorus between plant organs (in % of total) | |||
|---|---|---|---|---|---|---|
| Water | Potassium humate | Water | Potassium humate | Water | Potassium humate | |
| Tuber | 0.098 | 0.105 | 69.25 | 75.84 | 84.5 | 85.2 |
| Sprout | 0.216 | 0.159 | 10.76 | 10.59 | 13.0 | 12.0 |
| Root | 0.237 | 0,170 | 2.04 | 2.58 | 2.5 | 2.8 |
| Total | 82.05 | 89.01 | 100 | 100 | ||
| Plant organs | Phosphorus content on a wet basis, % | Total phosphorus content, mg | Distribution of phosphorus between plant organs (in % of total) | |||
|---|---|---|---|---|---|---|
| Water | Potassium humate | Water | Potassium humate | Water | Potassium humate | |
| Tuber | 0.383 | 0.338 | 270.63 | 244.14 | 84.9 | 82.2 |
| Sprout | 0,620 | 0.535 | 30.38 | 35.63 | 9.7 | 11.9 |
| Root | 2,010 | 1,140 | 17.29 | 17.32 | 5.4 | 5.9 |
| Total | 318.8 | 297.1 | 100 | 100 | ||
| Plant organs | Phosphorus content on a wet basis, % | Total phosphorus content, mg | Distribution of phosphorus between plant organs (in % of total) | |||
|---|---|---|---|---|---|---|
| Water | Potassium humate | Water | Potassium humate | Water | Potassium humate | |
| Tuber | 0.026 | 0.026 | 18.37 | 18.78 | 79.5 | 76.5 |
| Sprout | 0.097 | 0.063 | 3.83 | 4.20 | 16.6 | 17.1 |
| Root | 0.104 | 0.104 | 0.89 | 1.58 | 3.9 | 6.4 |
| Total | 23.09 | 24.56 | 100 | 100 | ||
| Plant organs | Phosphorus content on a wet basis, % | Total phosphorus content, mg | Distribution of phosphorus between plant organs (in % of total) | |||
|---|---|---|---|---|---|---|
| Water | Potassium humate | Water | Potassium humate | Water | Potassium humate | |
| Tuber | 0.072 | 0.079 | 50.88 | 57.06 | 86.3 | 88.5 |
| Sprout | 0.139 | 0.096 | 6.93 | 6.39 | 11.7 | 9.9 |
| Root | 0.133 | 0.066 | 1.15 | 1.00 | 2.0 | 1.6 |
| Total | 58.96 | 64.45 | 100 | 100 | ||
The influence of humate on the distribution of elements
The effect of potassium humate on the distribution of common forms of nitrogen and phosphorus is clearly visible only on the sprout. At the same time, the flow of nitrogen-containing substances from the tuber to the sprout increases under its influence, while phosphorus, on the contrary, decreases somewhat. It should be borne in mind, however, that the lower phosphorus content in the sprout for potassium humate is due to the form associated with protein. The content of physiologically active forms of phosphorus does not decrease, and in the roots it even increases sharply. This is clearly visible if we calculate the ratio of the form soluble in trichloroacetic acid to protein phosphorus (Table 9).
| Parts of a plant | Water | Potassium humate |
|---|---|---|
| Tuber | 0.36 | 0.33 |
| Sprout | 0.69 | 0.66 |
| Root | 0.78 | 1.58 |
Peroxidase activity
The high mobility of phosphoric acid in the roots is obviously related to the biological significance of this organ for the entire organism and indicates the intensity of the oxidation-reduction processes occurring there. Indeed, a special study (Table 10) noted a direct connection between peroxidase activity and the content of mobile phosphorus in plant organs.
| Parts of a plant | Water | Potassium humate |
|---|---|---|
| Tuber | 2.12 | 4.0 |
| Sprout | 106.0 | 140.0 |
| Root | 212.0 | --- |
Conclusions
Thus, the obtained material gives grounds to believe that humic substances of peat are absorbed by potatoes in the early period. Considering their close chemical and genetic similarity with soil organic substances, it can be considered that the consumption of humic substances is the same natural necessity developed by the plant in the process of evolution, as the perception of mineral salts.