ANALYSIS OF PLANT MICRONUTRIENT COMPOSITION USING THE ANE METHOD

Jolanta Korzeniowska, Ewa Stanisławska-Glubiak

ABSTRACT

The authors calculated the total sum of microelements in plants and determined the percentage share of specific elements in this sum according to the ANE method. Then, both the changes of the microelements share in the sum and the changes of absolute microelement concentrations in plant tissues depending on soil pH were investigated. The sample collections of four plant species from the Silesia region, Poland, constituted the research material (156 samples in total). It was found that, in general, the Mn share in the sum decreased and the Fe share increased with increasing pH level. Moreover, the change of micronutrient weight-concentrations in plant tissues, which was caused by the pH changes, did not correspond with the change of the micronutrient relationship in the total sum. This result suggests that the assessment of micronutrient status in plants is not a reliable enough method when basing solely on the absolute weight-concentration in plant tissues.

Key words: ANE method, micronutrients, soil pH.

INTRODUCTION

Investigation of the plant micronutrient composition most often does not take into consideration the relationship between micronutrients, but treats each element separately. Some authors do describe this kind of relationship, but usually only between the chosen pair of microelements. However, they often fail to show its impact on all the others. Some papers broadly describe nutrient connection, usually considering macronutrients only [2,3,4,6,10,17]. Only in a few cases did authors consider micronutrients as well. Gunes et al. studied antagonistic and synergistic relationship among macro and some micronutrients [8]. Bhargava and Raghupathi [1] and Raghupathi et al. [16] developed multivariate diagnosis of nutrient norms for grape and banana concerning not only microelements but also Fe, Mn and Zn.

An interesting interpretation of plant chemical composition, called the ANE (Accumulation Nutrient Elements) method, which is used to judge all nutrient relationships in plants, has been proposed by Ostrowska [14,15]. The ANE method calculates the total sum of elements in plant tissue and determines the percentage share of a specific element in this sum. Macronutrients and micronutrients are summed separately because of the difference in their concentration level in the plant.

The working hypothesis assumed that the changes in micronutrient weight-concentration in plant tissue caused by soil pH changes correspond with the change in the micronutrient relationship in their total sum.

MATERIAL AND METHODS

The research material was composed of four sets of soil and plant samples. They were taken from the Silesia region in Poland. Winter wheat (3 top leaves at ear formation stage), oat (shoots at shooting stage), sugar beet (leaf blades in June to July) and red clover (shoots at the beginning of flowering) were tested. The number of samples in individual collections was 45, 41, 36 and 34, respectively. There were 156 soil samples and 156 plant samples collected in total.

Cu, Fe, Mn and Zn in plant tissue after dry mineralization, and in soil after 1 mol HClˇdm^-3 extraction, were determined with the AAS method. B was determined calorimetrically with curcumin and Mo with the thiocyanate method [12]. Basic soil features were determined, such as the pH value in 1 mol of KClˇdm^-3, content of organic carbon with the Tiurin method [11], and granulometric composition following Casagrande method modified by Prószyński [11].

The general characteristics of sample collections are given in Tables 1 and 2. Absolute microelement weight-concentrations in plant tissues ranged widely (Table 1). There were found considerable differences between particular species, as well as within the same species, caused by different soil conditions such as: pH, granulometric composition, concentration of organic matter and available forms of micronutrients (Table 2). Thus, to calculate the sum of micronutrients, average value of weight-concentrations for particular plant species were used.

To calculate the sum of micronutrients, the ANE, accumulated in dry mass unit of plant, the weight-concentration of each micronutrient was reduced to univalent ions and expressed in mmol(c)^.kg^-1. The ANE value (B + Cu + Fe + Mn + Mo + Zn) was computed using the following formula [15]:

ANE = S Z/z

where:
Z – weight-concentration of micronutrient, mg·kg^-1,
z – atomic weight/ion valence.

The ANE values and the percentage share of individual elements in these values were presented as ring charts, except Mo. The share of Mo in the sum of all micronutrients was too small to be visible on these charts. Therefore, it was shown as a number only.

RESULTS AND DISCUSSION

General characteristics of the Ane value and proportion of micronutrient in tested plants

The ANE value and the percentage share of specific elements in this ANE value differed in tested plants (Fig. 1). The increasing order of the ANE values was: clover<oat<what<beet. Beet leaves revealed 3 times larger ANE value than leaves of oat and clover, and over 2 times larger than leaves of wheat. This result indicated that sugar beet have higher requirements for micronutrients than other plants [5,18].

Iron constituted the largest part of the total sum of micronutrients (50-59%) for wheat, beet and clover. The second large was the Mn share (14-28%). Only in oat was the Mn share larger (47%) than the Fe share (39%), perhaps due to lower pH levels of soils. In Ostrowska’s investigation Mn and Fe were above 60% of the total sum as well [15].

Unexpectedly, a small share of B (11%) in the ANE was observed for beet, even though this crop has high requirements for boron for growth. This result suggests insufficient B supply for the beet collection. However for clover, which has also high requirements for boron, the share of B in ANE was 25%, much higher than for beet. The share of B was only 1-2% for wheat and oat.

Zn share in the total sum of micronutrients did not exceed 10% for all the plants investigated. Cu and Mo were always the smallest part of the ANE, about 1-2% and below 1%, respectively.

Impact of soil pH on the ANE value and micronutrient share in this ANE value

To investigate the pH influence on the relationship between micronutrients in plant tissue, each of four sample collections was further divided into 3 groups with different average pH values. The identical division of each collection was impossible because of various pH ranges in these collections. For instance, while there were 28 soil samples in the oat collection with pH < 5.0, only 3 samples with as low pH could be found in the beet collection. The remaining beet collection samples had a higher pH.

As shown in Figs 2-5, ANE values in plant tissue were always inversely proportional to soil pH. Surely, it was due to increasing micronutrient bioavailability with decreasing soil pH. Mo is an exception here, but the small amount of it did not affect ANE values.

In most cases, the Mn share in the ANE value decreased and Fe share increased with increasing pH, despite lower Mn and Fe bioavailability in natural and calcareous soils in comparison to acidic soils. It is understandable that when the share of one element in sum increases, the share of others must decrease. However, the increase of Fe share at the expense of Mn share can also result from Fe-Mn antagonism [7,9,13].

It was found that both Mn share and Fe share decreased with the pH increase only in clover tissues. Additionally, the share of B doubled. However, the B share did not change as significantly for any other plant, and the direction of these changes was not as obvious. The increase in pH had the smallest influence on the Cu and Zn share in the total sum of micronutrients for all the tested plants.

It is important to notice that Mo represents a very small percentage share in the ANE value (0.02-0.14%). In spite of small Mo share, its change in relation to pH increase was most significant in comparison to other micronutrients. For example, in oat leaves, Mo share was 3 times greater at pH > 5.5 then at pH < 4.2.

Comparing the changes of micronutrient relationships in ANE (Fig. 2 and 3) with changes of absolute micronutrient weight-concentrations in plant tissues (Tables 3 and 4), it was clear that the direction of these changes, most often, was not compatible. Thus, when the share of Fe increased in the sum of micronutrients, most often the increase in the weight-concentration in leaves was not observed. Moreover, even though the share of B doubled in reference to pH change ranging from 4.8 to 6.4, the B weight-concentration in clover tissue decreased. There was also a similar lack of correspondence for other micronutrients, except Mn. A decrease in the Mn share in the ANE always corresponded with a decrease in the Mn weight-concentration in plants. This is perhaps due to the decrease in Mn bioavailability with corresponding pH increase.

Perhaps the most interesting observation to come from this study is the discrepancy between the changes of micronutrient share in total sum and the changes in micronutrient weight-concentration in plant tissues. This result suggests that the assessment of micronutrient status in plants is not reliable enough when drawing solely on the absolute weight-concentration in plant tissues. Undeniably, the relationship between micronutrients in plants should also be used in such an assessment.

CONCLUSIONS

1. The change of soil pH influenced both the sum of micronutrients accumulated in plants and the percentage share of specific micronutrients in this sum.

2. The share of Mn, Fe and Mo in total sum of micronutrients varied significantly depending on pH level, while the share of Zn and Cu was more stable.

3. Along with pH increase, the Fe share in the ANE value usually increased as well, while Mn share decreased. The direction of change of other micronutrient share could not be as clearly defined.

4. The change of micronutrient weight-concentrations in plant tissues, caused by pH changes, did not correspond with the change of micronutrient relationships in the ANE. Frequently, the increase in weight-concentration was accompanied by the decrease in share in the sum, and vice versa.

5. Besides the absolute weight-concentration of micronutrients in plant tissues, the relationship between these micronutrients should be used to assess micronutrient status in plants.

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