ENZYMATIC ACTIVITY OF FOREST LUVISOLS

Ewa Błońska, Jarosław Lasota
Department of Forest Soils, Krakow Agriculture University

ABSTRACT

The aim of this study was to determine the dehydrogenases and urease activity in forest luvisols of various fertility and plant community on them. It attempts to find out whether the conditions of occurrence of the lessivage process relation exist between soil biological activity expressed as enzymatic activity and their physico-chemical properties. Dehydrogenases and urease activity varied across the subtypes of luvisols and proved to be a better parameter differentiating the particular subtypes of soils compared to the physico-chemical properties. The lower enzymatic activity of hypocambic luvisols made of boulder clay, compared with the activity of enzymes in the haplic luvisols, implies a significant effect of particle size on the biological activity of forest soils, shown previously in bibliography. Studies confirm that the enzymatic activity reflects initial imperceptible changes in the horizon of humus as a result of the impact of vegetation.

Key words: enzymatic activity, dehydrogenases, urease, forest soil, luvisols.

INTRODUCTION

Luvisols occupy 500–600 million hectares, mainly in temperate regions [17]. The process of lessivage involves the movement of fine particles of clay from the upper to the deeper horizons of the soil profile. In subsequent stages the partially soluble salts, free iron and aluminum  are moved. The result of these processes is a depletion of surface horizons and formation of the horizon of luvic Eet and enriched horizons of  argic Bt [12].

Polish forest soils classification [12] distinguishes four subtypes of luvisols, which are formated with different glacial boulder clay, dust of different origins (loess, water dust origin), sandy loam and  occasionally clay.

The bio-physicochemical properties are conditioned not only by the soil parent material and climatic conditions, but also the methods of soil management. In forest soils one of the basic factors affecting the properties of the soil profile is the forest stand species composition [9].

The aim of this study was determination of dehydrogenases and urease activity in forest luvisols with different fertility and plant community on them. This paper attempts to determine whether the conditions of occurrence of the lessivage process relation exist between soil biological activity expressed as enzymatic activity and their physico-chemical properties. Efforts were made to determine how vegetation affects the enzymatic activity of forest luvisols.

METHODS

Ten sample plots have been selected for the research, localized in forest reserves in the Polish lowland and upland. The research concerned forest peat soils in haplic luvisols (6 plots), cambic luvisols (2 plots)  and stagnic luvisols (2 plots). The cambic luvisols and stagnic luvisols represent a smaller number of samples because there are fewer than haplic luvisols in forest areas. At each sample plot a detailed description of soil profile was carried out, samples were taken from each genetic horizon in order to perform the basic markings of the soil properties. Soil reaction was marked in the samples using potentiometric method in water and 1M KCl, hydrolytic acidity was marked with Kappen method, exchangeable acidity with Sokolov method, general nitrogen content and carbon content was marked using the LECO determinator, with calculating C/N ratio, alkaline cation content in 1M ammonium acetate with calculation of the degree of soil saturation with alkaline cations (V%), available phosphorus with Bray–Kurtz method.

For determination of enzymatic activity fresh samples of natural moisture were taken, constituting collective sample of the soil from the pit and from 4 places around it. Enzymatic activity was marked at the first genetic horizon of peat soils (0–20 cm on average). Dehydrogenase activity was marked with Lenhard's method according to the Casidy et al procedure (1964) [2], expressing their activity in triphenyl formazan milligrams (TFF) to 100g of soil within 24 hours. Urease activity was marked with Tabatabai and Bremner method (1972) [2],  expressing it in µg N-NH₄ for 1 g of soil during 2 hours.

RESULTS

Luvisols

The haplic luvisols are diagnosed at six research plots, accompanied by community  of Tilio- Tilio-Carpinetum  typicum, Stellario-Carpinetum and Galio odorati-Fagetum related mainly to eutrophic upland broadleaf forest sites and broadleaf forest sites. In one case, the community was described as Luzulo pilosae-Fagetum. The analyzed haplic luvisols evolved on  boulder clay or loess compositions.

The cambic luvisols formed mesotrophic mixed broadleaf forest sites with Tilio-Carpinetum calamagrostietosum and Luzulo pilosae-Fagetum community. Described soils  are developed on stronger sandy boulder clay.

The stagnic luvisols developed on the boulder sands, formed a strong fresh forest habitat  with the Galio odorati-Fagetum community and moist mixed forest with a Tilio-Carpinetum abietetosum community.

Physical and chemical properties

The highest average pH in H₂O in the surface horizons were characterized haplic luvisols 4.69 while the cambic luvisols  had the lowest 4.01. These subtypes of luvisols showed a similar degree of decomposition of organic matter, which is expressesed by the ratio C / N on 18–19 level. The highest average organic carbon content of soil 4.12%  was shown cambic luvisols, the stagnic luvisols had the lowest 2.98%. Horizontal surfaces of cambic luvisols were characterized by the highest average total nitrogen content of 0.22%, the lowest was in stagnic luvisols 0.16%. Luvisols subtypes studied were varied in the abundance of silt expressed in kg·1,5m^-3. The haplic luvisols showed the abundance over 900 kg·1,5m^-3, and the hypocambic luvisols a little over 300 kg·1,5m^-3 [Figure 1].

Enzymatic activity

Dehydrogenase and urease activity varied within the studied soils [Fig.2].  The highest average dehydrogenase activity in soil surface level was noted in haplic luvisols (34,27 mg TFF/100g^-1/24h^-1),  and the lowest in stagnic luvisols (15,05 mg TFF/100g^-1/24h^-1).  The results of urease activity were similar: from 12,31 µg N-NH₄/1g^-1/2h^-1 in haplic luvisols through 9,50 µg N-NH₄/1g^-1/2h^-1 in cambic luvisols to 7,14 µg N-NH₄/1g^-1/2h^-1  in stagnic luvisols. In the studied subtypes of luvisols dehydrogenase activity correlated with nitrogen and carbon content (r = -0.73, r = -0.66). Urease activity in the surface soil horizons did not correlate with the physico-chemical properties.

DISCUSSION

Dehydrogenases and urease activity varied across the subtypes of luvisols and proved to be a better parameter differentiating the particular subtypes of soils in comparison to the physico-chemical properties. Soil enzyme activities are used as indices of microbial activity [4] and react quickly to changes in environmental conditions [3] and microbial community structure [16,11] and vegetation [14]. In the case of the studied soils the differences in enzyme activity were caused by varied vegetation, which directly affects  the properties of surface levels of soils. Physico-chemical properties proved to be less sensitive to the influence of vegetation. The haplic luvisols were characterized by the highest enzymatic activity and the cambic luvisols, the stagnic luvisols showed the lowest activity. In the case of  haplic luvisols dominated varied compositions of species at the stands with a high proportion of hornbeam and lime trees and undergrowth vegetation was full of the typical components of the rich forests of beech and linden-oak-hornbeam (Galium odoratum, Galeobdolon luteum, Asarum europaeum, holostea Stellaria, Viola reichenbachiana, Anemone nemorosa). The analyzed hapli luvisols with the poorer in terms of floristic plant communities, in the stand showed the dominance of beech or oak. In the undergrowth covering these a bit poorer soils, it was a combination of species encountered in oligo-mesotrophic habitats (Maianthemum bifolium, Calamagrostis arundinacea, Convallaria majalis, Polytrichastrum formosum, Melica uniflora, Carex digitata). Plants characteristic of the rich beech or linden-oak-hornbeam on hypocambic luvisols occur sporadically. The stagnic luvisol vegetation with characteristics intermediate, at high proportion the species of plants of mesotrophic habitats the admixture of typical plants for Querco-Fagetea class were found, and indicators of higher moisture. The stagnic luvisol overgrown by beech or fir stands. It is interesting why the luvisols with the characteristics of the soil stagnic process considered in the assessment of physico-chemical parameters to be eutrophic soil, in the light of studies appear to be the poorest in terms of biological activity. Suppose that a limiting effect on the biological processes can have a regular, excessive moisture due to the water suspended over a concise and highly impermeable luvisols level and deteriorating air relations in the horizontal surface which is heavily overgrown by the roots. Soil enzyme activity reflects the intensity and direction of biochemical processes in the soil changes, indicates the biological capacity of the soil. It is related to biochemical processes that are important in maintaining soil quality [8]. Błońska and Januszek [5] confirm that the enzymatic activity reflects initial imperceptible changes in the horizon of humus as a result of the impact of vegetation. Dahm [7], Burns [6] showed that the effects of plants on biochemical properties, which is the enzyme activity depends on the chemical composition of plants, that even in the  root exudates in different genera, species and even varieties show significant differences. This is confirmed by studies Januszek and Błońska [10] which found a significantly lower activity of phosphatases in the extra-rhizosphere soil than rhizosphere soil of scots pine seedlings. Reich et al. [13] indicated that species richness and functional group richness independently influence biomass accumulation and its response to elevated CO₂ and N. The functions of ecosystems and communities are not only related to the functional characteristics of the dominant species, but also to species number. Changes in the composition of plant species (or of functional groups) modify resource availability for heterotrophic microbial communities in the soil, which, in turn, also modifies their composition and function. These changes in microbial community composition and function will then directly influence the rates of carbon and nitrogen soil cycling [18]. Soil enzymes play key roles in the biochemical functioning of soils, including soil organic matter production, the decomposition of xenobiotics [1], and the cycling of nutrients such as carbon (invertase), nitrogen (urease and protease), and phosphorus (phosphatase). Wang et al. [15] suggests that urease activity may be affected not only by soil resources, such as soil organic carbon, soil total nitrogen, and soil available nitrogen supply, but also by community aboveground biomass in all the four examined meadows.

CONCLUSIONS

• Different levels of dehydrogenase and urease activity in subtypes of luvisols associated with different plant communities indicates the possibility of using soil enzymes in the evaluation of soil quality and habitat.
• The lower enzymatic activity of cambic luvisols made of boulder clay compared to the activity of enzymes in the haplic luvisols, confirms a significant effect of particle size on the biological activity of forest soils, shown previously in bibliography.
• The relation between activity of the soil enzymes studied and the abundance of undergrowth vegetation suggests that the dehydrogenase and urease may be considered a sensitive indicator of processes occurring in the surface soil horizons and thus of the rate of current status and quality of soils and habitats.
• Under the conditions of vegetation transformation, to compare the quality horizons of humus (using enzymatic activity) in relation to production potential designated on the basis of relatively stable elements of the soil environment will allow assessing the intensity of the distortion or degradation of forest habitats.

ACKNOWLEDGMENTS

The project was financed by Polish–Norwegian Research Fund.

REFERENCES

Accepted for print: 25.03.2013

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