Bajouco, Rui1; Fraga, Irene2; Pinheiro, Jorge3, Coutinho, João1*
1CQVR, Dep Biologia e Ambiente, ECVA, UTAD, 5000-801 Vila Real, Portugal * j_coutin@utad.pt 2CITAB, Dep Biologia e Ambiente, ECVA, UTAD, 5000-801 Vila Real, Portugal
3 CITA-A, DCA, Universidade dos Açores, 9700 Angra do Heroísmo, Portugal
Abstract
Volcanic ash soils contain a disproportionate amount of soil carbon. Several hypotheses may explain its accumu- lation, namely the deactivation of enzymes related with the organic matter mineralization by adsorption on short-
range order mineral surfaces. The exoenzymeβ-glucosidase is of particular interest, whose activity is particularly
useful for soil quality monitoring. The aim of this work was to understand the effect of the Al and Fe in the poten-
tial β-Glucosidase activity in volcanic derived soils, under grassland and subjected to superficial fertilization. On
stratified subsamples of the 0-15 cm layer of six soils collected at Pico Island, Azores, the OC content presented
a decreasing gradient, which was followed by a similar gradient of the β-Glucosidase potential activity within the
same soil, although no overall relashionsip was observed. Simultaneously, the Al and Fe contents increased
along the profile depth. The results led to a negative relationship between β-glucosidase potential activity and (Al
+ Fe) contents in all the 30 stratified samples across the six soils, r = 0.709 ***. This results are in agreement with the hypothesized repressive effect of the of volcanic products over the enzyme activities.
Keywords: volcanic soils, organic carbon, β-glucosidase, (hydroxides (oxides)-Al/Fe) minerals
Resumo
Solos derivados de cinzas vulcânicas contêm elevados teores de carbono orgânico no solo. Várias hipóteses têm sido propostas para explicar este fenómeno: o fósforo é um fator limitante na mineralização SOM, associações com minerais (hidróxidos (óxidos) -Al/Fe) reduzem a mineralização ou “desativação” da atividade enzimática do
solo devido a adsorção em superfícies minerais de enzimas e micróbios subprodutos. A exoenzimaβ-glucosidase
é de particular interesse, pois é particularmente útil na monitorização da qualidade do solo. Este trabalho teve
como objetivo compreender o efeito de minerais Al/Fe na atividade potencial da β-glicosidase em solos derivados
de materiais vulcânicos, submetidos a fertilização superficial. Numa camada superficial, de 15cm, estratificada,
verificou-se que o teor de OC se apresenta em gradiente decrescente. A atividade da β-glicosidase, apresentou o
mesmo comportamento, estando correlacionada com OC em cada um dos solos estudados, embora nenhuma relação possa ser estabelecida com a totalidade dos solos em estudo. Os teores de minerais Al e Fe aumenta- ram ao longo do perfil, em todos os solos estudados. Através de regressão logarítmica, verificou-se correlação
inversa entre a atividade potencial da β-glicosidase e os teores de Al + Fe, r = 0.709 (p< 0.001), válida para o
conjunto das 30 amostras respeitantes aos seis solos. O comportamento observado está em concordância com a hipótese de efeito repressivo de produtos vulcânicos sobre atividade das enzimas.
132
Introduction
Soil organic matter (SOM) is a key compo- nent of terrestrial ecosystems, and varia- tions in its abundance and composition has important effects on many of the processes that occur within the system. The carbon balance of terrestrial ecosystems can be changed markedly by the direct impact of human activities like deforestation, biomass burning, land use change and environmental pollution [1].Although comprising only 0.84%
of the global land area,volcanic ash soils usually contain a disproportionate amount of soil C, storing approximately 5% of the glob- al soil C [2],[3].The hypotheses that may ex-
plain SOM accumulation in volcanic ash soil are: (i) phosphorus is a rate-limiting factor for SOM mineralization; (ii) associations with mineral (hydroxides(oxides)-Al/Fe) reduce SOM mineralization, since enzymes and microbial by-products may be deactivated by adsorption on short-range order mineral surfaces of andic soils and (iii) the microbial decomposition of organic matter may be limited by Al toxicity [4]. Of the extracellular
enzymes in soils, β-glucosidase is one of particular interest, whose activity may be particularly useful for soil quality monitoring
[5]. The objective of this work was to under-
stand the effect of the active forms of Al and Fe constituents on the β-glucosidase activity in pastures over volcanic derived ash soils, subjected to superficial fertilization.
Material and Methods
Six pasture soils with andic characteristics from the Pico island, Azores archipelago, were selected and the 15 cm superficial layer was stratified (0–1, 1–2, 2–5, 5–10 and 10–15 cm) in each of them, giving a total of 30 soil samples. Samples were air-dried, sieved through a 2-mm screen, and stored for the analysis, which were conducted in duplicate. The Organic Carbon (OC) was quantified by NIRD in a carbon elementar analyzer (Primac SC); Fe and Al were ex- tracted with ammonium-oxalate-oxalic acid
[6] and determined by atomic absorption
spectrometry (ICE 3000 Series AA). The potential enzymatic activity of β-glucosidase was assessed according to the method de- scribed by Tababatai[7].
Results and Discussion
The OC content shows a stratified gradient along the profiles within each of the studied soils, with the top 0-2cm layer presenting an average of 169 g OC kg-1 across all soils
(Figura 1a). A superficial accumulation of OC was also reported in Japanese volcanic ash soils [8], being a characteristic reported
by FAO [9] for andic soils. The potential β-
glucosidase activity followed the stratification of the OC gradient, with the top layers hav- ing higher activities (Figura 1b). This β- glucosidase profile distribution along soil depth was also reported in volcanic soils from the Canary islands [10] .
Figure 1. Average profile distribution of the assessed OC
content (a) and potential β-glucosidase activity (b) on the stratified layers of the six soil studied.
Figure 3a presents the linear regressions of potential β-glucosidase activity versus OC content for each studied soil. The re- sults show positive correlations, but only within each soil. This relationship is espe- cially high in soils IV and V (R2>0.939,
p<0.001) presenting both the lowest OC
contents in the 15 cm layer. In pasture soils, a correlation (p<0.001) between β- glucosidase and OC, on a similar range of
β-glucosidase activity (165-851 µg p-NP g- 1 h-1) was reported [5],although for a lower
The active Al (oxalate extracted) is present in higher contents than Fe in all soils and layers, as also reported for andic soils from this region [11]. The content of oxi-hydroxide
forms of Al and Fe increased along the studied profiles, having an inverse gradient when compared with the OC and β- glucosidase potential activity (Figure 2a and 2b).
Figure 2. Average profile distribution of the assessed Al
(a) and Fe (b) content on the stratified layers of the six soils studied.
Concerning the relationship between β- Glucosidase potential activity and Al+Fe content (Figure 3b), a highly significant logarithmic regression with a negative slope has been observed. These results suggest that the β-glucosidase activity may be in- hibited by oxi-hydroxide forms of Al and Fe. Since it is pointed out by some authors that Al and Fe may stabilize OM and decrease its mineralization rate [6],[7],[12], it can be hy-
pothesized that this protection effect may be due to the lower β-glucosidase activity in these conditions.
In the soils under study, it is to enhance that soils IV and V, with the lowest OM con- tent among the six soils, simultaneously presented the lowest Al and Fe contents and the highest β-glucosidase activities.
Figure 3. (a) Linear Regression of potential β-Glucosidase activity versus Organic Carbon content in each studied soil; (b) Logarithmic regression of potential β-Glucosidase activity versus Al + Fe content (p < 0.001).
Conclusion
Although the increase ofβ-glucosidase activity is related with the OC content of the layers within the same soil, there was no overall relationship across the six soils. Nevertheless, the obtained data showed a repression effect of Al and Fe constituents on the β-glucosidase potential activity across all the thirty samples, which may explain the OC accumulation verified in most of the soils derived from volcanic ashes.
References
[1] Batjes, N. H. 1996. Total Carbon and Nitrogen in the Soils of the World . European Journal of Soil Science47 (1): 151–163.
[2] Dahlgren, R. A., M. Saigusa, and F. C. Ugolini. 2004. The Nature, Properties and Management of Volcanic Soils.
Advances in Agronomy82: 113–82.
[3] Eswaran, H., E.V.D. Berg, and P. Reich. 1993. Organic carbon in soils of the world. Soil Science Society of
America Journal57: 192–94.
[4] Matus, F., C. Rumpel, R. Neculman, M. Panichini, and M. L. Mora. 2014. Soil Carbon Storage and Stabilisation in Andic Soils: A Review. Catena120: 102–110.
[5] Turner, B.L., D.W. Hopkins, P.M. Haygarth, and N. Ostle. 2002. β-Glucosidase Activity in Pasture Soils. Applied
Soil Ecology20 (2): 157–162.
[6] Scherwertmann, U. 1964. Differenziurung der eisenoxide des bodens durch photochemiste extraction mit saurer
134 ammoniumoxalaat-lӧsung. Z. Pflonzenornӧhr. Düng Bondek. 105:194-202.
[7] Tabatabai, M.A. Methods of Soil Analysis. Part 2, SSSA, Madison, Wisconsin, USA. 1994.
[8] Otani, T, and N Ae. 1997. The Status of Inorganic and Organic Phosphorus in Some Soils in Relation to Plant Availability. Soil Science and Plant Nutrition43 (2): 419–429.
[9] WRB, IUSS Working Group. 2006. World Reference Base for Soil Resources. World Soil Resources Report 103. Rome: Food and Agriculture Organization of the United Nations. Experimental Agriculture43 (02): 264.
[10] Armas, C.M., J.L. Mora, CD Arbelo, and A Rodríguez. 2013. Labile Carbon Pools and Biological Activity in Volcanic Soils of the Canary Islands. Spanish Journal
of Soil Sciences3 (1): 7–27.
[11] Pinheiro, J., M. Madeira, F. Monteiro, and J. Medina. 2001. Características E Classificação Dos Andossolos Da Ilha Do Pico ( Arquipélago Dos Açores ). 24(3,4): 48-60.
[12]Tabatabai, A.M., and W.A. Dick. 2002. Enzymes in Soils. Research and Developments in Measuring Activities.
Enzymes in the Environment. Activity, Ecology, and Applications., 567–596.
VII Congresso Ibérico das Ciências do Solo (CICS 2016) VI Congresso Nacional de Rega e Drenagem