Taxocenotic and biocenotic analysis over time of edaphic mesofauna in organic Vaccinium sp. plantations southern central Chile

Análisis temporal de la taxocenosis y biocenosis de la mesofauna edáfica en plantaciones de Vaccinium sp. con manejo orgánico en el centro-sur de Chile

Santiago F. Peredo-P.^1,2*, Claudia P. Barrera-S.¹, Esperanza Parada-Z.³, Marcela Vega-C.³

¹ Grupo de Investigación en Agroecología y Medio Ambiente.

³ Escuela de Ciencias Ambientales. Facultad de Recursos Naturales. Universidad Católica de Temuco-Chile.

Received: January, 2011.
Approved: February, 2012.

Abstract

Soil functioning is determined by the diversity of organisms inhabiting the soil and their role in the edaphic ecosystem, and the variety of forms and functions of the roots of the plants where they live. Invertebrates are an integral part of soil and are important in determining the suitability of the soil for the sustainable production of healthy crops or trees. In Chile there are no studies on edaphic mesofauna in plantations subjected for a longer period to certified organic management. The aim of the present study was to analyze the taxocenotic and biocenotic similarities over time of taxa of edaphic mesofauna in a cranberry plantation (Vaccinium sp.) subjected to organic management practices in farms in Southern Central Chile (37° 28' S). In July 2006 two farms were chosen: 1) with one year under certified organic management as a transition organic plantation (OM1) and 2) under six years of certified organic management (OM6); both with similar climate and edaphic features. Each farm was divided in four quadrants, each one with 2500 m². In each quadrant, was extracted at random one sample with six replicas (188.5 cm³ each), 24 replicas on each plantation. Samples were processed in the laboratory using the Berlesse-Tullgren system for the extraction of mesofauna and the subsequent counting and identification of specimens. To analyze changes over time in the structure of the edaphic mesofauna community, in July 2007 sampling was repeated in OM1 and OM6 plantations under organic management (OM2 and OM7). The richness, abundance of taxa and density (nm^-2) per plot were evaluated, as well as the diversity (H') and evenness (J') of the mesofauna taxa in each plantation (OM1, OM2, OM6 and OM7). The α diversity and dominance were calculated using the Shannon (H') Index and the Evenness (Equity) Index (J'). In addition, β diversity was determined to establish the taxocenotic and biocenotic similarities using the Bray Curtis Index estimated with the Biodiversity Pro software. Significant differences between diversity (H') values were determined with Student's t test (p≤0.05). There was a high taxocenotic similarity on time in the edaphic community structure of Vaccinium sp. organic plantations. Fourteen taxa form edaphic mesofauna taxocenosis, being Acaridida, Oribatida and Entomobryomorpha the most abundant. There were differences (p≤0.05) between the diversity (H') of mesofauna taxa in organic plantations with one year of transition to organic management (OM1) respect to OM2, OM6 and OM7. The communities of edaphic mesofauna in the organic plantations of Vaccinium sp. were stabilized two years after conversion from conventional to organic management.

Key words: edaphic mesofauna, organic farming, cranberries, mediterranean climate, Chile.

El funcionamiento del suelo está determinado por la diversidad de organismos que lo habitan y su función en el ecosistema edáfico, y por la variedad de formas y funciones de las raíces de las plantas en las que viven. Los invertebrados son parte integral del suelo e importantes para la determinación de la idoneidad del suelo para la producción sostenible y saludable de cultivos. En Chile, no hay estudios sobre mesofauna edáfica presentes en plantaciones sometidas durante un largo período a manejo orgánico certificado. El objetivo del presente estudio fue analizar las similitudes taxocenóticas y biocenóticas, a través del tiempo, de los taxa mesofaunísticos edáficos en una plantación de arándanos (Vaccinium sp.), sometidos a prácticas de manejo orgánico en predios de la zona centro sur de Chile (37° 28' S). En julio de 2006 se seleccionaron dos predios: 1) una con un año bajo manejo orgánico certificado, considerada como una plantación en transición orgánica (OM1) y 2) otra con seis años de manejo orgánico certificado (OM6), ambas bajo condiciones edafoclimáticas similares. Cada predio se dividió en cuatro cuadrantes, cada uno de 2500 m². En cada cuadrante se extrajo una muestra al azar con seis réplicas (188.5 cm³ cada una), 24 réplicas en cada plantación. Las muestras fueron procesadas en el laboratorio utilizando el sistema de Berlesse-Tullgren para la extracción de mesofauna y después se contaron e identificaron los especímenes. Para analizar los cambios en el tiempo en la estructura de la comunidad de mesofauna edáfica, en julio de 2007 se repitió el muestreo en las plantaciones OM1 y OM6 bajo manejo orgánico (OM2 y OM7). La riqueza, abundancia de taxa y densidad (nm^-2) por parcela fueron evaluadas, así como la diversidad (H') y homogeneidad (J') de taxa de mesofauna en cada plantación (OM1, OM2, OM6 y OM7). La diversidad α y dominancia se calcularon usando el índice de Shannon (H') y el Indice de Homogeneidad (Equitatividad) (J'). Además, la diversidad β se determinó para establecer las similitudes taxocenóticas y biocenóticas usando el índice de Bray Curtis con el software Biodiversity Pro. Las diferencias significativas entre los valores de la diversidad (H') se determinaron con la prueba t de Student (p≤0.05). Hubo una gran similitud taxocenótica en el tiempo en la estructura de la comunidad edáfica de las plantaciones orgánicas de Vaccinium sp. Catorce taxa conforman la taxocenosis edáfica de la mesofauna, siendo Acaridida, Oribatida y Entomobryomorpha los más abundantes. Hubo diferencias significativas (p≤0.05) entre la diversidad (H') de taxa de mesofauna en las plantaciones orgánicas con un año de transición hacia el manejo orgánico (OM1) respecto a OM2, OM6 y OM7. Las comunidades de mesofauna edáfica en las plantaciones orgánicas de Vaccinium sp. se estabilizaron dos años después de la conversión de manejo convencional a orgánico.

Palabras clave: mesofauna edáfica, agricultura orgánica, arándanos, clima mediterráneo, Chile.

INTRODUCTION

Agroecology as scientific discipline establishes in their principles the provision of optimal edaphic conditions by organic matter management and improving soil biology and nutrient recycling, among others (Gliessman, 1998; Altieri, 1999; Altieri and Nicholls, 2000). The application of such principles assumes a sustainable management of productive systems based upon agrobiodiversity through the agroecosystem design determined by the peasants, according to their wishes and requirements (Dumaresq et al., 2010). To accomplish those purposes, it is essential the utilization of specific parameters that guide studies such as soil organism diversity among others (Gliessman, 2001). In this sense, it is important to promote practices that increase soil organism diversity such as reduced use of synthetic fertilizers (Altieri and Rogé, 2010). These biodiversity friendly management options are characteristics of most organic farming operations and they are not ubiquitous or unique.

Soil functioning is determined by the diversity of organisms and their role in the edaphic ecosystem, and the variety of forms and functions of the roots of the plants where they live. Invertebrates are an integral part of soil and are important in determining the suitability of the soil for the sustainable production of healthy crops or plantations (Stork and Eggleton, 1992). Studies on edaphic ecosystems have concentrated on exploring edaphic diversity and the factors regulating the distribution and abundance of species, and whether diversity changes affect the functioning of the ecosystem (André et al., 2002). According to André et al. (2001) there were several publications outlining soil organism diversity in the 1970s, including the recognition of the enigma of high species diversity associated with apparent trophic overlap. This overlap (redundancy) would determine that the absence of certain species would not afect general soil functions, such as the cycling of nutrients and the mineralization of carbon (Grofman and Bohlen, 1999; Cragg and Bardgett, 2001; Hunt and Wall, 2002).

Although progress has been made in the knowledge of certain edaphic ecosystems, due to their significance in plant growth and as a tool for sustainable agriculture, the great bottle-neck is the difficulty of achieving significant levels in taxonomic resolution (André et al., 2001). This means that progress in knowledge of the structure and functioning of the edaphic ecosystem has been oriented towards studies based on the determination of the presence and abundance of taxa of functional groups (Hooper et al., 2002). In this respect, the functional role of soil-inhabiting animals in driving ecosystem processes has been reviewed by Grifths and Bardgett (1997), Cole and Bardgett (2002) and Mikola et al. (2002). Taxa richness of edaphic mesofauna is similar in Vaccinium sp. plantations with conventional and organic management, whereas abundance of each taxon individually is diferent between both types of management (Peredo et al., 2009).

In Chile there are no studies on edaphic mesofauna in plantations subjected for a long period to organic management. In the context explained above, the question that oriented the present study was: are there temporal variations in the edaphic mesofauna communities resident in Vaccinium sp. plantation fertilized with compost? Thus, the aim of the present study was to evaluate the effect over time of organic certified management practices on the taxocenotic and biocenosis of edaphic mesofauna in a Vaccinium sp. plantation in Southern Central Chile.

Study area

This study was carried out in a plantation (600 ha) located 15 km west of Los Angeles city, Bío Bío Region, Chile. The main crop consists of berries on approximately 200 ha, of which around 40 % correspond to plantations of cranberries (Vaccinium sp.). The climate is Mediterranean, with a Santa Rosa agro-climate (Del Pozo and Del Canto, 1999). The mean annual precipitation is 1303 mm, the majority concentrated between March and August. The maximum average temperature of the hotest month (January) is 29 °C and the minimum average temperature of the coldest month (July) is 5 °C. The soils originated from volcanic ash deposited recently on an unrelated substrate, which is compacted but not cemented and permits slow permeation. The soils are very deep, well drained, with high humidity retention (Tosso, 1985); the textures are medium, predominantly silt loam, well structured at the surface, and abundant porosity associated with good rooting throughout the soil base. The permeability is moderate with slow surface run-off (CIREN, CORFO, 1999).

Organic management utilizes compost as inputs allowed by International Certification Norms (IFOAM-EC, 2007; USDA-NOP, 2007).

Sampling design

In July 2006, two farms of cranberry plantation were chosen, one with one year under organic management certified as a transition organic plantation (OM1) and a second one under six years of certified organic management (OM6). The OM1 was considered as a transition organic plantation, since it had previously been conventionally managed. Each farm was divided in four quadrants (2500 m²). In each quadrant was extracted one random sample with six replicas of 188.5 cm³ each, and 24 replicas on each plantation. The extraction of soil samples was done with a corer to a depth of 15 cm (sensu Neher and Barbercheck, 1999). The samples were mounted during 7 d using a modifed Berlesse-Tullgren system (Lara et al., 1986) to ensure the extraction of the edaphic organisms. The organisms were collected in 75 % alcohol and the specimens obtained were studied under a stereo microscope, counted and identifed taxonomically at the level of order and sub-order.

To evaluate and compare the communities of edaphic mesofauna over time, in July 2007, sampling was repeated in the one and six year plantation (OM2 and OM7).

Data analysis

RESULTS AND DISCUSSION

The taxa richness recorded in the present study, with their respective abundances and densities, is shown in Table 1. Although the presence/absence of edaphic mesofauna groups was similar in the four plantations, clear diferences were observed in the abundance of each taxon in the different plantations. OM1, plantation with only one year of transition to organic management, recorded the lowest value for the total abundance. OM2, OM6 and OM7 plantations showed high total abundance values, being very similar among them. The most abundant taxa were Acarina and Collembola. Respect to Acarina, Acaridida was the most abundant taxon of edaphic mesofauna in OM1 y OM6, followed by Oribatida; OM2 y OM7 showed a reverse tendency, being Oribatida the most abundant taxa followed by Acaridida. In all plantations, Tarsonemida, Gamasida and Prostigmata y Uropodina showed less abundance. Among the Collembola, Entomobryomorpha was the most abundant, with similar abundance, except in OM6 where it was reduced. Symphypleona was only recorded in the plantations with seven years of organic management (Table 1 and Figure 1). The lowest value for the abundance of Oribatidae was recorded in OM1 as might be expected, given that populations of Oribatidae diminish rapidly when the microhabitat is altered (Behan-Pelletier, 2003). According to Neher and Barbercheck (1999), additions of mineral fertilizer decrease populations of oribatids. If the Oribatidae abundance values between the organic plantations are analyzed, OM1 (with one year of transition to organic management) recorded only 235 individuals in the 25 samples, which increased to almost double the following year (OM2) with annual fuctuations in the plantations with six (OM6) and seven (OM7) years of organic management (Table 1). The above result could be explained given that organic amendments also contain microbes and their respectives food resources according to Neher and Barbercheck (1999). Tarsonemida increased considerably in OM1, stabilising at lower abundances in plantations with longer periods of organic treatment. Next in abundance was Gamasida with very similar abundances between the plantations, except for OM2. Among the Collembola, Entomobryomorpha is the most abundant in organic plantations and with similar abundance, except in OM6, where it is reduced. Nematoda registered low abundance throughout the study. The low abundance values recorded in Collembola and Nematoda could be explained by their omnivore and predator condition. According to Stirling (1991) certain Orders of nematodes predators and insect-parasitic nematodes present in the soil may affect population of their prey. Collembolans may also be facultative predators of nematodes (Snider et al., 1990).

The highest values for diversity (H') and homogeneity (J') for each type of Vaccinium sp. plantations were recorded in OM1 (Table 2). The differences in the H' values between OM1 and other Vaccinium sp. plantations were significant (p≤0.05). The similar H' values (p>0.05) in OM2, OM6 and OM7 in the present study allow to assume that the edaphic mesofauna community stabilices after two years under organic management. According to Peredo et al. (2009), there are significant differences between H' values of edaphic mesofauna in Vaccinium sp. conventional plantations and the H' values of organic plantations.

In field experiments abundance of soil microarthropods (Acarina and Collembolla) increase significantly with the food supply of straw and green manure, but not with farmyard manure (Kautz et al., 2006). Nutrient release from a mixture of plant litter and soil increased with increasing microarthropod density but decreased with increasing species richness (Cole et al., 2004). The use of compost in the present study shows that total abundance of mesoedaphic community increases after two years under organic management, compared to OM1 (plantation with only one year of transition to organic management), which recorded the lowest values for the total abundance (Table 1).

As indicated above, there is a high taxocenotic (qualitative) similarity between the groups of edaphic mesofauna recorded among the plantations of cranberries subjected to organic management (Figure 2). The dendrogram shows only one group of taxocenotic similarity which ranges from 95 to 100 %, given that Symphypleona was registered only in OM7 and Diplododa was absent only in OM2 (Figure 2A, Table 1). However, there are quantitative differences in the biocenosis of the edaphic communities where the dendrogram shows three similar groups separated: at 85 %, which separates the OM2 and OM7 community; at 83 % and 75 % which separate the plantation with one year of transition to organic management (OM1) from others communities (Figure 2B). The great biocenotic similarity between these last three, over 83 %, would be explained by the similar niche conditions generated after the transition year.

The OM1 and OM6 show 100 % of taxocenotic similarity which indicates that in both communities the same taxa are present. But, both communities difer at biocenotic level since the H' value in OM1 was higher (p≤0.05) than in OM6. However, total organism abundance is lower in OM1 than OM6. The latter is explained by the higher homogeneity in the abundances of the diferent taxa present in OM1, showed in the Evenness Index (J'=0.79) respect to OM6 (J'=0.66). Similar values of H' and J' in OM2, OM6 and OM7 (p>0.05) would indicate that the communities of edaphic mesofauna in the organic cranberry plantantions (Vaccinium sp.) stabilize two years after conversion from conventional to organic management.

The importance of soil organisms for plants has been shown in the last century and at present edaphic diversity is considered as a tool for sustainable agriculture. According to Neher (2001), higher diversity values would be expected in plantations with seven years under organic management because a long-term perennial crop is related more closely to an undisturbed site. However, the low diversity values registered in the present study could be explained by the fact that the organic farms used for the study are highly specialized, large-scale and monocultural operations managed with the same input-substitution approach that characterizes conventional agriculture (Altieri and Rogé, 2010). Such farms usually contain low levels of plant, arthropod and microbial biodiversity despite their compliance with organic certification standards (Altieri, 2002).

The decrease in biodiversity recorded in this study does not necessarily lead to conclude that the agroecosystem is not on the way to its stability. According Neher and Barbercheck (1999), short food webs that exhibit little omnivory are more stable than longer food webs with much omnivory. Stability can develop if numbers of species increase but not if omnivory increases (Lawton and Brown, 1993).

Finally, the results of the present study constitute a first contribution to the knowledge on edaphic mesofauna community dynamics under organic management using compost in Chile. However, it is necessary to point out that results are valid under the established conditions because factors such as quality and composition of fertilizer used (Neher and Barbercheck, 1999) and other macro factors such as soil type, latitude, altitude (Stork and Eggleton, 1992) may condition the structure and functioning of edaphic communities.

CONCLUSIONS

There is a high taxocenotic and biocenotic similarity on time in the edaphic community structure of Vaccinium sp. organic plantations. Fourteen taxa conform edaphic mesofauna taxocenosis, being Acaridida, Oribatida and Entomobryomorpha the most abundant. Significant differences among diversity values of OM1 vs OM2, OM6 and OM7 allow assuming that the communities of edaphic mesofauna in the organic plantations of Vaccinium sp. stabilize two years after conversion from conventional to organic management.

ACKNOWLEDGEMENTS

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