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CHEMICAL COMPOSITION OF MOUNDS OF Nasutitermes SP. (ISOPTERA: TERMITIDAE) AND OF THE ADJACENT SOIL.

Maria Luisa T. Buschini 1, Ana Maria C. Leonardo2

1Departamento de Ecologia, Universidade Estadual Paulista, Rio Claro - SP - Brazil

2 Departamento de Biologia, Universidade Estadual Paulista, Rio Claro - SP - Brazil.

 

ABSTRACT

The influence of Nasutitermes sp. on the dynamics of nutrients in different areas of the nest and the surrounding soil was studied. Samples of the upper, middle and lower area of 5 nests were collected, as well as of the soil immediately below and beside each mound, at a distance of 50 cm. The contents of organic carbon and of the main mineral macro-elements, were measured as well as the pH and the text of aluminium. A multivariate analysis of variance (MANOVA) was carried out with these data, and the results showed that the amounts of these elements in the mound are larger than in the adjacent soil, with the largest values found in its middle area.

Key Words: Isoptera, Nasutitermes, mounds, soil, mineral concentration


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INTRODUCTION

The productivity of an ecosystem depends on the amount of nutrients stored in the vegetation, in the litter, in the soil and in animal biomass, as well as of the transfer of nutrients among them. Nutrient cycling in all the ecosystems is affected by a combination of biological and physical factors. However, the relative importance of these factors varies considerably among the ecosystems as a result of differences in climate types, soil, vegetation, and management practices (5).

The mineralization of organic matter by fire, the loss of nutrients present in the soil through the lixiviation and/or erosion and the loss due to atmospheric factors are physical factors responsible for the nutrient cycling (5). As biological factor stands out the microorganisms (bacteria and fungus), which assume a predominant role in the mineralization process.

Studies accomplished in temperate areas demonstrated that the direct contribution of invertebrates in the organic decomposition is small (less than 10%) when compared with the contribution of the microbial populations present in the soil (16, 18).

 

 

In semi-arid tropical environments, primary decomposition is largely a function of several species of detritivorous arthropods and, in several areas, they have an important role in the nutrient cycling (19). As they have true ability to modify the microenvironment inside their nests and in their foraging galleries (9), termites are considered some of the most efficient detritivorous insects in dry tropical areas (5). Like ants, termites differ from many organisms present in the soil because they modify their microenvironment, creating, in this way, a more favourable environment. These insects are abundant and they play an important role in several ecosystems (21). Through their nutritional dynamics, termites also play an important role in the recycling of cellulose-rich material (6).

When compared with the nests of others insects, termite nests present the largest structural complexity and, in most of the species, the population is found in its interior together with the brood and the royal pair (Desneux 1948, 1952 apud 20). For the construction of their nests, termites use soil, faeces and saliva in varied proportions. During this process, termites select, transport and rearrange the particles of the soil, cementing each other together with the organic matter. Based on the use (or not) of these materials in the construction of the termites nests, it was recognized different structures of nests (7). This structural diversity results in the transport of soil from deep and/or superficial horizons for the local where the nests and galleries will be built, as well as for the areas where the termites will feed.

According to Lepage (1974b) apud (21), Macrotermes subhyalinus Rambur transports annually to the soil surface 2000kg/ha. Thus, termites can cause a physical disturbance in the soil profiles, a change in its texture, as well as in the nature and distribution of organic matter and of nutrients (20). Most of the termite nests have more organic matter than the soil used for their construction, because they use organic materials (saliva or faeces) to cement their particles (2, 7).

This research had as objective the study of the influence of Nasutitermes sp. on the dynamics of the nutrients in different areas of the nest and in the soil where they are distributed.

MATERIAL AND METHODS

This research was carried out in a Cerrado area in the Municipality of Itirapina - Brazil (22° 15’ S and 47° 49’W, altitude of 765 meters). The word Cerrado is a Portuguese term meaning "half-closed" or "dense". In Brazilian terminology it also describes a particular kind of vegetation similar to savannah, although having much broader physiogonomic variation in size and density of trees. That is, the word Cerrado would describe a gradient of vegetation comprising "savannah grassland", "low trees and shrub savannah" and "savannah woodland". It is important to point out that the similarities to savannah are only physiogonomic and not floristic. It covers about 2 million km2, or 25% of the whole Brazilian territory (3).

The studied area is an alluvial plain covered by a sandy sediment, with a deep, quartzes' sand soil type (15). Mean annual rainfall is 1425mm, with the rain season extending from October to March, when 84% (1199mm) of the precipitation occurs. The most rainy months are December, January and February, with precipitation values equal to 288, 266 and 262mm, respectively. The driest months are July and August, with 16 and 19mm of precipitation, respectively. The mean annual temperature is 19.7° C, with January and February being the hottest months with respective mean values of 22.2 and 22.3° C. The coldest months are June and July with respective mean temperatures of 16.4 and 16.2° C.

 

 

Due to the difficulties in determining the Isoptera, mainly the genus Nasutitermes, the species studied in this paper was just identified till genus even after being enquiries to Brazilian taxonomists and abroad Dr. Reginaldo Constantino (University of Brasilia - Brazil) compared specimens of this work to all types of the American Museum, and he concluded that it is very

 

close to Nasutitermes ephratae Holmgren. But, according to Dr. Kumar Krishna (New York Natural History Museum), it is very close to Nasutitermes feytaudi Holmgren from Diamantina (MG, Brazil). In face of this, we deposited reference specimens in the Museu de Zoologia da USP (MZUSP 9921) at São Paulo capital city.

Since the nests of Nasutitermes sp. have the spherical calotte shape (Figure 1), samples of the upper, middle and lower area of 5 nests were collected. Samples from each area corresponded to the treatments 1, 2 and 3, respectively. Samples of the soil immediately below each mound (treatment 4) and of the adjacent soil at a distance of 50cm, to a depth of 1 meter (treatment 5), were also collected. This protocol was necessary because we has no knowledge of which horizon the particles used by the termites were being removed.

The chemical analyses of mound samples as well as of the soil helped to determine the content of organic carbon and of the main mineral macro-elements, being also measured the pH and the text of aluminium (12). The analyses were made in the Laboratory of Geology of UNESP - Rio Claro (Brazil). With these data, a multivariate analysis of variance (MANOVA) was used, because, there is more than one response variable (Ca, Mg, pH, P, Na, K, Al, Co, H+) to be analysed (10).

Figure 1- Nest of Nasutitermes sp. External (1) and Internal (2) view.

RESULTS

The results of the chemical analyses of the mounds and of the soils can be seen in Table 1. The value of Wilkens' Lambda obtained (l = 0.001; F = 9.457), approximated by the F distribution, was highly significant, indicating that there are differences among the established groups. Later on, it was made the multiple discriminant analysis or the canonical variables analysis, through which it was observed that the factors 1 and 2 explained, respectively, 91.73% and 6.65% of the variation among the groups (Table 2). Only these first two factors were significant by the test of Bartlett (10).

Table 1- Mean values and standard deviations (in parentheses) of the chemical composition of the soil and of the mound.

 

Table 2- Canonical variable analysis.

The analysed variables exercised influence on the differences among the groups, being the variables Ca, Na, K and P highly correlated with the canonical factor 1, and the variable pH more correlated with canonical factor 2 (Table 3).

Table 3- Correlation among the dependent variables and the canonical factors I and II.


In the dispersion scores of the canonical factor 1 against the canonical factor 2 (Figure 2), it can be seen that the treatments 1 and 3 differed from the treatments 2, 4 and 5 with respect to both canonical factors. These same treatments seem to present a slight difference from each other. The treatment 2 only presented differences in relation to the other treatments as a function of the canonical factor 1. Faced the canonical factor 2, it only presented differences in relation to treatments 1 and 3. There was a sobreposition of the treatments 4 and 5, that is, they did not present any difference to each other in relation to both canonical factors.

Faced with these results, it can be seen that the middle region of the mound (treatment 2) presented amounts of organic matter, aluminium and macro-elements significantly larger (higher scores in factor 1) than the other areas. In the soil samples (treatments 4 and 5), the amounts of these nutrients were significantly smaller than in the three regions of the nests. Intermediary amounts of these elements were found in the upper and lower parts of the mound.

With respect to the pH, the middle region presented a pH a little higher than that of the soil; there was not significant difference among them. Comparing the pH of these areas with those of upper and lower areas of the mound, it was noticed that there was a significant difference among them (Figure 2). The largest pH found corresponded to the upper area of the nest (Table 1).

 

 

Figure 2- Canonical factors I and II for each treatment: 1, 2 and 3 correspond to the upper, middle and lower regions of the mound, respectively. Treatments 4 and 5 correspond to the soil immediately below the mound and the soil down to a depth of one meter.

DISCUSSION

Like the nests of other species, the nests of Nasutitermes sp. present concentrations of nutrients larger than that of the soil, with the largest and smallest concentrations occurring in the central and superior areas of the mounds, respectively. The fact that the superior area of the mounds present smaller amounts of nutrients may be due to the larger rate of lixiviation suffered by this region. The central area in termite’s nests is constantly re-worked (7). In the nests of Nasutitermes triodiae Froggatt, the concentrations of organic carbon in this area, in relation to the soil from which it was built, are larger (10%) than those of less worked areas, as the galleries (2.7%).

Through chemical studies of macronutrientes in nests of four species of termites, it was observed that the nests of Nasutitermes minimus Holmgren and, especially, of Nasutitermes surinamensis Holmgren, presented the largest concentrations of organic matter and of inorganic nutrients (1). According to this author, in the nests of N. surinamensis, these results were obtained not only because this species feeds on relatively dense wood, but also because the nests are arboreal, impermeable to rainwater and without proliferation of roots.

Contrary to the nests of N. surinamensis, the nests of Nasutitermes sp. are epigeal, with reasonable amount of roots in the inferior part of the nest. The largest average amount of Ca found in this work was of 6.7 and 6.2 times smaller than the average amount found immediately below in the soil and of the soil beside the mounds, respectively. In the nests of N. surinamensis, the average amount of Ca was 100 times superior to the amount found in the soil of the area (1).

The concentration of nutrients in the nests of termites results from the foraging activity of these insects and of the use of faeces and saliva as cement of the particles of the soil, used in the construction of its nests (14). Gnathamitermes perplexus Banks and, particularly, Heterotermes aureus Snyder increase the level of organic carbon considerably in the surface of the soil as a result of their alimentary activity, as well as from the habit of depositing saliva and faeces together with the particles of the soil (13). It was observed that Nasutitermes ephratae controls not only the level but also the distribution of P in the soils of the savannah, being the concentration of these nutrients larger in the nests of this species than in the adjacent soil (8).

The nests of most of termite species generally have a pH lower than that of the soil, and similar or slightly lower than that of the superficial soil (21). In this experiment, although the differences among the pH values have not been significant, it was noticed that the pH of the central area, where there is a high concentration of organic matter, was smaller than the pH of the superior and inferior areas of the nest. Moreover, the pH of the central area was also

 

smaller than the pH of the soil down to a depth of one meter, but equal to that of the soil immediately below the mound.

A logical consequence of the concentration of nutrients in mounds, or in nests of other animals, would be the shortage of these elements in the neighbourhood. In this regard, a soil of low fertility becomes still poorer after the activity of construction of the mounds, whilst with localized points of high fertility (1). High concentrations of nutrients in nests of several species of termites, in Venezuela, were found (17). Those authors concluded that these have importance for the establishment of plants, partly due to the improvement of conditions for seed, also favouring a larger vegetal diversity.

 

It was observed that nests of Armitermes neotenicus Holmgren contain high amounts of organic matter, coming from the faeces of this termite, with many roots inside the nest. The roots developed better inside the mounds because this material has larger capacity of water retention and its disponibility of nutrients is larger than that of the soil (11). This same author believes that the termites, on the other hand, feed on the juice of these roots.

In the area of the Serra of Cipó - Minas Gerais (Brazil), where Paepalanthus bromelioides seems to be endemic, it was found association, probably a mutualistic one, between termites nests and the above mentioned plant (4). According to those authors, the soils of this area are shallow and poor in nutrients and organic matter, suffering constant action of the fire. In this way, P. bromelioides would supply a more amenable climate than the adjacent environment, with the continuous renewal of food for those insects. The mounds, on the other hand, besides present larger concentration of nutrients, can attenuate the degree of exhibition of P. bromelioides to the fire.

Although the studied area suffers the action of the fire annually and its soil is sandy, poor in nutrients, it is believed that the mutualistic association of this sort does not exist, because few nests of Nasutitermes sp. present grasses in its interior. Moreover, a larger concentration of plants was not observed in the proximity of the mounds of this species. What was being constantly observed is the presence of live roots in the inferior area of the mounds, the one with the second largest concentration of nutrients.

In high concentrations, the aluminium can be toxical for the plants (Etherington 1975 apud 1). Faced with this consideration, it is believed that the non-existence of plants inside the mounds of Nasutitermes sp. and in its proximity it is not due to this factor, since the concentration of this element did not suffer larger increments, when compared with the other nutrients.

ACKNOWLEDGMENTS

We would like to thank Prof. Dr. Miguel Petrere Jr. for the suggestions and to Prof. Edson Gomes de Oliveira for the orientation and help in the collection of the material. Thanks are also due to Profa. Dra. Maria M. Torres for the chemical analyses and to Prof. Dr. José Alexandre Filizola Diniz Filho for the help in the statistical analyses. This study was supported by grants from CNPq.


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RESUMO

Composição química dos ninhos de Nasutitermes sp. (Isoptera, Termitidae) e solo adjacente. Foi estudada a influência de Nasutitermes sp. sobre a dinâmica dos nutrientes em diferentes regiões do ninho, e no solo circundante. Coletou-se amostras das regiões superior, média e inferior de 5 ninhos e do solo imediatamente abaixo de cada cupinzeiro e do solo a 50 cm de distância. O conteúdo de carbono orgânico e dos principais macroelementos minerais foi determinado, sendo medidos também o pH e o teor de alumínio. Com estes dados, realizou-se uma análise de variância multivariada (MANOVA) através da qual observou-se que as quantidades destes elementos no cupinzeiro é maior que no solo, sendo os maiores valores obtidos em sua região média.

 

 

Palavras-chave: Isoptera, Nasutitermes, montículo, solo, concentração mineral.


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