Soil microarthropod population responses as evaluation indices for afforestation practices in laterite wastelands

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1 Res. Environ. Life Sci. ISSN: (3) (21) Soil microarthropod population responses as evaluation indices for afforestation practices in laterite wastelands Sonalika Das, Saswati Mukhopadhyay and V.C. Joy* Soil Ecology Laboratory, Department of Zoology, Visva-Bharati University, Santiniketan , India * (Received: April 4, 21; Revised received: July 12, 21; Accepted: July 15, 21) Abstract: Impact of afforestation in improving the biological activity of soil in tropical laterite wastelands was compared from the population responses of soil microarthropods and the zone of preference of Collembola to soil nutrients. The soil microarthropod fauna predominated by detritivorous and fungivorous groups are functionally very important components of soil food web. The study was conducted in selected afforested stands of Cassia siamea (Lamk.), Shorea robusta (Gaertn), Dalbergia sissoo (Roxb.) and Acacia auriculiformes (A.Cunn. ex. Benth) trees. Microarthropod density was more in the soil of C. siamea and D. sissoo as compared to the area dominated by S. robusta and A. auriculiformes during all the seasons. Collembola was the major group in all the sites and Collembola and Acari together formed more than 8% of total population. High density of soil micro-arthropods during monsoon months followed by significant decline in the dry seasons (p<.5) showed their sensitivity to soil parameters. A similar trend of distribution of Collembola was observed in a mature stand of C. siamea trees also. The nutrient status showed clear difference between soils, C. siamea and D. sissoo were nutrient-rich but S. robusta and A. auriculiformes were nutrient-poor sites. Except soil temperature, all parameters were positively correlated with the population, and significantly for EC, organic carbon and moisture content (p<.5); the negative relation of Collembola with temperature was also valid (p<.5). Multiple regression analysis ascertained cumulative effect of soil parameters (p<.2) on population buildup. The zone of preferences of Collembola to soil factors was evident from their abundance; the number was less at high temperature and at low moisture, abundant at more or less neutral ph and moderate EC, but preferred high OC and low nitrate- N. The present results showed that C. siamea and D. sissoo trees are more suitable than A. auriculiformes and S. robusta trees for restoration of soil health in eroded laterite wastelands. Key words: Soil microarthropods, Collembola, Afforestation, Laterite wastelands, Soil nutrients, Zone of preference Introduction The humus-rich soil in natural forests provides a variety of habitats for the organisms of detritus food web. Effect of soil biota in rhizosphere is linked to their size, small organisms like bacteria, fungi, protozoan, springtails, mites, nematodes contribute to energy utilization and nutrient cycle, whereas larger animals like earthworms, millipedes, isopods are dominant habitat transformers (Lavelle et al., 1997; Anderson, 2). Therefore functional dissimilarity among soil fauna has very significant impact on litter decomposition and nutrient cycling (Heemsbergen et al., 24; Bardgett et al., 25). For example, high density and diversity of soil microarthropods occur in most forests, in the fermentation layer or in the zone of intergradations between litter and soil (Wallwork, 197; Crossley, 1977). They enhance energy flow and nutrient release through feeding on the litter and have stimulatory effects on the structure and activity of microbes in soil (Mikola et al., 22). Wardle et al. (26) showed that litter diversity in monoculture forests had notable effects on abundance and diversity of litter fauna and that different litter types promoted different subsets of fauna. In this context, an ecological assessment of afforestation practices is very pertinent in tropical soils because the efforts are aimed to achieve higher nutrient status of soil and stability as well as diversity of decomposer community. Several fast growing and drought resistant native and exotic trees are used in India for afforestation and land reclamation. However, the ecological suitability of even dominant tree types in terms of nutrient enrichment and biological activity in soil has not been properly evaluated. This paper deals with the impact of afforestation Research in Environment and Life Sciences 115 on edaphic properties in eroded laterite areas by comparing the population responses of soil microarthropods and the nutrient status in monoculture stands of different forest tree species, and from the zone of preference of Collembola to soil parameters. August, 21 Materials and Methods Description of study site, soil and climate conditions: The study was conducted during in selected monoculture stands of Ballavpur Reserve Forest at Santiniketan (23 29 North Latitude, East Longitude) in the Eastern region of India. Several trees are used for afforestation of eroded laterite areas, of these, the exotic Cassia siamea (Lamk.) Cesalpiniaceae and Acacia auriculiformis (A.Cunn. ex. Benth) Mimosaceae and the native Shorea robusta (Gaertn) Dipterocarpaceae and Dalbergia sissoo (Roxb.) Fabaceae are common in the locality. The study sites comprised of monoculture stands of above trees (5 5 m each, approx. 2 years old) and a mature stand of C. siamea trees (1 1 m, approx. 4 years old) within one km 2 (approx.) area of the forest. The eroded laterite soil is brick red in colour and sandy loam in texture, has poor water holding capacity and low electric conductivity, acidic ph and has very poor nutrient status, but rich in oxides of aluminum and iron (Bhattacharya, 1979). However, Joy (26) showed that afforestation practice could improve the physicochemical and biological properties of wasteland soil. This area has tropical climate of summer (March to May), monsoon (June to August), post monsoon (September to November), and winter (December to February) seasons. The average climatic

2 Table - 1: Seasonal variation in the density of soil microarthropod groups in afforested monoculture plantations (Number/m 2 ± S.E.) Afforested sites Microarthro-pod Winter Summer Monsoon Post-monsoon Total Relative groups (February) (May) (August) (November) abundance (%) Cassia siamea Acari 38 ± ± ± ± ± Collembola 486 ± ± ± ± ± Other groups 194 ± ± ± ± ± Total 988 ± ± ± ± ± 923 Shorea robusta Acari 32 ± ± ± ± ± Collembola 26 ± ± ± ± ± Other groups 74± 19 48± ± 5 58± ± Total 582 ± ± ± ± ± 668 Acacia auriculiformis Acari 32± ± 4 342± ± ± Collembola 37± ± 7 662± ± ± Other groups 11± 21 8± 46 26± 51 12± ± Total 782± ± ± ± ± 694 Dalbergia sissoo Acari 268± 97 33± ± ± ± Collembola 424± ± ± ± ± Other groups 178± ± ± 91 7± 2 664± Total 87± 32 74± ± ± ± 932 data during showed that annual rainfall was mm, monthly temperature was 25.4 C and monthly relative humidity was 78.2%. Collection of soil samples and extraction of microarthropods: Soil samples were collected at seasonal intervals from the monoculture stands and monthly from the mature stand of C. siamea trees. From each site five samples of cm size were taken randomly during morning (8.-9. hours) after removing the upper dry litter carefully. Soil and litter inhabiting microarthropods were extracted from the samples using Tullgren funnels for 24 hours into vials containing.4% formalin. Sorting, identification and counting of specimens were done by examining the contents of each vial under a dissecting microscope. After the extraction, the dry soil samples from each site were pooled, powdered and sieved (72 mesh) for the estimation of major chemical parameters. Physico-chemical analysis of soil samples: Standard methods were employed for physicochemical analysis of soil, using six replicates for each interval. During each sampling occasion soil temperature was recorded by inserting soil thermometer to a depth of 5 cm and moisture content of soil was measured in Infrared moisture meter at 15 C. Soil ph and conductivity were tested in a soil-water suspension (1:2.5 ratio) and readings were taken using digital ph meter (Model 361, Systronics) and digital EC meter (Model 34, Systronics), respectively (Trivedy et al., 1987). Soil organic carbon content was estimated by Walkley-Black titration method.however, nitrate and available phosphorus contents were determined using spectrophotometer (Model DU-73, Beckman Coulter) by nitrophenol-di-sulphonic yellow colour method and ammonium molybdate blue colour method, respectively (Jackson, 1962). Nutrients namely sodium, calcium and potassium were extracted from the soil samples in.5 (N) HCl and estimated using flame photometer (Model 125, Systronics) calibrated against sodium chloride, calcium carbonate and potassium chloride solutions, respectively (Jackson, 1962). Statistical analysis: Statistical interpretation and graphical representation of the experimental data were done using Excel and OriginLab computer programmes. The error values of replicates were included with average values. Statistical significance of variations in the densities of microarthropod groups with respect to seasonal intervals of estimation was worked out using t-test. Monthly variations in the density of Collembola and the concentrations of soil parameters were compared using simple correlation and regression, and multiple regression analysis. The zone of preference of Collembola to different soil parameters was computed from their abundance corresponding to low, medium and high levels within the estimated range of each parameter. Results Seasonal distribution of microarthropods in afforested soil: Comparison of soil microarthropod population in afforested monoculture sites (Table 1) showed higher density in D. sissoo (4138 m -2 ) and C. siamea (3914 m -2 ) soils than in A. auriculiformis (376 m -2 ) and S. robusta (2526 m -2 ) soils. The variations in microarthropod density between sites were also evident in all seasons. Collembola dominated in all the sites and during all the seasons except in S. robusta soil where the number of Acari was more except during monsoon. These two groups represented more than 8% of total microarthropod population in all the sites. High incidence of microarthropod groups other than Collembola and Acari were observed during monsoon. However, in all the sites the highly significant increase in density of microarthropod fauna in monsoon season (p<.1) was temporary, which declined (p<.5) in post monsoon months (Table 2). This trend was mainly due to drastic fluctuations of in all the sites. In mature stand of C. siamea also the density of Collembola depicted same Research in Environment and Life Sciences 116 August, 21

3 Collembola density Temperature (oc) Organic carbon (%) Moisture content (%) ph EC (mmho/cm2) Nitrate N (ppm) ( A ) ( B ) ( C ) ( D ) ( E ) ( F ) ( G ) Fig. 1: Seasonal variation of density of Collembola (Number per sample ± S.E.) and soil parameters (Average ± S.E.) in the mature stand of Cassia siamea trees (W = winter, S = summer, M = monsoon, PM = post monsoon) seasonal trend (Fig. 1A), population was very low during summer (6.8/sample) when compared to high numbers in other seasons and population peak was observed during monsoon (4.27/ sample). Seasonal changes of soil parameters in afforested sites: Comparison of soil parameters between afforested sites (Table 3) showed negligible variations in the moisture content ( %) and temperature ( C). However, soil was more acidic in A. auriculiformis and S. robusta (ph 5.18) than in C. siamea and D. sissoo (ph 6.83). The electrical conductivity was also low in S. robusta (.83 mmho cm -2 ) but improved in A. auriculiformis and C. siamea to excel in D. sissoo (.217 mmho cm -2 ). Organic carbon, nitrate nitrogen and available phosphorus contents were highest in D. sissoo and C. siamea soils. S. robusta had the lowest organic carbon content (.42%) where as A. auriculiformis had the lowest concentrations of nitrate nitrogen (.5 mg g -1 dry soil) and available phosphorus (3.63 µg g -1 dry soil). The concentrations of sodium, potassium and calcium were also high in the soils of C. siamea and D. sissoo trees. A clear distinction of afforested soils could be seen, C. siamea and D. sissoo represented nutrient-rich habitats but A. auriculiformis and S. robusta were nutrient-poor sites. This was confirmed by low C/N and P/N ratio in the soils of C. siamea and D. sissoo, when compared to high ratio in A. auriculiformis and S. robusta stands. In mature stand of C. siamea trees, the soil temperature was high in summer (34.78 C), which declined (17.17 C) during winter (Fig. 1B). The moisture content of soil was high in monsoon and post monsoon months (Fig. 1C) but low in summer (5.45%). Regarding chemicals, the ph was acidic during summer and monsoon (Fig. 1D), improved in post monsoon to record slightly alkaline ph in winter (7.16). The electrical conductivity of soil (Fig. 1E) decreased in summer and monsoon but was highest in winter season (.41 mmho cm -2 ). However, organic carbon content of soil was low in summer (.81%) but improved in monsoon and post monsoon times (Fig. 1F). Similarly, nitrate content of soil (Fig. 1G) increased notably during monsoon and post monsoon months ( ppm). Correlation and preference of Collembola to soil parameters: Correlation and regression analysis (Fig. 2) between Collembola population and soil parameters in mature C. siamea stand showed that all parameters except soil temperature were positively correlated and was statistically significant (p<.5) for electrical conductivity, organic carbon and moisture contents of soil. The negative correlation of Collembola with soil temperature was also significant (p<.5). Scatter diagram showed that population was inclined towards alkaline ph, and for nitrate-n the relation was towards a low range. Multiple regression analysis (Table 4) indicated significant cumulative effect of major soil parameters (F value = 3.215, p<.2) on the population. The zone of preferences of Collembola to soil parameters validated these inferences. Their abundance at different levels of each parameter yielded a preference pattern (Table 5). The population was negligible at high soil temperature and more than 55% of animals occurred in the medium level ( C). Research in Environment and Life Sciences 117 August, 21

4 Table - 2: Statistical significance of differences (t-test) between the seasonal densities of total Acari, Collembola, and total soil microarthropods in monoculture forests Litter type Groups Seasons Difference t-value P X 1 X 2 Cassia siamea Acari W S n.s. S M <.5 M P M n.s. Collembola W S <.1 S M <.5 M P M n.s. Total W S <.1 S M <.1 M P M <.5 Shorea robusta Acari W S n.s. S M n.s. M P M n.s. Collembola W S n.s. S M <.1 M P M <.1 Total W S n.s. S M <.1 M P M <.1 Acacia auriculiformis Acari W S <.1 S M <.1 M P M n.s. Collembola W S n.s. S M n.s. M P M n.s. Total W S <.1 S M <.1 M P M n.s. Dalbergia sissoo Acari W S n.s. S M <.5 M P M <.1 Collembola W S n.s. S M <.1 M P M <.1 Total W S n.s. S M <.1 M P M <.1 Note: t-test based on average number per sample, N = 5 in each seasonal interval, n.s. = not significant; W = winter, S = summer, M = monsoon, PM = post-monsoon seasons Opposite pattern was seen for soil moisture content, only 14% of total population existed in the low level (<1% soil moisture). Collembola did not prefer low soil ph, more than 85% of population existed in medium and high ph ( ). Similarly, they did not prefer low electrical conductivity of soil, and more than 85% of fauna existed in higher levels ( mmho cm -2 ). On the contrary, Collembola preferred high organic carbon content of soil (54% of population were in the level of %) and low nitrate content of soil (>69% population existed in the low level of <1692 ppm). Discussion Impact of seasons and litter types on soil microarthropod population: Population density of soil microarthropods varied with respect to litter types and seasons in the afforested monoculture Research in Environment and Life Sciences 118 stands. Their high density in C. siamea and D. sissoo soils was attributed to litter traits like small and fragile nature of leaves, fast degradation and detritivore feeding (Joy and Joy, 1991), high preference and colonization of microarthropods (Maity and Joy, 1999) and low concentrations of non-nutrient chemicals (Das and Joy, 29), which differed significantly with A. auriculiformis and S. robusta litters. In tropical soils most of the litter deposited in dry season undergoes mineralization within the wet season (Satchell, 1974). But litters of different plants do not decompose at the same rates due to their variations in structure and composition. Maity and Joy (2) showed fast rate of degradation of C. siamea litter than A. auriculiformis litter in litterbags of different mesh sizes. Mukhopadhyay and Joy (21) observed significant variations in microbial functions and nutrient status of soil in afforested wastelands August, 21

5 16 y y = 139.7x , df = 23 df = r r = , p<.5 P < Tem Temperature (( oo C) C) 16 y = 49.77x +3.72, , df = 23 df = 23 r =.433, p<.5 P < Soil Soil moisture moisture (%) C ollem bola population 16 y = x , , df = 23d f = r = -.2,.22, ns n.s Soil ph S oil ph y = 13.43x , df = 23 r y = =.565, 13.43x p< , df = 23 r =.565, P < Electrical conductivity (m Mho cm -2 ) E lectrical C onductivity (m M ho/cm 2 ) 16 y = 1.84x 1.84x , , df = 23 df = 23 r =.45,.45, p<.5 P < Organic carbon (%) (%) Nitrate Nitrate nitrogen (ppm) Fig. 2: Correlation of with major soil parameters in the mature stand of Cassia siamea trees and showed higher rates of soil enzyme activities, MBC and soil respiration in the decomposition pits of C. siamea and D. sissoo litters than in the pits of A. auriculiformis and S. robusta litters. Similarly, the climate fluctuations in monoculture forests controlled the population of soil microarthropod groups; monsoon months favoured high density whereas summer was unsuitable for population growth. Reddy and Toky (199) and Tripathi et al. (25) recorded very few soil arthropods in dry season, but collected large densities during wet period from July to December. Maity and Joy (1999) compared colonization and succession of 16 y y = 58.25x 58.25x +.1, +.1, df = df 23= 23 r r =.38, nsn.s microarthropod groups in 12 different forest tree litter types in decomposition pits and showed that Collembola was the predominant initial colonizer in the litters and Acari gained importance as decomposition progressed. This would explain for the higher abundance of Acari observed by several workers in the tropical deciduous forest soils (Singh, 1977; Sarkar et al., 2; Wiwatwitaya and Takeda, 24). Anichkin et al. (27) studied the abundance, biomass, vertical distribution, and taxonomic composition of soil invertebrates in different monsoon tropical forests of Southern Vietnam, and observed relatively low density of Collembola in a Research in Environment and Life Sciences 119 August, 21

6 Table - 3: Variation of soil parameters in afforested monoculture plantations Soil parameters Table - 4: Multiple regression between density of Collembola (Y) and soil parameters (X) in mature stand of Cassia siamea trees (based on average monthly data for 24 months) Parameter Value Error t-value Prob> t Y-Intercept X X X X X X ANOVA Table: R-Square(COD) Adj. R-Square Root-MSE(SD) Afforested sites Cassia Shorea Acacia Dalbergia Temperature ( o C) ± ± ± ± 12.2 Moisture content (%) ± ± ± ± 9.84 ph 5.76 ± ± ± ±.39 EC (mmho cm -2 ).133 ±.2.83 ±.2.12 ± ±.3 Organic carbon (%) 1.7 ±.9.42 ±.1.49 ± ±.54 Nitrate nitrogen (mg g -1 dry soil) 9.9 ± ±.34.5 ± ± 1.24 Phosphorus (µg g -1 dry soil) ± ± ± ± Sodium (µg g -1 dry soil) 24.9 ± ± ± ± 2.24 Potassium (µg g -1 dry soil) 45.9 ± ± ± ± 8.98 Calcium (µg g -1 dry soil) ± ± ± ± C / N ratio P / N ratio Note: Average of all seasonal estimations ± S.E., Number of samples = 6 in each seasonal interval Degrees of Sum of Mean Item Freedom Squares Square F Statistic Prob>F Model Error Total Note: Independent parameters (X 1 -X 6 ): moisture, temp, ph, Ec, organic carbon, nitrate nitrogen; Dependent parameter (Y): lowland forest of Lagerstroemia sp. than in a mountain pine (Pinus kesiya) forest. The trophic relations and food utilization efficiencies of soil fauna would indicate their functional significance in the transformation of energy and nutrients from detritus. The diversity and ecology of mangrove litter inhabiting microarthropods was investigated by Dey et al. (21), to assess their functional role in the nutrient cycling; Acari represented 36.3% and Collembola 27.2% of total microarthropod population, which displayed distinct seasonal fluctuation with regard to their population density and community structure in relation to fluctuating major physico-chemical parameters. According to Baldock (27) the organic molecules synthesized by the soil decomposer community (fauna and microorganisms) create a secondary source of decomposable organic carbon once the decay of plant residues is initiated. Correlation between soil parameters and Collembola population: Soil microarthropod fauna is mostly comprised of detritivore and fungivore groups and therefore governed by factors that control microbial activity and decomposition. They are often numerous in the fermentation layer of forest soils and able to opportunistically utilize the available edaphic conditions. Present study showed direct effect of soil parameters on microarthropod population, density was low in summer but the optimum temperature and moisture during monsoon and post monsoon months favoured population growth. Structure and properties of the medium and the morphological characteristics of the species determine the distribution of soil microarthropods in environmental gradients. Badejo and Van Straalen (1993), Jain et al. (1998) and several others have found high density of Collembola in increased soil moisture conditions, and Research in Environment and Life Sciences 12 August, 21

7 Table - 5: Zone of preference of to soil parameters in mature stand of Cassia siamea trees Soil parameters Range / Density Level of soil parameters (% occurrence) Low Medium High Soil temperature ( o C) Collembola (38.1) (56.9) 33.6 (4.9) Soil moisture (%) Collembola (13.9) (48.2) (37.9) ph Collembola (14.3) (43.8) 284. (41.8) EC (mmho cm -1 ) Collembola (14.2) (52.9) (32.9) Organic carbon (%) Collembola (1.7) (35.3) (54.) Nitrate-N (ppm) Collembola (69.7) 13. (19.2) 76. (11.2) therefore this parameter appeared to be the initiating factor for microarthropod population in tropical soils. On the contrary, soil temperature had negative relation with density of Collembola. Choi et al. (22) showed that temperature could control the population of Paronychiurus kimi, a common soil dwelling Collembola in S. Korea. Like the present results Badejo et al. (1998) also showed that moisture and temperature were, respectively, positively and negatively related with populations of Collembola. We found that the ph and EC of C. siamea soil improved during post monsoon and winter seasons and registered positive correlations with Collembola. Bonnett et al. (26) noted that microbial redox reactions (nitrification), increase of humus content, weathering of minerals and cation exchange capacity are the major causes for change in soil ph. Hazra and Bhattacharya (26) showed high abundance of microarthropod fauna in neutral ph of soil than in acidic ph of soil. The relationship between organic matter and nitrogen contents is an index of soil fertility and biological activity in soil. Organic matter is a fundamental source of energy and nutrients in soil habitats and like the present results Kumar et al. (1999) observed that high level of organic carbon was associated with diverse and dense soil fauna. Hannam et al. (27) found greater concentration of soil organic matter in the forest floors of Aspen (Populus tremuloides) than in Spruce (Picea glauca) and noticed strong effect of stand type on the quantity of nitrate in these forest floors. The relationship between Collembola and soil chemistry and humus types in different forest sites in Southern France was studied by Cassagne et al. (23) and showed strong relationship between Collembola and soil chemical characteristics other than ph. Comparison of major soil parameters could distinguish the afforested sites into nutrient-rich and nutrient-poor habitats. The low C/N and P/N ratios in the soil of C. siamea and D. sissoo trees indicated fast rates of carbon utilization and nutrient release than that in the soils of S. robusta and A. auriculiformis stands. Soil organic matter is a major determinant of carbon and nutrient cycling and it contributes to soil structure and offers resistance to erosion (Herrick and Wander, 1997). Garcia et al. (25) observed wide variations in total organic carbon content of soil under several plant Research in Environment and Life Sciences 121 systems and suggested that the species with higher TOC values might be used for soil restoration under semiarid climate conditions. Multiple regression analysis confirmed the cumulative impact of soil parameters in regulating. Reddy (1984) noted that combination of two or more soil factors exerted significant influence on the microarthropod populations. According to Wallwork (197) the distribution of soil fauna is a function of their dependence to a combination of the micro-environmental factors like moisture, organic content, ph, salinity and ground cover. Zone of preference of collembola to soil parameters: Comparison of zone of preferences of Collembola to soil parameters showed that the population did not prefer high temperature and low moisture conditions of soil, occurred abundantly in more or less neutral ph and moderate EC of soil, and preferred high organic carbon and low nitrate-n contents of soil (high C/N ratio). This combination of edaphic parameters occurred in monsoon and post-monsoon periods and to some extent during winter and favoured the population growth. According to Mitra et al. (1981) changes in relative humidity of soil, combined with changes in soil temperature, played a significant role in limiting populations of Collembola. Tripathi et al. (25) showed that silvipastoral systems with highest concentrations of soil nutrients had highest densities of soil arthropods. On the other hand, Baldock (27) noted that the year round activity of decomposers including the involvement of detritivorous and fungivorous soil animals ensure continuous nutrient availability to plants and creation of a secondary source of decomposable organic carbon. The tropical environment would favour rapid life cycle and short life span of most soil animals, which suggested that microarthropods like Collembola would produce many generations during a seasonal cycle characterized by drastic variations in climatic and soil parameters. High density of Collembola coincided with moderate levels of soil temperature and moisture, more or less neutral ph and medium level of EC of soil, and high organic carbon and low nitrate-n contents of soil. This study showed the biological potential of soil microarthropods especially groups like Collembola to respond promptly to edaphic August, 21

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