Faculty of Agriculture, Shahed University, Tehran, Iran
Corresponding author Email: email@example.com
Article Publishing History
Accepted After Revision: 19/06/2017
This study was undertaken to evaluate the factors affecting the abundance of rhabditid nematodes in the farms of Khorramabad city of Lorestan province, Iran. Nematode communities as well as rhabditids population reacted to the soil pH and the type of crops cultivated at each sample point. Crop type affected nematode populations mainly due to their root systems. Also, the abundance of rhabditid nematodes decreased at lower pH of the soil. Since some of the nematodes are entomopathogenic hence, results of the present study are important in terms of biological control of soil pests which leads to preservation of agro-ecosystem through less use of chemical pesticides and achievement of a sustainable agriculture.
Nematodes, Root System, Soil Ph
Vafa A, Saeedizadeh A, Bostani A. Abundance of Rhabditid Nematodes in Agricultural Soil of Khorramabad, Iran. Biosc.Biotech.Res.Comm. 2017;10(2).
Vafa A, Saeedizadeh A, Bostani A. Abundance of Rhabditid Nematodes in Agricultural Soil of Khorramabad, Iran. Biosc.Biotech.Res.Comm. 2017;10(2). Available from: https://bit.ly/32lPisT
Rhizosphere soil often contains a variety of soil pests that are harmful to the host plant. Potentially, chemical method is the first choice of farmers to cope with this problem. However, in addition to forcing heavy costs, it either endangers the health of human and animals or has harmful side effects on the environment.As stated by Brussaard (2012), soil ecosystem services are benefits derived from ecosystems that are necessary to maintain soil health and productivity; they are delivered by the ecosystem functions of soil organisms. Studies have shown that many soil mesofauna, including nematodes in several trophic levels, are one or two steps higher in the food chain than microbes. Also, their generation time is longer than that of the metabolically-active microbes, making them more temporally stable rather than fluctuating with ephemeral nutrient flushes (Nannipieri et al. 1990) . Furthermore, nematodes have been widely used as indicators of soil biodiversity and functioning and as indicators of environmental disturbances (Bongers & Ferris 1999; Neher 2001, Ferris et al. 2001; Yeates 2003 Ferris & Tuomisto 2015; Steel & Ferris 2016) .
Soil nematodes play a central role in the soil food web and linkage to ecological processes therefore, they have been considered as a tool for testing ecological hypotheses and understanding biological mechanisms in soil (Neher 2010).Guilds of soil biota are closely associated with different ecosystem functions. In this regard, Carrascosa et al. (2014) reported a positive and significant relationship between soil suppressiveness, soil food web structure and nematode diversity. Suppression of pest and disease organisms is an ecosystem service that is the outcome of the ecosystem function of biological population regulation (Brussaard 2012, Steel & Ferris 2016) .
Rhabditid nematodes are an interesting zoological taxon. They are very abundant in all types of soil and sediments of freshwater bodies and play important ecological roles mainly as primary consumers their free-living forms display saprophagous or bacteriophagous feeding habits but also as animal parasites, in particular enthomopathogenic forms (Abolafia & Peña-Santiago 2003). Previous researches have shown that some soil physico-chemical characteristics such as texture, pH, bulk density, soil water potential, temperature, organic content” can affect the nematodes behavior (Gruner et al. 2007; FAO, 2017).
However, further investigation is still needed on factors affecting their population distribution all over the world (Stuart et al. 2006). Lorestan province with an area of about 28,392 km2 (1.7% of the country area) is located in the south-western Iran at the Zagros Mountain hillside and is influenced by the Mediterranean climate. According to statistics released by the Ministry of Agriculture in 2015, the province is one of the most important centers of agriculture (535,947 hectares of cultivation area with 2,169,818 tons of agricultural products). Therefore, development of biological control in the province could lead to saving on the costs of agriculture, as well as protection of the environment.The aim of this research was to study the abundance of Rhabditid nematodes under the effect of pH and crop type cultivated in the farms of Khorramabad city of Lorestan, Iran.
Materials and Methods
Study Site and Soil Sampling
The study site (longitude from 48° 0› to 48° 55’ E and latitude from 33° 20’ to 33° 42’ N) is located in the region of the Khorramabad’s agricultural lands, Lorestan province, Iran (Fig. 1). Samples were randomly taken from a depth of 15 to 30 cm of rhizosphere soil during the growing season of September and October. Depending on each farm area, sampling intervals was varied from 20 to 25 m. The geographical coordinates as well as altitude were recorded by a GPS device model Garmin ETrex Vista HCX (data are not presented). Also, the type of cultivated crop in each sampling point was recorded. In total, 175 soil samples were taken from 24 different crop types including: alfalfa, apple, apricot, barley, clover, corn, eggplant, garlic, grape, green beans, mung, oak, pea, peach, pepper, pomegranate, radish, red beans, rice, tomato, turnip, vegetable, walnut, wheat. The acidity of the soil samples was also determined in the laboratory by using a pH meter.
|Figure 1: Geographical location of the study sitelocated in the region of Khorramabad city (marked with green on the left side) of Lorestan province (colored in red)|
Nematodes were extracted from soil samples using a modified Baermann funnel procedure (Viglierchio & Schmitt 1983). For this purpose, plastic trays having a sieve (mesh no 10) were used. First, trays were filled with water and covered with a layer of tissue paper. Afterward, soil samples were spread on tissue paper. After four days, nematodes were extracted using a sieve (mesh no 400) from the water and were transferred to Petri dishes. The total number of nematodes as well as the number of Rhabditids were counted using a stereomicroscope at 40x of magnification. Statistical analyses were carried out using SAS, Excel and Minitab software.
Results and Discussion
Association Between Nematode Abundance And Crop Type
Soil ecosystem functioning is of topics in ecological and agricultural studies (Steel & Ferris 2016). Researches have shown that plant composition, soil properties, and microclimates cause changes in composition and structure of nematode populations among soil ecosystems (Neher 2010). The results of counting nematodes revealed that the overall mean abundance of all nematodes in the study site was 89.33±3.94 nematode per 100 g of the soil (n = 175). Also, the mean abundance of Rhabditid nematodes was 3.55±0.23 nematode per 100 g of the soil. According to this result, approximately 4% of the total population of assayed nematodes belonged to the Rhabditids. This ratio was 7.12% (highest) for pea and 1.70% (lowest) for rice. One way ANOVA showed that the abundance of all nematode types as well as Rhabditid nematodes was statistically significantly different among studied crop types (Table 1).
|Table 1: ANOVA of frequency of nematode populations studied in some different farms/gardens of Khoramabad of Lorestan province, Iran.|
|Type of cultivated crop||23||4910.86 *||15.06 *|
|*significant difference at the 0.05 of probability level|
Averagely, the highest and lowest mean abundance of all nematodes was found in the rhizosphere soil of farms of turnip (130.17±12.05, n=12) and garlic (23±18, n=2), respectively. Also, the highest and lowest mean abundance of Rhabditid nematodes belonged to radish (6.5±0.5, n=2) and rice (0.71±0.42, n=8), respectively (Table 2). The result revealed that rice rooting system and/ or paddy soil was not a suitable environment for reproduction and growth of Rhabditida nematodes. Also, it seems that glandular root system provided a more suitable environment for the growth and mobility of Rhabditid nematodes than a superficial root system.
|Table 2: Descriptive statistics related to the frequency of nematode populations studied in some different farms/gardens of Khoramabad of Lorestan province, Iran.|
|All nematodes||Rhabditid nematodes|
|Sum||Mean ± SE||Min||Max||Sum||Mean ± SE||Min||Max|
|Alfalfa||9||993||110.33±18.58 ab||27||230||47||5.22±0.81 ab||1||9|
|Apple||13||1394||107.23±18.4 abc||9||264||44||3.38±0.59 ab||0||7|
|Apricot||5||523||104.6±18.85 abc||53||157||22||4.4±1.5 ab||1||10|
|Barley||25||2257||90.28±10.57 abc||8||205||82||3.42±0.6 ab||0||10|
|Clover||7||593||84.71±16.16 abc||16||146||32||4.57±1.56 ab||0||13|
|Corn||16||1894||118.38±14.37 ab||30||288||67||4.19±0.44 ab||2||7|
|Eggplant||7||528||75.43±9.34 abc||43||104||21||3±0.72 ab||1||7|
|Garlic||2||46||23±18 c||5||41||2||1±1 b||0||2|
|Grape||7||426||60.86±18.33 abc||3||136||20||2.86±1.08 ab||0||8|
|Green beans||3||129||43±16.77 bc||13||71||4||1.33±0.88 b||0||3|
|Mung||6||391||65.17±11.99 abc||18||97||20||3.33±0.56 ab||1||5|
|Oak||6||331||55.17±15.9 abc||4||100||6||1±0.37 b||0||2|
|Pea||3||112||37.33±4.91 bc||31||47||8||2.67±0.88 ab||1||4|
|Peach||2||236||118±75 ab||43||193||10||5±3 ab||2||8|
|Pepper||3||322||107.33±22.7 abc||62||132||8||2.67±1.33 ab||0||4|
|Pomegranate||3||280||93.33±22.58 abc||56||134||10||3.33±1.33 ab||2||6|
|Radish||2||228||114±38 ab||76||152||13||6.5±0.5 a||6||7|
|Red beans||2||75||37.5±5.5 bc||32||43||3||1.5±0.5 b||1||2|
|Rice||8||336||42±15.59 bc||2||122||5||0.71±0.42 b||0||3|
|Tomato||5||403||80.6±11.95 abc||58||122||16||3.2±0.73 ab||1||5|
|Turnip||12||1562||130.17±12.05 a||36||188||78||6.5±1.25 a||1||16|
|Vegetable||6||500||83.33±17.69 abc||43||152||11||1.83±0.54 ab||0||3|
|Walnut||2||230||115±30 ab||85||145||9||4.5±0.5 ab||4||5|
|Wheat||21||1883||89.67±13.52 abc||10||247||80||3.81±0.99 ab||0||18|
|Means have been compared using Duncan multiple range method.
Means with the same letter are not significantly different.
As demonstrated earlier, crop type affects the soil ecosystem in different ways. For instance, breeding programs for improving yield lead to the introduction of new high-yielding varieties. Such modified crops have a high potential of absorption of minerals from the soil as well as higher photosynthetic capacity that affect the quantity and quality of nutrients and energy flowing through the soil (Neher 2010). Also, plant life cycle has been known as another factor affecting soil ecosystem. Perennial crops have a more extensive root web and rooting depth than annual crops leading to support a soil community with many omnivores and predators. Populations of terrestrial ecosystems in perennial crops is more similar to that of natural soil ecosystem as compared to annual crops (Freckman & Ettema 1993; Neher & Campbell 1994). Wardle et al. (2003), believe that plant species have greater effects on microbes and plant-parasitic nematodes than they do on predatory nematodes. Moreover, rooting pattern of different functional groups of plants (i.e., legumes, forbs) constructs habitats which are more favorable to some species of nematodes than others (Neher 2010). Furthermore, Pis´kiewicz et al. (2008) reported that communities of plant-parasitic nematodes can be complex within the rhizosphere of a single plant species. Such as those obtained in this study, the above reports confirm that there are significant differences in soil ecosystems arising from various crops cultivation.
Figure 2 shows the results obtained from cluster analysis of 24 different crops based on nematode abundance observed in each cultivated crop. On this basis, studied crops were classified into 3 groups. The average abundance of nematodes along with the standard error corresponding to each group has been shown in Table 3. Clusters 1, 2 and 3 had 9, 10 and 5 members, respectively. The highest frequency of nematodes belonged to cluster 1 where some crops such as alfalfa, apple, apricot, corn, peach, pepper, radish, turnip and walnut were grouped in it. Also, cluster 3 comprising of garlic, green beans, pea, red beans and rice had the lowest frequency of nematodes (Table 3). With respect to the members of cluster 1 “which had the highest abundance of Rhabditid nematodes” it can be concluded that the root systems arisen by perennial crops (alfalfa), glandular plants (turnip, radish) and trees (apple, apricot, peach, walnut) were more favorable for Rhabditid nematodes. Therefore, in agreement with Freckman & Ettema (1993) and Neher (2010), the result showed that perennial plants had an impact on Rhabditid nematodes population.
|Table 3: Properties of clusters obtained on the basis of data recorded for Nematode and Rhabditids abundance in some different farms/gardens of Khoramabad of Lorestan province, Iran.|
|Cluster||Number of observations||Cluster membership (crop type)||All nematodes
mean ± SE
mean ± SE
|1||9||Alfalfa, Apple, Apricot, Corn, Peach, Pepper, Radish, Turnip, Walnut||114.16±2.53||4.71±0.43|
|2||10||Barley, Clover, Eggplant, Grape, Mung, Oak, Pomegranate, Tomato, Vegetable, Wheat||77.85±4.20||3.02±0.31|
|3||5||Garlic, Green beans, Pea, Red beans, Rice||36.57±3.58||1.43±0.34|
|Cluster analysis has been carried out using complete linkage method and Euclidean similarity matrix|
Effect of Soil Ph on Nematode Abundance
Data obtained from the study showed that soil pH in the area of study ranged from 6.5 (Grape) to 8.16 (Vegetable) (Table 4). Figure 2 shows mean abundance of nematodes at different amounts of pH of the soil. Results revealed that the mean abundance of nematodes rose up in soils with slightly alkaline property (soil pH more than 7). The average frequency of Rhabditid nematodes in the soil with pH more than 8 was numerically higher than that of 7-8. However, this superiority was not statistically significant. In general, results of this study showed that the nematode populations significantly decreased at the soil pH less than 7.
|Figure 3a: The effect of pH on mean abundance of all nematode types (above) and Rhabditid nematodes (below) per 100 g of the soil extracted from some different farms of Khoramabad city of Lorestan province, Iran|
As described by Garbeva et al. (2004) and Šalamún et al. (2014), changes in soil pH could have led to direct and indirect effects on the nematode community. Likewise, results of this study revealed that the abundance of Rhabditid nematodes decreased at lower pH of the soil. Korthals et al. (1996), believe that a lower pH enhances the toxicity of heavy-metals through increase of their adsorption to the soil.
Korthals et al. (1996), have shown that nematodes exchange several ions through their cuticle in order to regulate their osmotic pressure. It has been suggested that soil acidification can lead to increasing ion concentrations in the soil pore water to such an extent that nematodes might experience problems in regulating their water status. They also stated that, soil pH indirectly affected the nematode community by influencing food availability, by interfering with the competitive interactions between species, or by affecting the abiotic environment.
In conclusion, results of the present study indicated that crop type as well as soil pH could affect Rhabditid nematodes communities. The outcome is important in terms of biological control of soil pests which leads to preservation of agro-ecosystem through less use of chemical pesticides and achievement of a sustainable agriculture.
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