Assessing the impact of cultivation and plant domestication of highbush blueberry (Vaccinium corymbosum) on soil properties and associated plant-parasitic nematode communities

We investigated the interactive effects of plant domestication and perennial cultivation on diversity and richness of plant-parasitic nematode (PPN) communities associated with highbush blueberry (Vaccinium corymbosum). Rhizospheric soil of V. corymbosum plants was sampled in coupled wild and cultivated sites within the Pinelands National Reserve. Although PPN diversity was higher in cultivated plant soil samples, richness was higher in wild plant soil samples. The most important soil properties, iron and calcium, were associated with cultivated soil and were the best predictors of genera abundance patterns. Nematodes in the genus Criconemoides were 187 more abundant in wild sites than cultivated and thus, were significant indicators of wild sites. In this study cultivation of V. corymbosum appears to benefit the PPN community but alters the community composition considerably. © 2015 Elsevier Ltd. All rights reserved. Over the past decade, interest in the response of belowground communities to plant species and land management practices has grown considerably (Duncan et al., 2007; Maron et al., 2011; Bever et al., 2012; Monroy et al., 2012). Soil ecosystems support an astounding diversity of microbes, microfauna, and mesofauna that provide multiple levels at which the impact of human intervention can be assessed. Similarly, nematode communities have been a focus of many studies because of their multi-faceted importance to the soil food-web (Yeates, 2010). Both abundant and diverse, nematodes are responsive bioindicators which provide a measure of the impact of human landscape management on the soil system (Bongers and Ferris, 1999). Furthermore, in specific trophic roles, nematodes are labeled as both beneficial, by providing ecosystem services (e.g., entomopathogenic nematodes (EPN)) (Denno et al., 2008) and as pest organisms such as plant parasites (Kandji et al., 2001). [email protected] Terrestrial plants are the primary source of organic carbon in both above and below-ground environments and are thereby integral to the soil food-web (Bukovinszky et al., 2008). The function and diversity of nematode communities within the soil food-web is mediated by various factors such as plant species identity, soil amendments, and land management practices (Robertson and Freckman, 1995; De Deyn et al., 2004; Liang et al., 2009; Palomares-Rius et al., 2015). While the impact of plant species identity on nematode communities has been addressed qualitatively (Palomares-Rius et al., 2012) and empirically (Bezemer et al., 2010), there has been no previous work directly investigating the interactive effects of plant genotypic identity through plant domestication and land management. Frequently, nematode communities are assessed dichotomously in undisturbed wild settings or highly disturbed agricultural cropping systems which creates a bias in the literature towards the impact of land management rather than plant identity (e.g., Freckman and Ettema, 1993; Rahman et al., 2007). Plant-parasitic nematodes (PPN) are of particular interest to this study because, unlike other trophic groups, they appear to have little to no spatial correlation across highly disturbed agroecosystems (Robertson and Freckman, 1995) M.J. Rivera et al. / Soil Biology & Biochemistry 88 (2015) 25e28 26 indicating a potentially more connected relationship to individual plants rather than other soil factors, an idea which is increasingly apparent with recent research (Kostenko et al., 2015). Highbush blueberry (Vaccinium corymbosum) is a perennial woody shrub. Native to the eastern United States, it was first domesticated and cultivated in Chatsworth, New Jersey, USA in the early 20th century. To assess the impact of perennial cultivation on diversity and abundance of PPN, we compared soil characteristics and nematode communities associated with the roots of wild stands of undomesticated V. corymbosum plants with those from adjacent stands of cultivated V. corymbosum. Cultivated fields with wild V. corymbosum in nearby wooded field border were selected within the Pinelands National Reserve (Burlington County, New Jersey, USA). At each of five sites, two 15.24 m by 15.24 m plots were established, one in the cultivated site, the other in an adjacent wild Vaccinium stand within the wooded field border at no more than 30 m distance. All plots were sampled three times during the 2011 season: 19May,13 July, and 13 September. Eight vertical soil cores (30.5 cm L 2.1 cm D) were taken radially 15e30 cm from the basal point of the main trunk of each of ten randomly selected plants. The cores from each plant were combined (~800 g) and homogenized and nematodes were extracted or baited from 100 g subsamples. All PPN counts are the sum the soil extractions from the ten plants (100 g per plant, 1000 g per site) within each plot to assess PPN communities (Wiesel et al., 2015). PPN were extracted, identified to genus and counted with the help of the Rutgers Plant Diagnostic Laboratory. The centrifugal-flotation technique (Jenkins, 1964) was used for extractions to ensure the retrieval of all life-stages as well as both dead and alive specimens. Note that totals for endoparasites are likely underestimates as root-dwelling stages are not extracted with this method. A 500 g subsample of the soil from each plot was used by the Rutgers Soil Testing Laboratory to measure the following properties including: soil moisture, pH, cation exchange capacity, and total nutrients: P, K, Ca, Mg, B, Zn, Mn, Cu, and Fe. EPN abundance was also assessed by exhaustive baiting with 10 Galleria mellonella larvae of a 200 g subsample from the same plant soil samples (Koppenh€ ofer et al., 1998). Diversity was measured using the Shannon Index (H) (Shannon and Weaver, 1949). We then used canonical correspondence analysis (CCA) to explore the relationships between PPN, soil properties, and EPN abundance. Significance was assessed with forward selection to identify the most parsimonious model (Borcard et al., 2011). Indicator species analysis (ISA) was used to determine which genus-treatment associations were greater than expected by