COLONIZATION AND SUCCESSION OF ALGAE AND SOIL-ALGAL INTERACTIONS ASSOCIATED WITH DISTURBED AREAS1

The number and abundance of algal species were not significantly different between non-topsoiled areas and top-soiled areas. Successional trends were evident at both sites, since the number of species and their abundance increased over time. Soil-algal interactions were determined by regression analysis. A conceptual model was developed that illustrated the influence of soil chemical properties on algal abundance. Important factors affecting the soil algae were sodium, calcium, potassium, magnesium and certain trace elements. The possible influence of these factors on algal growth is discussed.     

Using Stable Isotopes to Differentiate Trophic Feeding Channels within Soil Food Webs

The soil is probably the most diverse habitat there is, with organisms ranging in sizes from less than 1 μm to several metres in length. However, it is increasingly evident that we know little about the interactions occurring between these organisms, the functions that they perform as individual species, or together within their different feeding guilds. These interactions between groups of organisms and physical and chemical processes shape the soil as a habitat and influence the nature of the soil food web with consequences for the above‐ground vegetation and food web. Protists are known as one of the most abundant groups of bacterivores within the soil; however, they are also consumers of a number of other food sources. Even though they are responsible for a large proportion of the mineralisation of bacterial biomass and have a large impact on the C and N cycles within the soil they are regularly overlooked when investigating the complete soil food web. Recently, stable isotopes have been used to determine trophic interactions and here we describe how this technique has been used to highlight linkages between protists and the soil food web.     

Faunal changes and geographic crypticism indicate the occurrence of a biogeographic transition zone along the southern East Pacific Rise

Aim Deep‐sea hydrothermal vents have now been reported along all active mid‐ocean ridges and back‐arc basins, but the boundaries of biogeographic entities remain questionable owing to methodological issues. Here we examine biogeographic patterns of the vent fauna along the East Pacific Rise (EPR) and determine the relative roles of regional and local factors on the distribution of biodiversity associated with mussel beds along a poorly explored zone, the southern EPR (SEPR). Location East Pacific Rise. Methods A species list of macrobenthic invertebrates along the EPR was compiled from the literature and supplemented with data recovered during the French research cruise BIOSPEEDO carried out in 2004 along the SEPR. Biogeographic patterns were assessed by combining the identification of morphological species with a molecular barcoding approach. A multivariate regression tree (MRT) analysis was performed to identify any geographic breaks, and an empirical distribution of species richness was compared with predictions provided by a mid‐domain effect model. Macrofaunal community structure associated with mussel beds along the SEPR was analysed in relation to environmental factors using cluster and canonical redundancy analyses. Results Sequencing of the cytochrome c oxidase subunit I gene revealed the occurrence of several cryptic species complexes along the EPR, with the equator separating the southern and northern clades. Furthermore, during the BIOSPEEDO cruise at least 10 still unnamed species were collected between 7°25′ S and 21°33′ S. The shift in community structure identified by MRT analysis was located south of 17°34′ S or south of 13°59′ S, depending on the data used, suggesting that the southern part of the SEPR (17°25′–21°33′ S) constitutes a biogeographic transition zone in the vent fauna along the EPR. At a regional scale, latitude combined with the type of venting was significantly correlated with the community structure associated with mussel beds. Main conclusions Together, the molecular data, in situ observations, and the distribution of species suggest that the high diversity of vent fauna species presently observed between 17°25′ S and 21°33′ S is probably a result of the overlap of several distinct biogeographic provinces. We argue that this area thus constitutes a biogeographic vent fauna transition zone along the EPR.     

Effect of Tylenchorhynchus robustoides on Growth of Buffalo Grass and Western Wheatgrass

Tylenchorhynchus robustoides reduced (P = 0.05) growth of Agropyron smithii (western wheatgrass) at soil temperatures of 20, 25, 30, and 35 C. Growth reduction increased with increasing soil temperatures. Highest populations of T. robustoides were recovered at 25 and 30 C. Clipping weights of Buchloe dactyloides (buffalo grass) were reduced at 25 and 30 C; however, root/crown weights were reduced at 15, 20, 30, and 35 C in nematode infested vs. noninfested soil. Reproduction of T. robustoides was greater at 25, 30, and 35 C than at 20 C on B. dactyloides. In a greenhouse study, T. robustoides reduced clipping and root/crown weights of both grasses 24-64%.     

Vertical Migration of Meloidogyne chitwoodi and M. hapla under Controlled Temperature

Migratory ability of second-stage juveniles (J2) of two Meloidogyne chitwoodi races and a M. hapla population were compared in soil-filled columns at 12, 18, and 24 C. J2 of all populations migrated farthest at 18 C and least at 12 C. Nematode survival was significantly reduced (P = 0.05) at 24 C.M. chitwoodi J2 migrated further and in greater numbers than M. hapla J2 at all temperatures. A comparison with and without a host plant demonstrated no preferential migration toward the plant. Water percolation through the migration columns stimulated upward migration.     

An evaluation of carbon disulphide as a sulphur fertilizer and as a nitrification inhibitor

There was little release of extractable SO₄-S during four weeks from CS₂ applied by injecting into two S-deficient soils. In this incubation experiment, the rate of CS₂ was 30 μg S g⁻, placement was injection at 9 cm depth, soil temperature was 20°C, and soil moisture tension was 33 kPa. The yield of barley forage after seven weeks in the greenhouse showed only small increases from 10 or 30 μg S g⁻¹ of CS₂ as compared to Na₂SO₄, on the two soils. While CS₂ supplied little plant available S in the short term, it was an effective inhibitor of nitrification. In the laboratory, or in the field, the injection of CS₂ (with N fertilizers) at a point 9 cm into the soils either stopped or reduced nitrification. In one laboratory experiment, 35 μg of CS₂ g⁻¹ of soil with urea reduced nitrification for at least four weeks; and in another experiment 20 μg of CS₂ g⁻¹ of soil with aqua NH₃ nearly or completely inhibited nitrification at 20 days. In two field experiments, 3 and 12 μg of CS₂ g⁻¹ of soil (or 6 and 24 kg ha⁻¹) with aqua NH₃ inhibited nitrification from October to the subsequent May. In addition, CS₂ reduced the amount of ammonium produced from the soil N, both in these two field experiments and in the laboratory experiments. That is to say, CS₂ injected at a point, inhibited both nitrification and ammonification. In other field experiments, CS₂ at a rate of 10 kg ha⁻¹ was injected in bands 9 cm deep with urea in October, and by May there was still reduced nitrification. Less than half of the fall-applied urea alone was recovered as mineral N, but with the application of CS₂ the recovery was increased to three-quarters. The yield and N uptake of barley grain was increased where fall-applied banded urea or aqua NH₃ received banded CS₂, (NH₄)₂CS₃, or K₂CS₃. The average increase in yield from fall-applied fertilizer, from inhibitor with fall-applied fertilizer, and from spring-applied fertilizer was 800, 1370, and 1900 kg ha⁻¹, respectively. In the same order, the apparent % recovery of fertilizer N in grain was 24, 42, and 60.     

Local grassland restoration affects insect communities

1. It is hypothesised that ecological restoration in grasslands can induce an alternative stable state shift in vegetation. The change in vegetation influences insect community assemblages and allows for greater functional redundancy in pollination and refuge for native insect species. 2. Insect community assemblages at eight coastal California grassland sites were evaluated. Half of these sites had undergone restoration through active revegetation of native grassland flora and half were non‐restored. Insects were collected from Lupinus bicolor (Fabaceae) within 2 × 2‐m² plots in spring 2017. Lupinus bicolor is a common native species that is used in California restoration projects, and home and state landscaping projects. 3. Ordination demonstrated that insect community assemblages were different between restored and non‐restored sites. These differences were seen in insect functional groups as well as taxa‐specific differences and were found to be driven by environmental characteristics such as non‐native forb cover. 4. Functional redundancy of herbivores decreased at restored sites, while pollinators became more redundant compared with non‐restored sites. The assemblages of the common species found at restoration sites contained more native insects than those found at non‐restored sites, including species such as Bombus vosnesenskii. 5. Local grassland restoration has the potential to induce an alternative stable state change and affect insect community assemblages. Additionally, it was found that grassland restoration can be a potential conservation tool to provide refugia for bumblebees (Bombus), but additional studies are required to fully understand its broader applicability.