Environmental responses of plants and ecosystems as predictors of the impact of global change

An understanding of plant responses to fluctuations in environment is critical to predictions of plant and ecosystem responses to climate change. In the northern hemisphere, the northern limits of distribution of major biomes are probably determined by the tolerance of their dominant physiognomic types (e.g., deciduous hardwood trees) to minimum winter temperatures and can thus be predicted from long-term patterns of temperature fluctuations. At a more detailed level, the responses of functional groups of plants to altered climate can be predicted from their known responses to fluctuations in soil resources (nutrients and water) and the expected effect of climatic change on these soil resources. Laboratory and field experiments demonstrate the feasibility of this approach.     

Molecular characterization of mouse-virulent poliovirus type 1 Mahoney mutants: involvement of residues of polypeptides VP1 and VP2 located on the inner surface of the capsid protein shell.

Most poliovirus (PV) strains, including PV PV-1/Mahoney, are unable to cause paralysis in mice. Determinants for restriction of PV-1/Mahoney in mice have been identified by manipulating PV-1 cDNA and located on the viral capsid protein VP1. These determinants consist of a highly exposed amino acid sequence on the capsid surface corresponding to the B-C loop (M. Murray, J. Bradley, X. Yang, E. Wimmer, E. Moss, and V. Racaniello, Science 241:213-215, 1988; A. Martin, C. Wychowski, T. Couderc, R. Crainic, J. Hogle, and M. Girard, EMBO J. 7:2839-2847, 1988) and of residues belonging to the N-terminal sequence located on the inner surface of the protein shell (E. Moss and V. Racaniello, EMBO J. 10:1067-1074, 1991). Using an in vivo approach, we isolated two mouse-neurovirulent PV-1 mutants in the mouse central nervous system after a single passage of PV-1/Mahoney inoculated by the intracerebral route. Both mutants were subjected to two additional passages in mice, plaque purified, and subsequently characterized. The two cloned mutants, Mah-NK13 and Mah-NL32, retained phenotypic characteristics of the parental PV-1/Mahoney, including epitope map, heat lability, and temperature sensitivity. Mah-NK13 exhibited slightly smaller plaques than did the parental virus. The nucleotide sequences of the mutant genomes were determined, and mutations were identified. Mutations were independently introduced into the parental PV-1/Mahoney genome by single-site mutagenesis. Mutated PV-1/Mahoney viruses were then tested for their neurovirulence in mice. A single amino acid substitution in the capsid proteins VP1 (Thr-22-->Ile) and VP2 (Ser-31-->Thr) identified in the Mah-NK13 and Mah-NL32 genomes, respectively, conferred the mouse-virulent phenotype to the mouse-avirulent PV-1/Mahoney. Ile-22 in VP1 was responsible for the small-plaque phenotype of Mah-NK13. Both mutations arose during the first passage in the mouse central nervous system. We thus identified a new mouse adaptation determinant on capsid protein VP1, and we showed that at least one other capsid protein, VP2, could also express a mouse adaptation determinant. Both determinants are located in the inside of the three-dimensional structure of the viral capsid. They may be involved in the early steps of mouse nerve cell infection subsequent to receptor attachment.     

Gene-rich plastid genomes of two parasitic red algal species,Laurencia australis and L. verruciformis (Rhodomelaceae,Ceramiales), and a taxonomic revision of Janczewskia

Parasitic red algae are an interesting system for investigating the genetic changes that occur in parasites. These parasites have evolved independently multiple times within the red algae. The functional loss of plastid genomes can be investigated in these multiple independent examples, and fine-scale patterns may be discerned. The only plastid genomes from red algal parasites known so far are highly reduced and missing almost all photosynthetic genes. Our study assembled and annotated plastid genomes from the parasites Janczewskia tasmanica and its two Laurencia host species (Laurencia elata and one unidentified Laurencia sp. A25) from Australia and Janczewskia verruciformis, its host species (Laurencia catarinensis), and the closest known free-living relative (Laurencia obtusa) from the Canary Islands (Spain). For the first time we show parasitic red algal plastid genomes that are similar in size and gene content to free-living host species without any gene loss or genome reduction. The only exception was two pseudogenes (moeB and ycf46) found in the plastid genome of both isolates of J. tasmanica, indicating potential for future loss of these genes. Further comparative analyses with the three highly reduced plastid genomes showed possible gene loss patterns, in which photosynthetic gene categories were lost followed by other gene categories. Phylogenetic analyses did not confirm monophyly of Janczewskia, and the genus was subsumed into Laurencia. Further investigations will determine if any convergent small-scale patterns of gene loss exist in parasitic red algae and how these are applicable to other parasitic systems.     

Local-regional relationships and the geographical distribution of species

Aim Local‐regional (LR) species diversity plots were conceived to assess the contribution of regional and local processes in shaping the patterns of biological diversity, but have been used also to explore the scaling of diversity in terms of its alpha, beta, and gamma components. Here we explore the idea that patterns in the geographical ranges of species over a continent can determine the shape of small region to large region (SRLR) plots, which are equivalent to LR plots when comparing the diversity of sites at two regional scales. Location To test that idea, we analysed the diversity patterns at two regional scales for the mammals of North America, defined as the mainland from Alaska and Canada to Panama. Method We developed a theoretical model relating average range size of species over a large‐scale region with its average regional point species diversity (RPD). Then, we generated a null model of expected SRLR plots based on theoretical predictions. Species diversities at two scales were modelled using linear and saturation functions for Type I and Type II SRLR relationships, respectively. We applied the models to the case of North American mammals by examining the regional diversity and the RPD for 21 large‐scale quadrats (with area equal to 160,000 km²), arranged along a latitudinal gradient. Results Our model showed that continental and large‐scale regional patterns of distribution of species can generate both types of SRLR relationship, and that these patterns can be reflected in LR plots without invoking any kind of local processes. We found that North American nonvolant mammals follow a Type I SRLR relationship, whereas bats follow a Type II pattern. This difference was linked to patterns in which species of the two mammalian groups distribute in geographical space. Conclusion Traditional LR plots and the new SRLR plots are useful tools in exploring the scaling of species diversity and in showing the relationship between distribution and diversity. Their usefulness in comparing the relative role of local and regional processes is, however, very limited.     

Seasonal and long-term soil water regime in West African tropical forest

Abstract. Variation of soil matric potential of a Wet Evergreen and a Moist Semi-deciduous West African forest were compared. The two forest types differed strongly in their soil water regime. Wet Evergreen forest experienced matric potentials below ?100 kPa only occasionally, while in Moist Semi-deciduous forest matric potentials were less than ?2.5 MPa for periods of several weeks or more each season. A water balance equation was used to simulate the soil water regime at both sites and predict severity and length of the dry period. The predictions showed good agreement with the field measurements of soil water potential over a 2-yr period. The methodology was used to estimate the occurrence and severity of droughts over longer periods at the two sites. The balance calculations suggest that droughts occur occasionally in the Wet Evergreen forest under study. The potential impact of droughts on species distribution and vegetation disturbance in tropical forests is discussed.     

Distribution and production ofChironomus salinarius (Diptera: Chironomidae) in a shallow coastal lagoon in the Bay of Cádiz

The abundance, generation time and production ofChironomus salinarius larvae in a lagoon fish-pond system in the Bay of Cádiz were studied by taking monthly samples at 3 sites during 1991 and 1992. Numerical abundance and biomass of larvae showed considerable spatial, seasonal and interannual variation (ANCOVAs,P<0.001). The maximum mean annual density was 7048 larvae m^–2, and corresponded to a biomass of 3.08 g dry weight (DW) m^–2. It was recorded at the site with the lowest rate of water renewal. Seasonal patterns were similar at all sites, with main annual peaks of abundance and biomass in autumn-early winter. Chironomid density was positively related to the biomass of benthic macroalgae (P<0.001). The population studied was multivoltine with a probable average of five generations per year, with overlapping cohorts and a predominance of third- and fourth-instar larvae. Estimates of annual production ranged between 72.2 g DW m^–2 yr^–1 at the site with the lowest rate of water renewal in 1991 and 0.1 g DW m^–2 yr^–1 at the site with the highest rate of water renewal in 1992. Mean annual production and the production/biomass ratio for the system was estimated to be 16.8 g DW m^–2 yr^–1 and 12.7, respectively. Possible factors leading to the observed density fluctuations are discussed, as well as possible sources of error in production estimates.     

Lignin and manganese peroxidase activity in extracts from straw solid substrate fermentations

Manganese and lignin peroxidase (MnP, LiP) activities were measured in straw extracts from cultures of Phanerochaete chrysosporium. Out of six MnP substrates, the MBTH/DMAB (3-methyl-2-benzothiazolinone hydrazone/3-(dimethylamino)benzoic acid), gave the highest MnP activity. Detection of LiP activity as veratryl alcohol oxidation was inhibited by phenols in the straw culture extracts. Appropriate levels of veratryl alcohol and peroxide (4 mM and 0.4 mM, respectively), and a restricted sample volume (not larger than 10%) were necessary to detect activity.