Debating the greening vs. browning of the North American boreal forest: differences between satellite datasets

A number of remote sensing studies have evaluated the temporal trends of the normalized difference vegetation index (NDVI or vegetation greenness) in the North American boreal forest during the last two decades, often getting quite different results. To examine the effect that the use of different datasets might be having on the estimated trends, we compared the temporal trends of recently burned and unburned sites of boreal forest in central Canada calculated from two datasets: the Global Inventory, Monitoring, and Modeling Studies (GIMMS), which is the most commonly used 8 km dataset, and a new 1 km dataset developed by the Canadian Centre for Remote Sensing (CCRS). We compared the NDVI trends of both datasets along a fire severity gradient in order to evaluate the variance in regeneration rates. Temporal trends were calculated using the seasonal Mann–Kendall trend test, a rank‐based, nonparametric test, which is robust against seasonality, nonnormality, heteroscedasticity, missing values, and serial dependence. The results showed contrasting NDVI trends between the CCRS and the GIMMS datasets. The CCRS dataset showed NDVI increases in all recently burned sites and in 50% of the unburned sites. Surprisingly, the GIMMS dataset did not capture the NDVI recovery in most burned sites and even showed NDVI declines in some burned sites one decade after fire. Between 50% and 75% of GIMMS pixels showed NDVI decreases in the unburned forest compared with <1% of CCRS pixels. Being the most broadly used dataset for monitoring ecosystem and carbon balance changes, the bias towards negative trends in the GIMMS dataset in the North American boreal forest has broad implications for the evaluation of vegetation and carbon dynamics in this region and globally.     

Bacterial 'cosmopolitanism' and importance of local environmental factors for community composition in remote high-altitude lakes

1. In October 2004, plankton samples were collected from six permanent lakes located between 4960 and 5440 m a.s.l. in the Mount Everest region (Nepal) to assess how spatial and local environmental factors affect natural bacterial community composition. Fingerprinting analysis of the bacterial 16S rRNA gene fragment was done by denaturing gradient gel electrophoresis (DGGE).
2. The number of DGGE bands (range: 12–23) was not correlated with lake area or remoteness, but there was a strong negative correlation with the ratio of catchment to lake area ( r  = −0.826, P  <   0.05), suggesting that hydraulic retention time affects the establishment of the bacterial community in these seepage lakes.
3. Most dominant sequences belonged to Betaproteobacteria except in two lakes where members of Bacteroidetes made the largest relative contribution. Up to 81% of the phylotypes had high similarity (>98 to 100%) in partial 16S rRNA gene sequence to those reported from other alpine lakes and glaciers around the world, suggesting the presence of 'cosmopolitan' bacteria.
4. An analysis based on dissimilarity matrices and the Mantel test revealed the existence of dissimilarities in bacterial community composition related to geographical distance over a small spatial scale (<6 km), but determined by local environmental constraints.
5. Our results suggest that several bacterial phylotypes are ubiquitous in the freshwater aquatic realm, but taxon sorting by local environmental constraints is important.     

Immune function, parasitization and extended phenotypes in colour polymorphic pygmy grasshoppers

Ecological and evolutionary consequences of host–parasite interactions have attracted considerable attention from evolutionary biologists. Previous studies have suggested that immune responsiveness may be genetically or developmentally linked with colour pattern, such that the evolution of animal colour patterns may be influenced by correlated responses to selection for parasite resistance. We studied interactions between the endoparasitic fly Leiophora innoxia (Meigen) (Diptera: Tachinidae) and its colour polymorphic pygmy grasshopper host Tetrix undulata (Sow.) (Orthoptera: Tetrigidae) to test for morph‐specific differences in parasitization and immune defence, and host‐induced variation in parasite phenotypes. Our results revealed that c. 2 and 30% of adult grasshoppers collected from the same natural population in two subsequent years, respectively were parasitized. Parasite prevalence was independent of host sex and colour morph. Pupae were larger if the parasite had developed in a female than in a male host, possibly reflecting host resource value or a physical constraint on larval growth imposed by host body size. Pupal size was also associated with host colour morph, with individuals that had developed in dark morphs being smaller at pupation compared to those that developed in paler morphs. However, immune defence, measured as the encapsulation response to a novel antigen, did not differ among individuals belonging to alternative colour morphs or sexes. Darker morphs warm up more quickly and prefer higher body temperatures than paler ones. Encapsulation was not influenced by maintenance temperature (15 vs. 30 °C), however, suggesting that indirect effects of coloration on parasite resistance mediated via differential body temperature are unlikely. The dependence of parasite body size on host colour morph may thus reflect plasticity of growth and development of the larvae in response to differential host body temperature, rather than variable host immune defence. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 85 , 373–383.     

Two closely linked tomato HKT coding genes are positional candidates for the major tomato QTL involved in Na+/K+ homeostasis

The location of major quantitative trait loci (QTL) contributing to stem and leaf [Na⁺] and [K⁺] was previously reported in chromosome 7 using two connected populations of recombinant inbred lines (RILs) of tomato. HKT1;1 and HKT1;2, two tomato Na⁺‐selective class I‐HKT transporters, were found to be closely linked, where the maximum logarithm of odds (LOD) score for these QTLs located. When a chromosome 7 linkage map based on 278 single‐nucleotide polymorphisms (SNPs) was used, the maximum LOD score position was only 35 kb from HKT1;1 and HKT1;2. Their expression patterns and phenotypic effects were further investigated in two near‐isogenic lines (NILs): 157‐14 (double homozygote for the cheesmaniae alleles) and 157‐17 (double homozygote for the lycopersicum alleles). The expression pattern for the HKT1;1 and HKT1;2 alleles was complex, possibly because of differences in their promoter sequences. High salinity had very little effect on root dry and fresh weight and consequently on the plant dry weight of NIL 157‐14 in comparison with 157‐17. A significant difference between NILs was also found for [K⁺] and the [Na⁺]/[K⁺] ratio in leaf and stem but not for [Na⁺] arising a disagreement with the corresponding RIL population. Their association with leaf [Na⁺] and salt tolerance in tomato is also discussed.     

In Vitro Culture of Phytomonas Sp. Isolated from Euphorbia characias. Metabolic Studies by 1H NMR

ABSTRACT. We describe the in vitro culture of Phytomonas species isolated from Euphorbia characias . The best choice between tested media was SDM-79, in which promastigotes, after 6 days of culture, reached cell densities as high as 4 × 10⁷ cells/ml. Cells growing in LIT or MTL medium showed longer division times and lower cell densities. We succeeded in obtaining Phytomonas sp. amastigote and spheromastigote forms in modified GRACE's medium, yielding transformation rates of up to 70%. Electron microscopy studies were performed in order to characterize the ultrastructural features of these forms obtained in vitro. On the other hand, metabolic studies based on qualitative (nuclear magnetic resonance spectroscopy) and quantitative metabolic methods (enzymatic assays) showed that promastigote forms secreted mainly ethanol, acetate, glycine, glycerol, piruvate and succinate in SDM-79 medium, whereas the major metabolites found after transformation in modified Grace's medium were ethanol, acetate, glycine, piruvate and smaller amounts of glycerol.     

Regulation by light of ammonium transport systems in Chlamydomonas reinhardtii

The unicellular green alga Chlamydomonas reinhardtii is able to take up methylammonium/ammonium from the medium at different stages of its sexual life cycle. Vegetative cells and pre‐gametes mostly used a low‐affinity system (LATS) component, but gametes obtained after light treatment of N‐deprived pre‐gametes expressed both LATS and high‐affinity system (HATS) components for the uptake of methylammonium/ammonium. The activity of the LATS component was stimulated by light in only 5 min in a process independent of protein synthesis. By using the lrg6 mutant that produces sexually competent gametes in the dark, light effects on ammonium transport and gamete differentiation have been separately analysed. We have found light regulation of four Amt1 genes: Amt1; 1, Amt1; 2, Amt1; 4 and Amt1; 5. Whereas light‐dependent expression of Amt1; 1, Amt1; 2 and Amt1; 4 was independent of gametogenesis, and that of Amt1; 5 was activated in the lrg6 mutant, suggesting a connection between this transporter and the subsequent events taking place during gametogenesis.     

Rats dying for mice: Modelling the competitor release effect

Abstract Introduced vertebrate predators are one of the most important threats to endemic species throughout a range of ecosystems, in particular on islands in biodiversity hot spots. Consequently, the reduction of predator numbers is considered a key conservation action in the management of many native vertebrates vulnerable to predators. It is now established that control attempts may affect non‐target species through trophic interactions, but little is known concerning their consequences on competitive relationships. We study a mathematical model mimicking the effects of controlling introduced species in the presence of their competitors. We used two competing rodents to illustrate our study: black rats, Rattus rattus, and mice, Mus musculus. Analyses of the model show that control of only one introduced species logically results in the dramatic increase of the overlooked competitor. We present empirical data that confirm our theoretical predictions. Less intuitively, this process, which we term ‘the competitor release effect’, may also occur when both introduced competitors are simultaneously controlled. In our setting, controlling both predators can promote their coexistence. This occurs as soon as the inferior competitor benefits from the differential effect of the simultaneous control of both competitors, that is, when the indirect positive effect of control (the removal of their competitors) exceeds its direct negative effect (their own removal). Both control levels and target specificity have a direct influence on the extent of this process: counter‐intuitively, the stronger and more specific the control, the greater the effect. The theoretical validation of the competitor release effect has important implications in conservation, especially for control management.     

Effect of removing a dominant competitor,Akodon azarae (Rodentia,Sigmodontinae) on community and population parameters of small rodent species in Central Argentina

Abstract We studied the effect of removing Akodon azarae (Muridae, Sigmodontinae) on community and demographic parameters of rodent species in crop field borders of Central Argentina. We applied three replicated treatments: enclosure and removal of A. azarae, enclosure without removal, and a control without removal or enclosure. We conducted 14 monthly capture–mark–recapture samplings between October 1988 and March 1990. During the study period we observed an increase in Mus domesticus (Muridae, Murinae) abundance in removal areas. Other species did not respond to A. azarae removal. When A. azarae was removed, M. domesticus appeared to be competitively dominant over the remaining species of the community, increasing its relative abundance. Reproductive parameters of M. domesticus were more sensitive to treatments than survival parameters.