Water use efficiency of twenty-five co-existing Patagonian species growing under different soil water availability

The variation of plant water use efficiency (WUE) with water availability has two interacting components: a plastic response, evident when individuals of the same genotype are compared (e.g. wet versus dry years), and an interspecific response, evident when different species living in habitats with different water availability are compared. We analysed the WUE of 25 Patagonian species that belong to four life forms (grasses, shrubs, annual herbs and perennial herbs) in relation to the climatic conditions of 2 years and the mean historic water availability experienced by each species. To estimate water availability, we calculated the effective soil water potential (EWP) of each species, based on available information about soil water dynamics, phenology and root system structure. To estimate WUE, we used isotopic discrimination of leaf C (Delta(13)C) and mean annual water vapour difference between leaves and atmosphere (Deltae) measured in situ. For the plastic response, for every species and life form, WUE increased from the dry to the wet year. We hypothesize that photosynthesis was less nutrient limited in the wet than in the dry year, facilitating higher net photosynthesis rates per unit of stomatal conductance in the wet year. For the interspecific response, WUE was lower in species native to drier habitats than in species native to wetter habitats. This response was mostly accounted for by a decrease in Deltae with EWP. Annual herbs, which avoid drought in time (they have the earliest growth cycle), and shrubs, which avoid drought in space (they have the deepest roots), showed the highest EWP and WUE. We conclude that the conventional wisdom which states that the highest WUE occurs within a species during the driest years, and among species in the driest habitats, does not always hold true, and that co-existing life forms drastically differ in water availability and water economy.

MIPS: analysis and annotation of proteins from whole genomes in 2005

The Munich Information Center for Protein Sequences (MIPS at the GSF), Neuherberg, Germany, provides resources related to genome information. Manually curated databases for several reference organisms are maintained. Several of these databases are described elsewhere in this and other recent NAR database issues. In a complementary effort, a comprehensive set of >400 genomes automatically annotated with the PEDANT system are maintained. The main goal of our current work on creating and maintaining genome databases is to extend gene centered information to information on interactions within a generic comprehensive framework. We have concentrated our efforts along three lines (i) the development of suitable comprehensive data structures and database technology, communication and query tools to include a wide range of different types of information enabling the representation of complex information such as functional modules or networks Genome Research Environment System, (ii) the development of databases covering computable information such as the basic evolutionary relations among all genes, namely SIMAP, the sequence similarity matrix and the CABiNet network analysis framework and (iii) the compilation and manual annotation of information related to interactions such as protein–protein interactions or other types of relations (e.g. MPCDB, MPPI, CYGD). All databases described and the detailed descriptions of our projects can be accessed through the MIPS WWW server ().

Global biodiversity scenarios for the year 2100

Scenarios of changes in biodiversity for the year 2100 can now be developed based on scenarios of changes in atmospheric carbon dioxide, climate, vegetation, and land use and the known sensitivity of biodiversity to these changes. This study identified a ranking of the importance of drivers of change, a ranking of the biomes with respect to expected changes, and the major sources of uncertainties. For terrestrial ecosystems, land-use change probably will have the largest effect, followed by climate change, nitrogen deposition, biotic exchange, and elevated carbon dioxide concentration. For freshwater ecosystems, biotic exchange is much more important. Mediterranean climate and grassland ecosystems likely will experience the greatest proportional change in biodiversity because of the substantial influence of all drivers of biodiversity change. Northern temperate ecosystems are estimated to experience the least biodiversity change because major land-use change has already occurred. Plausible changes in biodiversity in other biomes depend on interactions among the causes of biodiversity change. These interactions represent one of the largest uncertainties in projections of future biodiversity change.

Global biodiversity scenarios for the year 2100

Scenarios of changes in biodiversity for the year 2100 can now be developed based on scenarios of changes in atmospheric carbon dioxide, climate, vegetation, and land use and the known sensitivity of biodiversity to these changes. This study identified a ranking of the importance of drivers of change, a ranking of the biomes with respect to expected changes, and the major sources of uncertainties. For terrestrial ecosystems, land-use change probably will have the largest effect, followed by climate change, nitrogen deposition, biotic exchange, and elevated carbon dioxide concentration. For freshwater ecosystems, biotic exchange is much more important. Mediterranean climate and grassland ecosystems likely will experience the greatest proportional change in biodiversity because of the substantial influence of all drivers of biodiversity change. Northern temperate ecosystems are estimated to experience the least biodiversity change because major land-use change has already occurred. Plausible changes in biodiversity in other biomes depend on interactions among the causes of biodiversity change. These interactions represent one of the largest uncertainties in projections of future biodiversity change.

Rooting depth, water availability, and vegetation cover along an aridity gradient in Patagonia

Above-and belowground biomass distribution, isotopic composition of soil and xylem water, and carbon isotope ratios were studied along an aridity gradient in Patagonia (44-45°S). Sites, ranging from those with Nothofagus forest with high annual rainfall (770 mm) to Nothofagus scrub (520 mm), Festuca (290 mm) and Stipa (160 mm) grasslands and into desert vegetation (125 mm), were chosen to test whether rooting depth compensates for low rainfall. Along this gradient, both mean above-and belowground biomass and leaf area index decreased, but average carbon isotope ratios of sun leaves remained constant (at-27‰), indicating no major differences in the ratio of assimilation to stomatal conductance at the time of leaf growth. The depth of the soil horizon that contained 90% of the root biomass was similar for forests and grasslands (about 0.80-0.50 m), but was shallower in the desert (0.30 m). In all habitats, roots reached water-saturated soils or ground water at 2-3 m depth. The depth profile of oxygen and hydrogen isotope ratios of soil water corresponded inversely to volumetric soil water contents and showed distinct patterns throughout the soil profile due to evaporation, water uptake and rainfall events of the past year. The isotope ratios of soil water indicated that high soil moisture at 2-3 m soil depth had originated from rainy periods earlier in the season or even from past rainy seasons. Hydrogen and oxygen isotope ratios of xylem water revealed that all plants used water from recent rain events in the topsoil and not from water-saturated soils at greater depth. However, this study cannot explain the vegetation zonation along the transect on the basis of water supply to the existing plant cover. Although water was accessible to roots in deeper soil layers in all habitats, as demonstrated by high soil moisture, earlier rain events were not fully utilized by the current plant cover during summer drought. The role of seedling establishment in determining species composition and vegetation type, and the indirect effect of seedling establishment on the use of water by fully developed plant cover, are discussed in relation to climate change and vegetation modelling.

Intraspecific variation in the resistance to flooding and drought in populations of Paspalum dilatatum from different topographic positions

Many studies have analysed plant responses to flooding or drought separately, without addressing the relations between plant resistance to each of these factors. In this paper, we compare the responses to drought and flooding under glasshouse conditions of three populations of Paspalum dilatatum, a perennial C₄ grass dominant at different positions along a topographic gradient in the flooding pampa of Argentina. Our results showed that flooding effects on yield were negative on an upland, null on an intermediate, and positive on a lowland population, whereas drought reduced yield equally across populations, showing that resistance to flooding was not related to resistance to drought at a population level. Drought decreased height and aerenchyma, and increased the proportion of roots, while flooding had opposite effects on these traits. The responses of the single clones that made up each population showed a positive relation between the resistances to both factors: along the ecocline formed by 58 clones, those more resistant to drought were also more resistant to flooding. In addition, the combined resistance of each clone to both factors was negatively related to yield at field capacity, (i.e. the most resistant clones were less productive) and unrelated to the proportion of roots and aerenchyma. This result agrees with predictions of Grime's plant strategy theory and differs from a few previous studies, which showed negative relations between the resistances to flooding and drought among genera and species.

Effect of animal husbandry on herbivore-carrying capacity at a regional scale

All significant properties of the herbivore trophic level, including biomass, consumption and productivity, are significantly correlated with primary productivity across a broad range of terrestrial ecosystems. Here we show that livestock biomass in South American agricultural ecosystems across a 25-fold gradient of primary productivity exhibited a relationship with a slope essentially identical to unmanaged ecosystems, but with a substantially greater y-intercept. Therefore the biomass of herbivores supported per unit of primary productivity is about an order of magnitude greater in agricultural than in natural ecosystems, for a given level of primary production. We also present evidence of an increase in livestock body size with primary productivity, a pattern previously characterized in natural ecosystems. To our knowledge this is the first quantitative documentation at a regional scale of the impact of animal husbandry practices, such as herding, stock selection and veterinary care, on the biomass and size-structure of livestock herds compared with native herbivores.

Ecosystem-level patterns of primary productivity and herbivory in terrestrial habitats

Ecosystems are structurally organized as food webs within which energy is transmitted between trophic levels and dissipated into the environment. Energy flow between two trophic levels is given by the amount of production at the lower level and by the proportion of production that is consumed, assimilated and respired at the higher level. Considerable evidence indicates that food-web structure varies predictably in different habitats, but much less is known about quantitative relationships among food web fluxes. Many of the energetic properties of herbivores in African game parks are associated with rainfall and, by inference, with net primary productivity. Respiratory costs per unit production at the consumer trophic level are higher for homeotherms than for heterotherms. Plant secondary chemicals affect herbivore dietary choices and the allocation of plant resources to those chemicals varies with resource availability. How these phenomena are translated into ecosystem fluxes is unknown. We present evidence that herbivore biomass, consumption and productivity are closely correlated with plant productivity, suggesting that the latter is a principal integrator and indicator of functional processes in food webs.

Ecosystem-level patterns of primary productivity and herbivory in terrestrial habitats

Ecosystems are structurally organized as food webs within which energy is transmitted between trophic levels and dissipated into the environment. Energy flow between two trophic levels is given by the amount of production at the lower level and by the proportion of production that is consumed, assimilated and respired at the higher level. Considerable evidence indicates that food-web structure varies predictably in different habitats, but much less is known about quantitative relationships among food web fluxes. Many of the energetic properties of herbivores in African game parks are associated with rainfall and, by inference, with net primary productivity. Respiratory costs per unit production at the consumer trophic level are higher for homeotherms than for heterotherms. Plant secondary chemicals affect herbivore dietary choices and the allocation of plant resources to those chemicals varies with resource availability. How these phenomena are translated into ecosystem fluxes is unknown. We present evidence that herbivore biomass, consumption and productivity are closely correlated with plant productivity, suggesting that the latter is a principal integrator and indicator of functional processes in food webs.