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

Abstract

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.

Soil water availability and rooting depth as determinants of hydraulic architecture of Patagonian woody species

“…This is not consistent with results of earlier studies suggesting that most woody species in the Patagonian shrub steppe had similar rooting depths, either exploring deeper soil layers compared to grasses or perennial herbs (e.g., Golluscio and Sala 1993;Golluscio and Oesterheld 2007), or using water from recent rain events in the topsoil where roots of most grasses preferentially occur . Hydraulic architecture and water relations traits such as wood density, eYciency of water transport, and predawn or minimum Leaf , were consistent with patterns of soil water uptake.…”

“…Physiological processes in plants from cold arid environments such as the Patagonian steppe are inXuenced by low soil water availability during periods when temperatures are favorable for growth (Soriano and Sala 1983;Sala et al 1989;Jobbagy and Sala 2000;Austin and Sala 2002;Golluscio and Oesterheld 2007). Several studies of Patagonian ecosystems indicate that shrubs and grasses diVer in their adaptations to cope with limited water availability (Soriano and Sala 1983;Sala et al 1989).…”

Photodegradation alleviates the lignin bottleneck for carbon turnover in terrestrial ecosystems

“…We collected senescent leaf material from 23 species across a range of life forms, families, and functional types from temperate ecosystems of South America (Table S1). Leaf litter came from the Pampas grassland region of central Argentina (native mixed C 3 -C 4 prairie and agroecosystems) (50), the Patagonian semiarid steppe (51), and temperate mixed deciduous-evergreen forest (52). All leaf litter was carefully collected from the field sites at the natural time of senescence or, in the case of evergreen species, brought to the laboratory and separated for only recently senesced, fully intact litter.…”

Allometric Scaling and Resource Limitations Model of Tree Heights: Part 1. Model Optimization and Testing over Continental USA

“…However, evergreen forests generally showed higher optimized γ values compared to deciduous forests in relatively dry regions. Water availability is spatially heterogeneous for an individual species within a location [72]. For example, evergreen and deciduous plants in dry regions have different root systems and water use efficiencies (evergreen > deciduous as in [73,74]).…”