Search

Questions: Niche complementarity has been proposed as the underlying mechanism for optimizing resource use of plants in diverse ecosystems, usually associated with their functional traits and not with the species number per se. Our main questions were: (a) does species diversity optimize the use of resources in arid ecosystems; (b) is there redundancy of species in the use of water and nutrients; and (c) what diversity components most affect ecosystem functions of water regulation and material cycling? Location: Central Monte desert, Argentina. Methods: We selected vegetation patches with different species (SD) and functional diversities (FD), where we measured indicators of water regulation and material cycling. At two soil depths, we measured soil nitrate, phosphate, organic matter, chloride, electrical conductivity, and pH. We also determined decomposition, plant water use efficiency (foliar δ13C of C3 plants), and nitrogen use (δ15N). These variables were used as response variables, while total plant cover, species richness, Shannon, Simpson, evenness, and Rao's functional diversity indexes were used as predictors. Results: At the soil surface, response variables were better explained by models that included diversity (SD, FD or both) instead of evenness, total plant cover or null model. A diversity effect was not detected in deeper soil layers for most variables, except for electric conductivity, which had a positive effect on FD. Richness explained plant δ13C but had no influence on plant δ15N. Conclusions: Diversity of plant community influences ecosystem processes, as it increases decomposition, soil organic matter, and nutrient availability at the surface, and decreases water losses to the subsoil and plant water use efficiency. Both SD and FD explained one or more ecosystem processes of water regulation and material cycling, suggesting that individual species contribute to ecosystem functioning, with a low redundancy for arid areas. [ABSTRACT FROM AUTHOR]

Abstract. Between 2010 and 2015 the Central Andes of Chile and Argentina (32–37° S) suffered the effects of a mega drought without precedents in the instrumental period, where 71 % of weather stations showed more than 30 % of rainfall scarcity in Central Chile. The Cordillera Principal geological province, in the Upper Mendoza River basin, receives almost exclusively winter precipitation originated from the Pacific Ocean moisture. In addition to the snow that precipitates in this area of 3023 km2, there are 951 ice bodies, covering an area of 404 km2. The Mendoza River flow provides fresh water for more than 1.1 million inhabitants in this agriculture based arid region. Given the high inter–annual variability of snowfall, strongly affected by ENSO events, and the aridity of the region, it is crucial to quantify the contribution from different water sources to the Mendoza River flow. Glaciers play an important role regulating water availability, with mass accumulation in wet and cold years, and melting in hot, dry years. Understanding their dynamics as a function of environmental variables will help us predict water availability under a changing climate. Combining the instrumental record of streamflow from glaciers and rivers, meteorological data, remote sensing of snow covered area and chemical analysis of different water sources, this study attempts to understand climatic variables that control thawing, and the hydrological contribution of different glaciers to the streamflow during a dry period. Isotopic composition allowed us to differentiate snowmelt from glacier ice melt. In addition, it was possible to detect contributions of summer rainfall from Atlantic origin, in their unique storms that reach the Cordillera Principal, even when they had not been registered at weather stations. Finally, with end member mixing analysis, the relative contribution from different water sources were quantified over time, showing the temporally increasing contribution of glacial and periglacial environments as the melting season progresses. [ABSTRACT FROM AUTHOR]

Spatial variation in mean annual precipitation is the principal driver of plant water and nitrogen status in drylands. The natural abundance of carbon stable isotopes (δ13C) in photosynthetic tissues of C3 plants is an indicator of time-integrated behaviour of stomatal conductance; while that of nitrogen stable isotopes (δ15N) is an indicator of the main source of plant N (soil N vs. atmospheric N2). Previous studies in drylands have documented that plant δ13C and δ15N values increase with decreasing mean annual precipitation due to reductions in stomatal conductance, and soil enriched in 15N, respectively. However, evidence for this comes from studies focused on stable isotopes measurements integrated at the plant community level or on dominant plants at the site level, but little effort has been made to study C and N isotope variations within a species growing along rainfall gradients. We analysed plant δ13C, δ15N and C/N values of three woody species having different phenological leaf traits (deciduous, perennial and aphyllous) along a regional mean annual precipitation gradient from the central-western Argentinian drylands. Noticeably, plant δ13C and δ15N values in the three woody species did not increase towards sites with low precipitation or at the start of the growing season (drier period), as we expected. These results suggest that environmental factors other than mean annual precipitation may be affecting plant δ13C and δ15N. The short-term environmental conditions may interact with species-specific plant traits related to water and nitrogen use strategies and override the predictive influence of the mean annual precipitation on plant δ13C and δ15N widely reported in drylands. [ABSTRACT FROM AUTHOR]

In the woodlands of the Central Monte desert (Argentina), phreatophyte vegetation is exposed to different levels of disturbance. Livestock and settlement activity produce mainly nutrient inputs and partial vegetation removal, with a consequent reduction on water use by vegetation. We hypothesize that because of the increased soil water and nutrient resources associated with livestock stations, water stress will be relieved for the remaining Prosopis flexuosa trees, favouring water and nutrient status, and plant growth at the plant scale. The goal of this research was to analyse the physiological responses of P. flexuosa trees that grow in interdune valleys under different land uses, and the changes in relative importance of environmental factors controlling these responses. We compared the ecophysiological responses of adult P. flexuosa trees in two contrasting types of disturbance: disturbed (livestock stations) and relatively undisturbed (control woodlands) stands, in the 2011-2013 growing seasons. Pre-dawn and midday leaf water potential and stomatal conductance were higher in livestock stations than in control woodlands, suggesting a better water status of P. flexuosa in livestock stations. Isotopic composition (lower δ13C, and higher δ15N) and foliar nitrogen concentration (lower C:N ratios) indicated lower water use efficiency and higher nitrogen absorption from the soil in livestock stations. Both growth of new leaves (foliar area) and the length of young branches were higher in the first season for both land uses, but branch length was higher in livestock stations. This is consistent with the idea that vegetation removal and nutrient contribution of settlement activities improved water and nutrient status of remaining vegetation, and modified the relative importance of factors controlling ecophysiological processes. We concluded that physiological responses and vegetative growth of P. flexuosa were not only affected by meteorological conditions (rainfalls, vapour pressure deficit), but also by the ecohydrological changes caused by changes in land use. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Nitrogen (N) cycling was analyzed in the Kalahari region of southern Africa, where a strong precipitation gradient (from 978 to 230 mm mean annual precipitation) is the main variable affecting vegetation. The region is underlain by a homogeneous soil substrate, the Kalahari sands, and provides the opportunity to analyze climate effects on nutrient cycling. Soil and plant N pools, 15N natural abundance ( δ15N), and soil NO emissions were measured to indicate patterns of N cycling along a precipitation gradient. The importance of biogenic N2 fixation associated with vascular plants was estimated with foliar δ15N and the basal area of leguminous plants. Soil and plant N was more 15N enriched in arid than in humid areas, and the relation was steeper in samples collected during wet than during dry years. This indicates a strong effect of annual precipitation variability on N cycling. Soil organic carbon and C/N decreased with aridity, and soil N was influenced by plant functional types. Biogenic N2 fixation associated with vascular plants was more important in humid areas. Nitrogen fixation associated with trees and shrubs was almost absent in arid areas, even though Mimosoideae species dominate. Soil NO emissions increased with temperature and moisture and were therefore estimated to be lower in drier areas. The isotopic pattern observed in the Kalahari (15N enrichment with aridity) agrees with the lower soil organic matter, soil C/N, and N2 fixation found in arid areas. However, the estimated NO emissions would cause an opposite pattern in δ15N, suggesting that other processes, such as internal recycling and ammonia volatilization, may also affect isotopic signatures. This study indicates that spatial, and mainly temporal, variability of precipitation play a key role on N cycling and isotopic signatures in the soil–plant system. [ABSTRACT FROM AUTHOR]