Carlos Bernardo Passera

Water and nitrogen supply effects on four desert shrubs with potential use for rehabilitation activities

Desert evergreen shrubs, which are adapted to low-fertility ecosystems, generally exhibit limited responses to increased nutrient availability and tend to absorb and store nutrients rather than synthesize new tissues. The objective of this work was to analyze the effect of nitrogen fertilization combined with soil water availability on growth, nitrogen content, and nitrogen use efficiency on four shrubs (Atriplex lampa, Capparis atamisquea, Larrea cuneifolia, and Senecio subulatus) from the Monte Desert. In a 120-day glasshouse experiment in Mendoza, Argentina, we compared the effects of three levels of nitrogen fertilization combined with two levels of water availability on seedling biomass, nitrogen content, water potential, and nitrogen use efficiency. Fertilization induced a higher biomass on A. lampa under high water availability and on C. atamisquea regardless of water level. Shoot:root ratios of these two species were lower under water stress without fertilization. On the other hand, L. cuneifolia presented lower root biomass and lower water potential with N fertilization. All species when fertilized exhibited higher nitrogen content and lower nitrogen use efficiency. Also, A. lampa and L. cuneifolia presented higher nitrogen content under water stress conditions. In conclusion, some desert shrubs (A. lampa and C. atamisquea) were able to take advantage of increased nitrogen availability producing more biomass. Understanding seedlings response to nitrogen and water availability on arid lands is critically important to develop adequate revegetation techniques of degraded areas.

Whole plant open chamber to measure gas exchange on herbaceous plants

Much of our understanding about CO2 and H2O gas exchange in plants has been gained from studies at leaf level. Extrapolation of results to whole plant is difficult and not always accurate. In order to overcome this limitation, a chamber was designed to measure gas exchange at the whole plant level. The chamber developed in this work consisted on an acrylic cylinder 0.70 m high and 0.60 m wide. An incorporated blower was used to circulate air through the chamber and plant canopy from the bottom inlet upwards to the outlet tube providing a maximum flow of 0.072 m3 s-1. Air CO2 and water concentration were monitored with an infrared gas analyzer and temperature gradients were measured periodically with sensors. Air flow rates inside the chamber were 0.007, 0.012, 0.022, 0.047, and 0.072 m3 s-1. A comparative study showed that 0.022 or 0.047 m3 s-1 air flow rates did not modify substantially the natural environment within the chamber; measurements are close to real and exterior ones; temperature increased below 4 °C; photosynthetically active radiation (PAR) was reduced by 5%; and photosynthesis and evapotranspiration showed mean values with nonsignificant variations (22 ± 3.8 μmol CO2 m-2 s-1, and 15 ± 4.0 mmol H2O m-2 s-1, respectively). This chamber could be a useful tool to measure gas exchange of whole plants in herbaceous species under conditions of high evapotranspiration and for extended periods of time.