Assessing the protective effect of vertically heterogeneous canopies against radiative frost-The case of quinoa on the Andean Altiplano

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1396/09/13
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Agricultural and Forest Meteorology 149 (2009) 1759–1768

Night radiative frost is a highly limiting factor for agriculture in Andean highlands. Nevertheless, a
diversity of crop species have been domesticated there, commonly showing high heterogeneity in plant
growth at the field level. The possible protective effect of crop canopy heterogeneity against nocturnal
radiative frost is examined using a dual approach, combining a field experiment and a simplified energy
balance model at the leaf level. Leaf and air temperatures were registered over an entire quinoa crop
cycle in the Andean highlands of Bolivia, comparing two cultivars: Blanca de Yanamuyu, a traditional
landrace with high plant height heterogeneity, and Surumi, a more homogeneous selected variety. In
both cultivars, inverted air density profiles during calm and clear nights result in air temperature
changes up to 3 8C over 0.5 m height, with minimum air temperature concentrated at the upper part of
the canopy. In these conditions, leaf temperature gradients of up to 2.6 8Cm1 develop within the
canopy of the traditional landrace, with minimum leaf temperature significantly higher (P < 0.001) in
shaded plants of the landrace than in the selected cultivar. A dynamic model of leaf temperature based
on canopy parameters and climatic records at screen level adequately simulates leaf temperature
differences in the case of a vertically heterogeneous quinoa canopy. A sensitivity analysis of the model
reveals that canopy height, leaf area index, and sky cloudiness have the most important influences on the
development of the sheltering effect, while air temperature and air humidity play a minor role under
typical radiative frost conditions. As for wind speed, its actual influence remains unclear due to
experimental and modelling limitations at low wind speeds. The significance of these results is discussed
in terms of the trade-off between stress adaptation and biomass productivity.

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