International audienceStudies on the periodicity of wood formation provide essential data on tree age and factors related to the control of tree growth. The aim of this work was to investigate the cambial phenology and its relation with leaf phenology and climatic seasonality in two tropical rainforest species belonging to the genus Parkia known for having a contrasted leaf phenology. From wood samples collected at 15 day intervals from April 2009 to February 2012 in five trees of both species, we quantified cambial activity by counting layers of cells in cambial zone, enlarging cells zone and wall thickening cells zone from wood prepared anatomical micro sections. In the same time, we observed leaf shedding behaviors in the crown of the studied trees. In both species, cambial activity was significantly reduced during leafless period. However, the cambial activity of P. velutina was not affected by seasonality while in P. nitida, we found a significant positive effect of the dry season on cambial activity. This diminution of activity associated to leaf shedding occurred annually during the dry season in P. nitida whereas the trees were not synchronous in time for P. velutina. On the contrary that is often admitted, the rest cambial period can be independent of environmental restriction such as dry season. Leaf phenology remains the best proxy to estimate cambial activity

International audienc

International audienceArchitectural descriptors were used to understand root system structure and development in white yam (Dioscorea rotundata Poir., Dioscoreaceae), a tuber monocot. Observations were made on seedlings and plant derived from tuber fragments, cultivated in greenhouses over a developmental cycle. This study demonstrated that both seedlings and plants derived from tubers have two distinct root systems that are highly organized. The first (seminal or tubercular) has been called the temporary root system which is small and short lived. The architectural unit here is made up of two root axis categories. The second (adventitious in both cases) has been called the definitive root system. It is larger and has a far longer lifespan than temporary root systems. The architectural unit here is made up of three root axis categories. Adventitious root systems are formed by structural repetitions of their own architectural unit. The temporary and definitive root systems possess the same structural and functional properties and become established and succeed one another in time following an identical developmental sequence. Neo tuber development is coupled with the root system development. Our results highlight to what extent it is important to study simultaneously the different parts of a root system in order to understand its development. This study confirms how architectural tools can be used to understand root system structure and development and prove accurate informations on root system development for use in agricultural management