Physiological characterization of leaf senescence of Jatropha curcas L. populations

The objective of this paper was to assess and identify the causes of senescence in Jatropha curcas L. plants. Morphological, physiological and agricultural parameters in non-irrigated and daily irrigated plants by drip irrigation system were evaluated. The characteristics evaluated were soil humidity, the number of leafs, rate of branches growth, increase of branches diameter, relative water content, photosynthesis, transpiration, stomatal conductance, internal CO2 concentration/environment ratio, nitrogen content, specific leaf area, carotenoids, total chlorophyll, chlorophyll/carotenoids ratio, a/b chlorophyll ratio, total chlorophyll/nitrogen ratio, maximum and minimum air temperature, temperature range and nitrate reductase activity. We used four wild populations of 4-year old J. curcas. The evaluations were conducted every 10 days, between 7 a.m. and 11 a.m. The four populations assessed had the same behavior regarding the leaf senescence, acting uniformly regarding the reactions regulating their development. The photosynthetic activity, chlorophyll content, nitrate reductase activity, vegetative growth and nitrogen content were reduced during senescence. The little variation in day length, appropriate concentration of nitrogen in leaves and high soil water potential throughout the experiment suggest that these variables were not determining to trigger senescence. However, the reduced minimum temperature and the increased thermal range seemed to be determinant for the occurrence of leaf senescence.