Reserve carbohydrate levels in the boles and structural roots of five multipurpose tree species in a seasonally dry tropical climate

It is important to know the seasonal cycles of reserve carbohydrates in agr oforestry trees because their ability to sprout after cutting may depend on reserve carbohydrate levels. Such information is lacking for tropical agro forestry trees. Reserve carbohydrate trends were examined in uncut, 12-year -old multipurpose trees in the seasonally dry climate of Ibadan, Nigeria. S pecies included Dactyladenia barteri, Gliricidia sepium, Leucaena leucoceph ala, Pterocarpus soyauxii, and Senna siamea. Definite seasonal trends were observed. Concentrations of sugar and total reserve carbohydrates (sugar+st arch) were highest during the dry season. Starch had two maxima, one early in the dry season, and one early in the wet season. Conversion of starch to sugar seemed to occur as trees developed drought tolerance. All carbohydra te values decreased as active growth resumed during the wet season. In gene ral, all carbohydrate values were relatively low as active growth continued ; they increased only when dry weather slowed growth. In several species, c arbohydrate concentrations in the lower holes decreased during reproductive growth, especially during the last phase of fruit maturation. Significant linear correlations were found between concentrations of sugar and total re serve carbohydrates and a number of weather variables - rainfall, temperatu re, relative humidity, and solar radiation. Correlations with starch were m uch lower than for sugar, although several were significant, suggesting tha t seasonal trends in starch are too complex to be described adequately by l inear correlations. (C) 2001 Elsevier Science B.V. All rights reserved.