Chemical analysis and nutrient resorption of hybrid American chestnut

Background/Question/Methods

The American chestnut, Castanea dentata, was once the dominant tree species in the hardwood forests of eastern North America. Since 1904, the pathogen Cryphonectria parasitica has killed the majority of mature chestnuts throughout the range. Three decades of breeding has produced a new, pathogen-resistant hybrid variety. The possibility now exists for large-scale reintroduction, but the chemical composition of the chestnut hybrid (tannins, specifically) and its potential effects on forests floors is unknown. It is possible that Castanea can alter nutrient cycling because its leaf litter chemistry is different or contains high levels of tannin, which is know to limit the availability of nutrients. During 2008, live foliage and leaf litter were collected from chestnut hybrids (4 different crosses), as well as pure American chestnut (C. dentata), and pure Chinese chestnut (C. mollissima). Live leaves were also removed from Quercus alba (white oak) and Acer rubrum (red maple) for comparison. Both foliage and litter were tested for tannins, P, S, Ca, Mg, K, Na, Fe, and Al. Tannins were extracted using Hagerman’s radial diffusion method. Macro-nutrients were extracted in hydrochloric acid and analyzed on an ICP-OES. 

Results/Conclusions

Tannin was generally resorbed in Castanea varieties by 8%. Leaves from Castanea varieties contain 11% more tannin than leaves of Acer rubrum, but 31% less tannin than Quercus alba. Chemistry was found to be similar in hybrid chestnut, C. dentata, C. mollissima, Q. alba, and A. rubrum trees. Na (67%), Mg (100%), K (54%), P (143%), S (41%), Cu (4%), and B (52%) were resorbed from Castanea foliage prior to senescence. We detected 26% more Ca and 86% more Mn in Castanea varieties leaf litter than in live foliage. Castanea varieties, compared with A. rubrum, had greater concentrations of Al (335%) and Mg (227.9%), and lower concentrations of Mn (55%). We observed this same pattern when comparing Castanea varieties with Q. alba. Results will help forward the effort to return one of North America’s most historically significant, economically important, and intrinsically valuable species to its original native habitat.