Soil moisture and temperature affect condensed tannin concentrations and growth in Lotus corniculatus and Lotus pedunculatus

Abstract

Maku big trefoil and Dewey birdsfoot trefoil were grown at 14/10, 20/16, 26/22 and 32/28¦C (14/10 h) in growth cabinets. Growth rates and condensed tannin (CT) concentrations were measured as soil moisture was changed from field capacity (FC) to 20% FC to FC again in three regrowth cycles. Seasonal dry matter accumulation and CT concentrations were also measured on these cultivars together with Sharnee big trefoil, Monarch cicer milkvetch, Chemung crownvetch and WL605 lucerne at two sites in the field. Condensed tannin concentrations were not greatly affected by temperature alone. However, moisture stress induced proportionately larger reductions in growth rates of big trefoil as temperature increased, and correspondingly larger rises in CT concentrations. Condensed tannin concentrations in birdsfoot trefoil were largely unaffected by these factors. In big trefoil, the responses in CT levels and growth rates continued even when soil moisture was returned to FC. Low temperature did not appear to affect CT concentrations in big trefoil, but caused some slight elevation in concentrations in birdsfoot trefoil. In the field, CT levels in the big trefoil cultivars, and in birdsfoot trefoil, were elevated in summer and autumn, when temperatures were high and periods of soil moisture stress occurred. The potential for elevated CT levels in big trefoil appears to be enhanced when growth rates are reduced by moisture stress and temperaturs are high. Big trefoil should be carefully screened for CT concentrations in the process of cultivar development. High CT levels are not a problem in birdsfoot trefoils such as Dewey.