Photosynthesis of white clover (Trifolium repens L.) germplasms with contrasting leaf size

In a growth chamber experiment, we determined net photosynthetic rate (P-N) and leaf developmental characteristics of cultivars of a relatively small-, intermediate-, and a large-leaf genotype grown under irradiance of 450-500 mu mol(photon) m(-2) s(-1) (HI), shade [140-160 mu mol(photon) m(-2) s(-1)] (LI), and after a shade-to-irradiation (LI -->HI) transfer. Differences in physiological responses of the genotypes were more pronounced in HI and LI-->HI plants than in LI plants. The small- and intermediate-leaf sizes had greater P-N in the first measured leaf than the large-leaf type by 70 and 63 % in HI plants, and by 23 and 18 % in LI-->HI plants, respectively. Similar relationships were observed in the next developed leaf. The LI plants did not differ significantly in P-N Greater P-N in the small- and intermediate-leaf size genotypes were not associated with greater total dry matter of the plant. Under irradiation, the large-leaf genotype accumulated more total nonstructural saccharides (TNS) and starch than the small- or intermediate-leaf size plants. TNS and starch concentrations in LI plants were about one-half those of HI and LI-->HI plants. These results should help to develop management practices that capitalize upon the competitive features of white clover in mixed-species swards.