Abstract
ABSTRACTStem and leaf photosynthetic responses to environmental parameters were studied in Spartium junceum L., a legume with chlorophyllous stems. Stem net photosynthesis (Pn) was consistently lower than leaf Pn. The low stem Pn was due to lower quantum yield, lower mesophyll conductance and lower CO2‐saturated Pn than that of leaf Pn. Stomatal limitations to leaf and stem Pn were similar (25%). Water stress caused a greater reduction in leaf Pn than that of stems. Leaf Pn was also reduced in water‐stressed plants following rehydration. The reduced leaf Pn was associated with a reduced photon saturated Pn rate and a reduced CO2 saturated Pn rate. Apparent quantum yield, mesophyll conductance and stomatal limitation of leaves were unaffected by water‐stress. Stem Pn following rehydration was not influenced by the water‐stress treatment. In general, leaf Pn was more responsive to environmental parameters and more sensitive to water stress than stem Pn. These data support the hypothesis that stem Pn has greater tolerance of water stress, but is limited to low Pn by biochemical means compared to leaves.
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