Leaf CO2 assimilation and leaf dynamics in catch crops during autumn and winter at two levels of nitrogen supply

This study relates the leaf CO2 assimilation and leaf dynamics of nitrogen catch crops to environmental conditions. Winter rye (Secale cereale L.) and fodder radish (Raphanus sativus L.) were grown as catch crops in an outdoo r pot experiment at two rates of nitrogen supply (N2 higher than N1) in Wag eningen, the Netherlands, from August 1993 until April 1994. Biomass increa sed with increasing N supply. There was no net growth after mid-November. T he number of tillers in rye and of appeared leaves in radish were higher in N2 than in N1. Leaf appearance rate increased with temperature in fodder r adish and rye. Tillering in rye ceased in mid-October. Leaf lifespan was re lated to the temperature sum between leaf emergence and leaf death. Leaf li fespan was 478 +/- 68 degrees C day in fodder radish. In rye, the leaf life span gradually decreased from 592 +/- 66 to 389 +/- 25 degrees C day and fr om 545 (1 observation) to 401 +/- 64 degrees C day in N1 and N2, respective ly. In young leaves, A(max) (light-saturated CO2 assimilation rate) was app roximately 1.2 mg CO2 m(-2) leaf s(-1) in September and 0.5 mg CO2 m(-2) le af s(-1) later on, independent of species and N supply. N supply affected t he organic N concentrations only in the older leaves. A(max) was not depend ent on temperature at measurement (range: 12-19 degrees C in September: 5-1 5 degrees C from November until March), but, in contrast, strongly related to temperature and irradiance during the preceding growth period. Leaf nitr ate concentrations increased with N supply. Water-soluble carbohydrate conc entrations were higher in N1 than in N2 and higher in rye than in fodder ra dish. They fluctuated during the season. It is concluded that overall growt h rates were limited by process rates other than that of leaf CO2 assimilat ion per unit leaf area in both N1 and N2.