Abstract:

The concept of nitrogen use efficiency (NUE) offers a powerful tool to study plant strategies with respect to nutrient limitation. We studied the NUE of an annual herb, Chenopodium album, in a dense monospecific stand using the concept introduced by Berendse and Aerts. Larger individuals absorbed more N in greater proportions relative to their size, suggesting that the competition for soil nitrogen was asymmetric (one-sided) among individual plants in the stand. Nitrogen loss from individuals also increased with plant size. Nitrogen influx (rin, the rate of N uptake per unit aboveground N) was greater in larger individuals while nitrogen outflux (rout, the rate of N loss per unit aboveground N) was the reverse. Therefore, the relative rate of nitrogen increment (rin-rout) was greater in larger individuals whereas it was around zero in the smallest plants. Larger individuals decreased their N concentration with time while smaller individuals showed little change in N concentration. These results suggested that the growth of smaller individuals was limited by light availability rather than by N availability, and N limitations were greater in larger individuals. Individual plants in this dense stand of C. album differed in their N economy. NUE and its components, i.e., MRT and NP, were different among individuals in the stand. Both NP and MRT were positively related to plant size. Larger individuals had longer MRT and higher NP, both of which contributed to higher NUE, than the smaller individuals. No trade-off relationship between NP and MRT was found at the intraspecific level. This study showed that the concept of NUE defined by Berendse and Aerts offered a powerful tool in studing plant strategies within species as well as among species.