We experimentally produced moderate water stress that reduced leaf, stem, root and fruit biomass of peppers, and severe nitrogen (N) limitations that almost stopped their development. Root/shoot ratios (R/S) were higher in N-limited plants. Low water availability (and also low N availability) produced lower stomatal conductance (g,). Specific leaf mass was higher and chlorophyll (Chl) concentration was lower under low N-availability. The same experimental conditions produced smaller differences among treatments in beans (with N-fixing symbionts). Water stress increased its relative importance as shown by the induced increase in root/shoot ratio. N stress was less important as shown by the absence of effects on Chl concentrations and g^. Both peppers and beans responded to limited availability of nitrogen and water by allocating to structures involved in uptake (roots), by longer organ duration, and by increasing the efficiency of N and water use.
The influence of phosphorus (P) and nitrogen (N) supply on biomass, leaf area, photon saturated photosynthetic rate (Pmax), quantum yield efficiency (α), intercellular CO2 concentration (Ci), and carboxylation efficiency (CE) was investigated in Vicia faba. The influence of P on N accumulation, biomass, and leaf area production was also investigated. An increase in P supply was consistently associated with an increase in N accumulation and N productivity in terms of biomass and leaf area production. Furthermore, P increased the photosynthetic N use efficiency (NUE) in terms of Pmax and α. An increase in P supply was also associated with an increase in CE and a decrease in Ci. Under variable daily meteorological conditions specific leaf nitrogen content (NL), specific leaf phosphorus content (PL), specific leaf area (δL), root mass fraction (Rf), Pmax, and α remained constant for a given N and P supply. A monotonic decline in the steady-state value of Rf occurred with increasing N supply. δL increased with increasing N supply or with increasing NL. We tested also the hypothesis that P supply positively affects both N demand and photosynthetic NUE by influencing the upper limit of the asymptotic values for Pmax and CE, and the lower limit for Ci in response to increasing N. and Y. Jia, V. M. Gray.