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.
Plants of pepper (Capsicum amuum L.) were grown in controlled environment chambers at ambient (360 pmol mol"*) and fluctuating pulse-enriched CO2 concentrations (700 pmol mol"* daily average, ranging from 500 to 3500 pmol mol"* = ECO2) under two water regimes. A decrease in plant growth and yield together with frequent visual injuries was found in plants growing under ECO2. Root/shoot ratio was greater, chlorophyll concentration and respiration rates were lower, and stomatal conductance and relative importance of alternativě pathway respiration were higher under ECO2. The negative effects of ECO2 were more intense under high water availability. The symptoms produced by ECO2 were similar to those of resource limitation, and were alleviated with increased nutrient supply. Constant elevated CO2 concentrations (700 pmol mol"*) increased pepper production and did not produce any of the injuries described for this erratic ECO2 treatment. Thus, it is probably the erratic nátuře of the CO2 concentration and not the gas itself that was causing the injiuy.
The ratío between carotenoid and chlorophyll a concentrations (Car/Chla) is indicative of the physiology and phenology of plants. With the aim of assessing this Car/Chla pigment ratio from reflectance (R), a wide range of leaves from several species and conditions were measured with high spectral resolution spectroradiometers for X between 400 and 800 nm. The performances of three pigment reflectance indices; (7) simple ratio pigment index (SRPI = R^*/R^2), (2) normalized difference pigment index [NDPI = (R^’ - R^^y^^RXi + R^2)]^ g^d (i) the structure insensitive pigment index [SIPI = (R**^ - R^i)/(R®*^ - R^^)] were tested. For each pigment index, every set of wavebands [Aj, X'^ was systematically tested. High correlations with Car/Chla were found for all these pigment indices in the blue-red domain [400 nm<A,i<530 nm, 600 nm<A,2<700 nm] as expected since both Chl and Car absorb in the blue, while only Chl absorbs in the red. The best semi-empirical estimation of the Car/Chla ratio was provided by SIPI for the wavelengths 445 and 680 nm: Car/Chla = 4.44 - 6.77 exp[-0.48 (R^oo. r445)/(r800 . R680)j| This index minimizes the confounding effects of leaf surface and mesophyll structure. These reflectance pigment indices provide new insight in the use of remote sensing for the assessment of physiology and phenology of vegetation.