Relationship of leaf anatomy with photosynthetic acclimation of Valeriana jatamansi was studied under full irradiance [FI, 1 600 μmol(PPFD) m-2 s-1] and net-shade [NS, 650 μmol(PPFD) m-2 s-1]. FI plants had thicker leaves with higher respiration rate (RD), nitrogen content per unit leaf area, chlorophyll a/b ratio, high leaf mass per leaf area unit (LMA), and surface area of mesophyll cell (Smes) and chloroplasts (Sc) facing intercellular space than NS plants. The difference between leaf thickness of FI and NS leaves was about 28 % but difference in photon-saturated rate of photosynthesis per unit leaf area (PNmax) was 50 %. This indicates that PNmax can increase to a larger extent than the leaf thickness with increasing irradiance in V. jatamansi. Anatomical studies showed that the mesophyll cells of FI plants had no open spaces along the mesophyll cell walls (higher Sc), but in NS plants wide open spaces along the mesophyll cell wall (lower Sc) were found. Positive correlation between Sc and PNmax explained the higher PNmax in FI plants. Increase in mesophyll thickness increased the availability of space along the mesophyll cell wall for chloroplasts (increased Sc) and hence PNmax was higher in FI plants. Thus this Himalayan species can acclimate to full sunlight by altering leaf anatomy and therefore may be cultivated in open fields. and S. Pandey, R. Kushwaha.
Morpho-anatomical leaf traits and photosynthetic activity of two alpine herbs, Podophyllum hexandrum (shade-tolerant) and Rheum emodi (light-requiring), were studied under field (PAR>2 000 µmol m-2 s-1) and greenhouse (PAR 500 µmol m-2 s-1) conditions. Mesophyll thickness, surface area of mesophyll cells facing intercellular spaces (Smes), surface area of chloroplasts facing intercellular spaces (Sc), intercellular spaces of mesophyll cells (porosity), photon-saturated rate of photosynthesis per unit leaf area (PNmax), and ribulose-1,5-bisphosphate carboxylase/oxygenase activity decreased in the greenhouse with respect to the field and the decreases were significantly higher in R. emodi than in P. hexandrum. P. hexandrum had lower intercellular CO2 concentration than R. emodi under both irradiances. The differences in acclimation of the two alpine herbs to low irradiance were due to their highly unlikely changes in leaf morphology, anatomy, and PNmax which indicated that the difference in radiant energy requirement related to leaf acclimation had greater impact under low than high irradiance. and S. Pandey, N. Kumar, R. Kushwaha.