The role of leaf nitrogen content in protecting photo-inhibitory damage in Hevea seedlings under low temperature stress

An experiment was conducted on Hevea brasiliensis seedlings with different levels of leaf chlorophyll content index (CCI) to study the role of leaf nitrogen in protecting young leaves from photoinhibitory damage during winter period. Seedlings were categorized as low nitrogen (LN), medium nitrogen (MN) and high nitrogen (HN) with corresponding 6.14, 16.41 and 34.84 CCI values and 0.51%, 1.18% and 1.95% leaf nitrogen content. During peak winter period, the photosynthetic rate was significantly lower (1.48 μmol CO₂ m⁻²s⁻¹) in LN in comparison to MN (5.9 μmol CO₂ m⁻²s⁻¹) and HN (7.2 μmol CO₂ m⁻²s⁻¹) seedlings. The mesophyll efficiency (Ci/gs) was higher in HN plants than in LN plants. The potential quantum efficiency of PSII (dark adapted Fv/Fm) was reduced by 67%, 22% and 17% in LN, MN and HN leaves respectively at peak winter period (January) in relation to an optimum period (September). Similarly, the efficiency of PSII photochemistry (φ_PSII) was reduced by 65%, 30% and 25% in these three categories of seedlings respectively. The results of this experiment suggest that higher leaf nitrogen content can protect the plants from photosynthetic down regulation caused by low temperature stress during winter season.