Salinity strongly drives the survival, growth, leaf demography, and nutrient partitioning in seedlings of Xylocarpus granatum J. König

Salinity is increasing in the Sundarbans (Bangladesh) due to sea-level rise and the reduction of fresh water flow. Xylocarpus granatum is one of the most valuable mangrove tree species of the Sundarbans. We conducted a six-month long study to investigate the effect of salinity on the survival, growth, leaf demography, and nutrient partitioning in parts of X. granatum seedlings. Our results showed that most of the seedlings (90%) survived at 0 to 5 PSU salinity, and this survival percentage was found to decrease at higher saline conditions. Salinity of more than 25 PSU was lethal to the plants as no seedlings survived under these conditions. In this salinity (25 PSU), accelerated leaf fall coupled with a reduction in the new leaves caused loss of leaves. The relative growth rate (RGR) was higher at 0 to 5 PSU salinity, and conversely, a lower growth rate was observed with increased salinity. Higher saline conditions created stress, which inhibited nutrient (N, P and K) accumulation in different parts (leaf, stem, bark and root) of the seedlings. We concluded that salinity is a critical factor for the growth and survival of X. granatum either by inhibiting plant nutrient uptake or due to salinity related toxicity

Allometric models for estimating biomass, carbon and nutrient stock in the Sal zone of Bangladesh

Allometric models are commonly used to estimate biomass, nutrients and carbon stocks in trees, and contribute to an understanding of forest status and resource dynamics. The selection of appropriate and robust models, therefore, have considerable influence on the accuracy of estimates obtained. Allometric models can be developed for individual species or to represent a community or bioregion. In Bangladesh, the nation forest inventory classifies tree and forest resources into five zones (Sal, Hill, Coastal, Sundarbans and Village), based on their floristic composition and soil type. This study has developed allometric biomass models for multi-species of the Sal zone. The forest of Sal zone is dominated by Shorea robusta Roth. The study also investigates the concentrations of Nitrogen, Phosphorus, Potassium and Carbon in different tree components. A total of 161 individual trees from 20 different species were harvested across a range of tree size classes. Diameter at breast height (DBH), total height (H) and wood density (WD) were considered as predictor variables, while total above-ground biomass (TAGB), stem, bark, branch and leaf biomass were the output variables of the allometric models. The best fit allometric biomass model for TAGB, stem, bark, branch and leaf were: ln (TAGB) = -2.460 + 2.171 ln (DBH) + 0.367 ln (H) + 0.161 ln (WD); ln (Stem) = -3.373 + 1.934 ln (DBH) + 0.833 ln (H) + 0.452 ln (WD); ln (Bark) = -5.87 + 2.103 ln (DBH) + 0.926 ln (H) + 0.587 ln (WD); ln (Branch) = -3.154 + 2.798 ln (DBH) - 0.729 ln (H) - 0.355 ln (WD); and ln (Leaf) = -4.713 + 2.066 ln (DBH), respectively. Nutrients and carbon concentration in tree components varied according to tree species and component. A comparison to frequently used regional and pan-tropical biomass models showed a wide range of model prediction error (35.48 to 85.51%) when the observed TAGB of sampled trees were compared with the estimated TAGB of the models developed in this study. The improved accuracy of the best fit model obtained in this study can therefore be used for more accurate estimation of TAGB and carbon and nutrients in TAGB for the Sal zone of Bangladesh