Nutrient limitation and stable nitrogen isotope ratios in two plOneer species Robinia pseudoacacia and SalLx: gilgiana colonized on the nutrient poor sediment barof a regulated river

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Flow regulation through dam construction in the upstream of large rivers enables the colonization of vegetation on the downstream sediment bar with organic matter acctunulation and silt trap. Robinia pseudoacacia, a woody legume and Salix gilgiania, a nood-tolerant shnlb colonize on the mid-stream sediment bar where soil nutrient levels are relatively low. This two species can colonize along the gradients of the sediment bar withdistinct soil characteristics. Total nitrogen (TN) to total phosphorus (TP) ratios has been widely used as diagnostic indicators of nitrogen saturation and limitation of plant growth. Samples of above-ground organs, roots and soils were collected and analyzed. High TN content was found in nodule followed by leaf, rootand then shoot tissue of. pseudoacacia whereas in S, gilgiania, it was the highest in leaf followed by shoot and the root tissue.TP content was found high in the leaf tissues of both species. High ratio of nitrogen and phosphorus in the tissue of R.pseudoacacia indicating that plant growth is P limited whereas the ratio was very low in the soil samples. The growth of S. gilgiania is nitrogen limited as the N and P ratio in the plant tissues was low. Mean nitrogen stable isotope ratio 815N in S. gilgiania was relatively higher thanthe R. pseudoacacia. Nitrogen sattlration in the tissues of R. pseudo-acacia occurs asthe symbiotic bacteria fix atmospheric nitrogen.
2010-02-10