EFFECT OF THE INTERACTION OF EARTHWORMS AND SUBSTRATES ON PHOTOSYNTHETIC CHARACTERISTICS, NITROGEN AND PHOSPHORUS UPTAKE BY Iris pseudacorus IN CONSTRUCTED WETLAND SYSTEM

This study investigates the effects of earthworms and a variety of substrates on photosynthetic characteristics and rate of uptake of nitrogen (N) and phosphorus (P) by Iris pseudacorus L. (Iridaceae) in a constructed wetland system under greenhouse conditions. The study seeks to identify those factors that maximize the efficient removal of N and P. Four substrates were tested: pure sand, sand and soil, sand and organic matter, and a mixture of sand, soil and organic matter. The photosynthetic characteristics and uptake of N and P by I. pseudacorus were influenced by the presence of earthworms and the type of substrate. The addition of organic matter enhanced the photosynthetic rate (P-n), transpiration rate (T-r), stomatal conductance (C-ond), root and shoot weight. The addition of earthworms increased the pod production and dry weight of I. pseudacorus, especially on the sand and soil, and sand and organic matter substrates. It also increased P-n, T-r and C-ond, and resulted in an increase in the root and above-ground weight, and root and above-ground N and P uptake. A correlation analysis showed that P-n were significantly positively correlated with root and shoot weight, root N and P uptake, and above-ground N and P uptake (P < 0.05). The addition of earthworms into a constructed wetland could increase the photosynthetic characteristics and biomass of Iris pseudacorus, resulting in increased uptake of N and P.