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 (Pn), transpiration rate (Tr), stomatal conductance (Cond), 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 Pn, Tr and Cond, 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 Pn 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.