Micronutrients and mangroves: Experimental evidence for copper limitation

Abstract

Testing the availability and requirements of micronutrients during early mangrove growth is essential for understanding their recruitment success across intertidal gradients. Recent research has highlighted the role of dissolved iron in mangrove growth, but the role of other trace metals (Cu, Zn, Mo) in supporting and possibly limiting tree growth is unknown. In outdoor experiments, dissolved copper, supplied at a rate mimicking those in natural forests, limited early growth of five species of mangroves. Rates of stem extension and biomass increase from seedling to sapling stage of Rhizophora apiculata, Bruguiera gymnorrhiza, Avicennia marina, and Ceriops tagal increased linearly with increasing rates of Cu supply (0.0 μmol m−2 d−1, 0.005 μmol m−2 d−1, 0.01 μmol m−2 d−1, 0.02 μmol m−2 d−1, and 0.05 μmol m−2 d−1); early growth of Xylocarpus moluccensis best-fit Gaussian curves with maximal growth at a Cu supply rate of 0.02 μmol m−2 d−1 with toxicity evident at the highest Cu supply rate. Most copper was stored in roots and leaves. Zinc and molybdenum were not limiting for growth of any of the five species, but X. moluccensis growth declined with increasing Mo supply, suggesting lower tolerance and greater toxicity. Differences in such requirements among species, especially during early establishment, may be a key driver in fostering changing patterns in species composition among forests.