Ecophysiological responses of three native herbs to phytotoxic potential of invasive Acacia melanoxylon R. Br.

Acacia melanoxylon R. Br. (Blackwood) is a native Australian species that has invaded woodlands and degraded natural habitats in the north western Iberian Peninsula (Galicia), Spain. Several phenolic (p-hydroxybenzoic, vanillic, p-coumaric, syringic, protocatequic, ferulic acids) and flavonoids (catechin, luteolin, rutin, apigenin, and quercetin) were identified from methanol extracts of flowers and phyllodes of A. melanoxylon by HPLC. Flowers and phyllodes of A. melanoxylon were soaked separately in the water in a ratio of 1:1 (w/v) for 24 h to prepare aqueous extracts (100, 75, 50 and 25%) and distilled water was used as control. The seeds of three native plants, cocksfoot (Dactylis glomerata), perennial ryegrass (Lolium perenne), common sorrel (Rumex acetosa) and a general test crop lettuce (Lactuca sativa) were grown in perlite culture and aqueous extracts of A. melanoxylon (flowers and phyllodes) were applied exogenously at various concentrations. A. melanoxylon flowers extract (100%) inhibited the shoot length of D. glomerata and L. perenne by 31 and 20% of the control, respectively. Leaf and root fresh weights of L. perenne, D. glomerata, and L. sativa were reduced after treatment with acacia flowers and phyllodes extract. Leaf relative water content of D. glomerata and L. perenne was reduced by acacia flowers and phyllodes extract at all concentrations. Both extracts reduced leaf osmotic potential in D. glomerata, L. perenne and L. sativa. Quantum efficiency of open PSII reaction centers (F_v/F_m) and quantum yield (ΦPSII) of photosystem II were decreased in L. perenne, D. glomerata; R. acetosa and L. sativa after treatment with acacia flowers/phyllodes extract at 100% concentration. Acacia flowers and phyllodes extract (100%) inhibited the qP level during all 6 days in D. glomerata, L. perenne, R. acetosa and L. sativa. A significant reduction in NPQ was observed during different days in all four plant species due to Acacia flowers and phyllodes extract (100%). The δ¹³C ratios were less negative in L. perenne, D. glomerata and L. sativa as compared to the control. A. melanoxylon flowers and phyllodes extract (100%) significantly reduced leaf protein contents in D. glomerata, L. perenne and in L. sativa.