Enhanced soil and leaf nutrient status of a Western Australian Banksia woodland community invaded by Ehrharta calycina and Pelargonium capitatum

Increased nutrient availability can have a large impact in Australian woodland ecosystems, many of which are very poor in nutrients, particularly phosphorus. A study was conducted in an urban Banksia woodland remnant in Perth, southwest Western Australia to test the hypothesis that the soil nutrient status in areas in good condition (GC), poor condition invaded by the perennial grass Ehrharta calycina (PCe), and poor condition invaded by the perennial herb Pelargonium capitatum (PCp), is reflected in the nutrient status of the native and introduced species. Leaf concentrations of P, K, N, Na, Ca, Mg, S, B, Cu, Fe, Mn and Zn of six native (Banksia attenuata, Banksia menziesii, Allocasuarina humilis, Melaleuca systena, Macrozamia fraseri and Conostylis aculeata) and four introduced species (Ehrharta calycina, Pelargonium capitatum, Gladiolus caryophyllaceus and Briza maxima), were measured. Soil pH, electrical conductivity, N (total), P (total), available P, K, S and organic C were assessed beneath all species on all sites. Significantly higher concentrations of soil P (total) and P (HCO3) were found at PCe and PCp sites than GC sites, while PCp sites also had significantly higher soil concentrations for N (total) and S. Principal Components Analysis of the leaf analyses showed (a) individual species have characteristically different nutrient concentrations; (b) the introduced species Ehrharta calycina and Pelargonium capitatum clustered separately from each other and by vegetation condition. Leaf concentrations of P were significantly (P < 0.05) higher, and K and Cu were significantly lower in PCe and PCp sites compared with those at GC sites. Introduced species leaf nutrient concentrations were significantly greater than native species for all nutrients except Mn which was significantly lower, with no differences for Mg and B. The results indicate a key role for P in the Banksia woodland, and we conclude that higher levels of available P at invaded sites are having a detrimental impact on the ecosystem. These results provide new knowledge to enhance conservation practices for the management of the key threatening process of invasion within a biodiversity hot spot.