Abstract
Summary Phytase activity was investigated in 13 lichen species using a novel assay method. The work tested the hypothesis that phytase is a component of the suite of surface‐bound lichen enzymes that hydrolyse simple organic forms of phosphorus (P) and nitrogen (N) deposited onto the thallus surface.Hydrolysis of inositol hexaphosphate (InsP6, the substrate for phytase) and appearance of lower‐order inositol phosphates (InsP5–InsP1), the hydrolysis products, were measured by ion chromatography. Phytase activity in Evernia prunastri was compared among locations with contrasting rates of N deposition.Phytase activity was readily measurable in epiphytic lichens (e.g. 11.3 μmol InsP6 hydrolysed g−1 h−1 in Bryoria fuscescens) but low in two terricolous species tested (Cladonia portentosa and Peltigera membranacea). Phytase and phosphomonoesterase activities were positively correlated amongst species. In E. prunastri both enzyme activities were promoted by N enrichment and phytase activity was readily released into thallus washings. InsP6 was not detected in tree canopy throughfall but was present in pollen leachate.Capacity to hydrolyse InsP6 appears widespread amongst lichens potentially promoting P capture from atmospheric deposits and plant leachates, and P cycling in forest canopies. The enzyme assay used here might find wider application in studies on plant root–fungal–soil systems.
Highlights
Lichens typically grow in habitats with low availabilities of nitrogen (N) and phosphorus (P) (Crittenden, 1989; Crittenden et al, 1994)
P is not routinely measured in atmospheric deposits, there is a dearth of information on P deposition rates and how lichens respond to variation in P income is largely unknown
We develop a phytase assay procedure suitable for lichens using the common epiphyte Evernia prunastri and compare rates of activity among 13 lichens including 11 epiphytic and two terricolous species
Summary
Lichens typically grow in habitats with low availabilities of nitrogen (N) and phosphorus (P) (Crittenden, 1989; Crittenden et al, 1994). The majority of lichens acquire these nutrients from atmospheric deposits by efficiently scavenging inorganic N and P (Pi) from solutes in precipitation intercepted either directly or after being modified by plant canopies and delivered to thalli as canopy throughfall and stem flow (Crittenden, 1983, 1989, 1998). Nitrogen compounds are routinely monitored in both precipitation and air, and there is an abundance of data on rates of N deposition with which lichen N concentration ([N]) is frequently positively correlated (Bruteig, 1993; Hyv€arinen & Crittenden, 1998b; Remke et al, 2009; Hogan et al, 2010a; Boltersdorf et al, 2014). Detailed P-focused investigations suggest that Pi concentration in rainfall is in the range 0.03– 0.33 lmol lÀ1 (Grimshaw & Dolske, 2002; Neal et al, 2003; Yoshioka et al, 2009; He et al, 2011); Pi at these low concentrations is taken up rapidly by lichens via high affinity phosphate transport systems (Farrar, 1976; Hogan, 2009)
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