INTRODUCTION
Post-industrial wastelands are often reclaimed for forestry (Hüttl and
Weber, 2001; Sheoran et al., 2010; Macdonald et al., 2015;
Pietrzykowski, 2019). In this way of reclamation planted trees are to
transform the uppermost layer of barrens into functional soils. However,
a common feature of the substrates forming the uppermost layer of
post-industrial barrens is low concentration of essential nutrients, in
particular nitrogen and phosphorus (Zipper et al., 2011; Krzaklewski et
al., 2012; Cross et al., 2019; Manimel Wadu et al., 2017). Insufficient
nutrient contents in the dumped or excavated materials may hinder growth
of the introduced vegetation (Sheoran et al., 2010; Pietrzykowski,
2019). In order to alleviate N deficiency in developing technosols
planted are tree species capable of forming a symbiosis with N-fixing
bacteria (hereafter referred to as ‘N-fixers’). Owing to the symbiosis
with N-fixing bacteria these species may enrich the developing soils in
nitrogen (Zipper et al., 2011; Vlachodimos et al., 2013; Bissonette et
al., 2014; Pietrzykowski et al., 2015). However, the role of N-fixers in
alleviating P deficiency has been less recognized although it is known
that certain N-fixing plants can acquire P from compounds that are
unavailable for other plant species (Hinsinger, 2001; Hinsinger et al.,
2011) and in this way intensify P cycling in the forming soils.
Vegetation is one of the major factors affecting transformations and
cycling of soil P (Hinsinger, 2015). Plants take up phosphorus in
mineral forms and deposit P-containing organic residues that become
substrates for a variety of soil organic P forms (Hinsinger, 2015). In
the uppermost soil horizons the organic P may constitute more than 50%
of total P (Sulieman and Mühling, 2021). Organic P is not directly plant
available, however there are several mechanisms that enable plants
accessing organic P (Richardson et al., 2009). Chodak et al. (2021)
reported that N-fixing tree species (black locust and black alder)
improved capacity of technosols to release P by increasing the activity
of phosphatases and enhancing microbial uptake of P. Organic P in soils
occurs in a large variety of forms that differ in chemical composition,
reactivity and plant availability (Turner et al., 2005). Recent studies
suggest that organic P may be an important source of P for plants
(Sulieman and Mühling, 2021). However, the effect of N-fixing plant
species on the forms of organic phosphorus in soil is unclear and the
published results are inconsistent. Increased contents of available P
were reported for some N-fixing tree species and but not for others
(Wang et al., 2010; Orczewska et al., 2012). Discrepant results might
have been due to differences in the soil properties that obscured the
effect of trees.
The objective in this study was to compare the effect of N-fixing tree
species (black locust (Robinia pseudoacacia ) and black alder
(Alnus glutinosa )) and non-N-fixing species (silver birch
(Betula pendula ) and Scots pine (Pinus sylvestris )) on the
forms of organic P in the uppermost horizons of reclaimed technosols
developing from various parent materials.