Leaching of Phosphomonoesterase Activities in Beech Forest Soils: Consequences for Phosphorus Forms and Mobility

Abstract

Phosphomonoesterases play an important role in the soil phosphorus (P) cycle since they hydrolyze P monoester to phosphate. Their activity is generally measured in soil extracts, and thus, it remains uncertain how mobile these enzymes are and to which extent they can be translocated within the soil profile. The presence of phosphomonoesterases in soil solutions potentially affects the share of labile dissolved organic P (DOP), which in turn would affect P leaching. Our study aimed at assessing the production and leaching of phosphomonoesterases from organic layers and topsoil horizons in forest soils and its potential effect on dissolved P forms in leachates obtained from zero-tension lysimeters. We measured phosphomonoesterase activities in leached soil solutions and compared it with those in water extracts from litter, Oe/Oa, and A horizons of two beech forests with a contrasting nitrogen (N) and P availability, subjected to experimental N × P fertilization. In addition, we determined phosphate and DOP. In soil solutions leached from litter, Oe/Oa, and A horizons, phosphomonoesterase activities ranged from 2 to 8 μmol L–1 h–1 during summer, but remained below detection limits in winter. The summer values represent 0.1–1% of the phosphomonoesterase activity in soil extracts, indicating that enzymes can be translocated from organic layers and topsoils to greater soil depths. Activities of phosphomonoesterases obtained by water extracts were greater in the organic layer of the P-poor site, while activities of those in soil solutions were similar at the two sites. Nitrogen addition increased phosphomonoesterase activities in leached soil solutions of the organic layer of the N- and P-poor soil. Using a modeling approach, we estimated that approx. 76% of the initial labile DOP was hydrolyzed to dissolved inorganic P within the first 24 h. Back calculations from measured labile DOP revealed an underestimation of approx. 15% of total dissolved P, or 0.03 mg L–1. The observed leaching of phosphomonoesterases implies that labile organic P could be hydrolyzed in deeper soil horizons and that extended sample storage leads to an underestimation of the contribution of DOP to total dissolved P leaching. This has been neglected in the few field studies measuring DOP leaching.

Fine root biomass of European beech trees in different soil layers show different responses to season, climate, and soil nutrients

“…In the forests, which we studied here, the P respective N inputs by annual litter fall amount approximately (P/N) 0.16/2.9 g m −2 at the P-low, 0.21/3.6 g m −2 at the P-medium and 0.23/3.2 g m −2 at the P-high site (Lang et al, 2017). Nutrient release and leaching from leaf litter was found over the summer and caused cycling between higher spring and lower fall P and N contents in the organic layer (Fetzer et al, 2021(Fetzer et al, , 2022. Our results confirm this seasonal pattern for N and P in the organic soil layer.…”

Differential Responses of Soil Phosphorus Fractions to Nitrogen and Phosphorus Fertilization: A Global Meta‐Analysis

“…Fan et al., 2018; K. Yang et al., 2015) probably because N addition first increases soil labile P (e.g., resin P and NaHCO 3 ‐P), at least in part by the mineralization of NaOH‐Po related to higher ACP activity. Moreover, the enhanced mineralization of soil moderately labile Po under N addition occurs primarily when soil available Pi is insufficient and the mineralization of NaHCO 3 ‐Po does not fully meet the biological requirements (J. Fetzer et al., 2021). It is important to note that the response of soil P fractions to N addition varied depending on the soil pH range.…”

“…Moreover, the enhanced mineralization of soil moderately labile Po under N addition occurs primarily when soil available Pi is insufficient and the mineralization of NaHCO 3 -Po does not fully meet the biological requirements (J. Fetzer et al, 2021). It is important to note that the response of soil P fractions to N addition varied depending on the soil pH range.…”