Abstract
Information on the bioavailability and -accessibility of subsoil phosphorus (P) and how soil moisture affects its utilization by plants is scarce. The current study examined whether and to which degree wheat acquires P from subsoil allocated hydroxyapatite and how this could be affected by soil moisture. We investigated the 33P uptake by growing wheat in two rhizotron trials (soil and sand) with integrated 33P-labelled hydroxyapatite hotspots over a period of 44 days using digital autoradiography imaging and liquid scintillation counting. We applied two irrigation scenarios, mimicking either rainfall via topsoil watering or subsoil water storage. The plants showed similar biomass development when grown in soil, but a reduced growth in sand rhizotrons. Total plant P(tot) stocks were significantly larger in plants grown under improved subsoil moisture supply, further evidenced by enhanced P stocks in the ears of wheat in the sand treatment due to an earlier grain filling. This P uptake is accompanied by larger 33P signals, indicating that the plants accessed the hydroxyapatite because subsoil irrigation also promoted root proliferation within and around the hotspots. We conclude that even within a single season plants access subsoil mineral P sources, and this process is influenced by water management.
Highlights
Information on the bioavailability and -accessibility of subsoil phosphorus (P) and how soil moisture affects its utilization by plants is scarce
P originates from the weathering of rock material that becomes scarcer as pedogenesis p rogresses[4]
One major P containing mineral is apatite[5], which may still represent a major primary P source in subsoils. Plants may acquire this P source when added to surfaces s oils[6], little is known on how crops access this mineral P form from the subsoil
Summary
Information on the bioavailability and -accessibility of subsoil phosphorus (P) and how soil moisture affects its utilization by plants is scarce. Total plant P(tot) stocks were significantly larger in plants grown under improved subsoil moisture supply, further evidenced by enhanced P stocks in the ears of wheat in the sand treatment due to an earlier grain filling This P uptake is accompanied by larger 33P signals, indicating that the plants accessed the hydroxyapatite because subsoil irrigation promoted root proliferation within and around the hotspots. Even if a small proportion of the mineral-bound total subsoil P is released as plant-available inorganic orthophosphate ( Pi)[11,12], these phosphate ions may re-bind rapidly to other reactive soil constituents such as Fe- and Al-oxides as well as excessive Ca2+ ions[7,13] These reactions immobilize the otherwise available orthophosphate P 7,9,12, i.e., plants must develop specific P acquisition strategies to access subsoil P sources to overcome its limited b ioavailability[13,14]. Bioavailable, in different soil depths, assuming that plants can adjust their root activity along patches with higher nutrient contents, eventually even showing tendencies of root proliferation in response to such localized nutrient reservoirs[24,25]
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