Tree phosphorus uptake from argillic and saprolite horizons in a weathered Ultisol in the Calhoun Critical Zone Observatory, USA Zhine Wang1, Aaron Thompson2, Lori Sutter1, and Daniel Markewitz1 1Warnell School of Forestry and Natural Resources; 2Department of Crop and Soil Science University of Georgia, Athens, GA Phosphorus is a critical plant nutrient that is deficient in many soils worldwide. Soil P may combine with secondary Al, Fe, or Ca minerals, or be present in organic forms. Identifying the bioavailability of varied P pools and quantifying the amount of potential P uptake is important for defining long-term ecosystem productivity and understanding P-acquiring mechanisms of studied plants. Our research investigates how red maple (Acer rubum) and loblolly pine (Pinus teada) take up P from multiple soil fractions native to the Calhoun Critical Zone Observatory in the Piedmont of South Carolina USA. Red maple and loblolly pine seeds were grown in two different homogenized soil substrates: clay (60-100 cm) and saprolite (450-500 cm). Prior to planting we analyzed substrates using the Hedley P fractionation, which demonstrated bioavailable P (0.5M HCl Pi, NaHCO3 Pi and NaHCO3 Po) in saprolite (31.2±4.8 µg/g) is significantly higher than in clay (5.8±1.2 µg/g). Seedlings were fertilized with a P-free fertilizer mix twice per week to induce P-limitation and grown for ~1 year. We measured tree growth, changes in soil P pools, the extent of Fe reduction in microenvironments as a potential mechanism of P release, and plant exudation of phosphatase enzymes to access organic P. At harvest, plants were small. In clay and saprolite, average height of red maple was 6.0±1.6 and 6.2±1.4 cm and of loblolly pine was 8.6±1.6 and 10.6±3.1 cm, respectively. Pine trees grew significantly higher in saprolite (p=0.01) but maple tree heights did not differ (p=0.6). There was a higher iron reduction index in clay 16±10% (of the total iron bar surface) compared to saprolite 13±9% but this did not translate into improved growth. Preliminary data on plant P content indicated that plants were able to extract P in excess of resin extractable P and thus were making use of other forms of bioavailable P.
Wang, Z., A. Thompson, L. Sutter, and D. Markewitz (2019): Tree Phosphorus Uptake from Argillic and Saprolite Horizons in a Weathered Ultisol in the Calhoun Critical Zone Observatory, USA. ASA-CSSA-SSSA International Annual Meeting, 10-13 Nov. 2019, San Antonio, Texas.
This Paper/Book acknowledges NSF CZO grant support.