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Phosphorus (P) for carbon (C) exchange is the pivotal function of arbuscular mycorrhiza (AM), but how this exchange varies with soil P availability and among co-occurring plants in complex communities is still largely unknown. We collected intact plant communities in two regions differing c. 10-fold in labile inorganic P. After a 2-month glasshouse incubation, we measured 32 P transfer from AM fungi (AMF) to shoots and 13 C transfer from shoots to AMF using an AMF-specific fatty acid. AMF communities were assessed using molecular methods. AMF delivered a larger proportion of total shoot P in communities from high-P soils despite similar 13 C allocation to AMF in roots and soil. Within communities, 13 C concentration in AMF was consistently higher in grass than in blanketflower (Gaillardia aristata Pursh) roots, that is P appeared more costly for grasses. This coincided with differences in AMF taxa composition and a trend of more vesicles (storage structures) but fewer arbuscules (exchange structures) in grass roots. Additionally, 32 P-for- 13 C exchange ratios increased with soil P for blanketflower but not grasses. Contrary to predictions, AMF transferred proportionally more P to plants in communities from high-P soils. However, the 32 P-for- 13 C exchange differed among co-occurring plants, suggesting differential regulation of the AM symbiosis., (© 2024 The Authors. New Phytologist © 2024 New Phytologist Foundation.)

Many temperate forests of the Northeastern United States and Europe have received significant anthropogenic acid and nitrogen (N) deposition over the last century. Although temperate hardwood forests are generally thought to be N-limited, anthropogenic deposition increases the possibility of phosphorus (P) limiting productivity in these forest ecosystems. Moreover, inorganic P availability is largely controlled by soil pH and biogeochemical theory suggests that forests with acidic soils (i.e.,

Abstract: The biogeochemical cycling of phosphorus (P) in temperate forest ecosystems is poorly understood relative to nitrogen (N) cycling because of the assumption that N is the main factor that limits plant growth. This dichotomous way of understanding nutrient regimes is likely an oversimplification of these dynamic, interacting cycles within the evermore-dynamic framework of soil development. In order to better understand P cycling in temperate deciduous forests, we sought to quantify labile (resin) P flux and determine if soil shows signs of P stress. Labile P flux was quantified in nine ambient and nine elevated P plots on unglaciated eastern deciduous forests in Eastern Ohio. Anion exchange membranes (AEMs) were deployed in situ for two weeks, in the fall and the winter. Flux values were contextualized by resin P pools, N and P mineralization, and phosphatase enzyme activities determined from soil samples collected both at the time of AEM deployment and harvest. Phosphorus flux was 0.64±0.23μgPd−1 (mean±SD) in ambient plots and 3.47±2.39μgPd−1 in amended P plots. Resin P pools were 4.16mgkg−1 and 10.26mgkg−1 in the control and elevated plots, respectively. Phosphorus turnover rate increased from one week in control plots, to 3 days in elevated P plots. Results indicate mild P stress relative to N, as N was mineralized (0.84±0.18mgNkg−1 d−1) while P was immobilized (−0.22±0.09mgPkg−1 d−1). The elevated P treatment did not increase P mineralization. Phosphatase enzyme activities were significantly suppressed by 34% with P amendment. Results suggest labile P is a shallow pool, but is rapidly cycling. [Copyright &y& Elsevier]