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DIVISION S-7—FOREST & RANGE SOILS

Non-labile Soil ¹⁵Nitrogen Retention beneath Three Tree Species in a Tropical Plantation

^a Dep. of Forest Sciences, Colorado State Univ., Fort Collins, CO 80523
^b Terrestrial Ecology Division, Univ. of Puerto Rico, P.O. Box 363682, San Juan, PR 00936
^c USDA Forest Service, Research and Development, P.O. Box 96090, Washington, DC 20090-6090

* Corresponding author (jkaye{at}lamar.colostate.edu)

Soil organic matter is the largest sink for N additions to forests. Species composition may affect soil N retention by altering the amount or proportion of added N stored in non-labile organic pools. We measured ¹⁵N tracer retention in labile and non-labile pools of surface (0–20 cm) mineral soils, 7 yr after the tracer was applied to a 9 yr-old Puerto Rican tree plantation with replicated stands of three species (two N-fixers, one Eucalyptus, Euc). Laboratory incubations (13 mo) with repeated leaching separated total soil N into labile (inorganic N leached) and non-labile (total N minus leached N) pools, and a labile C treatment tested linkages between C availability and N retention. We hypothesized that species composition would alter the amount and proportion of recovered tracer N in non-labile organic matter. Surface soils contained 45% of the tracer, but the amount retained in labile and non-labile pools was similar among species. In contrast, the proportion of recovered tracer in non-labile pools was greater in soils beneath N-fixers (75%) than Euc (62%). Labile C additions increased the size of the non-labile tracer N pool. We conclude that tree species composition may affect long-term soil N retention by altering the proportion of N in slow-turnover, non-labile pools. Plants may also alter soil N retention by renewing labile C pools; a continuous supply of labile C increased the transfer of ¹⁵N into non-labile organic matter.

Abbreviations: AFE, atom fractional enrichment • ECEC, effective cation-exchange capacity • Cas, Casuarina • Euc, Eucalyptus • Leu, Leucaena • k_n, extraction efficiency • N_o, mass of labile N • N_a, the mass of tracer N in the labile pool • N_n, the mass of labile native soil N • ¹⁵N_o, AFE of the composite leachate sample • ¹⁵N_a, AFE of the tracer • ¹⁵N_n, AFE of the native soil • PNDFA, percent of tree N derived from the atmosphere • NPP, net primary productivity

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				A. E. Russell, J. W. Raich, O. J. Valverde-Barrantes, and R. F. Fisher Tree Species Effects on Soil Properties in Experimental Plantations in Tropical Moist Forest Soil Sci. Soc. Am. J., June 29, 2007; 71(4): 1389 - 1397. [Abstract] [Full Text] [PDF]