nutrient cycling

Interactive effects of native and exotic earthworms on resource use and nutrient mineralization in a tropical wet forest soil of Puerto Rico

Lachnicht, SL, PF Hendrix, and X. Zou. 2002. Interactive effects of native and exotic earthworms on resource use and nutrient mineralization in a tropical wet forest soil of puerto rico. Biology and Fertility of Soils 36 (1) (AUG): 43-52.

Abstract: 
Investigation of single or mixed assemblages of native Estherella sp. and exotic Pontoscolex corethrurus from a rain forest in Puerto Rico was undertaken to understand resource use patterns, and linkages with C and N mineralization in a 19-day incubation. Resource use was explored with addition of 15N-enriched leaf litter and 13Cenriched glucose to reconstructed organic and mineral soil horizons. Juvenile Estherella sp. became at least 6.06‰ more enriched in 13C than sub-adult Estherella sp. or adult P. corethrurus. Sub-adult Estherella sp. became >3.6‰ enriched in 13C over P. corethrurus. δ15N acquired by P. corethrurus was greater by 0.83–1.56‰ in the mixed-species than the single-species assemblages. δ15N of subadult Estherella sp. was enriched by 0.73–0.81‰ over juvenile Estherella sp. in the single-species assemblage. Net N immobilization occurred in the organic layer of all 15Nenriched treatments. Net N mineralization in mineral soil layers was significantly greater in microcosms with P. corethrurus than in those containing only Estherella sp.. Cumulative respiration was greatest in P. corethrurus assemblages, however, assemblages with only Estherella sp. released more 13C in respiration. P. corethrurus assimilated different N resources when incubated with, as compared to without, native Estherella sp.. δ13C and δ15N signatures acquired by assimilation of 13C and 15N differed by species, developmental stage, and competitive interactions. The results showed that alone, exotic P. corethrurus induced higher mineralization rates than native Estherella sp., but that the interaction of exotic and native species impinged on resource use by P. corethrurus, reducing the effect of the exotic species on C and N mineralization. Invasion of exotic P. corethrurus may change the mineralization potentials of C and N and their biogeochemical cycling in soils.

Contributions of dust to phosphorus cycling in tropical forests of the Luquillo Mountains, Puerto Rico

Pett-Ridge, Julie C. 2009. Contributions of dust to phosphorus cycling in tropical forests of the luquillo mountains, puerto rico. Biogeochemistry 94 (1) (MAY): 63-80.

Abstract: 
The input of phosphorus (P) through mineral aerosol dust deposition may be an important component of nutrient dynamics in tropical forest ecosystems. A new dust deposition calculation is used to construct a broad analysis of the importance of dust-derived P to the P budget of a montane wet tropical forest in the Luquillo Mountains of Puerto Rico. The dust deposition calculation used here takes advantage of an internal geochemical signal (Sr isotope mass balance) to provide a spatially integrated longer-term average dust deposition flux. Dust inputs of P (0.23 ± 0.08 kg ha-1 year-1) are compared with watershed-average inputs of P to the soil through the conversion of underlying saprolite into soil (between 0.07 and 0.19 kg ha-1 year-1), and with watershed-average losses of soil P through leaching (between 0.02 and 0.14 kg ha-1 year-1) and erosion (between 0.04 and 1.38 kg ha-1 year-1). The similar magnitude of dust-derived P inputs to that of other fluxes indicates that dust is an important component of the soil and biomass P budget in this ecosystem. Dust-derived inputs of P alone are capable of completely replacing the total soil and biomass P pool on a timescale of between 2.8 ka and 7.0 ka, less than both the average soil residence time (*15 ka) and the average landslide recurrence interval (*10 ka).

Contributions of dust to phosphorus cycling in tropical forests of the Luquillo Mountains, Puerto Rico

Pett-Ridge, J. C. 2009. Contributions of dust to phosphorus
cycling in tropical forests of the Luquillo Mountains, Puerto
Rico. Biogeochemistry 94:63-80.

Abstract: 
The input of phosphorus (P) through mineral aerosol dust deposition may be an important component of nutrient dynamics in tropical forest ecosystems. A new dust deposition calculation is used to construct a broad analysis of the importance of dust-derived P to the P budget of a montane wet tropical forest in the Luquillo Mountains of Puerto Rico. The dust deposition calculation used here takes advantage of an internal geochemical signal (Sr isotope mass balance) to provide a spatially integrated longer-term average dust deposition flux. Dust inputs of P (0.23 ± 0.08 kg ha-1 year-1) are compared with watershed-average inputs of P to the soil through the conversion of underlying saprolite into soil (between 0.07 and 0.19 kg ha-1 year-1), and with watershed-average losses of soil P through leaching (between 0.02 and 0.14 kg ha-1 year-1) and erosion (between 0.04 and 1.38 kg ha-1 year-1). The similar magnitude of dust-derived P inputs to that of other fluxes indicates that dust is an important component of the soil and biomass P budget in this ecosystem. Dust-derived inputs of P alone are capable of completely replacing the total soil and biomass P pool on a timescale of between 2.8 ka and 7.0 ka, less than both the average soil residence time (*15 ka) and the average landslide recurrence interval (*10 ka).

Relative scales of time and effectiveness of watershed processes in a tropical montane rain forest of puerto rico

Scatena FN. 1995. Relative scales of time and effectiveness of watershed
processes in a tropical montane rain forest of Puerto Rico. Pages 103–111
in Costa JE, Miller AJ, Potter KW, Wilcock PR, eds. Natural and Anthropogenic
Influences in Fluvial Geomorphology.Washington (DC):
American Geophysical Union. Geophysical Monograph 89.

Nutrient availability in a montane wet tropical forest: Spatial patterns and methodological considerations

Silver, W.L., F.N. Scatena, A.H. Johnson, T.G. Siccama, and M.J.
Sanchez. 1994. Nutrient availability in a montane wet tropical forest: Spatial patterns and methodological considerations. Plant Soil 164:129–145.

Abstract: 
Soils and forest floor were sampled quantitatively from a montane wet tropical forest in Puerto Rico to determine the spatial variability of soil nutrients, the factors controlling nutrient availability to vegetation, and the distribution of nutrients in soil and plants. Exchangeable cation concentrations were measured using different soil extracting procedures (fresh soil with NH4C1, air-dried and ground soil with KC1, and a Modified Olsen solution) to establish a range of nutrient availability in the soil, and to determine the relationship between different, but commonly used laboratory protocols. The availability of exchangeable Ca, Mg, and K was significantly lower in soils extracted fresh with NHaCI than from soils which were dried and ground prior to extraction with KCI or a modified Olsen solution. Soil nutrient availability generally decreased with depth in the soil. Several soil properties important to plant growth and survival varied predictably across the landscape and could be viewed in the context of a simple catena model. In the surface soils, exchangeable base cation concentrations and pH increased along a gradient from ridge tops to riparian valleys, while soil organic matter, exchangeable Fe and acidity decreased along this gradient. On the ridges, N, P, and K were positively correlated with soil organic matter; on slopes, N and P were positively correlated with organic matter, and Ca, Kg, and pH were negatively correlated with exchangeable Fe. Nutrient availability in the upper catena appears to be primarily controlled by biotic processes, particularly the accumulation of organic matter. The Ca, K, and P content of the vegetation was higher on ridges and slopes than in the valley positions. Periodic flooding and impeded drainage in the lower catena resulted in a more heterogeneous environment. A comparison of the Bisley, Puerto Rico soils with other tropical montane forests (TMF) revealed that the internal heterogeneity of soils in the Bisley Watersheds is similar to the range of average soil nutrient concentrations among TMF's for Ca, Mg, and K (dry/ground soils). Phosphorus tended to be slightly higher in Bisley and N was lower than in other TMFs.

Can uptake length in strams be determined by nutrient addition experiments? Results from an interbiome comparison study

Mulholland, P. J; Tanks, J. L.; Webster, J. R.; Bowden, W. B.; Dodds, W. K; Gregory, S. V.; Grimm, N. B; Meriam, J. L.; Meyer, J. L.; Peterson, B. J.; Valett, H. M.; Wollheim, W. M. 2002. Can uptake length in strams be determined by nutrient addition experiments? Results from an interbiome comparison study. J. N. Am. Bethol. Soc. 2002, 21(4): 544-560.

Abstract: 
Nutrient uptake length is an important parnmeter tor quantifying nutrient cycling in streams. Although nutrient tracer additions are the preierred method for measuring uptake length under ambient nutrient concentrations, short-term nutrient addition experiments have more irequently been used to estimate uptake length in streams. Theoretical analysis of the relationship between uptake length determined by nutrient addition experiments (Sw') and uptake length determined by tracer additions (Sw)predicted that Sw' should be consistently longer than 5,", and that the overestimate of uptake length by Sw( should be related to the level of nutrient addition above ambient concentrations and the degree of nutrient limitation. To test these predictions, we used data irom an interbiorne study of NH,- uptake length in which 15NH,- tracer and short-term NH,-a ddition experiments were performed in 10 streams using a uniform experimental approach. The experimental results largely contirmed the theoretical predictions: sw' was consistently longer than Sw and Sw':Sw ratios were directly related to the level of NH,- addition and to indicatvrs of N limitation. The experimentally derived Sw':Sw, ratios were used with the theoretical results to infer the N limitation status of each stream. Together, the theoretical and experimental results showed the tracer experiments should be used whenever possible to determine nutrient uptake length in streams. Nutrient addition experiments may be useful for comparing uptake lengths between different streams or cliiferent times in the same stream. however, provided that nutrient additions are kept as low as possible and of similar miagnitude.

Fine Litterfall and Related Nutrient Inputs Resulting From Hurricane Hugo in Subtropical Wet and Lower Montane Rain Forests of Puerto Rico

Fine Litterfall and Related Nutrient Inputs Resulting From Hurricane Hugo in Subtropical Wet and Lower Montane Rain Forests of Puerto Rico
D. Jean Lodge, F. N. Scatena, C. E. Asbury and M. J. Sanchez
Biotropica
Vol. 23, No. 4, Part A. Special Issue: Ecosystem, Plant, and Animal Responses to Hurricanes in the Caribbean (Dec., 1991), pp. 336-342

Abstract: 
On 18 September 1989 Hurricane Hugo defoliated large forested areas of northeastern Puerto Rico. In two severely damaged subtropical wet forest sites, a mean of 1006-1083 g/m$^2$, or 419-451 times the mean daily input of fine litter (leaves, small wood, and miscellaneous debris) was deposited on the forest floor. An additional 928 g/m$^2$ of litter was suspended above the ground. A lower montane rain forest site received 682 times the mean daily fine litterfall. The concentrations of N and P in the hurricane leaf litter ranged from 1.1 to 1.5 and 1.7 to 3.3 times the concentrations of N and P in normal leaffall, respectively. In subtropical wet forest, fine litterfall from the hurricane contained 1.3 and 1.5-2.4 times the mean annual litterfall inputs of N and P, respectively. These sudden high nutrient inputs apparently altered nutrient cycling.

Fine Litterfall and Related Nutrient Inputs Resulting From Hurricane Hugo in Subtropical Wet and Lower Montane Rain Forests of Puerto Rico

Fine Litterfall and Related Nutrient Inputs Resulting From Hurricane Hugo in Subtropical Wet and Lower Montane Rain Forests of Puerto Rico
D. Jean Lodge, F. N. Scatena, C. E. Asbury and M. J. Sanchez
Biotropica
Vol. 23, No. 4, Part A. Special Issue: Ecosystem, Plant, and Animal Responses to Hurricanes in the Caribbean (Dec., 1991), pp. 336-342

Abstract: 
On 18 September 1989 Hurricane Hugo defoliated large forested areas of northeastern Puerto Rico. In two severely damaged subtropical wet forest sites, a mean of 1006-1083 g/m$^2$, or 419-451 times the mean daily input of fine litter (leaves, small wood, and miscellaneous debris) was deposited on the forest floor. An additional 928 g/m$^2$ of litter was suspended above the ground. A lower montane rain forest site received 682 times the mean daily fine litterfall. The concentrations of N and P in the hurricane leaf litter ranged from 1.1 to 1.5 and 1.7 to 3.3 times the concentrations of N and P in normal leaffall, respectively. In subtropical wet forest, fine litterfall from the hurricane contained 1.3 and 1.5-2.4 times the mean annual litterfall inputs of N and P, respectively. These sudden high nutrient inputs apparently altered nutrient cycling.

A nitrogen budget for late-successional hillslope tabonuco forest, Puerto Rico

A Nitrogen Budget for Late-Successional Hillslope Tabonuco Forest, Puerto Rico
Tamara J. Chestnut, Daniel J. Zarin, William H. McDowell and Michael Keller
Biogeochemistry
Vol. 46, No. 1/3, New Perspectives on Nitrogen Recycling in the Temperate and Tropical Americas (Jul., 1999), pp. 85-108

Abstract: 
Nitrogen budgets of late successional forested stands and watersheds provide baseline data against which the effects of small- and large-scale disturbances may be measured. Using previously published data and supplemental new data on gaseous N loss, we construct a N budget for hillslope tabonuco forest (HTF) stands in Puerto Rico. HTF stands are subject to frequent hurricanes and landslides; here, we focus on N fluxes in the late phase of inter-disturbance forest development. N inputs from atmospheric deposition (4-6 kg N/ha/yr) are exceeded by N outputs from groundwater, gaseous N loss, and particulate N loss (6.3-15.7 kg N/ha/yr). Late-successional HTF stands also sequester N in their aggrading biomass (8 kg N/ha/yr), creating a total budget imbalance of 8.3-19.7 kg N/ha/yr. We surmise that this imbalance may be accounted for by unmeasured inputs from above- and belowground N-fixation and/or slow depletion of the large N pool in soil organic matter. Spatial and temporal variability, especially that associated with gaseous exchange and soil organic matter N-mineralization, constrain the reliability of this N budget.

C and N dynamics in the riparian and hyporheic zones of a tropical stream, Luquillo Mountains, Puerto Rico

C and N Dynamics in the Riparian and Hyporheic Zones of a Tropical Stream, Luquillo Mountains, Puerto Rico
Tamara J. Chestnut and William H. McDowell
Journal of the North American Benthological Society
Vol. 19, No. 2 (Jun., 2000), pp. 199-214

Abstract: 
Hydrologic and chemical characteristics were determined for both riparian and hyporheic subsurface flow along a 100-m reach of a sandy-bottom tributary of the Rio Icacos in the Luquillo Experimental Forest, Puerto Rico. Hydrologic data (vertical hydraulic gradient and hydraulic conductivity of streambed sediments) and the topographic and morphological features of the watershed indicated diffuse inputs of groundwater from the near-stream riparian zone along this site. Cumulative groundwater discharge, determined by tracer dilution techniques, was ∼1.5 L/s or 10% of the total stream discharge. Spatial heterogeneity in hydrologic and chemical properties of riparian and hyporheic sediments was large. Hydraulic conductivity explained much of the variation in NH<sub>4</sub>-N and dissolved organic carbon (DOC) concentrations, with highest concentrations in sites having low conductivity. A mass-balance approach was used to examine the influence of the near-stream zone on nutrient transport and retention. Outwelling riparian groundwater had the potential to increase stream N concentrations by up to 84% and DOC concentrations by up to 38% along our 100-m reach. Because stream concentrations were constant downstream despite this input, we conclude that significant N and C retention or loss were occurring in the near-stream zone. Lotic ecosystems and their associated riparian groundwater can have a quantitatively significant impact on the nutrient budgets of tropical headwater catchments.
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