224 research outputs found
Climate and species affect fine root production with long-term fertilization in acidic tussock tundra near Toolik Lake, Alaska
Author Posting. Š The Author(s), 2007. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Oecologia 153 (2007): 643-652, doi:10.1007/s00442-007-0753-8.Long-term fertilization of acidic tussock tundra has led to changes in plant species
composition, increases in aboveground production and biomass and substantial losses of soil
organic carbon (SOC). Root litter is an important input to SOC pools, though little is known
about fine root demography in tussock tundra. In this study, we examined the response of fine
root production and live standing fine root biomass to short- and long-term fertilization, as
changes in fine root demography may contribute to observed declines in SOC. Live standing
fine root biomass increased with long-term fertilization, while fine root production declined,
reflecting replacement of the annual fine root system of Eriophorum vaginatum, with the long-lived
fine roots of Betula nana. Fine root production increased in fertilized plots during an
unusually warm growing season, but remained unchanged in control plots, consistent with
observations that B. nana shows a positive response to climate warming. Calculations based on
a few simple assumptions suggest changes in fine root demography with long-term fertilization
and species replacement could account for between 20 and 39% of observed declines in SOC
stocks.This project was supported by National Science Foundation research grants 9810222,
9911681, 0221606 and 0528748
Carbon cycling and budget in a forested basin of southwestern Hokkaido, northern Japan
Quantification of annual carbon sequestration is very important in order to assess the function of forest ecosystems in combatting global climate change and the ecosystem responses to those changes. Annual cycling and budget of carbon in a forested basin was investigated to quantify the carbon sequestration of a cool-temperate deciduous forest ecosystem in the Horonai stream basin, Tomakomai Experimental Forest, northern Japan. Net ecosystem exchange, soil respiration, biomass increment, litterfall, soil-solution chemistry, and stream export were observed in the basin from 1999â2001 as a part of IGBP-TEMA project. We found that 258 g C mâ2 yearâ1 was sequestered annually as net ecosystem exchange (NEE) in the forested basin. Discharge of carbon to the stream was 4 g C mâ2 yearâ1 (about 2% of NEE) and consisted mainly of dissolved inorganic carbon (DIC). About 43% of net ecosystem productivity (NEP) was retained in the vegetation, while about 57% of NEP was sequestered in soil, suggesting that the movement of sequestered carbon from aboveground to belowground vegetation was an important process for net carbon accumulation in soil. The derived organic carbon from aboveground vegetation that moved to the soil mainly accumulated in the solid phase of the soil, with the result that the export of dissolved organic carbon to the stream was smaller than that of dissolved inorganic carbon. Our results indicated that the aboveground and belowground interaction of carbon fluxes was an important process for determining the rate and retention time of the carbon sequestration in a cool-temperate deciduous forest ecosystem in the southwestern part of Hokkaido, northern Japan
Reconstructing terrestrial nutrient cycling using stable nitrogen isotopes in wood
Although recent anthropogenic effects on the global nitrogen (N) cycle have been significant, the consequences of increased anthropogenic N on terrestrial ecosystems are unclear. Studies of the impact of increased reactive N on forest ecosystemsâimpacts on hydrologic and gaseous loss pathways, retention capacity, and even net primary productivityâ have been particularly limited by a lack of long-term baseline biogeochemical data. Stable nitrogen isotope analysis (ratio of šâľN to šâ´N, termed δšâľN) of wood chronologies offers the potential to address changes in ecosystem N cycling on millennial timescales and across broad geographic regions. Currently, nearly 50 studies have been published utilizing wood δšâľN records; however, there are significant differences in study design and data interpretation. Here, we identify four categories of wood δšâľN studies, summarize the common themes and primary findings of each category, identify gaps in the spatial and temporal scope of current wood δšâľN chronologies, and synthesize methodological frameworks for future research by presenting eight suggestions for common methodological approaches and enhanced integration across studies. Wood δšâľN records have the potential to provide valuable information for interpreting modern biogeochemical cycling. This review serves to advance the utility of this technique for long-term biogeochemical reconstructions
Nitrogen stable isotopes indicate differences in nitrogen cycling between two contrasting Jamaican montane forests
Background and aims
The aim of this study is to enhance our knowledge of nitrogen (N) cycling and N acquisition in tropical montane forests through analysis of stable N isotopes (δ15N).
Methods
Leaves from eight common tree species, leaf litter, soils from three depths and roots were sampled from two contrasting montane forest types in Jamaica (mull ridge and mor ridge) and were analysed for δ15N.
Results
All foliar δ15N values were negative and varied among the tree species but were significantly more negative in the mor ridge forest (by about 2 â°). δ15N of soils and roots were also more negative in mor ridge forests by about 3 â°. Foliar δ15N values were closer to that of soil ammonium than soil nitrate suggesting that trees in these forests may have a preference for ammonium; this may explain the high losses of nitrate from similar tropical montane forests. There was no correlation between the rankings of foliar δ15N in the two forest types suggesting a changing uptake ratio of different N forms between forest types.
Conclusions
These results indicate that N is found at low concentrations in this ecosystem and that there is a tighter N cycle in the mor ridge forest, confirmed by reduced nitrogen availability and lower rates of nitrification. Overall, soil or root δ15N values are more useful in assessing ecosystem N cycling patterns as different tree species showed differences in foliar δ15N between the two forest types
The demography of fine roots in response to patches of water and nitrogen
Fine root demography was quantified in response to patches of increased water and nitrogen availability in a natural, second-growth, mixed hardwood forest in northern Michigan, USA. As expected, the addition of water and water plus nitrogen resulted in a significant overall increase in the production of new fine roots. New root production was much greater in response to water plus nitrogen when compared with water alone, and the duration of new root production was related to the length of resource addition in the water plus nitrogen treatments; the average difference in new root length between the 20 vs. 40 d additions of water plus nitrogen amounted to almost 600%. Roots produced in response to the additions of water and water plus nitrogen lived longer than roots in the control treatments. Thus, additions of water and water plus nitrogen influenced both the proliferation of new roots and their longevity, with both proliferation and longevity related to the type and duration of resource supply. Results suggest that root longevity and mortality may be plastic in response to changes in soil resource availability, as is well known for root proliferation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65770/1/j.1469-8137.1993.tb03905.x.pd
Simulated Atmospheric N Deposition Alters Fungal Community Composition and Suppresses Ligninolytic Gene Expression in a Northern Hardwood Forest
High levels of atmospheric nitrogen (N) deposition may result in greater terrestrial carbon (C) storage. In a northern hardwood ecosystem, exposure to over a decade of simulated N deposition increased C storage in soil by slowing litter decay rates, rather than increasing detrital inputs. To understand the mechanisms underlying this response, we focused on the saprotrophic fungal community residing in the forest floor and employed molecular genetic approaches to determine if the slower decomposition rates resulted from down-regulation of the transcription of key lignocellulolytic genes, by a change in fungal community composition, or by a combination of the two mechanisms. Our results indicate that across four Acer-dominated forest stands spanning a 500-km transect, community-scale expression of the cellulolytic gene cbhI under elevated N deposition did not differ significantly from that under ambient levels of N deposition. In contrast, expression of the ligninolytic gene lcc was significantly down-regulated by a factor of 2â4 fold relative to its expression under ambient N deposition. Fungal community composition was examined at the most southerly of the four sites, in which consistently lower levels of cbhI and lcc gene expression were observed over a two-year period. We recovered 19 basidiomycete and 28 ascomycete rDNA 28S operational taxonomic units; Athelia, Sistotrema, Ceratobasidium and Ceratosebacina taxa dominated the basidiomycete assemblage, and Leotiomycetes dominated the ascomycetes. Simulated N deposition increased the proportion of basidiomycete sequences recovered from forest floor, whereas the proportion of ascomycetes in the community was significantly lower under elevated N deposition. Our results suggest that chronic atmospheric N deposition may lower decomposition rates through a combination of reduced expression of ligninolytic genes such as lcc, and compositional changes in the fungal community
The Accumulation of Organic Carbon in Mineral Soils by Afforestation of Abandoned Farmland
The afforestation of abandoned farmland significantly influences soil organic carbon (OC). However, the dynamics between OC inputs after afforestation and the original OC are not well understood. To learn more about soil OC dynamics after afforestation of farmland, we measured the soil OC content in paired forest and farmland plots in Shaanxi Province, China. The forest plots had been established on farmland 18, 24, 48, 100, and 200 yr previously. The natural 13C abundance of soil organic matter was also analyzed to distinguish between crop- and forest-derived C in the afforested soils. We observed a nonlinear accumulation of total OC in the 0â80 cm depth of the mineral soil across time. Total soil OC accumulated more rapidly under forest stands aged 18 to 48 yr than under forest stands aged 100 or 200 yrs. The rate of OC accumulation was also greater in the 0â10 cm depth than in the 10â80 cm depth. Forest-derived OC in afforested soils also accumulated nonlinearly across time, with the greatest increase in the 0â20 cm depth. Forest-derived OC in afforest soils accounted for 52â86% of the total OC in the 0â10 cm depth, 36â61% of the total OC in the 10â20 cm depth, and 11â50% of the total OC in the 20â80 cm depth. Crop-derived OC concentrations in the 0â20 cm depth decreased slightly after afforestation, but there was no change in crop-derived OC concentrations in the 20â80 cm depth. The results of our study support the claim that afforestation of farmland can sequester atmospheric CO2 by increasing soil OC stocks. Changes in the OC stocks of mineral soils after afforestation appear to be influenced mainly by the input of forest-derived C rather than by the loss of original OC
Foliar δ15N values characterize soil N cycling and reflect nitrate or ammonium preference of plants along a temperate grassland gradient
The natural abundance of stable 15N isotopes in soils and plants is potentially a simple tool to assess ecosystem N dynamics. Several open questions remain, however, in particular regarding the mechanisms driving the variability of foliar δ15N values of non-N2 fixing plants within and across ecosystems. The goal of the work presented here was therefore to: (1) characterize the relationship between soil net mineralization and variability of foliar Îδ15N (δ15Nleaf â δ15Nsoil) values from 20 different plant species within and across 18 grassland sites; (2) to determine in situ if a plantâs preference for NO3â or NH4+ uptake explains variability in foliar Îδ15N among different plant species within an ecosystem; and (3) test if variability in foliar Îδ15N among species or functional group is consistent across 18 grassland sites. Îδ15N values of the 20 different plant species were positively related to soil net mineralization rates across the 18 sites. We found that within a site, foliar Îδ15N values increased with the speciesâ NO3â to NH4+ uptake ratios. Interestingly, the slope of this relationship differed in direction from previously published studies. Finally, the variability in foliar Îδ15N values among species was not consistent across 18 grassland sites but was significantly influenced by N mineralization rates and the abundance of a particular species in a site. Our findings improve the mechanistic understanding of the commonly observed variability in foliar Îδ15N among different plant species. In particular we were able to show that within a site, foliar δ15N values nicely reflect a plantâs N source but that the direction of the relationship between NO3â to NH4+ uptake and foliar Îδ15N values is not universal. Using a large set of data, our study highlights that foliar Îδ15N values are valuable tools to assess plant N uptake patterns and to characterize the soil N cycle across different ecosystems
Fungi Unearthed: Transcripts Encoding Lignocellulolytic and Chitinolytic Enzymes in Forest Soil
BACKGROUND: Fungi are the main organisms responsible for the degradation of biopolymers such as lignin, cellulose, hemicellulose, and chitin in forest ecosystems. Soil surveys largely target fungal diversity, paying less attention to fungal activity. METHODOLOGY/PRINCIPAL FINDINGS: Here we have focused on the organic horizon of a hardwood forest dominated by sugar maple that spreads widely across Eastern North America. The sampling site included three plots receiving normal atmospheric nitrogen deposition and three that received an extra 3 g nitrogen m(2) y(1) in form of sodium nitrate pellets since 1994, which led to increased accumulation of organic matter in the soil. Our aim was to assess, in samples taken from all six plots, transcript-level expression of fungal genes encoding lignocellulolytic and chitinolytic enzymes. For this we collected RNA from the forest soil, reverse-transcribed it, and amplified cDNAs of interest, using both published primer pairs as well as 23 newly developed ones. We thus detected transcript-level expression of 234 genes putatively encoding 26 different groups of fungal enzymes, notably major ligninolytic and diverse aromatic-oxidizing enzymes, various cellulose- and hemicellulose-degrading glycoside hydrolases and carbohydrate esterases, enzymes involved in chitin breakdown, N-acetylglucosamine metabolism, and cell wall degradation. Among the genes identified, 125 are homologous to known ascomycete genes and 105 to basidiomycete genes. Transcripts corresponding to all 26 enzyme groups were detected in both control and nitrogen-supplemented plots. CONCLUSIONS/SIGNIFICANCE: Many of these enzyme groups are known to be important in soil turnover processes, but the contribution of some is probably underestimated. Our data highlight the importance of ascomycetes, as well as basidiomycetes, in important biogeochemical cycles. In the nitrogen-supplemented plots, we have detected no transcript-level gap likely to explain the observed increased carbon storage, which is more likely due to community changes and perhaps transcriptional and/or post-transcriptional down-regulation of relevant genes
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