Soil ecology

Potensi cadangan biji di dalam tanah pada hutan sekunder Wornojiwo (Potency of Soil Seed Bank in Wornojiwo Secondary Forest)

by Zaenal Mutaqien

Co-authored with Musyarofah Zuhri, Published in National Seminar Proceeding of Tropical Plant Conservation; Current Status and the Future Challange, Cibodas Botanic Garden. 2011.

We studied the soil seed bank in Wornojiwo tropical secondary forest, Cibodas. The forest vegetation has been... more We studied the soil seed bank in Wornojiwo tropical secondary forest, Cibodas. The forest vegetation has been influenced by both natural forest of Mount Gede Pangrango National Park and intensive management of Cibodas Botanic Garden. The seed bank consisted of 37 germinable plant seed species where only 10 species of which were represented in the aboveground vegetation. There were 688 individual seeds per m2 on
average with the highest seed number located in the 5-10 cm soil layer. There was no significant correlation between soil depth with seed density and species richness. The highest seed density (45.8%) and seed plant species (43.6%) belonged to trees and herbs respectively. Maoutia diversifolia, Villebrunea rubescens, and Trema orientalis were the most abundant species in the soil seed bank and all were represented in the
existing vegetation. A poor correspondence occurred between aboveground vegetation and soil seed bank. Our results suggested the need for enrichment planting in order to accelerate Wornojiwo forest succession.

Agrarian legacy in soil nutrient pools of urbanizing arid lands

by David Lewis

David Bruce Lewis, Jason P. Kaye, Corinna Gries, Ann P. Kinzig, and Charles L. Redman
Global Change Biology (2006) 12:703–709

Today's worldwide expansion of dry land cities consumes cultivated and native ecosystems, providing laboratories for... more Today's worldwide expansion of dry land cities consumes cultivated and native ecosystems, providing laboratories for investigating imprints of former land use in places where people now live. Around Phoenix, USA, we compared soil nutrient pools in residential yards converted from farms with nutrient pools in yards developed on native desert. Organic matter, carbon (C), nitrogen (N), and soluble ions were >2-fold greater in yards that were previously agrarian than in yards that were not. These pools remain elevated 40 years after land conversion to residential use. Present N accumulation (1.5 g per m2 per yr) is not affected by prior land use, suggesting that rates of residential fertilizer application and retention are not affected by antecedent soil fertility. Bioavailable, inorganic phosphorus (Pav) is elevated in soil with a recent agrarian past, but this signal disappears after 10–30 years of residential use owing to an accumulation of Pav in never-farmed yards. Our results indicate a ‘direct agrarian legacy,’ wherein agrarian amendment of nutrient pools endures urbanization, more so than an ‘indirect legacy,’ wherein present land management is molded by former land use. Agriculture in dry lands thus sequesters material in soils, and—as we also found higher material contents in residential soils than in contemporary agrarian soils—residential land use simply adds to the agrarian legacy these soils already bear. Intense human use of arid lands may cause increases in material pools in soils, a condition with potential global consequence.

Inorganic nitrogen immobilization in live and sterile soil of old-growth conifer and hardwood forests: implications for ecosystem nitrogen retention

by David Lewis

David Bruce Lewis and Jason P. Kaye
Biogeochemistry (2011) DOI: 10.1007/s10533-011-9627-6

Rapid immobilization of inorganic nitrogen (N) in soil contributes to ecosystem N accumulation, even in old-growth and... more Rapid immobilization of inorganic nitrogen (N) in soil contributes to ecosystem N accumulation, even in old-growth and chronically-fertilized forests once thought to have poor N retention capacity. In old-growth conifer and hardwood stands in Pennsylvania, we tested the hypotheses that biotic and abiotic N immobilization are regulated by N form and forest type. We added 15NH4+, 15NO2-, and 15NO3- to sterile (gamma-irradiated) and live organic-horizon soil and define N immobilization as the mass of added 15N remaining in soil following extractions conducted 15 min, 24 h, and 21 days later. Immobilization of NO2- (19–25% of added N) occurred in sterile soils within 15 min and was little changed thereafter. Tracer NO3- immobilization was not observed, although soils had been pretreated (refrigerated) so as to quantify the lower limit of immobilization potential. Immobilization of NH4+ (27%) occurred in live conifer soils by 21 days but not in other treatments. In 21-day incubations, tracer N immobilization was greater in NO3-poor and humic-rich soils. Immobilization was greater in sterile than in live soil, perhaps owing to artifacts of sterilization. Conifer stands exhibited more massive O-horizons, so NO2- immobilization per unit area was greater in conifer (1.46 mg N m-2) than hardwood (0.43 mg N m-2) stands, possibly accounting for lower N leaching from conifer forests. Areal immobilization rates appear to be fast enough to retain all N transformed to NO2-, so NO2- production may be a limiting step in soil N retention in old-growth ecosystems.

Punching above their weight: low‐biomass non‐native plant species alter soil properties during primary succession

by Duane Peltzer

Some effects of a buried electricity transmission cable on bulk soil

by riccardo scalenghe

A case study in NW Italy investigating an underground electric line (1 m depth triple cable at operative voltages... more A case study in NW Italy investigating an underground electric line (1 m depth triple cable at operative voltages 220–380 kV) measured electric fields in the surrounding soil virtually close to zero but magnetic fields (µTs) 20 times the background level. After 6 months, the influence radius around the cable on microbial activity (estimated by soil ATP), organic carbon, and total nitrogen follows exactly the inverse trend of the MF, shifting the biological activity with a lag distance of 5 m from the 220 kV cable.

Soil microbial activity and N availability with elevated CO2 in Mojave Desert soils

by Sean Schaeffer

Billings, SA, SM Schaeffer, and RD Evans (2004)

Global Biogeochemical Cycles. 18:GB1011

Water pulses and biogeochemical cycles in arid and semiarid ecosystems

by Sean Schaeffer

Austin, AT, ML Yahdijan, JM Stark, J Belnap, A Porporato, IC Burke, U Choromanska, D Ravetta, and SM Schaeffer (2004)

Oecologia. 141:221-235

Pulses of soil carbon and nitrogen affect soil nitrogen dynamics in an arid Colorado Plateau shrubland

by Sean Schaeffer

Schaeffer, SM and RD Evans (2005)

Oecologia. 145:425-433

Laboratory incubations reveal potential responses of soil nitrogen cycling to changes in soil C and N availability in Mojave Desert soils exposed to elevated atmospheric CO2

by Sean Schaeffer

Schaeffer, SM, SA Billings, and RD Evans (2007)

Global Change Biology, 13:854-865

Soil water availability and microsite mediate changes in microbial community structure of Mojave Desert soils in response to long-term exposure to elevated atmospheric CO2

by Sean Schaeffer

Jin, VA, SM Schaeffer, S Ziegler, RD Evans (in press)

JGR:Biogeosciences doi:10.1029/2010JG001564

Responses of soil nitrogen dynamics in a Mojave Desert ecosystem to manipulations in soil carbon and nitrogen availability

by Sean Schaeffer

Schaeffer, SM, SA Billings, and RD Evans (2003)

Oecologia. 134:547-553

Effects of elevated CO2 and carbon addition on N2 fixation by biological soil crusts and free-living bacteria in an intact Mojave Desert ecosystems

by Sean Schaeffer

Billings, SA, SM Schaeffer, and RD Evans (2003)

Soil Biology and Biochemistry. 35:643-649

Effects of elevated CO2 on green tissue and litter quality and quantity in an intact Mojave Desert ecosystem

by Sean Schaeffer

Billings, SA, S Zitzer, H Weatherly, SM Schaeffer, T Charlet, J Arnone, and RD Evans (2003)

Global Change Biology. 9:729-735

Trace N gas losses and N mineralization in an intact Mojave Desert ecosystem with elevated CO2

by Sean Schaeffer

Billings, SA, SM Schaeffer, and RD Evans (2002)

Soil Biology and Biochemistry. 34:1777-1784

Alterations of nitrogen dynamics under elevated CO2 in an intact Mojave Desert ecosystem: evidence from δ15N

by Sean Schaeffer

Billings, SA, SM Schaeffer, S Zitzer, T Charlet, SD Smith, and RD Evans (2002)

Oecologia. 131:463-467

Modelling C and N Mineralisation In Soil Food Webs During Secondary Succession on Ex-Arable Land

by Paul Kardol

The rate of secondary succession after land abandonment depends on the interplay between aboveground and belowground... more The rate of secondary succession after land abandonment depends on the interplay between aboveground and belowground processes. Changes in vegetation composition lead to altered amounts and composition of soil organic matter (SOM) with consequences for the abundance and functioning of the soil food web. In turn, soil food web structure determines the mineralisation rate of nutrients that can be taken up by plants. This study analyses changes in the C and N mineralisation rates along with soil food web structure during secondary succession after land abandonment. In a previous study, changes in soil food web structure and SOM quantity and quality were measured at different stages of secondary succession on abandoned arable fields (abandoned for 2, 9 and 22 years and a heathland, which is the assumed target of the secondary succession). Based on these measurements we expected the C and N mineralisation rates to increase during secondary succession. The key hypothesis is that with a description of the soil food webs in terms of quantified biomasses, natural death rates, energy conversion efficiencies and diets enables a calculation of C and N mineralisation rates in soils. The basic assumptions connected to this hypothesis are that on a time-scale of years the population
sizes are in steady state. We also calculated mineralisation rates per trophic level and energy channel. Based on the same measurements we expected that the contributions by the lower trophic level groups will increase as well as the mineralisation rates by bacterial and fungal energy channels. Measured C and N mineralisation indeed increased during the 22-year period of abandonment. The calculated C and N mineralisation rates showed the same trend after land abandonment as the measured values.
Calculated contributions to mineralisation of organisms at trophic level 1 increase during secondary succession following land abandonment. The fungal decomposition channel contributed more to N mineralisation than the bacterial decomposition channel, whereas both channels contributed equally to C mineralisation rates. Direct contributions by higher trophic levels to mineralisation decreased during secondary succession. However, higher trophic levels were direct important for N mineralisation and indirect for both C and N mineralisation due to their effect on biomass turnover rates of groups at lower trophic levels. The increasing total N mineralisation rate of the soil food web, however, does not benefit plants, as during succession plant species that mainly grow under high nutrient availability are replaced by species that can grow in nutrient poor condition.

Modelling C and N mineralisation in soil food webs duringsecondary succession on ex-arable land

by Paul Kardol

The rate of secondary succession after land abandonment depends on the interplay between aboveground and belowground... more The rate of secondary succession after land abandonment depends on the interplay between aboveground and belowground processes. Changes in vegetation composition lead to altered amounts and composition of soil organic matter (SOM) with consequences for the abundance and functioning of the soil food web. In turn, soil food web structure determines the mineralisation rate of nutrients that can be taken up by plants. This study analyses changes in the C and N mineralisation rates along with soil food
web structure during secondary succession after land abandonment. In a previous study, changes in soil food web structure and SOM quantity and quality were measured
at different stages of secondary succession on abandoned arable fields (abandoned for 2, 9 and 22 years and a heathland, which is the assumed target of the secondary succession). Based on these measurements we expected the C and N mineralisation rates to increase during secondary succession. The key hypothesis is that with a description of the soil food webs in terms of quantified biomasses, natural death rates, energy conversion efficiencies and diets enables a calculation of C and N mineralisation rates in soils. The basic assumptions connected to this hypothesis are that on a time-scale of years the population sizes are in steady state. We also calculated mineralisation rates per trophic level and energy channel. Based on the same measurements we expected that the contributions by the lower trophic level groups will increase as well as the mineralisation rates by bacterial and fungal energy channels. Measured C and N mineralisation indeed increased during the 22-year period of abandonment. The calculated C and N mineralisation rates showed the same trend after land abandonment as the measured values. Calculated contributions to mineralisation of organisms at trophic level 1 increase during secondary
succession following land abandonment. The fungal decomposition channel contributed more to N
mineralisation than the bacterial decomposition channel, whereas both channels contributed equally to C mineralisation rates. Direct contributions by higher trophic levels to mineralisation decreased during secondary succession. However, higher trophic levels were direct important for N mineralisation and indirect for both C and N mineralisation due to their effect on biomass turnover rates of groups at lower
trophic levels. The increasing total N mineralisation rate of the soil food web, however, does not benefit plants, as during succession plant species that mainly grow under high nutrient availability are replaced by species that can grow in nutrient poor condition.

Soil Ecosystem Functioning Under Climate Change: Plant Species and Community Effects

by Paul Kardol

Feedbacks of terrestrial ecosystems to atmospheric and climate change depend on soil ecosystem dynamics. Soil... more Feedbacks of terrestrial ecosystems to atmospheric and climate change depend on soil ecosystem dynamics. Soil ecosystems can directly and indirectly respond to climate
change. For example, warming directly alters microbial communities by increasing their activity. Climate change may also alter plant community composition, thus indirectly altering
the soil communities that depend on their inputs. To better understand how climate change may directly and indirectly alter soil ecosystem functioning, we investigated old-field plant
community and soil ecosystem responses to single and combined effects of elevated [CO2], warming, and precipitation in Tennessee (USA). Specifically, we collected soils at the plot level (plant community soils) and beneath dominant plant species (plant-specific soils). We used
microbial enzyme activities and soil nematodes as indicators for soil ecosystem functioning. Our study resulted in two main findings: (1) Overall, while there were some interactions,
water, relative to increases in [CO2] and warming, had the largest impact on plant community composition, soil enzyme activity, and soil nematodes. Multiple climate-change factors can interact to shape ecosystems, but in our study, those interactions were largely driven by changes in water. (2) Indirect effects of climate change, via changes in plant communities, had a significant impact on soil ecosystem functioning, and this impact was not obvious when
looking at plant community soils. Climate-change effects on enzyme activities and soil nematode abundance and community structure strongly differed between plant community soils and plant-specific soils, but also within plant-specific soils. These results indicate that accurate assessments of climate-change impacts on soil
ecosystem functioning require incorporating the concurrent changes in plant function and plant community composition. Climate-change-induced shifts in plant community composition
will likely modify or counteract the direct impact of atmospheric and climate change on soil ecosystem functioning, and hence, these indirect effects should be taken into account when predicting the manner in which global change will alter ecosystem functioning.

The South African Soil Environment

by Shoana Leigh Hutton

The pressures and impacts on the environment which constitute environmental change highlights the increased generation... more The pressures and impacts on the environment which constitute environmental change highlights the increased generation of human pollution and waste. Environmental change, soil erosion and land degradation are key factors in reduced productivity, natural communities, loss of habitats, increased sea levels and increased health risks.

Plant and microbe contribution to community resilience in a directionally changing environment

by Megan Mobley

co-authored with REU advisor, Dr. William Bowman, and others. Published in Ecological Monographs in August 2008.

To understand the role biota play in resilience or vulnerability to environmental change, we investigated soil, plant,... more To understand the role biota play in resilience or vulnerability to environmental change, we investigated soil, plant, and microbial responses to a widespread environmental change, increased nitrogen (N). Our aim was to test the plant–soil threshold hypothesis: that changed biotic structure influences resilience to accumulated changes in N. For six years, we removed one of two codominant species, Geum rossii and Deschampsia caespitosa, in moist-meadow alpine tundra in Colorado, USA. We also manipulated nutrient availability by adding carbon (C) or N, separately and in combination with the species removals.

Consistent with our hypothesis, Geum was associated with soil feedbacks that slowed rates of N cycling and Deschampsia with feedbacks that increased rates of N cycling. After a four-year initial resilience period, Geum dramatically declined (by almost 70%) due to increasing N availability. In contrast, Deschampsia abundance did not respond to changes in N supply; it only responded to the removal of Geum. Forbs and graminoids responded more positively to Deschampsia removal than to Geum removal, indicating stronger competitive effects by Deschampsia. The changed biotic interactions appear to have community-level consequences: after six years of Geum (but not Deschampsia) removal, evenness of the community declined by over 35%.

Increased N affected the soil–microbial feedbacks, particularly in association with Geum. Microbial biomass N declined at higher N, as did the activities of two C-acquiring and one N-acquiring extracellular microbial enzymes. In the presence of Geum, N fertilization slowed the activity of phenol oxidase, a tannin-degrading enzyme, suggesting that microbes shift from degrading Geum-derived compounds. In the absence of Geum, acid phosphatase activity increased, suggesting increased phosphorus limitation in association with Deschampsia.

With continued N deposition forecast for this system, these results suggest that initial resilience of Geum to increased N will be overwhelmed through elimination of microbial feedbacks. Once Geum declines, the loss will indirectly facilitate Deschampsia via competitive release. Because Deschampsia exerts strong competitive effects on subordinate species, increased Deschampsia abundance may be accompanied by a community-wide drop in diversity. We conclude that plant–soil feedbacks through the microbial community can influence vulnerability to exogenous changes in N and contribute to threshold dynamics.