20 research outputs found
Compared to conventional, ecological intensive management promotes beneficial proteolytic soil microbial communities for agro-ecosystem functioning under climate change-induced rain regimes
Projected climate change and rainfall variability will affect soil microbial communities, biogeochemical cycling and agriculture. Nitrogen (N) is the most limiting nutrient in agroecosystems and its cycling and availability is highly dependent on microbial driven processes. In agroecosystems, hydrolysis of organic nitrogen (N) is an important step in controlling soil N availability. We analyzed the effect of management (ecological intensive vs. conventional intensive) on N-cycling processes and involved microbial communities under climate change-induced rain regimes. Terrestrial model ecosystems originating from agroecosystems across Europe were subjected to four different rain regimes for 263 days. Using structural equation modelling we identified direct impacts of rain regimes on N-cycling processes, whereas N-related microbial communities were more resistant. In addition to rain regimes, management indirectly affected N-cycling processes via modifications of N-related microbial community composition. Ecological intensive management promoted a beneficial N-related microbial community composition involved in N-cycling processes under climate change-induced rain regimes. Exploratory analyses identified phosphorus-associated litter properties as possible drivers for the observed management effects on N-related microbial community composition. This work provides novel insights into mechanisms controlling agro-ecosystem functioning under climate change
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Effects of experimental nitrogen deposition on soil organic carbon storage in Southern California drylands
Atmospheric nitrogen (N) deposition is enriching soils with N across biomes. Soil N enrichment can increase plant productivity and affect microbial activity, thereby increasing soil organic carbon (SOC), but such responses vary across biomes. Drylands cover ~45% of Earth's land area and store ~33% of global SOC contained in the top 1 m of soil. Nitrogen fertilization could, therefore, disproportionately impact carbon (C) cycling, yet whether dryland SOC storage increases with N remains unclear. To understand how N enrichment may change SOC storage, we separated SOC into plant-derived, particulate organic C (POC), and largely microbially derived, mineral-associated organic C (MAOC) at four N deposition experimental sites in Southern California. Theory suggests that N enrichment increases the efficiency by which microbes build MAOC (C stabilization efficiency) if soil pH stays constant. But if soils acidify, a common response to N enrichment, then microbial biomass and enzymatic organic matter decay may decrease, increasing POC but not MAOC. We found that N enrichment had no effect on C fractions except for a decrease in MAOC at one site. Specifically, despite reported increases in plant biomass in three sites and decreases in microbial biomass and extracellular enzyme activities in two sites that acidified, POC did not increase. Furthermore, microbial C use and stabilization efficiency increased in a non-acidified site, but without increasing MAOC. Instead, MAOC decreased by 16% at one of the sites that acidified, likely because it lost 47% of the exchangeable calcium (Ca) relative to controls. Indeed, MAOC was strongly and positively affected by Ca, which directly and, through its positive effect on microbial biomass, explained 58% of variation in MAOC. Long-term effects of N fertilization on dryland SOC storage appear abiotic in nature, such that drylands where Ca-stabilization of SOC is prevalent and soils acidify, are most at risk for significant C loss
Systematic Fluorination of P3HT: Synthesis of P(3HT-<i>co</i>-3H4FT)s by Direct Arylation Polymerization, Characterization, and Device Performance in OPVs
We present a strategy
for tuning physical properties of P3HT-based
copolymers by incorporating a fluorinated thiophene repeat unit. The
synthesis and characterization of a series of fluorinated polythiophene
P(3HT-<i>co</i>-3H4FT) materials are described, where the
percentage of fluorinated repeat units in the polymer backbone is
systematically varied from 0 to 100%. These P(3HT-<i>co</i>-3H4FT)s (<b>P0</b>, <b>P25</b>, <b>P50</b>, <b>P75</b>, and <b>P100</b>) were synthesized via direct arylation
polymerization (DArP) methods. By varying the feed ratio of the two
monomers, the percent of fluorinated repeat units (3H4FT) could be
precisely controlled. As fluorination is increased, there is a strong
effect on the electronic properties of the polymers, evidenced by
a 0.4 eV drop in the <i>E</i><sub>HOMO</sub> level for <b>P100</b> when compared to <b>P0</b>. GIWAXS and TEM were
used to determine the crystallinity and morphology. TEM analysis of
thin film polymer/PCBM bulk-heterojunction blends indicates that increased
fluorination does not result in stronger phase separation. Organic
photovoltaic devices were fabricated to evaluate changes in device
performance as a result of fluorination
Structural changes in the protease domain of prothrombin upon activation as assessed by N-bromosuccinimide modification of tryptophan residues in prethrombin-2 and thrombin
Characteristics of wood wastes in British Columbia and their potential suitability as soil amendments and seedling growth media
Diagnosed Prevalence and Health Care Expenditures of Mental Health Disorders Among Dual Eligible Older People
The internal and watershed controls on hypolimnetic sediment phosphorus release in Lake Auburn, Maine, USA
Assessing Nitrogen-Saturation in a Seasonally Dry Chaparral Watershed: Limitations of Traditional Indicators of N-Saturation
To evaluate nitrogen (N) saturation in xeric environments, we measured hydrologic N losses, soil N pools, and microbial processes, and developed an N-budget for a chaparral catchment (Sierra Nevada, California) exposed to atmospheric N inputs of approximately 8.5 kg N ha⁻¹ y⁻¹. Dual-isotopic techniques were used to trace the sources and processes controlling nitrate (NO₃ ⁻) losses. The majority of N inputs occurred as ammonium. At the onset of the wet season (November to April), we observed elevated streamwater NO₃ ⁻ concentrations (up to 520 µmol l⁻¹), concomitant with the period of highest gaseous N-loss (up to 500 ng N m⁻² s⁻¹) and suggesting N-saturation. Stream NO₃ ⁻ δ¹⁵N and δ¹⁸O and soil N measurements indicate that nitrification controlled NO₃ ⁻ losses and that less than 1% of the loss was of atmospheric origin. During the late wet season, stream NO₃ ⁻ concentrations decreased (to <2 µmol l⁻¹) as did gaseous N emissions, together suggesting conditions no longer indicative of N-saturation. We propose that chaparral catchments are temporarily N-saturated at ≤8.5 kg N ha⁻¹ y⁻¹, but that N-saturation may be difficult to reach in ecosystems that inherently leak N, thereby confounding the application of N-saturation indicators and annual N-budgets. We propose that activation of N sinks during the typically rainy winter growing season should be incorporated into the assessment of ecosystem response to N deposition. Specifically, the N-saturation status of chaparral may be better assessed by how rapidly catchments transition from N-loss to N-retention