Scott X. Chang

Wheat straw and its biochar have contrasting effects on inorganic N retention and N2O production in a cultivated Black Chernozem

A laboratory incubation experiment was conducted to investigate the effects of direct incorporation of either wheat straw or its biochar into a cultivated Chernozem on gross N transformations calculated by the 15N pool dilution technique and nitrous oxide (N2O) production rates. Incorporation of wheat straw stimulated gross NH4+ (ammonium) and NO3− (nitrate) immobilization rates by 302 and 95.2xa0%, respectively, suppressed gross nitrification rates by 32.2xa0%, and increased N2O production by 37.7xa0%. In contrast, the addition of a biochar produced from the wheat straw did not influence any of the above N cycling processes. Therefore, application of biochar could be a possible management strategy for long-term C sequestration (through soil storage of stable C contained in the biochar) in soils without increasing N2O production rates, but could not effectively immobilize NO3− in the soil.

Soil compaction and forest floor removal reduced microbial biomass and enzyme activities in a boreal aspen forest soil

Soil enzymes are linked to microbial functions and nutrient cycling in forest ecosystems and are considered sensitive to soil disturbances. We investigated the effects of severe soil compaction and whole-tree harvesting plus forest floor removal (referred to as FFR below, compared with stem-only harvesting) on available N, microbial biomass C (MBC), microbial biomass N (MBN), and microbial biomass P (MBP), and dehydrogenase, protease, and phosphatase activities in the forest floor and 0–10 cm mineral soil in a boreal aspen (Populus tremuloides Michx.) forest soil near Dawson Creek, British Columbia, Canada. In the forest floor, no soil compaction effects were observed for any of the soil microbial or enzyme activity parameters measured. In the mineral soil, compaction reduced available N, MBP, and acid phosphatase by 53, 47, and 48%, respectively, when forest floor was intact, and protease and alkaline phosphatase activities by 28 and 27%, respectively, regardless of FFR. Forest floor removal reduced available P, MBC, MBN, and protease and alkaline phosphatase activities by 38, 46, 49, 25, and 45%, respectively, regardless of soil compaction, and available N, MBP, and acid phosphatase activity by 52, 50, and 39%, respectively, in the noncompacted soil. Neither soil compaction nor FFR affected dehydrogenase activities. Reductions in microbial biomass and protease and phosphatase activities after compaction and FFR likely led to the reduced N and P availabilities in the soil. Our results indicate that microbial biomass and enzyme activities were sensitive to soil compaction and FFR and that such disturbances had negative consequences for forest soil N and P cycling and fertility.

Effects of plant diversity on nutrient retention and enzyme activities in a full-scale constructed wetland

This study focused on the relationship between plant diversity (six species richness levels) and nutrient retention and enzyme activities associated with carbon, nitrogen and phosphorus cycling in a full-scale constructed wetland (CW) fed with post-treatment domestic wastewater. Effects of plant species richness on nutrient retention and enzyme activities were assessed using soil chemical and zymological methods, respectively. Retention of NH(4)-N and NO(3)-N in the wetland substrate increased with increasing species richness, while phosphorus retention significantly decreased under the richness level of 16 species per plot. Activities of enzymes such as dehydrogenase, beta-glucosidase, invertase, phenol oxidase, L-arsparaginase, protease and nitrate reductase, while they were affected by plant species richness, were strongly depended on the presence or absence of plants in CW substrate, while activities of enzymes such as CM-cellulase, urease and acid phosphatase were strongly depended on plant species richness. We conclude that plant species richness influenced nutrient retention and enzyme activities in the substrate in our subtropical CW; increase plant species richness in CW will likely improve the efficiency of wastewater treatment.

Spatial vegetation patterns as early signs of desertification: a case study of a desert steppe in Inner Mongolia, China

Proper assessment and early detection of land degradation and desertification is extremely important in arid and semi-arid ecosystems. Recent research has proposed to use the characteristics of spatial vegetation patterns, such as parameters derived from power-law modeling of vegetation patches, for detecting the early signs of desertification. However, contradictory results have been reported regarding the suitability of those proposed indicators. We used an experiment with multiple grazing intensities as an analog of a desertification gradient and evaluated the performance of two predictors of desertification: percent plant cover and a transition from a patch-area distribution characterized by a power law to another portrayed by a truncated power law, in a desert steppe in Inner Mongolia, China. We found that spatial metrics, such as the largest patch index and coefficient of variation of mean patch area had negative linear relationships with grazing intensity, suggesting that vegetation patches became more fragmented and homogeneous under higher grazing pressure. Using a binning-based method to analyze our dataset, we found that the patch-area relationship deviated from a power-law to a truncated power-law model with increasing grazing pressure, while the truncated power law was a better fit than the power law for all plots when binning was not used. These results suggest that the selection of methodology is crucial in using power-law models to detect changes in vegetation patterns. Plant cover was significantly correlated with stocking rate and all spatial metrics evaluated; however, the relationship between cover and vegetation spatial pattern still deserves a thorough examination, especially in other types of ecosystems, before using cover as a universal early sign of desertification. Our results highlight a strong connection between the vegetation spatial pattern and the desertification associated with heavy grazing and suggest that future studies should incorporate information about vegetation spatial pattern in monitoring desertification processes.

Sulfate adsorption properties of acid-sensitive soils in the Athabasca oil sands region in Alberta, Canada

The risk of soil acidification is high in the Athabasca oil sands region (AOSR) in Alberta, Canada, due to elevated SO(2) emission and the resultant acid deposition to sensitive, coarse-textured soils. Understanding the sulfate adsorption characteristics of soils sensitive to acidification will help establish critical loads of acid deposition in AOSR. Sulfate adsorption properties were evaluated and relationships between sulfate adsorption and soil properties were examined for soils in two contrasting watersheds (NE7 and SM8) in AOSR. The experimental data fitted well to both the Langmuir and the Freundlich models. The sulfate adsorption capacity was greater for soils in SM8 than in NE7 (p<0.01), even though it was relatively low in both watersheds as compared to other acid-sensitive soils in eastern North America. Based on the additional sulfate adsorbed when a soil was treated with 40mL of 200mg SO(4)(2-) L(-1) solution, the weakly developed Podzolic B horizon (Bfj)in NE7 could adsorb more sulfate than the Ae horizon while no difference was found among other horizons. In SM8, the Bfj and illuviated B (Bt) horizons had greater ability to adsorb sulfate than the other horizons, likely caused by the presence of muscovite in the Bfj and Bt horizons. The additional sulfate adsorbed accounted for about 80% of the total sulfate adsorption capacity and was correlated with pH(NaF) (soil pH extracted with 1 MNaF) and ΔpH(NaF)(the difference between pH(NaF) and pH measured with deionized water), with the following relationships: sulfate adsorption (mg SO(4)(2-) kg(-1))=exp(2.03 pH(NaF) - 18.0)+50.2 (R(2)=0.63, p<0.001) and sulfate adsorption (mg SO(4)(2-) kg(-1))=exp(1.83 ΔpH(NaF) - 6.57) + 48.9 (R(2)=0.70, p<0.001). The ΔpH(NaF) was likely a better indicator of the soils sulfate adsorption capacity than pH(NaF) as the former excludes the effect of soil acidity. Our study indicates that the soils capacity to adsorb sulfate should be considered in determining the critical load for acid deposition in AOSR in Alberta.

Drainage affects tree growth and C and N dynamics in a minerotrophic peatland.

The lowering of the water table resulting from peatland drainage may dramatically alter C and N cycling in peatland ecosystems, which contain one-third of the total terrestrial C. In this study, tree annual ring width and C (delta(13)C) and N (delta(15)N) isotope ratios in soil and plant tissues (tree foliage, growth rings, and understory foliage) in a black spruce-tamarack (Picea mariana-Larix laricina) mixed-wood forest were examined to study the effects of drainage on tree growth and C and N dynamics in a minerotrophic peatland in west-central Alberta, Canada. Drainage increased the delta(15)N of soil NH4+ from a range of +0.6% per hundred to +2.9% per hundred to a range of +4.6% per hundred to +7.0% per hundred most likely through increased nitrification following enhanced mineralization. Plant uptake of 15N-enriched NH4+ in the drained treatment resulted in higher plant delta15N (+0.8% per hundred to +1.8% per hundred in the drained plots and -3.9% per hundred to -5.4% per hundred in the undrained plots), and deposition of litterfall N enriched with 15N increased the delta15N of total soil N in the surface layer in the drained (+2.9% per hundred) as compared with that in the undrained plots (+0.6% per hundred). The effect of drainage on foliar delta(13)C was species-specific, i.e., only tamarack showed a considerably less negative foliar delta(13)C in the drained (-28.1% per hundred) than in the undrained plots (-29.1% per hundred), indicating improved water use efficiency (WUE) by drainage. Tree ring area increments were significantly increased following drainage, and delta(13)C and delta(15)N in tree growth rings of both species showed responses to drainage retrospectively. Tree-ring delta(13)C data suggested that drainage improved WUE of both species, with a greater and more prolonged response in tamarack than in black spruce. Our results indicate that drainage caused the studied minerotrophic peatland to become a more open ecosystem in terms of C and N cycling and loss. The effects of forested peatland drainage or drying on C and N balances deserve further research in order to better understand their roles in future global change.

Sensitivity to Acidification of Forest Soils in Two Watersheds with Contrasting Hydrological Regimes in the Oil Sands Region of Alberta

Abstract Input of large amounts of N and S compounds into forest ecosystems through atmospheric deposition is a significant risk for soil acidification in the oil sands region of Alberta. We evaluated the sensitivity of forest soils to acidification in two watersheds (Lake 287 and Lake 185) with contrasting hydrological regimes as a part of a larger project assessing the role of N and S cycling in soil acidification in forest ecosystems. Fifty six forest soil samples were collected from the two watersheds by horizon from 10 monitoring plots dominated by either jack pine ( Pinus banksiana ) or aspen ( Populus tremuloides ). Soils in the two watersheds were extremely to moderately acidic with pH (CaCl 2 ) ranging from 2.83 to 4.91. Soil acid-base chemistry variables such as pH, base saturation, Al saturation, and acid-buffering capacity measured using the acetic acid equilibrium procedure indicated that soils in Lake 287 were more acidified than those in Lake 185. Acid-buffering capacity decreased in the order of forest floor > subsurface mineral soil > surface mineral soil. The most dramatic differences in percent Ca and Al saturations between the two watersheds were found in the surface mineral soil horizon. Percent Ca and Al saturation in the surface mineral soil in Lake 287 were 15% and 70%, respectively; the percent Ca saturation value fell within a critical range proposed in the literature that indicates soil acidification. Our results suggest that the soils in the two watersheds have low acid buffering capacity and would be sensitive to increased acidic deposition in the region.

Grain 15N of crops applied with organic and chemical fertilizers in a four-year rotation

Variations in crop grain and soil N isotope composition (δ15N) in relation to liquid hog manure (δ15N of total N was +5.1‰), solid cattle manure (+7.9‰) and chemical fertilizer (+0.7‰ for urea and −1.9‰ for ammonium phosphate) applications, and control (no fertilizer application) were examined through a 4-year crop rotation under field conditions. Canola (Brassica napus), hull-less barley (Hordeum vulgare), wheat (Triticum aestivum), and canola were grown sequentially from 2000 (year 1) to 2003 (year 4). From year 2, hog manure or chemical fertilizers, but not cattle manure, treatments increased grain N concentrations over the control. Grain δ15N (+0.3 to +2.5‰) of crops applied with chemical fertilizers was lower than those in the other treatments, reflecting the effects of the N source with a lower δ15N, while the manure treatments tended to increase grain δ15N. The higher grain δ15N of crops applied with hog manure (+5.6 to +8.4‰) than those applied with cattle manure (+2.2 to +4.1‰) reflected the higher N availability of liquid hog manure (up to 70% as NH4+) than solid cattle manure (99% organic N) and higher potentials for ammonia volatilization loss in hog manure rather than differences in manure δ15N signatures. Soil total- and extractable-N concentrations and δ15N tended to vary with the application of N sources with different N isotope composition and availability. Our study expanded the application of the δ15N technique for detecting N source (organic vs chemical) effects on N isotopic composition to field conditions and across a 4-year rotation, and revealed that N availability played a greater role than the δ15N signature of N sources in determining crop δ15N under the studied conditions.

Soil respiration in four different land use systems in north central Alberta, Canada

agriculture and 2 year old hybrid poplar plantation, respectively. We found that � 75% of soil respiration in the native aspen stand originated from the top 7.5–10 cm litter-fibrichumus layer. Seasonal heterotrophic and autotrophic respiration among the land uses ranged from 97 to 272 and 333 to 560 g C m � 2 , respectively, contributing up to 35% and 83% of total soil respiration, respectively. The variability in soil respiration across different land uses was explained mainly by site differences in soil temperature (88– 94%). Soil respiration followed a pronounced seasonal trend: increasing during the growing season and converging to a minimum in the fall. Soil respiration under different land uses was influenced by (1) ecosystem C stock, (2) temperature sensitivity (Q10 )o f organic matter present, and (3) organic matter decomposability as indicated by the natural abundance of d 13 C. Heterotrophic respiration was influenced by soil temperature, while autotrophic respiration was influenced by fine root biomass and nutrient (NO3 and P) availability. These results are useful in estimating potential responses of soil respiration and its components to future land management and climate change.

Understory competition effect on tree growth and biomass allocation on a coastal old-growth forest cutover site in British Columbia

We studied the effect of salal (Gaultheria shallon Pursh.) competition on height, diameter and biomass growth and biomass partitioning in coniferous trees planted to a recent clearcut site of old growth western red cedar-western hemlock (CH) forest on northern Vancouver Island, British Columbia. Tree species used were western red cedar (Thuja plicata Donn ex D. Don), western hemlock (Tsuga heterophylla (Raf.) Sarg.), and Sitka spruce (Picea sitchensis (Bong.) Carr). Salal removal treatment was initiated at the time of planting in spring 1987. Plots were fertilized with 200 kg N ha−1 in spring 1991 and destructively sampled in fall 1992. Height growth from planted to 1989, in 1992 and total height growth were significantly greater in treated plots (salal removed) than in the control plots (salal remaining). Salal removal had a rather uniform impact on height growth for the three species tested. Total root collar diameter was 38% (P < 0.1), 88% (P < 0.05), and 65% (P < 0.05) greater in the treated plots than in the control plots, for red cedar, hemlock and spruce, respectively. Exclusion of understory vegetation had resulted in biomass increases of all the components (namely in the 1-year and 2-year foliage and branches and the older than 3-year components and various sized roots) we studied. Improved tree growth in the treated plots was attributed to the reduced uptake and immobilization of N and other nutrients by the competing understory. Below-ground understory was found to be quite persistent to surviving even after a prolonged period (6 years) of above-ground understory vegetation removal n nBiomass allocation among the components studied was virtually unchanged by the presence of the competing understory, except in two instances. This result was quite different from most of the other reports on biomass partitioning under competition. Our hypothesis that salal competition for nutrients increases biomass partitioning to current year foliage and branch and roots was rejected. Unchanged partitioning is prooably a way of response to nutrient deficiencies according to the resource depletion model of competition processes. Non-significantly higher biomass partitioning was observed in the 1-year foliar and branch and 0.25–1 cm root components. It was therefore possible that the 1991 fertilization alleviated the nutrient shortage problem which led to the rejection of the hypothesis.