Biol Fertil Soils (2008) 44:471–479 DOI 10.1007/s00374-007-0229-3
ORIGINAL PAPER
Soil compaction and forest floor removal reduced microbial biomass and enzyme activities in a boreal aspen forest soil Xiao Tan & Scott X. Chang & Richard Kabzems
Received: 3 November 2006 / Revised: 11 July 2007 / Accepted: 12 July 2007 / Published online: 1 August 2007 # Springer-Verlag 2007
Abstract 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, X. Tan : S. X. Chang (*) Department of Renewable Resources, University of Alberta, 442 Earth Sciences Building, Edmonton, AB T6G 2E3, Canada e-mail:
[email protected]
R. Kabzems Ministry of Forests and Range, Dawson Creek, BC V1G 4A4, Canada Present address: X. Tan Albian Sands Energy Inc., P.O. Box 5670, Hwy 63 North, Fort McMurray, AB T9H 4W1, Canada
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. Keywords Microbial biomass . Protease . Phosphatase . Available N . Available P . Long-term soil productivity (LTSP)
Introduction Soil enzymes are known to be involved in nutrient cycling, and as such, their activities can be used as potential indicators of nutrient cycling processes. In addition, soil enzymes are specific for the types of chemical reactions in which they participate. For example, dehydrogenase plays an important role in the initial oxidation of soil organic matter and occurs only in viable cells; therefore, it is believed that dehydrogenase is an intracellular enzyme involved in microbial respiratory processes (Dick 1994). In contrast, protease and phosphatase have extracellular component. Protease activity is involved in breaking down proteins, resulting in the release of NH 4 N (Ladd and Butler 1972). Phosphatase activity plays a critical role in the production of inorganic P, catalyzing the hydrolysis of organic P esters to inorganic P (Speir and Ross 1978). Soil enzyme activities may be sensitive to both natural and human-induced disturbances, and measurements of the
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activities of a range of enzymes may provide a valid estimation of the metabolic response of soils to management practices and environmental stress (Dick et al. 1988; Nannipieri 1994). Soil compaction and forest floor removal are two most common disturbances caused by forest harvesting practices and mechanical site preparation in boreal forests (Corns 1988; McMinn and Hedin 1990). Many studies have found that soil physical and chemical properties such as soil porosity, aeration, water content, temperature, and substrate availability are affected by soil compaction and forest floor removal (Tew et al. 1986; Zabowski et al. 1994; Gomez et al. 2002; Tan et al. 2005). By changing the percentage of macro- and microporosity, soil compaction may cause oxygen deficiency by reducing oxygen diffusion rates which then affect the activities of enzymes such as catalase and phosphatase (Glinski et al. 1986; Pagliai and De Nobili 1993). Soil compaction has been found to reduce phosphatase, amidase, and dehydrogenase activities (Dick et al. 1988; Jordan et al. 2003); however, higher phosphatase activity has been found in compacted soils, suggesting that microbial communities may be tolerant and resilient to soil compaction (Buck et al. 2000; Shestak and Busse 2005). Postharvest forest management practices have been found to reduce extracellular enzyme activities (e.g., glucosidase, cellobiohydrolase, and phenol oxidase) involved in litter decomposition (Waldrop et al. 2003; Hassett and Zak 2005). Quilchano and Marañón (2002) found that site factors (soil pH, available nutrients, and soil texture) and sampling season had greater influence on enzyme activities than management factors (shrub-clearing and stand thinning). Changes in soil enzyme activities after soil compaction and forest floor removal can be complicated and maybe dependant on enzyme type, site or soil types, and climatic conditions (Dick et al. 1988; Li et al. 2002). In an earlier study, we found that soil compaction reduced microbial biomass N in the mineral soil and forest floor removal tended to reduce microbial biomass C and N in the surface mineral soil (Tan et al. 2005). We hypothesize that soil compaction and forest floor removal will also reduce soil enzyme activities at this study site. The link between enzyme activities and microbial biomass may help provide microbial community parameters that can be related to potential rates of organic compound degradation. For example, enzyme activity to microbial biomass ratio gives a measure of the enzyme activity per unit biomass, which may be used as a better index to evaluate the response of soil enzyme activities to management practices (Landi et al. 2000). Because dehydrogenase, protease, and phosphatase play important roles in carbon, nitrogen, and phosphorus cycling, the objectives of this study were to determine the effects of soil compaction and forest floor removal on these enzyme activities and to relate enzyme
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activities to soil physical and chemical properties and microbial biomass in a boreal aspen (Populus tremuloidesMichx.) forest long-term soil productivity (LTSP) site near Dawson Creek in British Columbia, Canada.
Materials and methods Study site and experimental design The study site is located near Dawson Creek (55°58′ N, 120°28′ W), in north-eastern British Columbia. The site is representative of mesic aspen ecosystems in the moist and warm subzone of the Boreal White and Black Spruce biogeoclimatic zone (BWBSmw) (DeLong et al. 1991). Elevation is approximately 720 m, and the average slope is 4%, with a south aspect. The area has a mean annual temperature of 1.6°C and mean annual precipitation of 482 mm, with approximately half of which fall as snow, and about 70% of rainfall occurs in the growing season between May and August (Environment Canada 2006). Soils on the study site were developed on a silt loam veneer, 20 to 30 cm thick, laid over a clay loam. The soil is classified as Orthic Luvic Gleysols (Soil Classification Working Group 1998). Details of soil properties before harvesting or posttreatment can be found in Tan et al. (2005). The LTSP study uses a 3×3 completely randomized factorial experimental design with three replications implemented over a 4-year period. Treatment plots measuring 40 × 70 m were delineated before logging and were randomly assigned to one of nine combinations of soil compaction and organic matter removal treatments. Plots were harvested on frozen ground to ensure that minimal soil disturbance occurred during the harvesting phase. In this study, we investigated the extreme treatment levels within each factor to form a factorial combination of two compaction (C0: no soil compaction, the undisturbed plots did not receive any postharvest compaction and C2: severe soil compaction, the mineral soil was depressed by 4 to 5 cm using a vibrating pad mounted on an excavator) and two organic matter removal levels (OM1: stem-only harvesting, the trees were delimbed on-site, with tree tops, limbs and all non-merchantable woody materials left on the forest floor; and OM3: whole-tree harvesting plus forest floor removal (referred to as FFR hereafter). In the OM3 treatment, all the woody and nonwoody material was removed from the plot, and the forest floor was stripped to expose the mineral soil using an excavator. As was indicated in Tan et al. (2005), all 12 studied plots were not established in the same year. In the statistical analysis described below, we treated the year since plot establishment as a covariable to remove the effect of year
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since plot establishment on the measured soil biological parameters. Soil sampling Forest floor and 0–10 cm mineral soil samples were collected on June 20 and August 20 of 2005. Three soil cores (6.3 cm in diameter) were collected in each plot from randomly selected locations and bulked to form a composite sample for each layer. Forest floor and mineral soil samples were immediately placed on ice and shipped to the laboratory in a cooler. Fresh samples were homogenized, then sieved (4 mm) and stored at 4°C until further analysis. Half of each sample was used for enzyme activities and microbial biomass. The other half was promptly air-dried, ground, and sieved (
