亚热带气候环境条件下不同森林类型的土壤CO2通量的研究

The flux of carbon dioxide(CO2) from soil surface presents an important component of carbon(C) cycle in terrestrial ecosystems and is controlled by a number of biotic and abiotic factors. In order to better understand characteristics of soil CO2 flux(FCO2) in subtropical forests,soil FCO2 rates were quantified in five adjacent forest types(camphor tree forest,Masson pine forest,mixed camphor tree and Masson pine forest,Chinese sweet gum forest,and slash pine forest) at the Tianjiling National Park in Changsha,Hunan Province,in subtropical China,from January to December 2010. The influences of soil temperature(Tsoil),volumetric soil water content(θsoil),soil pH,soil organic carbon(SOC) and soil C/nitrogen(N) ratio on soil FCO2 rates were also investigated. The annual mean soil FCO2 rate varied with the forest types. The soil FCO2 rate was the highest in the camphor tree forest(3.53 ± 0.51 μmol m-2s-1),followed by,in order,the mixed,Masson pine,Chinese sweet gum,and slash pine forests(1.53 ± 0.25 μmol m-2 s1). Soil FCO2 rates from the five forest types followed a similar seasonal pattern with the maximum values occurring in summer(July and August) and the minimum values during winter(December and January). Soil FCO2 rates were correlated to Tsoiland θsoil,but the relationships were only significant for Tsoil. No correlations were found between soil FCO2 rates and other selected soil properties,such as soil pH,SOC,and C/N ratio,in the examined forest types. Our results indicated that soil FCO2 rates were much higher in the evergreen broadleaved forest than coniferous forest under the same microclimatic environment in the study region.     

Effects of nitrogen deposition on soil organic carbon fractions in the subtropical forest ecosystems of S China

Experiments were conducted between 2003 and 2008 to examine how N additions influence soil organic C (SOC) and its fractions in forests at different succession stages in the subtropical China. The succession stages included pine forest, pine and broadleaf mixed forest, and old‐growth monsoon evergreen broadleaf forest. Three levels of N (NH₄NO₃)‐addition treatments comprising control, low‐N (50 kg N ha^–1 y^–1), and medium‐N (100 kg N ha^–1 y^–1) were established. An additional treatment of high‐N (150 kg N ha^–1 y^–1) was established in the broadleaf mixed forest. Soil samples were obtained in July 2008 for analysis. Total organic C (TOC), particulate organic C (POC, > 53 μm), readily oxidizable organic C (ROC), nonreadily oxidizable organic C (NROC), microbial biomass C (MBC), and soil properties were analyzed. Nitrogen addition affected the TOC and its fractions significantly. Labile organic‐C fractions (POC and ROC) in the topsoil (0–10 cm) increased in all the three forests in response to the N‐addition treatments. NROC within the topsoil was higher in the medium‐N and high‐N treatments than in the controls. In the topsoil profiles of the broadleaf forest, N addition decreased MBC and increased TOC, while no significant effect on MBC and TOC occurred in the pine and mixed forests. Overall, elevated N deposition increased the availability of labile organic C (POC and ROC) and the accumulation of NROC within the topsoil irrespective of the forest succession stage, and might enhance the C‐storage capacity of the forest soils.     

Nutrient limitations to soil microbial biomass and activity in loblolly pine forests

We performed an assay of nutrient limitations to soil microbial biomass in forest floor material and intact cores of mineral soil collected from three North Carolina loblolly pine (Pinus taeda) forests. We added solutions containing C, N or P alone and in all possible combinations, and we measured the effects of these treatments on microbial biomass and on microbial respiration, which served as a proxy for microbial activity, during a 7-day laboratory incubation at 22 °C. The C solution used was intended to simulate the initial products of fine root decay. Additions of C dramatically increased respiration in both mineral soil and forest floor material, and C addition increased microbial biomass C in the mineral soil. Additions of N increased respiration in forest floor material and increased microbial biomass N in the mineral soil. Addition of P caused a small increase in forest floor respiration, but had no effect on microbial biomass.     

Effects of phosphorus addition on soil microbial biomass and community composition in three forest types in tropical China

Elevated nitrogen (N) deposition in humid tropical regions may aggravate phosphorus (P) deficiency in forest on old weathered soil found in these regions. From January 2007 to August 2009, we studied the responses of soil microbial biomass and community composition to P addition (in two monthly portions at level of 15 g P m^?2 yr^?1) in three tropical forests in southern China. The forests were an old-growth forest and two disturbed forests (mixed species and pine dominated). The objective was to test the hypothesis that P addition would increase microbial biomass and change the composition of the microbial community, and that the old-growth forests would be more sensitive to P addition due to its higher soil N availability. Microbial biomass C (MBC) was estimated twice a year and the microbial community structure was quantified by phospholipid fatty acid (PLFA) analysis at the end of the experiment. Addition of P significantly increased the microbial biomass and altered the microbial community composition in the old-growth forest, suggesting that P availability is one of the limiting factors for microbial growth. This was also reflected by significant increases in soil respiration after P addition. In contrast, P addition had no effect on the microbial biomass and the microbial community composition in the pine forests. Also in the mixed forest, the microbial biomass did not significantly respond to P addition, but soil respiration and the ratio of fungal-to-bacteria was significantly increased.     

Effect of Simulated N Deposition on Soil Exchangeable Cations in Three Forest Types of Subtropical China

The effects of simulated nitrogen (N) deposition on soil exchangeable cations were studied in three forest types of subtropical China.Four N treatments with three replications were designed for the monsoon evergreen broadleaf forest (mature forest):control (0 kg N ha-1 year-1),low N (50 kg N ha-1 year-1),medium N (100 kg N ha-1 year-1) and high N (150 kg N ha-1 ycar-1),and only three treatments (i.e.,control,low N,medium N) were established for the pine and mixed forests.Nitrogen had been applied continuously for 26 months before the measurement.The mature forest responded more rapidly and intensively to N additions than the pine and mixed forests,and exhibited some significant negative symptoms,e.g.,soil acidification,Al mobilization and leaching of base cations from soil.The pine and mixed forests responded slowly to N additions and exhibited no significant response of soil cations.Response of soil exchangeable cations to N deposition varied in the forests of subtropical China,depending on soil N status and land-nse history.     

亚热带2种针叶林土壤碳氮磷储量及化学计量比对混交的响应

针叶林混交阔叶树是改善土壤肥力、增强林地养分循环的重要措施,而混交效应受到针叶树种自身特性的影响,马尾松(Pinus massoniana)和湿地松(P.elliottii)是亚热带地区广泛种植的针叶树种,但目前2种针叶林对阔叶树混交的响应特征还不清楚。选取马尾松、湿地松纯林以及木荷(Schima superba)补植后形成的马尾松—木荷和湿地松—木荷混交林为研究对象,采集剖面土壤样品,测定土壤容重、有机碳(OC)、全氮(TN)和全磷(TP)含量,计算碳氮磷储量及化学计量特征,比较不同森林类型间的异同。混交阔叶树显著增加了马尾松林0—60cm各土层OC含量,而湿地松纯林与其混交林间OC含量无显著差异。同时,混交增加了2种针叶林土壤TN含量。马尾松林混交后0—60cm土层碳储量显著增加95.8%,而混交阔叶树对湿地松林土壤碳储量无显著影响。混交阔叶树后马尾松和湿地松林0—60cm土壤总氮储量分别增加了15.8%和28.4%,但混交对土壤磷储量无显著影响。混交显著增加了马尾松林0—40cm各土层C/N,而降低了湿地松林0—10cm土层C/N。混交阔叶树后马尾松林0—20cm土层C/P和0—10cm土层N/P显著增加,而混交仅增加湿地林0—10cm土层N/P。混交阔叶树增加了针叶林土壤氮储量,但对磷储量无显著影响,同时混交改变了土壤碳氮磷生态化学计量特征。与湿地松林相比,马尾松林土壤养分含量、储量及其化学计量特征对混交的响应更敏感。     

南亚热带三种不同土地利用历史的森林生态系统土壤可交换阳离子对模拟氮沉降的响应

The effects of simulated nitrogen (N)deposition on soil exchangeable cations were studied in three forest types of subtropical China. Four N treatments with three replications were designed for the monsoon evergreen broadleaf forest (mature forest):control (0 kg N ha^-1 year^-1), low N (50 kg N ha^-1 year^-1), medium N (100 kg N ha^-1 year^-1)and high N (150 kg N ha^-1 year^-1), and only three treatments (i.e., control, low N, medium N)were established for the pine and mixed forests. Nitrogen had been applied continuously for 26 months before the measurement. The mature forest responded more rapidly and intensively to N additions than the pine and mixed forests, and exhibited some significant negative symptoms, e.g., soil acidification, Al mobilization and leaching of base cations from soil. The pine and mixed forests responded slowly to N additions and exhibited no significant response of soil cations. Response of soil exchangeable cations to N deposition varied in the forests of subtropical China, depending on soil N status and land-use history.     

Soil microbial biomass, activity and community composition in adjacent native and plantation forests of subtropical Australia

Purpose

Soil nitrogen (N) availability is a critical determinant of plantation productivity in subtropical Australia and is influenced by the soil microbial community. The size, structure and function of the soil microbial community can be impacted by land-use change and residue management. The objectives of this study were to examine the impact of land-use change from (1) native forest (NF) to first rotation (1R) hoop pine plantation and (2) 1R hoop pine plantation to second rotation (2R) hoop pine plantation on the soil microbial community. The impact of residue management on the soil microbial community was also investigated in the 2R forest, where soil microbial parameters were measured in tree rows (2R-T) and windrows (2R-W). In addition, relationships between soil microbial parameters and soil N parameters were investigated.

Materials and methods

Each of the four treatments (NF, 1R, 2R-T and 2R-W) had five 24-m² replicate plots from which 15 soil cores were collected and bulked at three depths (0–10, 10–20, 20–30 cm). Microbial biomass carbon (MBC) and N (MBN) and soil respiration were measured on field moist soils. In addition, carbon (C) source utilisation patterns were assessed using the whole soil MicroResp? technique (Campbell et al. 2003).

Results and discussion

Results indicate that the land-use change from NF to 1R hoop pine plantation significantly reduced MBC, respiration rate, soil total C and total N. Furthermore, the land-use change appeared to have a significant impact on the soil microbial community composition measured using MicroResp? profiles. Land-use change from 1R to 2R hoop pine plantation resulted in a decline in total C and MBN and a shift in microbial community composition. When compared to the 2R-T soils, the 2R-W soils tended to have a greater microbial biomass and respiration rate. Residue management also influenced the microbial community composition measured in the MicroResp? profiles.

Conclusions

Results indicate that land-use change had a significant impact on the soil microbial community, which was likely to be related to shifts in the quality and quantity of organic inputs associated with the change in land use. This may have significant implications for the long-term productivity of the soil resource. Further studies are required to confirm a difference in microbial community composition associated with residue management. In addition, long-term experiments in subtropical Australia are necessary to verify the results of this snapshot study and to improve our understanding of the impact of single-species plantation forestry and residue management on the soil microbial community, soil N dynamics and ultimately the long-term sustainability of the soil resource.     

氮添加对紫花苜蓿根区土壤养分及土壤微生物量的影响

采用人工氮添加研究了紫花苜蓿根区土壤养分及微生物量对不同氮添加水平[CK;低氮LN,10 g/（m²·a）;中氮MN,20 g/（m²·a）;高氮HN,30 g/（m²·a）]的响应。结果表明:氮添加对紫花苜蓿根区土壤养分及微生物量的影响表现为正的增加效应,对根区土壤全氮含量无明显影响（P > 0.05）;土壤养分及微生物量随氮素的添加呈先增加后降低趋势,均表现为MN > HN > LN > CK,以中水平的氮添加对紫花苜蓿根区土壤微生物量增加效应最为明显;除了土壤全氮以外,不同水平的氮添加处理下土壤养分和微生物量均与CK达到差异显著水平（P < 0.05）;紫花苜蓿根区土壤微生物量对氮添加的敏感性高于土壤养分,其中土壤活性有机碳是不同水平氮添加处理后紫花苜蓿根区土壤养分变化的敏感指标。Pearson相关性分析表明,土壤微生物量和土壤养分与土壤含水量之间具有较强的正相关,二者与土壤pH有较强的负相关,表明了氮添加处理下紫花苜蓿根区土壤理化因子、养分和微生物量等地下生态系统各指标之间的统一性及相互作用和影响。     

The effects of N and P additions on soil microbial properties in paired stands of temperate secondary forests and adjacent larch plantations in Northeast China

The conversion of secondary forests to larch plantations in Northeast China has resulted in a significant decline in soil available nitrogen (N) and phosphorus (P), and thus affects plant productivity and ecosystem functioning. Microbes play a key role in the recycling of soil nutrients; in turn, the availability of soil N and P can constrain microbial activity. However, there is little information on the relationships between available soil N and P and the microbial biomass and activity in larch plantation soil. We studied the responses of soil microbial respiration, microbial biomass and activity to N and P additions in a 120-day laboratory incubation experiment and assessed soil microbial properties in larch plantation soil by comparing them with the soil of an adjacent secondary forest. We found that the N-containing treatments (N and N + P) increased the concentrations of soil microbial biomass N and soluble organic N, whereas the same treatments did not affect microbial respiration and the activities of β-glucosidase, N-acetyl-β-glucosaminidase and acid phosphatase in the larch plantation. In addition, the concentration of microbial biomass P decreased with N addition in larch plantation soil. In contrast, N and N + P additions decreased microbial respiration, and N addition also decreased the activity of N-acetyl-β-glucosaminidase in the secondary forest soil. The P treatment did not affect microbial respiration in either larch plantation or secondary forest soils, while this treatment increased the activities of β-glucosidase and acid phosphatase in the secondary forest soil. These results suggested that microbial respiration was not limited by available P in either secondary forest or larch plantation soils, but microbial activity may have a greater P demand in secondary forest soil than in larch plantation soil. Overall, there was no evidence, at least in the present experiment, supporting the possibility that microbes suffered from N or P deficiency in larch plantation soil.     

Responses of Soil Acid Phosphomonoesterase Activity to Simulated Nitrogen Deposition in Three Forests of Subtropical China

Soil acid phosphomonoesterase activity(APA)plays a vital role in controlling phosphorus(P)cycling and reflecting the current degree of P limitation.Responses of soil APA to elevating nitrogen(N)deposition are important because of their potential applications in addressing the relationship between N and P in forest ecosystems.A study of responses of soil APA to simulated N deposition was conducted in three succession forests of subtropical China.The three forests include a Masson pine(Pinus massoniana)forest (MPF)-pioneer community,a coniferous and broad-leaved mixed forest(MF)-transition community and a monsoon evergreen broad-leaved forest(MEBF)-climax community.Four N treatments were designed for MEBF:control(without N added),low-N(50 kg N ha^-1 year^-1),and medium-N(100 kg N ha^-1 year^-1)and high-N(150 kg N ha^-1 year^-1),and only three N treatments(i.e.,control, low-N,medium-N)were established for MPF and MF.Results showed that soil APA was highest in MEBF,followed by MPF and MF.Soil APAs in both MPF and MF were not influenced by low-N treatments but depressed in medium-N treatments.However,soil APA in MEBF exhibited negative responses to high N additions,indicating that the environment of enhanced N depositions would reduce P supply for the mature forest ecosystem.Soil APA and its responses to N additions in subtropical forests were closely related to the succession stages in the forests.     

Soil biological changes for a natural forest and two plantations in subtropical China

Conversion of natural forests into pure plantation forests is a common management practice in subtropical China. To evaluate the effects of forest conversion on soil fertility, microbe numbers and enzyme activities in topsoils (0-10 cm) were quantified in two 33-year-old monoculture plantations of Castanopsis kawakamii Hayata (CK) and Cunninghamia lanceolata Lamb. (Chinese fir) (CF), and compared to a neighboring relict natural C. kawakamii forest (NF), in Sanming, Fujian. Five soil samples were collected once each in January, April, July, September and November in 2000 in each forest for laboratory analysis. Over the sampling year, there were significant differences for bacteria, fungi and actinomycetes between forests and between seasons (P < 0.05). The largest bacteria and fungi populations were in NF, while CF contained the greatest number of actinomycetes. There were also significant differences (P < 0.05) with microbial respiration for forests and seasons. Additionally, compared with NF, urease and acid phosphatase were significantly lower (P < 0.05) in CK and CF. Also, the correlations of soil hydrolysable N and available P to soil microbial and enzymatic activities were highly significant (P < 0.01). Thus, to alter the traditional Chinese fir monoculture so as to mimic the natural forest conditions, managing mixed stands of Chinese fir and broadleaf trees or conducting crop rotation of conifers and broadleaf trees as well as minimizing forest disturbances like clear-cutting, slash burning and soil preparing, could be utilized.     

Composition of the microbial communities in the mineral soil under different types of natural forest

Phospholipid fatty acid (PLFA) patterns were used to describe the composition of the soil microbial communities under 12 natural forest stands including oak and beech, spruce-fir-beech, floodplain and pine forests. In addition to the quantification of total PLFAs, soil microbial biomass was measured by substrate-induced respiration and chloroform fumigation-extraction. The forest stands possess natural vegetation, representing an expression of the natural site factors, and we hypothesised that each forest type would support a specific soil microbial community. Principal component analysis (PCA) of PLFA patterns revealed that the microbial communities were compositionally distinct in the floodplain and pine forests, comprising azonal forest types, and were more similar in the oak, beech and spruce-fir-beech forests, which represent the zonal vegetation types of the region. In the nutrient-rich floodplain forests, the fatty acids 16:1ω5, 17:0cy, a15:0 and a17:0 were the most prevalent and soil pH seemed to be responsible for the discrimination of the soil microbial communities against those of the zonal forest types. The pine forest soils were set apart from the other forest soils by a higher abundance of PLFA 18:2ω6,9, which is typical of fungi and may also indicate ectomycorrhizal fungi associated with pine trees, and high amounts of PLFA 10Me18:0, which is common in actinomycetes. These findings suggest that the occurrence of azonal forest types at sites with specific soil conditions is accompanied by the development of specific soil microbial communities. The study provides information on the microbial communities in undisturbed forest soils which may facilitate interpretation of data derived from managed or even damaged or degraded forests.     

Long‐term changes of aggregate‐associated and labile soil organic carbon and nitrogen after conversion from forest to grassland and cropland in northern Turkey

Soil management systems can have great effect on soil chemical, physical and biological properties. Conversion of forest to grassland and cropland can alter C and N dynamics. The objective of this study was to evaluate the changes in aggregate‐associated and labile soil organic C and N fractions after conversion of a natural forest to grassland and cropland in northern Turkey. This experiment was conducted on plots subject to three different adjacent land uses (forest, grassland and cropland). Soil samples were taken from 0–5, 5–15 and 15–30 cm depths from each land use. Some soil physical (soil texture, bulk density), chemical (soil pH, soil organic matter, lime content, total organic C and N, inorganic N, free and protected organic C) and biological (microbial biomass C and N, mineralizable C and N) properties were measured. The highest and lowest bulk densities were observed in grassland (1.41 g cm⁻³) and cropland (1.14 g cm⁻³), respectively. Microbial biomass C and total organic C in forest were almost twice greater than grassland and four‐times greater than cropland. Cultivation of forest reduced total organic N, mineralizable N and microbial biomass N by half. The great portion of organic C was stored in macroaggregates (>250 µm) in all the three land uses. Free organic C comprised smaller portion of soil organic C in all the three land uses. Thus, this study indicated that long‐term conversion of forest to grassland and cropland significantly decreased microbial biomass C, mineralizable C and physically protected organic C and the decreases were the greatest in cropland. Copyright © 2011 John Wiley & Sons, Ltd.     

Effects of root and litter exclusion on soil CO2 efflux and microbial biomass in wet tropical forests

We examined the effects of root and litter exclusion on the rate of soil CO₂ efflux and microbial biomass at a soil depth of 25 cm in a secondary forest (dominated by Tabebuia heterophylla) and a pine (Pinus caribaea) plantation in the Luquillo Experimental Forest in Puerto Rico. The experimental plots were initially established in 1990, when root, forest floor mass and new litterfall were excluded for 7 y since then. Soil respiration was significantly reduced in the litter and root exclusion plots in both the secondary forest and the pine plantation compared with the control. Root exclusion had a greater effect on soil CO₂ efflux than the litter exclusion in the plantation, whereas a reversed pattern was observed in the secondary forest. The reduction of microbial biomass in the root exclusion plot was greater in the secondary forest (59%) than in the plantation (31%), while there was no difference of the reduction in the litter exclusion plots between these forests. Our results suggest that above-ground input and roots (root litter and exudates) differentially affect soil CO₂ efflux under different vegetation types.     

Soil microbial biomass C and N changes in relation to forest conversion in the Northwestern Turkey

Tree species differ in their effect on soil development and nutrient cycling. Conversion of beech coppice to pine plantations can alter soil physical and chemical properties, which in turn may have significant impacts on soil microbial biomass C and N (C_mic, N_mic). The major objective of this study was to evaluate soil quality changes associated with the forest conversion in humid NW Turkey. Results from this study showed that levels of soil organic carbon (C_org), total nitrogen (N_t), moisture, C_mic and N_mic under beech coppice were consistently higher but levels of pH, CaCO₃ and EC were lower compared to pine plantation. Differences between the forest stands in C_mic and N_mic were mainly related to the size of the C_org stores in soil and to tree species. In addition, high level of CaCO₃ is likely to reduce pools of soil organic C and possibly even microbial biomass C and N in pine forests. The average C_mic:N_mic ratios were higher in soils under beech coppice than pine plantation, while C_mic:C_org and N_mic:N_t percentages were similar in both forest types. These results revealed the differences in microbial community structure associated with different tree species and the complex interrelationships between microbial biomass, soil characteristics, litter quantity and quality. Copyright © 2008 John Wiley & Sons, Ltd.     

Earthworms increase soil microbial biomass carrying capacity and nitrogen retention in northern hardwood forests

Earthworms have been shown to produce contrasting effects on soil carbon (C) and nitrogen (N) pools and dynamics. We measured soil C and N pools and processes and traced the flow of ¹³C and ¹⁵N from sugar maple (Acer saccharum Marsh.) litter into soil microbial biomass and respirable C and mineralizable and inorganic N pools in mature northern hardwood forest plots with variable earthworm communities. Previous studies have shown that plots dominated by either Lumbricus rubellus or Lumbricus terrestris have markedly lower total soil C than uncolonized plots. Here we show that total soil N pools in earthworm colonized plots were reduced much less than C, but significantly so in plots dominated by contain L. rubellus. Pools of microbial biomass C and N were higher in earthworm-colonized (especially those dominated by L. rubellus) plots and more ¹³C and ¹⁵N were recovered in microbial biomass and less was recovered in mineralizable and inorganic N pools in these plots. These plots also had lower rates of potential net N mineralization and nitrification than uncolonized reference plots. These results suggest that earthworm stimulation of microbial biomass and activity underlie depletion of soil C and retention and maintenance of soil N pools, at least in northern hardwood forests. Earthworms increase the carrying capacity of soil for microbial biomass and facilitate the flow of N from litter into stable soil organic matter. However, declines in soil C and C:N ratio may increase the potential for hydrologic and gaseous losses in earthworm-colonized sites under changing environmental conditions.     

Tree girdling increases soil N mineralisation in two spruce stands

Tree girdling is a common practice in forestry whenever trees are to be killed without felling. The effect of tree girdling on soil nitrogen (N) mineralisation was estimated in both an old and a young spruce forest. The dynamics of mineral N (NO₃⁻–N and NH₄⁺–N) and soil microbial biomass carbon (MBC) and N (MBN) were determined for different seasons. The in situ net N mineralisation was measured by incubating soil samples in stainless steel cylinders and the gross N mineralisation rates were measured by ¹⁵N pool dilution method. Mineral N concentrations increased significantly in the girdled plots in both old and young spruce forests and showed variations between soil horizons and between sampling times. Tree girdling significantly increased net N mineralisation in both spruce forests. Annual net N mineralisation was 64 and 39 kg N ha⁻¹ in O horizon of the girdled plots in old and young forest plots, respectively, compared to 25 and 21 kg N ha⁻¹ in the control plots. Annual N mineralisation in A horizon was similar between girdled and control plots (31 kg N ha⁻¹) in the old forest whereas in the young forest A horizon N mineralisation was about 2.5 times higher in the girdled plots. As a result, the annual carbon budget was significantly more positive in the girdled plots than in the control plots in both old and young forests. However, we found significantly higher gross N mineralisation rates in both horizons in the control plots than the girdled plots in the old forest, but no differences between the treatments in the young forest. The MBC and MBN contents only showed significant changes during the first three months of the experiment and were similar later on. They first decreased as girdling removed the root carbohydrate, amino and organic acid exudation from the C sources for microorganisms then increased two months after the treatment root dieback acted as a new source of C. Mineralising microorganisms enhanced the mineral N concentrations in girdled plots as a result of greater activity rather than larger population size.     

Soil biochemical and microbial indices in wet tropical forests: Effects of deforestation and cultivation

Little information is available about the long‐term effects of deforestation and cultivation on biochemical and microbial properties in wet tropical forest soils. In this study, we evaluated the general and specific biochemical properties of soils under evergreen, semi‐evergreen, and moist deciduous forests and adjacent plantations of coconut, arecanut, and rubber, established by clear felling portions of these forests. We also examined the effects of change in land use on microbial indices and their interrelationships in soils. Significant differences between the sites occurred for the biochemical properties reflecting soil microbial activity. Microbial biomass C, biomass N, soil respiration, N mineralization capacity, ergosterol, levels of adenylates (ATP, AMP, ADP), and activities of dehydrogenase and catalase were, in general, significantly higher under the forests than under the plantations. Likewise, the activities of various hydrolytic enzymes such as acid phosphomonoesterase, phosphodiesterase, casein‐protease, BAA‐protease, β‐glucosidase, CM‐cellulase, invertase, urease, and arylsulfatase were significantly higher in the forest soils which suggested that deforestation and cultivation markedly reduced microbial activity, enzyme synthesis and accumulation due to decreased C turnover and nutrient availability. While the ratios of microbial biomass C : N and microbial biomass C : organic C did not vary significantly between the sites, the ratios of ergosterol : biomass C and ATP : biomass C, qCO2 and AEC (Adenylate Energy Charge) levels were significantly higher in the forest sites indicating high energy requirements of soil microbes at these sites.     

Microbial community structure and activity in a Colorado Rocky Mountain forest soil scarred by slash pile burning

Tree thinning and harvesting produces large amounts of slash material which are typically disposed of by burning, often resulting in severe soil heating. We measured soil chemical properties and microbial community structure and function over time to determine effects of slash pile burning in a ponderosa pine forest soil. Real time data were collected for soil temperature, heat flux, and soil moisture contents in one of two slash piles burned in April 2004. During the burn, soil temperatures reached 300 °C beneath the pile center and 175 °C beneath the pile edge. Slash pile burning increased soil pH, extractable N and P, and decreased total C levels within the first 15 cm of soil. Burning reduced soil bacterial biovolumes within the first 15 cm of soil and fungal biovolumes within the first 5 cm of soil. One month after the burn, soil microbial communities under the pile center were enriched in Gram-positive bacterial fatty acid markers compared to communities from under the pile edge and control (nonburned) soil. Fifteen months later, soil chemical properties had not returned to background levels, and microbial community structure in fire-affected soil, regardless of pile location, was distinct from communities of control soil. In fire-affected soil, concentrations of fungal fatty acid biomarkers were low and arbuscular mycorrhizal fungal biomarkers were absent, regardless of pile location. Slash pile burning also reduced fungal and bacterial respiration and resulted in large fluctuations in microbial potential N mineralization and immobilization activities. By altering soil properties important to soil conservation and plant reestablishment, slash pile burning negatively impacts forest ecosystems at localized scales.