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1.
Forest fragmentation in tropical ecosystems can alter nutrient cycling in diverse ways. We have analysed the effects of the
forest-pasture edge on nutrient soil dynamics in a tropical deciduous forest (TDF) in Mexico. In two remnant forest fragments,
both larger than 10 ha, litterfall, litter and soil samples associated to the tree Caesalpinia eriostachys were collected at five distances from the pasture edge into the inner forest (10 m in the pasture and 0–10, 30–40, 70–80
and 100–110 m towards the forest interior). We measured the concentrations of carbon (C), nitrogen (N) and phosphorus (P)
in litterfall, surface litter and soil, and soil microbial C (C mic) and microbial N (N mic). Soil nutrient concentrations and C mic and N mic were lower in the pasture soils than in the forest soil samples. Total C and N pools, and C mic and N mic in the pasture were lower than in the forest. In contrast, net N immobilization and the increase in N mic from rain to dry season increased from the edge to the inner forest. Soil P concentration was lower in the pasture and at
the first distance class in the forest margin (0–10 m) than in the sites located further into the forest, while litter P concentration
had the inverse pattern. Litterfall P was also reduced near the edge and increased towards the forest interior. As a consequence,
litterfall C:P and N:P ratios decreased from the edge to the inner forest. These results suggest that the forest–pasture edge
disrupts P dynamics within the first 10 m in the forest. Thus, plants' use of nutrients and productivity could be altered
in the edge of fragmented forests. 相似文献
2.
土壤微生物是森林生态系统中的重要分解者,在森林生态系统物质循环和能量转换中占有特别重要的地位。以典型喀斯特峰丛洼地为试验对象,利用经典统计学和地统计方法分析了土壤微生物量的空间变异特征。结果表明:土壤微生物量的变异程度均很大,土壤微生物量碳(Cmic)、土壤微生物量氮(Nmic)、土壤微生物量磷(Pmic)的变化范围依次为:44.29—5209.63,20.91—1894.37,0.34—77.06 mg/kg。Cmic、Nmic呈极显著的相关关系,Cmic/Nmic为4.78,明显低于其它生态系统。半变异函数分析表明,Cmic和Nmic的最佳拟合模型为高斯模型,Pmic的最佳拟合模型为球状模型,Cmic/Nmic的最佳拟合模型为指数模型。土壤微生物量的块金值/基台值均介于25%—75%之间,表现为中等空间相关性,说明其受随机因素和结构因素的综合影响。Cmic、Nmic的自相关距离约为50 m,随着滞后距离的增大,自相关函数逐渐向负方向增长,达到显著的负相关。Pmic的Moran’s I在滞后距大于70 m后反而增大,表现为正相关。Cmic/Nmic的Moran’s I较小,在-0.2—0.2之间波动。Cmic、Nmic的空间分布具有很高的相似性,呈凸型片状分布,坡中含量高且向两边递减。Pmic表现为明显不同的分布格局,其在坡中上位和洼地含量较高。Cmic/Nmic呈相反的凹形零星斑块状分布。土壤微生物存在着一定的空间格局,受干扰后其含量急剧降低,因此应加强喀斯特原生生态系统的保护。 相似文献
3.
The impact of atmospheric N deposition on the dynamics of various carbon fractions was investigated in two Scots pine forest
soils (cambisol, podzol) of Northern Germany in microcosm experiments. Total organic carbon (TOC), CO 2 emission, microbial carbon (C mic) as well as organic hot- and coldwater extractable carbon fractions (C hwe, C cwe) were analyzed before, during, and after soil incubation in microcosms, run in three treatments: 0, +45, and +90 kg N ha −1a −1. On both sites, the N treatment showed no response to total organic carbon (TOC) contents in most of the investigated soil
layers. Microbial carbon (C mic) was significantly increased in the organic layer of both soil types by the N application. Subsequent to the N application,
the CO 2 emission increased in all mineral soil layers of the cambisol but remained almost unaffected in the podzol. After the N application,
a remarkable increase of hotwater extractable C (C hwe) was detected for the organic layer of the cambisol but not for the podzol, whereas coldwater extractable C (C cwe) concentrations decreased at both sites. The N application did not have a significant impact on the leachate concentrations
of total organic carbon (TOC), dissolved organic carbon (DOC), and particulate organic carbon (POC) in the podzol, whereas
the concentrations of these C fractions were decreased in the organic layer and the 35–70~cm mineral soil layer of the cambisol.
The N treatment changed the contents of most of the investigated C fractions in both soil types and resulted in a considerable
C~mobilization. But the processes of the C~mobilization between the cambisol and the podzol were completely different. According
to the presented data, the cambisol obtaining moderate atmospheric N loads is much more sensitive to additional N inputs than
the podzol that already received high amounts of atmospheric N. 相似文献
4.
To evaluate the microbial diversity of Fushan forest soils, the variation of soil properties, microbial populations, and soil
DNA with soil depth in three sites of different altitude were analyzed. Microbial population, moisture content, total organic
carbon (C org), and total nitrogen (N tot) decreased with increasing soil depth. The valley site had the lowest microbial populations among the three tested sites
due to the low organic matter content. Bacterial population was the highest among the microbial populations. The ratios of
cellulolytic microbes to the total bacteria in organic layers were high, implying their roles in the carbon cycle. The microbial
biomass carbon (C mic) and nitrogen (N mic) contents ranged from 130.5 to 564.1 μg g −1 and from 16.7 to 95.4 μg g −1, respectively. The valley had the lowest C mic and N mic. The organic layer had the highest C mic and N mic and decreased with soil depth. Analysis using denaturing gradient gel electrophoresis (DGGE) of polymerase chain reaction
(PCR) amplicons of 16S rDNA showed that the bacterial diversity of the three sites were very similar to each other in the
major bands, and the variation was in the minor bands. However, the patterns in PCR-DGGE profile through gradient horizons
were different, indicating the prevalence of specific microbes at different horizons. These results suggest that the microbial
diversity in the deeper horizons is not simply the diluted analogs of the surface soils and that some microbes dominate only
in the deeper horizons. Topography influenced the quantity and diversity of microbial populations. 相似文献
5.
开展不同恢复演替阶段天然次生林土壤-微生物生物量及其化学计量特征关系的研究,可为有效和持续管理川西亚高山次生林提供科学依据。以川西亚高山米亚罗林区20世纪60、70、80年代3种采伐迹地经自然恢复演替形成的次生林(SF60、SF70和SF80)和岷江冷杉( Abies faxoniana)原始林(PF)为研究对象,探讨了表层(0-20 cm)土壤有机碳(C soil)、全氮(N soil)、全磷(P soil)含量及微生物生物量碳(C mic)、氮(N mic)、磷(P mic)含量随自然恢复演替的变化特征,分析了它们的化学计量比与微生物熵( qMB)之间的相互关系。结果表明:(1)随着恢复演替年限的增加,C soil和N mic含量显著降低,N soil和P soil及C mic和P mic含量呈现先升后降的显著变化趋势,且3种次生林的表层土壤碳、氮、磷及其微生物生物量的含量均低于PF。(2)次生林恢复年限对土壤微生物熵C( qMBC)和P( qMBP)没有显著影响,但对土壤微生物熵N( qMBN)存在显著影响。(3)土壤-微生物化学计量不平衡性C imb:N imb随自然恢复演替进程呈先降后升的显著变化趋势,C imb:P imb呈不显著的降低趋势,N imb:P imb呈现显著降低趋势。冗余分析显示,N imb:P imb和C mic:N mic是影响 qMB变化的主导因子,其中N imb:P imb解释了 qMB变化的62.6%,说明土壤氮磷及其活性组分(N mic和P mic)含量变化可能会影响到 qMB变化。综上可知,次生林近60 年的自然恢复演替引起了土壤碳氮磷含量的显著变化;天然次生林土壤-微生物生物量碳氮磷化学计量比主要受到氮磷的协同影响,且SF60土壤质量状况较差,为此,对SF60林分可适当增加氮素供给以促进其林木生长,进而提升土壤质量。 相似文献
6.
土壤微生物是地球生物演化进程中的先锋种类,具有重要的生态修复功能,但空间分布格局是否存在的争议很大。以云贵高原典型喀斯特坡耕地为对象,基于网格法取样,用经典统计学和地统计学综合分析了土壤微生物生物量的空间变异特征。结果表明,云贵高原喀斯特坡耕地土壤微生物生物量碳(C mic)、磷(P mic)以及碳氮比(C mic/N mic)适宜,氮(N mic)的含量较低,变异均很大,空间自相关性明显,最佳拟合模型均为指数模型。块金值 C0较小(0.0016-0.0087), C0/( C0+ C)均<25%(2.6%-10.2%),变程 a较短(22.2-51.0 m),其强烈的空间变异主要由结构性变异引起。Kriging等值线图表明,C mic、N mic和C mic/N mic的高值区分布在坡的中上部,P mic的高值区则在坡的中下部和坡脚。云贵高原喀斯特坡耕地土壤微生物不仅存在着小尺度的空间分布格局,而且不同土壤微生物属性的空间分布不同。 相似文献
7.
We investigated microbial responses in a late successional sedge-dominated alpine grassland to four seasons of CO 2 enrichment. Part of the plots received fertilizer equivalent to 4.5g N m −2 a −1. Soil basal respiration (R
mic
), the metabolic quotient for CO 2 (qCO 2=R
mic
/C
mic
), microbial C and N (C
mic
and N
mic
) as well as total soil organic C and N showed no response to CO 2 enrichment alone. However, when the CO 2 treatment was combined with fertilizer addition R
mic
and qCO 2 were statistically significantly higher under elevated CO 2 than under ambient conditions (+57% and +71%, respectively). Fertilizer addition increased microbial N pools by 17%, but
this was not influenced by elevated CO 2. Microbial C was neither affected by elevated CO 2 nor fertilizer. The lack of a CO 2-effect in unfertilized plots was suprising in the light of our evidence (based on C balance) that enhanced soil C inputs
must have occurred under elevated CO 2 regardless of fertilizer treatment. Based on these data and other published work we suggest that microbial responses to elevated
CO 2 in such stable, late-successional ecosystems are limited by the availability of mineral nutrients and that results obtained
with fertile or heavily disturbed substrates are unsuitable to predict future microbial responses to elevated CO 2 in natural systems. However, when nutrient limitation is removed (e.g. by wet nitrogen deposition) microbes make use of the
additional carbon introduced into the soil system. We believe that the response of natural ecosystems to elevated CO 2 must be studied in situ in natural, undisturbed systems. 相似文献
8.
Soil microbial biomass C (C mic) is a sensitive indicator of trends in organic matter dynamics in terrestrial ecosystems. This study was conducted to determine the effects of tropospheric CO 2 or O 3 enrichments and moisture variations on total soil organic C (C org), mineralizable C fraction (C Min), C mic, maintenance respiratory (qCO 2) or C mic death (qD) quotients, and their relationship with basal respiration (BR) rates and field respiration (FR) fluxes in wheat‐soybean agroecosystems. Wheat ( Triticum aestivum L.) and soybean ( Glycine max. L. Merr) plants were grown to maturity in 3‐m dia open‐top field chambers and exposed to charcoal‐filtered (CF) air at 350 μL CO 2 L ?1; CF air + 150 μL CO 2 L ?1; nonfiltered (NF) air + 35 nL O 3 L ?1; and NF air + 35 nL O 3 L ?1 + 150 μL CO 2 L ?1 at optimum (? 0.05 MPa) and restricted soil moisture (? 1.0 ± 0.05 MPa) regimes. The + 150 μL CO 2 L ?1 additions were 18 h d ?1 and the + 35 nL O 3 L ?1 treatments were 7 h d ?1 from April until late October. While C org did not vary consistently, C Min, C mic and C mic fractions increased in soils under tropospheric CO 2 enrichment (500 μL CO 2 L ?1) and decreased under high O 3 exposures (55 ± 6 nL O 3 L ?1 for wheat; 60 ± 5 nL O 3 L ?1 for soybean) compared to the CF treatments (25 ± 5 nL O 3 L ?1). The qCO 2 or qD quotients of C mic were also significantly decreased in soils under high CO 2 but increased under high O 3 exposures compared to the CF control. The BR rates did not vary consistently but they were higher in well‐watered soils. The FR fluxes were lower under high O 3 exposures compared to soils under the CF control. An increase in C mic or C mic fractions and decrease in qCO 2 or qD observed under high CO 2 treatment suggest that these soils were acting as C sinks whereas, reductions in C mic or C mic fractions and increase in qCO 2 or qD in soils under elevated tropospheric O 3 exposures suggest the soils were serving as a source of CO 2. 相似文献
9.
Lowland rice paddy soils may accumulate significant amounts of organic matter. Our aim was to investigate the role of prolonged paddy management on the nitrogen (N) status of the soils, and to elucidate the contribution of bacteria and fungi to long‐term N accumulation processes. For this purpose, we sampled a chronosequence of 0–2000 years of rice cropping with adjacent non‐paddy systems in the Bay of Hangzhou, China. The samples were analyzed for bulk density, total, mineral and microbial N (N mic), and amino sugars as markers for microbial residues. The results showed that during the first 100 years of land embankment, both paddy and non‐paddy soils accumulated N at a rate of up to 61 and 77 kg ha ?1 per annum, reaching steady‐state conditions after 110–172 years, respectively. Final N stocks in paddy fields exceeded those of the non‐paddies by a factor of 1.3. The contribution of amino sugars to total N increased to a maximum of 34 g N kg ?1 N in both land‐use systems, highlighting a significant accumulation of N in microbial residues of the surface soils. Correspondingly, the ratio of N mic to microbial residue‐N decreased to a constant value. In the paddy subsoils, we found that bacterial residues particularly contributed to the pool of microbial residue‐N. Nevertheless, the absolute contents of amino sugars in paddy subsoils decreased during the last 1700 years of the chronosequence. We conclude that under paddy cultivation, soil microorganisms may accumulate parts of this N in their residues despite low overall N availability. However, this N accumulation is limited to initial stages of paddy soil development and restricted to the surface horizons, thus challenging its sustainability with future land‐use changes. 相似文献
10.
土地利用方式的变化导致土壤碳氮含量及其化学计量关系的变化,然而土壤微生物化学计量及其驱动的碳氮矿化过程如何响应这种变化仍不明确。以帽儿山地区天然落叶阔叶林、人工红松林、草地和农田4种不同土地利用类型为对象,测定其土壤有机碳(C_(soil))、全氮(N_(soil))、微生物生物量碳和氮(C_(mic)和N_(mic))、土壤碳和氮矿化速率(C_(min)和N_(min)),旨在比较不同土地利用方式对土壤、微生物碳氮化学计量特征及矿化速率的影响,探索土壤-微生物-矿化之间碳氮化学计量特征的相关性,揭示微生物对土壤碳氮化学计量变化的响应和调控机制。结果显示:C_(soil)、N_(soil)、C_(mic)、N_(mic)和C_(min)均呈现天然落叶阔叶林人工红松林草地农田,而天然落叶阔叶林和草地的N_(min)显著高于人工红松林和农田。土地利用方式显著影响土壤和微生物碳氮比(C∶N_(soil)和C∶N_(mic)),均呈现农田最高。不同土地利用方式的数据综合分析发现:碳氮矿化速率比与C∶N_(mic)呈负相关,而和微生物与土壤碳氮化学计量不平衡性(C∶N_(imb))显著正相关。单位微生物生物量的碳矿化速率(qCO_2)随着C∶N_(mic)的增加而降低,而单位微生物生物量的氮矿化速率(qAN)随着C∶N_(mic)的增加而增加。C∶N_(imb)与qCO_2正相关,与qAN负相关。以上结果表明,微生物会通过改变自身碳氮化学计量、调整碳氮之间相对矿化速率,以适应土地利用变化导致的土壤碳氮及其化学计量的变异性,以满足自身生长和代谢的碳氮需求平衡。 相似文献
11.
Precise assessment of soil organic carbon (OC) storage requires understanding of soil type and depth specific differences in organic matter (OM) stabilization. Therefore, we aimed to analyze OC dynamics down the soil profile and to clarify the effect of depth on the importance of aggregate formation and mineral adsorption for OC storage in mature beech forest soils developed from different parent materials. Aggregate size and density fractions were separated from samples of top and subsoil horizons, which were quantified and analyzed by infrared spectroscopy. We also determined the microbial biomass C (Cmic) and the amount of C decomposed within incubation experiments (CO2-C) for the bulk soil samples. OC stabilized via aggregate formation and mineral association significantly increased with soil depth. However, this stabilized pool seemed to fuel the labile OM stronger in the subsoil than in the topsoil because the CO2-C/SOC and CO2-C/Cmic ratios increased with depth. Measured differences in the magnitude of the detected stabilization and destabilization patterns were attributed to parent material and soil horizon, indicating pronounced spatial and vertical heterogeneity in the contribution of soils under temperate broadleaf forest to terrestrial C sequestration. Considering such site and depth specific differences will improve assessment and modelling of soil OC storage for areas covered with the same forest type but with high pedogenetic diversity. 相似文献
12.
土壤微生物是陆地生态系统中最活跃的成分,它推动着生态系统的能量和物质循环,被公认为土壤生态系统变化的预警及敏感指标。以西南峡谷型喀斯特坡地为研究对象,基于网格法取样,结合经典统计学和地统计学方法,揭示了土壤微生物生物量的空间分布与格局及其主要影响因子。结果表明,西南峡谷型喀斯特坡地土壤微生物生物量碳(MBC)、氮(MBN)、磷(MBP)、碳氮比(MBC/MBN)、碳磷比(MBC/MBP)适宜,MBC、MBN、MBP变异均很大;空间自相关性明显,除MBP最佳拟合模型为球状模型外,其他指标均为指数模型。C0/(C0+C)均25%(4.9%—6.2%),呈强烈的空间相关,这主要由结构性变异引起。Kriging等值线图表明,MBC、MBN的高值区集中在坡中上部;MBP的格局明显不同,高值区集中在坡脚;MBC/MBN斑块较大,变化缓和;MBC/MBP的空间分布规律不明显,斑块多而破碎。西南峡谷型喀斯特坡地土壤微生物量空间分布的影响因子很多,其中,影响土壤微生物量碳和氮的主要因子有土层厚度、pH、碱解氮。西南峡谷型喀斯特坡地土壤微生物不仅存在着小尺度的空间分布格局,而且不同土壤微生物属性的空间分布不同。因此,应采取适宜措施,激活土壤微生物活性。 相似文献
13.
The carbon content of microbial biomass and the kinetic characteristics of microbial respiration response to substrate addition have been estimated for chernozem soils under different land use: arable lands used for 10, 46, and 76 years, mowed meadow, natural forest, and forest shelter belt. Microbial biomass and the content of microbial carbon in humus (C mic /C org) decreased in the following order: soils under forest cenoses—mowed meadow—10-year arable land—46- and 75-year arable land. The amount of microbial carbon in the long-plowed horizon was 40% of its content in the upper horizon of natural forest. Arable soils were characterized by a lower metabolic diversity of microbial community and by the highest portion of microorganisms able to grow directly on glucose introduced into soil. The effects of different scenarios of carbon sequestration in soil on the amounts and activity of microbial biomass are discussed. 相似文献
14.
Accurate estimation of soil nitrogen (N) supply in the field is required to optimize fertilizer N management and to minimize
environmental N losses in humid environments. Laboratory-based measures of N availability were evaluated as predictors of
field-based indices of soil N supply within potato production systems. Pre-plant soil samples (0–15 cm) were collected from
a series of forty treatments in established potato trials located in Atlantic Canada and Maine, USA. Total plant N uptake
at topkill with no fertilizer N applied (PNU 0N), PNU 0N plus soil mineral N to 30 cm depth at harvest and relative yield were considered as field-based indices of soil N supply.
The potentially mineralizable N (N 0) was determined by aerobic incubation at 25°C and periodic leaching for 24 weeks. A series of laboratory-based measures of
soil N supply were measured in soil samples. Pre-plant soil nitrate or total mineral N at 0–30 cm depth was the best single
predictor of PNU 0N ( r = 0.67 and 0.71, respectively) and relative yield ( r = 0.58 and 0.61). The ultraviolet absorbance of 0.01 M NaHCO 3 extract at 205 nm (NaHCO 3-205) was suitable as a predictor of PNU 0N and relative yield in each growing season, however, the relationship between this parameter and PNU 0N or relative yield varied somewhat among years. A combination of pre-plant mineral N plus N mineralized in the first 2 weeks
period of incubation after re-wetting is proposed as a more robust measure of N availability compared with use of mineral
N alone. 相似文献
15.
Despite the extensive literature on the effect on soil properties of afforestation of former arable land, we still lack full
understanding of whether the changes proceed in the same direction and at the same rate, and of how long is required to achieve
a state of soil equilibrium typical of a natural forest ecosystem. Therefore, as part of a study comparing post-arable sandy
soils (Dystric Arenosols) afforested with Scots pine (Pinus silvestris L.) with arable soils and soils of continuous coniferous forests, the range and direction of changes in pH, organic carbon
(C org), total nitrogen (N tot), ammonium (N-NH 4) and nitrates (N-NO 3) in soil solution, total (P tot) and available (P av) phosphorus were determined. The studies were carried out in south-east Poland (51°30′-51°37′N, 22°20′-22°35′E). Ten paired
sites of afforested soils (five with 14- to 17-year-old stands and five with 32- to 36-year-old stands) with adjacent cultivated
fields, and five sites of continuous forest with present stands of ca. 130–150 years old were selected. Soil samples were
taken from the whole thickness of master horizons and, in the case of the A horizon of the afforested soils, from three layers:
0–5 (A 0–5), 5–10 (A 5–10) and 10–20 cm (A 10–20). The cultivated soils in the Ap horizon showed higher pH (by ca. 1.0 unit), lower C org and C:N, similar N tot, lower N-NH 4, higher N-NO 3, higher P tot and P av contents compared with the Ah horizon of continuous forest soils. The results indicated decreased soil pH in the former plough
layer of the afforested soils, with the greatest decrease observed in the 0–5 cm layer. In these soils, the C org content was considerably higher in the A 0–5 layer, but lower in the two deeper layers and in the whole A horizon (0–20 cm) compared with the Ap horizon of the arable
soils. The results indicate that the C org content, after an initial phase of decline, again achieved a level characteristic of arable soils. The N tot content in all layers of the A horizon of the afforested soils was lower than in the Ap horizon of the arable soils, and
showed a reduction with stand age, especially in deeper layers. The C:N ratios in the mineral topsoil increased with stand
age. N-NH 4 content increased and N-NO 3 decreased after afforestation. The P tot and P av contents in all layers and in the whole A horizon of the afforested soils, on stands of both ages, was lower than in the
Ap of the cultivated soils. From the results, it could be concluded that, after more than 30 years of tree growth, the soils
of the A horizon were still more similar to arable than to continuous forest soils with respect to C org, P tot and P av. With respect to pH, N-NH 4 and N-NO 3, especially in the 0–5 cm layer, they were more similar to continuous forest soils than to cultivated soils, but with respect
to N tot and C:N ratio they were somewhere in between. 相似文献
16.
Microbiological and physico-chemical characteristics of tropical forest, grassland and cropfield soils from India were investigated.
The study revealed that the conversion of natural forest led to a reduction of soil organic C (26–36%), total N (26–35%),
total P (33–44%), microfungal biomass (44–66%) and total microbial biomass C, N and P (25–60%) over a period of 30–50 years.
Comparative analysis of microbial activity in terms of basal soil respiration revealed maximum activity in the forest and
minimum in the cropfield soil. Analysis of microbial metabolic respiratory activity (qCO 2) indicated relatively greater respiratory loss of CO 2-C per unit microbial biomass in cropfield and grassland than in forest soil. Considering the importance of the microbial
component in soil, we conclude that the conversion of the tropical forest to different land uses leads to the loss of biological
stability of the soil. 相似文献
17.
The effects of forest management (thinning) on gross and net N conversion, the balance of inorganic N production and consumption, inorganic N concentrations and on soil microbial biomass in the Ah layer were studied in situ during eight intensive field measuring campaigns in the years 2002–2004 at three beech ( Fagus sylvatica L.) forest sites. At all sites adjacent thinning plots (“T”) and untreated control plots (“C”) were established. Since the sites are characterized either by cool-moist microclimate (NE site and NW site) or by warm-dry microclimate (SW site) and thinning took place in the year 1999 at the NE and SW sites and in the year 2003 at the NW site the experimental design allowed to evaluate (1) short-term effects (years 1–2) of thinning at the NW site and (2) medium-term effects (years 4–6) of thinning under different microclimate at the SW and NE site. Microbial biomass N was consistently higher at the thinning plots of all sites during most of the field campaigns and was overall significantly higher at the SWT and NWT plots as compared to the corresponding untreated control plots. The size of the microbial biomass N pool was found to correlate positively with both gross ammonification and gross nitrification as well as with extractable soil NO 3− concentrations. At the SW site neither gross ammonification, gross nitrification, gross ammonium (NH 4+) immobilization and gross nitrate (NO 3−) immobilization nor net ammonification, net nitrification and extractable NH 4+ and NO 3− contents were significantly different between control and thinning plot. At the NET plot lower gross ammonification and gross NH 4+ immobilization in conjunction with constant nitrification rates coincided with higher net nitrification and significantly higher extractable NO 3− concentrations. Thus, the medium-term effects of thinning varied with different microclimate. The most striking thinning effects were found at the newly thinned NW site, where gross ammonification and gross NH 4+ immobilization were dramatically higher immediately after thinning. However, they subsequently tended to decrease in favor of gross nitrification, which was significantly higher at the NWT plot as compared to␣the␣NWC plot during all field campaigns after␣thinning except for April 2004. This increase␣in␣gross nitrification at the NWT plot (1.73 mg N kg −1 sdw day −1 versus 0.48 mg N kg −1 sdw day −1 at the NWC plot) coincided with significantly higher extractable NO 3− concentrations (4.59 mg N kg −1 sdw at the NWT plot versus 0.96 mg N kg −1 sdw at the NWC plot). Pronounced differences in relative N retention (the ratio of gross NH 4+ immobilization + gross NO 3− immobilization to gross ammonification + gross nitrification) were found across the six research plots investigated and could be positively correlated to the soil C/N ratio ( R = 0.94; p = 0.005). In sum, the results obtained in this study show that (1) thinning can lead to a shift in the balance of microbial inorganic N production and consumption causing a clear decrease in the N retention capacity in the monitored forest soils especially in the first two years after thinning, (2)␣the resistance of the investigated forest ecosystems to disturbances of N cycling by thinning may vary with different soil C contents and C/N ratios, e. g. caused by differences in microclimate, (3) thinning effects tend to decline with the growth of understorey vegetation in the years 4–6 after thinning. 相似文献
18.
By using multivariate statistical analysis, the influence of Scots pine climatypes on a set of chemical and microbiological properties of soil, i.e., soil C/N, C mic/C org, and C mic/N mic, was revealed in a series of long-term (ca. 30 years) field experiments, which were carried out according to the same scheme under contrasting environmental and soil conditions of Siberian forestries. 相似文献
19.
Large amounts of terrestrial organic C and N reserves lie in salt-affected environments, and their dynamics are not well understood.
This study was conducted to investigate how the contents and dynamics of ‘native’ organic C and N in sandy soils under different
plant species found in a salt-affected ecosystem were related to salinity and pH. Increasing soil pH was associated with significant
decreases in total soil organic C and C/N ratio; particulate (0.05–2 mm) organic C, N and C/N; and the C/N ratio in mineral-associated
(<0.05 mm) fraction. In addition, mineral-associated organic C and N significantly increased with an increase in clay content
of sandy soils. During 90-day incubation, total CO 2-C production per unit of soil organic C was dependent on pH [CO 2-C production (g kg −1 organic C) = 22.5 pH – 119, R
2 = 0.79]. Similarly, increased pH was associated with increased release of mineral N from soils during 10-day incubation.
Soil microbial biomass C and N were also positively related to pH. Metabolic quotient increased with an increase in soil pH,
suggesting that increasing alkalinity in the salt-affected soil favoured the survival of a bacterial-dominated microbial community
with low assimilation efficiency of organic C. As a result, increased CO 2-C and mineral N were produced in alkaline saline soils (pH up to 10.0). This pH-stimulated mineralization of organic C and
N mainly occurred in particulate but not in mineral-associated organic matter fractions. Our findings imply that, in addition
to decreased plant productivity and the litter input, pH-stimulated mineralization of organic matter would also be responsible
for a decreased amount of organic matter in alkaline salt-affected sandy soils. 相似文献
20.
Pseudomonas fluorescens strains are used in agriculture as plant growth-promoting rhizobacteria (PGPR). Nontarget effects of released organisms should
be analyzed prior to their large-scale use, and methods should be available to sensitively detect possible changes in the
environments the organism is released to. According to ecological theory, microbial communities with a greater diversity should
be less susceptible to disturbance by invading organisms. Based on this principle, we laid out a pot experiment with field-derived
soils different in their microbial biomass and activity due to long-term management on similar parent geological material
(loess). We investigated the survival of P. fluorescens CHA0 that carried a resistance toward rifampicine and the duration of potential changes of the soil microflora caused by
the inoculation with the bacterium at the sowing date of spring wheat. Soil microbial biomass ( C
mic, N
mic) basal soil respiration (BR), qCO 2, dehydrogenase activity (DHA), bacterial plate counts, mycorrhiza root colonization, and community level substrate utilization
were analyzed after 18 and 60 days. At the initial stage, soils were clearly different with respect to most of the parameters
measured, and a time-dependent effect between the first and the second set point were attributable to wheat growth and the
influence of roots. The effect of the inoculum was small and merely transient, though significant long-term changes were found
in soils with a relatively low level of microbial biomass. Community level substrate utilization as an indicator of changes
in microbial community structure was mainly changed by the growth of wheat, while other experimental factors were negligible.
The sensitivity of the applied methods to distinguish the experimental soils was in decreasing order N
mic, DHA, C
mic, and qCO 2. Besides the selective enumeration of P. fluorescens CHA0 rif +, which was only found in amended soils, methods to distinguish the inoculum effect were DHA, C
mic, and the ratio of C
mic to N
mic. The sampling time was most sensitively indicated by N
mic, DHA, C
mic, and qCO 2. Our data support the hypothesis—based on ecosystem theory—that a rich microflora is buffering changes due to invading species.
In other words, a soil-derived bacterium was more effective in a relatively poor soil than in soils that are rich in microorganisms. 相似文献
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