The effect of regeneration burning upon the nutrient status of soil in two forest types in southern Tasmania

In two forest types in southern Tasmania, eucalypt rainforest (mixed forest) and eucalypt dry sclerophyll forest, surface soils (0–10 cm) from stands that had been clear-felled and burned between 1976 and 1979 were compared with those from uncut, unburned stands. Factors compared were total organic C, N, P, K, Mg, Ca, Zn, Mn; pH; exchangeable Ca, Mg, and K; cation exchange capacity; extractable P; soil phosphate buffering capacity; and N-mineralisation rates. Sampling started in April 1979 and ended in October 1980. Within each forest type, soils from burned coupes had higher mean values for pH, exchangeable cations, percent base saturation, and nitrate-N produced during aerobic incubation, and had lower mean values for exchangeable acidity and ammonium-N produced during aerobic incubation than soils from unburned coupes. In mixed forest only, soils from burned coupes had higher mean values for extractable P and soil phosphate buffering capacity, and lower mean values for total organic C than those of unburned coupes. There were only small differences between burned and unburned soils in cation exchange capacity and ammonium-N produced during anaerobic incubation. For each burned coupe in mixed forest, with increase in time since burning there was a decrease in pH, an increase in exchangeable acidity, and a decrease in rate of production of nitrate: no changes were detected in other factors. It is concluded that, for clay soils developed on dolerite, the nutritional status of soil in both forest types is probably improved by burning. The improvement lasts for more than 4 years in mixed forest and more than two years in dry sclerophyll forest. Only minor leaching of nutrients to below 10 cm in depth is likely to occur in either type.     

Soil chemical properties as related to forest succession in a highland area in north-east Tasmania

The relationship between vegetational type and a number of soil chemical factors was examined in secondary successions from fire-maintained eucalypt/grass to climax rainforest communities growing on uniform granitic soil parent material. Canonical variates analysis, which utilized the following variables: pH; loss on ignition; total N, P, K, Ca, and Mg; cation exchange capacity and exchangeable Ca, K, and Mg; and potentially mineralizable N, revealed close overall similarity between surface soils of adjacent types, and significant differences among those of types distant from each other in the successional sequences. Exchangeable Ca, mineralizable N, total N. P, and Mg, and pH all differed significantly among soils of the vegetational types. However, the only identifiable gradients in soil properties that were detected within a successional sequence were in total and mineralizable N, which tended to increase, and pH, which generally tended to decrease with progression towards the climax vegetation. Nitrification was promoted by the presence of Acacia dealbata and apparently inhibited by the presence of Leptospermum lanigerum; it was more rapid in soils beneath late successional vegetation than in those from climax vegetation or early stages of succession, and was inhibited in soil from old (> 200 years) grassland. It was concluded that differences among soils in chemical composition and rates of mineralization of N were due to differences in species composition of the vegetational types that they carried for the time being.     

保护性耕作对土壤交换性盐基组成的影响

以辽宁省彰武县保护性耕作示范推广基地土壤为研究对象,通过实地调查和取样分析,对比研究了传统犁耕和6年保护性耕作（免耕秸秆覆盖）条件下的土壤交换性盐基组成.结果表明：在15 cm土层内,保护性耕作土壤的交换性K、Ca、Mg含量和盐基总量（SEB）较传统犁耕均有不同程度增加,表明保护性耕作使土壤的保肥和缓冲能力增强.相关分析表明,这与土壤的有机质和粘粒含量的变化密切相关;保护性耕作土壤的K/SEB和Ca/Mg高于传统犁耕,而(Ca+Mg)/SEB、Ca/K和Mg/K低于传统犁耕,说明保护性耕作对土壤交换性盐基比例关系的影响以交换性Ca、K特别是K的相对富集为主要特征;保护性耕作提高了交换性K、Ca、Mg含量与SEB的分层比率(0～5 cm/5～15 cm和0～5 cm/15～30 cm),表明交换性盐基在耕层剖面的垂直变异性增强.     

Long-term effect of superphosphate on accumulation of soil phosphorus and exchangeable cations on a grazed,irrigated pasture site

The annual herbage dry matter yield, herbage P concentrations and quantities of P, K, Mg and Ca cycled by grazing sheep were calculated for a 37 year-old grazed pasture supplied with superphosphate at rates of 0, 188 and 376 kg ha^-1 annually. The amount and distribution of inorganic and organic P and exchangeable K, Mg and Ca in the soil below the three grazed treatments was also measured and compared with that below a wilderness area which had not been used for agriculture. Increasing rates of superphosphate increased herbage dry matter yield, herbage P concentrations and thus the amounts of P ingested and, in turn, excreted by the grazing sheep. Annual quantities of K, Mg and Ca cycled back to the pasture in the form of excreta were also increased. The increased cycling of K by animals induced by increasing superphosphate applications resulted in greater losses of K and consequently concentrations of exchangeable and non-exchangeable ‘fixed’ K in soil decreased in the order wilderness > control > 188 > 376. Differences were evident to a depth of 20 cm. Some losses of Mg during cycling also occurred and concentrations of exchangeable Mg followed the order: wilderness > control >188=376. Concentrations of exchangeable Ca increased with pasture development due to additions of Ca in lime and superphosphate. Concentrations of total soil organic P (0–4 cm) increased in the order: wilderness < control <188<376 but for inorganic P and total P the control had a lower content than wilderness indicating losses of P during cycling in the grazed control treatment. Phosphorus fractionation suggested that with increasing superphosphate rates inorganic P primarily accumulated in a form adsorbed to Al hydrous oxides and as calcium phosphate compounds whilst organic P accumulated in both labile forms and forms associated with humic compounds. In the fertilised sites both inorganic and organic P accumulated in the soil profile to a depth of 20 cm.     

Impacts of forest gaps on soil properties and processes in old growth northern hardwood-hemlock forests

We examined the influence of treefall gaps on soil properties and processes in old growth northern hardwood-hemlock forests in the upper Great Lakes region, USA. We found significantly greater solar radiation, soil moisture contents and soil temperatures in gaps compared to adjacent closed canopy plots. Gaps had significantly less exchangeable base cations (K, Ca, and Mg) compared to forest plots in the upper mineral soil (0–25 cm). Gaps also had significantly more dissolved organic N and extractable nitrate at depth (25–50 cm), indicating increased nutrient leaching in gaps. In-situ N mineralization was significantly greater in gaps and edge plots compared to forest plots. We found significantly greater potential N mineralization (measured in the laboratory at 25°C and 40% water holding capacity) in forest compared to gap plots. Microbial biomass N was significantly greater (ca. two-fold) in the gap edge compared to both gaps and closed forest. Using principal component analyses we found that edge plots were positively correlated with all principal components, indicating increased in-situ and potential N mineralization, microbial biomass N, soil NO₃⁻ and NH₄⁺, and soil organic matter. The gap edge may be a region of optimal microclimate and substrate to enhance microbial biomass and activity within these forest ecosystems. Responsible Editor: Bernard Nicolardet     

Base Cation and Nitrogen Budgets for a Mixed Hardwood Catchment in South-central Ontario

There is growing concern that available base cation pools in soil are declining in eastern North America and that some forests are approaching nitrogen (N) saturation due to the combined effects of acid deposition and harvesting. To assess these concerns, elemental mass balances for calcium (Ca), magnesium (Mg), potassium (K), and N were conducted over a 17-year period in a representative mixed hardwood forest (HP4) in the Muskoka-Haliburton region in central Ontario, Canada. On average, 76% of the N measured in bulk deposition, which is a conservative estimate of total N deposition, was retained in HP4, with tree uptake accounting for over half of the retained N. Year-to-year variations in annual NO₃ export were affected by climate variations, although the low annual NO₃-N concentrations (80–156 g/L) suggest that HP4 is not approaching N saturation. Losses of Ca, Mg, and K in stream export plus accumulation in trees (more than 12 cm in diameter at breast height) exceeded inputs in deposition by 296, 76.2, and 53.6 kg/ha, respectively, over the 17-year period. Inclusion of mineral weathering estimates obtained using PROFILE, zirconium (Zr) depletion, and total analysis correlation failed to balance Ca losses from HP4, and calculations indicate that between 98 and 145 kg/ha (depending on mineral weathering estimate) was lost from the soil exchangeable pool between 1983 and 1999. These losses were supported by repeated field measurements, which showed that the exchangeable Ca concentrations and soil pH decreased over the 17-year period, particularly in the upper soil horizons. When mineral weathering estimates are included, mass balance calculations generally indicated that there was no net loss of Mg and K from HP4, which was confirmed by our soil measurements. At present, there is sufficient Ca in the soil exchangeable pool to sustain forest growth at HP4; however, continued losses of Ca due to leaching and harvesting at the present rate may ultimately threaten the health and productivity of the forest within just a few decades.     

Effects of litter incorporation and nitrogen fertilization on the contents of extractable aluminium in the rhizosphere soil of tea plant (Camallia sinensis (L.) O. Kuntze)

The effects of litter incorporation and nitrogen application on the properties of rhizosphere and bulk soils of tea plants (Camellia sinensis (L.) O. Kuntze) were examined in a pot experiment. Total of 8 treatments included four levels of tea litter additions at 0, 4.9, 9.8, and 24.5 g kg^–1 in combination with two N levels (154.6 mg kg^–1 and without). After 18 months of growth the rhizosphere soil was collected by removing the soil adhering to plant roots and other soil was referred to as bulk soil. The dry matter productions of tea plants were significantly increased by N fertilization and litter incorporation. The effect of litter was time-depending and significantly decreased the content of exchangeable Al (Al_ex, by 1 mol L^–1 KCl) and Al saturation at 9 months after litter incorporation whereas soil pH was not affected, although the litter contained high Al content. After 18 months, the contents of extractable Al by dilute CaCl₂, CuCl₂ + KCl, NH₄OAC, ammonium oxalate and sodium citrate (Al_CaCl2, Al_Cu/KCl, Al_NH4OAC, Al_Oxal, and Al_Cit respectively) and Al_ex, were not affected by litter application, except that of Al_CaCl2 in the rhizosphere soil which was decreased following litter additions. Nitrogen fertilization with NH₄ ⁺ (urea and (NH₄)₂SO₄) significantly reduced soil pH, the contents of exchangeable Ca, K, Mg and base saturation while raised extractable Al levels (Al_CaCl2, Al_Cu/KCl, Al_NH4OAC, and Al_ex). In the rhizosphere soils exchangeable K accumulated in all treatments while exchangeable Ca and Mg depleted in treatments without litter application. The depletions of Ca and Mg were no longer observed following litter incorporation. This change of distribution gradients in rhizosphere was possibly due to the increase of nutrient supplies from litter decomposition and/or preferable root growth in soil microsites rich in organic matter. Lower pH and higher extractable Al (Al_CaCl2, Al_ex, and Al_NH4OAC) in the rhizosphere soils, regardless of N and litter treatments, were distinct and consistent in all treatments. Such enrichments of extractable Al in the rhizosphere soil might be of importance for tea plants capable of taking up large amounts of Al.     

Effects of fertilization and liming on the chemical soil conditions and element distribution in forest soils

Summary The distribution and storage of major elements in acid soils from a spruce and a beech forest was investigated after fertilization of NH₄NO₃ and KCl followed by Ca and Mg fertilization by 2 liming applications. All fertilizers were applied on top of the soil without mixing. Most of the added Ca and Mg was detected in the humus layer, a significant part of it still in carbonatic form. The effect of liming on mineral soil pH is very low, and was only observed in the 0–10 cm layer. However, base saturation of the mineral soil increased. The storage of C and N of the humus layer was not affected. N fertilization increased the N storage of the soil only under beech, but was followed by heavy NO₃-losses with seepage water under spruce. High leaching rates for K were also found in the spruce stand. The amount of K that was not leached increased the pool of exchangeable K in the deeper soil layer.     

Soil physiochemical changes following 12 years of annual burning in a humid–subtropical tallgrass prairie: a hypothesis

Burning is known to stimulate growth of grassland vegetation, promote species diversity, and inhibit natural invasion by woody plants. However, the frequency at which grasslands are burned as part of their management can affect soil nutrient content and, ultimately, productivity. The objective of this study was to characterize changes in soil physical and chemical properties in a native tallgrass prairie after 12 years of annual burning. In 1989, five soil samples from the 0 to 10 cm depth were collected along a transect through a 3 ha parcel of native tallgrass prairie in central Arkansas. Soil sampling was repeated in 2001 to assess changes over time. Results showed that soil bulk density, electrical conductivity, extractable P, Na, Fe, and Mn decreased significantly (P < 0.05), while soil organic matter, total N and C, and the C/N ratio increased significantly (P < 0.05) within the 12-year period during which annual burning was the only imposed management practice. Mean extractable K, Ca, Mg, S, and Zn levels were all lower in 2001 than in 1989, but differences were not significant, while soil pH did not change. The results of this study indicate that annual export of several essential plant nutrients during prescribed burning of relatively small, remnant prairie fragments exceeds annual imports from atmospheric deposition and/or organic matter mineralization. Annual prescribed burning may be too frequent to maintain optimal ecosystem functioning and productivity. Decreasing the frequency of prescribed burning for native grassland management may help to retain more soil nutrients to sustain a higher level of productivity.     

The relationship of vegetation to environmental factors in Wangsuk stream and Gwarim reservoir in Korea: II. Soil environments

This paper presents a quantitative account of vegetation–soil environmental factor relationships in the Wangsuk stream (WS) and the Gwarim reservoir (GR) in Korea. Vegetation and the following soil variables were investigated in May, August and October 2004: pH, conductivity, water content, organic matter, total nitrogen content, NH₄–N content, PO₄–P content, total Ca, Mg, K, and Na content, extractable Ca, Mg, K and Na content, soil texture, distance from the channel, and elevation above water level. Species richness, diversity and ratio of hydrophyte occupation in WS were different from those in GR. Species richness was higher in WS, whereas the ratio of hydrophyte occupation was higher in GR. There were large temporal and spatial variations in plant distribution in the riparian and aquatic zones of WS but only slight variations in those of GR. These differences might have arisen from differences in flooding regime, distance from the stream channel related to elevation above water level, and soil properties such as soil texture and available nutrients. The median values of organic matter, total nitrogen, NH₄–N, PO₄–P and extractable Ca, Mg, K and Na contents in the soil were higher in GR than in WS. Sandy loam and loamy sand were common soil types in WS and clay loam and sandy clay loam in GR. Ten vegetation groups in WS and six in GR were identified using TWINSPAN. DCCA indicated that the distance from the stream channel was most strongly related to plant distribution and this reflected the spatial distribution of plant species in WS. In both WS and GR, NH₄–N content in soil and soil texture were important factors for the distribution of species in May, August and October. Spatial and temporal heterogeneity of soil variables were related to species distribution.     

鼎湖山主要森林类型土壤交换性阳离子含量及其季节动态特征

研究鼎湖山自然保护区马尾松林、马尾松荷木混交林和季风常绿阔叶林三种代表性森林类型表层土壤(0~20cm)交换性阳离子含量及其季节动态。结果表明:土壤交换性阳离子含量因元素种类、森林类型和季节不同而异。三种森林土壤交换性阳离子含量都表现为:Al3+>H+>K+>Ca2+、Mg2+、Na+。几乎所有调查的阳离子含量在阔叶林显著高于马尾松林和混交林,但后两者之间大多数阳离子含量差异不显著。鼎湖山森林土壤可交换性阳离子含量虽然较高,但盐基饱和度却很低。马尾松林、混交林和阔叶林土壤可交换性阳离子含量在1997年6月份分别为:58.3、84.5和118.7mmolc/kg,盐基饱和度分别为:5.5%、3.2%和4.5%。三种森林土壤交换性Ca2+、Mg2+、K+和H+含量季节差异极显著(P<0.001),但交换性Al3+含量只在马尾松林土壤存在极显著的季节性差异(P<0.001)。同一元素季节变化大小程度趋向马尾松林>混交林>阔叶林。森林土壤交换性Ca2+、Na+和H+含量与土壤pH值相关关系不明显,但交换性Mg2+、K+和Al3+与土壤pH值间呈极显著负相关。     

The effects of pruning,fertilizers, and organic amendments on lowbush blueberry production

A four-year field study was conducted on a Hebert gravelly sandy loam (pH 4.5) in Nova Scotia to assess the effects of pruning management and seven fertility amendments on lowbush blueberry (Vaccinium augustifolium Ait) production (yield, above ground and root tissue composition) and soil fertility. Pruning by oil burning produced higher fruit yields than flail mowing but burning had the opposite effect on the plant N content (with a lesser influence on above ground Mn and Zn). None of the fertility treatments (chicken manure, dairy manure, swine manure, urea, sawdust, NPK, NPK+S+Lime+Micronutrients) produced fruit yields significantly greater than the control. Treatments provided the equivalent of 50kg total N/ha/2-yr cycle. Treatments influenced tissue N, P, K, Ca, Mg, B, Mn, Cu, Zn and Mo levels. In general, the three manure treatments produced the highest levels of plant macronutrients; the urea treatment produced the lowest levels of plant nutrients. In most cases, extractable levels of soil P, K, Ca and Mg were highly correlated with the plant tissue content of these elements. Overall, the dairy manure treated soils were the highest in soil fertility.     

黔中喀斯特山区村域稻田土壤理化特性的空间变异特征及空间自相关性

以贵州省安顺市西秀区旧州镇文星村为研究区域,采用地统计学方法,研究了黔中喀斯特山区土壤容重、总孔隙度、毛管持水量、毛管孔隙度、通气孔隙度等物理特性与土壤pH、有机质、速效养分(S、Si、N、P、K、Fe、Zn、Cu、Mn)、全量养分(N、P、K)、交换性盐(Ca、Mg)及阳离子交换量等化学特性的空间变异特征及自相关性。在土壤各特征值中,pH、毛管孔隙度变异系数分别为4.59%、8.28%、9.83%,为弱变异;其他变异系数在10%-100%之间,为中等程度变异。半方差分析表明,土壤毛管持水量、通气孔隙度、毛管孔隙度、速效养分(S、Si、Cu、Mn)、全量养分(N、P、K)、交换性盐(Ca、Mg)及阳离子交换量的C₀/(C₀+C)<25%,表现为强烈的空间自相关性;容重、pH、速效养分(N、P、K、Fe、Zn)及有机质的C₀/(C₀+C)在25%-75%之间,表现为中等空间自相关性,而Moran''s I指数分析表明,除毛管孔隙度、有效S、速效P及有效Mn的空间自相关性较弱外,其他均呈正的显著空间自相关性。根据克里金插值图,在研究区域内土壤毛管孔隙度及毛管持水量与pH、速效养分(S、Si、Zn、Cu、)全P、全N、有机质、交换性Ca、Mg及阳离子交换量在东北方向和西北角分布较低,在西南角方向土壤容重及通气孔隙度分布较低,而pH、速效K、有效Cu、全P、全K、有机质、阳离子交换量分布较高,且速效养分(N、K、S、Cu)、全P、有机质的含量及阳离子交换量均存在从西南向东北方向递减的趋势。     

模拟氮沉降下南方针叶林红壤的养分淋溶和酸化

以中国科学院红壤生态实验站林草生态试验区针叶林红壤为研究对象,在恒温(20 ℃)条件下,通过大土柱（直径10 cm、高60 cm）,8个月间隙性淋溶试验模拟研究了不同氮输入量（0、7.8、26和52 mg N/月/柱）对针叶林红壤NO₃^-、NH₄⁺、H⁺和土壤盐基离子(Ca²⁺、Mg²⁺、K⁺、Na⁺⁾淋溶以及土壤酸化的影响.结果表明,土壤交换态盐基总量、Ca²⁺和Mg²⁺淋溶量随氮输入量的增加而增加,土壤交换态Na⁺和K⁺则无明显影响.4种N输入处理的土壤交换态盐基总量净淋溶（淋溶出的盐基与淋洗液累计输入的盐基之差）分别占土壤交换性盐基总量的13.9%、18.6%、31.8% 和57.9％,土壤交换态Ca²⁺净淋溶分别占土壤交换性Ca²⁺总量的19.6%、25.8%、45.3%和84.8%,土壤交换态Mg²⁺净淋溶分别占土壤交换性Mg²⁺总量的4.4%、6.1%、10.9%和17.1%.随氮输入量增加,表层土壤pH值逐渐下降,4种N输入处理的表层土壤pH（KCl）分别为3.85、3.84、3.80和3.75;随氮输入量增加,淋溶液中无机氮、NO₃^-和H⁺逐渐增加.氮沉降可促进针叶林红壤的有机氮矿化,加速养分淋失和土壤酸化.     

Effects of throughfall manipulation on soil nutrient status: results of 12 years of sustained wet and dry treatments

To investigate the potential effects of changing precipitation on forest ecosystems, the Throughfall Displacement Experiment (TDE) was established on Walker Branch Watershed, Tennessee, in 1993. Three different throughfall amounts were tested: ?33% (DRY); ambient (no change, AMB); and +33% (WET). Throughfall manipulations had no statistically significant effects on total C, N, exchangeable Ca²⁺, Mg²⁺, bicarbonate‐extractable P, or extractable SO₄^2? in soils after 12 years of sustained treatments. Increased K⁺ inputs in the WET treatment resulted in relative increases in exchangeable K⁺compared with the AMB and DRY treatments. Soil C, N, and extractable P declined in all treatments over the 12‐year study, and the declines in N were inexplicably large. Field observations contrasted with earlier simulations from the Nutrient Cycling Model (NuCM), which predicted greater decreases in exchangeable K⁺, Ca²⁺, Mg²⁺, and extractable P in the order WET>AMB>DRY, and no change in C, N, and extractable SO₄^2?. The failure of the NuCM model to accurately predict observed changes is attributed to the lack of mechanisms for deep rooting and the transfer of throughfall K⁺ from one plot to another in the model. Measurements of element availability using resin membranes during the final years showed higher values in wet and lower values in dry treatments compared with ambient conditions for mineral N, K, Mn, Zn, and Al, but the opposite for B, Ca, and Mg. In the cases of Ca and Mg, the patterns in resin values were similar to those at the soil exchange sites (greatest in the dry treatment) and appeared to reflect pretreatment differences. This study showed that while longer term changes in soil nutrients are likely to occur with changes in precipitation, potential changes over this 12‐year interval were buffered by ecosystem processes such as deep rooting.     

Chemical composition of forest floor and consequences for nutrient availability after wildfire and harvesting in the boreal forest

In boreal forests of eastern Canada, wildfire has gradually been replaced by clearcut harvesting as the most extensive form of disturbance. Such a shift in disturbance may influence the chemical properties of the forest floor and its capacity to cycle and supply nutrients, with possible implications for forest productivity. We compared the effects of stem-only harvesting (SOH), whole-tree harvesting (WTH) and wildfire on the chemical composition of forest floor organic matter and nutrient availability for plants, 15–20 years after disturbance in boreal coniferous stands in Quebec (Canada). The forest floor on plots of wildfire origin was significantly enriched in aromatic forms of C with low solubility, whereas the forest floor from SOH and WTH plots was enriched with more soluble and labile C compounds. The forest floor of wildfire plots was also characterized by higher N concentration, but its high C:N and high concentration of ¹⁵N suggest that its N content could be recalcitrant and have a slow turnover rate. Total and exchangeable K were associated with easily degradable organic structures, whereas total and exchangeable Ca and Mg were positively correlated with the more recalcitrant forms of C. We suggest that the bulk of Ca and Mg cycling in the soil–plant system is inherited from the influx of exchangeable cations in the forest floor following disturbance. The buildup of Ca and Mg exchangeable reserves should be greater with wildfire than with harvesting, due to the sudden pulse of cation-rich ash and to the deposition of charred materials with high exchange capacity. This raises uncertainties about the long-term availability of Ca and Mg for plant uptake on harvested sites. In contrast, K availability should not be compromised by either harvesting or wildfire since it could be recycled rapidly through vegetation, litter and labile organic compounds.     

Vegetation-soil relations in the lowlands of south-west Tasmania

A geographic survey of 14 south-west Tasmanian sedgeland-heaths revealed that soil organic matter is related to: water content: total nitrogen (N): total and exchangeable sodium (Na), calcium (Ca) and magnesium (Mg); exchangeable potassium (K) cation exchange capacity; and total exchangeable bases. However, total and available phosphorus (P), total K and Iron (Fe). pH level and percentage base saturation were found to be Independent of organic content. Most of the soil nutrient capital is contained In the A₀ horizon, the depth of which was found to be positively related to the time elapsed since the last fire. There is no clear relationship between rock type and soil fertility, but there is evidence of soil-vegetation interaction. The sedgeland-heath species have lower concentrations of P, Ca and Mg in their foliage and are more efficient In the withdrawal of P and K upon tissue senescence than the surrounding scrub and forest species. Over a vegetation transition from sedgeland-heath to forest on uniform geology there was a change in soil type. The forest was found to have more fertile soils and a higher concentration of nutrients in the above-ground biomass than the adjacent sedgeland-heath. The ecotone was burnt between 20–30 years prior to sampling, but the fire did not kill all the forest trees, and the structural differences suggest a mare rapid recovery of forest species. Soil fertility appears to be an important factor in controlling the rate of recovery and succession following a fire, especially if the nutrient-rich organic layer is burnt.     

祁连山西水林区土壤阳离子交换量及盐基离子的剖面分布

以祁连山西水林区分布的棕钙土、灰褐土、栗钙土和高山草甸土为对象,研究了阳离子交换量和盐基离子(K+、Na+、Ca2+、Mg2+)的剖面分布规律及其与土壤理化因子的关系。结果表明:土壤阳离子交换量(CEC,介于4.80—48.10 cmol/kg)和盐基总量(TEB,介于4.67—21.34 cmol/kg)随剖面深度的增加逐渐减小,不同土壤类型的大小顺序为:灰褐土>高山草甸土>栗钙土>棕钙土;土壤盐基组成以Ca2+、Mg2+为主(占TEB的比例平均为71.6%、22.9%),K+、Na+所占比例较低(占TEB的比例平均为3.3%、2.2%);棕钙土、灰褐土和栗钙土盐基离子的剖面分布由浅至深呈现:K+≈Ca2+>Na+≈Mg2+,高山草甸土盐基离子则呈现:K+>Na+>Mg2+>Ca2+。不同土壤类型间盐基离子的含量及饱和度随发生层次不同存在较大差异。土壤有机质是CEC的主要贡献因素,粉粒对CEC也有显著的促进作用,而砂粒、CaCO3对CEC有显著抑制作用。土壤生物复盐基作用弱于淋溶作用,造成盐基饱和度较大(BSP,介于44.4%—97.2%),并随剖面深度的增加逐渐增大。相关性分析表明,土壤交换性Na+、Mg2+的含量及饱和度均呈极显著正相关,交换性Na+、Mg2+饱和度与CaCO3含量呈极显著正相关;pH值与BSP呈极显著正相关;土壤速效P含量与CEC呈极显著正相关,速效K含量与交换性K+含量呈极显著正相关。     

Changes in the soil after clearing tropical forest

Summary About one-and-a-half acres of tropical forest, of known mass and chemical composition, was cleared and burned. Soil changes during clearing and two years' cropping were studied.Following burning, approximately all the K, Ca, and Mg in the vegetation were accounted for by the rise in exchangeable K, Ca, and Mg in the soil. There was a marked rise in soil pH. A small but significant increase in C and N was attributed to admixture of parts of the vegetation with the soil.Following cultivation, there was a rapid loss of nutrients by leaching and erosion during the first year and a substantial loss of K and Mg, but smaller loss of Ca in the second year. Losses of calcium were less and of potassium more under the local practice of shifting cultivation than under cultivation treatments involving clearing of roots followed by bare fallow or a maize-cassava rotation. Depths of cultivation had little effect on nutrient losses. Losses of organic matter in the first year were rapid due to oxidation of unhumified material. They were much reduced in the second year. Greater production of food was obtained from the maize-cassava rotation than by local practice.     

Is decline in high altitude eucalypt forests related to rainforest understorey development and altered soil bacteria following the long absence of fire?

Abstract The objective of this study was to identify attributes of the understorey vegetation, soil root biomass, soil chemistry and microbial community that may be associated with tree decline in high altitude eucalypt forests in Tasmania. The sites studied were in healthy eucalypt forest, forest in decline and forest containing dead eucalypts dominated by rainforest, in north‐east (Eucalyptus delegatensis forest) and in north‐west (Eucalyptus coccifera forest) Tasmania. In both regions bare ground, rock and shrubby species were associated with healthy sites whereas decline sites were associated with moss and a tall understorey with a high percentage cover of rainforest species. Healthy sites had low root biomass in the top 10 cm of the soil profile relative to decline and rainforest sites. Seedlings of high altitude species were grown in rainforest soil (0.314% N and 0.060% P) and healthy eucalypt soil (0.253% N and 0.018% P). The four eucalypt species studied had similar root to shoot ratio in the two soils, but the rainforest species, Nothofagus cunninghamii and Leptospermum lanigerum, had higher root to shoot ratio in the healthy eucalypt than in the rainforest soil. We produced three soil filtrates: (i) fungi and bacteria present; (ii) bacteria only present and; and (iii) sterile, from healthy, decline and rainforest sites in north‐east and in north‐west Tasmania and used linseed as a germination bioassay. Filtrates from the north‐east decline and rainforest sites induced a significantly greater dysplastic germination response than healthy sites in (i) and (ii) filtrates, but this was not found in filtrates from sites in the north‐west. We conclude that while the development of a rainforest understorey and elevated soil root biomass in the long absence of fire is generally associated with high altitude eucalypt decline, altered bacterial and/or chemical attributes of soil are not always associated with high altitude eucalypt decline.