Rhizospheric and heterotrophic respiration of a warm-temperate oak chronosequence in China

Plot trenching and root decomposition experiments were conducted in a warm-temperate oak chronosequence (40-year-old, 48-year-old, 80-year-old, and 143-year-old) in China. We partitioned total soil surface CO₂ efflux (R_S) into heterotrophic (R_H) and rhizospheric (R_R) components across the growing season of 2009. We found that the temporal variation of R_R and R_H can be well explained by soil temperature (T₅) at 5 cm depth using exponential equations for all forests. However, R_R of 40-year-old and 48-year-old forests peaked in September, while their T₅ peaks occurred in August. R_R of 80-year-old and 143-year-old forests showed a similar pattern to T₅. The contribution of R_R to R_S (RC) of 40-year-old and 48-year-old forests presented a second peak in September. Seasonal variation of R_R may be accounted for by the different successional stages. Cumulative R_H and R_R during the growing season varied with forest age. The estimated R_H values for 40-year-old, 48-year-old, 80-year-old and 143-year-old forests averaged 431.72, 452.02, 484.62 and 678.93 g C m⁻², respectively, while the corresponding values of R_R averaged 191.94, 206.51, 321.13 and 153.03 g C m⁻². The estimated RC increased from 30.78% in the 40-year-old forest to 39.85% in the 80-year-old forest and then declined to 18.39% in the 143-year-old forest. We found soil organic carbon (SOC), especially the light fraction organic carbon (LFOC), stock at 0-10 cm soil depth correlated well with R_H. There was no significant relationship between R_R and fine root biomass regardless of stand age. Measured apparent temperature sensitivity (Q₁₀) of R_H (3.93 ± 0.27) was significantly higher than that of R_R (2.78 ± 0.73). Capillary porosity decreased as stand age increased and it was negatively correlated to cumulative R_S. Our results emphasize the importance of partitioning soil respiration in evaluating the stand age effect on soil respiration and its significance to future model construction.     

我国东南丘陵山区土壤肥力的综合评价

土壤肥力是土壤的养分状况以及土壤在供应植物生理所需物质时所处的环境条件这两者的有机结合，本文根据模糊（Ｆｕｚｚｙ）数学和多元数理统计分析原理，建立了一个定量的土壤肥力综合评价方法。     

农用化学品及废弃物对土壤环境与食物安全的影响

综述了农用化学品和废弃物(化肥、农药、酸沉降、污水污泥、畜禽粪便和“三废”等)利用现状及其对土壤环境污染与食物安全的影响。     

紫云英添加对土壤团聚体组成及有机碳分布的影响

以湖北省武汉市稻田土壤为研究对象,分别设置不添加紫云英(CK)、添加2%土壤质量的紫云英(G1)、添加4%土壤质量的紫云英(G2)3个处理,进行干湿交替模拟培养试验,研究培养60、120和180d土壤团聚体组成及团聚体内有机碳的分布特征。结果表明:添加紫云英培养120 d增加了各处理2 mm团聚体含量,培养60 d时G1处理的增幅最大(78.08%),培养120 d时G2处理的增幅最大(77.31%),且显著提高了团聚体的平均重量直径。不同培养时期添加紫云英均提高了土壤的有机碳含量,且G2处理土壤有机碳含量高于G1处理,各处理随着培养时间的增加有机碳含量先增加后降低。团聚体中有机碳含量均随着粒级的减小而降低,紫云英添加培养180 d时团聚体各粒级有机碳含量均有所提升,且2 mm团聚体的有机碳含量增幅最大(17.17%～43.67%)。紫云英添加培养120 d时主要增加大团聚体内各有机碳组分的相对含量,180 d时显著增加了微团聚体内细颗粒有机碳的含量。     

不同土壤熏蒸剂对烤烟苗床杂草的药效试验

以烟草品种龙江911为供试材料,对适每地、维博亩和斯美地这3种不同土壤熏蒸剂防除烟草苗床杂草效果进行了试验。结果表明,适每地和斯美地这两种土壤熏蒸剂对苗床杂草均有较好的防除效果。综合防除效果及安全性等因素．以斯美地效果最理想,其次是适每地,均可在黑龙江省烟区推广使用。     

Recovery of saturated hydraulic conductivity under secondary succession on former pasture in the humid tropics

Landscapes in the humid tropics are undergoing a continuous change in land use. Deforestation is still taking its toll on forested areas, but at the same time more and more secondary forests emerge where formerly agricultural lands and pastures are being abandoned. Regarding soil hydrology, the extent to which secondary succession can recover soil hydrological properties disturbed by antecedent deforestation and pasture use is yet poorly understood. We investigated the effect of secondary succession on saturated hydraulic conductivity (Ks) at two soil depths (0-6 and 6-12 cm) using a space-for-time approach in a landscape mosaic in central Panama. The following four land-use classes were studied: pasture (P), secondary forest of 5-8 years of age (SF5), secondary forest of 12-15 years of age (SF12) and secondary forest of more than 100 years of age (SF100), each replicated altogether four times in different micro-catchments across the study region. The hydrological implications of differences in Ks in response to land-use change with land use, especially regarding overland flow generation, were assessed via comparisons with rainfall intensities.Recovery of Ks could be detected in the 0-6 cm depth after 12 years of secondary succession: P and SF5 held similar Ks values, but differed significantly (α = 0.05) from SF12 and SF100 which in turn were indistinguishable. Variability within the land cover classes was large but, due to sufficient replication in the study, Ks recovery could be detected nonetheless. Ks in the 6-12 cm depth did not show any differences between the land cover classes; only Ks of the uppermost soil layer was affected by land-use changes. Overland flow - as inferred from comparisons of Ks with rainfall intensities - is more likely on P and SF5 sites compared to SF12 and SF100 for the upper sample depth; however, generally low values at the 6-12 cm depth are likely to impede vertical percolation during high rainfall intensities regardless of land use.We conclude that Ks can recover from pasture use under secondary succession up to pre-pasture levels, but the process may take more than 8 years. In order to gain comprehensive understanding of Ks change with land use and its hydrological implications, more studies with detailed land-use histories and combined measurements of Ks, overland flow, precipitation and throughfall are essential.     

草甘膦对毛竹笋用林土壤理化性质的影响分析

在毛竹笋用林中长期使用草甘膦且又不进行施肥等抚育措施,会对土壤的结构产生影响,造成容重增加,总孔隙度降低,不利于竹鞭的正常生长,通过增施有机肥可有效降低草甘膦对土壤结构的影响.试验结果表明,长期使用草甘膦对土壤有机质有一定影响,但对全氮、全磷、水解氮、速效磷、速效钾、pH值、交换性氢和交换性铝均未有显著差异.     

The response of land snail assemblages below aspens to forest fire and clear-cutting in Fennoscandian boreal forests

Species can persist in a landscape with recurrent disturbances either through local survival or by dispersing to sites of a preferred successional stage. This study investigated in what extent forest floor dwelling land snails survived forest fires and clear-cutting. Snail fauna in LFH (litter, fermenting litter and humus) samples below retained aspen trees in disturbed areas were compared with samples under scattered aspens in adjacent forests by extracting snails from LFH samples below five aspens in several stands of each type (five forest fires, six clear-cuts, and seven undisturbed forests). LFH samples from burnt sites had a higher pH than from forests, but on average a lower abundance of individual snails (11 vs. 30 in 0.5 l LFH) and 50% lower species density (3 vs. 6 species). The abundances and species densities in the clear-cuts were less affected. There was generally a positive relationship between pH and both species density and abundance in all the stand types. Burning apparently depleted the snail fauna considerably and some species may be dependent on dispersal if they are to recover within the burnt area, while the snail assemblages at clear-cuts did not differ significantly in species composition from adjacent forests. The positive relationship between pH and snail prevalence on the burnt sites raises questions regarding the pre- and post-fire spatial variation in pH (and available minerals) within and among stands and how it relates to snail survival rates and their capacity to track suitable places after the disturbance. Retained aspens at clear-cuts seem to harbour a forest like land snail fauna.     

A case of habitat complementation in forest pests: Pine processionary moth pupae survive better in open areas

Little attention has been given to the relevance of habitat complementation concept to the population dynamics of insect herbivores. Late instar larvae of the pine processionary moth (PPM) Thaumetopoea pityocampa move in late winter from pine stands, their feeding habitat, to neighbouring habitats where they pupate until next summer. They search for sunny exposed soil which they can find in open areas. We investigated the effect of both forest cover and soil origin, with three matching types (pine stand, broadleaved stand and open area) on the survival of PPM pupae. The microclimatic soil variables which significantly differentiated cover types and soil origins were the maximum temperature and the mean relative humidity in spring, soon after pupation has occurred. A significant effect of the cover type, but not of the soil origin, was detected on the proportion of dead, emerged or diapausing pupae. Open areas were more suitable for pupae survival than forest covers (pine or broadleaved stands), due to warmer and more humid soil conditions. In this study, we provide one of the first examples of habitat complementation for an insect herbivore, as PPM population can benefit from the combination of pine habitats for the feeding of larvae with open habitats for pupation. The presence of broadleaved stands next to pine stands might also represent an ecological trap for PPM pupae, as broadleaved habitats may turn to be less suitable for pupae survival in spring when the apparition of leaves creates cooler conditions.     

Soil CO2 efflux in an Afromontane forest of Ethiopia as driven by seasonality and tree species

Variability of soil CO₂ efflux strongly depends on soil temperature, soil moisture and plant phenology. Separating the effects of these factors is critical to understand the belowground carbon dynamics of forest ecosystem. In Ethiopia with its unreliable seasonal rainfall, variability of soil CO₂ efflux may be particularly associated with seasonal variation. In this study, soil respiration was measured in nine plots under the canopies of three indigenous trees (Croton macrostachys, Podocarpus falcatus and Prunus africana) growing in an Afromontane forest of south-eastern Ethiopia. Our objectives were to investigate seasonal and diurnal variation in soil CO₂ flux rate as a function of soil temperature and soil moisture, and to investigate the impact of tree species composition on soil respiration. Results showed that soil respiration displayed strong seasonal patterns, being lower during dry periods and higher during wet periods. The dependence of soil respiration on soil moisture under the three tree species explained about 50% of the seasonal variability. The relation followed a Gaussian function, and indicated a decrease in soil respiration at soil volumetric water contents exceeding a threshold of about 30%. Under more moist conditions soil respiration is tentatively limited by low oxygen supply. On a diurnal basis temperature dependency was observed, but not during dry periods when plant and soil microbial activities were restrained by moisture deficiency. Tree species influenced soil respiration, and there was a significant interaction effect of tree species and soil moisture on soil CO₂ efflux variability. During wet (and cloudy) period, when shade tolerant late successional P. falcatus is having a physiological advantage, soil respiration under this tree species exceeded that under the other two species. In contrast, soil CO₂ efflux rates under light demanding pioneer C. macrostachys appeared to be least sensitive to dry (but sunny) conditions. This is probably related to the relatively higher carbon assimilation rates and associated root respiration. We conclude that besides the anticipated changes in precipitation pattern in Ethiopia any anthropogenic disturbance fostering the pioneer species may alter the future ecosystem carbon balance by its impact on soil respiration.