Comments on the paper by Kemmitt et al. (2008) ‘Mineralization of native soil organic matter is not regulated by the size, activity or composition of the soil microbial biomass - A new perspective’ [Soil Biology & Biochemistry 40, 61-73]: The biology of the Regulatory Gate

Kemmitt et al. (Kemmitt, S.J., Lanyon, C.V., Waite, I.S., Wen, Q., Addiscott, T.M., Bird, N.R.A., O'Donnell, A.G., Brookes, P.C., 2008. Mineralization of native soil organic matter is not regulated by the size, activity or composition of the soil microbial biomass - a new perspective. Soil Biology & Biochemistry 40, 61-73) recently proposed the “Regulatory Gate” hypothesis, which states that decomposition of soil organic matter (SOM) is regulated solely by abiotic factors. Without studying the mechanisms of such regulation, Kemmitt with coauthors challenged the classical Winogradsky theory of soil microbiology and questioned the concept of autochtonous and zymogenous microbial populations. In this letter, we revive the significance of microbial activity for SOM decomposition especially for the short-term (hours to weeks) processes and show that the “Regulatory Gate” is (micro)biologically driven.We explain the results of the three experiments in Kemmitt et al. (2008) from a microbiological point of view and suggest that SOM decomposition is mainly regulated by exoenzymes. We criticize the abiotic Regulatory Gate hypothesis based on bottleneck processes and pools limiting the SOM decomposition rate, comparison of constant and changing environmental conditions, as well as the connection between community structure and functions. We explain the results of Kemmitt et al. (2008) according to the properties of soil microbial community: functional redundancy and inconsistency between the excessive (but largely inactive) pool of total microbial biomass and the real mineralization activity. Finally, we suggest that to gain new perspectives on SOM decomposition and many other biochemical processes, future studies should focus on hot spots of (micro)biological activity (i.e., the rhizosphere, drillosphere, detritosphere, biopores, etc.) rather than on the bulk soil.     

Climate change effects on soil carbon dynamics and greenhouse gas emissions in Abies fabri forest of subalpine, southwest China

The Abies fabri forest on the eastern slope of the Gongga Mountain is a typical subalpine dark coniferous forest in southwestern China. The soil carbon dynamics and greenhouse gas emissions in the A. fabri forest in future climates were simulated by the Forest-DNDC (denitrification-decomposition) model. Three future climate scenarios (B1, A1B and A2) predicted by the Intergovernmental Panel on Climate Change (IPCC) were selectively investigated. The simulation showed that at elevated temperature and precipitation, the annual change of soil organic carbon (SOC) decreased in the forest floor pool but increased in the mineral soil pool. The increases in the CO₂, N₂O and NO emissions from soil were also quantified. The results indicated that elevated temperature and precipitation influenced the soil carbon dynamics, and significantly increased the greenhouse gas emissions from the soil in the A. fabri forest of subalpine.     

Methane uptake in soils from Pinus radiata plantations, a reverting shrubland and adjacent pastures: Effects of land-use change, and soil texture, water and mineral nitrogen

Afforestation and reforestation of pastures are key land-use changes in New Zealand that help sequester carbon (C) to offset its carbon dioxide (CO₂) emissions under the Kyoto Protocol. However, relatively little attention has been given so far to associated changes in trace gas fluxes. Here, we measure methane (CH₄) fluxes and CO₂ production, as well as microbial C, nitrogen (N) and mineral-N, in intact, gradually dried (ca. 2 months at 20 °C) cores of a volcanic soil and a heavier textured, non-volcanic soil collected within plantations of Pinus radiata D. Don (pine) and adjacent permanent pastures. CH₄ fluxes and CO₂ production were also measured in cores of another volcanic soil under reverting shrubland (mainly Kunzea var. ericoides (A. Rich) J. Thompson) and an adjacent pasture. CH₄ uptake in the pine and shrubland cores of the volcanic soils at field capacity averaged about 35 and 14 μg CH₄-C m⁻² h⁻¹, respectively, and was significantly higher than in the pasture cores (about 21 and 6 μg CH₄-C m⁻² h⁻¹, respectively). In the non-volcanic soil, however, CH₄-C uptake was similar in most cores of the pine and pasture soils, averaging about 7-9 μg m⁻² h⁻¹, except in very wet samples. In contrast, rates of CO₂ production and microbial C and N concentrations were significantly lower under pine than under pasture. In the air-dry cores, microbial C and N had declined in the volcanic soil, but not in the non-volcanic soil; ammonium-N, and especially nitrate-N, had increased significantly in all samples. CH₄ uptake was, with few exceptions, not significantly influenced by initial concentrations of ammonium-N or nitrate-N, nor by their changes on air-drying. A combination of phospholipid fatty acid (PLFA) and stable isotope probing (SIP) analyses of only the pine and pasture soils showed that different methanotrophic communities were probably active in soils under the different vegetations. The C18 PLFAs (type II methanotrophs) predominated under pine and C16 PLFAs (type I methanotrophs) predominated under pasture. Overall, vegetation, soil texture, and water-filled pore space influenced CH₄-C uptake more than did soil mineral-N concentrations.     

中国生态用地研究: 内涵、分类与时空格局

  目的  从数量和质量双重角度分析生态用地的时空演化特征,探讨生态用地数量与质量变化的耦合关系,可推动区域生态环境保护及其可持续发展。  方法  引入景观连通性指数,提出了一种改进的基于数量和质量视角（QBQ,Quality-based quantity）的生态用地时空演变综合评估方法,对研究区生态用地的净变化和改进前、后基于数量和质量的生态用地变化进行了探讨。  结果  大南昌都市圈生态用地不断向非生态用地转变,生态用地净面积共减少1345.86 km²;不少县市生态用地出现了不同程度的碎片化现象,耕地和水域稳定性下降,二者QBQ值均有所减少;1 km阈值距离下,各县市不同类型生态用地的景观连通性存在较大差异,改进后除水域的QBQ值增加外,其余生态用地QBQ值均呈减少趋势。  结论  研究期内大南昌都市圈生态用地数量与质量的变化均呈下降趋势,通过引入景观连通性指数,能够深入了解生态用地数量与质量结构的变化,从而更真实地反映生态用地实际变化特征。     

虫口密度和温度对乌蔹莓鹿蛾生长发育的影响

为探索乌蔹莓鹿蛾的人工饲养条件, 就幼虫饲养密度(每瓶1 头、3 头、5 头、7 头、9 头)和温度(25 ℃、28 ℃、31 ℃)对乌蔹莓鹿蛾的发育历期、存活率和取食等进行了研究。结果显示, 与群体饲养相比, 单头饲养的乌蔹莓鹿蛾幼虫的发育历期长, 成活率低, 取食量较大。在25~31 ℃的环境温度下, 乌蔹莓鹿蛾幼虫的发育历期随温度升高而缩短, 28~31 ℃较有利于幼虫生长发育, 28 ℃的存活率最高(79.47%), 31 ℃时幼虫取食量最大(2.45 g·头^-1)。在人工饲养条件下, 初龄幼虫以3~5 头群体饲养为宜, 3 龄以后以单头饲养为宜, 饲养温度以28~31 ℃为宜。     

Temporal change in spatial variability of soil respiration on a slope of Japanese cedar (Cryptomeria japonica D. Don) forest

Although information regarding the spatial variability of soil respiration is important for understanding carbon cycling and developing a suitable sampling design for estimating average soil respiration, it remains relatively understudied compared to temporal changes. In this study, soil respiration was measured at 35 locations by season on a slope of Japanese cedar forest in order to examine temporal changes in the spatial distribution of soil respiration. Spatial variability of soil respiration varied between seasons, with the highest coefficient variation in winter (42%) and lowest in summer (26%). Semivariogram analysis and kriged maps revealed different patterns of spatial distribution in each season. Factors affecting the spatial variability were relief index (autumn), soil hardness of the A layer (winter), soil hardness at 50 cm depth (spring) and the altitude and relief index (summer). Annual soil respiration (average: 39 mol m⁻² y⁻¹) varied from 26 mol m⁻² y⁻¹ to 55 mol m⁻² y⁻¹ between the 35 locations and was higher in the upper part of the slope and lower in the lower part. The average Q₁₀ value was 2.3, varying from 1.3 to 3.0 among the locations. These findings suggest that insufficient information on the spatial variability of soil respiration and imbalanced sampling could bias estimates of current and future carbon budgets.     

Effects of haying and agricultural practices on a declining species: The North American wood turtle, Glyptemys insculpta

In North America, the spatio-temporal scale of deforestation has resulted in a 94% decrease in temperate forests within 360 years. Despite the enormous scale of this disturbance, agriculture is so pervasive in modern society that its impacts are highly underappreciated. We investigated the impact of current agricultural practices on a disturbance-dependent species in southern Québec, Canada. Of 30 wood turtles (Glyptemys insculpta) followed via radio-telemetry, 20% died as a result of agricultural activities. Anthropogenic mortality estimates for adults and juveniles in 1998 were 0.10 and 0.18, respectively. For 1999, these values were 0.13 and 0.17, respectively. Of those turtles that survived, many had injuries inflicted by agricultural machinery. Sub-lethal mutilation rates for adults were 90 ± 3% in both years, whereas the maximum frequency for juveniles was 57%. A Carapace Mutilation Index was derived to quantify the distribution and severity of injuries observed. Only male and juvenile Carapace Mutilation Index values differed significantly. Adults had significantly more carapace injuries and limb amputations on their right sides. This bilateral asymmetry of injuries resulted from of a combination of turtle flight behavior and traditional harvesting practices. We reiterate the recommendations of forage researchers: setting the cutting height of disc mowers to 100 mm increases harvest yields, reduces wear on machinery, and decreases soil erosion. A by-product of such a change in cutting height is that turtle mortality and injury rates should be reduced, as wood turtle carapace height is <87 mm. Without changes in agricultural practices, this population will be extirpated.     

幼虫密度对小菜蛾生长发育和繁殖的影响

为明确小菜蛾幼虫密度对其种群增长的影响,在室内条件下[温度(22±1)℃,RH70%~80%,光周期12L∶12D]对不同幼虫密度[1头.皿1、10头.皿1、20头.皿1、30头.皿1、40头.皿1(直径为9 cm)]饲养的小菜蛾生长发育及繁殖进行了研究。结果表明,幼虫密度对小菜蛾幼虫、蛹的发育历期和存活率、蛹重及成虫生殖等有显著影响。幼虫和蛹历期均以10头.皿1处理最短,且随幼虫密度增加而显著延长。幼虫至蛹的存活率以10头.皿1、20头.皿1处理较高,显著高于1头.皿1和40头.皿1处理。蛹重以1头.皿1处理最重,并随幼虫密度的增加而显著变轻。不同幼虫密度下羽化的成虫畸形率差异显著,以10头.皿1处理最低,其余随幼虫密度的增加而升高。成虫产卵量以1头.皿1处理最高,随着幼虫密度增加,产卵量逐渐下降。雌、雄蛾寿命分别以40头.皿1、10头.皿1处理最长,密度过高时或过低雌雄蛾寿命显著缩短。生命表分析表明,幼虫密度对小菜蛾种群增长指数影响显著,以10头.皿1处理种群增长指数最高,幼虫密度过高或过低,种群增长指数下降。因此,幼虫密度是影响小菜蛾种群增长的重要因子之一。     

Effects of elevated atmospheric CO2, prolonged summer drought and temperature increase on N2O and CH4 fluxes in a temperate heathland

In temperate regions, climate change is predicted to increase annual mean temperature and intensify the duration and frequency of summer droughts, which together with elevated atmospheric carbon dioxide (CO₂) concentrations, may affect the exchange of nitrous oxide (N₂O) and methane (CH₄) between terrestrial ecosystems and the atmosphere. We report results from the CLIMAITE experiment, where the effects of these three climate change parameters were investigated solely and in all combinations in a temperate heathland. Field measurements of N₂O and CH₄ fluxes took place 1-2 years after the climate change manipulations were initiated. The soil was generally a net sink for atmospheric CH₄. Elevated temperature (T) increased the CH₄ uptake by on average 10 μg C m⁻² h⁻¹, corresponding to a rise in the uptake rate of about 20%. However, during winter elevated CO₂ (CO₂) reduced the CH₄ uptake, which outweighed the positive effect of warming when analyzed across the study period. Emissions of N₂O were generally low (<10 μg N m⁻² h⁻¹). As single experimental factors, elevated CO₂, temperature and summer drought (D) had no major effect on the N₂O fluxes, but the combination of CO₂ and warming (TCO₂) stimulated N₂O emission, whereas the N₂O emission ceased when CO₂ was combined with drought (DCO₂). We suggest that these N₂O responses are related to increased rhizodeposition under elevated CO₂ combined with increased and reduced nitrogen turnover rates caused by warming and drought, respectively. The N₂O flux in the multifactor treatment TDCO₂ was not different from the ambient control treatment. Overall, our study suggests that in the future, CH₄ uptake may increase slightly, while N₂O emission will remain unchanged in temperate ecosystems on well-aerated soils. However, we propose that continued exposure to altered climate could potentially change the greenhouse gas flux pattern in the investigated heathland.     

聚天门冬氨酸钙盐对水稻田面水中三氮动态变化的影响

利用桶栽试验探究不同浓度水平的聚天门冬氨酸钙盐(PASP-Ca)对水稻田面水中铵态氮(NH_4~+)、硝态氮(NO_3~-)和总氮(TN)浓度动态变化的影响。结果表明,施氮后,田面水中TN、NH_4~+和NO_3~-分别于第1,3,9天达到最大值,随后逐渐降低。NO_3~-/TN多在0.1以下,(NH_4~++NO_3~-)/TN多在0.5以上。因此,可以将NH_4~+和TN作为农田水污染防治的主要监测指标,NO_3~-作为辅助指标。添加一定浓度的PASP—Ca能对田面水中氮素浓度的变化起到缓释作用,其中0.3%浓度水平的PASP—Ca效果相对较好,田面水中NH_4~+和TN的下降速率分别为3.452,4.806mg/(L·d),与单施氮肥(CK)相比,分别降低了11.68%和16.25%;同时,NH_4~+的平均浓度为6.999mg/L,较CK低了3.88%;NO_3~-的平均浓度为0.396mg/L,较CK低了24.83%;TN的平均浓度为20.077mg/L,较CK提升了3.10%。施氮后田面水中TN浓度随时间呈对数递减,而NH_4~+浓度在施氮后3天内随时间呈对数增加,之后随时间呈对数递减趋势。施氮后的9天内是防止稻田田面水中氮素流失的关键时期。