Soil aggregate formation and stability induced by starch and cellulose

Soil aggregate (SA) can be formed and stabilized when soil organic matter (SOM) is decomposed in the soil. However, the relationships between the SA dynamics and SOM with different decomposition rates have not been clarified. Therefore, this study examined the effects of the addition of polysaccharides to soil on SA formation and stability. A Japanese tropical soil was incubated for 99 d at 30 °C in a dark environment following the addition of 0.5% (w/w) starch or cellulose. The decomposition rates of the amendments, and SA formation and stability were evaluated by measuring soil respiration rates, and distribution fractions of soil aggregate sizes and mean weight diameter (MWD) of SA, respectively. The cumulative soil respirations with all treatments rapidly increased until Day 12 of the incubation. The initial slope of the cumulative soil respiration in the soil with starch was significantly higher than that in the soil with cellulose. In either soil with starch or cellulose, the fractions of macro-aggregates (>1000 μm in diameter) significantly increased, respectively, compared with control soil. However, the fractions of meso-aggregates (250–1000 μm) and nano-aggregate (<20 μm) in the soil with starch significantly decreased, while those fractions in the soil with cellulose fluctuated until Day 6. The MWDs reached the maximum on Day 6, indicating the SA formation in the soils with starch or cellulose. The increasing rate of the SA formation in the starch-amended soil was greatly higher than that in the cellulose-amended soil. After Day 6, the MWDs in the soils with either polysaccharide decreased with similar trends with no significant differences between treatments, indicating similar stability of the SA in both treatments. This study showed that the different decomposability of the organic amendments might influence the SA formation differently, but not the SA stability.     

印楝素对中华稻蝗若虫呼吸作用的影响

呼吸测定试验表明，以每头印楝素5.0μg点滴3龄中华稻蝗蝗蝻前胞背板，4hCO2释放量减少，抑制率达到33％。对6龄蝗蝻测定，处理后试虫CO2释出量降低，呼吸受到抑制，而且随着时间的推移，呼吸失去了节律，图线变得近于直线。点滴法与注射法，在前期呼吸影响有所不同，点滴法随着经过的时间，呼吸抑制率提高；而注射法48h呼吸抑制率才提高，到72h达到最高，其图形为U形。     

Soil organic‐C accumulation and N availability under improved pastures established in Mediterranean oak woodlands

Long‐term effects of improved pasture establishment (with high proportion of legumes) on soil organic‐C status and N availability in Mediterranean cork oak (Quercus suber L.) woodlands were assessed. Soils were sampled beneath scattered crowns and in open areas, considering two systems: unmanaged and managed woodlands where improved pastures were installed 26 and 32 years ago. Total and labile C and N pools were measured and C and N mineralization were determined over 24 weeks laboratory incubation. Soils under improved pastures showed higher organic‐C, total‐N and net N mineralization than those under unmanaged pasture, mainly when established beneath trees. Potentially mineralizable C, C mineralization rate and microbial C were not statistically different between the unmanaged and improved pasture sites, but were higher closer to the tree than in the open area (1.8, 1.2 and 1.2 times, respectively). The qCO₂ was higher in improved pastures (1.7 times). Labile pool of C and N extracted with hot water increased under improved pasture (3.4 and 1.7 times, respectively). Results indicate that soil quality amelioration by improved pastures is stronger in the presence of oak trees. Management systems that favour oak tree maintenance and regeneration should be taken into account to reverse soil degradation.     

不同形态氮素对东北山樱幼苗根系呼吸代谢及生物量的影响

 以东北山樱（Cerasus sachalinensis Kom.）幼苗为试材，研究了不同形态氮素对根系呼吸代谢及植株生物量的影响。结果表明，在施氮量相同的条件下，施加硝态氮和酰胺态氮在整个试验过程中（28 d）均显著提高了幼苗根系活力及呼吸底物的积累，而施加铵态氮对根系活力的促进作用只延续到处理后14 d，随后根系活力和呼吸底物含量逐渐降低；硝态氮处理促进了三羧酸循环（TCA）关键酶的活性，TCA循环在呼吸代谢途径中的比例较对照提高了30.4%，呼吸代谢中间产物丙酮酸和柠檬酸增加，而磷酸戊糖途径（PPP）和交替途径（AP）较对照分别下降了35.0%和32.7%。铵态氮处理效应基本与之相反。酰胺态氮处理除对EMP关键酶活性及电子传递途径无明显影响外，与硝态氮处理效应相似；3种形态氮素处理对幼苗生长均有促进作用，对植株生物量促进作用的大小表现为硝态氮 > 酰胺态氮 > 铵态氮 > 对照。     

根际加温对无土栽培非洲菊冬季产花的影响

 试验结果表明, 非洲菊7 个切花品种冬季无土栽培根际加温可促进其产花。根温为20 ℃时显著提高了切花的产量与质量, 单株产量、花茎长、茎粗、花重较对照分别提高了71. 34 %、19. 14 %、8. 5 %、23. 72 % , 但对花径的增大作用不显著。根温为15 ℃时可显著提高切花产量, 较对照切花增产33. 21 %; 对花茎长、茎粗生长也有促进作用, 但对花径、花重无显著影响。根际加温对不同品种增加产量与提高质量效果不同, 根际加温至20 ℃时, 品种‘日’、‘签证’与‘莫尔’产量较高, 质量优良: 冬季84 d 产量可达9. 90、9. 56 与9. 30 支/株, 花径为10. 21、9. 92 与10. 05 cm , 花茎长为55. 10、53. 61 与54. 82 cm , 茎粗为0. 65、0. 63与0. 61 cm , 花重为21. 52、22. 68 与22. 50 g。     

Interaction of benzimidazole-N-sulfonamides with the cytochrome b/c1 complex of Pythium aphanidermatum

Experiments with intact cells and submitochondrial fractions of Pythium aphanidermatum (Edson) Fitz. indicated an interference of benzimidazole-N-sulfonamides with the NADH- or succinate-driven electron transport system between cytochromes b and c. Comparison with Ustilago maydis (DC) Corda and Botrytis cinerea Pers. ex Fr. revealed that this effect is Oomycetes specific. The molecular interaction between benzimidazole-N-sulfonamides and the mitochondrial cytochrome b/c₁ complex from P. aphanidermatum has been investigated. Binding assays with [¹⁴C]52232 RP (dimefluazole) indicated a time- and dose-dependent labelling of two proteins. The molecular mass of one labelled protein and the competition of the binding with antimycin A suggest that benzimidazole-N-sulfonamides interact with the Q₁-centre of cytochrome b. Furthermore, experiments with doubly labelled [³H][¹⁴C]CGA 323103 revealed a possible irreversible inactivation of the b/c₁ complex leading to covalent linkage of the dimethylsulfonamoyl moiety to the target site.     

大青叶樱桃根际微生物种群结构及其变化动态

利用选择性培养基,对2年生大青叶樱桃(Cerasus pseudocerasus)根际微生物进行了分离、鉴定和分类,分析了不同物候期根际微生物种群结构的变化。结果表明,从大青叶樱桃根际分离纯化获得的细菌分别属于15个属,以芽孢杆菌属(Bacillus)、假单胞菌属(Pseudomonas)为主;放线菌属于链霉菌属的6个类群,以白色类群(Albosporus)、黄色类群(Flavus)为主;真菌以镰刀菌(Fusarium)和木霉属(Trichoderma)为主。不同生育期根际微生物种群结构不同,落叶期根际细菌种群结构最丰富,萌芽期最少。     

An upper limit for elevated root zone dissolved oxygen concentration for tomato

It is well understood that insufficient oxygen within plant root zones can greatly diminish plant productivity. However, little is known about the effect of elevated root zone oxygen concentrations. Tomato (Lycopersicon lycopersicum Mill., cv. Trust) seedlings were grown in nutrient solutions containing dissolved oxygen (DO) concentration ranging from 5.3 to 40 mg L⁻¹ for 4 weeks. There were no visible symptoms observed on the leaves or stems in any of the treatments. Leaf chlorophyll content was higher in the 40 mg L⁻¹ treatment than with 20 and 30 mg L⁻¹ DO treatments. Two weeks from the start of the experiment, roots in the 40 mg L⁻¹ treatment exhibited stunted growth, became thicker, and had fewer side and fine roots compared to roots in the lower levels of DO treatment. Almost all the measured growth parameters (fresh and dry weights of root, stem, and leaf, leaf area, stem diameter) were significantly reduced in plants grown in the 40 mg L⁻¹ treatment compared to plants in the lower level of DO treatments, except that the plant height increased with the increasing DO concentration. Root respiration increased linearly with increasing DO concentration; however, there was no effect on leaf net CO₂ exchange rate. It is suggested that it was safe to enrich root zone DO to as high as 30 mg L⁻¹, although the growth benefit was minor by increasing DO from ambient air saturated level (∼8.5 mg L⁻¹) to 30 mg L⁻¹. Higher than 30 mg L⁻¹ could cause reduction in tomato plant growth.     

水分胁迫对抗旱性不同小麦品种叶片光合及根呼吸等生理特性的影响

以两个抗旱性不同的小麦品种西农1043、陕253为材料，采用盆栽与水培试验相结合的方式，研究水分亏缺对小麦不同生育期叶片光合及根呼吸速率等生理指标的影响。结果表明：相同水分处理下，抗旱品种西农1043与水分敏感品种陕253相比，具有较高的光合和根呼吸速率、以及相对较高的保护酶活性；水分胁迫下，两个小麦品种叶片光合和根呼吸速率及苗期叶保护酶活性均降低；两种水分处理下抗旱性强的西农1043根呼吸所占光合的比例相对高于陕253。     

Simulated rain addition modifies diurnal patterns and temperature sensitivities of autotrophic and heterotrophic soil respiration in an arid desert ecosystem

The timing and magnitude of rainfall events in arid and semiarid regions are expected to change dramatically in future decades, which will likely greatly affect regional carbon cycles. To understand how increases in rainfall affect the diurnal patterns and temperature sensitivities (Q₁₀) of soil respiration (R_S) and its key components (i.e. heterotrophic respiration (R_H) and autotrophic respiration (R_A)), we conducted a manipulative field experiment in a desert ecosystem of Northwest China. We simulated five different scenarios of future rain regimes (0%, 25%, 50%, 75% and 100% increase over local annual mean precipitation) each month from May to September in 2009. We measured R_S and R_H every three hours on 6 and 16 days after the rain addition, and estimated R_A by calculating the difference between R_S and R_H. We found that rain addition significantly increased the daily mean R_S and its components on the two measurement days during the growing season. However, the diurnal pattern was different between the two respiration components. Rain addition significantly increased the daily Q₁₀ value of R_H but suppressed that of R_A on Day 6. Rain addition had no influence on daily Q₁₀ value of both respiration components on Day 16 when soil moisture was lower. In addition, we observed significantly higher daily Q₁₀ of R_H than R_A under all five rain addition treatments, indicating that microbial respiration is more temperature sensitive than root respiration in a short-time scale in this desert ecosystem. Thus, partitioning soil respiration into its two components, and analyzing the differential responses of R_H and R_A to future climate changes should be considered for more accurate predictions of soil respiration and regional carbon cycle in these arid and semiarid regions.