Size matters: What have we learnt from microcosm studies of decomposer fungus–invertebrate interactions?

The ongoing research ‘boom’ in soil ecology has been advanced by a widespread use of laboratory experiments to investigate mechanisms that could not be unravelled with field observations alone. Interactions between soil fungi and invertebrates have received considerable attention due to their trophic and functional importance in belowground systems. Saprotrophic cord-forming basidiomycete fungi are major agents of primary decomposition in woodland ecosystems, where they are also an important source of nutrition for fungal-feeding soil invertebrates. A plethora of microcosm experiments, with their main benefit being that they enable most variables to be kept constant while just a few are manipulated, have provided detailed insights into the ecology of fungus–invertebrate interactions. This review identifies important trends from this body of work (including a meta-analysis of grazing effects on fungal growth and wood decomposition) and explores the extent to which these patterns are supported by the few related experiments conducted in more complex mesocosm and field systems. Grazing in microcosms reduced fungal growth and increased decomposition, but with interaction-specific magnitude, reflecting invertebrate feeding preferences for different fungi. Macro-invertebrates (woodlice and millipedes) had stronger effects than micro- (e.g. nematodes) and meso- (e.g. collembola) invertebrates. This greater grazing pressure generally increased enzyme activities beneath mycelia during interactions in which wood decay was increased. Top-down effects of fungal-feeding can be extrapolated to more complex systems, but only for macro-invertebrates, particularly woodlice. Soil enzyme activity was stimulated, in microcosms and more complex systems, by short-term or low intensity grazing, but reduced when large areas of mycelium were removed by high-intensity grazing. Effects of differential fungal palatability on invertebrate populations are evident in microcosm studies of collembola. These bottom-up effects can be extrapolated more broadly than top-down effects; fungal community dominance determined collembola abundance and diversity, in mesocosms, and woodlouse abundance in the field. Using, as a case study, a series of experiments conducted at a range of scales, mechanisms underlying potential climate change effects on grazing interactions and decomposition are also explored. Biotic effects on decomposer community functioning are heterogeneous, depending on fungal dominance and the density of key macro-invertebrate taxa.     

腰果叶片氮磷钾年周期变化及再吸收效率

以6龄腰果无性系FL30为对象,采集全年12个月腰果成熟叶片样品,分析腰果叶片N、P、K年周期变化规律;并采集腰果衰老叶片样品,分析腰果树N、P、K再吸收效率.结果表明:腰果叶片N、P、K含量随生育期的改变而变化;叶片N含量从抽梢期至果实成熟呈上升趋势,果实成熟后明显下降,休眠期叶片N含量变化不大;叶片P含量从抽梢期至初果期总体呈下降趋势,初果期至休眠期则呈上升趋势；叶片N/P呈现出与N相似的年周期变化规律;叶片K含量在抽梢期呈下降趋势,初花期骤然上升,盛花坐果期继续缓慢上升,果实生长期至休眠期则呈下降趋势;腰果成熟叶片N、P、K含量显著高于衰老叶片,N、P、K再吸收率较高,再吸收效率顺序为REp＞REN＞REk.     

马铃薯缺素症状与预防措施

马铃薯在召陵区普遍种植,为增加产量和提高品质,详细介绍了马铃薯缺素症状与预防措施,以供广大薯农朋友参考.     

Assessing biogas digestate,pot ale,wood ash and rockdust as soil amendments: effects on soil chemistry and microbial community composition

Applying by-products as soil amendments to agricultural systems is growing in popularity. We aimed to assess the efficacy of some contemporary by-products to provide nutrients to crops as well as the potential harm of adding toxic elements to the environment. Four different by-products widely available in Northern Europe were tested for their effects on two nutrient-poor agricultural soils in terms of increasing available macro- and micro-nutrients as well as toxic elements. Assessing soil microbial community as a sensitive tool for evaluating soil quality was conducted with the focus on microbial activity, carbon metabolism and on Rhizobium/Agrobacterium. Wood ash increased pH and Ca_EDTA, K_EDTA and Mg_EDTA in the soils. The only increase in EDTA-extractable micronutrients in the soils was observed by applying pot ale, increasing Cu. None of the amendments increased the availability of Pb and Cd in the soils. Soils amended with the by-products thus remained similar to the unamended control but were quite different from fully mineral fertilised soils. There were no detectable adverse effects on the physiological and genetic profiles of microbial communities. The by-products were moderately beneficial and did not change the soil microbial community as much as the fully fertilised treatment with mineral fertilisers. Changes in the microbial community profiles were probably due to direct effects on microbes limited by K, Ca and N as opposed to indirect effects on plant growth. This is potentially significant in understanding how to improve impoverished and marginal soils as microbial activity affects many other ecosystem functions.     

科尔沁沙地燕麦间作箭筈豌豆与施肥对饲草养分累积、产量及水分利用的影响

为研究内蒙古科尔沁沙地水分和养分高效利用的饲用作物栽培模式，于2020-2021年在中国科学院西北奈曼沙漠化研究站开展大田试验。在燕麦灌浆期刈割后进行饲草复播，复播设置种植模式及施肥处理双因素试验，3种种植模式分别为单作燕麦（‘蒙燕1号’，SO）,单作箭筈豌豆（SV），2行燕麦与4行箭筈豌豆间作（IOV）；4种施肥处理分别为不施肥（N），施化肥（磷酸二铵，C，150 kg/hm²），施生物有机肥（润泽生物有机肥，O，900 kg/hm²），有机肥和无机肥配施（生物有机肥＋磷酸二铵，G，全量配施），探讨间作与施肥对复种燕麦、箭筈豌豆饲草养分累积、产量及水分利用的影响。结果表明：间作与施肥可显著增加饲草产量，2020年和2021年G处理较N处理鲜草产量显著提高74.0%和63.5%，干草产量显著提高55.4%和57.0%；燕麦箭筈豌豆间作系统的土地当量比大于1，表明该间作模式提高土地生产力，具有土地利用优势。间作与施肥显著增加0~60 cm土层的土壤含水量；有机肥与无机肥配施提高作物水分利用效率，整体表现为SO>IOV>SV。燕麦箭筈豌豆间作系统的养分优势主要体现在饲草氮累积量的增加，而磷钾累积量则低于单作燕麦，高于单作箭筈豌豆；2020年和2021年G处理下的燕麦间作箭筈豌豆的饲草氮累积量分别比N、C、O处理增加152.2%、21.7%、47.1%和119.8%、17.6%、41.2%。综合分析得出有机肥与无机肥配施处理是最适宜的燕麦与箭筈豌豆间作施肥方式。     

Development and detection of phosphorus deficiency in Atlantic salmon, Salmo salar L., parr and post-smolts

A pathological condition was induced in Atlantic salmon, Salmo salar L., by feeding a diet severely deficient in phosphorus. Parallel results were obtained in two consecutive experiments, one in fresh water and one in sea water. The deficiency condition was first manifest as a reduction in whole-body calcium (Ca) and phosphorus (P) levels and the development of abnormally soft and malformed bones. In later stages, growth was severely impaired and there was elevated mortality compared with fish fed a diet with sufficient phosphorus.
Two semipurified casein-based test diets were used in the experiments. The low-P diet contained only the P from casein, 3.5 g kg⁻¹ or 0.35%, whereas the reference diet was supplemented with P and contained 9.0 g kg⁻¹ or 0.9%, The diets were fed to salmon parr in fresh water (initial weight 4.7 g) and to post-smolts in sea water (initial weight 113 g) for 12 and 15 weeks, respectively. In both experiments, the fish grew adequately for a prolonged period, whereas the whole-body Ca and P levels declined almost immediately. Within a few weeks, the whole-body P content was reduced to ≊ 65% of the initial value, and Ca to 40%. The reductions in mineral content were most severe in the mineral-rich tissues, bones and scales. On gross examination, all bony structures were abnormally soft. The ribs were wrinkly, and the spine displayed scoliotic changes. These changes were correlated to the reduction in bone mineralization, and were manifest at the time when reductions in growth rate could be noted.
After the deficient fish were fed adequate levels of P for 9 weeks, their whole-body mineral levels returned to normal. The bone lesions did not heal completely during the same period of time.     

Digesta characteristics in relation to nutrient digestibility and mineral absorption in Nile tilapia (Oreochromis niloticus L.) fed cereal grains of increasing viscosity

Soluble non-starch polysaccharides (NSP) present in cereal grains may affect performance of Nile tilapia through changes in digesta characteristics. The objective of this study was to investigate whether dietary cereal grains of increasing viscosity induce changes in digesta viscosity, dry matter and volatile fatty acids (VFA) and if these changes explain differences in nutrient digestibility and mineral absorption. Four experimental diets were formulated by adding 40% grains to a basal diet to obtain a range of dietary viscosities, increasing in the order of maize, barley, wheat and rye. The diets were assigned to 16 tanks with 40 fish (mean weight 70 g) each. Digesta viscosity increased with increasing grain viscosity (P < 0.001), whereas digesta dry matter decreased with increasing grain viscosity (P < 0.05). No significant differences were found among diets in total concentration and type of VFA. Nutrient digestibility was not significantly correlated with digesta viscosity. Of all nutrients, only starch digestibility was significantly negatively correlated with digesta dry matter in the middle intestine (r = − 0.57; P = 0.03). Absorption of sodium was significantly negatively correlated with digesta viscosity in all intestinal segments (r = − 0.76 to − 0.82; P < 0.001) and positively correlated with digesta dry matter in all intestinal segments (r = + 0.60 to + 0.67; P < 0.05), except for the proximal intestine (P = 0.18). Of the other minerals, potassium and magnesium absorption were positively correlated with digesta dry matter in the distal (r = + 0.56; P = 0.03) and proximal (r = + 0.54; P = 0.04) intestine, respectively. Phosphorus absorption was significantly negatively correlated with dry matter in the stomach (r = − 0.55; P = 0.03), middle (r = − 0.58; P = 0.02) and distal (r = − 0.54; P = 0.04) intestine. In conclusion, viscous cereal grains induce increases in digesta viscosity and decreases in digesta dry matter in Nile tilapia. These changes do not explain differences in nutrient digestibility among diets, but seem more related to differences in mineral absorption. The strong negative correlations between digesta viscosity and sodium absorption suggest negative effects of dietary viscous grains on intestinal water balance.     

植物铁蛋白在人类铁营养中的作用

铁是人体所必需的微量营养元素,铁缺乏是世界上最主要的营养问题之一。笔者综述了铁的生理功能与吸收机制、植物铁蛋白的结构与功能,以及植物铁蛋白铁的饮食利用度。展望了应用天然的或转基因植物的铁蛋白作为铁补充剂改善人类铁营养缺乏问题的前景。     

花卉水培不同营养液效果比较试验初报

选择不同种类的花卉水培,采用3种不同成分的营养液进行比较试验,以清水为对照,通过对其地上部和地下部的生长状况进行比较观测,筛选出最适宜的营养液及最佳的浓度。结果表明:最适合金边虎尾兰,条纹十二卷,芦荟,石莲,绿巨人,玛丽桉,富贵竹和太阳神水培的营养液浓度组合分别是BT4,BT4,AT3,AT4,AT4,AT4,AT3和AT4。     

不同营养元素对阿月浑子苗期缺素症的影响

为防治大棚育苗期间阿月浑子常见的各种缺素症,进行了营养元素喷施试验。结果表明:当幼苗叶片由正常的绿色转变成病态的红褐色时,磷酸二氢钾有很好的防治作用,当质量分数为0.5%时,发病率仅为1.50%,比对照低13.50%,当质量分数为1.0%时,发病率为零,2个处理与对照相比差异极显著;当幼苗叶片由绿色转变成病态的淡黄色时,氯化锌和硫酸铁均有很好的防治效果,0.1%和0.2%的微量元素处理中,质量分数为0.1%时发病率分别为2.00%和3.00%,比对照分别低14.5%和13.5%,质量分数为0.2%时发病率分别为1.00%和2.50%,比对照分别低15.5%和14.0%,与对照相比差异均极显著。