车载式变量施药机控制系统设计与试验

施药控制是提高作业质量、减少化学污染、降低生产成本的关键技术。该文基于单片机AT89C52,采用滞环控制法,设计了一种车载式变量施药机控制系统。该系统能够根据施药机行走速度自动变更喷药量,实现施药量不变。试验表明：加速度小于0.4 m/s2时,实际施药量与设定施药量之间的误差不超过8%,且雾化效果良好、生产效率高,还可以减少农药的残留和对环境的污染,能够满足农业生产的需要。     

Nutrient limitation of litter decomposition with long-term secondary succession: evidence from controlled laboratory experiments

Purpose

Understanding ecosystem processes such as litter decomposition in response to dramatic land-use change is critical for modeling and predicting carbon (C) cycles. However, the patterns of litter decomposition along with long-term secondary succession (over 100 years) are not well reported, especially concerning nutrient limitations on litter decomposition.

Materials and methods

To clarify the response of litter decomposition to changes in soil nutrient availability, we conducted four incubation experiments involving soil and litter and nutrient addition from different successional stages and investigated the changes in microbial respiration and litter mass loss.

Results and discussion

Our results revealed that microbial respiration increased with succession without any litter addition (1.19~1.73 mg C g^?1 soil), and litter addition significantly promoted microbial respiration (16.5~72.9%), especially in the early successional stage (grassland and shrubland). The decomposition rate of the same litter decreased with succession. In addition, nitrogen (N) and phosphorus (P) addition showed significant effects on litter decomposition and microbial respiration; P addition promoted litter decomposition (2.4~15.3%) and microbial respiration (10.1~34.5%) in all successional stages, while N addition promoted litter decomposition (4.0~10.3%) and microbial respiration (5.4~27.2%) in all except the last stage of succession, which showed a negative effect on litter decomposition (??7.5%) and microbial respiration (??6.1%), indicating possible N saturation of litter decomposition and microbial respiration.

Conclusions

This work highlights that soil nutrient availability and successional stages need to be taken into account to predict the changes to litter decomposition in response to global changes.

     

基于高通量测序的土壤微生物群落结构对土地利用方式的响应

为探究土地利用方式对土壤微生物群落的影响,对彭州市境内5种常见土地利用方式(城市绿地、农业用地、人工林地、滩涂地、撂荒地)下的土壤细菌和真菌进行了高通量测序.共检测到细菌37门106纲278目491科959属2137种,主要优势菌门为变形菌门(Proteobacteria)、放线菌门(Actinobacteria)、酸...     

施用CO_2气肥对保护地黄瓜产量的影响

本文通过对保护地黄瓜施用ＣＯ２气肥，结果表明，施肥后促进了黄瓜的生长发育，株高、叶片数及座果率增加，增强了抗病性，前期增产４０．５４～４７．９４％，总产量增加２１．１０～２８．５６％。阐明了在保护地施用ＣＯ２气肥是黄瓜高产高效生产的有效措施之一。     

陕西省耕地生产能力的时空分布

为了明确陕西省耕地生产能力的现状,该文利用2008-2010年陕西省各县平均粮食产量数据,结合GIS分析描述陕西省各县耕地实际利用强度、理论利用强度、耕地可实现增产潜力和理论增产潜力及其空间分布变化规律;利用1978-2008年陕西省粮食产量和消费数据计算耕地压力指数的时序变化规律。结果表明:耕地实际利用强度较小地区集中在陕北中部、关中西部,这些地区提高利用强度空间较大,是生产技术投入和劳动力投入的主要区域;耕地理论利用强度呈现出中西部地区高,北部和东南部地区低的分布规律;耕地压力指数时序表明陕西省自1978年以来,耕地压力年级间波动较大,近几年由于科技进步和政策导向致使耕地压力减小,耕地保护与耕地占用之间矛盾缓和;可实现增产潜力较大区域分布于陕北中部和关中西部,而陕南大部分地区可实现增产潜力较小,陕北北部和关中北部可实现生产潜力居中;耕地理论增产潜力呈东南部高,西北部低的空间分布规律,该文为陕西省耕地利用规划、土地整理和粮食安全提供科学依据。     

Aboveground dominant functional group predicts belowground properties in an alpine grassland community of western China

Purpose  

It has been suggested that above and belowground interactions produce important feedbacks in natural ecosystems. It is necessary to study the relationships between aboveground plant functional group traits and belowground biomass and soil chemical properties in natural grasslands.     

The Cd‐tolerant rice mutant cadH‐5 is a high Cd accumulator and shows enhanced antioxidant activity

To investigate the mechanism of cadmium (Cd) detoxification in rice (Oryza sativa L.), a Cd‐tolerant mutant cadH‐5, obtained by an Agrobacterium tumefaciens‐based gene‐delivery system, was used for a Cd‐tolerance and accumulation study. After 15 d of exposure to 0.75 mM CdCl₂, significant phenotypic differences were observed between the wild type (WT) and cadH‐5. When exposed to 0.5 mM CdCl₂, higher Cd levels were accumulated in cadH‐5 root cell wall, root cytosol, and membranes than those in WT. However, Cd concentrations in root tissues varied in both WT and cadH5. No significant difference of hydrogen peroxide (H₂O₂) concentrations was observed between WT and cadH‐5, while contents of cell‐wall polysaccharides and phytochelatins (PCs) in the mutant were higher compared to WT. The ratios of reduced glutathione to oxidized glutathione (GSH : GSSG) and ascorbate to dehydroascorbate (ASC : DHA) were lower in WT than in cadH‐5, while the NADPH : NADP⁺ ratio was different to the ratios of GSH : GSSG and ASC : DHA; the ascorbate peroxidase (APX, EC 1.11.1.11), glutathione peroxidase (GR, EC 1.6.4.2), dehydroascorbate reductase (DHAR, EC 1.8.5.1), and monodehydroascorbate reductase (MDHAR, EC 1.6.5.4) activities were lower in WT compared to cadH‐5. Our results indicate that under long‐term Cd stress, cadH‐5 plants can accumulate more Cd with more PC. Also, the redox status of ASC‐GSH cycle was more inhibited in WT than in cadH‐5 plants, rendering WT less able to scavenge reactive oxygen species (ROS). The cadH‐5 mutant maintains relatively high ASC, GSH, and NADPH concentrations, ratios of ASC : DHA, GSH : GSSG, and NADPH : NADP⁺, as well as antioxidative enzymatic activities and PC concentrations. Thus, it is tolerant of relatively high Cd accumulation.     

中国超级杂交稻育种研究的进展与策略探讨

介绍了中国超级杂交稻育种的目标,技术路线和育种理论,综述了中国超级杂交稻育种研究的概况,以及在亲本选育,品种选育和分子育种技术等方面取得的进展,阐述了通过加强水稻种质资源的创新与利用,扩大亲本遗传差异,提高水稻生物学产量,改善水稻生理机能等技术策略,选育出综合性状优良的超级杂交稻新组合,进一步提高中国超级杂交稻产量水平。     

青钱柳悬浮培养细胞三萜酸的分离及结构鉴定

通过大孔树脂吸附、硅胶柱层析、Sephadex LH-20凝胶层析、半制备高效液相色谱及重结晶对青钱柳悬浮培养细胞三萜酸进行分离纯化,获得5个单体三萜酸,经高分离度快速液相-飞行时间质谱(RRLC-TOF/MS)、核磁共振氢谱(1H NMR)和核磁共振碳谱(13C NMR)等分析,分别被鉴定为2α-羟基齐墩果酸、2α-羟基熊果酸、白桦脂酸、齐墩果酸、熊果酸,其中2α-羟基齐墩果酸和白桦脂酸是首次在青钱柳中得到分离鉴定.