Microbiotic Crusts and Ecosystem Processes

Microbiotic crusts are biological soil crusts composed of lichens, cyanobacteria, algae, mosses, and fungi. The biodiversity of these crusts is poorly understood; several cosmopolitan species dominate in most areas, but many species are confined to one or a few sites. Nitrogen fixation by organisms within the crust can be the dominant source of nitrogen input into many ecosystems, although rates of nitrogen input are limited by water availability, temperature, and nitrogen loss from the crust. Photosynthetic rates of the microbiotic crust can be 50% of those observed for higher plants, but the contribution of crusts to carbon cycling is not known. The microbiotic crust binds soil particles together, and this significantly increases soil surface stability and resistance to erosion. Greenhouse studies have found that crusts can enhance seed germination, seedling survivorship, and plant nutrient status, but further experiments are needed under field conditions. Crusts are extremely susceptible to surface disturbance and fire, and disruption of crusts can decrease soil fertility and stability resulting in lower nutrient availability for vascular plants and significant soil loss from the ecosystem.     

根系氮吸收过程及其主要调节因子

氮（N）是植物根系吸收最多的矿质元素之一．全球变化将使土壤中N的有效性发生改变,影响陆地生态系统碳分配格局与过程．研究根系N吸收及其调控对预测生态系统结构和功能具有重要理论意义．由于土壤中存在多种形态的N源,长期的生物进化和环境适应导致植物根系对不同形态N的吸收部位、机理及调控有较大差别．因此,植物长期生长在以某一形态N源为主的土壤上就形成了不同的N吸收机制和策略．本文简述了近年来在植物根系N吸收和调控方面的最新研究进展,重点评述了不同形态N在土壤中的生物有效性,根系N吸收部位,N在木质部中的装载和运输,不同形态N（NO3^-、NH4^＋和有机氮）的吸收机制,以及根系N吸收的自身信号调控和环境因子对根系N吸收的影响．在此基础上,提出了目前根系N吸收研究中存在的几个问题．     

显脉金花茶的光合生理特性研究

采用LI-6400便携式光合测定系统(Li-Cor Inc., USA)对显脉金花茶光合特性进行研究。结果表明：(1)在夏季,显脉金花茶叶片的P_n日变化呈单峰曲线,最高峰出现在中午11：00。其最大净光合速率（P_max）为3.81 μmol·m^-2·s^-1、光饱和点（LSP）为459.9 μmol·m^-2·s^-1、光补偿点（LCP）为6.9 μmol·m^-2·s^-1。显脉金花茶的光饱和点和光补偿点都比较低,表明其是一种阴生植物。（2）在控制光照强度和温度的条件下,CO₂浓度小于800 μmol·mol^-1,P_n几乎呈直线上升,升高CO₂浓度可使显脉金花茶的净高合速率增大,提高了叶片对光能的利用率。其叶片CO₂饱和点(CSP)大约在1 200 μmol·mol^-1左右,CO₂的补偿点（Г^*）为70.1 μmol·mol^-1,最大羧化速率（V_cmax）为17.5 μmol·m^-2·s^-1,最大电子传递速率（J_max）为40 μmol·m^-2·s^-1。     

温度和水分对草甸草原土壤氧化亚氮产生速率的调控

通过试验室模拟试验,研究了调控草甸草原黑钙土N₂O产生速率的因素.结果表明,土壤水分对草甸草原土壤N₂O产生速率有重要影响(F=6.149,P＜0.01).但相关性分析表明,草甸草原土壤含水量与N₂O的产生速率间线性相关不显著.就土壤N₂O的产生速率而言,温度的影响远低于土壤水分的影响(F=2.275,P=0.106).土壤水分和温度对不同生长阶段的草甸草原土壤N₂O产生速率的调控作用主要表现为阶段性的多阶多项式关系：y=ax³+bx²+cx+d,其中a、b、c、d是常数.     

Low rates of expression profile divergence in highly expressed genes and tissue-specific genes during mammalian evolution

Evolutionary rates provide important information about the pattern and mechanism of evolution. Although the rate of gene sequence evolution has been well studied, the rate of gene expression evolution is poorly understood. In particular, it is unclear whether the gene expression level and tissue specificity influence the divergence of expression profiles between orthologous genes. Here we address this question using a microarray data set comprising the expression signals of 10,607 pairs of orthologous human and mouse genes from over 60 tissues per species. We show that the level of gene expression and the degree of tissue specificity are generally conserved between the human and mouse orthologs. The rate of gene expression profile change during evolution is negatively correlated with the level of gene expression, measured by either the average or the highest level among all tissues examined. This is analogous to the observation that the rate of gene (or protein) sequence evolution is negatively correlated with the gene expression level. The impacts of the degree of tissue specificity on the evolutionary rate of gene sequence and that of expression profile, however, are opposite. Highly tissue-specific genes tend to evolve rapidly at the gene sequence level but slowly at the expression profile level. Thus, different forces and selective constraints must underlie the evolution of gene sequence and that of gene expression.     

太行山南麓坡面土壤碳氮空间变异性及其影响因素

太行山南麓是我国华北平原的重要生态屏障,研究该区域土壤养分的空间变异性对土石山区林业生态建设具有重要意义.本研究以太行山南麓典型坡面(人工林坡地和自然荒坡地)为对象,采用网格法布设采样点,运用经典统计学、地统计学和约束性排序相结合的方法对土壤养分的空间变异性进行分析.结果 表明:1)太行山南麓的土壤全碳(TC)含量为6...     

象山港日本对虾增殖放流的效果评价

日本对虾是中国近海重要的增殖品种,2010年象山港分两批次放流日本对虾苗种约1.67亿尾。通过对放流苗种存活状况、洄游分布、生长特性及回捕情况的跟踪调查,对象山港日本对虾的增殖效果做出初步评价。结果表明:(1)日本对虾放流苗种在8月中旬成为补充群体,集中于港区底部进行索饵育肥;9月中旬,第1、2批放流苗种的平均体长分别达到95.4 mm和71.4 mm,成活率分别约为0.79%和1.06%;10月上旬,随着港区水温降低,增殖苗种资源量锐减。(2)协方差分析表明:日本对虾增殖群体和自然群体的体长-体重关系存在显著性差异,增殖群体的体征状况明显优于自然群体。(3)日本对虾放流苗种在港区主要为桁杆拖虾和地笼网渔业所利用,在港区滞留期间,回捕率约为0.25%。总结发现:栖息地破坏及放流苗种的过早利用是制约象山港日本对虾增殖效果的重要因素,优化增殖策略、保护港区生态环境应是今后港区增殖工作的重点。     

烯效唑干拌种对小麦氮素积累和运转及籽粒蛋白质品质的影响

通过田间试验,研究了不同烯效唑干拌种剂量对3个不同筋力小麦品种植株氮素积累、运转和籽粒蛋白质品质的影响,结果表明,基因型、环境及烯效唑处理对小麦品质的影响效应依次减小,且均达到了极显著水平,但三者的互作效应较小。烯效唑处理后提高了不同生态点下不同小麦品种籽粒蛋白质含量和产量,处理后的面筋含量和沉淀值增加,面团形成时间和稳定时间延长;干拌种增加了开花期各营养器官中的氮素含量和单株氮素积累量,花后氮素总转移量、总转移率及其对籽粒氮的贡献率极显著提高,且处理后旗叶中可溶性蛋白质含量在花后15 d内均显著高于对照;对籽粒中氮含量而言,烯效唑处理后提高了灌浆初期籽粒中的非蛋白氮含量,花后5—20 d内均高于对照,灌浆期间籽粒蛋白氮含量均高于对照,因而处理后的粗蛋白质含量变化动态特点为谷底高、回升快。研究认为,烯效唑处理如同基因、环境一样独立影响小麦籽粒品质,而烯效唑处理后提高了开花初期旗叶中的可溶性蛋白质含量和花前营养器官中氮素含量及花后氮素转运量,可能是其提高籽粒非蛋白氮含量、促进籽粒蛋白质含量增加和蛋白质质量提高的重要原因之一,烯效唑干拌种对小麦籽粒蛋白质品质的改善具有广适性。     

Growth and nutrition of birch seedlings in relation to potassium supply rate

Summary Growth of hydroponically cultivated birch seedlings (Betula pendula Roth.) at sub- and supra-optimum potassium supply rates was investigated. Potassium was supplied either as a relative addition rate (r _k = 5, 10, 15 and 20% increase day^-1) or as fixed concentrations (0.2, 3, 6, 12 and 15 mM) in the culture solution. After an acclimation period the growth rate of the seedlings in the suboptimum treatments reached values close to the treatment variable, the relative rate of K-addition. Deficiency symptoms, in the form of chlorosis and necroses along the leaf margins, developed initially in all suboptimum treatments, but very few new symptoms appeared once the seedlings had reached the phase of steady-state nutrition and growth. At supra-optimum K-supply levels, i.e. at 0.2–15 mM K in the culture solution, no symptoms of deficiency or toxicity developed, and the relative growth rate of the seedlings remained maximum. The relative growth rate of the seedlings was linearly related to the plant K-status for K contents ranging from 0.2 to 1.0% of dry weight (DW). At higher internal K-concentrations, 1.0–3.0% DW, no further increase in relative growth rate was achieved. A shortage of K resulted in a decrease in the net assimilation rate. This effect was counterbalanced by the absence of shift in he leaf weight ratio as well as by the production of relatively thin leaves. The fraction of dry matter allocated to roots decreased in K-limited plants, as did the leaf contents of soluble carbohydrates and starch.     

Analysis of bacterial populations in a grassland soil according to rates of development on solid media

Abstract The process of colony formation by bacteria from grassland soil sampled in April, July and September was simulated by a colony-forming curve (CFC). The CFC was a super-imposition of several component curves (cCFC) given theoretically by the first order reaction (FOR) model [3,6]. The pattern of FOR model curves was not influenced by the time of sampling and four cCFCs were always recognized during an incubation period of 160 h. It was considered that the CFC describes an inherent property of the bacterial population of the field. Bacterial isolates were obtained from colonies produced in each of four cCFCs on agar plates. Isolates corresponding to one cCFC were classified as one group. The bacterial isolates were characterized by morphological and physiological tests and subsequently clustered. Few oligotrophic bacteria were obtained among bacteria which produced visible colonies within 63 h of incubation time. On the other hand, approx. 50% of bacteria which produced v colonies after 63 h were oligotrophic bacteria. The time required for the appearance of the first colony, t _r of the FOR model, was very similar in the isolates belonging to one group. A close linear relationship was observed between t _r value and doubling time of isolates.