不同覆盖方式对旱地果园水热特征的影响

采用垄膜覆盖(T1)、覆草(T2)和免耕无覆盖(T3)等方法,测定分析陇东旱地果园水热状况,结果表明,0—60 cm土壤温度全年T1最高,萌芽开花期至果实膨大期T2温度最低,新梢停止生长期至落叶期T3温度最低。T1地表和20 cm土壤最高温度出现在6月上旬,40 cm和60 cm出现在8月上旬,表现为浅层(0—40 cm)最高温度出现提前,而T2和T3不同土层最高温度均在8月上旬。0—25 cm不同处理土壤温度表现为晴天最高,雨天最低。除7月至8月土壤温差以T1最大外,其余时期均以T3最大,全年T2温差最小。梨树生长前期(4—6月),T3土壤含水量最小,7月以后,T3最高。梨年生长周期中,T1土壤含水量变化最小,T3最大。不同土层T1土壤容重最小,孔隙度最大,T3土壤容重最大,孔隙度最小;0—120 cm土层T1和T3土壤容重均表现为先升后降,T2为先降后稳定变化的特点。不同处理土壤营养元素含量随时间变化而降低,T3降幅最大。地面覆盖减缓了土壤养分的流失,同时增加了土壤铁、锌、硼等元素含量。     

西北旱地春小麦不同覆盖措施的温度和产量效应

在西北半干旱雨养条件下,以春小麦为材料,研究了夏季覆膜(T1)、秋季覆膜(T2)、春季覆膜(T3)、小麦碎秆覆盖(T4)、小麦整秆覆盖(T5)、夏季覆膜+麦秆还田(T6)和无覆盖对照(CK)7个处理间0—20 cm土壤温度、产量和重要农艺指标的差异。结果表明:处理间在不同生育时期、不同土层的土壤温度存在显著差异。生育时期间比较,处理间土壤温度差异以播种期—分蘖期最大、蜡熟期—成熟期次之、拔节期—灌浆中期较小;土层间比较,处理间土壤5 cm处的温度差异依次大于10 cm、15 cm、20 cm处。T6在各时期、各土层均表现出突出的增温效应,全生育期土壤平均温度较CK高0.57℃,以成熟期、播种期及分蘖期增温效果较大;其它覆盖处理存在增温和降温的双重效应,增温效应覆膜秸秆覆盖,而降温效应则秸秆覆盖覆膜,各处理的32个土壤温度测试点中,增温点次以T4最少(仅有9个),降温点次为23个,且T4降温幅度最大,全生育期0—20 cm土壤平均温度较CK低0.63℃,降温效果在播种期和分蘖期尤为突出。覆盖处理全生育期土壤平均温度表现为覆膜CK秸秆覆盖。温差最高值出现在分蘖期土壤5 cm处的T6与T4间,T6高出T44.23℃。T6可以平抑生育期间土壤温度的变化,其它5个覆盖处理则加剧土壤温度的波动,以T4处理的土壤温度波动最明显(CV为32.4%)。处理间产量、单位面积穗数、穗粒数间差异显著,而千粒重差异不显著。无论覆膜还是秸秆覆盖,都较CK穗粒数显著增加(17.4%—36.3%)。除T5较CK显著减产14.1%外,其它覆盖处理均较CK显著增产21.7%—37.3%,其中以全膜覆土穴播基础上的秋季覆膜(T2)增产最显著,适宜在西北旱地春小麦产区推广应用。土壤温度主要影响营养生长,拔节—开花期0—20 cm的土壤温度与株高高度正相关(0.77*—0.92**),但覆盖引起土壤温度的变化最终对西北旱地春小麦产量没有关键影响。     

模拟氮沉降对长江滩地杨树林土壤呼吸温度敏感性的影响

研究氮沉降量增加对土壤呼吸温度敏感性的影响,对于研究土壤呼吸在气候变化中的作用有重要意义。以长江中下游滩地杨树人工林为对象,通过定位模拟氮沉降实验的方法,研究了滩地杨树人工林生态系统土壤呼吸的变化特征和土壤呼吸各组分的温度敏感性对几种氮沉降量浓度的短期响应。结果表明:(1)各处理土壤总呼吸、土壤微生物呼吸、根系呼吸与各层次土壤温度均呈显著正相关关系,和5cm层土壤温度相关性最大。5cm层土壤温度可以解释土壤总呼吸、土壤微生物呼吸和根系呼吸季节变化的比例分别为50.5%—71.0%、51.5%—73.9%、35.7%—63.2%;(2)对照组(CK,0g N m-2a-1)土壤总呼吸、土壤微生物呼吸与根呼吸的Q10值分别为2.54、2.72和1.94;(3)在各氮添加水平中,中氮水平(MN,10g N m-2a-1)促进了土壤总呼吸、土壤微生物呼吸和植物根呼吸的温度敏感性。高氮水平(HN,20g N m-2a-1)都降低了土壤总呼吸、土壤微生物呼吸和植物根呼吸的温度敏感性,低氮水平(LN,5g N m-2a-1)降低了土壤总呼吸和土壤微生物呼吸的温度敏感性,促进了根呼吸的敏感性。     

祁连山中段林草交错带土壤水热特征及其对气象要素的响应

利用综合环境观测仪(ENVIS)的长期监测数据,分析了2002-06-01—2008-05-31期间祁连山阴坡林草交错带土壤水热特征及其与气象要素的统计关系,结果表明:1)土壤温度与空气温度年内变化格局相似,但存在滞后期,滞后时间随土壤深度增加而增加;土壤温度年际变化与气温一致,呈逐渐降低趋势。2)土壤水分表现为20—80 cm土壤水分易受外界降水过程影响,120 cm和160 cm深度土壤水分变化相对平缓;土壤水分季节性冻融过程中的主要控制因子为温度,但20—80 cm冻土的融化还受上层土壤水分融化和降雨下渗影响。3)月尺度上土壤水分和温度与气象要素的统计关系优于日尺度。利用气象要素在月尺度上建立的经验模型上对20—60 cm深度土壤温度的估算效果相对较好。     

基于FLUXNET的CLM模型总初级生产力模拟评价与误差分析

总初级生产力(gross primary productivity,GPP)的准确估计是陆地生态系统碳循环研究以及未来气候变化预测的基础。本文利用全球通量网的通量观测数据评估了CLM4.5的GPP模拟效果,结合叶面积指数(leaf area index,LAI)观测数据分析了CLM4.5模型GPP模拟误差的主要原因,并对CLM4.5模型主要的光合参数进行敏感性分析,探讨改善光合作用模拟精度的可能途径。结果表明:CLM4.5对GPP的模拟效果优于CLM4,月尺度和年尺度GPP模拟值的平均绝对偏差分别降低15%和29%。但与观测值相比,CLM4.5模拟的GPP年总量仍然具有较大偏差,平均偏差为366.06 g C·m-2·a-1。不同植被功能型GPP模拟误差具有不同的季节变化特征,误差主要发生在春季和夏季。冠层顶部比叶面积、叶片碳氮比和叶片氮含量中Rubisco氮含量所占比例是GPP模拟的3个敏感参数。未来应主要从物候期及LAI模拟的改进、磷循环过程的影响、生态系统水平光合参数集的构建等方面实现对GPP模拟精度的提高。     

桉树人工林冠层气象因子对雨季土壤水分的影响

对雷州桉树人工林集水区土壤水分及林冠层气象因子一年内(1999／10／01—2000／09／30)雨季的定位观测结果进行了典型相关分析,得出如下结果：(1)在雨季,土壤含水量(SMC)随着土壤深度变化而变化,在0-4m范围内层间含水量差异显著;雨季各层SMC主要受降雨量的影响：(2)受充沛降雨量的强烈影响,雨季各层SMC随着时间推移而逐渐升高;雨季各层含水量变异系数较干季同层次的变异系数大;(3)雨季地下50cm深(SM50)处SMC变化曲线波动较大,与太阳辐射(N、降雨量(P)、风速(W)、水汽压差(VPD)、最高温度(Tmax)相关性极显著(α=0．001);(4)较深层次(即150cm,250cm,350cm)土壤含水量变化的影响因素具有某种程度的相似性：但与较浅层(50cm)SMC的主要影响因素和变化趋势均不同;(5)在雨季,三个典型相关系数均达到显著性水平(α=0．01)。三组典型相关及重叠数值以第一典型相关值较大,第二、第三的重叠量较小,故林冠层气象因子主要由第一典型因素影响土壤含水量。林冠层气象因子通过3个典型变量可说明SMC总变异量的30．9％。     

沙质草地营造樟子松林后土壤容重的变化及其影响因子

采用野外调查和室内试验相结合,以辽宁省章古台地区不同生长阶段(包括幼龄林、中龄林、成熟林和过熟林)的20块樟子松人工固沙林样地(以临近的7块天然草地为对照)为研究对象,研究了沙质草地营造樟子松人工林后不同生长阶段0—100 cm土层土壤容重的变化及其影响因子。结果表明:天然沙质草地营造樟子松人工固沙林后,不同生长阶段樟子松林在0—10 cm土层土壤容重变化的变异系数为78%,其他土层变异系数范围为1.08%—4.35%。随着樟子松人工林林龄的增加,土壤容重变化量在0—20 cm和60—100 cm层逐渐降低,在20—60 cm层先降低,到37年左右后逐渐升高,过熟林较成熟林显著增大。林龄对不同土层容重变化的决定系数由大到小依次为40—60、60—80、20—40、10—20、0—10、80—100 cm层。土壤容重变化在60—80 cm层与土壤粗颗粒(粒径0.05 mm)含量、在0—10、20—40 cm和60—80 cm层与土壤全氮含量、在0—10、20—60 cm和80—100 cm层与土壤全磷含量、在20—40 cm和80—100 cm层与土壤全钾含量显著负相关,且土壤全氮和全磷含量对土壤容重的影响效果随土层深度的增加逐渐降低,土壤容重变化在10—20 cm层与土壤含水率、在20—40 cm层与土壤有机碳含量呈显著的正相关。总体上,沙质草地营造樟子松人工林可以改善土壤结构,提高土壤质量,建议采取封育禁牧等营林措施增加樟子松林下枯落物积累,提高土壤养分含量,同时对37年樟子松人工林逐渐进行更新。     

不同林龄柠条细根现存量比较

采用微根管技术(Minirhizotron technique)对晋西北黄土丘陵区幼林(5a)与成林(30a)柠条(Caragana korshinskii)细根动态进行了为期5a的原位观测。基于2008—2011年的观测数据,对两林龄柠条不同土层细根现存量动态进行了比较研究,并探讨了两林龄柠条细根现存量与不同年际间水热条件的差异。结果表明:在0—100 cm土壤剖面,柠条幼林与成林细根现存量的峰值均位于50 cm土层以下,成林细根现存量峰值位于50—60 cm土层,幼林细根现存量峰值则从观测期初的90—100 cm土层到观测期末的80—90 cm土层。各观测年内,两林地各土层每年生长季初(3—4月)会出现细根现存量的积累;30—100 cm土层中,幼林细根最大现存量出现时间均较成林早,而生长季末(9—10月),所有土层幼林细根现存量下降均较成林快。柠条细根现存量的垂直分布主要受土壤水分影响,季节变化受温度的影响更大,年际间细根现存量的差异主要是由于年降雨量变化;幼林细根现存量受降水、土壤水分、土壤温度等的影响比成林大。     

基于SHAW模型对农田小气候要素的模拟

能量平衡是作物冠层水热传输的基础,气象因子(如空气温度、湿度、风速和土壤温度)是影响作物活动的外界条件,而叶温反映作物的整体健康状况。对冠层状况的理解和模拟有利于了解小气候特征并加强农田管理。采用SHAW(theSimultaneousHeatandWater)模型模拟:冠层表面能量平衡,表面辐射温度,冠层中叶温、气象要素和土壤温度廓线,模型的输入数据来源于华北平原禹城综合试验站。模型很好的模拟了表面能量平衡、冠层表面辐射温度、土壤温度、冠层2/3高度以下叶温和2/3高度以上气象要素。模型模拟净辐射(Rn)的效率达到0.97,潜热(LE)和感热通量(Hs)的模拟效率分别为0.81和0.78,模拟的表面辐射温度与实测值吻合较好,其模拟效率为0.91,冠层2/3高度以下的叶温模拟效率为0.76～0.86,但该高度以上的模拟结果不理想。除了2cm深度外,各层土壤温度模拟较好。     

太岳山油松人工林土壤呼吸对模拟氮沉降的短期响应

通过对山西太岳山油松人工林进行模拟氮沉降实验,探究土壤呼吸对模拟氮沉降刺激的短期响应动态。2015年7—8月,分3次分别对同一样地进行模拟氮沉降处理,水平皆为100 kg hm~(-2)a~(-1),同时采用LI-COR8150土壤碳通量自动观测系统全天候连续监测土壤呼吸动态,探究土壤施氮前后呼吸速率的动态变化以及呼吸速率与土壤温度和湿度的关联。结果表明:3次氮沉降处理均呈现出相同规律,土壤呼吸值在施氮后1 d内达到最大值,随即下降,在施氮后第3天土壤呼吸趋于稳定;第一、二次氮沉降处理3 d后土壤呼吸恢复到处理前的状态,并未表现出显著差异(P0.05)。第三次氮沉降处理后土壤呼吸并未恢复到施氮前的状态,土壤呼吸均值由1.99μmol m~(-2)s~(-1)显著上升到3.39μmol m~(-2)s~(-1)(P0.05)。这表明,氮处理对土壤呼吸产生了持续效应。施氮后土壤呼吸与土壤温度呈极显著(P0.001)指数相关(R_s=ae~(bT)),随着时间的推移,施氮处理解释土壤呼吸的相对贡献值由60%—69%下降到14%—59%。施氮提高了土壤温度敏感系数Q_(10)值;土壤温度和湿度(R_s=ae~(bT)W~c)能更好的解释土壤呼吸变化,解释率达到49%—91%。在全球变化的背景下,研究模拟氮沉降对土壤呼吸、Q_(10)的影响,可以对进一步模拟、预测全球暖温带地区森林碳循环和碳储量提供理论基础。     

On the Transport of Nematodes by the Wind

The possible effectiveness of atmospheric transport of nematode forms (dry larvae or eggs) as a means for introducing new species to a given environment is examined. Given the measured sedimentation velocities for a range of forms (0.1 ≥ Ws ≥ 0.6 mps), the necessary conditions on the wind speed required for natural erosion are defined. With these results scenarios for lofting, transport, and diffusion of these forms are examined using relevant gaussian plume models. Results indicate that on rare occasions individuals can be deposited up to 40 km from their original location. Redepositions up to 5 km per erosion event should be fairly common occurances when dry loose soil conditions or dry tillage operations combine with optimal atmospheric conditions and the presence of significant numbers of nematodes at the surface.     

Predicting the species composition of Nardus stricta communities by logistic regression modelling

Question: Predictive models in plant ecology usually deal with single species or community types. Little effort has so far been made to predict the species composition of a community explicitly. The modelling approach presented here provides a conceptual framework on how to achieve this by combining habitat models for a large number of species to an additive community model. Our approach is exemplified by Nardus stricta communities (acidophilous, low‐productive grassland). Location: Large areas of Germany, 0–2040 m a.s.l. Methods: Logistic regression is applied for individual species models which are subsequently combined for an explicit prediction of species composition. Several parameters reflecting soil, management and climatic conditions serve as predictor variables. For validation, bootstrap and jackknife resampling procedures are used as well as ordination techniques (DCA, CCA). Results: We calculated significant models for 138 individual species. The predictions of species composition and species richness yield good agreements with the observed data. DCA and CCA results show that the community model preserves the main patterns in floristic space. Conclusions: Our approach of predicting species composition is an effective tool that can be applied in nature conservation, e.g. to assess the effects of different site conditions and alternative management scenarios on species composition and richness.     

Ion channels induced by the prion protein

Prion diseases comprise a group of rapidly progressive and invariably fatal neurodegenerative disorders for which there are no effective treatments. While conversion of the cellular prion protein (PrP^C) to a β-sheet rich isoform (PrP^Sc) is known to be a critical event in propagation of infectious prions, the identity of the neurotoxic form of PrP and its mechanism of action remain unclear. Insights into this mechanism have been provided by studying PrP molecules harboring deletions and point mutations in the conserved central region, encompassing residues 105–125. When expressed in transgenic mice, PrP deleted for these residues (Δ105–125) causes a spontaneous neurodegenerative illness that is reversed by co-expression of wild-type PrP. In cultured cells, Δ105–125 PrP confers hypersensitivity to certain cationic antibiotics and induces spontaneous ion channel activity that can be recorded by electrophysiological techniques. We have utilized these drug-hypersensitization and current-inducing activities to identify which PrP domains and subcellular locations are required for toxicity. We present an ion channel model for the toxicity of Δ105–125 PrP and related mutants and speculate how a similar mechanism could mediate PrP^Sc-associated toxicity. Therapeutic regimens designed to inhibit prion-induced toxicity, as well as formation of PrP^Sc, may prove to be the most clinically beneficial.     

Modelling corticothalamic feedback and the gating of the thalamus by the cerebral cortex

Morphological studies have shown that excitatory synapses from the cortex constitute the major source of synapses in the thalamus. However, the effect of these corticothalamic synapses on the function of the thalamus is not well understood because thalamic neurones have complex intrinsic firing properties and interact through multiple types of synaptic receptors. Here we investigate these complex interactions using computational models. We show first, using models of reconstructed thalamic relay neurones, that the effect of corticothalamic synapses on relay cells can be similar to that of afferent synapses, in amplitude, kinetics and timing, although these synapses are located in different regions of the dendrites. This suggests that cortical EPSPs may complement (or predict) the afferent information. Second, using models of reconstructed thalamic reticular neurones, we show that high densities of the low-threshold Ca2+ current in dendrites can give these cells an exquisite sensitivity to cortical EPSPs, but only if their dendrites are hyperpolarized. This property has consequences at the level of thalamic circuits, where corticothalamic EPSPs evoke bursts in reticular neurones and recruit relay cells predominantly through feedforward inhibition. On the other hand, with depolarized dendrites, thalamic reticular neurones do not generate bursts and the cortical influence on relay cells is mostly excitatory. Models therefore suggest that the cortical influence can either promote or antagonize the relay of information, depending on the state of the dendrites of reticular neurones. The control of these dendrites may therefore be a determinant of attentional mechanisms. We also review the effect of corticothalamic feedback at the network level, and show how the cortical control over the thalamus is essential in co-ordinating widespread, coherent oscillations. We suggest mechanisms by which different modes of corticothalamic interaction would allow oscillations of very different spatiotemporal coherence to coexist in the thalamocortical system.     

Australian wheat production expected to decrease by the late 21st century

Climate change threatens global wheat production and food security, including the wheat industry in Australia. Many studies have examined the impacts of changes in local climate on wheat yield per hectare, but there has been no assessment of changes in land area available for production due to changing climate. It is also unclear how total wheat production would change under future climate when autonomous adaptation options are adopted. We applied species distribution models to investigate future changes in areas climatically suitable for growing wheat in Australia. A crop model was used to assess wheat yield per hectare in these areas. Our results show that there is an overall tendency for a decrease in the areas suitable for growing wheat and a decline in the yield of the northeast Australian wheat belt. This results in reduced national wheat production although future climate change may benefit South Australia and Victoria. These projected outcomes infer that similar wheat‐growing regions of the globe might also experience decreases in wheat production. Some cropping adaptation measures increase wheat yield per hectare and provide significant mitigation of the negative effects of climate change on national wheat production by 2041–2060. However, any positive effects will be insufficient to prevent a likely decline in production under a high CO₂ emission scenario by 2081–2100 due to increasing losses in suitable wheat‐growing areas. Therefore, additional adaptation strategies along with investment in wheat production are needed to maintain Australian agricultural production and enhance global food security. This scenario analysis provides a foundation towards understanding changes in Australia's wheat cropping systems, which will assist in developing adaptation strategies to mitigate climate change impacts on global wheat production.     

建立心脏功能研究的计算机模型

用计算机模拟建立生物学模型在现代生物学研究中是一种非常重要的方法.就心脏而言,从基因到细胞到整个器官,现在都建立了大量的计算机模型.这些模型在帮助我们证实心脏功能机制的假说、预测和评估药物的作用以及诊断疾病等方面都起着重要作用.就心脏不同层面的计算机模型进行了简要的综述.     

温度导致的我国东北三省玉米产量波动模拟

东北三省处在我国高纬度地区,一直以来玉米生长季由温度导致的低温冷害是影响东北三省玉米生产波动的主要农业气象灾害;作物模式能对作物重要生理生态过程及其与气象、土壤等环境条件的关系进行数值模拟,人为再现农作物生长发育过程.借助WOFOST作物模型在东北三省玉米生产适应性验证的基础上,对该三省区近46a来(1961～2006年)因温度导致的玉米产量波动情况进行了模拟分析.结果显示,黑龙江、吉林、辽宁三省区的玉米产量波动趋势基本相一致,且随着年份的增加产量波动有减小的趋势,产量波动最大的是黑龙江省,波动范围-20%～12%;产量波动最小的是辽宁省,波动范围-15%～8%.