生育后期干旱胁迫对玉米碳氮分配及生理特征的影响

为给解析干旱胁迫下的碳、氮代谢调控机制提供参考,以玉米品种‘郑单958’为材料,在防雨棚中设置吐丝期后干旱胁迫和正常供水两个处理,测定不同部位碳、氮同化物含量及分配情况,碳、氮代谢关键酶活性及叶片基因表达谱差异。结果表明,干旱胁迫显著降低生物量在籽粒中的分配比例,可溶性糖、淀粉、全氮等在籽粒中的分配比例均显著降低,而茎秆和穗轴中的分配比例显著增加。干旱胁迫下生育后期叶片碳、氮同化物含量及分配比例均呈下降趋势,这与可溶性淀粉合成酶、谷氨酰胺合成酶等活性的改变有关。采用转录组测序对生育后期叶片差异基因表达进行了分析,共得到差异表达基因51个,这些基因富集在细胞壁组织、碳水化合物代谢、光合作用等代谢途径中。其中纤维素、木质素合成等关键酶基因在干旱胁迫下均显著下调表达,表明干旱胁迫抑制了细胞壁的合成,导致叶片早衰。干旱胁迫下己糖激酶、核糖体蛋白等基因显著下调表达,而甘露糖异构酶基因显著上调表达。综上所述,干旱胁迫抑制了生育后期碳、氮同化物向籽粒的分配,茎秆中的分配比例显著上升。干旱胁迫下叶片碳、氮同化物含量及分配比例显著降低,这与叶片早衰及相关碳氮代谢关键酶活性及基因表达的变化有关。     

基于Landsat遥感影像和1∶50 000土壤数据库的福州市耕地有机碳动态变化研究

耕地土壤碳库是全球碳库中最为活跃的部分,其变化对全球气候变化产生重要影响。目前对耕地土壤有机碳估算多采用中、小系列比例尺的土壤数据库,较少结合遥感影像与大比例尺土壤数据库进行估算。基于此,本研究采用Landsat遥感影像和1∶50 000高精度土壤数据库,以福建省福州市为例,基于遥感与碳循环过程模型对1987年和2016年耕地土壤有机碳动态变化进行研究。结果表明,利用Landsat影像反演得到的耕地土壤基础呼吸与土壤有机碳相关性强,建立的1987年和2016年模型R²分别为0.637和0.752。研究期间,全市耕地土壤有机碳密度从东部沿海向西部内陆地区递增,整体发挥着“碳汇”作用,有机碳密度和储量分别增加0.20 kg·m^-2和2.946×10⁵ t。从不同土壤类型比较得出,黄壤、红壤和水稻土是“碳汇”,有机碳密度分别增加0.70 kg·m^-2、0.40 kg·m^-2和0.19 kg·m^-2;其他土类为“碳源”,其中,水稻土碳储量最大,两期在全市总碳储量中占比均超过90%。从不同行政区比较得出,仓山区、长乐区、马尾区和连江县为“碳源区”,其他地区为“碳汇区”,其中,仓山区碳储量一直为全市最低,两期占比均不足0.5%,而福清市则一直居于全市首位,占比均高于20%。总体而言,福州市耕地土壤有机碳30年间空间动态变化显著,在不同土类和行政区间存在差异,今后应根据不同耕地土壤类型和行政区的有机碳情况有针对性进行耕地管理。     

不同冬种模式对稻田土壤碳库管理指数的影响

长江中下游地区是我国水稻生产的重要基地,在保障我国粮食安全中占有重要地位,但该地区农田可持续性不高,稻田冬季利用率较低。本研究通过探讨不同冬季种植模式对土壤质量的影响,为冬闲田合理开发利用,提高稻田可持续性提供理论依据。设置5种冬种模式,分别为冬季休闲、冬种紫云英、冬种油菜、冬种大蒜和冬季轮作（马铃薯、紫云英、油菜）模式,通过测定不同土层土壤养分、土壤有机碳、活性有机碳和微生物生物量碳等,进一步分析不同冬种模式的土壤碳库管理指数及其综合效应。结果表明,在0~30 cm稻田土壤,与冬闲处理相比,不同冬季种植模式土壤有机碳提高6.12%~7.17%、活性有机碳提高13.56%~20.76%、微生物生物量碳提高0.13%~14.34%、可溶性有机碳提高3.49%~19.15%,土壤活性有机碳有效率提高6.74%~17.20%,冬季轮作（马铃薯、紫云英、油菜）模式能显著促进稻田土壤总有机碳及可溶性有机碳的积累;不同冬种模式提高了稻田土壤碳库活度指数和碳库指数,并且土壤碳库管理指数增加14.37%~27.29%。土壤有机碳与活性有机碳呈极显著相关（P<0.01）,土壤碳库管理指数与总有机碳呈显著相关（P<0.05）、与活性有机碳间存在极显著（P<0.01）的相关性。对土壤碳库管理指数影响因素的灰色关联度综合分析表明,冬季轮作（马铃薯、紫云英、油菜）模式排名第1。可见,不同冬季种植模式能增加土壤有机碳含量和提高土壤碳库管理指数,冬季轮作（马铃薯、紫云英、油菜）模式的综合评价最好,其次为冬种大蒜模式。     

作物水分利用效率研究方法及尺度传递研究进展

提高作物水分利用效率（WUE）是缓解农业生产水资源匮乏压力的有效途径,而水分利用效率尺度传递是各尺度WUE相互表征、验证并应用于实际生产的基础。本文概述了作物叶片、植株、群体尺度WUE的主要观测技术,包括叶片气体交换测定、碳同位素判别、桶栽称重、涡度相关观测等,其中碳同位素判别法为研究作物水分利用的长期累积效应提供了新的思路,且适用于多个尺度;总结了各尺度WUE的影响因子及作物耗水的生理机制,阐明各尺度WUE均受气孔导度调控。讨论了叶片到植株、叶片/植株到群体的尺度传递的可行性,集中分析了尺度传递的主要限制因素,指出叶片到植株的传递研究难点集中于叶片分布和光分布的不确定性、植物夜间呼吸和蒸腾以及植物适应环境的生理调节机制等过程;而叶片/植株到群体的传递研究主要受冠层形态学差异、冠层阻力、土壤蒸发及植物同化物分配机制等限制。最后总结了尺度传递方法的现有研究成果。目前作物WUE尺度传递主要依靠模型的完善和观测手段的提高,叶片到单株的尺度传递需关注日间与夜间耗水的分离及作物各部分的光合特性;叶片/单株到群体的传递可先明确蒸散结构,了解耗水特征,再以气孔导度和冠层导度的关系为切入点,利用模型探究传递机制。     

Improved dispersion of carbon nanotubes in chitosan

Carbon nanotubes (CNT)/chitosan films and fibers can find use in specialized applications like the artificial muscles and other intelligent switching devices. The dispersion state of the single walled carbon nanotubes (SWCNTs) in chitosan matrix plays a major role in deciding the ultimate properties of composite. A suitable chemical treatment for purification and functionalization of SWCNTs is reported. Optimal conditions to prepare water soluble and stable, dispersion of SWCNT in chitosan are presented. The dispersion behavior of purified and functionalized SWCNT was characterized by visual observations, transmission electron microscopy (TEM), and Raman spectroscopy. The dispersion obtained using functionalized SWCNT was stable, while the purified SWCNT dispersion showed limited stability. The better stability of functionalized SWCNT dispersion in chitosan was evidenced by improved interaction between chitosan and carboxyl functional groups of SWCNT.     

Soil processes as affected by replacement of natural mesquite ecosystem with maize crop

 In the central highlands of Mexico, the vegetation is dominated by mesquite (Prosopis spp.), a leguminous tree or shrub. An experiment was carried out to investigate how cultivating the land and the disappearance of the natural ecosystem affected the biological functioning of the soil. Soil was sampled from under the canopy of isolated (MESQ treatment) and densely growing mesquite trees (DENS treatment), from the surrounding soil not covered by the canopies of the trees (BARE treatment) and from adjacent land cultivated with maize (ARABLE treatment). Soil was characterized and then incubated aerobically for 39 days at 22±1  °C and CO₂, N₂O production, microbial biomass C and inorganic N concentrations were monitored. The organic C content was 2.3 times and 1.1 times greater in the MESQ and the BARE treatments, respectively, than in the ARABLE treatment, while microbial biomass C was 3.5 times and 1.3 times greater. The microbial biomass activity as expressed by CO₂ production was 5.9 times and 3.9 times greater in the MESQ and the BARE treatments, respectively, than in the ARABLE treatment, while N mineralization, as witnessed by the increase in NO₃ ^– concentrations, was 3.4 times and 1.7 times greater. No significant amounts of N₂O were produced in any of the treatments. It was found that cultivating land characterized by the presence of mesquite changed its characteristics profoundly, and even soil not covered by tree canopies had higher microbial biomass C, and C and N mineralization than soil cultivated with maize and beans. Received: 1 December 1997     

Temperature dependence of organic matter decomposition: a critical review using literature data analyzed with different models

 The literature was reviewed regarding laboratory incubation studies where C mineralization was measured. Experiments were selected in which the same substrate was incubated at least at two different temperatures and where time-series were available with at least four measurements for each substrate and temperature. A first-order one-component model and a parallel first-order two-component model were fitted to the CO₂–C evolution data in each experiment using a least-squares procedure. After normalising for a reference temperature, the temperature coefficient (Q ₁₀ ) function and three other temperature response functions were fitted to the estimated rate constants. The two-component model could describe the dynamics of the 25 experiments much more adequately than the one-component model (higher R², adjusted for the number of parameters), even when the rate constants for both were assumed to be equally affected by temperature. The goodness-of-fit did not differ between the temperature response models, but was affected by the choice of the reference temperature. For the whole data set, a Q ₁₀ of 2 was found to be adequate for describing the temperature dependence of decomposition in the intermediate temperature range (about 5–35  °C). However, for individual experiments, Q ₁₀ values deviated greatly from 2. At least at temperatures below 5  °C, functions not based on Q ₁₀ are probably more adequate. However, due to the paucity of data from low-temperature incubations, this conclusion is only tentative, and more experimental work is called for. Received: 1 December 1997     

Forest–atmosphere carbon dioxide exchange in eastern Siberia

We investigated the daily exchange of CO₂ between undisturbed Larix gmelinii (Rupr.) Rupr. forest and the atmosphere at a remote Siberian site during July and August of 1993. Our goal was to measure and partition total CO₂ exchanges into aboveground and belowground components by measuring forest and understory eddy and storage fluxes and then to determine the relationships between the environmental factors and these observations of ecosystem metabolism. Maximum net CO₂ uptake of the forest ecosystem was extremely low compared to the forests elsewhere, reaching a peak of only ∼5 μmol m⁻² s⁻¹ late in the morning. Net ecosystem CO₂ uptake increased with increasing photosynthetically active photon flux density (PPFD) and decreased as the atmospheric water vapor saturation deficit (D) increased. Daytime ecosystem CO₂ uptake increased immediately after rain and declined sharply after about six days of drought. Ecosystem respiration at night averaged ∼2.4 μmol m⁻² s⁻¹ with about 40% of this coming from the forest floor (roots and heterotrophs). The relationship between the understory eddy flux and soil temperature at 5 cm followed an Arrhenius model, increasing exponentially with temperature (Q₁₀∼2.3) so that on hot summer afternoons the ecosystem became a source of CO₂. Tree canopy CO₂ exchange was calculated as the difference between above and below canopy eddy flux. Canopy uptake saturated at ∼6 μmol CO₂ m⁻² s⁻¹ for a PPFD above 500 μmol m⁻² s⁻¹ and decreased with increasing D. The optimal stomatal control model of Mäkelä et al. (1996) was used as a `big leaf' canopy model with parameter values determined by the non-linear least squares. The model accurately simulated the response of the forest to light, saturation deficit and drought. The precision of the model was such that the daily pattern of residuals between modeled and measured forest exchange reproduced the component storage flux. The model and independent leaf-level measurements suggest that the marginal water cost of plant C gain in Larix gmelinii is more similar to values from deciduous or desert species than other boreal forests. During the middle of the summer, the L. gmelinii forest ecosystem is generally a net sink for CO₂, storing ∼0.75 g C m⁻² d⁻¹.     

我国水稻品种改良过程库源特征的变化

观察了不同时期水稻主栽品种库源结构的演变,主要结果如下：（１）４０多年来,福建省水稻品种经历了高秆品种、矮秆品种、杂交稻的演变,使稻谷产量提高５５％;（２）随着品种的改良,水稻库容量增加６３％．其中,２０％依靠穗数的增加,８０％依靠每穗粒数的增加,而粒重和结实率变化不大;（３）随着品种的改良,反映源强的干物质积累总量（Ｗ）增加４０％．Ｗ的增加主要依靠叶面积指数（ＬＡＩ）的扩大和生长日数（Ｄ）的延长,净同化率（ＮＡＲ）却有所下降．但由于冠层叶片由披散型改变为直立型,阳光可透入群体深层,减少了ＮＡＲ随ＬＡＩ增大而降低的速率,显著增加了非结构性碳水化合物在营养器官的贮藏量和抽穗后干物质生产量,从而提高经济系数,确保在更高产量水平上的库源协调．     

中国农业系统碳汇功能

研究我国现实和未来农业系统碳汇功能,提出该系统碳排放和碳固定清单。以１９９０、１９９５和２０００年为例,对周年碳平衡进行计算分析,绘制出全国农业系统碳平衡概图。碳的排放、固定、转移量占当年吸收量的百分比分别为８２．６％—８４．４％、１４．５％—１５．７％和１．１％—１．７％,年固碳量为１．１×１０８—１．４×１０８ｔ。无论是现阶段还是气候变化后,我国农业系统对碳的吸收均大于排放,对大气ＣＯ２而言,不是源而是汇。在全球温室气体逐年增加的情况下,应采取积极措施,加强农业系统碳汇功能,为减缓大气ＣＯ２浓度的增加做出贡献。