玉米叶片水分利用效率的保守性

水分利用效率是植物个体或生态系统水分利用过程的重要特征参数,可表征不同时空尺度的植物碳-水耦合关系,对植物适应气候变化研究具有重要意义。以玉米为例,利用中国气象局固城农业气象野外科学试验基地2013—2014年玉米不同灌溉方案模拟试验资料,对不同叶位叶片的水分利用效率特征及其影响因素进行分析。结果表明:植株顶部第1片叶片水分利用效率在拔节期和乳熟期呈现明显的峰值,反映出明显的周期变化规律及其与叶片生理生态特征的紧密相关。在相同环境条件下,不同叶位叶片的水分利用效率不存在显著性差异,即玉米叶片水分利用效率具有空间稳定性与叶龄保守性。同时,研究指出叶片光合速率和蒸腾速率在叶位之间的协调变化是导致空间稳定性和叶龄保守性的主要原因。研究结果可为植物水分关系研究提供参考,也可为水分利用效率的尺度化研究提供依据。     

Environmental induced variations in leaf dark respiration and net photosynthesis of <Emphasis Type="Italic">Quercus ilex</Emphasis> L.

The relationships between dark respiration rate (R _D) and net photosynthetic rate (P _N) in Quercus ilex L. shrubs growing at the Botanical Garden in Rome were analysed. Correlation analysis of the data sets collected in the year 2006 confirmed the dependence among the considered leaf traits, in particular, R _D was significantly (p<0.05) correlated with P _N (r = 0.40). R _D and P _N increased from March to May [1.40±0.10 and 10.1±1.8 μmol(CO₂) m⁻² s⁻¹ mean values of the period, respectively], when air temperature was in the range 14.8–25.2 °C, underlining the highest metabolic activity in the period of the maximum vegetative activity that favoured biomass accumulation. On the contrary, the highest R _D [1.60±0.02 μmol(CO₂) m⁻² s⁻¹], associated to the lowest P _N rates (44 % of the maximum) and carbon use efficiency (CUE) in July underlined the mobilization of stored material during drought stress by a higher air temperature (32.7 °C).     

青海省沙珠玉治沙站17种主要植物叶性因子的比较

国外大量研究结果表明,具有高叶氮含量和低比叶面积的干旱地区植物往往具有较高的水分利用效率。选取青海省沙珠玉治沙站地区17种主要植物(野生9种,人工8种) ,分别测定其比叶面积(SL A) ,单位重量叶氮含量(Nmass)及单位面积叶氮含量(Narea) ,并与贡嘎山湿润森林样带测定数据进行比较分析。结果表明,Nmass随SL A的增加而增加,但Nmass与SL A关系格局在固定沙丘野生多年生草本-灌木植物(类群1,Narea>3.0 g m- 2 )与流动沙丘野生短命草本植物(类群2 ,Narea<3.0 g m- 2 )之间存在策略位移现象,即在相同SL A下,类群1比类群2具有更高的叶氮含量,或在相同Nmass时类群1比类群2具有更小的比叶面积。在8个人工物种中,柠条锦鸡儿、中间锦鸡儿、绵柳和西北沙柳等灌木属于类群1,而甘草、小叶锦鸡儿、柽柳和青杨属于类群2 ,前者比后者具备更好的干旱适应机制,建议在生产上优先考虑前者。流动沙丘野生短命草本植物具有较低的叶氮含量和较高的比叶面积,这一特征与流动沙丘土壤贫瘠及其生长期内降水集中和土壤水分含量相对丰富密切相关。     

植物叶片水分利用效率研究综述

植物能否适应当地的极限环境条件,最主要的看它们能否很好地协调碳同化和水分耗散之间的关系,即植物水分利用效率(WUE)是其生存的关键因子.就近来研究最多的叶片水平上的WUE,从叶片WUE的定义,方法,进展等方面对其进行总结概括,并就今后植物叶片水分利用效率的研究提出了几点看法:方法上,叶片碳同位素方法是目前植物叶片长期水分利用效率研究的最佳方法,而δ13C的替代指标将继续是方法研究中的一个方向,前景乐观;研究内容上,要加强极端干旱区河岸林木的δ13C和WUE的研究;结合植物生理生态学,生物学和稳定同位素技术,探究植物叶片长期水分利用效率的机理,特别是要加强运用双重同位素模型加深和理解植物叶片长期水分利用效率变化规律和内在机制的研究;要结合多种方法,加强多时空尺度植物叶片WUE及其之间的转换研究.     

叶脉网络功能性状及其生态学意义

叶脉网络结构是叶脉系统在叶片里的分布和排列样式。早期叶脉网络结构研究主要集中在其分类学意义上; 近年来叶脉网络功能性状及其在植物水分利用上的意义已成为植物生态学研究的热点。该文介绍了叶脉网络功能性状的指标体系(包括叶脉密度、叶脉直径、叶脉之间的距离、叶脉闭合度等), 综述了叶脉网络功能性状与叶脉系统功能(包括水分、养分和光合产物等物质运输、机械支撑和虫害防御等)的关系, 叶脉网络功能性状与叶片其他功能性状(包括比叶重、叶寿命、光合速率、叶片大小、气孔密度等)的协同变异和权衡关系, 以及叶脉网络功能性状随环境因子(包括水分、温度、光照等)的变化规律等方面的最新研究进展。此外, 叶脉网络功能性状的研究成果也被应用于古环境重建、城市交通规划、流域规划及全球变化研究中。由于叶脉网络功能性状是环境因子与系统发育共同作用的结果, 未来开展分子—叶片—植物—生态系统等多尺度的叶脉网络功能性状研究, 理清叶脉网络功能性状与气孔失水—茎干导水—根系吸水等植物水分利用的关系, 将为预测植物及生态系统对全球变化的响应提供新的启示。     

Small trees,big problems: Comparative leaf function under extreme edaphic stress

Premise of the Study

The pygmy forest, a plant community of severely stunted conifers and ericaceous angiosperms, occurs on patches of highly acidic, nutrient‐poor soils along the coast of Northern California, USA. This system is an excellent opportunity to study the effect of severe nutrient deficiency on leaf physiology in a naturally‐occurring ecosystem. In this study, we seek to understand the physiological mechanisms stunting the plants' growth and their implications for whole plant function.

Methods

We measured 14 traits pertaining to leaf photosynthetic function or physical structure on seven species. Samples were taken from the pygmy forest community and from conspecifics growing on higher‐nutrient soils, where trees may grow over 30 m tall.

Key Results

Pygmy plants of most species maintained similar area‐based photosynthetic and stomatal conductance rates to conspecific controls, but had lower specific leaf area (leaf area divided by dry weight), lower percent nitrogen, and less leaf area relative to xylem growth. Sequoia sempervirens, a species rare in the pygmy forest, had a categorically different response from the more common plants and had remarkably low photosynthetic rates.

Conclusions

Pygmy plants were not stunted by low photosynthetic rates on a leaf‐area basis; instead, several species had restricted whole‐plant photosynthesis due to low leaf area production. Pygmy plants of all species showed signs of greater carbon investment in their leaves and higher production of nonphotosynthetic leaf tissue, further contributing to slow growth rates.     

Growth, radiation use efficiency and yield potential of enset (Ensete ventricosum) at different sites in southern Ethiopia

Knowledge on the physiological parameters that determine the growth of enset (Ensete ventricosum) and on how these parameters develop over time and affect yield under field conditions is scarce. Field experiments were carried out at three sites in southern Ethiopia using suckers of several clones to generate crop physiological parameters and to describe the time course of leaf number, leaf area and plant height. Yield potentials at different sites were estimated using these parameters and weather data, and compared with the actual yield. Plant height and LAI increased faster at Awassa and Areka than at Hagereselam because of a higher leaf appearance rate associated with temperatures being closer to the optimum. The trend in plant height was best described by a logistic function, whereas the trend in LAI was best described by a logistic function only at Awassa and Areka. A high leaf appearance rate (0.18 leaves day^?1) during early growth at Awassa and Areka made it possible that leaves that were senesced during unfavourable climatic conditions could be rapidly replaced without strong fluctuation in leaf area index. At Hagereselam, however, the rate of leaf appearance (0.09 leaves day^?1) was too small to compensate for the decline in the number of green leaves per plant during adverse conditions and thus LAI fluctuated over the whole growing period. The trend in fraction of PAR intercepted was best described by a generalised logistic function. At 300 days after transplanting the suckers, LAI reached a value of 4.5 and enset clones intercepted 92–97% of incoming PAR. The mean extinction coefficient was between 0.56–0.91 and radiation use efficiency (RUE) ranged from 1.43–2.67 g MJ^?1. Dry matter kocho yield potentials of 17.1 to 33.9 t ha‐1 yr‐1 were estimated for enset clones. Important yield potential differences existed between clones mainly because of differences in radiation use efficiency that was probably partly associated with viral infection. The average ratio of actual yield:yield potential (0.24) was low mainly because of large losses associated with traditional fermentation techniques, yield reducing cultivation methods such as repetitive transplanting and leaf pruning, presence of diseases, lack of adequate fertilisation and shortage and uneven distribution of rainfall.     

Population variation and natural selection on leaf traits in cork oak throughout its distribution range

A central issue in evolutionary biology is the exploration of functional trait variation among populations and the extent to which this variation has adaptive value. It was recently proposed that specific leaf area (SLA), leaf nitrogen concentration per mass (N_mass) and water use efficiency in cork oak play an important role in adaptation to water availability in the environment. In order to investigate this hypothesis, we explored, first, whether there was population-level variation in cork oak (Quercus suber) for these functional traits throughout its distribution range; if this were the case, it would be consistent with the hypothesis that different rainfall patterns have led to ecotypic differentiation in this species. Second, we studied whether the population-level variation matched short-term selection on these traits under different water availability conditions using two fitness components: survival and growth. We found high population-level differentiation in SLA and N_mass, with populations from dry places exhibiting the lowest values for SLA and N_mass. Likewise, reduced SLA had fitness benefits in terms of growth for plants under dry conditions. However, contrary to our expectations, we did not find any pattern of association between functional traits and survival in nine-year-old saplings despite considerable drought during one year of the study period. These results together with findings from the literature suggest that early stages of development are the most critical period for this species. Most importantly, these findings suggest that cork oak saplings have a considerable potential to cope with dry conditions. This capacity to withstand aridity has important implications for conservation of cork oak woodlands under the ongoing climate change.     

Genotype differences in 13C discrimination between atmosphere and leaf matter match differences in transpiration efficiency at leaf and whole‐plant levels in hybrid Populus deltoides ×nigra

¹³C discrimination between atmosphere and bulk leaf matter (Δ¹³C_lb) is frequently used as a proxy for transpiration efficiency (TE). Nevertheless, its relevance is challenged due to: (1) potential deviations from the theoretical discrimination model, and (2) complex time integration and upscaling from leaf to whole plant. Six hybrid genotypes of Populus deltoides×nigra genotypes were grown in climate chambers and tested for whole‐plant TE (i.e. accumulated biomass/water transpired). Net CO₂ assimilation rates (A) and stomatal conductance (g_s) were recorded in parallel to: (1) ¹³C in leaf bulk material (δ¹³C_lb) and in soluble sugars (δ¹³C_ss) and (2) ¹⁸O in leaf water and bulk leaf material. Genotypic means of δ¹³C_lb and δ¹³C_ss were tightly correlated. Discrimination between atmosphere and soluble sugars was correlated with daily intrinsic TE at leaf level (daily mean A/g_s), and with whole‐plant TE. Finally, g_s was positively correlated to ¹⁸O enrichment of bulk matter or water of leaves at individual level, but not at genotype level. We conclude that Δ¹³C_lb captures efficiently the genetic variability of whole‐plant TE in poplar. Nevertheless, scaling from leaf level to whole‐plant TE requires to take into account water losses and respiration independent of photosynthesis, which remain poorly documented.     

Partitioning controls on Amazon forest photosynthesis between environmental and biotic factors at hourly to interannual timescales

Gross ecosystem productivity (GEP) in tropical forests varies both with the environment and with biotic changes in photosynthetic infrastructure, but our understanding of the relative effects of these factors across timescales is limited. Here, we used a statistical model to partition the variability of seven years of eddy covariance‐derived GEP in a central Amazon evergreen forest into two main causes: variation in environmental drivers (solar radiation, diffuse light fraction, and vapor pressure deficit) that interact with model parameters that govern photosynthesis and biotic variation in canopy photosynthetic light‐use efficiency associated with changes in the parameters themselves. Our fitted model was able to explain most of the variability in GEP at hourly (R² = 0.77) to interannual (R² = 0.80) timescales. At hourly timescales, we found that 75% of observed GEP variability could be attributed to environmental variability. When aggregating GEP to the longer timescales (daily, monthly, and yearly), however, environmental variation explained progressively less GEP variability: At monthly timescales, it explained only 3%, much less than biotic variation in canopy photosynthetic light‐use efficiency, which accounted for 63%. These results challenge modeling approaches that assume GEP is primarily controlled by the environment at both short and long timescales. Our approach distinguishing biotic from environmental variability can help to resolve debates about environmental limitations to tropical forest photosynthesis. For example, we found that biotically regulated canopy photosynthetic light‐use efficiency (associated with leaf phenology) increased with sunlight during dry seasons (consistent with light but not water limitation of canopy development) but that realized GEP was nonetheless lower relative to its potential efficiency during dry than wet seasons (consistent with water limitation of photosynthesis in given assemblages of leaves). This work highlights the importance of accounting for differential regulation of GEP at different timescales and of identifying the underlying feedbacks and adaptive mechanisms.