Relationship between photochemical reflectance index and leaf ecophysiological and biochemical parameters under two different water statuses: towards a rapid and efficient correction method using real‐time measurements

The use of the photochemical reflectance index (PRI) as a promising proxy of light use efficiency (LUE) has been extensively studied, and some issues have been identified, notably the sensitivity of PRI to leaf pigment composition and the variability in PRI response to LUE because of stress. In this study, we introduce a method that enables us to track the short‐term PRI response to LUE changes because of photosynthetically active radiation (PAR) changes. The analysis of these short‐term relationships between PRI and LUE throughout the growing season in two species (Quercus robur L. and Fagus sylvatica L.) under two different soil water statuses showed a clear change in PRI response to LUE, which is related to leaf pigment content. The use of an estimated or approximated PRI0, defined as the PRI of perfectly dark‐adapted leaves, allowed us to separate the PRI variability due to leaf pigment content changes and the physiologically related PRI variability over both daily (PAR‐related) and seasonal (soil water content‐related) scales. The corrected PRI obtained by subtracting PRI0 from the PRI measurements showed a good correlation with the LUE over both of the species, soil water statuses and over the entire growing season.     

Drought-induced dynamics of carbon and water use efficiency of global grasslands from 2000 to 2011

Drought is frequently recorded as a result of climate warming and elevated concentration of greenhouse gases, which affect the carbon and water cycles in terrestrial ecosystems, particularly in arid and semi-arid regions. To identify the drought in grassland ecosystems and to determine how such drought affects grassland ecosystems in terms of carbon and water cycles across the globe, this study evaluated the drought conditions of global grassland ecosystems from 2000 to 2011 on the basis of the remotely sensed Drought Severity Index (DSI) data. The temporal dynamics of grassland carbon use efficiency (CUE) and water use efficiency (WUE), as well as their correlations with DSI, were also investigated at the global scale. Results showed that 57.04% of grassland ecosystems experienced a dry trend over this period. In general, most grassland ecosystems in the northern hemisphere (N.H.) were in near normal condition, whereas those in the southern hemisphere (S.H.) experienced a clear drying and wetting trend, with the year 2005 regarded as the turning point. Grassland CUE increased continually despite the varied drought conditions over this period. By contrast, WUE increased in the closed shrublands and woody savannas but decreased in all the other grassland types. The drought conditions affected the carbon and water use mainly by influencing the primary production and evapotranspiration of grass through photosynthesis and transpiration process. The CUE and WUE of savannas was most sensitive to droughts among all the grassland types. The areas of grassland DSI that showed significant correlations with CUE and WUE were 52.92% and 22.11% of the total grassland areas, respectively. Overall, droughts sufficiently explained the dynamics of grassland CUE, especially in the S.H. In comparison with grassland CUE, the grassland WUE was less sensitive to drought conditions at the global scale.     

不同风沙条件对几种植物生态生理特征的影响

 在野外风洞条件下,就不同风况的风沙胁迫对几种固沙植物生态生理特征的影响进行了实验研究。实验采用了沙坡头地区的野外植物和盆栽植物。在不同风速(5.9 m·s-1, 7.9 m·s-1, 9.9 m·s-1,14 m·s-1, 10 m·s-1,15 m·s-1, 20 m·s-1)和吹袭时间间隔(2 d, 4 d, 9 d)下测定了植物3个生理生态参数的变化。实验结果表明：1）净风和风沙流胁迫均可使植物的净光合速率（Pn）降低,蒸腾速率（E）升高,从而导致水分利用效率（WUE）下降。净风和风沙流对植物生理生态特征的影响显著不同。同样为14 m·s-1的风速时,风沙流使植物的Pn降低40.7%,而净风使其降低了35.88%。2）吹袭的时间间隔越短,植物的净光合速率降幅越大;风沙流比净风的影响更大。在2 d, 4 d, 9 d为间隔的风沙流吹袭下,油蒿（Artemisia ordosica）的Pn分别下降了20.13%、 11.76%、 7.72%。风沙胁迫强度越大,物质积累越少,植物的高生长越慢。3）由于风沙流降低了水分利用率,从而增加了对植物的干燥作用。从总体来看,沙生植物对风沙流胁迫有一定的适应响应,实验所用灌木较草本植物有更强的抗风性。     

羊草群落的水分利用

羊草(Leymus chinensis (Trin.)Tzvel.)群落的土壤水分具有明显的成层性:0～40 cm是根系集中分布层,受降水和蒸散的直接影响,称为蒸散与降水相互作用层;40～120 cm贮水变化滞后于根系层贮水和群落蒸散的季节变化,称为主要贮水层;120 cm以下称为水分相对稳定/平衡层.1996年属平水年,生长季末土壤水盈余18 mm;1998年属丰水年,在连续强降雨时发生渗漏,生长季末土壤水亏缺15 mm.蒸腾-蒸散比(T/ET)不仅反映群落的繁茂和活力,而且反映植物对环境水资源的利用状况.1998年8月T/E7值较小(0.5),6月达0.7,7月受降水少影响而有所降低(0.6),8月水分利用效率达到最大(0.9),9月降到0.6.水分利用效率(WUE)在良好的水分条件下(1998年),主要受植物自身生长速度的限制,其季节变化与生长大周期吻合.深入分析WUE和T/E的内涵,提出蒸散效率(ETE)的概念,能更好地反映植物对环境水资源利用的状况或程度,具有实际意义.     

羊草群落的水分利用

羊草(Leymus chinensis (Trin．)Tzvel．)群落的土壤水分具有明显的成层性：O-40cm是根系集中分布层,受降水和蒸散的直接影响,称为蒸散与降水相互作用层;40-120cm贮水变化滞后于根系层贮水和群落蒸散的季节变化,称为主要贮水层;120cm以下称为水分相对稳定／平衡层。1996年属平水年,生长季末土壤水盈余18mm;1998年属丰水年,在连续强降雨时发生渗漏,生长季末土壤水亏缺15mm。蒸腾-蒸散比(T/ET)不仅反映群落的繁茂和活力,而且反映植物对环境水资源的利用状况。1998年8月T/ET值较小(0．5),6月达O．7,7月受降水少影响而有所降低(O．6),8月水分利用效率达到最大(O．9),9月降到O．6。水分利用效率(WUE)在良好的水分条件下(1998年),主要受植物自身生长速度的限制,其季节变化与生长大周期吻合。深入分析WUE和T/ET的内涵,提出蒸散效率(ETE)的概念,能更好地反映植物对环境水资源利用的状况或程度,具有实际意义。     

干旱胁迫下四倍体刺槐幼苗水分利用效率及稳定碳同位素组成的研究

在模拟自然干旱的条件下,测定2个四倍体刺槐品种(K2、K3)和普通二倍体刺槐(K1)一年生组培苗的长期和瞬时水分利用效率(WUE)及其稳定碳同位素组成(δ13C),以探讨四倍体刺槐的抗旱机理.结果表明,K2、K3的长期水分利用效率(WUEL)在不同水分胁迫条件下都显著高于K1,它们在同等供水条件下比K1具有更大的生物量产出;3个材料叶片的瞬时水分利用效率(WUEI)均随干旱胁迫的加剧表现先升后降的趋势,且胁迫处理均高于适宜水分处理.随水分胁迫的加剧,各品种刺槐苗木叶片的δ13C显著升高;K2、K3的δ13C在各水分条件下均高于K1;各材料叶片的δ13C与其WUEL有良好的正相关性,可以作为筛选高WUE刺槐品种的指标.     

亚热带人工林松树~(13)C/~(12)C比率和水分利用效率

1 引言 亚热带季风阔叶林自然林被破坏后,代之以人工林,由于自然林郁密的树冠层的消失,引起环境因素明显变化,如太阳辐射的增强,气温变幅变大,同时由于风速增大,加大了蒸腾的需要量,造成空气相对湿度降低和土壤水分亏缺,特别是在干旱季节尤为显著。该林地中除被动适应这一生境的1年生草本外,尚有灌木桃金娘(Rhodomyrtus tomentosa)、三叉苦(Euodia     

Effects of root pruning on the growth and water use efficiency of winter wheat

A pot experiment was conducted to study the effects of root pruning at the stem elongation stage on the growth and water use efficiency (WUE) of winter wheat (Triticum aestivum). The results showed that stomatal conductance (g) and transpiration (E) of wheat were very sensitive to root pruning. After root pruning, they declined rapidly and but returned to pre-pruning values 15 days after treatment. Under well-watered conditions, there was no significant difference in leaf water potential (ψ_leaf) between root pruned and control plants after root pruning. Under moderate drought stress, ψ_leaf of root pruned plants declined significantly compared to the control 3 days after root pruning. After 15 days, ψ_leaf of root pruned plants was similar to the controls. Under different soil moisture levels, net assimilation rate (A) of root pruned plants was lower than controls 3–7 days after root pruning, but was similar to the controls 15 days after pruning. At anthesis (50 days after root pruning), root pruned plants showed significantly higher A compared with the control. Leaf area per tiller and tiller number of root pruning plants was significant lower than the control at booting stage, which showed that root pruning restrained the growth of plants in the early growing stage, but leaf area per stem, of root pruned plants, was similar to the control at anthesis. Under both soil moisture levels, there was no significant difference in grain yield between root pruned and the control plants in the monoculture. In mixture with the control plants, the root pruned plants was less productive and had a lower relative yield (0.92 and 0.78, respectively) compared with the control (1.13 and 1.19, respectively), which suggested that the pruned plants lost some of its competing ability and showed a lower ability to acquire and use the same resources in the mixture compared with the control plant. Over the whole growing cycle, root pruning reduced water consumption (by 10% under well-watered conditions and 16% under moderate drought stress) of wheat significantly compared to the control (P < 0.05), and but there was no significant difference in grain yield between root pruned and control plants. Therefore root pruned wheat had a higher WUE with respect to grain yield compared with the controls. In conclusion, lowering water consumption by root pruning in the early growing stage is an effective way to improve water use efficiency in arid and semi arid areas.     

Enhancement of rice canopy carbon gain by elevated CO(2) is sensitive to growth stage and leaf nitrogen concentration

Increasing our understanding of the factors regulating seasonal changes in rice canopy carbon gain (C(gain): daily net photosynthesis -- night respiration) under elevated CO(2) concentrations ([CO(2)]) will reduce our uncertainty in predicting future rice yields and assist in the development of adaptation strategies. In this study we measured CO(2) exchange from rice (Oryza sativa) canopies grown at c. 360 and 690 micromol mol(-1)[CO(2)] in growth chambers continuously over three growing seasons. Stimulation of C(gain) by elevated [CO(2)] was 22-79% during vegetative growth, but decreased to between -12 and 5% after the grain-filling stage, resulting in a 7-22% net enhancement for the whole season. The decreased stimulation of C(gain) resulted mainly from decreased canopy net photosynthesis and partially from increased respiration. A decrease in canopy photosynthetic capacity was noted where leaf nitrogen (N) decreased. The effect of elevated [CO(2)] on leaf area was generally small, but most dramatic under ample N conditions; this increased the stimulation of whole-season C(gain). These results suggest that a decrease in C(gain) enhancement following elevated CO(2) levels is difficult to avoid, but that careful management of nitrogen levels can alter the whole-season C(gain) enhancement.     

Interactive effects of ozone and climate on tree growth and water use in a southern Appalachian forest in the USA

* A lack of data on responses of mature tree growth and water use to ambient ozone (O(3)) concentrations has been a major limitation in efforts to understand and model responses of forests to current and future changes in climate. * Here, hourly to seasonal patterns of stem growth and sap flow velocity were examined in mature trees from a mixed deciduous forest in eastern Tennessee (USA) to evaluate the effects of variations in ambient O(3) exposure and climate on patterns of stem growth and water use. * Ambient O(3) caused a periodic slowdown in seasonal growth patterns that was attributable in part to amplification of diurnal patterns of water loss in tree stems. This response was mediated by statistically significant increases in O(3)-induced daily sap flow and led to seasonal losses in stem growth of 30-50% for most species in a high-O(3) year. * Decreased growth and increased water use of mature forest trees under episodically high ambient O(3) concentrations suggest that O(3) will amplify the adverse effects of increasing temperatures on forest growth and forest hydrology.     

新疆古尔班通古特沙漠南缘多枝柽柳光合作用及水分利用的生态适应性

光合作用和水分利用是陆地生态系统中限制植物光合同化和个体生长发育的重要因素。为了从根本上认识到荒漠绿洲过渡带植物对特殊生境和气候变化的响应和适应机制,有必要深入的了解植被对不同环境因子适应过程的协调性。本文以新疆古尔班通古特沙漠南缘荒漠绿洲过渡带的建群种多枝柽柳（Tamarix ramosissima）为研究对象,分别在自然状态,模拟降水、遮光处理以及降水和遮光双因子处理下,利用LI-6400光合作用系统和Model 3500植物水分压力室分别测定光合作用和枝条水势,研究多枝柽柳枝条水势对浅层土壤水分和光照变化的响应,以及在不同条件下的水分利用效率（WUE）和光能利用效率（LUE）的日进程。结果表明：这四种处理方式下,枝条水势随土壤水分的变化没有明显的差异,趋势表现为黎明前枝条水势最高（-1.2 MPa）,正午枝条水势最低（-3.2 MPa）,太阳落山后枝条水势逐渐升高的趋势;WUE和LUE日变化呈现出近似双峰型抛物线,WUE日变化曲线在11:00和16:00有两个不明显的波峰,LUE日变化曲线在10:00和16:00出现两个明显波峰。当光照发生变化时,遮光处理下的WUE和LUE日变化都较自然状态下的日变化低,分别降低了1.5 ?mol CO2?mmol-1 H2O的WUE和0.20*10-2 ?mol CO2??mol-1APAR的LUE。研究表明,作为深根系植物的多枝柽柳,生存主要依靠地下水来补给水分,所以浅层土壤水分条件变化没有明显引起光合和蒸腾的响应。而午间光强、高温是构成多枝柽柳光抑制现象的主要原因,这是多枝柽柳长期在荒漠绿洲过渡带形成的对抗环境胁迫的一种表现。     

Phosphorus concentrations in the leaves of defoliated white clover affect abscisic acid formation and transpiration in drying soil

Increased leaf phosphorus (P) concentration improved the water-use efficiency (WUE) and drought tolerance of regularly defoliated white clover plants by decreasing the rate of daily transpiration per unit leaf area in dry soil. Night transpiration was around 17% of the total daily transpiration. The improved control of transpiration in the high-P plants was associated with an increased individual leaf area and WUE that apparently resulted from net photosynthetic assimilation rate being reduced less than the reductions in the transpiration (27% vs 58%). On the other hand, greater transpiration from low-P plants was associated with poor stomatal control of transpirational loss of water, less ABA in the leaves when exposed to dry soil, and thicker and smaller leaf size compared with high-P leaves. The leaf P concentration was positively related with leaf ABA, and negatively with transpiration rates, under dry conditions ( P < 0.001). However, leaf ABA was not closely related to the transpiration rate, suggesting that leaf P concentration has a greater influence than ABA on the transpiration rates.     

冬小麦光合特征及叶绿素含量对保水剂和氮肥的响应

以不施保水剂和氮（N）肥为对照,测定了保水剂（60 kg·hm^-2）与不同N肥水平（0、225、450 kg·hm^-2）及其配施条件下大田小麦的光合特征、叶绿素含量和水分利用效率等指标,研究了冬小麦拔节期和灌浆期光合生理特征、叶绿素含量及水分利用对保水剂和N肥的响应.结果表明：灌浆期各处理的光合速率、气孔导度、胞间CO₂浓度、叶片水分利用效率及叶绿素含量均大于拔节期.在拔节期,单施N肥条件下,随施N量的增加,单叶水分利用效率提高,光合速率、气孔导度、胞间CO₂浓度及蒸腾速率均先增后减;225 kg·hm^-2 N肥处理的叶绿素含量最高.施用保水剂后,随施N量的增加,胞间CO₂浓度降低,而光合速率等均提高;单施保水剂及其与N肥配施提高了叶绿素含量,而过多N肥效果不显著在灌浆期,单施N肥显著提高了小麦的光合速率及水分利用效率,降低了气孔导度、胞间CO₂浓度及蒸腾速率;叶绿素含量随N肥用量的增加而增加.施用保水剂后,随N肥用量的增加,光合速率和叶片水分利用效率均先增后减,而胞间CO₂浓度和蒸腾速率先减后增,但均低于对照,气孔导度随施N量的增加而提高.单施保水剂的叶绿素含量显著提高,但其与N肥配施叶绿素含量有所降低.保水剂与N肥配合施用显著提高了小麦的千粒重、产量及水分生产效率.其中,保水剂与225 kg·hm^-2N肥配施处理的产量及水分生产效率均最高.     

南昌市中心城区主要大气污染物分布模拟及土地利用对其影响

随着我国城市化、工业化的快速推进,城市大气污染问题日益突出,研究城市大气污染物的分布情况及其土地利用影响对解决城市大气污染问题具有重要意义.本研究以南昌市中心城区为研究区,基于土地利用回归模型(LUR)模拟了PM_2.5、PM₁₀、SO₂、NO₂、CO、O₃等6种主要大气污染物浓度,并分析其时空分布特征;基于主导土地利用类型,选择南昌市中心城区内居住、商业、教育和工业用地各15个样本区,为了减少气象因子的影响,分四季统计各样本区6类大气污染物浓度,运用双因素方差分析和多重比较,定量分析土地利用(样本区)对6类大气污染物的影响.结果表明: 采用LUR模型模拟研究区PM_2.5、PM₁₀、SO₂、NO₂、CO、O₃浓度的平均绝对误差率分别为11.9%、13.4%、12.5%、12.0%、12.7%和13.5%,模型误差较小,方法可行.研究区6类污染物浓度具有明显的时空分布特征,PM_2.5、PM₁₀、SO₂、NO₂和CO浓度在冬季最高,春季和秋季次之,夏季最低;O₃浓度则为夏季高,春季和秋季次之,冬季低.PM_2.5、PM₁₀、SO₂、NO₂、CO浓度整体呈现从城区中心到郊区递减的趋势,而O₃浓度则反之.不同季节与不同土地利用样本区间6种大气污染物浓度差异显著,表明在中心城区尺度上,气象条件和土地利用都对大气污染物有显著影响.不同土地利用对主要大气污染物浓度分布有不同程度的影响,其中,对PM_2.5、NO₂和O₃的影响较大,对CO的影响较小.     

土壤水分对返青期断根冬小麦补偿效应的影响

通过盆栽试验研究了不同土壤水分条件下返青期断根冬小麦的补偿效应.结果表明,断根小麦的早期生长受到抑制,叶面积在返青 拔节期间显著下降,到开花期能恢复至对照水平.高水分条件下断根小麦拔节期的叶绿素荧光参数包括表观光合电子传递速率、实际光化量子产量、光化学淬灭系数、非光化学淬灭值均显著大于对照,开花后单茎干物质积累为0.81 g,显著大于对照（0.56 g）,花后干物质积累系数比对照提高了38.79%,断根小麦根量虽有所下降但差异不显著;低水分条件下断根小麦的叶绿素荧光参数和花后干物质积累与对照之间没有显著差异,但断根小麦的根系生物量（7.83 g·pot^-1）显著小于对照（9.77 g·pot^-1）.土壤水分对断根小麦的地上生物量和籽粒产量的补偿效应没有显著影响.断根处理的冬小麦在两种土壤水分条件下均显著降低了耗水量,在整个生育期,高水分条件下冬小麦断根处理可节水2 000 ml左右,水分利用效率为1.97 g·kg ^-1,显著大于对照的1.70 g·kg ^-1;低水分条件下也可节水1 500 ml左右,水分利用效率虽有所提高,但未达到显著性差异.     

干旱胁迫对水稻水分利用效率的影响

通过特殊自然干旱胁迫的方法,研究不同干旱胁迫对水稻的水分利用效率（ＷＵＥ）的影响,在一定供水量时,水稻的ＷＵＥ随供水量的增加而下降,但水稻旱种时,却因供水量过低,干旱胁迫严重,ＷＵＥ值为最低。不同品种的水稻ＷＵＥ存在较大的差异,抗旱性强的品种具有较高ＷＵＥ,因此选用具有较高ＷＵＥ的品种,是水稻节水栽培的关键。     

Deconstructing crop processes and models via identities

This paper is part review and part opinion piece; it has three parts of increasing novelty and speculation in approach. The first presents an overview of how some of the major crop simulation models approach the issue of simulating the responses of crops to changing climatic and weather variables, mainly atmospheric CO₂ concentration and increased and/or varying temperatures. It illustrates an important principle in models of a single cause having alternative effects and vice versa. The second part suggests some features, mostly missing in current crop models, that need to be included in the future, focussing on extreme events such as high temperature or extreme drought. The final opinion part is speculative but novel. It describes an approach to deconstruct resource use efficiencies into their constituent identities or elements based on the Kaya‐Porter identity, each of which can be examined for responses to climate and climatic change. We give no promise that the final part is ‘correct’, but we hope it can be a stimulation to thought, hypothesis and experiment, and perhaps a new modelling approach.     

Revised algorithm of ecosystem water use efficiency for semi-arid steppe in the Loess Plateau of China

Aims We evaluated the applicability of different measures of water use efficiency through analyzing the coupled dynamics of GPP and evapotranspiration in the semi-arid steppe in the Loess Plateau of China. Our objective is to explore the applicability of two quantitative measures of ecosystem water use efficiency—inherent water use efficiency (IWUE) and underlying water use efficiency (uWUE) —for the semi-arid steppe and to endeavor necessary modifications.Methods The consistency and stability of three indices of water use efficiency formulations (i.e. WUE, IWUE, uWUE) were calculated and compared at hourly, daily and annual time scales before proposing an optimal water use efficiency (oWUE). These indices were additionally used to quantify their importances in modeling the diel change of gross primary production (GPP). The yielded-accuracy of the prediction was used for justifying their uses.Important findings IWUE and uWUE appeared suitable for examining the coupled water-carbon characteristics of vegetation at hourly and daily scales, whereas WUE was more plausible on the annual and interannual scales. The optimized water use efficiency index did not improve the prediction of the coupled water-carbon characteristics as compared with uWUE, but it improved the prediction of GPP and its dynamics. oWUE and uWUE improved the predictions of GPP in the peak growing period, while WUE predicted the GPP better at the early and late growing season. Interestingly, we found that IWUE was not suitable for predicting GPP and its dynamics. The results will be of great importance in modeling the effects of climate change on the carbon assimilation and water cycle for the future.     

A test of the generality of leaf trait relationships on the Tibetan Plateau

Leaf mass per area (LMA), nitrogen concentration (on mass and area bases, N(mass) and N(area), respectively), photosynthetic capacity (A(mass) and A(area)) and photosynthetic nitrogen use efficiency (PNUE) are key foliar traits, but few data are available from cold, high-altitude environments. Here, we systematically measured these leaf traits in 74 species at 49 research sites on the Tibetan Plateau to examine how these traits, measured near the extremes of plant tolerance, compare with global patterns. Overall, Tibetan species had higher leaf nitrogen concentrations and photosynthetic capacities compared with a global dataset, but they had a slightly lower A(mass) at a given N(mass). These leaf trait relationships were consistent with those reported from the global dataset, with slopes of the standardized major axes A(mass)-LMA, N(mass)-LMA and A(mass)-N(mass) identical to those from the global dataset. Climate only weakly modulated leaf traits. Our data indicate that covarying sets of leaf traits are consistent across environments and biogeographic regions. Our results demonstrate functional convergence of leaf trait relationships in an extreme environment.