Individual Plant Level Research Articles

Biomorphs Solanum dulcamara L. and their contribution in seasonal climate grasses origin

The paper demonstrates S. dulcamara ecobiomorphs: a long rhizome semi-woody liana (LSL), a long rhizome subshrub with ascending shoots (LSAS), a root sucker subshrub and a shortlived plants of vegetative origin; and ontobiomorphs: a taproot upright subshrub (TUS), a subshrub with a mixed root system (SMRS), LSL, and LSAS. Possible stages and modes are suggested of Solanum biomorph transformation: 1. TUS, as a result of prolongation on the shoot (adventitious roots) and shoot system level (two or more replacement shoots), deviations on individual plant level (shoot lodging), transforms into SMRS; 2. SMRS, through the plant’s ontogenesis abbreviation (fragmentation), prolongation (epigeogenum rhizome), and deviation (stem twisting), transforms into LSL. Further LSL habit transformations can occur in xerophylous and hygrophylous biomorph evolution lines. On dry soil, as a result of prolongation (adventitious buds on roots), a root sucker subshrub appears. A hygrophyle line is possible in case of prolongations on the shoot level (metamere number increase within a shoot, dicyclic shoots), of the individual plant abbreviations (shortened life-time of sympodial axes, early fragmentation) and end with a short-lived plants of vegetative origin. Possibly, mien changes in S. dulcamara ontogenesis show possible stages in Solanum life forms transformation, from tree forms to LSL.

Using Sensors and Unmanned Aircraft Systems for High-Throughput Phenotyping of Biomass in Perennial Ryegrass Breeding Trials.

Increasing herbage biomass is the predominant objective for pasture plant breeding programs. Three types of field trials are commonly involved during forage plant breeding, i.e., individually spaced plants, row plot, and sward trials. Assessments of biomass production at individual plant, row plot, and sward plot levels are through visual scoring and/or cutting of biomass manually or mechanically. Both visual scoring and cutting of plants are laborious, time consuming, and costly. The development of sensor technology such as multispectral sensors and unmanned aircraft systems (UAS) provide the opportunity to accelerate the process of biomass evaluation and to increase throughput, improve resolution, and reduce time and cost. We tested either the handheld Trimble GreenSeeker® or Parrot Sequoia multispectral sensors attached to a 3DR Solo Quadcopter to assess biomass in perennial ryegrass field trials sown as spaced individual plants, row plots, and simulated sward plots. Significant correlations were observed between visual score and normalized difference vegetation index (NDVI) in a spaced plant field trial and between biomass yield and NDVI in row plot and sward trials (r = 0.12 ~ 0.93). NDVI obtained from multispectral sensors and UAS can replace visual scoring in spaced plant trials. It was also a valuable proxy for yield estimation in row plot and sward trials. These technologies will assist in transition for the forage grass breeding from pen and notepad to digital and data era.

Foliar plasticity related to gradients of heat and drought stress across crown orientations in three Mediterranean Quercus species.

Studies on plasticity at the level of a single individual plant provide indispensable information to predict leaf responses to climate change, because they allow better identification of the environmental factors that determine differences in leaf traits in the absence of genetic differences. Most of these studies have focused on the responses of leaf traits to variations in the light environment along vertical gradients, thus paying less attention to possible differences in the intensity of water stress among canopy orientations. In this paper, we analyzed the differences in leaf traits traditionally associated with changes in the intensity of water stress between east and west crown orientations in three Quercus species. The leaves facing west experienced similar solar radiation levels but higher maximum temperatures and lower daily minimum water potentials than those of the east orientation. In response to these differences, the leaves of the west orientation showed smaller size and less chlorophyll concentration, higher percentage of palisade tissue and higher density of stomata and trichomes. These responses would confirm the role of such traits in the tolerance to water stress and control of water losses by transpiration. For all traits, the species with the longest leaf life span exhibited the greatest plasticity between orientations. By contrast, no differences between canopy positions were observed for leaf thickness, leaf mass per unit area and venation patterns.

Aggregation and Allocation of Greenhouse Gas Emissions in Oil and Gas Production: Implications for Life-Cycle Greenhouse Gas Burdens

Methods used for emission aggregation and allocation have significant impacts on life-cycle greenhouse gas (GHG) emission estimates for oil and gas products; however, because of limited data availability for upstream and mid-stream oil and gas operations, the influence of the allocation technique has not been extensively explored in previous studies. GHG emissions associated with oil and gas production and processing in the Eagle Ford Shale (with 34 gas processing plants and classified into 12 production regions) are estimated, using data from 2013, at three different scales of spatial aggregation (production region, gas plant and basin levels), to characterize the spatial variabilities in GHG emissions within the Eagle Ford Shale. GHG emissions per energy content of oil and gas products vary from 3.4 to 14 g CO2e/MJ among the regions within the Eagle Ford Shale, and from 3.5 to 23 g CO2e/MJ when assigned at the individual gas processing plant level, with a basin average of 6.8 g CO2e/MJ. GHG emissions ar...

Initial soil microbiome composition and functioning predetermine future plant health.

Plant-pathogen interactions are shaped by multiple environmental factors, making it difficult to predict disease dynamics even in relatively simple agricultural monocultures. Here, we explored how variation in the initial soil microbiome predicts future disease outcomes at the level of individual plants. We found that the composition and functioning of the initial soil microbiome predetermined whether the plants survived or succumbed to disease. Surviving plant microbiomes were associated with specific rare taxa, highly pathogen-suppressing Pseudomonas and Bacillus bacteria, and high abundance of genes encoding antimicrobial compounds. Microbiome-mediated plant protection could subsequently be transferred to the next plant generation via soil transplantation. Together, our results suggest that small initial variation in soil microbiome composition and functioning can determine the outcomes of plant-pathogen interactions under natural field conditions.

Multiple resistance of Papaver rhoeas L. to 2,4‐D and acetolactate synthase inhibitors in four European countries

SummaryThe issue of cross‐ or multiple resistance to acetolactate synthase (ALS) inhibitors and the auxinic herbicide 2,4‐D was investigated in Papaver rhoeas L., a common and troublesome weed in winter cereals, in a broad‐scale study across four European countries. A combination of herbicide sensitivity bioassays and molecular assays targeting mutations involved in resistance was conducted on 27 populations of P. rhoeas originating from Greece (9), Italy (5), France (10) and Spain (3). Plants resistant to the field rate of 2,4‐D were observed in 25 of the 27 populations assayed, in frequencies ranging from 5% to 85%. Plants resistant to ALS‐inhibiting herbicides (sulfonylureas) were present in 24 of the 27 populations, in frequencies ranging from 4% to 100%. Plants resistant to 2,4‐D co‐occurred with plants resistant to sulfonylureas in 23 populations. In four of these, the probability of presence of plants with cross‐ or multiple resistance to 2,4‐D and sulfonylureas was higher than 0.5. ALS genotyping of plants from the field populations or of their progenies, identified ALS alleles carrying a mutation at codon Pro197 or Trp574 in 2,4‐D‐sensitive and in 2,4‐D‐resistant plants. The latter case confirmed multiple resistance to 2,4‐D and ALS inhibitors at the level of individual plants in all four countries investigated. This study is the first to identify individual plants with multiple resistance in P. rhoeas, an attribute rarely assessed in other weed species, but one with significant implications in designing chemical control strategies.

Aerial photography and dendrochronology as tools for recreating invasion histories: do they work for bitou bush (Chrysanthemoides monilifera subsp. rotundata)?

There is an increasing need to understand demographic change to improve management outcomes for controlling invasive alien species. We applied three emerging techniques for recreating past population dynamics—high resolution aerial photography time series, stem growth ring analysis and population level field surveys—to recreate the introduction and invasion history for bitou bush (Chrysanthemoides monilifera subsp. rotundata) in Western Australia. We also compared across dating techniques to test the validity of using stem rings produced by successive cambia for dating purposes, and analysed for the influence of ontogenetic, environmental and morphological factors on stem ring formation. Aerial photography allowed for an accurate recreation of plant presence over time and individual plant age for 18 plants. In a sample of over 500 plants with up to 42 rings, canopy area was related to plant age and ring number, while stem diameter was related to canopy size and ring number. However, stem rings were not produced in a temporally consistent manner and could not be predicted reliably. Up to eight stem rings were produced in younger plants, for which the rate of ring production was greatest. While there was an ontogenetic growth pattern for ring width, no inter-plant synchronisation of ring size was detected, as would be expected if ring size were a response to landscape level climate factors. With aerial imagery and stem ring analysis providing new ways to recreate plant population dynamics at the individual plant level, managers can use this insight to refine conservation and invasion management programs. For bitou bush, such information will focus the duration and location of the current eradication program in Western Australia.

Cross acclimation effects of spring freezing and summer drought on plant functional groups and ecosystem properties

At the level of individual plants, exposure to prior freezing can increase drought tolerance, in a phenomenon referred to as cross acclimation. However, it is unclear how cross acclimation may contribute to the combined effects of freezing and drought on plants at the community or ecosystem levels, given that cross acclimation can vary among species. We used intact plant-soil mesocosms from an old field to examine how spring freezing influences summer drought tolerance, assessed via the responses of major functional groups (graminoids, legumes and non-leguminous forbs) and total plant productivity. We applied 15N tracer to the mesocosms in either spring or summer, to assess effects on early/late season nitrogen retention. Freezing and drought affected both aboveground production and 15N retention significantly, but their effects were additive, which was inconsistent with cross acclimation. The aboveground biomass responses differed from this trend at the functional group level, with an apparent cross acclimation effect for legumes, multiplicative effects of freezing and drought for non-leguminous forbs, and no significant freezing or drought effects for graminoids. These results suggest that despite variation in cross acclimation among functional groups, possible competitive and compensatory interactions can dilute cross acclimation effects at the ecosystem level.

Determination of natural rubber and resin content of guayule fresh biomass by near infrared spectroscopy

The determination of natural rubber and resin contents of guayule (Parthenium argentatum) requires a long and destructive methodology to be implemented in the laboratory. In order to achieve a large number of measurements, it is necessary to determine the contents directly in the field in a fast and non-destructive way. The recent emergence of portable near infrared spectroscopy makes possible the use of this technology directly on the plants, without preparation of samples in the laboratory. The aim is to check the possibility of quantifying natural rubber and resin by using such a portable device directly on the guayule plants. Our research hypothesis is that the measure in near infrared can be performed directly on the surface of the bark. A set of 200 branches of guayule was collected randomly in a single experimental plot for two selected genotypes showing very different morphological traits. A difference between average contents of natural rubber and resin measured using a solvent-based laboratory reference method was observed with relation to the variety. Models of near infrared spectroscopy have been developed for samples in the form of powders, dry branches and fresh branches harvested in the same plot. The standard error of prediction was two times higher for branches as for powders. This was due to the fact that the powders were analyzed in controlled conditions in the laboratory (moisture, sample homogeneity and particle size). Using near infrared spectroscopy directly on the plant allowed the determination of the average content of the plot before harvest. With a random sampling of 70 measures per plot, it was possible to estimate the average content of natural rubber and resin with a precision lower than 0.3%. Measurements made on fresh branches of very different diameters showed that the variability of the contents was lower in the plant than in the field. At the individual plant level, 40 measures were necessary to determine the average content of resin and 70 measures for natural rubber. These encouraging results obtained out of the field, with freshly cut biomass, showed that portable near infrared spectroscopy could be directly applied to the guayule bush in the field, for estimating natural rubber and resin production of a plot or for monitoring the seasonal evolution for breeding or agro-industrial production.

Evaluating maize phenotype dynamics under drought stress using terrestrial lidar

BackgroundMaize (Zea mays L.) is the third most consumed grain in the world and improving maize yield is of great importance of the world food security, especially under global climate change and more frequent severe droughts. Due to the limitation of phenotyping methods, most current studies only focused on the responses of phenotypes on certain key growth stages. Although light detection and ranging (lidar) technology showed great potential in acquiring three-dimensional (3D) vegetation information, it has been rarely used in monitoring maize phenotype dynamics at an individual plant level.ResultsIn this study, we used a terrestrial laser scanner to collect lidar data at six growth stages for 20 maize varieties under drought stress. Three drought-related phenotypes, i.e., plant height, plant area index (PAI) and projected leaf area (PLA), were calculated from the lidar point clouds at the individual plant level. The results showed that terrestrial lidar data can be used to estimate plant height, PAI and PLA at an accuracy of 96%, 70% and 92%, respectively. All three phenotypes showed a pattern of first increasing and then decreasing during the growth period. The high drought tolerance group tended to keep lower plant height and PAI without losing PLA during the tasseling stage. Moreover, the high drought tolerance group inclined to have lower plant area density in the upper canopy than the low drought tolerance group.ConclusionThe results demonstrate the feasibility of using terrestrial lidar to monitor 3D maize phenotypes under drought stress in the field and may provide new insights on identifying the key phenotypes and growth stages influenced by drought stress.

WIND TUNNEL TESTS OF HOW COASTAL PLANTS FEEDBACK ON DUNE SHAPE

Theoretical evolution of a coastal dune system starts at the individual plant level with the formation of bedforms, nebkha and shadow dunes, around plants. Over time, these initial bedforms can evolve into a fully developed foredune and eventually a complex dune system capable of buffering upland coastal areas against high tides and storms. Recent studies suggest that dunebuilding plant species may differ in their sand trapping efficiency and they may support different topographies, building dunes morphologically similar to their own stature – i.e. a taller steeper plant would build a taller and steeper dune. We believe that the bedforms created at the onset of dune evolution, i.e. after a storm or at the backbeach, may carry over through the life of the dune, such that understanding how plant morphology and density affects the initial formation stages of dune morphology is key to optimizing dune management, maintenance, and creation. With ERDC and USGS funding, we built a removable bed unilateral flow wind tunnel to test how the morphology among and within dominant US East coast foredune plants feeds back on bedform creation around individual plants at a baseline of zero (i.e. flat back beach or post storm).

Altitude, habitat type and herbivore damage interact in their effects on plant population dynamics.

Insects represent one of the most abundant groups of herbivores, and many of them have significant impacts on the dynamics of plant populations. As insects are very sensitive to changes in climatic conditions, we hypothesize that their effects on plant population dynamics will depend on climatic conditions. Knowledge of the variation in herbivore effects on plant population dynamics is, however, still rather sparse. We studied population dynamics and herbivore damage at the individual plant level of Salvia nubicola along a wide altitudinal gradient representing a range of climatic conditions. Using integral projection models, we estimated the effect of changes in herbivore pressure on plant populations in different climates and habitat types. Since we recorded large differences in the extent of herbivore damage along the altitudinal gradient, we expected that the performance of plants from different altitudes would be affected to different degrees by herbivores. Indeed, we found that populations from low altitudes were better able to withstand increased herbivore damage, while populations from high altitudes were suppressed by herbivores. However, the pattern described above was evident only in populations from open habitats. In forest habitats, the differences in population dynamics between low and high altitudes were largely diminished. The effects of herbivores on plants from different altitudes were thus largely habitat specific. Our results indicate potential problems for plant populations from high altitudes in open habitats because of increased herbivore damage. However, forest habitats may provide refuges for the plants at these high altitudes.

The assembly of a plant network in alpine vegetation

AbstractQuestionsPositive and negative associations among species influence the structure of plant communities. Yet how these plant associations are assembled at the community level is poorly understood. We propose a new approach that combines spatial ecology, network theory and trait‐based ecology to examine the assembly of plant–plant associations at the community level.LocationGemmipass, Swiss Alps.MethodsWe fully mapped an alpine plant community at the individual plant level, recording both plant coordinates and functional traits for each individual. We identified non‐random species associations using spatial point‐pattern analysis and partialled out the effect of abiotic heterogeneity. We then analysed the plant network structure and used plant traits to predict species associations.ResultsWe identified 36 significant spatial associations between plant species, 34 positive and two negatives. Dominant, stress‐tolerant species such as Dryas octopetala, Linaria alpina and Leontodon montanus were highly connected in the network, whereas rare, water‐ and nutrient‐demanding species such as Saxifraga aizoides, Galium anisophyllon and Thymus praecox were less connected compared to random expectation. The plant network was clustered, meaning that species were overall more connected among each other than expected by chance.ConclusionsPositive associations among species characterized the studied plant community. Besides the primary effect of associations of the “foundation” species D. octopetala with other species, these “subordinate” plants were also associated with each other. Our study reveals the assembly of plant communities as driven by positive associations among stress‐tolerant pioneer species, highlighting their role in supporting the cohesiveness of alpine plant communities.

Hydropower revenues under the threat of climate change in Brazil

Abstract This work analyzes the impacts of climate change in the revenues of hydropower plants. One important input for designing and evaluating investment opportunities in hydropower is the water inflows historical data. Unfortunately, the use of such information alone may not project well the future power generation due to the influence of climate change in the water inflow patterns. This paper introduces spatio-temporal information of the future climate into the operational planning of the Brazilian hydropower system. Global climate models from IPCC are considered along with downscaled regional climate models. Our results at the individual hydro plant level show the importance of taking into account climate change information when performing hydro generation planning studies.

Evaluating the efficacy of Hypogeococcus sp. as a biological control agent of the cactaceous weed Cereus jamacaru in South Africa

We evaluated the efficacy of Hypogeococcus sp. (Hemiptera: Pseudococcidae) as a biological control agent of the cactaceous weed Cereus jamacaru De Candolle (Queen of the Night cactus) in South Africa. This weed has been described as being under complete biological control due to the action of Hypogeococcus sp., although no formal post-release evaluation had been conducted prior to this study. Biological control was associated with significant reductions in fruiting, plant survival and plant densities, while plant population age structures were negatively affected. Weed populations infected by Hypogeococcus sp. were typified by low or non-existent recruitment and are expected to diminish with time. Populations where Hypogeococcus sp. was absent displayed extensive recruitment, and are predicted to expand or self-replace, if left unchecked. These data indicate that Hypogeococcus sp. has a significant negative effect on C. jamacaru at the individual plant and population level, and given sufficient time provides complete biological control over this weed in South Africa.

Estimation of biophysical parameters in wheat crops in Golestan province using ultra-high resolution images

ABSTRACTDue to various factors which impress wheat growth variability, we need short–term monitoring of biophysical parameters using ultra–high resolution images. These provide an ability to monitor crops at the individual plant level. Two flight missions were carried out at altitude of 40 m with a commercial quad copter and a commercial camera. The images were taken before and after tillage over an 8.8 ha field. The 2 cm orthoimages and surface models were generated using photogrammetric software. Then, the image variables including ratio of the blue and green band, ratio of the red and blue band,ratio of the red and green band, plant height were extracted from orthoimages and surface models. Field measurement included the leaf area index, plant height and biomass for 15 plots each of area 1 m × 1 m. Due to a linear relationship between the biophysical parameters and image variables, it was used a multivariate regression model for modelling. The model using the image variables resulted in coefficient of determination (R2) of 0.95 and the lowest error measures (RMSE = 0.24). The results show that ultra–high resolution images can be used for monitoring of biophysical parameters in wheat crops but it is limited for large area.

Investigations of 2,4-D and Multiple Herbicide Resistance in a Missouri Waterhemp (Amaranthus tuberculatus) Population

AbstractResearch was conducted from 2015 to 2017 to investigate the potential for 2,4-D and multiple herbicide resistance in a waterhemp [Amaranthus tuberculatus(Moq.) J. D. Sauer] population from Missouri (designated MO-Ren). In the field, visual control of the MO-Ren population with 0.56 to 4.48 kg 2,4-D ha−1ranged from 26% to 77% in 2015 and from 15% to 55% in 2016. The MO-Ren population was highly resistant to chlorimuron, with visual control never exceeding 7% either year. Estimates of the 2,4-D dose required to provide 50% visual control (I50) of the MO-Ren population were 1.44 kg ha−1compared with only 0.47 kg 2,4-D ha−1for the susceptible population. Based on comparisons to a susceptible population in dose–response experiments, the MO-Ren population was approximately 3-fold resistant to 2,4-D, and 7-, 7-, 22-, and 14-fold resistant to atrazine, fomesafen, glyphosate, and mesotrione, respectively. Dicamba and glufosinate were the only two herbicides that provided effective control of the MO-Ren population in these experiments. Examinations of multiple herbicide resistance at the individual plant level revealed that 16% of the plants of the MO-Ren population contained genes stacked for six-way herbicide resistance, and only 1% of plants were classified as resistant to a single herbicide (glyphosate). Results from these experiments confirm that the MO-RenA. tuberculatuspopulation is resistant to 2,4-D, atrazine, chlorimuron, fomesafen, glyphosate, and mesotrione, making this population the third 2,4-D–resistantA. tuberculatuspopulation identified in the United States, and the first population resistant to six different herbicidal modes of action.

Fire‐induced deforestation in drought‐prone Mediterranean forests: drivers and unknowns from leaves to communities

AbstractOver the past 15 years, 3 million hectares of forests have been converted into shrublands or grasslands in the Mediterranean countries of the European Union. Fire and drought are the main drivers underlying this deforestation. Here we present a conceptual framework for the process of fire‐induced deforestation based on the interactive effects of fire and drought across three hierarchical scales: resistance in individuals, resilience in populations, and transitions to a new state. At the individual plant level, we review the traits that confer structural and physiological resistance, as well as allow for resprouting capacity: deforestation can be initiated when established individuals succumb to fire. After individuals perish, the second step toward deforestation requires a limited resilience from the population, that is, a reduced ability of that species to regenerate after fire. If individuals die after fire and the population fails to recover, then a transition to a new state will occur. We document trade‐offs between drought survival and fire survival, as embolism resistance is negatively correlated with fire tolerance in conifers and leaf shedding or drought deciduousness, a process that decreases water consumption at the peak of the dry season, temporally increases crown flammability. Propagule availability and establishment control resilience after mortality, but different hypotheses make contrasting predictions on the drivers of post‐fire establishment. Mycorrhizae play an additional role in modulating the response by favoring recovery through amelioration of the nutritional and water status of resprouts and new germinants. So far, resprouter species such as oaks have provided a buffer against deforestation in forests dominated by obligate seeder trees, when present in high enough density in the understory. While diversifying stands with resprouters is often reported as advantageous for building resilience, important knowledge gaps exist on how floristic composition interacts with stand flammability and on the “resprouter exhaustion syndrome,” a condition where pre‐fire drought stress, or short fire return intervals, seriously restrict post‐fire resprouting. Additional attention should be paid to the onset of novel fire environments in previously fire‐free environments, such as high altitude forests, and management actions need to accommodate this complexity to sustain Mediterranean forests under a changing climate.

夏玉米叶片气体交换参数对干旱过程的响应

PDF HTML阅读 XML下载 导出引用 引用提醒 夏玉米叶片气体交换参数对干旱过程的响应 DOI: 10.5846/stxb201703260520 作者: 作者单位: 中国气象科学研究院,中国气象科学研究院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金重点项目（41330531）；国家重点研发计划项目（2016YFD0300106）；公益性行业（气象）科研专项（重大专项）（GYHY201506001-3） Effect of drought on leaf gas exchange in Summer Maize Author: Affiliation: Chinese Academy of Meteorological Sciences,Chinese Academy of Meteorological Sciences Fund Project: National Natural Science Foundation of China (41330531) and China Special Fund for Meteorological Research in the Public Interest (Major projects) (GYHY201506001-3) 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:目前已经开展了大量的干旱对作物叶片气体交换参数影响的研究，但关于作物叶片气体交换参数对干旱过程的响应及其关键阈值的研究仍较少。基于夏玉米七叶期开始的5个初始水分梯度的长时间持续干旱模拟实验资料，分析了不同强度持续干旱过程中夏玉米叶片气体交换参数（净光合速率Pn，气孔导度Gs，蒸腾速率Tr，胞间CO2浓度Ci和气孔限制值Ls）的变化规律及其关键阈值。结果表明，玉米的净光合速率（Pn），蒸腾速率（Tr）和气孔导度（Gs）在干旱发生初期呈大幅度下降，但随着干旱持续会出现一定的适应性。利用统计容忍限方法确定了夏玉米拔节期Pn，Tr和Gs响应干旱的临界土壤相对湿度（0-30cm）分别为53%，51%和48%，对应的临界叶含水率分别为81.8%，81.3%和81.2%。夏玉米光合作用由气孔限制向非气孔限制转换的0-30cm土壤相对湿度均为44%±2%，对应的叶含水率均为77.6%±0.3%。研究结果可为夏玉米干旱发生发展过程的监测预警提供依据。 Abstract:A large number of studies have been carried out to investigate how crop photosynthesis responds to drought, but few have investigated the response of crop leaf gas exchange to drought processes, and their response thresholds. Based on a prolonged drought experiment in summer maize conducted in 2013, which included five watering treatments, and began from the 7-leaf stage, we investigated how drought developed with different initial amounts of irrigation, and how leaf gas exchange parameters changed as the drought progressed. Then, we determined the thresholds of soil and leaf moisture content when leaf gas exchange parameters began to respond to drought. The results showed that treatments with different initial amounts of irrigation induced different drought processes. Drought occurred earlier, persisted longer, and was more severe with treatments receiving less irrigation. The net photosynthetic rate (Pn), transpiration rate (Tr), and stomatal conductance (Gs) of summer maize under different watering treatments decreased sharply at the initial stage of drought; however, these parameters declined slower as drought prolonged, and tended to be almost identical to those growing under normal environment conditions. This indicated the acclimation of maize photosynthesis in response to prolonged drought. The onset of agricultural drought was typically marked by a decline in soil moisture below a critical point, which significantly impact crops. As drought progressed, the plant constituents and physiological processes could be altered sequentially, while lower-level responses would lead to changes in higher-level responses, and eventually changes at an individual plant level. Plant leaf gas exchange was found to be more directly affected by leaf water status than soil moisture content. Therefore, we identified the tipping points when maize leaf gas exchange parameters started to be affected by drought based on the tolerance limits of normal distribution; these were then quantified by soil moisture and leaf moisture content, respectively. The results showed that, Pn, Tr, and Gs decreased sharply when the relative soil moisture of 0-30cm depth was lower than 53%, 51%, and 48%, respectively, and leaf moisture content was lower than 81.8%, 81.3%, and 81.2%, respectively. At the initial stage of drought, the intercellular CO2 concentration (Ci) decreased, and stomatal limitation value (Ls) increased, indicating that stomatal closure accounted for the major decline in maize photosynthesis. As drought progressed, Ci increased while Ls decreased, indicating that non-stomatal limitation, other than stomatal closure, contributes to the major decreases in maize photosynthesis. The point at which the dominant limiting factor of maize photosynthesis converted from stomatal to non-stomatal varied under different treatments. The conversion time was earlier in maize that received lower initial amounts of irrigation due to longer persistence and greater severity of drought, and later in maize that received relatively higher initial amounts of irrigation. However, the thresholds of relative soil moisture and leaf moisture content when the conversion occurred were almost identical under all five treatments. The critical relative soil moisture of 0-30cm depth was about 44%±2% and the corresponding leaf moisture content was about 77.6%±0.3%. The results could provide reference information for drought monitoring and assessment of summer maize. 参考文献 相似文献 引证文献

A generic individual-based model to simulate morphogenesis, C-N acquisition and population dynamics in contrasting forage legumes.

Individual-based models (IBMs) are promising tools to disentangle plant interactions in multi-species grasslands and foster innovative species mixtures. This study describes an IBM dealing with the morphogenesis, growth and C-N acquisition of forage legumes that integrates plastic responses from functional-structural plant models. A generic model was developed to account for herbaceous legume species with contrasting above- and below-ground morphogenetic syndromes and to integrate the responses of plants to light, water and N. Through coupling with a radiative transfer model and a three-dimensional virtual soil, the model allows dynamic resolution of competition for multiple resources at individual plant level within a plant community. The behaviour of the model was assessed on a range of monospecific stands grown along gradients of light, water and N availability. The model proved able to capture the diversity of morphologies encountered among the forage legumes. The main density-dependent features known about even-age plant populations were correctly anticipated. The model predicted (1) the 'reciprocal yield' law relating average plant mass to density, (2) a self-thinning pattern close to that measured for herbaceous species and (3) consistent changes in the size structure of plant populations with time and pedo-climatic conditions. In addition, plastic changes in the partitioning of dry matter, the N acquisition mode and in the architecture of shoots and roots emerged from the integration of plant responses to their local environment. This resulted in taller plants and thinner roots when competition was dominated by light, and shorter plants with relatively more developed root systems when competition was dominated by soil resources. A population dynamic model considering growth and morphogenesis responses to multiple resources heterogeneously distributed in the environment was presented. It should allow scaling plant-plant interactions from individual to community levels without the inconvenience of average plant models.