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Table of Content
    Volume 41 Issue 4
    10 April 2017

    The landscape of exotic cordgrass Spartina alterniflora in a mangrove wetland in Gaoqiao, Zhanjiang, Guangdong (Photographed by CHEN Quan). Chen et al. studied the effects of Spartina alterniflora invasion on enrichment of sedimental heavy metals in a mangrove wetland. The results showed S. alterniflora often significantly enriched sedimental heavy metals, and its dense above- and below-ground architectures likely played a predominant role in causing enri

    Cover and contents of Vol. 41, No. 4, 2017

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    Orginal Article
    An evaluation of four threshold selection methods in species occurrence modelling with random forest: Case studies with Davidia involucrata and Cunninghamia lanceolata
    Lei ZHANG, Lin-lin WANG, Shi-Rong LIU, Peng-Sen SUN, Zhen YU, Shu-Tao HUANG, Xu- Dong ZHANG
    Chin J Plan Ecolo. 2017, 41 (4):  387-395.  doi:10.17521/cjpe.2016.0184
    Abstract ( 399 )   HTML ( 9 )   PDF (1942KB) ( 780 )   Save
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    Aims Predictive species distribution models (SDMs) are increasingly applied in resource assessment, environmental conservation and biodiversity management. However, most SDM models often yield a predicted probability (suitability) surface map. In conservation and environmental management practices, the information presented as species presence/absence (binary) may be more practical than presented as probability or suitability. Therefore, a threshold is needed to transform the probability or suitability data to presence/absence data. However, little is known about the effects of different threshold-selection methods on model performance and species range changes induced by future climate. Of the numerous SDM models, random forest (RF) can produce probabilistic and binary species distribution maps based on its regression and classification algorisms, respectively. Studies dealing with the comparative test of the performances of RF regression and classification algorisms have not been reported.
    Methods Here, the RF was used to simulate the current and project the future potential distributions of Davidia involucrata and Cunninghamia lanceolata. Then, four threshold-setting methods (Default 0.5, MaxKappa, MaxTSS and MaxACC) were selected and used to transform modelled probabilities of occurrence into binary predictions of species presence and absence. Lastly, we investigated the difference in model performance among the threshold selection methods by using five model accuracy measures (Kappa, TSS, Overall accuracy, Sensitivity and Specificity). We also used the map similarity measure, Kappa, for a cell-by-cell comparison of similarities and differences of distribution map under current and future climates.
    Important findings We found that the choice of threshold method altered estimates of model performance, species habitat suitable area and species range shifts under future climate. The difference in selected threshold cut-offs among the four threshold methods was significant for D. involucrata, but was not significant for C. lanceolata. Species’ geographic ranges changed (area change and shifting distance) in response to climate change, but the projections of the four threshold methods did not differ significantly with respect to how much or in which direction, but they did differ against RF classification predictions. The pairwise similarity analysis of binary maps indicated that spatial correspondence among prediction maps was the highest between the MaxKappa and the MaxTSS, and lowest between RF classification algorism and the four threshold-setting methods. We argue that the MaxTSS and the MaxKappa are promising methods for threshold selection when RF regression algorism is used for the distribution modeling of species. This study also provides promising insights to our understanding of the uncertainty of threshold selection in species distribution modeling.

    Seasonality and drivers of stem CO2 efflux for four temperate coniferous tree species
    Fei XU, Chuan-Kuan WANG
    Chin J Plan Ecolo. 2017, 41 (4):  396-408.  doi:10.17521/cjpe.2016.0191
    Abstract ( 280 )   HTML ( 3 )   PDF (1382KB) ( 561 )   Save
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    Aims Stem CO2 efflux (Es) is an important component of annual carbon budget in forest ecosystems, but how biotic and environmental factors regulate seasonal and inter-specific variations in Es is poorly understood. The objectives of this study were: (1) to compare seasonal dynamics in Es for four temperate coniferous tree species in northeastern China, including Korean pine (Pinus koraiensis), Korean spruce (Picea koraiensis), Mongolian pine (Pinus sylvestris var. mongolica), and Dahurian larch (Larix gmelinii); and (2) to explore factors driving the inter-specific variability in Es during the growing and non-growing seasons.
    Methods Ten to twelve trees for each tree species were sampled for Es and stem temperature at 1 cm depth beneath the bark (Ts) measurements in situ with an infrared gas analyzer (LI-6400 IRGA) and a digital thermometer, respectively, from July to October 2013 and March to July 2014. The daily stem circumference increment (Si), sapwood nitrogen concentration ([N]), and related environmental factors were monitored simultaneously.
    Important findings The temporal variation in Es for the four tree species overall followed the changes in Ts throughout the study period, with the maxima occurring in the summer months (late May to early July) characterized by higher temperature and more rapid stem growth and the minima in spring (late March to April) or autumn (October) having lower temperature. Ts accounted for 42%-91% and 56%-89% of variations in Es during the growing (May to September) and non-growing (other months) seasons, respectively. Furthermore, apart from Ts, we also found significant regression relationships between Es and Si, relative air humidity and [N] during the growing season, but their forms and correlation coefficients were species-dependent. These results indicated that Ts was the dominant environmental factor affecting seasonal variations in Es, but the magnitude of the effect varied with tree species and growth rhythm. Mean Es for each of the four tree species was significantly higher in the growing season than in the non-growing season, whereas within the season there were also significant differences in mean Es among the tree species (all p < 0.05). The temperature sensitivity of Es (Q10 value) did not differ significantly among the tree species during the growing season, ranging from 1.64 for Dahurian larch to 2.09 for Mongolian pine, but did differ during the non-growing season which varied from 1.80 for Korean pine to 3.14 for Dahurian larch. Moreover, Korean spruce, Mongolian pine and Dahurian larch had significantly greater Q10 values in the non-growing season than in the growing season (p < 0.05). These findings suggested that the differences of the response of Es to temperature change for different tree species were mainly from the non-growing season. Because the seasonality and inter-specific variability in Es for these temperate coniferous tree species were primarily controlled by multiple factors such as temperature, we conclude that using a single annual temperature response curve to estimate the annual Es may lead to more uncertainty.

    Effects of Spartina alterniflora invasion on enrichment of sedimental heavy metals in a mangrove wetland and the underlying mechanisms
    Quan CHEN, Ke-Ming MA
    Chin J Plan Ecolo. 2017, 41 (4):  409-417.  doi:10.17521/cjpe. 2016.0338
    Abstract ( 380 )   HTML ( 7 )   PDF (4186KB) ( 528 )   Save
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    Aims The cordgrass Spartina alterniflora is one of the highly successful invasive plants in coastlines worldwide. Although the S. alterniflora invasion is threatening mangroves and the increasing heavy metal pollution of oceans and coasts are of growing concerns, especially in China, the effects of S. alterniflora invasion on the enrichment of sedimental heavy metals in mangrove wetlands are not known. The objectives of this study are to determine the effects of S. alterniflora invasion on enrichment of sedimental heavy metals in the mangrove wetland and the underlying mechanisms.
    Methods We investigated differences in the contents of sedimental heavy metals, including As, Cd, Cr, Cu, Ni, Pb, Zn, and Mn, for two pairs of comparisons (unvegetated shoal vs S. alterniflora monoculture and Avicennia marina monoculture vs A. marina + S. alterniflora mixture), and their relationships with environmental factors in Zhanjiang Mangrove National Natural Reserve, Guangdong, China.
    Important findings Spartina alterniflora invasions in mangrove wetlands increased the contents of sedimental heavy metals, with the effects being significant on Cr, Ni, Cu, Zn, and Mn. The intermediate level of pollution was only detected in the sedimental Cd. The presence of S. alterniflora resulted in enrichment in the sedimental heavy metals in the mangrove wetland in Zhanjiang, but not to the degree of concerns for contaminations. The contents of sedimental organic matter, total C, total N, total S and total K were strongly related to the contents of sedimental heavy metals in the invaded mangrove wetland. Ultimately, the dense above-and below-ground architectures of the invasive S. alterniflora likely play a predominant role in causing enrichment of sedimental heavy metals.

    Duration of mulching caused variable pools of labile organic carbon in a Phyllostachys edulis plantation
    Rui-Yu ZHAO, Zheng-Cai LI, Bin WANG, Xiao-Gai GE, Yun-Xi DAI, Zhi-Xia ZHAO, Yu-Jie ZHANG
    Chin J Plan Ecolo. 2017, 41 (4):  418-429.  doi:10.17521/cjpe.2016.0340
    Abstract ( 305 )   HTML ( 1 )   PDF (1083KB) ( 513 )   Save
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    Aims Soil total organic carbon and labile organic carbon are important indicators in evaluating soil quality. Mulching is widely applied to promote the emergence of bamboo shoot in winter time through stand management. Yet the consequences of mulching on soil quality in Phyllostachys edulis have not been well studied. We aim at the quantitative effect of mulching duration on soil quality in P. edulis stands.
    Methods Several P. edulis stands located in Huangyan District of Taizhou, Zhejiang Province of China, had been applied with mulching for 1-2 years and were used in this study to assess the mulching effects. We also selected stands without mulching treatment as the reference sites (or control, CK) for comparisons.||||Important findings Total soil organic carbon (TOC), light fraction organic matter (LFOM), and easily-oxidized carbon (EOC) contents at stands with 1-year and 2-year mulching treatments were significantly increased compared with those at the CK sites. The 1-year mulching increased TOC, LFOM and EOC by 11.2%-74.2%, 31.7%-196.9% and 5.0%-79.6%, respectively, than those of CK sites, while by 22.2%-90.8%, 36.7%-238.5%, and 21.9%-97.5% with 2-year treatment. However, the contents of water-soluble organic carbon (WSOC) changed insignificantly. Among the indicators, we found that WSOC:TOC in CK was higher than that with the mulching treatments, while EOC:TOC with 1-year treatment was higher than that with 2-year treatment, and EOC:TOC with 2-year treatment was higher than that of CK. Additionally, WSOC, EOC, and LFOM at all three treatments showed high correlations with TOC, with a higher correlation coefficient of WSOC with TOC of 0- 30 cm soil layers in CK than those with mulching treatments. The correlation coefficient of EOC and LFOM with TOC was the highest at the 2-year mulching sites. More importantly, TOC, WSOC, EOC, and LFOM were significantly (p < 0.05), or extremely significantly (p < 0.01), correlated with soil nutrient content, including total N, hydrolysis N, available P, available K, exchangeable Ca, and exchangeable Mg in all treatments. In sum, it appeared that mulching in short term can increase the contents of TOC, soil labile organic carbons and soil nutrients in bamboo soils, yielding an improved soil quality and thus can be promoted as a plausible practice for the sustainable management of P. edulis stands.

    Effects of tree mortality on the spatial patterns and interspecific associations of plant species in a Quercus aliena var. acuteserrata forest in Baotianman, Henan, China
    Bo-Liang WEI, Zhi-Liang YUAN, Shuai NIU, Xia LIU, Hong-Ru JIA, Yong-Zhong YE
    Chin J Plan Ecolo. 2017, 41 (4):  430-438.  doi:10.17521/cjpe.2016.0297
    Abstract ( 333 )   HTML ( 7 )   PDF (3176KB) ( 574 )   Save
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    Aims Tree mortality is an important ecological process in forest ecosystems. The aims of this study were to determine how tree mortality influences the spatial patterns and interspecific associations of plant species, and what are the causes of tree mortality in a 1 hm2 permanent plot in Baotianman National Nature Reserve, Nanyang City, Henan Province.
    Methods We conducted field investigations in the plot and used spatial point pattern analysis to examine the spatial patterns and interspecific associations of 17 species prior to and following mortality.
    Important findings (1) Most of the species in the study plot showed an aggregated distribution both pre- and post-mortality. However, the number of species showing aggregated distribution decreased and the number of species showing random distribution increased following the mortality event. (2) Most species were positively associated with Quercus aliena var. acuteserrata both pre- and post-mortality, while some had no apparent association. Following tree mortality, on fine scales, the number of species with positive associations increased, and the number of species with negative associations decreased. (3) Tree mortality was in consistency with the random death hypothesis. The interspecific associations of four species with Q. aliena var. acuteserrata completely changed following death. For most species, the spatial patterns and the interspecific association with Q. aliena var. acuteserrata either changed at minor scales or did not change. The variations in spatial patterns or interspecific associations were inconsistent among species. (4) The dead trees of Q. aliena var. acuteserrata were significantly associated with the living trees in 13 species, but the associations between dead and living trees were not in agreement with the changes in interspecific association following mortality. Only five living tree species competed with the dead trees of Q. aliena var. acuteserrata, and the competition between each of these species and Q. aliena var. acuteserrata intensified after individual death. Tree mortality is the result of a variety of factors. Although the tree mortality in the study plot was in accordance with the random death hypothesis, there were also a few individuals which were dead from competition.

    Effects of glyphosate on interspecific competition between Solidago canadensis and Imperata cylindrica
    Chun-Feng GU, Xiao-Qi YE, Ming WU, Xue-Xin SHAO, Sheng-Wu JIAO
    Chin J Plan Ecolo. 2017, 41 (4):  439-449.  doi:10.17521/cjpe.2016.0331
    Abstract ( 339 )   HTML ( 5 )   PDF (1365KB) ( 557 )   Save
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    Aims The extensive use of herbicide to control invasive plants would change the relationship between alien and neighboring plants. In order to provide data for rational use of herbicide and a theoretical reference for further studies on the ecological effects of glyphosate, we explored the variation of the relationship between an invasive plant Solidago canadensis and a native plant Imperata cylindrica when they were sprayed glyphosate.
    Methods A replacement series experiment was conducted from June to August 2016 in Wetland Ecosystem Research Station of Hangzhou Bay, State Forestry Administration, to examine the effects of glyphosate at seven concentration levels (0, 0.3, 0.6, 0.9, 1.2, 1.5, 1.8 mL·L-1) on the growth and interspecific competition of S. canadensis and I. cylindrica.
    Important findings (1) Glyphosate treatment significantly inhibited the growth of S. canadensis and I. cylindrica (p < 0.05). During the test, cumulative growth of height and leaf number of S. canadensis were apparently reduced with the increase of glyphosate concentration, but the leaf number of S. canadensis treated with 0.3- 1.5 mL·L-1 glyphosate was re-growing with time, while the one treated with 1.8 mL·L-1 was mostly dead. The withering rate of tiller and green leaf of I. cylindrica also significantly increased with the increase of glyphosate concentration, and the growth indices of this plant treated with 0.3-0.6 mL·L-1 were also re-growing with time. (2) Glyphosate treatment significantly affected interspecific competition (p < 0.05), which diminished as the glyphosate concentration increased. (3) Interspecific competition has significant influence on the biomass allocation of S. canadensis (p < 0.05). When facing competition, S. canadensis would allocate more organic matter to root and thus increase the ratio of root to shoot. Competition only inhibited the tiller number and total biomass of I. cylindrica, but insignificantly affected its ratio of root to shoot. (4) The interaction between glyphosate treatment and S. canadensis-I. cylindrica interspecific relationship also significantly influenced the biomass of S. canadensis and I. cylindrica (p < 0.05), but insignificantly affected the root/shoot ratio of two plants. Different plants have different tolerance to glyphosate stress. Compared with native plant I. cylindrica, S. canadensis has stronger tolerance to glyphosate. Low-concentration glyphosate could decrease the competitive intensity between S. canadensis and I. cylindrica, which may disturb the structure and dynamics of plant communities.

    Plant nutrient dynamics and stoichiometric homeostasis of invasive species Spartina alterniflora and native Cyperus malaccensis var. brevifolius in the Minjiang River estuarine wetlands
    Li-Ling JIANG, Cong-Sheng ZENG, Jun-Jiong SHAO, Xu-Hui ZHOU
    Chin J Plan Ecolo. 2017, 41 (4):  450-460.  doi:10.17521/cjpe.2016.0193
    Abstract ( 456 )   HTML ( 3 )   PDF (1427KB) ( 598 )   Save
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    Aims Stoichiometric homeostasis is an important mechanism in maintaining ecosystem structure, function, and stability. The invasion of exotic species, Spartina alterniflora, has largely threatened the structure and function of native ecosystems in the Minjiang River estuarine wetland. However, how S. alterniflora invasion affect plant stoichiometric homeostasis is largely unknown. This could enhance our understanding on wetland ecosystem stability and expand the applications of ecological stoichiometry theory.
    Methods Nitrogen (N) and phosphorus (P) contents of plant organs and soils in the S. alterniflora, Cyperus malaccensis var. brevifolius, and S. alterniflora-C. malaccensis var. brevifolius mixture were measured, and the homeostatic index (H) was calculated according to the stoichiometric homeostasis theory.
    Important findings Our results showed that the invasion of S. alterniflora significantly increased soil N:P ratio (p < 0.05), but did not affect soil N or P contents. The N and P contents of leaf and stem were the highest for S. alterniflora, and those of the stem were the highest for C. malaccensis var. brevifolius. At the ecosystem level, the average of homeostatic index (H) of N (HN, 25.31) was larger than those of P (HP, 10.33) and N:P (HN:P, 2.50). At the organ level, root HN was significantly larger than stem HN (p < 0.05) and sheath HN:P was greater than root HN:P (p < 0.05), while there was no significant difference for HP among root, stem, leaf, and sheath (p > 0.05). As for species, root HN of S. alterniflora was significantly larger than that of C. malaccensis var. brevifolius in the mixture community (p < 0.05). In the monoculture, stem HN:P of S. alterniflora was significantly higher than that of C. malaccensis var. brevifolius (p < 0.05). Furthermore, root HN, leaf HN and sheath HN of S. alterniflora in the mixed community was significantly larger than that of S. alterniflora in the monoculture (p < 0.05), suggesting that S. alterniflora invasions increased their stoichiometric homeostasis. Meanwhile, the stoichiometric homeostasis of invasive and native plants were influenced by multiple factors, such as nutrients, organs, vegetation, and invasion. However, larger homeostasis was found in S. alterniflora than in C. malaccensis var. brevifolius in some particular organs either in mixture or monoculture communities. Therefore, the successful invasion of S. alterniflora may result from higher homeostatic index than the native species, C. malaccensis var. brevifolius.

    C, N and P stoichiometry in different organs of Vitex rotundifolia in a Poyang Lake desertification hill
    Hong-Yan ZHOU, Qin WU, Ming-Yue CHEN, Wei KUANG, Ling-Ling CHANG, Qi-Wu HU
    Chin J Plan Ecolo. 2017, 41 (4):  461-470.  doi:10.17521/cjpe.2016.0231
    Abstract ( 317 )   HTML ( 0 )   PDF (1334KB) ( 583 )   Save
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    Aims The objectives were to clarify the responses of C, N and P stoichiometry of Vitex rotundifolia to desertification, and determine the C, N and P stoichiometric relationships among the organs.
    Methods In this study, different organs (e.g. flowers, leaves, twigs, creeping stems, fine roots) of V. rotundifolia were sampled along a desertification gradient in a typical Poyang Lak sandy hill. Subsequently, C, N and P contents of various organs were measured.
    Important findings The results showed nutrient contents in different organs ranged from 386.28 to 449.47 mg·g-1 for carbon, 11.40 to 25.37 mg·g-1 for nitrogen and 0.89 to 1.54 mg·g-1 for phosphorus, respectively. C, N and P contents differed significantly among the five organs. The maximum N and P content were found in flowers, whereas the minimums were observed in twigs and creping stems. Moreover, desertification intensity only significantly affected C, N and C:P. C:N and N:P ratios maintained relatively stable. Except N:P, the other nutrient elements and associated stoichiometry significantly differed among the organs. Hence, organs, rather than desertification intensity mainly controlled the C, N and P content and their stoichiometry variability. Although there was a positive correlation between mass-based N content (Nmass) and P content (Pmass) across the three desertification zones, the Nmass-Pmass relationship in V. rotundifolia did not shift. Irrespective desertification intensity and organs, N:P stoichiometry of V. rotundifolia was well constrained. In addition, significant correlations of C, N and P contents among organs were mainly found in the above-ground parts, especially between twigs and creeping stems.

    Effects of enhanced UV-B radiation and nitrogen deposition on the growth of invasive plant Triadica sebifera
    Bang-Liang DENG, Qian LIU, Xi-Shuai LIU, Li-Ya ZHENG, Liang-Bo JIANG, Xiao-Min GUO, Yuan-Qiu LIU, Ling ZHANG
    Chin J Plan Ecolo. 2017, 41 (4):  471-479.  doi:10.17521/cjpe.2016.0292
    Abstract ( 381 )   HTML ( 2 )   PDF (1415KB) ( 489 )   Save
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    Aims Exotic plant invasions are important components of global change, threatening both the stability and function of invaded ecosystems. Shifts in competitive ability of invasive plants versus their native congeners have been documented. Enhanced UV-B radiation and nitrogen (N) deposition might interact with soil biota communities impacting the invasion process of exotic plant species. To understand the potential effects by UV-B and N with soil biota on plant growth would enhance our understanding of the mechanisms in plant invasions in the context of global change.
    Methods We conducted a full-factorial pot experiment in the native range (China) of Triadica sebifera invading US to investigate how UV-B radiation, N and soil biota together determined their seedling growth.
    Important findings The results showed that UV-B radiation, N and soil sterilization together impacted the growth of T. sebifera seedlings. UV-B radiation induced changes in biomass allocation with larger leaf biomass observed in response to UV-B radiation. In addition, N increased aboveground biomass and decreased root biomass simultaneously. Soil biota imposed positive effects on growth of T. sebifera, and the addition of N amplified these positive effects. The negative effects by UV-B radiation on growth of T. sebifera showed no response to N addition. Plant height, leaf biomass and total biomass of the invasive T. sebifera populations out- performed those of the native ones. In addition, invasive T. sebifera populations weakened the dependence of root/shoot ratio and root biomass on local soil microorganisms than native populations, but enhanced that of leaf area ratio.

    Effects of inoculation with arbuscular mycorrhizal fungi on photosynthetic physiology in females and males of Populus deltoides exposed to cadmium pollution
    Liang-Hua CHEN, Juan LAI, Xiang-Wei HU, Wan-Qin YANG, Jian ZHANG, Xiao-Jun WANG, Ling-Jie TAN
    Chin J Plan Ecolo. 2017, 41 (4):  480-488.  doi:10.17521/cjpe.2016.0210
    Abstract ( 410 )   HTML ( 0 )   PDF (1920KB) ( 577 )   Save
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    Aims Populus deltoides is an important plantation tree species in the middle and lower reaches of the Yangtze River and in Huai River Plain. The extensively cultivated varieties are consisted of both females and males of P. deltoides. The objective of this paper was to characterize the difference in cadmium (Cd) tolerance between the sexes and the effects of symbiosis with Rhizophagus intraradices on their Cd tolerance.
    Methods The experiment was carried out under semi-controlled conditions in a natural light greenhouse, protected from rain. Rhizophagus intraradices was inoculated on roots of both females and males when transplanting to a sand culture substrate. After one month, half of cuttings were exposed to Cd pollution (10 mg·kg-1). All cuttings were irrigated with sterile water to avoid infection by other microorganism. About three months later, the gas exchange rate, net photosynthesis rate (Pn)-intercellular CO2 concentration (Ci) curve, chlorophyll fluorescence, osmotic adjustment and phytohormone content of both females and males of P. deltoides were measured.
    Important findings Our main results are as follows: (1) when compared to the controls, decreases in Pn, stomatal conductance, Ci, transpiration rate, maximum photochemical efficiency of photosystem II (PSII), effective quantum yield of PSII, photo-chemical quenching coefficient, maximum rate of carboxylation of Rubisco, photosynthetically active radiation-saturated rate of electron transport and rate of triose phosphate utilization to a different degree in both sexes of P. deltoides under Cd pollution were found, and females exhibited a greater decrease in such parameters than males. Rhizophagus intraradices inoculation mitigated the toxic effect of Cd on such parameters to a different degree in females, not in males. (2) Under Cd pollution, there was an increase in proline content in both sexes when compared to the controls. A further increase in proline content occurred in females, not in males, when inoculated with R. intraradices. (3) When compared to the controls, there was a decrease in indoleacetic acid, but an increase in abscisic acid in leaves of both sexes when exposed to Cd pollution. The amplitude changed in both phytohormones in females was greater than that in males. Rhizophagus intraradices inoculation was helpful for recovery of phytohormone balance in females, which was not observed in males. Therefore, our results indicated that (1) there were a greater negative effect exerted by Cd pollution on gas exchange rate, carbon fixation capacity and phytohormone balance and a more impairment of photosynthetic apparatus in females when compared to males, showing a less tolerance to stress conditions in females; (2) Rhizophagus intraradices inoculation could enhance the osmotic adjustment capacity in females, thus mitigate the negative effect of Cd stress on ability of carbon fixation and phytohormone balance in females. However, such positive effects derived from R. intraradices symbiosis were not observed in males.

    Responses of apical ion fluxes to NaCl stress in Elaeagnus angustifolia seedlings
    Sheng YANG, Hua-Xin ZHANG, Qiu-Xia CHEN, Xiu-Yan YANG
    Chin J Plan Ecolo. 2017, 41 (4):  489-496.  doi:10.17521/cjpe.2016.0091
    Abstract ( 343 )   HTML ( 2 )   PDF (1025KB) ( 447 )   Save
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    Aims Elaeagnus angustifolia is one of the most salt-tolerant species. The objective of this study was to understand the mechanisms of ion transporation in E. angustifolia exposed to different salt concentrations through manipulations of K+/Na+ homeostasis.
    Methods Seedlings of two variants of the species, Yinchuan provenance (YC, salt-sensitive type) and the Alaer provenance (ALE, salt-tolerant type), were treated with three different NaCl application modes, and the ion fluxes in the apical regions were measured using non-invasive micro-test technology (NMT). In mode 1, Na+ and K+ fluxes were measured after 150 mmol·L-1 NaCl stress lasted for 24 h. In mode 2, K+ and H+ fluxes were quantified with a transient stimulation of NaCl solution. In mode 3, Amiloride (Na+/H+ antiporters inhibitor) and tetraethylammonium (TEA, K+ channel inhibitor) was used to treat apical regions of E. angustifolia seedlings after NaCl stress for 24 h, respectively.
    Important findings Under NaCl stress for 24 h, net effluxes of Na+ and K+ were increased significantly. The net Na+ effluxes of YC provenance seedlings (720 pmol·cm-2•s-1) were lower than that of ALE provenance (912 pmol·cm-2·s-1), but the net K+ efflux was higher in YC provenance. Under the instantaneous NaCl stimulation, net K+ efflux was remarkably increased, with the net K+ efflux of YC provenance always higher than that of ALE provenance. Interestingly, H+ at the apical regions was found from influx to efflux, with the net H+ efflux of ALE provenance greater than that of the YC provenance. Under the NaCl and NaCl + Amiloride treatment, the net Na+ efflux of ALE provenance seedlings was higher than that of YC provenance, while the net K+ efflux was less in ALE provenance seedlings. On the other hand, the differences in net Na+ and K+ effluxes were insignificant between the two provenances under the control group and NaCl + TEA treatment. In conclusion, NaCl stress caused Na+ accumulation and K+ outflows of E. angustifolia seedlings; The E. angustifolia seedlings utilize Na+/H+ antiporters to reduce Na+ accumulation by excretion; and the maintenance of K+/Na+ homeostasis in salt-tolerant E. angustifolia provenance seedlings roots accounted for a greater Na+ extrusion and a lower K+ efflux under NaCl stress. Results from this study provide a theoretical basis for further exploring salt-tolerant E. angustifolia germplasm resource.

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