For. Stud. China, 2011, 13(1): 52–56 DOI 10.1007/s11632-011-0102-1
RESEARCH ARTICLE
Differences in chlorophyll fluorescence parameters and water content in heteromorphic leaves of Populus euphratica from Inner Mongolia, China HAO Jian-qing1, ZHANG Li2, ZHENG Cai-xia1*, BAI Xue1, LI Wen-hai1 1 2
College of Biological Sciences and Biotechnology, Beijing Forestry University, Beijing 100083, P. R. China Shandong Foreign Languages Vocational College, Rizhao 276826, P. R. China
© Beijing Forestry University and Springer-Verlag Berlin Heidelberg 2011 Abstract We studied three typical heteromorphic leaves of Populus euphratica trees growing in the Wuhai region of Inner Mongolia, China, i.e., lanceolate, broad-ovate and dentate broad-ovate leaves and mainly focused on the changes in chlorophyll fluorescence parameters and free water and bound water content. The results show that the values of Fm (maximal fluorescence yield), Fv/Fm (maximum photochemical quantum yield of PSII) and Fv/F0 (potential quantum efficiency of PSII) of lanceolate leaves were the least on young trees, while these parameters were the least on the ovate leaves of old trees. Compared with young trees, the free water content of heteromorphic leaves of old trees increased significantly, i.e., by 78.94% in lanceolate leaves and in the leaves of broad-ovate and dentate broad-ovate by 10.99% and 10.60%, respectively. Correlation analysis showed that free water content is significantly related to Fv/Fm and Fv/F0 in young trees, while the relationship of total water content with Fv/Fm and Fv/F0 is positive in old trees. Key words chlorophyll fluorescence, free water, bound water, water status, Populus euphratica, heteromorphic leaves
1 Introduction Chlorophyll fluorescence analysis, based on the theory of photosynthesis, which uses chlorophyll as a natural probe, is a new measurement and diagnostic technique for in vivo plants to investigate and detect the physiological status of plants under various external effects. In photosynthetic research, this technique plays a unique role in measuring light absorption, transmission, dissipation and distribution of the photosystem (Feng et al., 2002). Over the past 10 years, analysis of chlorophyll fluorescence has been widely used in various areas of plants, because of its quick and accurate measurements without doing any damage (Hlaváčková et al., 2002; Wen et al., 2006; Burzynski and Zurek, 2007; Li et al., 2007a; Li et al., 2008). The ratio of the content of free water and bound water is fixed in plants, which is an important indicator of the status of plant water. To some extent, this ratio can be used to test plant resistance (Ding et al., 2008). Populus euphratica, one of the species growing in salinized desert belts, is a very ancient, primitive tree of the family Salicaceae (Zheng et al., 2006). In China, studies of P. euphratica have mainly focused on the anatomical structure of leaves, containing ma*
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terials, seed stores and germination, as well as the biochemical and molecular mechanism of resistance (Rottenberg et al., 2000; Ma et al., 2002; Zhang et al., 2004; Li and Zheng, 2005; Ge et al., 2007; Li et al., 2007b; Wei et al., 2008; Wiehile et al., 2009). Physiological studies usually use seedlings as material for growing in pots (Wu et al., 2007; Fu et al., 2008; Su et al., 2008; Li et al., 2009). Recently, chlorophyll fluorescence characteristics of P. euphratica seedlings under salt and drought stress have been reported (Ma et al., 1998; Shi et al., 2008; Li et al., 2009; Zhou et al., 2009). Qiu et al. (2005) reported the stomatal characteristics, photosynthetic rate and chlorophyll fluorescence of three typical heteromorphic leaves of P. euphratica trees planted in Beijing. However systematic studies are still insufficient, especially on the eco-adaptability of the heteromorphic leaves of P. euphratica trees in natural communities. We collected leaves from a natural P. euphratica forest in the Wuhai region of Inner Mongolia, China. It is the southernmost dense forest in China. We studied three typical heteromorphic leaves, i.e., lanceolate, broad-ovate and dentate broad-ovate leaves of P. euphratica and focused on the variation in their chlorophyll fluorescence parameters and free water
HAO Jian-qing et al.: Chlorophyll fluorescence parameters and water content in heteromorphic leaves...
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and bound water content. Investigating the correlation between physiological indices and these three typical heteromorphic leaves and analyzing their ecoadaptability will be both of theoretical and practical importance in this area.
rescence yields were made on dark-adapted (20 min) leaves and the maximum photochemical quantum yields of PSII (Fv/Fm) and the potential quantum efficiency of PSII (Fv/F0) were calculated. There were three replications of each determination.
2 Materials and methods
2.2.2 Water content
2.1 Plant material and growth conditions
The measurements of bound water and free water content followed the protocol by Ding et al. (2008). Heteromorphic leaves with similar status were selected to measure the content of free water (FWC) and bound water (BWC) using an Abbe Refractometer. There were also three replications of each determination.
The natural P. euphratica forest is located on an island of the Yellow River Basin, Wuhai region, Inner Mongolia, China (39°42′N, 106°48′E). The region has a temperate and monsoon climate. P. euphratica is the major vegetation in the plant community on the island, consisting of about 1650 mature trees and thousands of young trees. Due to pest damage, the end of top branches wilts on most of the old trees. The normal growth of these old trees depends on sprouting shoots. Three young, well growing trees (diameter at breast height about 5 cm) and three healthy old trees (diameter at breast height about 30 cm) were selected and the chlorophyll fluorescence of three typical leaves, i.e., lanceolate, broad-ovate and dentate broad-ovate leaves (Fig. 1) was measured.
(1) BWC (%) = TWC(%)－FWC (%)
(2)
where W1 is the weight of sucrose solution (g), W2 the fresh weight of plant issue (g), C1 the mass fraction of original sucrose solution, C2 the mass fraction of final sucrose solution and TWC is total water content. Total water content was measured by oven drying method using the same sampling method.
2.2 Methods
TWC (%) = W f - W d # 100% W
2.2.1 Chlorophyll fluorescence
where Wf is the fresh weight (g) of leaves and Wd the dry weight of leaves.
Chlorophyll fluorescence was measured everyday between 10:00 and 14:00 on fully-expanded heteromorphic leaves (shown as Fig. 1), using a PAM 2100 portable chlorophyll fluorometer (Walz, Germany). Measurements for basal (F0) and maximal (Fm) fluo-
f
(3)
3 Results and analyses 3.1 Changes in chlorophyll fluorescence parameters of heteromorphic leaves at different ages Changing patterns of chlorophyll fluorescence param-
Fig. 1 Heteromorphic leaves of P. euphratica. (A) Lanceolate leaf, (B) broad-ovate leaf and (C) dentate broad-ovate leaf.
Fig. 2 Changes in chlorophyll fluorescence parameters of heteromorphic leaves from young P. euphratica trees
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Forestry Studies in China, Vol.13, No.1, 2011
3.3 Correlation analysis of leaf water content and chlorophyll fluorescence parameters
Fig. 3 Changes in chlorophyll fluorescence parameters of heteromorphic leaves from old P. euphratica trees
eters are shown in Figs. 2 and 3. For the young trees, the trend in variation of F0, Fm, Fv/Fm and Fv/F0 of the three types of leaves (lanceolate, broad-ovate and dentate broad-ovate leaves) were the same: these parameters all decreased gradually in the order of broadovate, dentate broad-ovate and lanceolate leaves. For the old trees, the values of Fm, Fv/Fm and Fv/F0 gradually decreased in the order of the dentate broadovate, lanceolate and broad-ovate leaves. While the value of F0 varied among the leaves, it was the highest in broad-ovate and the lowest in lanceolate leaves. We conclude that the values of all the parameters of the heteromorphic leaves of young trees were lower than those in the old trees. The differences among the parameters in young trees were more significant than those of old trees.
Results of correlation analysis of leaf water content and chlorophyll fluorescence parameters are shown in Table 1. For the young trees, the correlation among Fv/F0, Fv/Fm and F0 (p < 0.01) was positive and highly significant, as well as that between F0 and Fm. The correlation between Fv/F0 and Fm was positive and significant (p < 0.05). Furthermore, the analysis of correlations shows that free water content was significantly related with Fv/Fm and Fv/F0 in the young trees, while the relationship of total water content with Fv/Fm and Fv/F0 was positive in the old trees. For the old trees, the correlation among Fm and Fv/F0, Fv/Fm was positive and highly significant (p < 0.01). The correlation of these parameters was stronger in young trees than in old trees.
4 Discussion Chlorophyll fluorescence is a very sensitive tool in the study of stress-induced damage to PSII (Li et al., 2007a). Fm reflects the electron transfer of PSII
3.2 Changes in the physiological properties of water of heteromorphic leaves at different ages Changing patterns in the physiology of water of heteromorphic leaves from P. euphratica are shown in Figs. 4 and 5. The content of bound water and free water decreased in the order of lanceolate, broad-ovate and dentate broad-ovate leaves of young trees. For the old trees, the water content was the highest in the dentate broad-ovate leaves and the lowest in broad-ovate leaves. The bound water content was the highest in the dentate broad-ovate and the lowest in the lanceolate leaves. We conclude that the water content of the heteromorphic leaves of the young trees is higher than that of old trees. Compared with the young trees, the free water content of heteromorphic leaves of the old trees increased significantly; it sharply increased by 78.94% in the lanceolate leaves and in the leaves of ovate and dentate broad-ovate it increased by 10.99% and 10.60%, respectively.
Fig. 4 Water physiology of heteromorphic leaves from young P. euphratica trees
Fig.5 Water physiology of heteromorphic leaves from old P. euphratica trees
HAO Jian-qing et al.: Chlorophyll fluorescence parameters and water content in heteromorphic leaves...
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Table 1 Correlation coefficient among water physiological characteristics and chlorophyll fluorescence parameters Factor
Fv/F0
F0
Fv/Fm
TWC
FWC
BWC
0.993**
–0.086
0.086
F0
0.958
1
Fm
0.924*
0.995**
1
0.957**
0.996**
Fv/Fm
0.975**
0.871
0.817
1
0.979**
0.229
–0.228
–0.882
–0.829
1
0.026
–0.026
0.874
0.821
1
–1
–0.876
–0.823
FWC BWC
**
–0.980 0.977** –0.977
0.999**
0.950**
1
TWC
–0.683
Fm
Fv/F0
–0.699
–0.876
–0.760
–0.999 0.999**
–0.999
–0.999
0.999**
0.669
0.669
–0.062
0.062
–1
1
Notes: The data on the bottom left corner is the young trees and that on the right corner is the old trees; and difference at 0.05 and 0.01 levels, respectively. ＊
(Zhang, 1999). Under drought conditions, the potential photochemical efficiency (Fv/Fm) of P. euphratica is significantly reduced (Shi et al., 2008; Li et al., 2009). In rice (Oryza sativa L.) seedlings, Fv/Fm also decreased under salt stress (Xu et al., 2008). On our old trees, the values of Fm, Fv/Fm and Fv/F0 all gradually decreased in the order of dentate broad-ovate, lanceolate and broad-ovate leaves, indicating that potential activity and photochemical efficiency of PSII are higher in dentate broad-ovate leaves. This is consistent with the results measured by Qiu et al. (2005), who measured chlorophyll fluorescence parameters of heteromorphic leaves (lanceolate, broad-ovate and dentate broad-ovate leaves) of P. euphratica trees growing in Beijing. The efficiency of light energy conversion of PSII is represented by Fv/Fm and is generally maintained at 0.832 ± 0.004. This value will decrease when photoinhibition occurs (Liu et al., 2006). In our young trees, the values of Fv/Fm of heteromorphic leaves were within the range of 0.6–0.8, suggesting that photoinhibition did occur in the PSII reaction centers. However, this value is within the range of 0.80–0.83 in the leaves of the old trees. This result shows that these trees did not suffer from photoinhibition. A possible reason is that in old trees with large crowns and luxuriant foliage the leaves shade each other and protect the photosynthetic membranes from direct sunlight, so that damage due to membrane radiation is reduced. Young trees with small crowns and thin foliage suffer significantly from photoinhibition. F0 reflects the energy which does not participate in photochemical reactions (Lv et al., 2009). An increase in the value of F0 may be induced by the inactivation of part of the PSII reaction centers. In our young trees, F0 decreased in the order of broad-ovate, dentate broad-ovate and lanceolate leaves. The increase in active oxygen and the degradation of D1 protein should intensify with the increase of light intensity. This situation can be alleviated with an increase in the value of F0, whereby the irreversible destruction of the reaction center of PSII can be avoided and
＊＊
represent significant
injury to the entire plant reduced. The values of F0 of broad-ovate and dentate broad-ovate leaves were clearly higher than that of lanceolate leaves, whether on young or old trees. This indicates that excess absorption energy was emitted as heat and fluorescence, protecting the reaction center of PSII from photo damage. Lanceolate leaves are major photosynthetic carbon assimilation organs of young trees. These leaves accumulate more photosynthetic products, leading to larger ratios of bound water and free water. For the old trees, broad-ovate leaves are major photosynthetic carbon assimilation organs, which can accumulate more osmotic substances than lanceolate leaves (Yang et al., 2004). With the growth of trees and environmental deterioration, the assimilation of lanceolate leaves cannot satisfy the nutrient requirements of tree growth. Consequently, broad-ovate and dentate broad-ovate leaves with their stronger ability of tolerating environmental stress, take the place of the lanceolate leaves and, in the end, become the major leaf types in adult trees. In the leaves of young trees, the positive correlations between free water content and Fv/F0, Fv/Fm are highly significant, suggesting that the free water content can be used to measure the potential activity of PSII. For the old trees, the total water content can be used to measure the potential activity of PSII, because the positive correlation between the total water content and Fv/F0, Fv/Fm is highly significant.
Acknowledgement This study was supported by the National Natural Science Foundation of China (Grant No. 30671655).
References Burzynski M, Zurek A. 2007. Effects of copper and cadmium on photosynthesis in cucumber cotyledons. Photosynthetica, 45(2): 239–244 Ding Y, Li D L, Wei Q S, Zhao M. 2008. Water physio-ecolog-
56 ical characteristics of chilopsis linearis under different soil water conditions. J Northwest Forest Univ, 23(3): 5–11 (in Chinese with English abstract) Feng J C, Hu X L, Mao X J. 2002. Application of chlorophyll fluorescence dynamics to plant physiology in adverse circum stance. Econom Forest Res, 20(4): 14–18 (in Chinese with English abstract) Fu A H, Chen Y N, Li W H. 2008. Change on water potential of differently shaped leaves in Populus euphratica in lower reaches of Tarim River Xinjiang. J Desert Res, 28(1): 83–88 (in Chinese with English abstract) Ge C H, Ji Q L, Liu Y P, Wang X H. 2007. The changes of protein bodies’ ultrastructure in cell of seeds of Populus euphratic Oliv. in the process of storage. Seed, 26(5): 27–29 (in Chinese with English abstract) Hlaváčková V, Špundová M, Nauš J, Navrátil M, Kouřil R, Kaňa R. 2002. Mechanical wounding caused by inoculation influences the photosynthetic response of Nicotiana benthamiana plants to plum pox potyvirus. Photosynthetica, 40(2): 269–277 Li M, Yang D, Li W. 2007a. Leaf gas exchange characteristics and chlorophyll fluorescence of three wetland plants in response to long-term soil flooding. Photosynthetica, 45(2): 222–228 Li X Y, Lin L S, Zhang X M, Zeng F J. 2007b. Characteristics of water status in Populus euphratica outside the oases in the Taklamkan Desert. Chin J Appl Environ Biol, 13(6): 763– 766 (in Chinese with English abstract) Li Y L, Wang K H, Du G J, Xu L Q, Yang H, Xiao J J. 2008. Effects of NaCl stress on chlorophyll fluorescence parameters in Cinnamomum japonicum var. chenii. J Anhui Agr Sci, 36(22): 9377–9379 (in Chinese with English abstract) Li Z J, Luo Q H, Wei W M, Han L. 2009. The effects of drought stress on photosynthetic and chlorophyll fluorescence characteristics of Populus euphratica and P. pruinosa. Arid Zone Res, 26(1): 45–52 (in Chinese with English abstract) Li Z X, Zheng C X. 2005. Structural characteristics and ecoadaptability of heteromorphic leaves of Populus euphratica. Forest Stud China, 7(1): 11–15 (in Chinese with English abstract) Liu W H, Gao D S, Shu H R. 2006. Effects of different photon flux density on the characteristics of photosynthesis and chlorophyll fluorescence of peach trees in protected culture. Sci Agr Sin, 39(10): 2069–2075 (in Chinese with English abstract) Lv H F, Pi E X, Wang L L, Shen H. 2009. Photosynthesis and chlorophyll fluorescence of Solanum lyratum Thunb after shade treatments. J Zhejiang Normal Univ (Nat Sci), 32(1): 1 –6 (in Chinese with English abstract) Ma H C, Wang S S, Jiang X N. 1998. Photosynthetic and growth response to salt stress in P. euphratica. J Southwest Forest Coll, 18(3): 33–40 (in Chinese with English abstract) Ma T J, Liu Q L, Li Z, Zhang X J. 2002. Tonoplast H+-ATPase in response to salt stress in Populus euphratica cell suspensions. Plant Sci, 163(3): 499 Qiu J, Zheng C X, Yu W P. 2005. Comparison of photosynthetic rate and fluorescence characteristics of heteromorphism leaf
Forestry Studies in China, Vol.13, No.1, 2011 of Populus euphratica. Jilin Forest Sci Technol, 34(3): 19– 21 (in Chinese with English abstract) Rottenberg A, Nevo E, Zohary D. 2000. Genetic variability in sexually dimorphic and monomorphic populations of Populus euphratica (Salicaceae). Can J Forest Res, 30(3): 482– 486 Shi Z, Shi S H, Xiao W F, Qi L W. 2008. Influence of dehydration on characteristics of chlorophyll fluorescence of detached leaves in Haloxylon ammodendron and Populus euphratica. Forest Res, 21(4): 566–570 (in Chinese with English abstract) Su Y H, Zhu G F, Feng Q, Chang Z Q, Si J H. 2008. The simulation of leaf stomatal conductance of Populus euphratica in desert riparian forest in Ejin. Acta Bot Boreal-Occident Sin, 28(7): 1434–1439 (in Chinese with English abstract) Wei L, Xu B L, Lei J L, Liu S, Tang Y X, Yin C C, Wu Y M. 2008. Cloning and characterization of a full-length cab gene encoding the light harvesting chlorophyll a/b binding protein from Populus euphratica. J Agr Sci Technol,10(4): 63–69 (in Chinese with English abstract) Wen G S, Tian H T, Zhang M R, Jiang W W. 2006. Application of chlorophyll fluorescence analysis in forest tree cultivation. Chin J Appl Ecol, 17(10): 1973–1977 (in Chinese with English abstract) Wiehle M, Eusemann P, Thevs N, Schnittler M. 2009. Root suckering patterns in Populus euphratica (Euphrates poplar, Salicaceae). Trees, 23(5): 991–1001 Wu W M, Li Z J, Luo Q H, Han L. 2007. Effects of Soil Water Stress on Light Response Curves of Photosynthesis of Populus euphratica and Populus pruinosa. Sci Silv Sin, 43(5): 30 –35 (in Chinese with English abstract) Xu J M, Li C S, Mao S G, Wang X, Fan C Y, Ma H L, Wang H R. 2008. Effects of zinc nutrition on leaves cell membrane and chlorophyll fluorescence characteristics of rice seedling under salt stress. J Anhui Agr Sci, 36(1): 119–121 (in Chinese with English abstract) Yang S D, Chen C G, Zhang C L, Chen J, Wang X C. 2004. Some difference of capacity of osmotic regulation between lanceolate and broad-ovate leaves in Populus euphratica. Acta Bot Boreal-Occident Sin, 24(9):1583–1588 (in Chinese with English abstract) Zhang F, Yang Y L, He W L, Zhao X, Zhang L X. 2004. Effects of salinity on growth and compatible solutes of callus induced from Populus euphratica. In Vitro Cell Develop BiolPlant, 40(5): 491–494 Zhang S R. 1999. A discussion on chlorophyll fluorescence kinetics parameters and their significance. Chin Bull Bot, 16(4): 444–448 (in Chinese with English abstract) Zheng C X, Qiu J, Jiang C N, Gao R F, Wang W F. 2006. Comparison of characteristics of stomas and photosynthesis of Populus euphratica polymorphic leaves. Sci Silv Sin, 42(8): 19–24 (in Chinese with English abstract) Zhou C B, Song Y Y, Wang B J, Li R, Li M Y, Li Y Y. 2009. Effects of drought stress on photosynthesis and chlorophyll fluorescence parameters of Populus euphratica. J Northwest Forest Univ, 24(4): 5–9 (in Chinese with English abstract) (Received October 15, 2010 Accepted December 2, 2010)
