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School of Food and Biological Engineering, Hezhou University, Hezhou 542899, China

AbstractIn this experiment, two-factor 7-level uniform design scheme was applied. Separate treatment of each factor was performed for single effect test. Then, it analyzed the effects of acid and aluminum stress under soilless culture on the water content of plant during the growth of Ginkgo biloba L. seedlings, so as to provide a theoretical basis for studying the connection between plant water and physiological stress. The results showed that the water content of G. biloba plants declined with the decrease of pH, but the water content of G. biloba plants declined with the increase in the concentration of aluminum treatment, indicating that the stronger the acid and aluminum stress, the lower the water content of the plants, affecting the normal absorption of water content of G. biloba plants, accordingly leading to lack of water. According to the analysis of the degree of influence on the water content, pH is the first factor influencing the growth of G. biloba plants. If pH is lower than 3.5, G. biloba plants will not growth, while pH is higher than 5.0, aluminum has no significant effect on the water content of G. biloba plants. In conclusion, the water content of G. biloba plants can be used as an essential indicator for acid and aluminum stress.

Key wordsAcid, Aluminum, Ginkgo biloba L.

1 Introduction

GinkgobilobaL. is not only an excellent landscape tree species, but also can be used as an important fruit tree species because of its ability to produce fruit (ginkgo). It has been widely cultivated in China. However, in southern China, the rainy and hot days are in the same period, as a result, the soil is highly weathered, most of effective nutrients are lost, and aluminum enrichment and acidification are serious[1-2]. It is generally believed that the rate of plant content declines under water stress[3-4], and some salt-tolerant plants can maintain stable water content under salt stress. For example,Puccinelliatenuifloracan reduce the osmotic potential of water through rapidly increasing the soluble sugar content, and alleviate the salt concentration, so as to resist the salt stress environment and keep stable water content[5]. The plant water content is associated with plant genotype, for example, the drought resistance. Thus, the plant water content is an essential indicator for environmental stress of plant. ForG.bilobawidely cultivated in southern China, there are few reports about the relationship between the water content of plants and acid and aluminum stress. In this experiment, we studied the effects of cid and aluminum stress on the growth ofG.biloba, and analyzed the effects of acid and aluminum stress under soilless culture on the water content of plant during the growth ofG.bilobaseedlings, so as to provide reference indicator for diagnosing stress degree of plants and provide a theoretical basis for studying the connection between plant water and physiological stress.

2 Experimental materials and design

The experimental materials were the annualG.bilobaseedling planted in Guilin of Guangxi. The nutrient solution used in this experiment was suitable for Hoagland’s formula suitable for terrestrial plants (the detail was specified inExperimentalResearchandStatisticalAnalysis)[6].

Experimental factors were acidity (X1) and aluminum (X2). We used U207 uniform design scheme to study the interactive effect of these two factors on the growth ofG.biloba, and the experiment scheme for interaction treatment is listed in Table 1.

Table 1 Experiment scheme for the interaction treatment

3 Cultivation management and analysis methods

Overwintering annualG.bilobaseedlings were planted in sand of greenhouses, watered to keep moist and maintain their vitality. In spring, when the temperature rises, seedlings were transplanted to 1/10 nutrient solution for culture, observed for 3-5 d, and selected uniform seedlings for experimental treatment. During the experiment, we regularly changed the treatment solution to keep relatively stable acidity and aluminum concentration. According to climatic conditions, we changed the treatment solution every 1-3 d. During sunny and hot days, water evaporates rapidly, it is necessary to promptly supplement or change the nutrient solution.

We washedG.bilobaplants was successively with tap water and deionized water, and cut the roots and stems with stainless steel scissors, and then weighed the fresh weight of the roots, stems and leaves separately. Later, we put theseG.bilobaplants into kraft paper envelope, heat treated at 80℃ for 30 min, dried at 60℃ to the constant weight, weighed the weight (dry weight), and water content is the percentage of fresh weight obtained through subtracting the dry weight to the fresh weight. Then, we crushed theG.bilobaplants with stainless steel pulverizer, screened with 0.5 mm sieve, then put into kraft paper envelope, and placed in a dryer for storage and experiment.

4 Results and analysis

4.1 Experimental results of water content of whole G. biloba plant treated by acid and aluminum

Treatments 1 and 2 in this experiment were treated at a single factor of pH 2.5 and pH 3.0 respectively. The roots of the youngG.bilobaseedlings had dead roots. Rotten roots affected the normal water content of the whole plant, so they were not included in the analysis. The acid and aluminum treatment results of youngG.bilobaseedlings were shown in Table 2.

Table 2 Experimental results of water content of acid and aluminum treated Ginkgo biloba

4.2 Establishing binary quadratic regression equation and effect analysis

According to the data in Table 2, with the aid of Excel software, we established a binary quadratic regression equation for the water content ofG.bilobain terms of pH and aluminum concentration:

(1)

Through the correlation analysis,R= 0.928 7 >R0.01= 0.633, it is found that the correlation between the water content ofG.bilobaand pH, and aluminum concentration reached extremely significant level.

4.3 Single effect analysis of pH and aluminum concentration on water content of G. biloba plants

Through substitutingX2 = 0 to the Equation (1), we could derive the single effect equation of pH on the water content:

(i)

Through substitutingX1= 0 to the Equation (1), we could derive the single effect equation of aluminum concentration on the water content:

(ii)

TakingXiat -1, 0, 1, 2, 3, and substituted into Equation (i) and Equation (ii), we calculated the single effect of pH and aluminum concentration of the water content of wholeG.bilobaplant, as listed in Table 3. According to the data in Table 3, with the aid of Excel software, we plotted Fig.1.

Table 3 Single effect of acid and aluminum concentration on water content of whole Ginkgo biloba

From Table 3 and Fig.1, we can see that the water content ofG.bilobaplant is positively correlated with the pH value, that is, the water content increases with the increase of the pH value, indicating that the same plant contains less water under higher acid stress. For series 2, with the increase of the aluminum concentration, the water content ofG.bilobaplant significantly declines.

Fig. 1 Single effect of acid and aluminum concentration on water content of whole Ginkgo biloba

4.4 Analysis of the interactive effects of acid and aluminum on water content of whole G. biloba plant

Separately substitutingX1 = -1, 0, 1, 2, 3 andX2 = -3, -2, -1, 0, 1, 2, 3 into the Equation (1), we could obtain the interactive effects of acid and aluminum on the water content of wholeG.bilobaplant. According to the data in Table 4, with the aid of Excel software, we plotted Fig.2.

According to Table 2 and Fig. 2, it can be known that the water content ofG.bilobaplant increases with the increase of pH, indicating that increasing pH is favorable for water absorption; with the increase of the aluminum concentration, the water content ofG.bilobaplant gradually declines, indicating that increasing the aluminum concentration will inhibit the water absorption. In general, whenG.bilobaplant suffers from higher acid and aluminum stress, the water content will be lower, indicating that acid and aluminum stress will influence the water content ofG.bilobaplant. This also indicates that under the same cultivation pattern, the water content of the same plant can reflect its growth status and the degree of external stress to a certain extent. Water sensitivity of different plant parts is different. For example, photosynthesis of leaves is the most sensitive to water, and it is necessary to make further studies.

Table 4 Interactive effects of acid and aluminum on water content of whole Gingko biloba plant

Fig. 2 Interactive effects of acid and aluminum treatment on water content of Gingko biloba5 Results and discussions

According to the analysis of this experiment, pH is the first factor influencing the growth ofG.bilobaplants. If pH is lower than 3.5,G.bilobaplants will not growth, while pH is higher than 5.0, aluminum has no significant effect on the water content ofG.bilobaplants. The results showed that the water content ofG.bilobaplants declined with the decrease of pH, but the water content ofG.bilobaplants declined with the increase in the concentration of aluminum treatment, indicating that the stronger the acid and aluminum stress, the lower the water content of the plants, affecting the normal absorption of water content ofG.bilobaplants, accordingly leading to lack of water. In conclusion, the water content ofG.bilobaplants can be used as an essential indicator for acid and aluminum stress.