Liping ZHAO,Jiayong LIU*,Peifang ZHAO,Fenggang ZAN,Jun ZHAO,Kun YANG,Caiwen WU,Xuekuan CHEN

1.Sugarcane Research Institute,Yunnan Academy of Agricultural Sciences,Kaiyuan 661699,China;

2.Yunnan Province Key Laboratory of Sugarcane Genetic Improvement,Kaiyuan 661699,China

Responsible editor:Xiaoxue WANG Responsible proofreader:Xiaoyan WU

Soil pH plays a key role in plant growth which will be adversely affected by inappropriate pH.In China,pH of soil tends to be volatile from south to north,and pH generally keeps acid over 81%[1].Furthermore,the soils with pH below 5.5 account for 62%.For example,arithmetic mean value and geometric mean of soil pH of sugarcane-producing areas are 4.35 and 4.34[2]in Liangjiang Town,Xingbin District,Guangxi Province.Hence,it is extremely strong acid soils.Although sugarcane is tolerant to soil infertility and acidity,excessive acidity would reduce use rate of P fertilizers and affect sugarcane root growth,decreasing yield[1].Currently,the researches available are mainly on wheat,rice,tobacco and peanut,in terms of relationship between biological activity and pH value[3-10].Less attention is paid to the effects of pH on seedling root growth of sugarcane[11].The research explored the effects of nutrient solutions with different pH values on biomass,root shape,root activity,stem diameter and plant height of seedlings in order to select the sugarcane varieties and the most suitable pH environment for sugarcane growth.

Materials and Methods

Materials

The hybrid generations of RB85-5156×Yunrui 05-407,Yunrui 06-3501×Tolodo,Yuetang 94-128×Ganzhe 75-65,ROC6 ×Yunrui 05-733,VMC87-95×Yunrui 05-171 were taken as materials,recorded as A,B,C,D,and E,respectively.

Methods

The hybrid seeds were sown in June 2012 in a greenhouse,Sugarcane Research Institute,Yunnan Academy of Agricultural Sciences.Then,seedlings of the 5 treatments were sampled randomly and cultivated as per local method.When 4-5 leaves of seedlings grew,the seedling growing similarly can be transplanted to a pot where substrates were river sands washed clean.After the transplanting,the seedlings were irrigated with running water and then treated with nutrient solutions with the seedlings matured.Specifically,pH was set at 5.0,7.0 and 8.5 and every treatment was with three repetitions,namely,3 pots were involved of every pH value for each hybrid seed treatment.It is notable that every pot was with a repetition at 15 plants per pot (height at 32 cm and diameter at 35 cm).The value of pH was measured with a pH meter(pH-3C) and the value of pH was adjusted to the ruled one with 1 mol/L H2SO4and 1 mol/L NaOH.The nutrient solution was Hoagland’s solution and seedlings were irrigated weekly.After the plant grew for 130 d,biomass,plant height,stem diameter,root shape,and root activity were measured accordingly.

Measurement index and methods

According to measurements of root system,a complete plant was collected from a cultivation pot and washed clean with running water.Subsequently,the clean seedlings were removed from a plant and surface water was dried with absorbent paper.The seedlings were then separated as per simple root and placed side by side on a specific root tray.The root system was then scanned with a Win-RHIZO LA6400XL and the scanned pictures were stored in different folders as per plant number,repetition,and classification.Then,total root length,root surface area,average diameter of root system,root volume and root length with different diameters were computed with a WinRHIZO.

Stem diameter and plant height were measured as per local method.

Biomass was measured as follows:Ground seedlings and roots were cleaned with running water and water was absorbed with absorbent paper to measure the weight.Then,the seedlings were killed out at 105 ℃for 0.5 h and dried to a constant weight at 70 ℃to measure the dry weight.

Root activity was measured as per TTC method[12].Specifically,the root tip was collected at 0.5 g and added with 0.4% TTC at 0.2 ml and 1/15 PBS at 5 ml,which was stored for 1 h in dark at 37 ℃.Then,1 mol/L H2SO4was added to end the reaction.The materials were then collected to dry with filter paper,added with ethyl acetate,followed by grinding.The red extracting solution was collected and solution was fixed to a constant volume at 10 ml with ethyl acetate.The reduction quantity (C) of TTC was measured with a spectrophotometer at 485 nm.

The root activity=C/(Wt×1 000),which C refers to the reduction quantity of tetrazole (μg/(g·h)),W refers to root mass (g),and t represents the reaction time(h).

Data processing

The test data were analyzed with SPSS 18.0 and Excel 2003.

Results and Analysis

Effects of pH treatments on seedling growth during seedling period

Effects on biomasses of root system and ground part of plantsAs shown in Table1,with pH at 8.5,fresh weight and dry weight of plant and root system in treatments A and D,as well as dry weight of plant and root system in treatment B,maintained higher compared with the treatment with pH at 5.0.In treatment E,the differences of biomass showed none statistical significance with Ph designed at three levels.It can be concluded that the value of pH at 5.0 has inhibition on seedling biomass accumulation.

Effects on morphological characteristics of root systemAs shown in Table2,morphological characteristics of root system changed dramatically in the five treatments and total root length,surface root area,root diameter and root volume in treatments A,C and D all reached the lowest with pH value at 7.0,and the highest with pH value at 8.5,when total root length,surface root area,and root volume were all significantly higher compared with the treatment with pH at 5.0.With pH at 7.0,except of root diameter,the rest characteristics of root system were all higher compared with the treatments with pH values at 5.0 and 8.5.In addition,for pH value at 8.5,total root length and surface root area ofthe seedlings were both higher compared with the treatments with pH at 5.0.It can be concluded that the effects of nutrient solution with pH value are of none statistical significance.

Table1 The biomasses of seedlings from three pH levels g

Table2 Root morphological features of seedlings from three pH levels

Effects on root activityAs shown in Fig.1,root activity of seedlings in treatment A was increasing upon pH,and reached the peak with pH value at 8.5; in treatment B,root activity changed from increasing to decreasing upon pH and achieved the peak at 316.04 μg/(g·h) with pH value at 7.0;in treatment C,root activity changed from substantial decrease to slow growth upon pH value,and the activity with pH value at 5.0 was significantly higher at 1 009.31 μg/(g·h) compared with rest treatments; in treatment D and E,root activity was decreasing as pH value enhanced,and the activity performed significantly higher with pH of 5.0 compared with the treatment with pH of 8.5.Of the 5 treatments,root activity achieved the peak with pH value at 5.0 in treatments C,D and E,and in treatments C and E with pH value at 5.0,root activity proved the highest.

Effects on stem diameterAs shown in Fig.2,stem diameter changed insignificantly with varying pH values.Specifically,stem diameters in treatments A,B,C and D all changed from increasing to decreasing; the stem diameter in treatment A with pH of 7.0 was significantly higher compared with the treatments with pH of 5.0; the stem diameter in treatment E changed from decreasing to increasing.

Table3 Root length of seedling at different diameters from three pH levels

Effects on plant heightAs shown in Fig.3,plant heights in treatments A,B,C,and D all reached the highest with pH of 8.5 and plant height was significantly higher in treatment C with pH of 8.5,compared with that with pH of 5.0; in treatment B,plant height changed from decreasing to increasing and increasing to decreasing in treatment E.

Effects on root lengthIt can be concluded from Table3 that the root with diameter below or equal to 1.0 mm was longer,and the range of root length in treatments A and C with pH of 8.5 was significantly larger compared with that with pH of 5.0 and 7.0;in treatment B,root length in the treatment B with pH of 7.0 was far higher compared with that with pH of 5.0 and 8.5; in treatment E,differences of diameter with pH values in treatment E showed none statistical significance,except of the diameter over 4.5 mm.

Conclusions and Discussions

Water,salt and P stress all have considerable effects on plant and root system growth[13-17].Li et al.[18]researched root system shape and root activity and the results indicated that as pH increased,growth of different plants was inhibited in varying degrees and biomasses of root and ground part both dropped substantially; the inhibition proved higher of ground part[18].The research incorporated that the accumulated biomass was more in the treatment with pH of 8.5; the values of pH at 7.0 and 8.5 were conductive for seedling growth;the value of pH at 5.0 was adverse for seedling growth.

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