Application of Bioorganic Fertilizer Containing Highefficient Nitrogenfixing Bacillus amyloliquefaciens on Strawberry

Lili JIANG Kaiyun WANG Yuguo WU Kaiyuan WANG Xinjun FANG

AbstractIn order to ascertain the soil carbon flux characteristics of poplar plantations and crop communities in the Dongting Lake area during the growing season and their correlation with hydrothermal conditions, soil respiration rate was monitored at fixed sites and time points with an LI8100A automated soil flux system. Meanwhile, the surface temperature and soil temperature and humidity were measured. The soil respiration variation in the two different vegetation types and its correlation with environmental factors were analyzed. The results showed that in the growing season, the diurnal variation curves of soil respiration rate in the two different vegetation types showed a single peak variation, but there was certain difference in the appearance time of the peak. The peak of the crop appeared around 11:00 am, while the peak of soil respiration in the poplar appeared around 13:00. The soil respiration rate of the poplar was also significantly higher than that of the crop, and the average difference of soil respiration rate between the two was 3.09 and 3.55 μmol/(m2?s) in April and August, respectively. Temperature and soil moisture were the main factors affecting soil respiration of the poplar plantation and crop community. Temperature had a greater effect on the soil respiration of the crop community, and soil humidity had a greater impact on soil respiration in the poplar plantation, showing a correlation coefficient reaching 0.952.

Key wordsDongting Lake; Growing season; Soil respiration rate; Temperature; Humidity; Correlation

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Received: October 7, 2018Accepted: December 18, 2018

Supported by National Key Research and Development Program (2016YFD0600402); Key Research and Development Program of Hunan Province (2016NK2160); Forestry Science and Technology Program of Hunan Province (XLK201657).

Yan YANG (1980-), female, P. R. China, PhD, devoted to research about tree cultivation and breeding and sustainable forest management.

*Corresponding author. Email: tangyx999@163.com.

Soil respiration is the main way to perform carbon interchange between land and atmosphere, including plant roots, soil microbial respiration process and the process of CO2 release from the oxidation of soil carbonaceous matter, which has a great impact on the carbon cycle of terrestrial ecosystems［1-3］. More than two thirds of the carbon in terrestrial ecosystems is stored in the soil, and the carbon emission from the earths respiration to the atmosphere each year accounts for 5%-25% of the global carbon emission［4］, which is closely related to global climate change. Therefore, soil respiration has become one of focuses of global carbon cycle and climate change research［5-6］.

The soil respiration of different ecosystems is quite different. At present, the research on soil respiration is more focused on forest ecosystems, while the soil respiration status of wetland vegetation and farmland ecosystems is less studied［7-13］. The carbon stock of wetland ecosystems accounts for about 12%-20% of terrestrial ecosystems, and is the largest carbon stock in terrestrial ecosystems that is second only to forest ecosystems［14］. Relevant scholars have published a few reports on wetland carbon balance, which analyzed the carbon emission and carbon sink function of wetland ecosystems, further verifying that the carbon stock of wetland ecosystems play an important role in the global carbon cycle［15-17］. Therefore, the study of wetland vegetation and farmland soil respiration characteristics is of great significance to further exploration of the carbon budget of wetland ecosystems. Due to the superior hydrothermal conditions in the Dongting Lake area, forest vegetations and underground microbes are diverse, and there is a certain spatial heterogeneity in soil respiration. In this study, the soil respiration characteristics and influencing factors of two vegetation types (poplar plantation and crop community) in the Dongting Lake area were investigated in growing season, so as to analyze the variation laws, differences and different influencing mechanisms of soil respiration in different vegetation types. This study provides reference for accurate assessment of carbon source and carbon sink function of different vegetation types in the Dongting Lake area.

Materials and Methods

General situation of study area

The test area is located in the Dongting Lake area of the Junshan island, Yueyang City (29°38′35″N，112°55′22″E), with an altitude of 31 m. The area is rainy and humid in spring and summer, dry and cold in autumn and winter, and distinct in four seasons, and has a subtropical monsoon climate. Due to the effects of the huge water bodies (the Yangtze River and Dongting Lake), the annual average temperature is 16.2-17.8 ℃, and the extreme high temperature is 39.3 ℃, and the extreme low temperature is -11.8 ℃, the annual average precipitation is 1 237.9 mm, and the annual average relative humidity is 80%［18］. The soil is a tidal soil developed from the alluvial parent material unique to the Beach weltland. This region is rich in plant resources and has a wide variety of species. The main types of vegetation include poplar plantations, aquatic plants, sedge, reed land, and cabbage and rapeseed grown by local farmers.

Experimental methods

Setting of sample plot

The experiment selected two representative vegetation types: poplar plantation (7 a) and crop community, each of which was set as a 20 m×20 m sample plot. The sample plot of each vegetation type was set with 3 replicates.

Determination of soil respiration

The soil was measured using the LI8100A automated soil flux system for different vegetation types. During the measurement, five soil respiration observation points were randomly selected in each plot, and the distance between various observation points was greater than 5 m. The base was a PVC pipe with a diameter of 22 cm and a height of 11 cm. It was inserted into the soil by about 6 cm in the gap of plants. The base was arranged 24 h before the measurement.

During the observation, the position of the base was fixed throughout the observation period. In the first, middle and late tenday of each month in 2016, three consecutive sunny days were selected, and the measurement was performed every 2 h in the period of 05:00-17:00. In case of rainy days, the observation time was postponed.

Determination of environmental factors

The measurement of surface temperature and soil temperature and humidity was carried out simultaneously with the determination of soil respiration rate. During each time of soil respiration rate observation, the surface temperature was measured by an atmospheric temperature and humidity meter, and a soil humidity meter and a geothermometer were used to measure the temperature and humidity of the soil with a depth about 5-10 cm.

Data analysis

After all the data were processed by Execel, diurnal variation and the growingseason variation law of soil respiration rate were drawn into figures for different vegetation types. Correlation analysis and regression analysis were performed between various environmental factors and the soil respiration rate by SPSS20.0, and regression equations of the environmental factors and the soil respiration rate were calculated.

Soil respiration sensitivity index Q10 was calculated using Vant Hoff model［19］:

Q10=R2R110T2-T1

Wherein R1 is the soil respiration rate in the previous moment, R2 is the soil respiration rate in the latter moment, T1 is the temperature measured in the previous moment, and T2 is the temperature measured in the latter moment.

Results and Analysis

Soil respiration variations of different vegetation types in growing season

The research on soil respiration is mainly about forest ecosystems, and few studies have been conducted on the differences of soil respiration between forests and crops. In view of this, this paper discussed the diurnal variation of the soil respiration rates of these two vegetation types and the differences therebetween. Fig. 1 shows the diurnal variation of soil respiration during such two months as the slowlygrowing (April) month and fastgrowing (August) month in the growing season. It could be seen from Fig. 1 that the soil respiration of the two vegetation types was quite different. The soil respiration rate of the poplar plot was significantly higher than that of the crop. The average difference of soil respiration rate between the two was 3.09 and 3.55 μmol/(m2?s) in April and August, respectively. In terms of the variation law of soil respiration, the diurnal variation curves of soil respiration of the two vegetation types in April both had a single peak, but there were some differences in the peak value and variation law between the two. The peak of the crop plot ［1.56 μmol/(m2•s)］ appeared around 11:00 am, and the whole variation process was relatively symmetrical, and the peak of soil respiration in the poplar plot ［6.07 μmol/(m2•s)］ appeared around 13:00, and the curve had an irregular single peak, and showed that the soil respiration rates in the morning and afternoon were quite different. In August, the daily variation of soil respiration rate of both vegetation types exhibited a peak at 9:00 am at 1.71 μmol/(m2•s) (crop) and 4.99 μmol/(m2•s) (poplar). Afterwards, the soil respiration variation of the crop plot tended to be stable, and the soil respiration differences at various time points were not large, while the soil respiration rate of the poplar plot fluctuated obviously, showed a low value at 11:00, and then increased with time.



Fig. 1Diurnal variation of the soil respiration rate during the growing season in April and August for different vegetation types

Effects of soil temperature on soil respiration

The root growth of plants and the activities of microorganisms in soil are affected by soil temperature, and the strength of soil respiration is directly related to the activities of microbes in plant root system and soil. It could be seen that soil temperature is one of the main factors affecting soil respiration. A large number of studies have shown that there is a clear correlation between them［20］. According to Table 1, it could be seen that the soil respiration rate of the crop plot in the Dongting Lake area had a correlation coefficient of 0.885 with the surface soil temperature and a correlation coefficient of 0.741 with the 5-10 cm soil temperature. The correlation coefficient of the soil respiration rate in the poplar plot was 0.708 and 0.780 with the surface and 5-10 cm soil temperatures, respectively, being extremely significant. The soil respiration rate and soil temperature were fitted using the Y=aebX exponential function (Table 1). The results showed that the fitted equations of soil respiration rate in the crop plot with the surface and 5-10 cm soil temperatures were, respectively, Y=0.289 2e0.043 5X and Y=0.253 2e0.054 3X, with the goodness of fit of 0.752 8 and 0.504 3, respectively; and the fitted equations of the soil respiration rate in the poplar plot with the surface and 5-10 cm soil temperatures were Y=2.381 2e0.026X and Y=1.223 9e0.055 4X, respectively, with the goodness of fit of 0.535 8 and 0.611 6, respectively.

In order to further explore the relationship between sudden respiration rate and soil temperature, the soil respiration sensitivity index Q10 values of different vegetation types of sample plots were analyzed (Table 1). The soil respiration sensitivity index Q10 values of the surface of the crop and poplar plots were 2.257 and 2.066, respectively, and those of the 5-10 cm soil were 2.206 and 2.801, respectively.

Table 1Correlation between soil respiration rate and soil temperature during the growing season for different vegetation types

Vegetation typeTemperature Fitted equation R2Q10Correlation coefficient P

Crop Earth surface Y=0.289 2e0.043 5X0.752 82.2570.885**＜0.01

5-10 cm soilY=0.253 2e0.054 3X0.504 32.2060.741**＜0.01

Poplar Earth surface Y=2.381 2e0.026 0X0.535 82.0660.708**＜0.01

5-10 cm soilY=1.223 9e0.055 4X0.611 62.8010.780**＜0.01

Agricultural Biotechnology2019

Effect of soil humidity on soil respiration

Plant physiological activity, microbial energy supply and distribution and soil permeability are all affected by soil humidity, thereby affecting soil respiration［21］. Related studies have pointed out that when soil water content is lower than field water holding capacity, soil surface CO2 emission will be reduced［22］. Without considering the influence of temperature, oil moisture can promote the increase of soil respiration rate within a certain range, and if the water content is too high or too low, soil respiration rate will be inhibited. Many scholars have tried to quantify the relationship between soil humidity and soil respiration rate, but the results are quite different［23］. Based on the basis of previous studies, this study used quadratic curve to fit the relation between soil humidity and soil respiration rate of different vegetation types, and the effect was good. The fitting equations of soil humidity and soil respiration rate of the crop and poplar plantation were, respectively, Y=-89.514X2+30.394X-1.254 2 and Y=21.966X2+4.786X+0.353 3, with the goodness of fit of 0.4876 and 0.9185, respectively (Table 2). According to the correlation analysis (Table 2), the correlation coefficients between soil humidity and soil respiration rate of the crop and poplar plots were, respectively, 0.504 and 0.952, which meant they were significantly correlated (P<0.01).

Table 2Correlation between soil respiration rate and soil humidity during the growing season for different vegetation types

Influencing factor Vegetation typeFitted equationR2Correlation coefficientP

Soil humidity Crop Y=-89.514X2+30.394X-1.254 20.487 60.504**＜0.01

Poplar Y=21.966X2+4.786X+0.353 30.918 50.952**＜0.01

Conclusions and Discussion

In the spring, the diurnal variation curves of soil respiration rate showed a single peak variation. The peak of the crop plot appeared at 11:00 am, and the soil respiration peak of the poplar plot appeared at 13:00. The result of this study was similar to research result obtained by Zhu and Wang et al.［24-25］ that the diurnal variation of soil respiration had a single peak and was linear and the peaks appeared at around 12:00 and 13:00, respectively. The time difference of the soil respiration peak between the two vegetation types might be due to that the crop had a small crown width, weaker light interception ability and strong light transmission, which led to faster ground warming, which further led to earlier peak of soil respiration. And the poplar trees were high with a large crown width and had more layered branches and leaves, which led to strong light transmission slower ground warming, which further caused delayed soil respiration peak.

During the vigorous growing period in summer, the soil respiration of the crop and poplar plots both showed a peak at 9:00 am, after which the soil respiration of the crop plot varied smoothly with small differences between various time periods, while the soil of the poplar plot showed another increasing trend at 17:00. The reason for this phenomenon might be related to the high temperature in summer. The temperature was suitable at around 9:00 am in summer, and the plant growth and metabolism were stable, which can promote the roots to breathe. With the progress of time, the temperature gradually rose, the soil temperature was greatly affected by the air temperature in the crop field due to short plant height, the microbial enzyme activity in the roots and soil of the plant was reduced, and the soil respiration was reduced, which continued until the evening. The air in the poplar plot circulated, the canopy itself had a certain shading effect, and with the double coverage of the understory vegetation, the soil temperature was less affected by the temperature. And in the evening, due to the weakening of the suns light intensity, the temperature in the forest land decreased rapidly, and the activity of various enzymes increased at a suitable temperature, so the soil respiration of the poplar plot showed a second peak at 17:00.

Soil water content and temperature are important environmental factors affecting soil respiration［26］. As a wetland in the lake area, the effects of hydrothermal conditions on soil respiration are more obvious. In this study, the correlation between soil respiration and hydrothermal factors was obtained. The correlation of the crop with environmental factors ranked as surface temperature (0.885)>soil temperature (0.741)>soil humidity (0.504). In the poplar plot, the correlation with environmental factors ranked as soil humidity (0.952) > soil temperature (0.780) > surface temperature (0.708). It could be seen that the correlation between soil respiration and environmental factors of different vegetation types was quite different, and the correlation of the poplar plot with environmental factors was basically higher than that of the crop with environmental factors. Due to the short plant height and the planting density of the crop, the planting density was much larger than that of the poplar trees, the air circulation capacity in the community was poor, and the surface temperature and soil temperature were higher than those in the poplar plantation, which resulted in accelerated soil microbial respiration and stronger plant root enzyme activity, which further increased soil microbial decomposition and thus the soil respiration intensity, which is consistent with the research result of Wu［27］. Poor air circulation leads to poor selfregulation of soil moisture in crop communitys small ecosystems, and the gas permeability of soil is poor when soil moisture is high, which further limits soil respiration intensity, while when soil moisture is too low, soil microbial activity rate is relatively slow, and soil respiration is weakened［28-29］. The poplar plantation had better ventilation effect due to high plant height, so the small ecosystem of the forest had better selfregulation ability, and the surface temperature, soil temperature and soil moisture were suitable for microbial activities in the soil and were strongly correlated with soil respiration, showing a correlation coefficient reaching 0.7 or above.

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