Effects Of Soil C/N Ratio On Nitrogen Balance Of Plant-Soil System In Apple Orchard

We studied the characteristics of soil carbon and nitrogen by investigating1573apple orchards in12major apple production provinces in China; we examined the changes of soil quality in the plowed layer of165apple orchards from1984to2012in Qixia city; Using the track technology of C and N double mark, we investigated growth parameters,15N parameters,13C parameters and N balance of two-year old Malus hupehensis seedling and two-year old apple trees(Malus hupehensis Borkh. cv.’Red Fuji’) under different soil C/N ratio treatments; Using the technology of Barometric Process Separation (BaPS), we studied the gross nitrification, denitrification and N2O fiux under different soil C/N ratio treatments; Using the technology of Digital gene expression-tag profiling (DGE), we have analyzed gene expression changes response to low pH in Malus hupehensis seedling roots; Using the track technology of C and N double mark, we investigated the effects of six different soil pH treatments on growth and the characteristics of distribution and utilization of15N and13C. The main results were as follows:1. Higher soil organic carbon content were observed in the provinces of Heilongjiang, Xinjiang, and Yunnan, whereas low content was found in the provinces of Shandong, Henan, Hebei, and Shaanxi with the values ranging between6.44and7.76g·kg-1. Similar to soil organic carbon, soil total nitrogen content also exhibited obvious differences in the12major apple producing provinces. Shandong apple orchard soil had the highest total nitrogen content (1.26g·kg-1), followed by Beijing (1.23g·kg-1), the lowest was found in Ningxia and Shaanxi. The highest soil C/N ratio was appeared in Heilongjiang (15.42), and the lowest was in Shandong (6.05). The average of soil organic carbon, total nitrogen, and C/N ratio were9.52、0.93g·kg-1and10.34, respectively.2. Soil organic carban (SOC) and total nitrogen (TN) values significantly increased with the long-term nutrients input and the planting years. SOC and TN values in1984,1998, and2012were4.34and0.45g·kg-1,5.99and0.69g·kg-1, and7.03and1.14g·kg-1, respectively. However, the soil C/N ratio tends to decrease with the long-term nutrients input and the planting years. Soil C/N ratios decreased from9.64(1984) to8.54(1998) and6.18(2012). Soil pH decreased from6.33in1984to5.96in1998, and then5.32in2012.3. With the increase of soil C/N ratio, the dry matter of root increased significantly; while the height, stem diameter, dry matter of above ground parts, and15N utilization efficiency increased at first, then decreased, and the highest value appeared when the soil C/N ratio ranged from20to25. With the increase of soil C/N ratio, Ndff value in leaves was the highest, followed by roots and stems.15N distribution ratio in leaves increased, while13C distribution decreased with the increase of soil C/N ratio, but the change trends were just opposite in roots. The proportion of plant absorption nitrogen from fertilizer was much higher when the value of soil C/N ratio in the range of15～25, but the percentage of plant absorption nitrogen from soil was much higher when the soil C/N ratio was too low (<20) or high (<25).4. The gross nitrification rate, denitrification rate and N2O fiux were extremely high when the soil C/N ratio was lower, and then decreased with the increase of soil C/N ratio, and the valus were very lower when the soil C/N ratio was extremely high.5. Considering the four biochemical processes (N cycling, uptake of BCs, P, and S) that influence soil acidification, the net H+production is90.61kmol·ha-1·y-1. H+production caused by N application is2.81times that of uptake of BCs. Therefore, a significant amount of N application is the major process that causes soil acidification. The nitriate loss rate had an significantly positive effect on H+production, and there had an significantly negative relationship between nitriate loss rate and soil C/N ratio. So, the lower soil C/N ratio can accelerate soil acidification process.6. The results show that low pH affects a broad range of genes. Overall,1,705genes were downregulated,44genes were upregulated by low pH. Two-year-old apple trees(Malus domestica Borkh. cv Red Fuji)/Malus hupehensis were used to study the effects of six different soil pH treatments (soil pH of T0～T5were6.83,6.40,5.87,5.29,4.58and3.82, respectively) on growth and the characteristics of distribution and utilization of15N and13C by using the track technology of C and N double mark. The biomass of root, above ground, total dry weight, root-cap ratio, net photosynthetic rate and15N utilization rate of apple trees decrease significantly with the decrease in soil pH value. The15N and13C distribution pattern were consistent in various organs amoung the different soil pH treatments:mainly in the leaves, followed by the annual stems, then the roots, and the biennial stems were the least. In the same organ (especially in roots and leaves), differences in15N and13C distribution ratio were found among the different soil pH treatments. With a decrease in soil pH value, the15N and13C distribution ratio in leaves increased, while those in the roots decreased.7. Application of additional carbon into soil significantly influences the nitrogen translation and utilization processes. A laboratory simulation test was used to study the effect of carbon application on nitrogen and phosphorus leaching in apple orchard soil columns under simulated raining condition. Compared with NP treatment, adding carbon can significantly reduced NH4+-N and NO3--N concentrations and cumulative amounts of leachate in B+NP and G+NP treatments. Nitrogen leaching amount in B+NP and G+NP treatments were only57.87%and82.73%of NP treatment at the end of the study. Fertilization had no obvious impact on dissolved phosphorus leaching quantity, but the total phosphorus leaching amount was significantly higher than CK when fertilization with P. Compared with NP treatment, adding carbon significantly reduced the total phosphorus leaching amount, and the lowest was appeared in B+NP treatment. Comparing with CK and single N treatments, the bulk density of0-5cm and5-10cm soil layer decreased significantly in N+B and N+S treatments, while the CEC of0-10cm soil layer increased significantly. The highest total weight of apple trees,15N uptake amount and15N utilization rate existed in N+B treatment, followed by N+S treatment, and the lowest of those values were found in N treatment. N+S and N+B treatments significantly reduced the N loss through ammonia volatilization, and slightly increased the N2O loss, but there were no significant differences in the three N application treatments. The highest15N residual rate in0-50cm soil layer appeared in N+B treatment, followed by N+S treatment, and N treatment was the lowest; but the highest was found in N treatment, followed by N+S treatment, and N+B treatment was the lowest in50-100cm. Application of straw and biochar into apple orchard soil can ameliorate the soil properties, improve plant growth, promote N uptake by plant, increase the N fixed by soil, decrease N gaseous loss, and the result will get better when application of biochar.