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The influence of actively growing roots and root exudates on nitrogen mineralization from soil organic matter in paddy rice soils

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Abstract
As plants interact with the soil to acquire and mobilise nutrients, their roots alter the soil biologically, chemically and physically over variable distances from its surface, defining the extent of the rhizosphere by the respective processes considered in space and time (Paterson, 2003). To date, very little is known on the influence of root growth and rhizodeposition of root exudates (i.e. mainly sugars and polysaccharides, organic and amino acids, peptides and proteins) on N turnover in paddy rice soils. Classical N mineralization experiments are done using uncropped soil, thus completely neglecting the influence of roots and root exudates on the N mineralization process. In this research we explicitly have taken into account this influence. Two experiments were conducted, one is an incubation experiment with artificial root exudates and the other, is a pot experiment with actively growing rice crops. In the first experiment, the effects of rice root exudates on net nitrogen mineralization were investigated in a six week incubation study at 25°C with three different paddy soils from Bangladesh under saturated conditions. This study consisted of four different treatments with artificial root exudates applications, namely (1) low molecular weight organic acids (a mixture of malic, tartaric, succinic, citric and lactic acid at a C-ratio of 80:9:5:4:2), (2) carbohydrates (glucose), (3) a mixture of organic acids and carbohydrate solutions (at a C-ratio of 50:50) along with a (4) control. Root exudates were artificially injected into the soil column at three fixed locations each week at a rate of 103 µg C g-1 week-1. An inconsistent treatment effect was found on the nitrogen mineralization over three different rice soils under saturated condition. In only one of the three studied sites, enhanced N mineralization was observed in all amended treatments. Hence the stimulatory effect on the N mineralization might derive from a ‘priming effect’. A second experiment was conducted to investigate the influence of rice roots on nitrogen mineralization from soil organic matter. Five selected soils from Bangladesh were filled in large plastic boxes (e.g. 0.4*0.6*0.2m) with 15 kg in each boxes and brought under saturated condition. Thirty five days old seedlings were transplanted in the plastic boxes. During the entire growing period, soil samples were taken to measure the mineralized NH4+ and NO3- at every two weeks interval from three spots of each plastic box at the middle of two hills with the help of a small augur. The total N uptake by the crop was measured at two occasions (during 35 days after transplanting and harvesting period). In four out of five soils, the sum of the N uptaken by the crop and N mineralization in cropped soil was found to be higher than the N mineralization in uncropped soils. Higher N mineralization in cropped soils than the uncropped soils suggests that there is a positive effect of actively growing roots on N mineralization. However, more experimental research is ongoing to reach a concrete conclusion.

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Chicago
Begum, Shamim Ara, MD Abdul Kader, Steven Sleutel, and Stefaan De Neve. 2010. “The Influence of Actively Growing Roots and Root Exudates on Nitrogen Mineralization from Soil Organic Matter in Paddy Rice Soils.” In SOM 2010, Abstracts, 48–49. Grignon, France: Bioemco. Soil Organic Matter Research Group.
APA
Begum, S. A., Kader, M. A., Sleutel, S., & De Neve, S. (2010). The influence of actively growing roots and root exudates on nitrogen mineralization from soil organic matter in paddy rice soils. SOM 2010, Abstracts (pp. 48–49). Presented at the SOM 2010 : Soil organic matter stabilization and ecosystem functions, Grignon, France: Bioemco. Soil Organic Matter Research Group.
Vancouver
1.
Begum SA, Kader MA, Sleutel S, De Neve S. The influence of actively growing roots and root exudates on nitrogen mineralization from soil organic matter in paddy rice soils. SOM 2010, Abstracts. Grignon, France: Bioemco. Soil Organic Matter Research Group; 2010. p. 48–9.
MLA
Begum, Shamim Ara, MD Abdul Kader, Steven Sleutel, et al. “The Influence of Actively Growing Roots and Root Exudates on Nitrogen Mineralization from Soil Organic Matter in Paddy Rice Soils.” SOM 2010, Abstracts. Grignon, France: Bioemco. Soil Organic Matter Research Group, 2010. 48–49. Print.
@inproceedings{1046451,
  abstract     = {As plants interact with the soil to acquire and mobilise nutrients, their roots alter the soil biologically, chemically and physically over variable distances from its surface, defining the extent of the rhizosphere by the respective processes considered in space and time (Paterson, 2003). To date, very little is known on the influence of root growth and rhizodeposition of root exudates (i.e. mainly sugars and polysaccharides, organic and amino acids, peptides and proteins) on N turnover in paddy rice soils. Classical N mineralization experiments are done using uncropped soil, thus completely neglecting the influence of roots and root exudates on the N mineralization process. In this research we explicitly have taken into account this influence. Two experiments were conducted, one is an incubation experiment with artificial root exudates and the other, is a pot experiment with actively growing rice crops. In the first experiment, the effects of rice root exudates on net nitrogen mineralization were investigated in a six week incubation study at 25{\textdegree}C with three different paddy soils from Bangladesh under saturated conditions.  This study consisted of four different treatments with artificial root exudates applications, namely (1) low molecular weight organic acids (a mixture of malic, tartaric, succinic, citric and lactic acid at a C-ratio of 80:9:5:4:2), (2) carbohydrates (glucose), (3) a mixture of organic acids and carbohydrate solutions (at a C-ratio of 50:50) along with a (4) control. Root exudates were artificially injected into the soil column at three fixed locations each week at a rate of 103 {\textmu}g C g-1 week-1. An inconsistent treatment effect was found on the nitrogen mineralization over three different rice soils under saturated condition. In only one of the three studied sites, enhanced N mineralization was observed in all amended treatments. Hence the stimulatory effect on the N mineralization might derive from a {\textquoteleft}priming effect{\textquoteright}. A second experiment was conducted to investigate the influence of rice roots on nitrogen mineralization from soil organic matter.  Five selected soils from Bangladesh were filled in large plastic boxes (e.g. 0.4*0.6*0.2m) with 15 kg in each boxes and brought under saturated condition. Thirty five days old seedlings were transplanted in the plastic boxes. During the entire growing period, soil samples were taken to measure the mineralized NH4+ and NO3- at every two weeks interval from three spots of each plastic box at the middle of two hills with the help of a small augur. The total N uptake by the crop was measured at two occasions (during 35 days after transplanting and harvesting period). In four out of five soils, the sum of the N uptaken by the crop and N mineralization in cropped soil was found to be higher than the N mineralization in uncropped soils. Higher N mineralization in cropped soils than the uncropped soils suggests that there is a positive effect of actively growing roots on N mineralization. However, more experimental research is ongoing to reach a concrete conclusion.},
  articleno    = {S1-P21},
  author       = {Begum, Shamim Ara and Kader, MD Abdul and Sleutel, Steven and De Neve, Stefaan},
  booktitle    = {SOM 2010, Abstracts},
  language     = {eng},
  location     = {Presqu'{\^i}le de Giens, France},
  pages        = {S1-P21:48--S1-P21:49},
  publisher    = {Bioemco. Soil Organic Matter Research Group},
  title        = {The influence of actively growing roots and root exudates on nitrogen mineralization from soil organic matter in paddy rice soils},
  year         = {2010},
}