The biotechnology approach for methane mitigation technology involves identification of rice cultivars which emit less methane. It also involves the tailoring of plants which translocate less photosynthate to the roots and more to reproductive parts. Rice cultivation is responsible for 10% of GHG emissions from agriculture. In developing countries, the share of rice in GHG emissions from agriculture is even higher, e.g., it was 16% in 1994.
See 'Rice production technologies' for an overview of all climate change mitigation technologies related to rice cultivation. See 'Crop varieties with enhanced carbon sequestration' for general information about agricultural biotechnology for carbon sequestration in crops.
To identify the use of rice cultivars with reduced methane emissions, Wang et al., (2000) demonstrated that rice cultivars with small root systems, high root oxidative activity, high harvest index, and productive tillers are likely to produce less methane than other cultivars. They have identified cultivar Zhongzhou (modern japonica) as less methane-emitting compared to Jingyou (japonica hybrid) and Zhonghua (tall japonica). Parashar and Bhattacharya (2002) identified Annada rice variety (commonly used in Andhra Pradesh, a major rice growing region in India) as high yielding, with comparatively low methane emissions. Although low methane-emitting rice cultivars have been identified, methane emission reductions due to cultivar selection have been shown to be less significant than those identified due to modifying water management regimes or adding organic amendments. In addition, the rice yield of low methane-emitting cultivars needs to be evaluated. If the low emitting rice cultivars produce less rice, then more rice would need to be cultivated to meet demand, and as a result, overall methane emissions may increase.
Methane emissions can be reduced by selecting rice cultivars like ‘Luit’ which transport a large portion of their photosynthates to panicle growth and grain development (high harvest index). Varieties like ‘Disang’ should be avoided which use their photosynthates for the development of vegetative parts such as roots, leaf sheaths, culm etc. (low harvest index) that later on contribute to the emission of methane (Das and Baruah, 2008).
Methane emissions can also be reduced by selecting cultivars like ‘Prafulla’ and ‘Gitesh’ which have slower transport of methane due to smaller cross-sectional areas of their medullary cavities. Das and Baruah (2008) recorded a positive correlation between methane flux and the size of medullary cavity. They observed that the rice varieties ‘Basumuthi’ and ‘Bogajoha’ with larger sizes of medullary cavities had greater cross-sectional areas with higher methane diffusion pathways. Uprety et al., (2011) reported that methane concentration in the medullary cavities of rice plants are about 2,900 times higher than that of ambient air.
Important plant anatomical parameters such as leaf number, tiller number and plant biomass, which regulate the emission of methane, are identified. Modification of these anatomical traits, as well as possible changes in physiological processes, can help rice breeders develop new low methane-emitting genetic lines of rice and developing site-specific technology packages, ascertaining synergies with productivity and accounting for methane emissions.
This approach is just starting, and it has not advanced beyond preliminary experiments. The barrier for the biotechnological approach is the positive correlation between methane emission and yield. However, the barriers can be disseminated by selecting correlation breaker varieties.
- Farmers have exclusive choice of designing and selecting low methane emitting rice cultivars with high yield without altering the farming operations.
- Methane emissions are not normally measured by rice breeders, so this would require additional effort, although if some anatomical traits are sufficiently well correlated with methane emissions, then the extra effort might be minimal.
- The degree to which emissions can be lowered using this approach may not be large.
- Varieties with the low-emissions trait may be lower yielding.
- Considerable time is required to develop new varieties.
If varieties can be developed that significantly reduce methane emissions without sacrificing yield, then this approach could be easily implemented, and the potential mitigation reduction could be high.
This approach is just starting, and it has not advanced beyond preliminary experiments. Methane emissions are not normally measured by rice breeders, so this would require additional effort, although if some anatomical traits are sufficiently well correlated with methane emissions, then the extra costs might be minimal.
Das, K. and Baruah K K. (2008): Methane emission associated with anatomical and morphophysiological characteristics of rice (Oryza sativa L.) plant. Physiologia plantarum 134: 303-312.
Parashar, D.C. and Bhattacharya, S. (2002): Considerations for methane mitigation from Indian paddy fields. Indian Journal of Radio and Space Physics. 31: 369-375.
Uprety, D. C., Baruah, K.K and Borah L. (2011): Methane in rice agriculture, J. Sci. and Indust. Res. 70(6):401-411.
Wang, Z.Y., Xu, Y.C., Li, Z., Guo, Y.X., Wassmann, R., Neue, H.U., Lantin, R.S., Buendia, L.V., Ding, Y.P. and Wang, Z.Z. (2000): Methane emissions from irrigated rice fields in northern China (Beijing). Nutr Cycling Agroecosyst 58(1/3):55-6.