Agriculture Reference
In-Depth Information
photosynthetic process. Legume plants are adapted to mild temperatures and have
the higher rate of N-fixation and yield production at the range of 20-30 °C. Higher
or lower temperatures can reduce plant growth and yield production (Lynch and
Smith 1993 ). Legume plants can grow well at the optimum soil moisture and hence
precipitation. High or low level of soil moisture can decrease plant growth and yield
production of legume plants (Sakthivelu et al. 2008 ; Sorensen et al. 2012 ).
The concentration of CO 2 can also affect plant performance by affecting the pro-
cess of photosynthesis. Higher rates of CO 2 (500-1000 µmol mol −1 ) decreased plant
efficiency by decreasing the rate of protein. As a result of elevated CO 2 concentra-
tion, the concentration of Rubisco reduces. It is because the expression of photo-
synthetic genes, which are dependent on carbohydrate concentration, is affected.
However, other mechanisms may also cause such alterations (Stitt and Krapp 1999 ;
Taub et al. 2008 ). The reduction in the leaf protein concentration can decrease seed
protein concentration, because usually the N content of senescing tissues is trans-
located to plants seeds (Fangmeier et al. 1999 ; Salon et al. 2001 ). However, com-
pared with cereals, soybean grains indicated much smaller rates of protein reduc-
tion, which is mostly due to its symbiotic association with rhizobium. Root nodules
are sinks for photosynthates, inhibiting plant leaf to increase the level of hexose,
which can adversely affect Rubisco concentration. The fluctuations in ozone can
also affect plant performance as higher rates of exposure can have negative effects
on plant growth by adversely affecting the structure of leaf mesophyll, and hence
decreased carbon assimilation and photosynthesis rate (Long and Naidu 2002 ; Garg
and Bhandari 2012 ).
However, the adverse effects of ozone exposure on plant leaf can be inhibited by
the elevated levels of CO 2 resulting in the enhanced protein seed concentration. It
is because ozone can have negative effects on the process of N fixation, and hence
decrease the translocation of photosynthates to the nodules (Pausch et al. 1996 ; Ti
et al. 2012 ). Accordingly, elevated CO 2 levels may enhance the rate of N-fixation
by increasing the level of C assimilation (De Graaff et al. 2006 ; Rogers et al. 2006 ).
Carbon cycling between soil and atmosphere is important affecting different bio-
logical processes such as N-fixation. The higher rate of carbon in soil can contribute
to higher biological activities by soil microbes, improve soil structure and enhance
soil fertility. However, for N-fixing rhizobium the atmospheric carbon may be of
more importance as photosynthesis process assimilates it into carbohydrate. Rhizo-
bium bacteria utilize hydrocarbons, supplied by plant as source of energy for their
activities. Accordingly, higher rate of atmospheric C up to some level can increase
the rate of photosynthesis and hence the process of N-fixation (Townsend et al.
2011 ; Finzi et al. 2011 ).
Hence, the process of N-fixation by legume plants and rhizobium is of high
importance significantly contributing to the necessary N for plant growth and yield
production while agriculturally and environmentally sustainable. This process is
affected by different parameters and hence it is pertinent to find methods that can
enhance its efficiency under different conditions including stress.
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