Improving Casuarina growth and symbiosis with Frankia under different soil and environmental conditions—review

Abstract

Casuarinas are very important plants for their various uses and survival in adverse sites or harsh environments. As nitrogen fixation, in symbiosis with Frankia, is an important factor for the survival of these plants under various conditions, the basis for selecting both effective and tolerant Frankia strains and Casuarina spp., are provided. Enhancement of the symbiotic relationship between Frankia and Casuarina, by mycorrhizal infection and other biofertilizing microorganisms such as Bacillus and Azospirillum, is reflected by superior plant growth. Casuarina leaf litter is also a great source for both inorganic and organic nutrients. Therefore, careful management of the top soil layer under Casuarina trees is very important. Litter decomposition ratio is affected by many physical chemical and biological factors including temperature, moisture conditions, lignin, and C-to-N and N-to-P ratios in addition to soil biota. In general, here the above relations are discussed and an alleviation model is presented for important disturbances of natural and human origin made in soil and environment, especially in the dry regions. In conclusion, we suggest how to optimize the nitrogen fixation and plant growth under the prevalent conditions.

Use ofFrankiaand Actinorhizal Plants for Degraded Lands Reclamation

“…These plants have an important ecological and economical role in tropical countries. They contribute to the improvement of soil fertility by fixing nitrogen and producing thick leaf litter from needles that can be used as compost by farmers [2, 39–41]. …”

“…They are used as windbreaks to protect adjacent crops and fix sand dunes in Senegal (Figure 2(a)), Tunisia, Egypt, China, and India [2, 36, 43]. In agroforestry system, these trees are used to improve soil fertility and increase crop yield (e.g, intercropping with legumes) in China and India [44].…”

“…In Asia, shelter belts formed by Casuarina trees have played a major protective role during typhoons and tsunami [44]. Association with Frankia increased Casuarina growth and biomass [2, 47, 48]. Furthermore, in this symbiotic relationship, bacteria confer to plants a high resistance to abiotic and biotic stresses [27, 49].…”

“…Thus, the rehabilitation of degraded lands is critical. To overcome the problem of the lack of fertility in degraded soils, fast growing nitrogen fixing trees such as actinorhizal plants in combination with biofertilizers are used [1, 2]. Actinorhizal plants are nitrogen-fixing plants from 8 families including Betulaceae , Casuarinaceae , Coriariaceae , Datiscaceae , Elaeagnaceae , Myricaceae , Rhamnaceae , and Rosaceae , [3, 4] distributed in 25 genera and approximately 200 angiosperms species.…”

“…Upon establishment, actinorhizal tree seedlings must be inoculated in nursery or in the field [10]. The success of establishment of Casuarina plantation in degraded sites depends on the effective nodulation by appropriate Frankia strains [2, 11]. However, studies related to the beneficial role of the nitrogen fixing actinorhizal bacteria on actinorhizal plants for the rehabilitation of degraded soils are very scarce.…”