Relative growth rate (RGR) of the different tropical species biofertilised with
In Southeast Mexico, deforestation in tropical forests is considered an environmental concern. Deforestation favours the growth of plants that compete with species of interest, which generally present slow growth. In order to promote greater growth in less time of the forest species used in reforestation and two crops of regional interest, the effect of including Rhizophagus intraradices in the seed or the root system of seedlings were investigated to evaluate its influence on growth and allocation of dry matter in the aerial and radical part, in addition to the concentration of N, P and Ca. Also, two additional collections with morphological characteristics of Glomus sps were included in T. donnell-smithii. The results indicate that biofertilisation with R. intraradices induces increased growth and is differential in stem and root dry matter allocation over time, in addition to increasing nutrient content in plant tissue.
- tropical spices
- root and shoot growth
- range relative growth
- nitrogen and phosphate
Forest ecosystems are affected by various environmental and anthropogenic factors such as drought and the establishment of annual crops; these actions have caused their degradation. The above situation has generated several reforestation programs in Mexico through the massive production of forest species in nurseries, however, when planted in the field, the survival of plants is less than 50%, due in part to the low quality of the plants produced in the nursery and the intermittent drought they face when taken to the field . In such procedures, the strengthening of the radical development of the host plant through biofertilisation with microorganisms has not been considered. Under these conditions, it is possible that microorganisms help plants survive in adverse environmental conditions .
Some bacteria and fungi that live in the rhizosphere interact with species present in agroforestry systems and may or may not manifest themselves in some morphological or physiological attribute of anthropocentric interest of the host plant, especially in sustainable or low input production systems, but their effective incidence depends on the microorganism and environmental and soil conditions . The interaction of the plant with endomycorrhizal fungi stimulates its growth , even in adverse environmental conditions [3, 5], such as drought , presence of nematodes  and also activate defence mechanisms against various pathogens [8, 9].
Endomycorrhizal fungi interact symbiotically with more than 80% of terrestrial plants . It is the most common symbiosis on earth  and important part of the development, maintenance and stability of ecosystems and represents an important mechanism for plant and reproductive development . They can be found in all terrestrial ecosystems and their universality implies vast taxonomic diversity . Native populations of endomycorrhizal fungi have favoured the sustainability of agricultural systems, while introduced ones may not be adapted to the environment and may have ecological specificity  or host preference . In the rhizosphere, in addition to microorganisms, there are abundant root exudates that have a selective effect on soil microbiota .
When endomycorrhizal fungi are introduced in the seed or in the soil to colonise the root, the establishment of symbiosis is facilitated and the benefits are expressed in early stages , as an increase in growth and in the case of nursery plants, a decrease of time to be taken to the field. Symbiosis improves the supply, availability and physical access of nutrients to the plant .
Currently, endomycorrhizal fungi are considered essential organisms for the sustainable management of agriculture. In general, when new species are introduced to a region and adapt quickly to the new environment, the possibility that the species has the capacity in its root system to establish symbiosis with the microorganisms is considered. They are capable of linking to the development of the subway community .
Radical colonisation by endomycorrhizal fungi initiates with the exchange of carbon from the host plant to the fungus, and in turn, establishes by exploring the soil through mycelium the transport of nutrients to the root , such as phosphorus [2, 21, 22], water  and other nutrients to the plant. If Phosphorus (P) is not available for the initial development of the plant, it becomes limiting  and being a low mobility ion, hyphae can be the bridge for phosphorus supplementation  and by supplying it, growth is significantly influenced . In addition, it improves the physical state of the soil by producing glomalin , to form more stable soil aggregates .
The beneficial effect of the application of endomycorrhizal fungi has been demonstrated in the increase of biomass in perennial crops such as
2. Influence of endomycorrhizal fungi on plant growth
Understanding growth, as the irreversible increase in the size of an individual almost always associated with an increase in its complexity, helps us to identify the effect of endomycorrhizal fungi on symbiosis with the host plant. The analysis of plant growth represents the first step in the analysis of primary production  in its different components, which are those that regulate the final production. In this way, the yield understood as the phenotypic expression of anthropocentric interest, is the final result of the physiological processes that are reflected in the plant’s morphology .
The assignment of dry matter to the different structures of the plant, such as the root system, the stem and the foliar lamina are modified when endomycorrhizal fungi are included, either in soil or in substrates with the addition of other components, such as bovine manure, from the poultry industry, or agro-industrial wastes, such as sugarcane bagasse, coffee husk, cocoa shell, among others. This symbiotic association between fungus and plant generates the enlargement of the root system and acts as a root complement . Endomycorrhizal fungi, together with the rest of microorganisms, are fundamental in the cycle of nutrients, even more, when considering that the availability of nutrients is heterogeneous in soils.
Mycelium is the means of transporting nutrients and water to the plant and is elemental in soil exploration. Especially in conditions of exploitation of monocultures that generate through time, the “depletion zone” of nutrients near its root system. Also, the tillage exercised in these production systems breaks the mycelium of the fungus and diminishes the beneficial effect it has on the structure of the soil, affecting the diversity and productivity of the communities [37, 38]. In addition, the applications of agrochemicals adversely affect the diversity and abundance of endomycorrhizal fungi in agroecosystems , causing the decrease or loss in the functioning of the plant community [40, 41].
In these conditions, the mycelium of the fungus can explore spaces in the soil where roots do not reach, that is, explore areas beyond the known “depletion zone” of the root and increase the absorption surface by exploring greater volume of soil compared to non-mycorrhised roots. This fact is more relevant when considering that they have the capacity to transport nutrients that are not very mobile, such as phosphorus .
The preference of endomycorrhizal fungi to transport phosphorus has been documented [21, 43] and this nutrient is fundamental for plant growth, even more so when considering that it has low availability in tropical soils . Its supply by the fungus favours plant growth, but the symbiosis can be reduced or inhibited if the P level in the soil is high and the plant root can absorb it by itself .  On the other hand, they cite that the efficiency in P absorption by the mycorrhised roots is mainly due to an acceleration of the dissociation of insoluble phosphate and it is extracted by the mycorrhizae according to the needs of the host plant. In general, it has been established that mycorrhised plants favour the absorption and transport of P, Zn, Ca, S, Cu, and Mg and their effects are more noticeable in low fertility soils .
When endomycorrhizal fungi are introduced into plants, the response can be diverse, influenced either by plant metabolism or by root architecture  and the interaction is considered non-specific, because any species of endomycorrhizal can colonise a plant , however, in different crops of the same species, the induction of growth is differential, according to the endomycorrhizal fungus introduced  or according to the tillage. In some forest species the root volume increases , in others, it decreases , or it is also expressed in an increase in the thickness of the stem needed to be taken to the field in less time compared to non-biofertilised plants. Also, it decreases mortality after transplantation  and improves its survival capacity in adverse conditions .
The growth of biofertilised plants with endomycorrhizal fungi presents changes in their aerial and root structure since the beginning of their evaluation. Generally, the dry weight of the aerial part of the plants is greater than the dry weight of the root system (Figure 1).
The root system development of biofertilised plants shows little difference in growth in
The response of microorganisms in plant development reflects differential growth in time and between their organs. The greater or lesser allocation of biomass to some plant organs, seems to be influenced by the biofertilisation applied to its radical system and in almost all cases, after the ample development of an organ in a period of time, it tends to diminish in the following period, but with important increase in another plant organ.
The relative growth rate or the amount of dry matter produced per unit of time induced by the symbiosis with endomycorrhizal fungi presents the highest growth rate during the first 56 days after planting (days) (Table 1). In the period between 112 and 40 das, all species show a decrease in growth rate. This can be mainly related to the higher proportion of cells that do not divide in relation to those that do , whereas, in annual crops, the highest growth occurs around 30 days after biofertilisation with an increase in the mean relative growth rate  and leaf area .
|Plant species||Time (days after sowing)|
On the other hand, in
3. Content of P and other nutrients in plant tissue
In all tropical forest species biofertilised with the endomycorrhizal fungus, a higher content of phosphorus was found in their plant tissue even though a large part of the available phosphorus in the soil is fixed in the andosol soils (Table 2). Many studies have shown that mycorrhised plants have benefits in their association with endomycorrhizal fungi under phosphorus-deficient conditions, especially in the acid soils of the tropics [62, 63, 64].
|Plant species||Time (days)*||Nutrient (%)|
P is captured by the external mycelium and subsequently transported through the hyphae or intraradical structures in the form of polyphosphate granules and finally the process of transfer by the bush to the host cells .
In general, it has been established that mycorrhised plants favour the absorption and transport not only of P but also of Zn, Ca, S, Cu, and Mg. The mycorrhizae are more active in soils of low fertility, especially when there is a deficiency of phosphorus .
The N content in the tissue of the biofertilised plants at 56 das was higher in the control with
In the case of
Nowadays, the knowledge of microorganisms and their interaction with the rhizosphere has demonstrated the importance of symbiosis in the soil-plant system.
4. Radical colonisation
The radical colonisation in the controls confirms the presence of other endomycorrhizal fungi in the soils used, as part of the regional microbiota, but with less capacity to stimulate growth. Even though it has been indicated that the symbiosis lacks taxonomic specificity , there is a certain functional compatibility with the host plant, the substrate and the introduced microorganisms.
On the other hand, in biofertilised species, the speed of colonisation of
At the end of the evaluation (140 days) the percentage of colonisation in the control was 44% and in the treatment with
The biofertilisation of tropical plants with
There are different periods in the vegetative growth of plants. At the beginning of the 28 to 56 days, the nutritional benefits are expressed by means of the increase in growth followed by a period of diminution and to continue in the following ones with the increase in biomass accumulation.
The content of nutrients such as phosphorus was always higher in the biofertilised plants.