The Effect of Mychorhizae Symbiosis on Nutrient Concentration in Common Almond (Prunus dulcis Mill.) Rootstocks in Drought Stress Condition

Almond (Prunusdulcis Mill.), native to West Asia to the Mediterranean, and Iran after the United States and Spain has a third rank in production of this product in the world. Drought stress is one of the most important factors limiting the yield and production of agricultural products. Many anatomical, physiological, enzymatic, nutritional, quantitative and qualitative characteristics of almonds are affected by drought stress. There are a lot of micro-organisms in soil can help plant nutrition and uptake of nutrient elements in different ways that can be mentioned by the dual symbiotic relation between micro-organism and plant. Mycorrhizae fungi are one of these microorganisms. The most important beneficial effects of mycorrhizal symbiosis is increasing the nutrient uptake, leaf gas exchange, photosynthesis, water use efficiency, productivity, improve plant nutrition and resistance to environmental stresses. Also, it helps the plant to absorb more water and nutrients by modification of rhizosphere environment, improvement of soil structure through formation of stable aggregates, expansion of external filaments and change of root morphology. The results of mycorrhizae symbiosis research in different plants show that the higher uptake of nitrogen (N), phosphorus (P), potassium (K), iron (Fe), zinc (Zn), copper (Cu) and manganese (Mn). The aim of this study was to evaluate the ability of mycorrhizal fungi, a symbiotic and environmentally friendly agent, in drought stress condition on increasing growth and absorption of water and nutrient elements on almond rootstocks commonly consumed in Chaharmahal-va- Bakhtiari province.

This field experiment was carried out as a factorial based on a randomized complete block design (RCBD) with three replications. The treatments consist of two level of mycorrhizal fungus (M0: without and M1 with using of mycorrhizal fungus), four kinds of rootstock (bitter, local Shorab 2, GF and GN) and four levels of drought stress (without stress as a control, slight, moderate and severe water stress which based on ratio of depletion of plant available water). Inoculation of mycorrhizal fungi at the rate of 100 g of a mixture of three species of mycorrhizal fungi (Clariodeoglumus etunicatum, Rhizophagus intraradices and Funneliformiss mosseae) was placed under the roots for each rootstock with a population of at least 100 active fungal organs including spores, vesicles, and hyphae per gram. The plants were exposed to drought stress for six weeks. Leaf samples were taken to measure the amount of nutrient elements. Nitrogen by Kjeldahl method, P by spectrophotometer, K by flame method with flame photometer and nutrients of iron, zinc, manganese, boron  and copper were measured by atomic absorption spectrophotometry with an atomic absorption spectrometer (PerkinElmer Analyst 400, Waltham, United States of America). Statistical analysis was done with SAS 9.3 statistical software. Duncan’s multiple range test was used to separate means.

The results revealed that there were significant differences between four cultivars in terms of nutrient concentrations except B. The maximum amounts of the studied characteristics were obtained from GF rootstock. The GN rootstock was in the second ranking. Water deficient treatment showed a significant effect on the examined nutrient elements except Mn and Cu concentrations. The maximum amounts of measured nutrient elements, except K, were obtained from I1 treatment. The highest rate of K was obtained from I3 and I4 treatments. With increasing drought stress the decreasing trend of nutrient elements, except K was observed. Mycorrhizae fungi treatment caused increase of nutrient elements except B. The maximum amounts of N, P, Fe and Zn were obtained from GF +I1. Using of mycorrhizae fungi in drought treatments caused significant increase in N, K, Fe, Mn and B. The maximum amount of nutrients was obtained from GF + M1 treatment. The maximum amounts of N, Fe and B were obtained from I1 + M1 + GN. Inoculation of mycorrhizae fungi caused increase of rootstock growth under drought stress. The change in the shape, volume and number of root branches of the root caused by the consumption of mycorrhizae fungi was due to increased nutrient uptake and changes in the amount of plant hormones such as auxin. Growth and absorption of water and nutrients decreased under water deficient stress. Therefore, the effect of symbiosis with mycorrhizae fungi under water deficient stress conditions was more important than non-stress conditions. This has been reported in the research of various researchers.

The results of this study showed that with increasing water deficient stress, the amount of nutrient elements decreased except for K. The effectively of GF rootstock to mycorrhizae fungi inoculation was higher due to higher growth potential and root velocity. Nutrients that were measured in inoculated rootstocks were higher than those without inoculation. Under drought stress conditions, the amount of nutrients measured was higher in inoculated rootstocks. Inoculation of mycorrhizal fungi can lead to increase nutrients absorption with some mechanisms such as effective increase in root uptake, root length, number of lateral roots, proton production, and secretion of organic acids, siderophores, chelating compounds, and acid phosphates. Consumption of mycorrhizae fungi increased nutrient uptake and improved almond rootstock resistance to drought stress.