Raw pH fall-out as a sign of a mycorrhizal modifier of Sorghum sudanensis

The management of symbiotic Microbial Biota (MB) in the soil as agents that promote the yield and health of crops, is aimed at inducing modifications of the phenotype of plants, both over and under the ground. It is here shown, in Sorghum sudanensis plants, that: i) a simple response to MB inoculation is the result of the fall out of the raw pH; ii) the simple NIR scans of leaves can be considered to rapidly classify the outcomes; iii) the raw pH can be considered a key-variable of leaf modifications. An experiment was carried out on Sorghum sudanensis. The plants were seeded in pots and grown for 66 d, and then a control non-inoculated group (C) was compared with thirteen Arbuscular Mycorrhizae (AM) Glomus inoculated groups and with two commercial MB products. A total of 374 raw pH measurements conducted on the leaves showed that the 5.18 pH units in the C group were scaled by -1.9% (P<0.0336) in the MB group and by -3.4% in the AM group (P<0.0001), with a relevant diversity between groups. Direct discrimination of these three groups, by means of smart NIR-SCIO, showed a % reclassification of the C, MB and AM groups of 74%, 59% and 96% in the fresh leaves and of 65%, 51% and 94% in the dried ground leaves, respectively. The composition of the dried leaves, based on a set of 14 variables predicted via NIRS models, plus the total foliar dry weight and percentage, showed a typical increase in protein, ash and hemicellulose, and a typical decrease in the cellulose, dry matter, crude fiber and crop maturity index. These variables were related to the foliar pH, as a key-variable, by means of a PLS standard model (R 0.81) in which a low pH steadily favored the dry mass weight and, to a lesser extent, the hemicellulose and the digestible NDF contents; on the other hand, a high pH increased the dry matter percentage and the cellulose content of the leaves. As expected, the leaves of the inoculated plants showed a more juvenile ontogenic status. The epigean botanical modifications can be considered harmonic expressions of a luxuriant symbiosis, as testified by the homologous NIR categorization. The outlook for a symbiotic agriculture, with mycorrhizal plants, should consider the raw pH as a multifaceted variable. DOI :10.14302/issn.2639-3166.jar-18-2264 Corresponding author: Giorgio Masoero, Accademia di Agricoltura di Torino, Via A. Doria 10, 10123, Torino, Italy. E-mail: giorgioxmasoero@gmail.com Running Title: Raw pH is a signal of a mycorrhizal modifier


Introduction
A credible increase of 50% in the world feed and food necessities can be expected at the end of the next thirty years 1 , and more fertilizers, water and pesticides will be needed to satisfy such needs. Starting all over again with a "Symbiotic agriculture" is a seductive Experiments with AM may be divided into two categories, that is, practical and scientific 7 . The first type analyses pure soils and substrates, such as those in a microbial desert, without agrarian biotas, while the second one studies extensive and multiple interactions in the presence of immense microbial charges 14 .
In a first field experiment with maize fertilized by a Micosat F® complex microbial consortium 15 , it was found that the in vivo raw pH of a plant was acidified according to a de-gradient from the roots (pH -7% in mycorrhizal maize) to the stem at an ear height (-4%).
Other researches in vineyards confirmed the tendency of the raw pH 16 , measured at the petiole insert, to be lowered after microbial fertilisation with 10 kg ha -1 of MB compound inoculated near the secondary roots. The authenticity of the raw pH parameter was highlighted by Cornelissen et al. 17 , who considered the leaf pH as a new plant trait that could explain variations in the foliar chemistry and carbon cycling processes of subarctic plant species and types. The first work was followed by a microcosm experiment 18 , the results of which upset the myth of a pH dominance of the soil: the pH in fresh leaves will only grow for +0.036 pH soil -1 (from -0.5 to -0.7%).
The aim of the present study has been to ascertain whether the decrease in the varied raw pH in leaves is due to AM or to a whole complex of a microbial consortium, and to assess how AM can be considered effective modifier agents of the Sorghum sudanensis phenotype, while considering the raw pH as a key-variable.

Experimental Procedure
Two rapid methods: the measurement of the raw pH, according to Masoero  were inoculated at seeding in 10 L pots (three seeds per pot), using 12 g pot -1 of crude inoculum. The growth substrate was volcanic lapillus rock (5 L) and peat (5 L).
The substrate was kept in the greenhouse and drip irrigation was adopted.

Raw pH
The raw pH of the leaves appeared as a very narrow-distributed variable, which was characterized by a variation coefficient of 3.8% (Tab. 2).

NIR-Tomoscopy
In general, the discriminations of the three categories when the SCIO instrument was used were highly significant (Tab. 4). The leaves from plants inoculated with AM were individuated more correctly, in the scans on the fresh leaves (96%) as well as in the scans on the dry leaves (94%); the performances pertaining to the MB leaves were significant, albeit not so high (59 and 51%, respectively), while the Control leaves were individuated more clearly (74 and 65%, respectively).

Mycorrhizal Modifier
A luxuriating effect has been displayed in foliar observed that an AM fungus was significant, at a level of 5%, on water soluble carbohydrates, which increased by 14%. The Authors hypothesised that inoculation with an AM fungus increased the cytokinins, and, moving nutrients from other parts to the leaves tended to delay their senescence.
Raw pH fall-out as a Key-Variable In our short modification experiment, low pH steadily favoured the dry mass weight and, to a lesser extent, the hemicellulose, digestible NDF and the ether extract contents of the leaves. If the raw pH is a real key-variable, the modifier direction in Sorghum sudanensis appears quite attractive for ruminants.
Phyto-evolution studies 17,28 of a subarctic flora suggest that tissue pH itself is controlled to a great extent for a given species, because of its direct or indirect functions in the plant; in fact, a low pH corresponds to poor digestibility and may therefore act as an anti-herbivore defence in the same subarctic flora.
The field surveys of AM communities over a wide range of soil pH suggest that it is also the major driving force in structuring these communities 29 .