An integrated, multisensor system for the continuous monitoring of water dynamics in rice fields under different irrigation regimes.

The cultivation of rice, one of the most important staple crops worldwide, has very high water requirements. A variety of irrigation practices are applied, whose pros and cons, both in terms of water productivity and of their effects on the environment, are not completely understood yet. The continuous monitoring of irrigation and rainfall inputs, as well as of soil water dynamics, is a very important factor in the analysis of these practices. At the same time, however, it represents a challenging and costly task because of the complexity of the processes involved, of the difference in nature and magnitude of the driving variables and of the high variety of field conditions. In this paper, we present the prototype of an integrated, multisensor system for the continuous monitoring of water dynamics in rice fields under different irrigation regimes. The system consists of the following: (1) flow measurement devices for the monitoring of irrigation supply and tailwater drainage; (2) piezometers for groundwater level monitoring; (3) level gauges for monitoring the flooding depth; (4) multilevel tensiometers and moisture sensor clusters to monitor soil water status; (5) eddy covariance station for the estimation of evapotranspiration fluxes and (6) wireless transmission devices and software interface for data transfer, storage and control from remote computer. The system is modular and it is replicable in different field conditions. It was successfully applied over a 2-year period in three experimental plots in Northern Italy, each one with a different water management strategy. In the paper, we present information concerning the different instruments selected, their interconnections and their integration in a common remote control scheme. We also provide considerations and figures on the material and labour costs of the installation and management of the system.

Improved plant resistance to drought is promoted by the root-associated microbiome as a water stress-dependent trait.

Although drought is an increasing problem in agriculture, the contribution of the root-associated bacterial microbiome to plant adaptation to water stress is poorly studied. We investigated if the culturable bacterial microbiome associated with five grapevine rootstocks and the grapevine cultivar Barbera may enhance plant growth under drought stress. Eight isolates, over 510 strains, were tested in vivo for their capacity to support grapevine growth under water stress. The selected strains exhibited a vast array of plant growth promoting (PGP) traits, and confocal microscopy observation of gfp-labelled Acinetobacter and Pseudomonas isolates showed their ability to adhere and colonize both the Arabidopsis and grapevine rhizoplane. Tests on pepper plants fertilized with the selected strains, under both optimal irrigation and drought conditions, showed that PGP activity was a stress-dependent and not a per se feature of the strains. The isolates were capable of increasing shoot and leaf biomass, shoot length, and photosynthetic activity of drought-challenged grapevines, with an enhanced effect in drought-sensitive rootstock. Three isolates were further assayed for PGP capacity under outdoor conditions, exhibiting the ability to increase grapevine root biomass. Overall, the results indicate that PGP bacteria contribute to improve plant adaptation to drought through a water stress-induced promotion ability.

Inducing hysteretic spin crossover in solution.

A hysteretic spin transition is induced in a solution assembly of a mononuclear Fe(III) amphiphilic complex which exhibits only gradual spin crossover in the solid state. The hysteretic behavior is dependent on dynamic solution assembly and removal of solvent causes reversion to the original bulk solid magnetic response.

A magnetic iron(III) switch with controlled and adjustable thermal response for solution processing.

Spin crossover requires cooperative behavior of the metal centers in order to become useful for devices. While cooperativity is barely predictable in solids, we show here that solution processing and the covalent introduction of molecular recognition sites allows the spin crossover of iron(III) sal(2)trien complexes to be rationally tuned. A simple correlation between the number of molecular recognition sites and the spin crossover temperature enabled the fabrication of materials that are magnetically bistable at room temperature. The predictable behavior relies on combining function (spin switching) and structure (supramolecular assembly) through covalent interactions in a single molecular building block.

Synthesis and self-assembly of spin-labile and redox-active manganese(III) complexes.

New amphiphilic and spin-labile Mn(III) complexes based on dianionic N(4)O(2)-hexadentate sal(2)trien or sal(2)bapen ligands, which contain OC(6)H(13), OC(12)H(25), or OC(18)H(37) alkoxy substituents at different positions of the salicylidene unit were prepared (H(2)sal(2)trien = N,N'''-bis(salicylidene)-1,4,7,10-tetraazadecane, H(2)sal(2)bapen = N,N'''-bis(salicylidene)-1,5,8,12-tetraazadodecane). According to electrochemical measurements, these complexes undergo two (quasi)reversible redox processes. Temperature-dependent magnetic measurements revealed a high-spin configuration for all sal(2)trien complexes (S = 2) and gradual spin crossover for sal(2)bapen complexes from high to low spin (S = 1). The chain length strongly influences the spin crossover, as C(18)-functionalization stabilizes the low spin state at much higher temperatures than shorter alkyl chains. Moreover, long alkyl chains allow for spontaneous self-assembly of the molecules, which was investigated in single crystals and in Langmuir-films at the air-water interface. Long alkyl chains (C(12) or C(18)) as well as a mutual syn-orientation of these molecular recognition sites were required for the Langmuir monolayers to be stable.

Room-temperature spin crossover and Langmuir-Blodgett film formation of an iron(II) triazole complex featuring a long alkyl chain substituent: the tail that wags the dog.

[Fe(II)(C(16)dpt)(2)(NCS)(2)].(2/3)H(2)O displays temperature-mediated spin crossover (SCO) with T((1/2)) = 290 K and the long alkyl chain substituent on the dipyridyltriazole ligand facilitates the formation of a stable Langmuir-Blodgett film at an air-water interface.

Organization of spin- and redox-labile metal centers into Langmuir and Langmuir-Blodgett films.

New sal2(trien) ligands that contain alkoxy substituents of various length in meta position of the phenolate entities were coordinated to electronically and magnetically active iron(III) and cobalt(III) centers. The electrochemical and spectroscopic properties of these amphiphilic complexes are virtually unaffected upon alteration of the alkoxy substituents, thus providing a system in which the physical behavior and the metal-centered chemical activity can be tailored independently. The amphiphilic character has been exploited for preparing Langmuir monolayers at the air-water interface and for constructing Langmuir-Blodgett films, hence allowing for hierarchical assembling of electronically and magnetically active systems. While Langmuir films were stable, transfer onto solid supports was limited, which restricted the magnetic analysis of the Langmuir-Blodgett assemblies.

Towards Langmuir-Blodgett films of magnetically interesting materials: solution equilibria in amphiphilic iron(II) complexes of a triazole-containing ligand.

As a first step towards amphiphilic spin crossover (SCO) systems where the hydrophobic part of the system is introduced by a non-coordinating anion (i.e. where no modification of the ligands to introduce hydrophobic substituents is required), [Fe(II)(OH(2))(2)(C(16)SO(3))(2)] and [Co(II)(OH(2))(2)(C(16)SO(3))(2)] have been prepared and reacted with the triazole-containing ligands adpt and pldpt (C(16)SO(3) = hexadecanesulfonate anion, adpt = 4-amino-3,5-bis(2-pyridyl)-1,2,4-triazole, pldpt = 4-pyrrolyl-3,5-bis(2-pyridyl)-1,2,4-triazole). In the solid state, two HS complexes of the form [Fe(II)(Rdpt)(2)(C(16)SO(3))(2)] and two of the form [Co(II)(Rdpt)(2)(CH(3)OH)(2)](C(16)SO(3))(2) are obtained, even when a six-fold excess of ligand is used (Rdpt = adpt or pldpt). In solution, the cobalt complexes remain in this form as evidenced by colour, Visible/NIR and IR spectroscopy. For the iron complexes, there is an equilibrium in solution between the neutral high-spin form of the complex [Fe(II)(Rdpt)(2)(C(16)SO(3))(2)] and the dicationic low-spin tris form [Fe(II)(Rdpt)(3)](C(16)SO(3))(2). Polar solvents favour the dicationic form, while less polar solvents favour the neutral form (as evidenced by solution colour and solution IR spectroscopy). Visible/NIR spectroscopy and Evans' method NMR spectroscopy show the equilibrium can be shifted towards the [Fe(II)(Rdpt)(3)](C(16)SO(3))(2) form by adding additional ligand to the solution. The X-ray crystal structures of [Fe(II)(adpt)(2)(C(16)SO(3))(2)] and [Co(II)(adpt)(2)(CH(3)OH)(2)](C(16)SO(3))(2).1.33CH(3)OH are presented. [Fe(II)(adpt)(2)(C(16)SO(3))(2)] has a 2D bilayer structure with alternating layers of polar Fe(adpt)(2) centres, and hydrophobic alkyl chains. The complex cations in [Co(II)(adpt)(2)(CH(3)OH)(2)](C(16)SO(3))(2).1.33CH(3)OH form 1-D columns in the solid state. The capacity of the amphiphilic complexes [Fe(II)(pldpt)(2)(C(16)SO(3))(2)] and [Fe(II)(adpt)(2)(C(16)SO(3))(2)] to self-assemble has been probed at the air-water interface using Langmuir techniques. The pertinent pressure-area isotherms reveal only a low tendency of the complexes to form films.

Improved cooperativity of spin-labile iron(III) centers by self-assembly in solution.

Supramolecular principles have been applied for improving the spin crossover activity of metal centers due to cooperative effects in solution. Thus, incorporation of alkyloxy tails at the phenyl group of Fe(sal2trien) 2a provides amphiphilic complexes Fe(sal-OR2trien) 2b-d (b, R = C6H13; c, R = C8H17; d, R = C18H37) comprising an apolar group for supramolecular organization and a polar headgroup with potential spin crossover activity due to the presence of a spin-labile iron(III) center. Self-assembly of these complexes in solution resulted in the formation of microsize and submicrosize particles when the alkyl chain was long enough (2d) but not with shorter chains (2a-c). Solutions of 2d showed enhanced spin crossover activity as compared to complexes 2a-c, both in terms of transition temperature and steepness of the transition. This observation has been correlated to an improved cooperativity of the metal centers in 2d due to self-assembly, thus facilitating a tandem spin transition.