The date palm tree rhizosphere is a niche for plant growth promoting bacteria in the oasis ecosystem.

Raoudha Ferjani,Hadda-Imene Ouzari,Maher Gtari,Abdellatif Boudabous,Hanene Cherif,Daniele Daffonchio,Ameur Cherif,Eleonora Rolli,Ramona Marasco

doi:10.1155/2015/153851

Abstract

In arid ecosystems environmental factors such as geoclimatic conditions and agricultural practices are of major importance in shaping the diversity and functionality of plant-associated bacterial communities. Assessing the influence of such factors is a key to understand (i) the driving forces determining the shape of root-associated bacterial communities and (ii) the plant growth promoting (PGP) services they provide. Desert oasis environment was chosen as model ecosystem where agriculture is possible by the microclimate determined by the date palm cultivation. The bacterial communities in the soil fractions associated with the root system of date palms cultivated in seven oases in Tunisia were assessed by culture-independent and dependent approaches. According to 16S rRNA gene PCR-DGGE fingerprinting, the shapes of the date palm rhizosphere bacterial communities correlate with geoclimatic features along a north-south aridity transect. Despite the fact that the date palm root bacterial community structure was strongly influenced by macroecological factors, the potential rhizosphere services reflected in the PGP traits of isolates screened in vitro were conserved among the different oases. Such services were exerted by the 83% of the screened isolates. The comparable numbers and types of PGP traits indicate their importance in maintaining the plant functional homeostasis despite the different environmental selection pressures.

Highlights

The southern regions of Tunisia are very arid and the date palm (Phoenix dactylifera L.) is a key plant determining in the oasis agroecosystem a microclimate that favours agriculture [1]
Since plants contribute to shape soil microbial diversity [12, 13], the aim of this work was to assess bacterial communities associated with the date palm rhizosphere soil, the root surrounding soil and the bulk soil fractions in seven Tunisian oases, in order to evaluate if along a north-south transect (i) the assemblage of bacterial communities in the palm root soil fractions was driven by the geoclimatic factors and (ii) the ecological services were preserved in the soil fractions of the root system
The diversity of bacterial communities associated with the date palm root system from each of the seven studied oasis was investigated through the analysis of the diversity of the 16S rRNA gene in the rhizosphere (R) and root surrounding soil (S) fractions

Summary

Introduction

The southern regions of Tunisia are very arid and the date palm (Phoenix dactylifera L.) is a key plant determining in the oasis agroecosystem a microclimate that favours agriculture [1]. The palms protection provides many ecosystem services, including ameliorating oasis temperature, changing floodwater dynamics and facilitating wildlife, and making agriculture possible under harsh environmental conditions [2]. In Tunisia more than four millions of date palm trees are spread onto 32 000 ha of oasis in the southern part of the country [3, 4]. Despite the oasis potential to tolerate several abiotic stresses typical of arid environment, the ongoing climate change is enhancing the environmental pressure on the date palm affecting growth and development, especially in the Middle East [5]

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