Protected cropping in warm climates : a review of humidity control and cooling methods

The projected increase of the world’s population, coupled with the shrinking area of arable land required to meet future food demands, is building pressure on Earth’s finite agricultural resources. As an alternative to conventional farming methods, crops can be grown in protected environments, such as traditional greenhouses or the more modern plant factories. These are usually more productive and use resources more efficiently than conventional farming and are now receiving much attention—especially in urban and peri-urban areas. Traditionally, protected cropping has been predominantly practised in temperate climates, but interest is rapidly rising in hot, arid areas and humid, tropical regions. However, maintaining suitable climatic conditions inside protected cropping structures in warm climates—where warm is defined as equivalent to climatic conditions that require cooling—is challenging and requires different approaches from those used in temperate conditions. In this paper, we review the benefits of protected cropping in warm climates, as well as the technologies available for maintaining a controlled growing environment in these regions. In addition to providing a summary of active cooling methods, this study summarises photovoltaic (PV)-based shading methods used for passive cooling of greenhouses. Additionally, we also summarise the current humidity-control techniques used in the protected cropping industry and identify future research opportunities in this area. The review includes a list of optimum growing conditions for a range of crop species suited to protected cropping in warm climates

Leaf mesophyll K+ and Cl- fluxes and reactive oxygen species production predict rice salt tolerance at reproductive stage in greenhouse and field conditions

Extensive research on salinity tolerance in rice has been mostly carried out at the seedling stage in single experimental trials. Here, we aimed to understand the roles of ion transport and oxidative responses of leaf mesophyll in salinity tolerance of rice (Oryza sativa L.) at its reproductive stage using comparative investigations in both greenhouse and field trials. Two experimental trials were conducted to assess the salt tolerance of three rice cultivars at their reproductive stage in greenhouse and field. We employed agronomic, physiological, electrophysiological, molecular and cell imaging techniques to compare physiological response of control and salinity stressed rice plants. Salinity had the most severe effect to Koshihikari, followed by Doongara and Reiziq. We found that K+ retention and low recovery Cl− efflux in mesophyll cells confers salt tolerance in rice. Moderate to strong correlations were found between growth parameters and net K+ flux (r2=0.45–0.60), and net Cl− flux (r2=0.47–0.72). Also, dynamic ROS production and regulation of the NADPH oxidase gene, OsRBOHD, in mesophyll cells is crucial for salt tolerance of rice at the reproductive stage. OsRBOHD expression was significantly correlated to recovery ion fluxes (r2=0.45–0.64). This study brings together, for the first time, potential links between cellular ionic stress and oxidative stress components of salinity tolerance in rice at the reproductive stage in both greenhouse and field conditions. Our study will provide guidance to examine crop salinity tolerance at reproductive stages in controlled environments and natural climatic conditions in the future