RESUMO
Land plants have an ancient and intimate relationship with microorganisms, which influences the composition of natural ecosystems and the performance of crops. Plants shape the microbiome around their roots by releasing organic nutrients into the soil. Hydroponic horticulture aims to protect crops from damaging soil-borne pathogens by replacing soil with an artificial growing medium, such as rockwool, an inert material made from molten rock spun into fibres. Microorganisms are generally considered a problem to be managed, to keep the glasshouse clean, but the hydroponic root microbiome assembles soon after planting and flourishes with the crop. Hence, microbe-plant interactions play out in an artificial environment that is quite unlike the soil in which they evolved. Plants in a near-ideal environment have little dependency on microbial partners, but our growing appreciation of the role of microbial communities is revealing opportunities to advance practices, especially in agriculture and human health. Hydroponic systems are especially well-suited to active management of the root microbiome because they allow complete control over the root zone environment; however, they receive much less attention than other host-microbiome interactions. Novel techniques for hydroponic horticulture can be identified by extending our understanding of the microbial ecology of this unique environment.
RESUMO
BACKGROUND: Low rainfall is a major limitation to expanding the dairy industry in semi-arid environments in East Africa. In such dry areas, plants need to keep their tissues hydrated and stomata open for carbon exchange and to grow. On this basis, we assessed the productivity of 10 lines of Napier grass (Pennisetum purpureum Schum.), which formed three yield clusters: low yielding (LYC), moderate yielding (MYC), and high yielding (HYC), in a wet highland (Muguga) and semi-arid lowland (Katumani) of Kenya. Stomatal conductance (gs ), leaf water potential (LWP) and relative water content (RWC) were monitored, and water use simulated, over four growth cycles in 2012. These were used with measurements of leaf area index (LAI) and plant dry weight to explore the possible use of these physiological parameters for assessing productivity potential of Napier grass accessions. RESULTS: The plants were less stressed at Muguga, where gs was 700-1000 mmol m-2 s-1 , LWP -0.4 to -0.9 MPa and RWC was 82-95%; these values at Katumani were 450-750 mmol m-2 s-1 , -0.7 to -1.4 MPa and 74-93%, respectively. Total water use at Katumani was of the order HYC ≈ MYC (390 mm) > LYC (370 mm), and water use efficiency (WUE, kg ha-1 mm-1 ) followed the same order HYC (34.3) > MYC (32.6) > LYC (24.9); whereas at Muguga water use averaged 710 mm for HYC and MYC, greater than 676 mm for LYC, and WUE (kg ha-1 mm-1 ) averaged 29.2 for HYC and MYC, and 19.4 for LYC. CONCLUSIONS: The three water stress indices were poor, whereas vigorous early canopy development (determined as LAI) was a more reliable predictor of productivity potential of Napier grasses. In these dry environments, therefore, early rapid canopy development can be an effective indicator of yield potential and a credible selection criterion. © 2016 Society of Chemical Industry.