## 4 The Impacts of Microalgae/Cyanobacteria and Their Extracts on Crops' Production
### Direct Growth Stimulation  
Apart from their beneficial effects at the soil level and on plants' protection, the use of microalgae and cyanobacteria (and/or their extracts) can directly stimulate plants' growth and development, through an improvement in germination rates and plant characteristics (e.g., increased shoot and root length, increased leaf area and higher nutritional contents). These improvements are achieved as a result of the activity of microalgal/cyanobacterial metabolites, which are able to trigger several metabolic responses, such as respiration, photosynthesis, nucleic acid synthesis, chlorophyll production and ions uptake [9]. Table 4 presents some examples where microalgae and cyanobacteria (biomass and/or extracts) have been successfully applied in direct growth stimulation of higher plants. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Algae/AlgaI Extracts** & **Target Crop** & **Observed Improvements** & **Ref.** \\ \hline _Anabauca_ strains (_Anabauca spiodics_, _Anabauca_ _catalas_ and _Anabauca_ _catalas_ & & Increase in germination rate \\  & & & Increase in plant height and shoots length \\  & & & Increase in fresh and dry weights of leaf, stem and root \\  & & & Improvement of soil properties (increase in soil moisture and porosity) \\ \hline _Laurencia obtasa_, _Cornilana elongata_ and _jania rubens_ & & & Increase in plant length and fresh and dry weight \\  & & & Increase in the number of leaves \\  & & & Increase in the number of leaves \\  & & & Improvement of plant nutritional value (increase in potassium, phosphorus and \\  & & & nitrogen contents) \\ \hline \multirow{2}{*}{Exopolysaccharide} & \multirow{2}{*}{Weheat} & \multirow{2}{*}{Increase in germination rate and seedling growth} \\  & & & Increase in root and colcoleties height \\  & & & Increase in tolerance to salt stress \\ \hline \multirow{2}{*}{Aqueous extracts from _Gracilaria corticata_ and _Entromorphin flexusa_} & \multirow{2}{*}{Maze and sunflower} & \multirow{2}{*}{Increase in shoot and root length and dry weight} \\  & & & Improvement of plant nutritional value (increase in photosynthetic pigments, \\  & & & carbohydrate, proteins and nutrients contents) \\ \hline \multirow{4}{*}{Liquid extracts from _Socnosospermum_ _marginatum_} & \multirow{2}{*}{Brinjal} & \multirow{2}{*}{Increase in host and root length} \\  & & & Increase in fresh and dry weight of leaves \\  & & & Increase in leaf area \\  & & & Improvement of leaves nutritional value (increase in moisture, photosynthetic \\  & & pigments, protein, amino acids, reducing sugars and ascorbic acid contents) \\ \hline \multirow{2}{*}{Total polysaccharides extract from _Spirulina platensis_} & \multirow{2}{*}{Tomato and pepper} & \multirow{2}{*}{Increase in plants’ size} \\  & & & Increase in roots’ weight \\  & & & Increase in size and number of nodes \\ \hline \multirow{2}{*}{_Ulva lactuca_ and _Jania rubens_} & \multirow{2}{*}{Spinach} & \multirow{2}{*}{Increase in plant yield and height} \\  & & & Improvement of plant nutritional value (increase in chlorophyll and nitrogen contents) \\ \hline _Arthrospira platensis_ & \multirow{2}{*}{Letuce} & \multirow{2}{*}{Increase in seedling growth} \\  & & & Increase in spermine content in leaves \\ \hline \multirow{2}{*}{_Chiodella vulgaris_ and _Spirulina platensis_} & \multirow{2}{*}{Maze} & \multirow{2}{*}{Increase in germination rate and plant yield} \\  & & & Increase in fresh and dry weights of shoot, root and whole plant \\  & & & Increase in shoot length and in the number of leaves \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Impacts of microalgae and cyanobacteria (and their metabolites) on direct growth stimulation of plants. Commonly involved metabolites include plant growth promoting factors, such as phytohormones, but also some amino acids, vitamins (e.g., vitamin B12 and biotin), polysaccharides and polypeptides [97].