From the wild to the field: effect of foliar or soil application of inorganic or semi-organic fertilizers on various parameters of four local endemic plant species of Crete (Greece)

Domestication of wild plant species of interest coupled with introduction of pilot cultivation practices and appropriate fertilization schemes could be an efficient alternative for addressing sustainable exploitation needs of threatened and/or declining wild phytogenetic resources. In this field study focusing on four threatened wild-growing plants ( Carlina diae , Origanum dictamnus , Origanum microphyllum , and Sideritis syriaca subsp. syriaca ) confined to Crete (local endemics), the effects of three types of fertilization (inorganic, plain semi-organic or co-applied with commercial biostimulants based on edible raw plant materials) by two methods (foliar/soil application) on plants’ growth were investigated. Specifically, plant parameters such as aboveground biomass yield, content and uptake of nutrients by plants as well as arbuscular mycorrhizal fungi root colonization were evaluated. Results revealed a distinction in plants’ multi-elemental stoichiometry, except in the case of Origanum species, in which the variance of their ionomics showed a significant overlap. The elements most closely related to yield were K and Zn, while Pearson tests showed various correlations between studied essential nutrients. Among them, the positive correlations between B and Ca, and Mg (with r value up to 0.9 at p ≤ 0.001, in all studied species except O. dictamnus ); the negative correlations between K and Mg (in O. dictamnus and S. syriaca subsp. Syriaca , r = − 0.5 at p ≤ 0.001); and the positive correlation patterns between Fe and Mn, or Cu and Zn, respectively (in all studied species) , were observed. Biostimulant application alone or in combination with semi-organic fertilizers increased the yield of C. diae (up to 161%) and of the two Origanum species studied (up to 70% and 68% for O. dictamnus and for O. microphyllum , respectively), while inorganic fertilization was beneficial for S. syriaca subsp. syriaca (up to 170% increase) and O. microphyllum (up to 79% increase). However, no solid conclusions could be derived in respect of the preference of the four species for any fertilizers' application method (foliar or by soil).