Mechanisms of adaptation of small grains to soil acidity

Abstract

Acid soils limit crop production on 30-40% of the world's arable land and up to 70% of the world's potentially arable land. Over 60% of the total arable lands in Serbia are acid soils. Soil acidity is determined by hydrogen (H+) in soil solution and it is influenced by edaphic, climatic, and biological factors. Major constraints for plant growth on acid mineral soils are toxic concentrations of mineral elements like Al of H+ and/or low mineral nutrient availability due to low solubility (e.g. P and Mo) or low reserves and impaired uptake (e.g. Mg2+) at high H+ concentrations. Aluminum (Al) toxicity is primary factor limiting crop production on acid soils. This review examines our current understanding of mechanisms of Al-toxicity, as well as the physiological and genetic basis for Al-toxicity and tolerance. Inhibition of root growth by Al leads to more shallow root systems, which may affect the capacity for mineral nutrient acquisition and increase the risk of drought stress. Of the two principal strategies (tolerance and avoidance) of plants for adaptation to adverse soil conditions, the strategy of avoidance is more common for adaptation to acid mineral soils. At the same, the short view of the most important genetics tolerance mechanisms, developed and determined in some small grains genotypes, is showed as well.

Kisela zemljišta ograničavaju biljnu proizvodnju na 30-40% ukupnih, kao i do 70% potencijalno obradivih svetskih površina. Kisela reakcija ovih zemljišta i nizak sadržaj najvažnijih biljnih hraniva, pre svega R i Sa su ograničavajući faktori postizanja visokih i stabilnih prinosa gajenih biljaka. Pored kisele reakcije, ova zemljišta karakteriše veoma često i povećan sadržaj toksičnih oblika Al, Fe i Mn, kao i nedostatak ili smanjena pristupačnost P, Ca, Mg i nekih mikroelemenata, posebno Mo, Zn i V. Toksičnost Al se smatra najvažnijim faktorom koji ograničava rast biljaka na kiselim zemljištima. Mehanizmi adaptacije strnih žita na kisela zemljišta mogu se podeliti na: spoljašnje, unutrašnje (fiziološke) i genetičke. Dejstvo spoljašnjih mehanizama tolerantnosti zasniva se na imobilizaciji Al u ćelijskom zidu, isticanju Al kroz plazma membranu, uspostavljanju pH barijere u rizosferi i lučenju organskih kiselina, fosfata, helata i drugih liganada korenom u spoljašnju sredinu. Unutrašnji mehanizmi tolerantnosti zasnivaju se na kompleksiranju Al sa proteinima, organskim kiselinama i enzimima, kao i helatiziranju u citoplazmi. Strna žita ispoljavaju različitu tolerantnost prema kiselosti zemljišta i povećanom sadržaju Al u zemljišnom rastvoru. Najosetljiviji je ječam, zatim pšenica, dok veću tolerantnost ispoljavaju ovas, tritikale i raž.