Growth response and radiation use efficiency in tomato exposed to short-term and long-term salinized soils

Farmlands are increasingly exposed to degradation phenomena associated to climate change and agri-cultural practices, including irrigation. It is estimated that about 20% of the world’s irrigated land issalt affected. In this paper we aimed at evaluating the effect of seasonal and multiannual soil salin-ization on growth, yield, and radiation use efficiency of tomato in open field. Two field experimentswere carried out at the Experimental Station of the University of Naples Federico II (latitude 40◦31Nlongitude 14◦58E) (Italy) on tomato during 2004 and 2005 to study the effect of five levels of watersalinity: NSC (EC = 0.5 dS m−1), SW1 (EC = 2.3 dS m−1), SW2 (EC = 4.4 dS m−1), SW3 (EC = 8.5 dS m−1) andSW4 (EC = 15.7 dS m−1) in a soil exposed to one-season salinization (ST = short-term) and an adjacent soilexposed to >20 years salinization (LT = long-term). Plant growth, yield and fruit quality (pH, EC, totalsoluble solids and the concentration of reducing sugars and of titratable acids), and plant water relationswere measured and radiation use efficiency (RUE) was calculated. Increasing water salinity negativelyaffected the leaf area index (LAI), radiation use efficiency (RUE) and above-ground dry weight (DW) accu-mulation resulting in lower total and marketable yield. Maximum total and marketable yield obtainedwith the NSC treatment were respectively 117.9 and 111.0 Mg ha−1in 2004 and 113.1 and 107.9 Mg ha−1in 2005. Although the smaller leaf area of salinized plants was largely responsible for reduced RUE, wefound approximately 50% of this reduction to be accounted for by processes other than changed croparchitecture. These may include an increased stomatal resistance, increased mesophyll resistance andother impaired metabolic functions that may occur at high salinity. Remarkably, we found that LT salin-ized plants had a slightly better efficiency of use of intercepted radiation (RUEIR) at a given EC of soilextract than ST salinized plants indicating that LT salinization, and consequent permanent modificationsof the soil physical properties, may trigger additional physiological mechanisms of adaptation comparedto ST salinized plants. These differences are relevant in light of the evolution of salinized areas, also inresponse to climate change.