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

- Salinization is a major constraint to crop production and is increasingly expanding in agricultural areas of the world.
- Seasonal (short-term) and multiannual (long-term) effects of salinization may be remarkably different.
- The response of radiation use efficiency (RUE) to salinization has not been sufficiently understood.
- The effects resulting from reduced light interception from other effects are addressed.

Farmlands are increasingly exposed to degradation phenomena associated to climate change and agricultural practices, including irrigation. It is estimated that about 20% of the world's irrigated land is salt affected. In this paper we aimed at evaluating the effect of seasonal and multiannual soil salinization on growth, yield, and radiation use efficiency of tomato in open field. Two field experiments were carried out at the Experimental Station of the University of Naples Federico II (latitude 40°31′ N longitude 14°58′ E) (Italy) on tomato during 2004 and 2005 to study the effect of five levels of water salinity: 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) and SW4 (EC = 15.7 dS m−1) in a soil exposed to one-season salinization (ST = short-term) and an adjacent soil exposed to >20 years salinization (LT = long-term). Plant growth, yield and fruit quality (pH, EC, total soluble solids and the concentration of reducing sugars and of titratable acids), and plant water relations were measured and radiation use efficiency (RUE) was calculated. Increasing water salinity negatively affected the leaf area index (LAI), radiation use efficiency (RUE) and above-ground dry weight (DW) accumulation resulting in lower total and marketable yield. Maximum total and marketable yield obtained with the NSC treatment were respectively 117.9 and 111.0 Mg ha−1 in 2004 and 113.1 and 107.9 Mg ha−1 in 2005. Although the smaller leaf area of salinized plants was largely responsible for reduced RUE, we found approximately 50% of this reduction to be accounted for by processes other than changed crop architecture. These may include an increased stomatal resistance, increased mesophyll resistance and other impaired metabolic functions that may occur at high salinity. Remarkably, we found that LT salinized plants had a slightly better efficiency of use of intercepted radiation (RUEIR) at a given EC of soil extract than ST salinized plants indicating that LT salinization, and consequent permanent modifications of the soil physical properties, may trigger additional physiological mechanisms of adaptation compared to ST salinized plants. These differences are relevant in light of the evolution of salinized areas, also in response to climate change.