Growth response, leaf gas exchange and fructans accumulation of Jerusalem artichoke (Helianthus tuberosus L.) as affected by different water regimes

Fructans can be used in the food industry and in several non-food industrial and medical applications. Several crops accumulate fructans as storage reserves, among these Jerusalem artichoke (JA) can be appreciated for its high fructans yield with low input techniques. Dry matter accumulation, leaf photosynthesis and fructans accumulation of JA were investigated under irrigated (W1) and rain-fed (W0) conditions over the 2 years 1999 and 2000. In both years, the time-course of the plant growth and biomass partitioning was significantly affected by water availability, especially during the period of the two first irrigations. The initially higher growth rate of W1 was explained by leaves and stems while tuber initiation was considerable faster in W0. Conversely, in the last part of the growing season the considerably faster tuber formation of W1 produced a higher tuber dry weight than W0. As expected by the higher dry matter yield of W1 the radiation use efficiency (RUE) was also affected by treatment with higher values in irrigated plots (2.9 g MJ−1 versus 2.2 g MJ−1). Conversely, if marketable product is considered instead of the total dry matter, RUE would be not statistically different between treatments. Leaf net photosynthesis (A) was weakly affected by treatment and strongly by leaf temperature (Tleaf) and stomatal conductance (gs). Tleaf over 33 °C seemed to cause non-stomatal limitations thus to decrease A more than gs did. Stem fructan yields (FYstem) did not vary between treatments despite the fructans content being generally significantly higher in W0. Otherwise, FYstem as well as the fructan chain length (DP) were significantly reduced by delaying the harvest from September to November. The highest tuber DP was slightly higher than that of the stems and it was reached 1800 GDD before the maximum tuber dry weight. Water restoration did not increase tuber DP, instead it delayed (700 GDD) the time taken to reach the maximum values. Assuming that fructans are extracted both from tubers and stems, the last but one harvest appeared more profitable than the last one. The irrigation slightly increased the fructan yield only in the first year when the meteorological conditions favoured a high aboveground development. In this year the yield was however satisfactory even in rain-fed conditions at least for the consistent water saving (318 L m−2). Moreover, the fructan chains were never affected by water regime. Thus irrigation seems to be not worthwhile for this area.