| ||||||||||||||||||||
Well-salted carrots
Salinization is a problem in irrigated land. However, it can also occur as a direct result of drought, e.g. in the south-eastern USA where decreased river flows in summer 2002 led to increases in tidal flows of sea water up river. Despite its importance in many regions of the world, we know very little about the effects of increased salinity on many crop species. This has led Gibberd and colleagues (CSIRO, Western Australia and CSIRO, Victoria; pp. 715-724) to investigate the responses to salt of carrot, a widely grown cash crop. They exposed plants to NaCl concentrations from 1 to 80 mM and monitored ion uptake, gas exchange and photosynthesis. At all concentrations, plants took up Cl- and transported it to the leaves. This uptake and transport was tightly regulated, and even an increase in NaCl concentration from 1 to 80 mM led to only a 1.5-fold increase in shoot Cl- concentration. In contrast, Na+ uptake and accumulation were more closely related to external NaCl concentrations, although there was clearly some ability to exclude Na+, the shoot concentration of which increased by about seven-fold in an 80-fold increase in NaCl concentration. Effects on gas exchange and photosynthesis were observed at external NaCl concentrations as low as 8 mM. At 80 mM NaCl, both were reduced very significantly. At the highest salt concentrations, there was evidence of impairment of both RuBP carboxylase and photosynthetic electron transport. However, effects on growth and yield were less dramatic, possibly indicating some ability to compensate for decreased photosynthesis. There was no decrease in yield at salt concentrations below 20 mM, but above this a 7 % reduction occurred for every 10 mM increase. The authors suggest that for NaCl, carrot is ‘in the upper range of the sensitive class’. Overall, the paper shows the importance of careful analysis in assessing the effects of salinity on crop growth.
Professor J. A. BryantUniversity of Exeter, UK
j.a.bryant{at}exeter.ac.uk
| ||||||||||||||||||||