Shoot Growth and Mineral Composition of Leaves and Fruits of Apple as Affected by Relative Air Humidity

Shoot growth and water consumption of potted Golden Delicious trees were studied under a controlled environment with respect to two lewels of air humidity, soil moisture content, and the availability of nitrogen. In the high-N treatment, high air humidity and high soil moisture content promoted growth; at the low-N level, growth did not respond to the treatments. Water consumption was enhanced at low air humidity but was not afiected by the moisture centent of the soil. In potted fruit&earing Cox's Orange Pippin trees exposed to two levels of air humidity, low humidity reduced shoot growth and, but to a much lower degree, fruit growth. It increased rhe spur-leaf levels of N, Mg, and, for part of the experimental period, K and Ca, but affected hardly the mineral level in fruits. It is concluded that the amount of the minerals reaching the fruit is determined by the relative im-portance of the xylem influx during the first few weeks after fruit set and the phloem influx occurring throughout. It is suggested that the xylem supply of the various minerals does not differ greatly; it is probably the main way for the influx of Ca, but for N, K, Mg, and P the phloem influx is com-pletely dominating.