Studies in the Growth of Young Plants of Pinus sylvestris L.: II. The Relation of Growth to Soil Moisture Tension

Plants of Pinus sylvestris in their first and third seasonsof growth were grown in containers under moisture regimes inwhich the maximum tensions were varied between 0.1 and about9 atm. Compared with plants growing in the o.1 atm. treatment,growth was significantly reduced in the first-year plants by0.3 atm. and in the third-year plants by a tension between 0.5and 1.5 atm. Further reductions were caused by the higher tensionsemployed. The plants appeared to be sensitive to differencesin soil moisture tension throughout the growing-season. Theeffects of soil moisture tension on growth were due mainly tovariations in net assimilation rate. It is pointed out thatthe growth of many plants is substantially reduced by soil moisturetensions of less than 1 atm. and possible interpretations ofthis are discussed.