The effects of severe mineral nutrient deficiencies on the demography of leaves

Abstract

Plants of flax (Linum usitatissimum) were grown in sand culture and provided with only deionized water or full nutrient solution or with nutrient solutions lacking nitrogen, phosphorus, potassium or calcium. The plants were exposed to these different nutritional régimes through­out their growth cycle, or the régimes were changed after 31 days of growth. The responses to the various treatments were measured by demographic methods, treating the foliage of a plant as a population of leaves. Leaves were allocated to cohorts as they unfolded so that leaf birth rates and death rates could be determined and survivorship could be related to age. The procedure allowed the process of senescence to be distinguished from ageing. The birth rate of leaves (as a measure of the activity of shoot apices) appeared to regulate the death rate of leaves on the same plant, presumably by determining in some way when minerals were withdrawn from older leaves. The linkage between birth and death rates was closest when potassium was deficient, and this is attributed to the high mobility of potassium in the plants. On calcium-deficient plants the older leaves had very long lives and low, eventually zero, leaf birth rates. Plants grown in deionized water produced very few leaves and leaf birth rate rapidly fell to zero but a few of the leaves had exceptionally long lives. The effects of mineral deficiencies on leaf demography are discussed in relation to known differences in the roles and mobilities of the various elements in plants and their different influences on leaf senescence. It is argued that the loss of nutrients from older leaves is a cause of, rather than a result of, leaf senescence.