A root-shoot interaction hypothesis for high productivity of field crops

Abstract

According to the results of high-yielding crop trials, a root-shoot interaction model is proposed to explain the high productivity of high-yielding crops. In our experiments the highest biological yields obtained varied considerably between different crops (1.45 kg m−2 dry matter for rice, 2.39 for winter wheat. 2.57 for maize, 2.13 for potato, 2.17 for beet, and 2.93 for sunflower). These differences could not be explained on the basis ot plant type. Since the photosynthetic rate (dry matter increase) and root activity (nutrient absorption) remained constant during maturation in the high-yielding varieties, it is suggested that in these varieties, root and shoot mutually interact so that a high photosynthetic rate secures high root activity by supplying a sufficient amount of photosynthates to the roots. High root activity then secures a high photosynthetic rate by supplying a sufficient amount of nutrients to shoots.To estimate the root activity, the specific absorption rate of nitrogen (SARN. mgN day−1 g−1root dry weight) is a useful criterion because in high-yielding crops, SARN remains high during the early maturation stage, while root dry weight does not relate to nitrogen absorption or dry matter production especially at the maturation stage.To maintain the high SARN during the maturation stage, the systems of photosynthates distribution into roots are important. Cereal and legume crops form strong sinks in aerial parts, and root-shoot interaction becomes weaker as growth progresses. Therefore, in legume crops and especially in cereal crops, plant type or canopy structure plays an important role in the maintenance of high root activity because the main supply of photosynthates comes from lower leaves to roots. Root crops benefit more than cereal and legume crops from the carbohydrate supply to roots because thev have roots directly attached to sink organs.