Photosynthesis and sink size: an explanation for the low productivity of grass swards in autumn.

Abstract

In glasshouse and field trials, axillary tillers of Italian ryegrass cv. Milamo were cut at weekly intervals or shaded and photosynthesis was measured in the youngest fully expanded leaf of main shoots; similar measurements were made on fertilized irrigated perennial ryegrass plants spaced at 5 plants/m2. Photosynthesis was stimulated to the high level characteristic of leaves from reproductive plants with reduced stomatal and internal diffusion resistances and lower soluble carbohydrate content and it was suggested that axillary tillers under stress acted as sinks for assimilates. It was concluded that the lack of sinks and poor light penetration into the area of leaf development were the main causes of poor production by vegetative grass crops in late summer and autumn. Various methods of improving DM production by increasing photosynthetic efficiency of individual leaves and creating sinks are discussed. (Abstract retrieved from CAB Abstracts by CABI’s permission)