Comparison of early development of three grasses: Lolium perenne, Agrostis stolonifera and Poa pratensis

Abstract

Background and aims: To improve the management of grass communities, early plant development was compared in three species with contrasting growth forms, a caespitose (Lolium perenne), a rhizomatous (Poa pratensis) and a caespitose-stoloniferous species (Agrostis stolonifera).

Methods: Isolated seedlings were grown in a glasshouse without trophic constraints for 37 d (761 degrees Cd). The appearance of leaves and their location on tillers were recorded. Leaf appearance rate (LAR) on the tillers and site-filling were calculated. Tillering was modelled based on the assumption that tiller number increases with the number of leaves produced on the seedling main stem. Above- and below-ground parts were harvested to compare biomass.

Key results: Lolium perenne and A. stolonifera expressed similar bunch-type developments. However, root biomass was approx. 30 % lower in A. stolonifera than in L. perenne. Poa pratensis was rhizomatous. Nevertheless, the ratio of above-ground : below-ground biomass of P. pratensis was similar to that of L. perenne. LAR was approximately equal to 0.30 leaf d(-1) in L. perenne, and on the main stem and first primary tillers of A. stolonifera. LAR on the other tillers of A. stolonifera was 30 % higher than on L. perenne. For P. pratensis, LAR was 30 % lower than on L. perenne, but the interval between the appearance of two successive shoots from rhizomes was 30 % higher than the interval between two successive leaf stages on the main stem. Above-ground parts of P. pratensis first grew slower than in the other species to the benefit of the rhizomes, whose development enhanced tiller production.

Conclusions: Lolium perenne had the fastest tiller production at the earliest stages of seedling development. Agrostis stolonifera and P. pratensis compensated almost completely for the delay due to higher LAR on tillers or ramets compared with L. perenne. This study provides a basis for modelling plant development.

Fig. 1.

Different growth strategies in grasses: (A) bunch-type, (B) rhizomatous-type, and (C) stoloniferous-type. MS indicates seedling main stem, T, seedling ramifications; S, orthotropic shoots on stolon (St); R, shoots on rhizomes (Rh). Coleoptile leaf on the MS (closed circles) and prophylls (small open circles) are called leaf 0 on tillers. True leaves are large open circles. Code used for tillers: e.g. T₃ is the primary tiller arising at the axil of the 3rd true leaf of MS, T₃₁ is the secondary tiller arising at the axil of the 1st true leaf on T₃.

Fig. 2.

Evolution of the leaf number (N) as a function of thermal time (T_th) in L. perenne (open triangles), A. stolonifera (open squares), P. pratensis (open circles) and R of P. pratensis (closed circles). (A) Whole plants of L. perenne and A. stolonifera, (B) whole plants of P. pratensis; (C) only the MS for the three species. Data are from 12 plants grown in a greenhouse for 37 DAT. Equations: (A) N_{L. perenne} = 3·6045e^0·0048Tth (R² = 0·94) and N_{A. stolonifera} = 2·4659e^0·0048Tth (R² = 0·89); (B) N_{P. pratensis} = 3·3026e^0·0032Tth (R² = 0·88), N_{R. P. pratensis} = 0·0123T_th – 1·3295 (R² = 0·66); (C) N_{MS L. perenne} = 0·0106T_th + 4·0997 (R² = 0·92), N_{MS A. stolonifera} = 0·011T_th + 3·2443 (R² = 0·94), N_{MS P. pratensis} = 0·0086T_th + 3·5643 (R² = 0·93).

Fig. 3.

Increase in the number of tillers and phytomers in relation to thermal time. Evolution of the number of MS and new shoots on rhizomes (closed circles), primary (open circles), secondary (filled squares) and tertiary tillers (open triangles) in (A) L. perenne, (B) A. stolonifera and (C) P. pratensis. Numbers of phytomers on primary (open circles), secondary (filled squares) and tertiary tillers (open triangles) in (D) L. perenne, (E) A. stolonifera and (F) P. pratensis. Data are means and standard errors from 12 plants grown in a greenhouse for 37 DAT.

Fig. 4.

Biomass of (A) above-ground parts, (B) below-ground parts and (C) ratio of above-ground : below-ground parts (Ab./(Bel.) in L. perenne (open columns), A. stolonifera (grey columns) and P. pratensis (black columns), sampled after 37 DAT. MS indicates the seedling main stem, T is used for seedling ramifications (primary, T I- tillers; secondary, -T II- tillers; tertiary, -T III-tillers), and R is used for shoots from rhizomes (Rh). Below-ground parts include roots and rhizomes. Means and standard error are given for six plants.