A comparative analysis of the temperature response of leaf elongation in Bromus stamineus and Lolium perenne plants in the field: intrinsic and size-mediated effects

Abstract

Background and aims: Growth of grass species in temperate-humid regions is restricted by low temperatures. This study analyses the origin (intrinsic or size-mediated) and mechanisms (activity of individual meristems vs. number of active meristems) of differences between Bromus stamineus and Lolium perenne in the response of leaf elongation to moderately low temperatures.

Methods: Field experiments were conducted at Balcarce, Argentina over 2 years (2003 and 2004) using four cultivars, two of B. stamineus and two of L. perenne. Leaf elongation rate (LER) per tiller and of each growing leaf, number of growing leaves and total leaf length per tiller were measured on 15-20 tillers per cultivar, for 12 (2003) or 10 weeks (2004) during autumn and winter.

Key results: LER was faster in B. stamineus than in L. perenne. In part, this was related to size-mediated effects, as total leaf length per tiller correlated with LER and B. stamineus tillers were 71% larger than L. perenne tillers. However, accounting for size effects revealed intrinsic differences between species in their temperature response. These were based on the number of leaf meristems simultaneously active and not on the (maximum) rate at which individual leaves elongated. Species differences were greater at higher temperatures, being barely notable below 5 degrees C (air temperature).

Conclusions: Bromus stamineus can sustain a higher LER per tiller than L. perenne at air temperatures > 6 degrees C. In the field, this effect would be compounded with time as higher elongation rates lead to greater tiller sizes.

Fig. 1.

Daily mean (solid line), minimum and maximum air temperatures (dotted line) and average temperature (circles) of each measurement period, during the 2003 (A) and 2004 (B) trials. Bars indicate the duration of each measurement period.

Fig. 2.

Leaf elongation rate (A, C, LER_T) and number of growing leaves (B, D, N_G) of cultivars of L. perenne (open circles, ‘Horizon’; open triangles, ‘Experimental’; solid line, cohort 1; dashed line, cohort 2) and B. stamineus (filled circles, ‘Zamba’; filled triangles, ‘Gato’) during the 2003 (A, B) and 2004 (C, D) trials. Bars indicate ± s.e. (n = 15–20). In (C), bold lines indicate values predicted for 2004 from a model based on 2003 data for B. stamineus (solid line) and L. perenne (dashed line).

Fig. 3.

Relationships between total leaf length per tiller (LL) and leaf elongation rate per tiller (LER_T) for two consecutive time periods with contrasting mean temperature (A, 6–9 June, 6·9 °C; B, 10–18 June, 10·4 °C) in cultivars of L. perenne (open circles, ‘Horizon’; open triangles, ‘Experimental’) and B. stamineus (filled circles, ‘Zamba’; filled triangles, ‘Gato’). Each data point is from an individual tiller. Lines are linear regressions for B. stamineus (solid line) and L. perenne data (dotted line).

Fig. 4.

Relationships between mean air temperature of each measurement period and the slope (A) and intercept (B) of the regression of leaf elongation rate per tiller (LER_T) against total leaf length per tiller (LL) in L. perenne (open circles, cohort 1; open triangles, cohort 2) and B. stamineus (filled circles). Bars indicate ± s.e. (n = 17–40). Lines are linear regressions for (A) B. stamineus (solid line) and L. perenne data (dotted line), and (B) all data.

Fig. 5.

The surface response of LER_T to tiller size (LL) and temperature for B. stamineus (grey) and L. perenne (black). The model was derived by combining the responses to temperature of the parameters of LL vs. LER_T relationships (intercept = A₁ + B₁ × temperature; slope = A₂ + B₂ × temperature) into one model: LER_T = A₁ + B₁ × temperature + A₂ × LL + B₂ × temperature × LL, where are A₁ and B₁ are equal to –3·7 and 0·64, respectively, in both species, and A₂ and B₂ are equal to –0·013 and 0·0037, respectively, for B. stamineus, and equal to –0·0056 and 0·0019, respectively, for L. perenne.

Fig. 6.

Relationships between total leaf length per tiller (LL) and maximal leaf elongation rate of individual leaves (LER_max) for two consecutive time periods with different mean temperatures (A, 6–9 June, 6·9 °C; B, 10–18 June, 10·4 °C) for cultivars of L. perenne (open circles, ‘Horizon’; open triangles, ‘Experimental’) and B. stamineus (filled circles, ‘Zamba’; filled triangles, ‘Gato’). Each point represents data for an individual tiller. Lines are linear regression for B. stamineus (solid line) and L. perenne data (dotted line).