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An understanding of the mechanisms by which temperature influences the distribution of species and vegetation has been attempted by modelling population growth and establishing those stages of the plant life cycle which, when diminished by extremes of temperature, for example, may have the greatest impact on plant survival. This analysis suggests that the heat sum of the growing season, measured as day-degrees, controls the distribution of annual vegetation. For perennial vegetation both the heat sum of the growing season and the annual, absolute minimum temperature are critical. Climatic correlations and experimental analyses indicate that, in northern Europe, the northern latitudinal and upper altitudinal limits of lowland and southern vegetation are directly controlled by climate. In contrast, the southern and lower altitudinal limits of upland and northern vegetation are likely to be controlled by temperature-sensitive competition with southern or lowland species. Many of the temperature-sensitive processes of plant growth and development, such as the non-linearity of extension growth and variations in the threshold temperatures of processes, may increase the realized heat sum at a particular geographical location. However, in more northerly climates, photoperiodic control is crucial in avoiding precocious development in the highly variable climatic conditions of early spring.

The maximum photosynthetic carboxylation rate (Vcmax ) is an influential plant trait that has multiple scaling hypotheses, which is a source of uncertainty in predictive understanding of global gross primary production (GPP). Four trait-scaling hypotheses (plant functional type, nutrient limitation, environmental filtering, and plant plasticity) with nine specific implementations were used to predict global Vcmax distributions and their impact on global GPP in the Sheffield Dynamic Global Vegetation Model (SDGVM). Global GPP varied from 108.1 to 128.2 PgC yr-1 , 65% of the range of a recent model intercomparison of global GPP. The variation in GPP propagated through to a 27% coefficient of variation in net biome productivity (NBP). All hypotheses produced global GPP that was highly correlated (r = 0.85-0.91) with three proxies of global GPP. Plant functional type-based nutrient limitation, underpinned by a core SDGVM hypothesis that plant nitrogen (N) status is inversely related to increasing costs of N acquisition with increasing soil carbon, adequately reproduced global GPP distributions. Further improvement could be achieved with accurate representation of water sensitivity and agriculture in SDGVM. Mismatch between environmental filtering (the most data-driven hypothesis) and GPP suggested that greater effort is needed understand Vcmax variation in the field, particularly in northern latitudes.

The response of plant respiration ( R) to temperature is an important component of the biosphere's response to climate change. At present, most global models assume that R increases exponentially with temperature and does not thermally acclimate. Although we now know that acclimation does occur, quantitative incorporation of acclimation into models has been lacking. Using a dataset for 19 species grown at four temperatures (7, 14, 21, and 28 °C), we have assessed whether sustained differences in growth temperature systematically alter the slope and/or intercepts of the generalized log–log plots of leaf R vs. leaf mass per unit leaf area (LMA) and vs. leaf nitrogen (N) concentration. The extent to which variations in growth temperature account for the scatter observed in log–log R–LMA–N scaling relationships was also assessed. We show that thermal history accounts for up to 20% of the scatter in scaling relationships used to predict R, with the impact of thermal history on R–LMA–N generalized scaling relationships being highly predictable. This finding enabled us to quantitatively incorporate acclimation of R into a coupled global climate–vegetation model. We show that accounting for acclimation of R has negligible impact on predicted annual rates of global R, net primary productivity (NPP) or future atmospheric CO2 concentrations. However, our analysis suggests that accounting for acclimation is important when considering carbon fluxes among thermally contrasting biomes (e.g. accounting for acclimation decreases predicted rates of R by up to 20% in high-temperature biomes). We conclude that acclimation of R needs to be accounted for when predicting potential responses of terrestrial carbon exchange to climatic change at a regional level. [ABSTRACT FROM AUTHOR]

Rising levels of atmospheric CO2, climate change, and fertilizer pollution provide the ecological imperative for investigating the interaction between plant responses to atmospheric CO2 concentration, temperature and nutrient supply. In this study spring wheat (Triticum aestivum L, cv. Wemhley) was grown at 40, 50, 60 and 70 Pa atmospheric CO2 pressure and three experiments were conducted to investigate interactions between growth responses to the CO2 treatment and: (i) temperature (24/16 °C vs. 18/10 °C day/night), (ii) nutrient solution nitrate concentration (2.5, 5, 10 and 15 mM Ca(NO3,)2. 4H2O). and (iii) phosphate concentration (0.025 and 0.5 mM KH2PO4. Dry mass and root/shoot ratio increased with CO2, level at the higher temperature. These responses were reversed at the lower temperature. The increase in yield with CO2 enhancement was limited by low rates of nutrient supply in both absolute and relative terms. In the elevated CO2 treatments, the shoot nitrogen concentration was reduced, as was the proportional allocation to the uppermost leaves. These results are discussed with respect to possible physiological mechanisms and physiological for improved crop performance in a future, elevated CO2 World. [ABSTRACT FROM AUTHOR]

It has been demonstrated that the decrease of temperature associated with an increase in altitude of 250 m is sufficient to reverse the outcome of competition between Sedum rosea (L) Scop. and S. telephium L. ssp. fabaria Syme. Growth analyses of S. rosea and S. telephium in a range of temperature conditions have shown that the change in the outcome of competition is due to the marked increase in growth of S. telephium and the insensitivity of S. rosea to an increase in temperature over the range recorded in the field. [ABSTRACT FROM AUTHOR]

When plants of Sedum rosea (L.) Scop. and S. telephium L. ssp. fabaria Syme are grown in competition at different altitudes it is found that the growth of the species is affected differentially. This effect is such that at low altitudes S. telephium is a larger plant than S. rosea, while the reverse is the case at high attitudes. The observed differences are caused by a marked sensitivity of the growth of S. telephium to differences in altitude, whileS. rosea is very insensitive. The most probable cause of these responses would appear to be differences of climate. The influence of altitude in northern England on air temperature, saturation deficit and irradiance has been investigated in order to establish the magnitude of the differences which may cause these responses. [ABSTRACT FROM AUTHOR]

Designs are described for sensors, integrators and a readout device which together measure temperature (or day-degrees) and photosynthetically active radiation (or short-wave radiation in the 300 to 3000 nm waveband). The equipment is cheap to produce (£15 to £18) and has a low electrical power requirement (3 mW at 20 °C). The integrators may be adjusted to measure temperature or irradiance above set thresholds. [ABSTRACT FROM AUTHOR]