Light inhibition of foliar respiration in response to soil water availability and seasonal changes in temperature Mediterranean holm oak. (quercus ilex forest)

In the present study we investigated variations in leaf respiration in darkness (RD) and light (RL), and associated traits in response to season, and along a gradient of soil moisture, in Mediterranean woodland dominated by holm oak (Quercus ilex L.) in central and north-eastern Spain respectively. On seven occasions during the year in the central Spain site, and along the soil moisture gradient in north-eastern Spain, we measured rates of leaf RD, RL (using the Kok method), light-saturated photosynthesis (A) and related light response characteristics, leaf mass per unit area (MA) and leaf nitrogen (N) content. At the central Spain site, significant seasonal changes in soil water content and ambient temperature (T) were associated with changes in MA, foliar N, A and stomatal conductance. RD measured at the prevailing daily T and in instantaneous R-T responses, displayed signs of partial acclimation and was not significantly affected by time of year. RL was always less than, and strongly related to, RD, and RL/RD did not vary significantly or systematically with seasonal changes in T or soil water content. Averaged over the year, RL/RD was 0.66 ± 0.05 s.e. (n = 14) at the central Spain site. At the north-eastern Spain site, the soil moisture gradient was characterised by increasing MA and RD, and reduced foliar N, A, and stomatal conductance as soil water availability decreased. Light inhibition of R occurred across all sites (mean RL/RD = 0.69 ± 0.01 s.e. (n = 18)), resulting in ratios of RL/A being lower than for RD/A. Importantly, the degree of light inhibition was largely insensitive to changes in soil water content. Our findings provide evidence for a relatively constrained degree of light inhibition of R (RL/RD ~ 0.7, or inhibition of ~30%) across gradients of water availability, although combined impacts of seasonal changes in both T and soil water content increase the range of values expressed. The findings thus have implications in terms of the assumptions made by predictive models that seek to account for light inhibition of R, and for our understanding of how environmental gradients impact on leaf trait relationships in Mediterranean plant communities

The productivity, metabolism and carbon cycle of two lowland tropical forest plots in south-western Amazonia

Background: The forests of western Amazonia are known to be more dynamic that the better-studied forests of eastern Amazonia, but there has been no comprehensive description of the carbon cycle of a western Amazonian forest. Aims: We present the carbon budget of two forest plots in Tambopata in south-eastern Peru, western Amazonia. In particular, we present, for the first time, the seasonal variation in the detailed carbon budget of a tropical forest. Methods: We measured the major components of net primary production (NPP) and total autotrophic respiration over 3-6 years. Results: The NPP for the two plots was 15.1 ± 0.8 and 14.2 ± 1.0 Mg C ha −1 year −1 , the gross primary productivity (GPP) was 35.5 ± 3.6 and 34.5 ± 3.5 Mg C ha −1 year −1 , and the carbon use efficiency (CUE) was 0.42 ± 0.05 and 0.41 ± 0.05. NPP and CUE showed a large degree of seasonality. Conclusions: The two plots were similar in carbon cycling characteristics despite the different soils, the most notable difference being high allocation of NPP to canopy and low allocation to fine roots in the Holocene floodplain plot. The timing of the minima in the wet-dry transition suggests they are driven by phenological rhythms rather than being driven directly by water stress. When compared with results from forests on infertile forests in humid lowland eastern Amazonia, the plots have slightly higher GPP, but similar patterns of CUE and carbon allocation

Bryophyte gas-exchange dynamics along varying hydration status reveal a significant carbonyl sulphide (COS) sink in the dark and COS source in the light

Carbonyl sulphide (COS) is a potential tracer of gross primary productivity (GPP), assuming a unidirectional COS flux into the vegetation that scales with GPP. However, carbonic anhydrase (CA), the enzyme that hydrolyses COS, is expected to be light independent, and thus plants without stomata should continue to take up COS in the dark. We measured net CO2 (A(C) ) and COS (A(S) ) uptake rates from two astomatous bryophytes at different relative water contents (RWCs), COS concentrations, temperatures and light intensities. We found large A(S) in the dark, indicating that CA activity continues without photosynthesis. More surprisingly, we found a nonzero COS compensation point in light and dark conditions, indicating a temperature-driven COS source with a Q10 (fractional change for a 10°C temperature increase) of 3.7. This resulted in greater A(S) in the dark than in the light at similar RWC. The processes underlying such COS emissions remain unknown. Our results suggest that ecosystems dominated by bryophytes might be strong atmospheric sinks of COS at night and weaker sinks or even sources of COS during daytime. Biotic COS production in bryophytes could result from symbiotic fungal and bacterial partners that could also be found on vascular plants.Funding was provided by the European Research Council (ERC) early career starting grant SOLCA (grant no. 338264) and the French Agence National de la Recherche (ANR) project ORCA. T.E.G. was funded by the IdEx post-doctoral programme of the Université de Bordeaux and by a Marie Skłodowska-Curie Intra-European fellowship (grant no. 653223). J.R. was funded by NERC grant NE/M00113X/1

Global variability in leaf respiration in relation to climate, plant functional types and leaf traits

• Leaf dark respiration (Rdark) is an important yet poorly quantified component of the global carbon cycle. Given this, we analyzed a new global database of Rdark and associated leaf traits. • Data for 899 species were compiled from 100 sites (from the Arctic to the tropics). Several woody and nonwoody plant functional types (PFTs) were represented. Mixed-effects models were used to disentangle sources of variation in Rdark. • Area-based Rdark at the prevailing average daily growth temperature (T) of each site increased only twofold from the Arctic to the tropics, despite a 20°C increase in growing T (8–28°C). By contrast, Rdark at a standard T (25°C, Rdark25) was threefold higher in the Arctic than in the tropics, and twofold higher at arid than at mesic sites. Species and PFTs at cold sites exhibited higher Rdark25 at a given photosynthetic capacity (Vcmax25) or leaf nitrogen concentration ([N]) than species at warmer sites. Rdark25 values at any given Vcmax25 or [N] were higher in herbs than in woody plants. • The results highlight variation in Rdark among species and across global gradients in T and aridity. In addition to their ecological significance, the results provide a framework for improving representation of Rdark in terrestrial biosphere models (TBMs) and associated land-surface components of Earth system models (ESMs)

The response of leaf respiration to changes in temperature in contrasting plant species

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Transient shade and drought have divergent impacts on the temperature sensitivity of dark respiration in leaves of Geum urbanum

The respiratory response of plants to temperature is a critical biotic feedback in the study of global climate change. Few studies, however, have investigated the effects of environmental stresses on the short-term temperature response of dark respiration (Rdark) at the leaf level. We investigated the effect of shade and transient drought on the temperature sensitivity (Q10; the proportional increase in respiration per 10°C increase in temperature) of Rdark of Geum urbanum L. in controlled experiments. Shade effects were most pronounced following sustained, near-darkness, when rates of leaf Rdark at a set measuring temperature (25°C) and the Q10 of Rdark were both reduced. By contrast, rates of leaf Rdark and the Q10 of Rdark both increased in response to the onset of severe water stress. Water stress was associated with a rapid (but reversible) decline in rates of light-saturated photosynthesis (Psat), stomatal closure (gs) and progressive wilting. Re-watering resulted in a rapid recovery of Psat, gs and a decline in the Q10 of Rdark (due to larger proportional reductions in the rate of Rdark measured at 25°C compared with those measured at 14°C). The concentration of soluble sugars in leaves did not decline during drought (5-7 day cycles) or shading, but during drought the starch concentration dropped, suggesting starch to sugar conversion helped to maintain homeostatic concentrations of soluble sugars. Thus, the drought and shade induced changes in Rdark were unlikely to be due to stress-induced changes in substrate supply. Collectively, the data highlight the dynamic responses of respiratory Q10 values to changes in water supply and sustained reductions in growth irradiance. If widespread, such changes in the Q10 of leaf respiration could have important implications for predicted rates of ecosystem carbon exchange in the future, particularly in areas that experience more frequent droughts

Leaf respiration in darkness and in the light under pre-industrial, current and elevated atmospheric CO2 concentrations

Our study sought to understand how past, low atmospheric CO2 concentrations ([CO2]) impact respiration (R) of soybean (Glycine max), when compared to plants grown under current and future [CO2]s. Experiments were conducted using plants grown under 290, 400 and 700ppm [CO2]. Leaf R was measured in both darkness (RD) and in the light (RL; using the Kok method), with short-term changes in measurement [CO2]. Leaf R was measured in both darkness (RD) and in the light (RL; using the Kok method), with short-term changes in measurement [CO2 and [O2] being used to explore the relationship between light inhibition of leaf R and photorespiration. Root R, photosynthesis (A), leaf [N] and biomass allocation traits were also quantified. In contrast to the inhibitory effect of low growth [CO2] on A, growth [CO2] had no significant effect on leaf RD or root R. Irrespective of growth [CO2], RL was always lower than RD, with light inhibiting leaf R by 17-47%. Importantly, the degree of light inhibition of leaf R was lowest in plants grown under low [CO2], with variations in RL being positively correlated with RD and photorespiration. Irrespective of whether leaf R was measured in the light or dark, a greater proportion of the carbon fixed by leaf photosynthesis was released by leaf R in plants grown under low [CO2] than under current/future [CO2]'s. Collectively, our results highlight the differential responses of A and R to growth of plants under low to elevated atmospheric [CO2]

Does growth irradiance affect temperature dependence and thermal acclimation of leaf respiration? Insights from a Mediterranean tree with long-lived leaves

Understanding the response of leaf respiration (R) to changes in irradiance and temperature is a prerequisite for predicting the impacts of climate change on plant function and future atmospheric CO2 concentrations. Little is known, however, about the interactive effects of irradiance and temperature on leaf R. We investigated whether growth irradiance affects the temperature response of leaf R in darkness (Rdark) and in light (R light) in seedlings of a broad-leaved evergreen species, Quercus ilex. Two hypotheses concerning Rdark were tested: (1) the Q 10 (i.e. the proportional increase in R per 10°C rise in temperature) of leaf Rdark is lower in shaded plants than in high-light-grown plants, and (2) shade-grown plants exhibit a lower degree of thermal acclimation of Rdark than plants exposed to higher growth irradiance. We also assessed whether light inhibition of Rlight differs between leaves exposed to contrasting temperatures and growth irradiances, and whether the degree of thermal acclimation of Rlight is dependent on growth irradiance. We showed that while growth irradiance did impact on photosynthesis, it had no effect on the Q10 of leaf R dark. Growth irradiance had little impact on thermal acclimation when fully expanded, pre-existing leaves were exposed to contrasting temperatures for several weeks. When Rlight was measured at a common irradiance, Rlight/Rdark ratios were higher in shaded plants due to homeostasis of Rlight between growth irradiance treatments and to the lower Rdark in shaded leaves. We also showed that Rlight does not acclimate to the same degree as Rdark, and that R light/Rdark decreases with increasing measuring and growth temperatures, irrespective of the growth irradiance. Collectively, we raised the possibility that predictive carbon cycle models can assume that growth irradiance and photosynthesis do not affect the temperature sensitivity of leaf Rdark of long-lived evergreen leaves, thus simplifying incorporation of leaf R into such models

Impact of growth temperature on scaling relationships linking photosynthetic metabolism to leaf functional traits

Scaling relationships linking photosynthesis (A) to leaf traits are important for predicting vegetation patterns and plant-atmosphere carbon fluxes. Here, we investigated the impact of growth temperature on such scaling relationships. We assessed whethe