Abstract
We explore here our mechanistic understanding of the environmental and physiological processes that determine the oxygen isotope composition of leaf cellulose (δ18 Ocellulose ) in a drought-prone, temperate grassland ecosystem. A new allocation-and-growth model was designed and added to an 18 O-enabled soil-vegetation-atmosphere transfer model (MuSICA) to predict seasonal (April-October) and multi-annual (2007-2012) variation of δ18 Ocellulose and 18 O-enrichment of leaf cellulose (Δ18 Ocellulose ) based on the Barbour-Farquhar model. Modelled δ18 Ocellulose agreed best with observations when integrated over c.400 growing-degree-days, similar to the average leaf lifespan observed at the site. Over the integration time, air temperature ranged from 7 to 22°C and midday relative humidity from 47 to 73%. Model agreement with observations of δ18 Ocellulose (R2 =0.57) and Δ18 Ocellulose (R2 =0.74), and their negative relationship with canopy conductance, was improved significantly when both the biochemical 18 O-fractionation between water and substrate for cellulose synthesis (εbio , range 26-30‰) was temperature-sensitive, as previously reported for aquatic plants and heterotrophically grown wheat seedlings, and the proportion of oxygen in cellulose reflecting leaf water 18 O-enrichment (1-pex px , range 0.23-0.63) was dependent on air relative humidity, as observed in independent controlled experiments with grasses. Understanding physiological information in δ18 Ocellulose requires quantitative knowledge of climatic effects on pex px and εbio .
Highlights
The oxygen isotope composition of plant cellulose (δ18Ocellulose) and its enrichment above source water (Δ18Ocellulose) are thought to record environmental and physiological information of great interest to a range of scientific disciplines, including functional plant ecology and climate change biology (e.g. Barbour, 2007; Battipaglia et al, 2013; Gessler et al, 2014)
Research 3 availability) on Δ18Ocellulose and δ18Ocellulose? Do environmentally driven adjustments of pexpx (RH) or εbio improve predictions of observed Δ18Ocellulose and δ18Ocellulose? Is canopy conductance reflected in Δ18Ocellulose or δ18Ocellulose? To that end, we developed a new allocation-and-growth model suitable for grassland ecosystems (Fig. 1) that we incorporated into the 18O-enabled soil–vegetation–atmosphere transfer model MuSICA
To constrain the integration time of the 18O-signal in the leaf cellulose samples, we compared the R2 between observed and predicted δ18Ocellulose (Fig. 4c) for predictions of δ18Ocellulose based on integration times of 50–600 GDD
Summary
The oxygen isotope composition of plant cellulose (δ18Ocellulose) and its enrichment above source water (Δ18Ocellulose) are thought to record environmental and physiological information of great interest to a range of scientific disciplines, including functional plant ecology and climate change biology (e.g. Barbour, 2007; Battipaglia et al, 2013; Gessler et al, 2014). The oxygen isotope composition of plant cellulose (δ18Ocellulose) and its enrichment above source water (Δ18Ocellulose) are thought to record environmental and physiological information of great interest to a range of scientific disciplines, including functional plant ecology and climate change biology Farquhar et al, 1998; Scheidegger et al, 2000; Barbour et al, 2000b) that can provide information about environmental or climate change effects on the processes regulating the water-use efficiency of C3 plants. Δ18Ocellulose depends on the oxygen isotope composition of water in sink tissues, often approximated by the δ18O of plant source water taken up by the roots (δ18Osource), and on the δ18O of leaf lamina water (δ18Oleaf), respectively. Δ18Osource is determined by the depth distribution of
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