Leaf Carbon Isotope Discrimination Research Articles

Effects of environmental salinity on carbon isotope discrimination and stomatal conductance in Spartina grasses

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 313:305-310 (2006) - doi:10.3354/meps313305 Effects of environmental salinity on carbon isotope discrimination and stomatal conductance in Spartina grasses Brian R. Maricle*, Raymond W. Lee School of Biological Sciences, Washington State University, PO Box 644236, Pullman, Washington 99164-4236, USA *Email: bmaricle@mail.wsu.edu ABSTRACT: High salinity levels have long been recognized as an important environmental factor influencing plant growth and performance. Salt stress and concomitant water stress are likely to affect photosynthesis by reductions in stomatal conductance necessary to prevent loss of water vapor. Despite inundation with saline water, salt marsh communities exhibit high primary productivity. This study tested the effects of 0 to 40‰ salinity on leaf carbon isotope discrimination (Δ), leaf stomatal conductance (gs), and leaf conductance to CO2 (gCO2) in the emergent estuarine C4 grasses Spartina alterniflora, S. anglica, and S. patens. Δ increased with increasing salinity in greenhouse and growth chamber experiments. gs and gCO2 peaked at moderate salinity levels (10 to 20‰) but significantly decreased at higher salinities in all species. KEY WORDS: Salt stress · Photosynthesis · Spartina · δ13C · Stable isotopes Full text in pdf format PreviousExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 313. Online publication date: May 11, 2006 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2006 Inter-Research.

Long-term impacts of stand management on ponderosa pine physiology and bark beetle abundance in northern Arizona: A replicated landscape study

Ponderosa pine ( Pinus ponderosa Dougl. ex Laws.) forests in northern Arizona have degraded due to overgrazing, logging, and fire suppression that accompanied Euro-American settlement in the late 1800s. Overstocked stands of suppressed trees with low structural diversity dominate the landscape. These conditions create high risk of catastrophic fires and insect outbreaks. We investigated long-term effects (8–16 years post-treatment) of thinning and thinning + prescribed burning on ponderosa pine water stress, leaf carbon isotope discrimination and nitrogen concentration, oleoresin exudation flow, phloem thickness, radial growth, and bark beetle abundance relative to unmanaged control stands over 2 years of measurement in 12 stands replicated across the landscape. Predawn water potential in late June, phloem thickness, and basal area increment were lower in unmanaged than managed stands. Oleoresin exudation flow in July was greater in unmanaged and thinned + burned stands than thinned stands, and greater in a warm year than a cooler year. Leaf nitrogen concentration differed between years, but not among treatments. Tree competition and water stress were positively correlated, and tree competition was negatively correlated with radial growth and phloem thickness. Pheromone-baited trap catches of Dendroctonus spp. ( D. brevicomis Leconte pooled with D. frontalis Zimmerman) were higher in unmanaged than managed stands, whereas catches of Ips spp. did not differ among treatments. We conclude that thinning with and without prescribed burning can have long-term effects on ponderosa pine water stress, growth, phloem thickness, resin flow, and bark beetle abundance. Low levels of tree mortality from bark beetles at our study sites suggest remarkable resistance of ponderosa pine in mid-elevation forests in northern Arizona, even at high tree densities.

Backcross reciprocal monosomic analysis of leaf relative water content, stomatal resistance, and carbon isotope discrimination in wheat under pre-anthesis water-stress conditions

Monosomic plants from an Australian variety (Oxley) having low stomatal resistance (SR), low leaf relative water content (LRWC), and high carbon isotope discrimination (Δ) were crossed with variety Falchetto having opposite characters in order to produce F2 backcross reciprocal monosomic families. The families were assessed under pre-anthesis water-stress conditions in a controlled growth chamber. F2 backcross reciprocal monosomic analysis suggested possible allelic variations between chromosomes 1A, 3A, 6A, 7A, 7B, 1D, and 4D of Falchetto and their homologues in Oxley for LRWC. This analysis also suggested possible allelic variation between chromosomes 5A, 1A, and 3A of Falchetto and their homologues in Oxley for SR. Extending the analysis to the F3 disomic generation and the assessment of LRWC at this generation confirmed that reciprocals for chromosomes 3A and 6A showed significant differences. F2 backcross reciprocal monosomic analysis for Δ suggested allelic variations on chromosomes 1D, 4D, and 5D. However, chromosome 1D from Falchetto had the highest difference from its homologue in Oxley. Assessing the reciprocals of this chromosome for vegetative evapotranspiration efficiency (ETEveg) at the F3 disomic generation indicated that the observed variation for Δ was translated into differences for ETEveg. These results indicate that chromosome 1D of Falchetto is promising in reducing Δ and that the improvement of wheat varieties for ETEveg can be done by selection for Δ. Finally, plieotropic effects of some chromosomes were observed for the characters under study. This suggests the existence of genetic factors on these chromosomes affecting more than one character. However, some pleiotropic effects could also be due to non-genetic developmental interactions.

CO2 exchange in three Canadian High Arctic ecosystems: response to long‐term experimental warming

AbstractCarbon dioxide exchange, soil C and N, leaf mineral nutrition and leaf carbon isotope discrimination (LCID‐Δ) were measured in three High Arctic tundra ecosystems over 2 years under ambient and long‐term (9 years) warmed (∼2°C) conditions. These ecosystems are located at Alexandra Fiord (79°N) on Ellesmere Island, Nunavut, and span a soil water gradient; dry, mesic, and wet tundra. Growing season CO2 fluxes (i.e., net ecosystem exchange (NEE), gross ecosystem photosynthesis (GEP), and ecosystem respiration (Re)) were measured using an infrared gas analyzer and winter C losses were estimated by chemical absorption. All three tundra ecosystems lost CO2 to the atmosphere during the winter, ranging from 7 to 12 g CO2‐C m−2 season−1 being highest in the wet tundra. The period during the growing season when mesic tundra switch from being a CO2 source to a CO2 sink was increased by 2 weeks because of warming and increases in GEP. Warming during the summer stimulated dry tundra GEP more than Re and thus, NEE was consistently greater under warmed as opposed to ambient temperatures. In mesic tundra, warming stimulated GEP with no effect on Re increasing NEE by ∼10%, especially in the first half of the summer. During the ∼70 days growing season (mid‐June–mid‐August), the dry and wet tundra ecosystems were net CO2‐C sinks (30 and 67 g C m−2 season−1, respectively) and the mesic ecosystem was a net C source (58 g C m−2 season−1) to the atmosphere under ambient temperature conditions, due in part to unusual glacier melt water flooding that occurred in the mesic tundra. Experimental warming during the growing season increased net C uptake by ∼12% in dry tundra, but reduced net C uptake by ∼20% in wet tundra primarily because of greater rates of Re as opposed to lower rates of GEP. Mesic tundra responded to long‐term warming with ∼30% increase in GEP with almost no change in Re reducing this tundra type to a slight C source (17 g C m−2 season−1). Warming caused LCID of Dryas integrafolia plants to be higher in dry tundra and lower in Salix arctic plants in mesic and wet tundra. Our findings indicate that: (1) High Arctic ecosystems, which occur in similar mesoclimates, have different net CO2 exchange rates with the atmosphere; (2) long‐term warming can increase the net CO2 exchange of High Arctic tundra by stimulating GEP, but it can also reduce net CO2 exchange in some tundra types during the summer by stimulating Re to a greater degree than stimulating GEP; (3) after 9 years of experimental warming, increases in soil carbon and nitrogen are detectable, in part, because of increases in deciduous shrub cover, biomass, and leaf litter inputs; (4) dry tundra increases in GEP, in response to long‐term warming, is reflected in D. integrifolia LCID; and (5) the differential carbon exchange responses of dry, mesic, and wet tundra to similar warming magnitudes appear to depend, in part, on the hydrologic (soil water) conditions. Annual net ecosystem CO2‐C exchange rates ranged from losses of 64 g C m−2 yr−1 to gains of 55 g C m−2 yr−1. These magnitudes of positive NEE are close to the estimates of NPP for these tundra types in Alexandra Fiord and in other High Arctic locations based on destructive harvests.

Leaf isotopic (?13C and ?15N) and nitrogen contents of Carex plants along the Eurasian Coastal Arctic: results from the Northeast Passage expedition

We conducted surrogate in-situ physiological performance measures (δ13C and δ15N) of Carex plants from 15 Eurasian Coastal Arctic sites. Leaf carbon isotope discrimination (LCID) of Carex plants exhibited significant differences between sites (populations). Additionally, LCID was inversely correlated with mean annual temperature and stomatal density, and to a lesser extent, with the depth of thaw. Leaf δ15N values of Carex plants exhibited significant differences between sites without differences among ramet age classes, and the leaf δ15N values were inversely correlated with mean annual precipitation. These ranges of Carex leaf gas exchange and mineral nutrition across the Eurasian Arctic may contribute to Carex’s dominance in coastal tundra systems. Also, the inverse correlation between LCID, precipitation, and temperature indicates that, as precipitation increases and temperatures continue to warm in Eurasia, leaf gas exchange may actually be lower in the future, leading to reductions in shoot growth and lower above-ground biomass production.

Leaf Carbon Isotope Discrimination and its Relation with Qualitative Root Traits and Harvest Index in Sugar Beet (Beta vulgaris L.)

AbstractTwenty commercial sugar beet varieties were grown at two sites in central Greece during the 2001 growing season (March to October), in a completely randomized block design with three replications. Carbon isotope discrimination (Δ) in sugar beet leaves was found to be affected by site and marginally by variety. No relation was found between fresh root yield and Δ, but significant correlations were found between Δ and sucrose content (positive) and between Δ and root α‐amino‐N (negative). Also, the harvest index, determined at one site, was negatively correlated with Δ.

Effects of different nitrogen forms and combination with foliar spraying with 6-benzylaminopurine on growth, transpiration, and water and potassium uptake and flow in tobacco

NH4+-N can have inhibitory effects on plant growth. However, the mechanisms of these inhibitory effects are still poorly understood. In this study, effects of different N forms and a combination of ammonium + 6-benzylaminopurine (6-BA, a synthetic cytokinin) on growth, transpiration, uptake and flow of water and potassium in 88-days-old tobacco (Nicotiana tabacum L. K 326) plants were studied over a period of 12 days. Plants were supplied with equal amounts of N in different forms: NO3−, NH4NO3, NH4+ or NH4++6-BA (foliar spraying every 2 days after onset of the treatments). For determining flows and partitioning upper, middle and lower strata of three leaves each were analysed. During the 12 days study period, 50% replacement of NO3−-N by NH4+-N (NH4NO3) did not change growth, transpiration, uptake and flow of water and K+ compared with the NO3−-N treatment. However, NH4+-N as the sole N-source caused: (i) a substantial decrease in dry weight gain to 42% and 46% of the NO3−-N and NH4NO3 treatments, respectively; (ii) a marked reduction in transpiration rate, due to reduced stomatal conductance, illustrated by more negative leaf carbon-isotope discrimination (δ13C) compared with the NO3− treatment, especially in upper leaves; (iii) a strong reduction both in total water uptake, and in the rate of water uptake by roots, likely due to a decrease in root hydraulic conductivity; (iv) a marked reduction of K+ uptake to 10%. Under NH4+ nutrition the middle leaves accumulated 143%, and together with upper leaves 206% and the stem 227% of the K+ currently taken up, indicating massive mobilisation of K+ from lower leaves and even the roots. Phloem retranslocation of K+ from the shoot and cycling through the root contributed 67% to the xylem transport of K+, and this was 2.2 times more than concurrent uptake. Foliar 6-BA application could not suppress or reverse the inhibitory effects on growth, transpiration, uptake and flow of water and ions (K+) caused by NH4+-N treatment, although positive effects by 6-BA application were observed, even when 6-BA (10−8M) was supplied in nutrient solution daily with watering. Possible roles of cytokinin to regulate growth and development of NH4+-fed plants are discussed.

Water resource partitioning, stem xylem hydraulic properties, and plant water use strategies in a seasonally dry riparian tropical rainforest.

This study investigated seasonal variation in the origin of water used by plants in a riparian tropical rainforest community and explored linkages between plant water source, plant xylem hydraulic conductivity and response to the onset of dry conditions. The study focused on five co-dominant canopy species, comprising three tree species ( Doryphora aromatica, Argyrodendron trifoliolatum, Castanospora alphandii) and two climbing palms ( Calamus australis and Calamus caryotoides). Stable isotope ratios of oxygen in water (delta(18)O) from soil, groundwater, stream water and plant xylem measured in the wet season and the subsequent dry season revealed water resource partitioning between species in the dry season. Measurement of stem-area-specific hydraulic conductivity ( K(S)) in the wet season and subsequent dry season showed a significant dry-season loss of K(S) in three of the five species ( Castanospora alphandii, Calamus australis and C. caryotoides) and a decrease in mean K(S) for all species. This loss of hydraulic conductivity was positively correlated with the difference between wet-season and dry-season midday leaf water potentials and with leaf carbon isotope discrimination, indicating that plants that were less susceptible to loss of conductivity had greater control over transpiration rate and were more water-use efficient.

Variation in Ginkgo biloba L. leaf characters across a climatic gradient in China.

Fossil leaves assigned to the genus Ginkgo are increasingly being used to reconstruct Mesozoic and Tertiary environments based on their stomatal and carbon isotopic characteristics. We sought to provide a more secure basis for understanding variations seen in the plant fossil record by determining the natural variability of these properties of sun and shade leaf morphotypes of Ginkgo biloba trees under the present atmospheric CO2 concentration and a range of contemporary climates in three Chinese locations (Lanzhou, Beijing, and Nanjing). Climate had no major effects on leaf stomatal index (proportion of leaf surface cells that are stomata) but did result in more variable stomatal densities. The effects of climate and leaf morphotype on stomatal index were rather conserved (<1%) and much less than the response of trees to recent CO2 increases. Leaf carbon isotope discrimination (delta) was highest for trees in Nanjing, which experience a warm, moist climate, whereas trees in the most arid site (Lanzhou) had the lowest delta values. Interestingly, the variation in delta shown by leaf populations of trees from China and the United Kingdom was very similar to that of fossil Ginkgo cuticles dating to the Mesozoic and Tertiary, which suggests to us that the physiology of leaf carbon uptake and regulation of water loss in Ginkgo has remained highly conserved despite the potential for evolutionary change over millions of years.

Leaf Gas Exchange of Pachyrhizus ahipa and P. erosus Under Water and Temperature Stress

Gas exchange, water relations, and leaf traits were studied in the tuberous-root producing legumes ahipa (Pachyrhizus ahipa) and yambean (P. erosus) under different environmental conditions. Differences in leaf traits (hairiness, leaf area, areal leaf mass, stomatal density) and paraheliotropism were found between ahipa and yambean. Under sufficient water supply, the increase in air temperature and decrease in air humidity increased stomatal conductance (gs) and net photosynthetic rate (PN) in yambean but reduced them in ahipa. In a drying soil (14 d after irrigation), inter-specific variation in gas exchange was only observed in the early morning, and yambean showed a greater sensitivity to water restriction than ahipa. High gs at low humidity increased PN of P. erosus but resulted in lower water-use efficiency (WUE). However, long-term WUE, estimated by leaf carbon isotope discrimination, showed little variation between species. Daily-irrigated ahipa and yambean grown in the greenhouse did not show significant differences in gas exchange. However, leaf temperature was significantly greater in yambean than in ahipa while a steepper relationship between E and PN and gs was observed in ahipa.

Use of decreasing foliar carbon isotope discrimination during water limitation as a carbon tracer to study whole plant carbon allocation

AbstractFoliar carbon isotope discrimination (Δ) of C3 plants decreases in water‐deficit situations as discrimination by the photosynthetic primary carboxylation reaction decreases. This diminished Δ in leaves under water deficit can be used as a tracer to study whole plant carbon allocation patterns. Carbon isotope composition (δ13C value) of leaf hot water extracts or leaf tissue sap represents a short‐term integral of leaf carbon isotope discrimination and thus represents the δ13C value of source carbon that may be distributed within a plant in water‐deficit situations. By plotting the δ13C values of source carbon against the δ13C values of sink tissues, such as roots or stems, it is possible to assess carbon allocation to and incorporation into sink organs in relation to already present biomass. This natural abundance labelling method has been tested in three independent experiments, a one‐year field study with the fruit tree species Ziziphus mauritiana and peach (Prunus persica), a medium‐term drought stress experiment with Ziziphus rotundifolia trees in the glasshouse, and a short‐term drought stress experiment with soybean (Glycine max). The data show that the natural abundance labelling method can be applied to qualitatively assess carbon allocation in drought‐stressed plants. Although it is not possible to estimate exact fluxes of assimilated carbon during water deficit the method represents an easy to use tool to study integrated plant adaptations to drought stress. In addition, it is a less laborious method that can be applied in field studies as well as in controlled experiments, with plants from any developmental stage.

Spatial distribution of leaf water‐use efficiency and carbon isotope discrimination within an isolated tree crown

AbstractThe spatial variations in the stable carbon isotope composition (δ13C) of air and leaves (total matter and soluble sugars) were quantified within the crown of a well‐watered, 20‐year‐old walnut tree growing in a low‐density orchard. The observed leaf carbon isotope discrimination (Δ) was compared with that computed by a three‐dimensional model simulating the intracanopy distribution of irradiance, transpiration and photosynthesis (previously parameterized and tested for the same tree canopy) coupled to a biophysically based model of carbon isotope discrimination. The importance of discrimination associated with CO2 gradients encountered from the substomatal sites to the carboxylation sites was evaluated. We also assessed by simulation the effect of current irradiance on leaf gas exchange and the effect of long‐term acclimation of photosynthetic capacity and stomatal and internal conductances to light regime on intracanopy gradients in Δ. The main conclusions of this study are: (i) leaf Δ can exhibit important variations (5 and 8‰ in total leaf material and soluble sugars, respectively) along light gradients within the foliage of an isolated tree; (ii) internal conductance must be taken into account to adequately predict leaf Δ, and (iii) the spatial variations in Δ and water‐use efficiency resulted from the short‐term response of leaf gas exchange to variations in local irradiance and, to a much lesser extent, from the long‐term acclimation of leaf characteristics to the local light regime.

GAS EXCHANGE, GROWTH, YIELD AND BEVERAGE QUALITY OF COFFEA ARABICA CULTIVARS GRAFTED ON TO C. CANEPHORA AND C. CONGENSIS

Gas exchange, leaf carbon isotope discrimination, growth, yield and beverage quality were evaluated for two Coffea arabica cultivars (Catuai and Mundo Novo), grafted on to C. canephora and C. congensis progenies growing in open fields. During the years 1994 to 1997, grafting resulted in an average increase in bean yield of 151 and 89% for Catuai and Mundo Novo respectively. As analysed by sensory analyses and by the ratio between the mono-isomers and di-isomers of caffeoylquinic acid, beverage quality of the C. arabica was not altered by grafting. Shoot growth was significantly greater in grafted plants, showing an increase of 52% in total leaf area compared with the non-grafted plants. Under conditions of water excess in the soil there was little difference in the transpiration and stomatal conductance rates between the grafted and non-grafted plants, but the net photosynthesis was higher in grafted plants. With an accentuated water deficit in the soil in the dry period, the grafted plants showed significantly higher transpiration and stomatal conductance rates than the non-grafted plants, and similar values to those of C. canephora. Carbon isotope discrimination was greater in the grafted plants, suggesting greater root hydraulic conductance. The results suggest that the better performance of the grafted plants during the dry period was due to the greater capacity of the root system of C. canephora to provide water to the shoot thereby maintaining greater gas exchange in the leaves and consequently a greater carbon gain.

Competition for water between walnut seedlings (Juglans regia) and rye grass (Lolium perenne) assessed by carbon isotope discrimination and delta18O enrichment.

Container-grown walnut seedlings (Juglans regia L.) were subjected to competition with rye grass (Lolium perenne L.) and to a 2-week soil drying cycle. One and 2 weeks after the beginning of the drought treatment, H2 18O (delta approximately equals +100%) was added to the bottom layer of soil in the plant containers to create a vertical H2 18O gradient. Rye grass competition reduced aboveground and belowground biomass of the walnut seedlings by 60%, whereas drought had no effect. The presence of rye grass reduced the dry weight of walnut roots in the upper soil layer and caused a 50% reduction in lateral root length. Rye grass competition combined with the drought treatment reduced walnut leaf CO2 assimilation rate (A) and leaf conductance (gw) by 20 and 39%, respectively. Transpiration rates in rye grass, both at the leaf level and at the plant or tiller level, were higher than in walnut seedlings. Leaf intrinsic water-use efficiency (A/gw) of walnut seedlings increased in response to drought and no differences were observed between the single-species and mixed-species treatments, as confirmed by leaf carbon isotope discrimination measurements. Measurement of delta18O in soil and in plant xylem sap indicated that the presence of rye grass did not affect the vertical profile of soil water uptake by walnut seedlings. Walnut seedlings and rye grass withdrew water from the top and middle soil layers in well-watered conditions, whereas during the drought treatment, walnut seedlings obtained water from all soil layers, but rye grass took up water from the bottom soil layer only.

Relationships between flag leaf carbon isotope discrimination and several morpho-physiological traits in durum wheat genotypes under Mediterranean conditions

Relationships between flag leaf carbon isotope discrimination (Δ), water status parameters, residual transpiration (RT) and stomatal density (SD) were examined on a collection of 144 durum wheat accessions. Associations between Δ, grain yield (GY) and harvest index (HI) were also studied. The field trial was conducted under Mediterranean conditions. The crop cycle was characterised by a period of drought from February until maturity. A broad range of values we obtained for Δ (16.5–19.9‰) and other physiological traits. Flag leaf Δ was positively and significantly correlated with both HI and GY. Δ was better correlated with HI than with GY, which suggests that higher Δ values indicate higher efficiency of carbon partitioning to the kernel, leading to higher GY. Δ was found positively related with RT and negatively related with SD. This relationship may indicate a possible SD component of RT due to the association between conductance and SD. Strong positive correlations were found between Δ and water status parameters, suggesting that Δ may provide a good indication of plant water status in durum wheat under rainfed Mediterranean conditions.

Relationships between carbon isotope discrimination, dry matter production, and harvest index in durum wheat

Carbon isotope discrimination has been proposed as a criterion for the indirect selection to improve transpiration efficiency and grain yield in bread wheat and barley. Less attention has been devoted to durumwheat (Triticum durumDesf.) despite its economic importance in the Mediterranean basin. The Δ genetic variation and its relationships to dry matter production and harvest index in durum wheat were investigated in this study. For this purpose, field experiments were conducted on 144 durum wheat accessions under Mediterranean conditions (South of France) during three consecutive years with contrasting climatic conditions. Grain yield, above-ground biomass, harvest index, and carbon isotope discrimination of flag leaf and kernel were measured. Differences between years, noted for both leaf and kernel carbon isotope discrimination, were probably related to the variation in water availability from year to year. A large genotypic variation was also noticed for both leaf and kernel carbon isotope discrimination. The two traits were found to be positively correlated with grain yield within and across years, which confirms the interest in carbon isotope discrimination for selection for grain yield improvement under Mediterranean conditions. Both kernel and leaf carbon isotope discrimination correlated better with harvest index than with grain yield, suggesting that carbon isotope discrimination could reflect the efficiency of carbon partitioning to the kernel. The lack of correlation between leaf carbon isotope discrimination and both harvest index and grain yield in favourable water conditions (1996) was probably due to the difference in water availability between the period until flag leaves sampling (favourable conditions) and the strong water stress which accompanied the grain filling. Kernel carbon isotope discrimination correlated better with both harvest index and grain yield than did leaf carbon isotope discrimination. Moreover, a higher broad-sense heritability was obtained for kernel carbon isotope discrimination than for leaf carbon isotope discrimination. As a result, kernel carbon isotope discrimination appeared to be a better predictive criterion for efficiency of the carbon partitioning to the kernel (harvest index), and hence for grain yield, than did flag leaf carbon isotope discrimination.

Factors affecting the relationship between carbon isotope discrimination and transpiration efficiency in blue oak (Quercus douglasii)

In a greenhouse study, variation in plant and leaf transpiration efficiency(W, A/E)and carbon isotope discrimination (D) were assessed forQuercus douglasii Hook &amp; Arn. (blue oak) from a‘wet’ (930 mm) and a ‘dry’ (500 mm) site. Plants weregrown at 75–100% (wet) and 50–75% (dry) of fieldcapacity. Family variation masked population level differences, and twocontrasting patterns emerged. The expected pattern was observed with drytreatment plants having lower leaf internal CO 2concentration (c i ) and D, andhigher W andA/E. For families with verylarge increases in plant size from dry to wet treatments, however, wettreatment plants had lower c i andD, and higher W andA/E, reflecting a greaterinfluence of the maximum assimilation rate (Amax ) compared with stomatal conductance(g s ) on ci . In addition, large within-population variation inplant size appears to have affected both n (the vapor pressure deficit) and&amp;oslash; c (a measure of respiredcarbon). Lower n for large plants may be due to the higher rates of stomatalconductance and greater leaf cooling. Values of &amp;oslash;c appear to have increased for plants below 2.5 g (drymatter, DM). Variation in these factors would directly affect the relationshipbetween W and D. This study illustrates a case where significant within-population variation can occur in the relative effect ofg s and Amax on c i .In addition this study indicates that &amp;oslash;c may not be a constant for a species.

Nitrogen nutrition and water stress effects on leaf photosynthetic gas exchange and water use efficiency in winter wheat

The responses of gas exchange and water use efficiency to nitrogen nutrition for winter wheat were investigated under well-watered and drought conditions. The photosynthetic gas exchange parameters of winter wheat are remarkably improved by water and nitrogen nutrition and the regulative capability of nitrogen nutrition is influenced by water status. The effects of nitrogen nutrition on photosynthetic characteristics and on the limited factors to photosynthesis are not identical under different water status. Intrinsic water use efficiency (WUE i) of the plants at the high-N nutrition was decreased by a larger value than that of the plants in the low-N treatment due to a larger decrease in photosynthetic rate than in transpiration rate. Carbon isotope composition of plant material ( δ p) is increased by the increase of drought intensity. The δ p at a given level of C i/ C a is reduced by nitrogen deficiency. Leaf carbon isotope discrimination ( Δ) is increased by the increase of nitrogen nutrition and decreased by the increase of drought intensity. Transpirational water use efficiency (WUE t) is negatively correlated with Δ in both nitrogen supply treatments and increased with the nitrogen supply.

Water- and nutrient-use efficiency of a deciduous species, Vaccinium myrtillus , and an evergreen species, V . vitis-idaea , in a subalpine dwarf shrub heath in the southern Alps, Italy

Periodic measurements of gas-exchange rates and determinations of foliar N and P concentrations were used for evaluating instantaneous water-use efficiency and photosynthetic nutrient-use efficiency in two co-existing dwarf shrubs of different growth form (V. myrtillus, deciduous, and V. vitis-idaea, evergreen) in a subalpine heath in the southern Alps of Italy. Those data were compared with cumulative assessments of water-use efficiency and photosynthetic nutrient-use efficiency obtained by measuring leaf carbon isotope discrimination in leaf tissues and by estimating nutrient resorption from senescing leaves. V. myrtillus presented higher dry-weight based rates of net photosynthesis (Aweight) compared to V. vitis-idaea. Aweight was positively correlated with foliar-nutrient status and intercellular-to-ambient gradient in CO2 concentrations. Aweight was, furthermore, negatively correlated with leaf specific mass. Instantaneous photosynthetic nutrient-use efficiency did not differ between the two species but the percentages of N and P pools resorbed from senescing leaves were somewhat higher in the deciduous species. The evergreen species showed lower P concentrations in senescing leaves which indicated a higher proficiency in resorbing phosphorus compared to the deciduous species. In addition, the evergreen species achieved a higher carbon gain per unit foliar N and P, due to a longer mean residence time of both nutrients. The two species did not differ from each other with respect to both instantaneous and long-term water-use efficiency. This was consistent with the climatic pattern, showing no sign of water deficiency through the growing season. Current-year V. vitis-idaea leaves had a significantly higher Δ13C compared to previous-year leaves, possibly mirroring a long term acclimation of evergreen leaves, as far as they age, to the habitat conditions in the understory where evergreen species are usually confined within mixed dwarf-shrub communities.

Carbon and water relations of Salix monticola in response to winter browsing and changes in surface water hydrology: an isotopic study using δ13C and δ18O.

To ascertain whether browsing or hydrologic conditions influence the physiological performance of Salix and whether Salix and graminoids (Carex) use and possibly compete for similar water resources, we quantified the in situ seasonal patterns of plant water and carbon relations over three growing seasons. Our studies were designed to address the physiological factors which may be responsible for poor woody plant regeneration in montane riparian habitats of Rocky Mountain National Park, Colo. As these systems act to insure the delivery of fresh water to downstream users, the maintenance of their integrity is critical. We quantified plant water potentials, instantaneous rates of carbon fixation, leaf carbon isotope discrimination (Δ), leaf nitrogen content and water sources using stable isotopes of water (δ18O). The carbon and water relations of Salix were significantly affected by winter browsing by elk and in some cases by landscape position with regard to proximity to active streams. Winter browsing of Salix by elk significantly increased summer plant water potentials and integrative measures of gas exchange (Δ), though browsing did not consistently affect instantaneous rates of photosynthesis, leaf nitrogen or the sources of water used by Salix. No effect of experimental manipulations of surface water conditions on Salix physiology was observed, likely due to the mesic nature of our study period. Using a two-member linear mixing model, from δ18O values we calculated that Salix appears to rely on streams for approximately 80% of its water. In contrast, the graminoid Carex derives almost 50% of its water from rainfall, indicating divergent water source use by these two life forms. Based on these findings, winter browsing by elk improved Salix water balance possibly by altering the shoot to root ratio which in turn leads to higher water potentials and higher degrees of season-long gas exchange, while experimental damming had in general no effect on the physiological performance of Salix plants. In addition, as the water sources of Salix and Carex were significantly different, competition for water may not influence the growth, development, and regeneration of Salix. Thus, under the conditions of our study, herbivory had a positive effect on the physiological performance of Salix, but it is still unclear whether these changes in physiology transcend into improved Salix regeneration and survivorship. However, under drier environmental conditions such as lower snowpacks and lower stream flows, the browsing resistance of Salix and ecosystem regeneration may be greatly hindered because the reliance of Salix on stream water makes it vulnerable to changes in surface water and hydrological conditions.