Plant δ13C Research Articles

Regional-scale patterns of δ13C and δ15N associated with multiple ecosystem functions along an aridity gradient in grassland ecosystems

Arid and semi-arid grassland ecosystems cover 41% of the global land surface but are currently being degraded by increases in aridity and changes in land use. As a consequence, ecosystem services, including carbon (C) and nitrogen (N) sequestration, are being reduced. In this study, we determined whether stable isotopic C (δ13C) and N (δ15N) values can be used to explain patterns of multiple ecosystem functions related to C and N cycling in arid and semi-arid grasslands at the regional scale. Ecosystem (plant and soil) δ13C and δ15N values and ecosystem functions related to C and N cycling were investigated along an aridity gradient on the Mongolian Plateau. The gradient covered four vegetation grassland types with distinct characteristics of aridity and soil. We found that ecosystem δ13C and δ15N values increased while ecosystem functions decreased as aridity increased. Structural equation modelling revealed that aridity directly and indirectly affected plant δ13C values by affecting plant C/N and indirectly affected soil δ13C values by affecting plant and soil C/N and plant δ13C. Aridity directly and indirectly affected soil δ15N values by affecting soil C/N and soil pH, and indirectly affected plant δ15N values by affecting plant and soil C/N and soil δ15N. As indicated by ecosystem δ13C and δ15N values, the negative effects of aridity on ecosystem functions were mainly derived from the direct and indirect effects of aridity on C cycling and N cycling, respectively. Our findings suggest that ecosystem δ13C and δ15N values can be used to explain patterns of multiple ecosystem functions related to C and N cycling in arid and semi-arid grasslands at the regional scale. Consideration of ecosystem δ13C and δ15N values in predictive models will greatly increase the ability to accurately simulate how ecosystem functions change in response to the rapid degradation of semi-arid grasslands.

Impacts of Phragmites australis Invasion on Soil Enzyme Activities and Microbial Abundance of Tidal Marshes.

The rapid expansion of Phragmites australis in brackish marshes of the East Coast of the USA has drawn much attention, because it may change vegetation diversity and ecosystem functions. In particular, higher primary production of Phragmites than that of other native species such as Spartina patens and Schoenoplectus americanus has been noted, suggesting possible changes in carbon storage potential in salt marshes. To better understand the long-term effect of the invasion of Phragmites on carbon storage, however, information on decomposition rates of soil organic matter is essential. To address this issue, we compared microbial enzyme activities and microbial functional gene abundances (fungi, laccase, denitrifier, and methanogens) in three depths of soils with three different plants in a brackish marsh in Maryland, USA. Laccase and phenol oxidase activities were measured to assess the decomposition potential of recalcitrant carbon while β-glucosidase activity was determined as proxy for cellulose decomposition rate. Microbial activities near the surface (0-15cm) were the highest in Spartina-community sites followed by Phragmites- and Schoenoplectus-community sites. A comparison of stable isotopic signatures (δ13C and δ15N) of soils and plant leaves suggests that deep organic carbon in the soils mainly originated from Spartina, and only the surface soils may have been influenced by Phragmites litter. In contrast, fungal, laccase, and denitrifier abundances determined by real-time qPCR exhibited no discernible patterns among the surface soils of the three vegetation types. However, the abundance of methanogens was higher in the deep Phragmites-community soil. Therefore, Phragmites invasion will accelerate CH4 emission by greater CH4 production in deep soils with abundant methanogens, although enzymatic mechanisms revealed the potential for larger C accumulation by Phragmites invasion in salt marshes in the east coast of the USA.

Stable isotope compositions of South American camelids in the Dry Puna of Argentina: A frame of reference for the study of prehistoric herding and hunting strategies

The prehistoric pastoralist groups that inhabited the Dry Puna of Argentina employed a combination of subsistence strategies that included the herding of domestic South American camelids and the hunting of wild ones since ca. 3500yearsBP. The relative importance of both subsistence strategies to the prehistoric economy of these groups can be established through traditional zooarchaeological techniques, although how exactly herding and hunting practices developed and interacted both in space and time remains unknown. The general purpose of this work is to provide a tool to explore these questions through stable isotope analyses of animal tissues.We measured bone collagen δ13C and δ15N values of modern llamas and vicuñas, with the aim to account for the variation in the isotopic compositions of domesticated and wild South American camelids from the Dry Puna of Argentina in order to develop an appropriate frame of reference to address archaeofaunal and paleodietary data. Both δ13C (n=140, mean=−18.4 ‰) and δ15N (n=109, mean=+6.3 ‰) values showed a negative and significant correlation with altitude for llamas and vicuñas, which can be explained by the variation identified in plant δ13C and δ15N values and their correlation with altitude, as discussed in previous investigations. Based on these results we elaborated linear regressions models for both δ13C and δ15N values of both species, which will allow us to predict expected δ13C and δ15N values for archaeofaunal materials recovered at archaeological sites using altitude as the explanatory variable.

A native parasitic plant affects the performance of an introduced host regardless of environmental variation across field sites.

Increasing evidence from glasshouse studies shows that native hemiparasitic plants can significantly impact the performance and growth of introduced host plants. We investigated the effect of the native Australian hemiparasite Cassytha pubescens R.Br. on the introduced shrub Ulex europaeus L. at three field sites in South Australia. Parasite infection significantly decreased midday PSII efficiency (ΦPSII) and the maximum electron transport rates (ETRmax) of U. europaeus across sites. The impact of C. pubescens on the photosynthetic performance of U. europaeus may have been caused by infected plants having significantly lower N and K, but higher Fe and Al than uninfected plants at all sites. Significant Al and Fe enrichment in infected plants may be possibly due to the parasite indirectly inducing rhizosphere acidification. At two sites, C. pubescens significantly affected host Fv/Fm, indicating chronic photoinhibition in response to infection. The impact of infection on Fv/Fm was greatest at the wettest site, in line with an experiment where C. pubescens had more impact under high water availability. At this site, infected plants also had the highest foliar Fe and Al. The C isotope (δ13C) of infected plants was significantly lower than that of uninfected plants at only one site. Unusually, the δ13C of the parasite was the same as or significantly higher than that of the hosts. There were no site effects on parasite Fv/Fm or ΦPSII; however, ETRmax and δ13C varied across sites. The results suggest that this native parasite has negative effects on U. europaeus in the field, as was found for glasshouse studies. The abundance of this introduced weed in Australia could be negatively affected by C. pubescens infection.

Summer moisture changes in the Lake Qinghai area on the northeastern Tibetan Plateau recorded from a meadow section over the past 8400 yrs

Abstract Holocene climatic and environmental changes on the northeastern Tibetan Plateau (TP) have been widely discussed based on the climatic records from sedimentary cores. However, differences in the reconstructed climatic history from various studies in this region still exist, probably due to influence of climatic proxies from multiple factors and the chronological uncertainties in lacustrine sediments. Here we present records of terrestrial plant δ13C, soil color and total organic carbon content over the past 8400 years from a well-dated meadow section on the northeastern TP. The terrestrial plant δ13C value serves as a good summer precipitation/moisture indicator in the studied region. Soil color property and TOC content are also able to disentangle the moisture evolution history. All the data show much wet climates at 8400–7400 cal yr BP, dry climates at 7400–6000 cal yr BP and then wet conditions with fluctuation at 6000–3200 cal yr BP. Late Holocene moisture appears to be comparable with moist conditions from 6000 to 3200 cal yr BP. By further comparing the climatic variations in the Lake Qinghai area with records of the reconstructed summer temperature and the Asian Monsoon precipitation, we believe that the pattern of moisture/precipitation evolution in the Lake Qinghai area was not completely consistent with regions around Lake Qinghai, probably due to complicated interaction between the East Asian Summer Monsoon and the Indian Summer Monsoon.

Severe drought-influenced composition and δ13C of plant and soil n-alkanes in model temperate grassland and heathland ecosystems

Drought events are predicted to increase under future climate change. In temperate ecosystems, plants are capable of resisting drought due to their hydrophobic wax layer, in which n-alkanes are important constituents. In soils, plant-derived n-alkanes are comparatively resistant to degradation. To improve understanding of the significance of n-alkanes in plant-soil systems during a severe drought period (104 days), we investigated bulk organic carbon (Corg) concentration, total lipid extract (TLE) concentration, and n-alkane molecular ratios such as average chain length (ACL), carbon preference index (CPI) and chain length ratios of different n-alkane compounds, in addition to the compound-specific isotope composition (δ13C) of n-alkanes in model temperate grassland and heathland plant-soil systems. Although plant communities of two (heathland) and four (grassland) species were available, only one representative species per biome was accessible for the current study.Heathland plants and soil revealed significantly higher concentrations of Corg and TLE compared with grassland. TLE and alkane composition responded quickly during the first drought phase (0–40 days). This indicates that plants were actively utilizing C and produced more n-alkanes in order to withstand drought, which was confirmed by increased (2–3‰) δ13C values for n-alkanes in shoot biomass. However, during later drought phases all the parameters remained constant for plants and soils. This suggests limited change in biosynthesis and cycling of plant lipids such as n-alkanes during intense drought. Surprisingly, during the first drought phase, increased ACL and CPI values in soil demonstrated a rapid input of plant-derived long chain n-alkanes to soil, which was not expected due to the decadal residence time of alkanes in soil. The study enabled tracing of plant metabolic response in terms of alkane biosynthesis under different phases of drought and rapid cycling of alkanes in the plant-soil system.

Seasonal variation in natural abundance of δ13C and 15N in Salicornia brachiata Roxb. populations from a coastal area of India

ABSTRACTHigh and fluctuating salinity is characteristic for coastal salt marshes, which strongly affect the physiology of halophytes consequently resulting in changes in stable isotope distribution. The natural abundance of stable isotopes (δ13C and δ15N) of the halophyte plant Salicornia brachiata and physico-chemical characteristics of soils were analysed in order to investigate the relationship of stable isotope distribution in different populations in a growing period in the coastal area of Gujarat, India. Aboveground and belowground biomass of S. brachiata was collected from six different populations at five times (September 2014, November 2014, January 2015, March 2015 and May 2015). The δ13C values in aboveground (−30.8 to −23.6 ‰, average: −26.6 ± 0.4 ‰) and belowground biomass (−30.0 to −23.1 ‰, average: −26.3 ± 0.4 ‰) were similar. The δ13C values were positively correlated with soil salinity and Na concentration, and negatively correlated with soil mineral nitrogen. The δ15N values of aboveground (6.7–16.1 ‰, average: 9.6 ± 0.4 ‰) were comparatively higher than belowground biomass (5.4–13.2 ‰, average: 7.8 ± 0.3 ‰). The δ15N values were negatively correlated with soil available P. We conclude that the variation in δ13C values of S. brachiata was possibly caused by soil salinity (associated Na content) and N limitation which demonstrates the potential of δ13C as an indicator of stress in plants.

Carbon isotopes of C3 herbs correlate with temperature on removing the influence of precipitation across a temperature transect in the agro-pastoral ecotone of northern China.

Plant δ13C–temperature (δ‐T) relation has been established in many systems and is often used as paleotemperature transfer function. However, it is still unclear about the exact contributions of temperature variation to plant 13C discrimination because of covariation between temperature and precipitation (aridity), which reduces confidence in reconstruction of paleoclimate. In this study, we measured carbon isotope composition (δ13C) of 173 samples of C3 perennial herbs from 22 sites across a temperature gradient along the 400 mm isohyet in the farming‐pastoral zone of North China. The results showed that precipitation obviously affected the correlations of temperatures and foliar δ13C. After removing the influence of precipitation by analysis of covariance (ANCOVA), a more strongly positive relationship was obtained between site‐mean foliar δ13C and annual mean temperature (AMT), with a regression coefficient of 0.1636‰/°C (p = .0024). For widespread species, Artemisia lavandulaefolia and Artemisia capillaries, the slopes (or coefficients) of foliar δ13C and AMT were significantly steeper (larger) than those of foliar δ13C and AMT where the precipitation influence was not excluded, whereas the δ‐T coefficients of Polygonum persicaria and Leymus chinensis showed little change across the transect after deducting the precipitation effect. Moreover, the positive relationship between temperature and δ13C over the transect could be explained by soil moisture availability related to temperature. Our results may afford new opportunities for investigating the nature of past climate variability.

Decrypting stable‐isotope (δ13C and δ15N) variability in aquatic plants

Abstract Variability in C and N stable isotopes has been acknowledged to hinder their use as tracers of food sources in the study of trophic interactions in ecosystems. This is particularly so whenever benthic primary production is substantial (variability in δ13C) and the ecosystem under study is affected by human impacts (variability in δ15N) in aquatic ecosystems. In this study, we aim to better understand the large and often unexplained variability in the natural abundance of δ13C and δ15N signatures of aquatic plants by analyzing the isotopic composition of plants from 81 lentic systems from NE Spain in relation to extrinsic (alkalinity, pH, nutrient concentrations, water body typology and basin land use) and intrinsic (functional group, carbon assimilation metabolism, elemental composition) predictors. We have encountered significant plasticity in isotopic signatures of aquatic plants associated with the variation in local conditions at the regional scale. The δ13C signature varied from −43.1‰ to −7.5‰ (35.7‰ range) and drivers were both intrinsic and extrinsic. The functional group was the most important factor as it is influenced by different carbon sources. Aquatic plants with leaves in contact with the atmosphere (helophytes, free floating and floating attached; −34.8‰ to −14.6‰) responded in a similar way as terrestrial plants. This contrasted with the enriched mean values of rooted submerged plants (−16.7‰ to −10.5‰) that were more enriched than the described terrestrial C3 range (−34‰ to −22‰) and completely overlapped the terrestrial C4 range (−20‰ to −8‰). Concentration of DIC and pH also emerged as important extrinsic factors driving δ13C variability. The δ15N signature ranged from −5.2‰ to 20.1‰ (25.2‰ range) and the variability was mostly associated with extrinsic factors such as water body type and basin land use, as they influence both the δ15N signature and concentration of the dissolved inorganic nitrogen in the aquatic ecosystems. Only one multifactorial model including the functional group (with the largest contribution), DIC and pH was selected as the best model explaining the variability in δ13C signatures of aquatic plants. The final model had a relatively large explained deviance and was consistent with the previous unifactorial results. Two different models were selected as the best models explaining variability in δ15N signatures of aquatic plants. The models included the geomorphological type of water body as the variable with the largest contribution, and the percentage of either natural or agricultural coverage in the basin. These results are summarized in a conceptual model showing the predictors and their range and direction of variation. This study shows that extrinsic factors are of greater importance in influencing the stable‐isotope signatures of aquatic plants compared to terrestrial plants, because of varied sources and an often limited isotopic discrimination.

The δ13C of cellulose from modern plants and its responses to the atmosphere – From the peatland records of Dajiuhu, China

In this study, the values of δ13C in modern plants of the Dajiuhu Basin were determined, and correlation analysis was performed on various climatic factors influencing the values of δ13C in plants ...

Complex agriculture during the second millennium bc: isotope composition of carbon studies (δ13C) in archaeological plants of the settlement Cerro del Castillo de Alange (SW Iberian Peninsula, Spain)

The isotope composition of fruits and seeds of Hordeum vulgare L. (barley), Triticum aestivum/durum (wheat) and Vicia faba var. minor (faba bean) from three chronological phases between 2200 and 1321 cal bc of the settlement Cerro del Castillo de Alange (SW Iberian Peninsula) have been studied. The δ13C values for cereals were between −24.40 and −20.39‰ (V-PDB), with a mean of −22.01‰, the discrimination (Δ) being 15.96‰. The legumes registered similar values, between −26.25 and −20.49‰ (mean = −22.59‰), with a differential for the period of 16.51‰. In both cases, a change was noted from the first phase, where water availability is clearly a limiting factor for plant development. In subsequent phases the growing conditions appear be wetter. By comparison, we measured samples of Quercus ilex-coccifera (oak) charcoal, which shows similar values throughout the series. This suggests that there was no significant climate shift to moister conditions that could explain the above results, but rather they were the consequence of a change in crop management. In addition, we measured samples of a current rainfed Triticum sp. (year 2014), which averaged Δ13C 15.56‰. The changes between the three phases could indicate the development of mixed models of exploitation that combine strategies based on the use of rainfed and potentially irrigated areas during the 2nd millennium bc. The implementation of such a cropping technique, taking advantage of the river banks, could be a response to the processes of climatic degradation that begin in the Middle Holocene. The situation of the Cerro del Castillo reservoir between the rivers of the Guadiana and Matachel rivers is consistent with the development of this type of practice indicated by the isotopic and archaeobotanical data.

Soil organic carbon dynamics study bias deduced from isotopic fractionation in corn plant

Carbon stable isotope techniques were extensively employed to trace the dynamics of soil organic carbon (SOC) across a land-use change involving a shift to vegetation with different photosynthetic pathways. Based on the isotopic mass balance equation, relative contributions of new versus old SOC, and SOC turnover rate in corn fields were evaluated world-wide. However, most previous research had not analyzed corn debris left in the field, instead using an average corn plant δ 13C value or a measured value to calculate the proportion of corn-derived SOC, either of which could bias results. This paper carried out a detailed analysis of isotopic fractionation in corn plants and deduced the maximum possible bias of SOC dynamics study. The results show approximately 3‰ isotopic fractionation from top to bottom of the corn leaf. The 13C enrichment sequence in corn plant was tassel > stalk or cob > root > leaves. Individual parts accounting for the total dry mass of corn returned distinct values. Consequently, the average δ 13C value of corn does not represent the actual isotopic composition of corn debris. Furthermore, we deduced that the greater the fractionation in corn plant, the greater the possible bias. To alleviate bias of SOC dynamics study, we suggest two measures: analyze isotopic compositions and proportions of each part of the corn and determine which parts of the corn plant are left in the field and incorporated into SOC.

Nitrogen and carbon isotopic dynamics of subarctic soils and plants in southern Yukon Territory and its implications for paleoecological and paleodietary studies.

We examine here the carbon and nitrogen isotopic compositions of bulk soils (8 topsoil and 7 subsoils, including two soil profiles) and five different plant parts of 79 C3 plants from two main functional groups: herbs and shrubs/subshrubs, from 18 different locations in grasslands of southern Yukon Territory, Canada (eastern shoreline of Kluane Lake and Whitehorse area). The Kluane Lake region in particular has been identified previously as an analogue for Late Pleistocene eastern Beringia. All topsoils have higher average total nitrogen δ15N and organic carbon δ13C than plants from the same sites with a positive shift occurring with depth in two soil profiles analyzed. All plants analyzed have an average whole plant δ13C of −27.5 ± 1.2 ‰ and foliar δ13C of –28.0 ± 1.3 ‰, and average whole plant δ15N of −0.3 ± 2.2 ‰ and foliar δ15N of –0.6 ± 2.7 ‰. Plants analyzed here showed relatively smaller variability in δ13C than δ15N. Their average δ13C after suitable corrections for the Suess effect should be suitable as baseline for interpreting diets of Late Pleistocene herbivores that lived in eastern Beringia. Water availability, nitrogen availability, spacial differences and intra-plant variability are important controls on δ15N of herbaceous plants in the study area. The wider range of δ15N, the more numerous factors that affect nitrogen isotopic composition and their likely differences in the past, however, limit use of the modern N isotopic baseline for vegetation in paleodietary models for such ecosystems. That said, the positive correlation between foliar δ15N and N content shown for the modern plants could support use of plant δ15N as an index for plant N content and therefore forage quality. The modern N isotopic baseline cannot be applied directly to the past, but it is prerequisite to future efforts to detect shifts in N cycling and forage quality since the Late Pleistocene through comparison with fossil plants from the same region.

Stable isotopes of carbon and nitrogen help to predict the belowground communities at a regional scale

At the regional scale, although environmental factors are known to shape the distributions of belowground communities in terrestrial ecosystems, these environmental factors account for relatively low percentages of the variation in belowground communities. More of this variation might be explained by considering ecosystem stable isotopic values, which can provide insight into environmental conditions. Here, we investigated ecosystem (plant and soil) δ13C and δ15N values and belowground communities (microbes and nematodes) as well as environmental factors (climates, soils, and plants) across the Mongolian Plateau. The regression analyses showed that plant isotopic values were more closely associated with belowground communities than soil isotopic values, while ecosystem δ13C values were more closely associated with the belowground communities than ecosystem δ15N values. We also found isotopic values were more closely associated with nematode communities than microbial communities. Variation partioning analyses indicated that environmental variables together explained 16–45% of total variation in belowground communities. After isotopic variables were added as predictors to the variation partition analyses, the explanation of the variance was improved by14–24% for microbial communities and was improved by 23–44% for nematode communities. These findings indicate that isotopic values could be used to predict the properties of belowground communities at a regional scale.

Foliar δ13C Showed No Altitudinal Trend in an Arid Region and Atmospheric Pressure Exerted a Negative Effect on Plant δ13C.

Previous studies have suggested foliar δ13C generally increases with altitude. However, some observations reported no changes or even decreased trends in foliar δ13C. We noted that all the studies in which δ13C increased with elevation were conducted in the human regions, whereas those investigations in which δ13C did not vary or decreased were conducted in areas with water stress. Thus, we proposed that the pattern of increasing δ13C with elevation is not a general one, and that δ13C may remain unchanged or decrease in plants grown in arid environments. To test the hypothesis, we sampled plants along altitude gradients on the shady and sunny slopes of Mount Tianshan characterized by arid and semiarid climates. The measurements of foliar δ13C showed no altitudinal trends for the plants grown on either of the slopes. Therefore, this study supported our hypothesis. In addition, the present study addressed the effect of atmospheric pressure on plant δ13C by accounting for the effects of temperature and precipitation on δ13C. This study found that the residual foliar δ13C increased with increasing altitude, suggesting that atmospheric pressure played a negative role in foliar δ13C.

Different Patterns of Changes in Foliar Carbon Isotope Composition Along Altitude

ABSTRACT Three types of alpine plant species, Carex montis-everestii, Quercus aquifolioides and Stipa capillacea, along an altitudinal gradient of 3005–5025 m on the Tibetan Plateau, were chosen to test the generality of the hypothesis that foliar carbon isotope composition (δ13C) of C3 plants increases significantly with altitude and to determine climate drivers shaping its altitudinal pattern. Temperature and relative humidity showed significantly negative correlations with altitude; however, precipitation and soil water potential remained unchanged with altitude. Foliar δ13C of C. montis-everestii, Q. aquifolioides, S. capillacea alone or combined together did not significantly increase with altitude, which does not support the leading hypothesis of increased foliar δ13C with altitude. There was no difference in foliar δ13C among all three species. Multi-factor correlation analyses showed that temperature, precipitation and relative humidity alone did not affect foliar δ13C of C. montis-everestii and S...

Depth profiles of soil carbon isotopes along a semi-arid grassland transect in northern China

Soil is an important organic carbon (C) pool in terrestrial ecosystems, but knowledge on soil organic carbon (SOC) decomposition rate and influencing factors remains limited, particularly in arid and semi-arid grasslands. Models show that global semi-arid regions are experiencing more extreme climate events, which may trigger more C loss from soils. We used the stable carbon isotope (δ13C) of plant and soil depth profile to examine decomposition rates of SOC along a 2200 km semi-arid grassland transect in northern China. Beta (β) was calculated from the relationship between δ13C and C concentrations of plant and soil profile (0–100 cm). Partial correlation analysis and structure equation models were used to analyze correlations between beta and climatic and edaphic variables. We found that the δ13C values increased from plant tissues to surface soil and then deep soil at all sites, while the SOC concentration decreased. The β values ranged from −0.33 to −2.27, with an average value at −1.37. There was a positive correlation between β value and SOC decomposition rate constant (k), supporting the hypothesis that enrichment of δ13C along soil depth profile was mainly due to isotopic fractionation during microbial SOC decomposition. The correlation between β value and aridity index was mainly due to the variations of edaphic properties such as soil C/N ratio with aridity index, pointing to the more important role of edaphic properties in β value than climatic factors. Despite uncertainties associated with the interpretation of soil δ13C along its depth profile, our results demonstrated that soil δ13C could provide an independent benchmark for examining model-based predictions of SOC decomposition in semi-arid grasslands. Incorporation of both climatic and edaphic variables into models may enhance the predictions for SOC dynamics under global climate changes.

Carbon, nitrogen, and water stable isotopes in plant tissue and soils across a moisture gradient in Puerto Rico

AbstractStable isotopes in the water molecule (2H or D and 18O), carbon, and nitrogen are useful tracers and integrators of processes in plant ecohydrological systems across scales. Over the last few years, there has been growing interest in regional to continental scale synthesis of stable isotope data with a view to elucidating biogeochemical and ecohydrological patterns. Published datasets from the humid tropics, however, are limited. To be able to contribute to bridging the “data gap” in the humid tropics, here, we publish a relatively novel and unique suite of δ13C, δ15N, δ2H, and δ18O isotope data from three sites across a moisture gradient and contrasting land use in Puerto Rico. Plant tissue (xylem and leaf) samples from two species of mahogany (Swietenia macrophylla and Swietenia mahagoni) and soil samples down to 60 cm in the soil profile were collected in relatively “wet” (July 2012) and “dry” (February 2013) periods at two sites in northeastern (Luquillo) and southwestern (Susua) Puerto Rico. The same sampling suite is also being made available from a highly urbanized site in the capital San Juan. Leaf samples taken in July 2012 and February 2013 were analyzed for δ13C and δ15N; all xylem and bulk soil samples were analyzed for δ2H and δ18O. Soil samples taken in July 2012 were analyzed for δ13C and δ15N. Leaf δ15N and δ13C dataset showed patterns that are possibly associated with site differences. While spatial patterns were also apparent in soil δ15N and δ13C dataset, the positively linear δ15N –δ13C relationship tends to weaken with site moisture. Soil depth and site moisture patterns were also observed in the δ2H and δ18O datasets of bulk soil and xylem samples. The purpose of these datasets is to provide baseline information on soil–plant water (δ2H and δ18O, N = 319), δ13C (N = 272), and δ15N (N = 269) that may be useful in a wide range of research questions from ecohydrological relations to biogeochemical patterns in soils and vegetation.

Environmental and species-specific controls on δ13C and δ15N in dominant woody plants from central-western Argentinian drylands

Spatial variation in mean annual precipitation is the principal driver of plant water and nitrogen status in drylands. The natural abundance of carbon stable isotopes (δ13C) in photosynthetic tissues of C3 plants is an indicator of time-integrated behaviour of stomatal conductance; while that of nitrogen stable isotopes (δ15N) is an indicator of the main source of plant N (soil N vs. atmospheric N2). Previous studies in drylands have documented that plant δ13C and δ15N values increase with decreasing mean annual precipitation due to reductions in stomatal conductance, and soil enriched in 15N, respectively. However, evidence for this comes from studies focused on stable isotopes measurements integrated at the plant community level or on dominant plants at the site level, but little effort has been made to study C and N isotope variations within a species growing along rainfall gradients. We analysed plant δ13C, δ15N and C/N values of three woody species having different phenological leaf traits (deciduous, perennial and aphyllous) along a regional mean annual precipitation gradient from the central-western Argentinian drylands. Noticeably, plant δ13C and δ15N values in the three woody species did not increase towards sites with low precipitation or at the start of the growing season (drier period), as we expected. These results suggest that environmental factors other than mean annual precipitation may be affecting plant δ13C and δ15N. The short-term environmental conditions may interact with species-specific plant traits related to water and nitrogen use strategies and override the predictive influence of the mean annual precipitation on plant δ13C and δ15N widely reported in drylands.

Variation in δ13C and water use efficiency of plant leaf at different slopes in an alpine mea-dow

Through the systematical measurements of δ13C values of samples representing 25 families and 86 C3 herb species along the slope aspects in an alpine meadow, the responses of δ13C va-lues and water use efficiency (WUE) for C3 plants to slope aspect changes and influence of environmental factors were analyzed and main environmental factors related to plant δ13C values change were revealed. Along the north-facing to south-facing slope, soil water content decreased gradually, the soil temperature and light intensity increased gradually, and plant community structure also had corresponding change. The δ13C values of C3 plant species in 5 slope aspects were from -31.19‰ to -21.8‰, with an average value of (-27.18±0.13)‰. The average δ13C value was the highest along the south-facing slope, followed by that along the southwest slope, west slope and northwest slope, with the lowest along the north slope during the whole growing season. The difference of δ13C values among the different slope aspects were caused by discrepancy in soil water content, soil temperature and light intensity. Soil water content was the main limiting factor. From north slope to south slope, plant δ13C value increased with the increasing soil temperature, light intensity and the reducing soil water content, which suggested that different species had different strategies to adapt to environmental changes of drought stress in different slope aspects, and water use efficiency was improved gradually in order to adapt to the environment of drought stress.