Correlations between net primary productivity and foliar carbon isotope ratio across a Tibetan ecosystem transect

Abstract

Warming climate could affect leaf-level carbon isotope composition (d 13 C) through variations in photosynthetic gas exchange. However, it is still unclear to what extent variations in foliar d 13 C can be used to detect changes in net primary productivity (NPP) because leaf physiology is only one of many determinants of stand productivity. We aim to examine how well site-mean foliar d 13 C and stand NPP co-vary across large resource gradients using data obtained from the Tibetan Alpine Vegetation Transects (1900Á4900 m, TAVT). The TAVT data indicated a robust negative correlation between foliar d 13 C and NPP across ecosystems (NPP 0(2.7224d 13 C-67.738, r 2 00.60, p B0.001). The mean foliar d 13 C decreased with increasing annual precipitation and its covariation with mean temperature and soil organic carbon and nitrogen contents. The results were further confirmed by global literature data. Pooled d 13 C data from global literature and this study explained 60% of variations in annual NPP both from TAVT-measures and MODIS-estimates across 67 sites. Our results appear to support a conceptual model relating foliar d 13 C and nitrogen concentration (N mass ) to NPP, suggesting that: 1) there is a general (negative) relationship between d 13 C and NPP across different water availability conditions; 2) in water-limited conditions, water availability has greater effects on NPP than N mass ; 3) when water is not limiting, NPP increases with increasing N mass .

Seasonal variations in leaf δ13C and nitrogen associated with foliage turnover and carbon gain for a wet subalpine fir forest in the Gongga Mountains, eastern Tibetan Plateau

“…(1) and (2) indicated that when the E/E m ratio was more than 0.85, NPP varied little with water availability but linearly increased with increasing N mass . The threshold of water limitation of E/E m < 0.85 has been confirmed by the Tibetan transect data (Luo et al 2009). Globally, forest NPP increases with increasing precipitation when annual precipitation is lower than the threshold level of 150 cm (Luyssaert et al 2007) consistent with the Tibetan transect data (Luo et al 2004).…”

“…(1). The TAVT data are found in Luo et al (2009) For 1-4(5)-year-old needles, the d 13 C showed significantly positive correlations with air temperature, soil temperature, pan evaporation, and photosynthetically active radiation (p < 0.01) ( Table 2). In contrast, the d 13 C in new and 6-7-year-old needles showed no significant relationships with climatic variables of current year (1999, Table 2) and previous years (1998 and before, data not shown).…”

Abiotic, Biotic, and Evolutionary Control of the Distribution of C and N Isotopes in Food Webs

“…The sole source of carbon for green plants is air carbon dioxide, and the C 3 photosynthetic pathway is adopted by all study species-aspects that simplify fractionation pathways and determine species' convergent responses. Mixed C 3 -C 4 plant assemblages typical of low latitudes in fact display abrupt divergence in this aspect (Körner et al 1988;Luo et al 2009). Conversely, strong phylogenetic dependence has been found for plant d 15 N and %N, and indeed a greater diversity of functional and physiological mechanisms govern the nitrogen compared with the carbon cycle.…”

“…; Vitousek et al 1990). These long-and short-term strategies indirectly determine d 13 C variation along elevation (Luo et al 2009) and also explain its responsiveness to changes in growing season precipitation (table 3). The value of d 13 C was also influenced by plant nitrogen content, possibly because of the photosynthetic requirement for this element.…”

“…The natural abundances of carbon and nitrogen isotopes are sen-sitive to changes and anomalies in nutrient cycles following abiotic and biotic forces. In particular, climate is the factor most frequently associated with geographic (latitudinal, elevational) variation of isotopic content in terrestrial organisms (Körner et al 1991;Hobson 1999;Luo et al 2009), especially with respect to water availability and temperature, which control the microbial transformation of nitrogen and the fixation of carbon dioxide by plant photosynthetic activity (Ehleringer and Dawson 1992;Lipson et al 1999;Huber et al 2007). Biotic components speed nutrient cycling rates and condition the stable isotope ratios of both producers (e.g., grazing, symbiotic associations) and consumers (trophic relationships; Frank et al 2000;Post 2002).…”