Compound-specific isotopic analysis of amino acids (CSIA-AA) has emerged in the last decade as a powerful approach for tracing the origins and fate of nitrogen in ecological and biogeochemical studies. This approach is based on the empirical knowledge that source AAs (i.e., phenylalanine), fractionate 15 N very little (<0.5‰) during trophic transfer, whereas trophic AAs (i.e., glutamic acid), are greatly (~6-8‰) enriched in 15 N during each trophic step. The differential fractionation of these two AA groups can provide a valuable estimate of consumer trophic position that is internally indexed to the baseline δ 15 N value of the integrated food web. In this paper, we critically review the analytical methods for determining the nitrogen isotopic composition of AAs by gas chromatography/isotope-ratio mass spectrometry. We also discuss methodological considerations for accurate trophic position assessment of organisms using CSIA-AA. We then discuss the advantages and challenges of the CSIA-AA approach by examining published studies including trophic position assessment in various ecosystems, reconstruction of ancient human diets, reconstruction of animal migration and environmental variability, and assessment of marine organic matter dynamics. It is clear that the CSIA-AA approach can provide unique insight into the sources, cycling, and trophic modification of organic nitrogen as it flows through systems. However, some uncertainty still exists in how biochemical, physiological, and ecological mechanisms affect isotopic fractionation of trophic AAs. We end this review with a call for continued exploration of the mechanisms of AA isotopic fractionation, through various studies to promote the evolution of the rapidly growing field of CSIA-AA.

Two termite functional classifications (Abe’s lifetypes and Donovan’s feeding groups) are evaluated, and then synthesized to make a single unified ‘lifeway’ matrix classification with eight categories. The systematics and biogeography of the lifeway groups are outlined. The lifeways are then tested against other relevant data on termite ecology (stable isotopes, molecular probes, survey data) to show that they consistently reflect real distinctions in termite biology. The advantages and disadvantages of each lifeway are discussed in the context of energy availability, nitrogen balance, foraging and nest‐building energetics, and biogeographical dispersal ability. Finally, an ecological evolutionary scheme is outlined for the global ecology of termites using the lifeway classification as a framework.

1. Nitrogen and carbon stable-isotope ratios (δ 15 N and δ 13 C) of body tissues, mound/nest materials and dietary substrates were determined in termite species with differing trophic habits, sampled from the Mbalmayo Forest Reserve, southern Cameroon.2. δ 15 N of termite tissues was enriched gradually along a spectrum of species representing a trophic gradient from wood-to soil-feeding. Species that could be identified from their general biology and from gut content analysis as feeding on well-rotted wood or as wood/soil interface feeders showed δ 15 N intermediate between sound-wood-feeders and soil-feeders. It is proposed that δ 15 N is therefore a possible indicator of the functional position of species in the humification process. Differences in δ 13 C were also observed between wood-feeding and soil-feeding forms.3. High values of δ 15 N in soil-feeding termites suggest that nitrogen fixation is of little importance in these species. 4. A wide range of isotope effects (the difference in isotope ratios between termites and their diet) was observed for both nitrogen (∆δ 15 N ϭ -1.6 to ϩ 8.8‰) and carbon (∆δ 13 C ϭ -2.2 to ϩ 3.0‰), which suggests a diversity of nutrient acquisition mechanisms within termites and diverse relationships between termites and their intestinal micro-organisms.

Summary 1.To investigate whether the role of symbiotic fungi in lignin degradation and food provision differs among fungus-growing termites (four species of Macrotermes , three species of Odontotermes , Hypotermes makhamensis , Ancistrotermes pakistanicus and Pseudacanthotermes militaris ), the chemical composition of fungus combs of different ages and the chitinolytic activity in the gut of termites were analysed. In addition, the carbon stable isotope ratios ( δ 13 C) in old combs, worker termite tissues and fungal nodules (aggregated conidia) were compared. 2. In Macrotermes spp., the carbohydrate : lignin ratio of the combs increased with increased comb age, but it decreased or remained the same in Odontotermes spp., H. makhamensis , A. pakistanicus and P. militaris. In contrast, the chitin : carbohydrate ratio and ash content increased more over time in the combs of Odontotermes spp., H. makhamensis , A. pakistanicus and P. militaris than in the combs of Macrotermes spp. 3. Chitinolytic activity in the gut of workers was higher in O. takensis , H. makhamensis and A. pakistanicus than in M. annandalei . 4. In all species examined, the δ 13 C value increased in the sequence: old combs < termites < fungal nodules. Based on a two-source model of δ 13 C, the contribution of fungi to termite nutrition was considered higher in Odontotermes spp., H. makhamensis , A. pakistanicus and P. militaris than in Macrotermes spp. 5. These results suggest that symbiotic fungi play different roles among fungus-growing termites. In Macrotermes spp., the main role of symbiotic fungi is to degrade lignin, so that the termites can utilize cellulose more efficiently, whereas in Odontotermes spp., H. makhamensis , A. pakistanicus and P. militaris , it is to serve as a food source.

In a warming climate, temperature-sensitive plants must move toward colder areas, that is, higher latitude or altitude, by seed dispersal [1]. Considering that the temperature drop with increasing altitude (-0.65°C per 100 m altitude) is one hundred to a thousand times larger than that of the equivalent latitudinal distance [2], vertical seed dispersal is probably a key process for plant escape from warming temperatures. In fact, plant geographical distributions are tracking global warming altitudinally rather than latitudinally, and the extent of tracking is considered to be large in plants with better-dispersed traits (e.g., lighter seeds in wind-dispersed plants) [1]. However, no study has evaluated vertical seed dispersal itself due to technical difficulty or high cost. Here, we show using a stable oxygen isotope that black bears disperse seeds of wild cherry over several hundred meters vertically, and that the dispersal direction is heavily biased towards the mountain tops. Mountain climbing by bears following spring-to-summer plant phenology is likely the cause of this biased seed dispersal. These results suggest that spring- and summer-fruiting plants dispersed by animals may have high potential to escape global warming. Our results also indicate that the direction of vertical seed dispersal can be unexpectedly biased, and highlight the importance of considering seed dispersal direction to understand plant responses to past and future climate change.

Methane and hydrogen emission rates and the δ13C of CH4 were observed for various termites in Australia, Thailand and Japan. Combined with the already reported emission rates of CH4 in the literature, the phylogenetic trend was examined. Emission rates of the observed termites were categorized into five groups: group I with high CH4 and low H2 emission rates with a CH4/H2 ratio of typically 10/1; group II with high CH4 and high H2 emissions with a CH4/H2 ratio of 4/1–1/2; group III with low emission rates of CH4 and H2; group IV with high H2 and insignificant CH4 emissions; and group V with insignificant emissions for both CH4 and H2. In lower termites, there are both colonies infected and uninfected with methanogens even in the same species, and no specific trend in CH4 and H2 emissions was observed within a genus. Whether protozoa in the hindgut of termites are infected with methanogens or not and the differences in species compositions of protozoa are possibly responsible for the inter‐colonial variations. The proportions of infected colonies were possibly small for the family Kalotermitidae (dry wood feeders), and relatively large for families of wet or damp wood feeders. The hydrogen emission rate possibly depends on the locality of methanogens: namely, whether they are intracellular symbionts of protozoa or whether they are attached to the hindgut wall. Emission rates of higher termites were classified into groups according to genera and the diet. Most species of soil or wood/soil interface feeders classified into group I, while the soil feeders Dicuspiditermes in Thailand and Amitermes in Australia were classified into groups with high H2 emission rates. Typical wood‐feeding termites and fungus‐growing termites were classified into group III. The results indicate that higher termites tend to increase the CH4 emission rate during dietary evolution from wood‐ to soil‐feeding, and two types of the system with different efficiencies of interspecies transfer of H2 have been formed. The δ13C of CH4 was discernible with a difference in the decomposition process in the termite–symbiont system among lower termites, fungus‐growing termites and other higher termites.

Summary1. Many tree species undergo large fluctuations from year to year in seed production, a phenomenon known as masting. The resource budget model, based on the assumption that abundant seeding in a masting year depends on the abundance of resources stored over several years, is a key hypothesis in explaining the mechanism of masting. But do masting species really need such long-term storage to produce a large seed crop? 2. To test this hypothesis, we studied the relationship between the carbon accumulation period for seed production, as estimated by radiocarbon ( 14 C) analyses, and the coefficient of variation of annual seed production in 10 canopy tree species in a temperate deciduous forest. These species differ widely in their reproductive intervals. 3. In all the species studied, the accumulation period was < 1.4 years before seed maturation. Moreover, without taking species or reproductive intervals into account, there was no significant correlation between the carbon accumulation period and the fluctuation of annual seed production; both remained at an even level. 4. Synthesis. Our results suggest that temperate canopy trees used photosynthates produced in the current and/or the previous year for seed production, regardless of reproductive intervals. It might therefore be necessary to reconsider the importance of stored carbohydrate resources for masting.

Summary Mycoheterotrophic plants depend entirely on fungal associations for organic nutrients. While most mycoheterotrophic plants are associated with the mycorrhizal partners of surrounding green plants, some mycoheterotrophs are believed to obtain carbon from decaying litter or dead wood by parasitising saprotrophic fungi, based on culture experiments and 13C and 15N isotopic signatures. The carbon age (the time since carbon was fixed from atmospheric CO2 by photosynthesis) can be estimated by measuring the concentration of 14C arising from the bomb tests of the 1950s and 1960s. Given that mycorrhizal fungi obtain photosynthate from their plant partners, and saprotrophic wood‐decaying fungi obtain carbon from older sources, radiocarbon could represent a new and powerful tool to investigate carbon sources of mycoheterotrophic plants. We showed that the Δ14C values of mycoheterotrophs exploiting ectomycorrhizal fungi were close to 0‰, similar to those of autotrophic plants. By contrast, the Δ14C values of mycoheterotrophs exploiting saprotrophic fungi ranged from 110.7‰ to 324.8‰, due to the 14C‐enriched bomb carbon from dead wood via saprotrophic fungi. Our study provides evidence supporting that some mycoheterotrophic orchids depend on forest woody debris. Our study also indicates that radiocarbon could be used to predict the trophic strategies of mycoheterotroph‐associated fungal symbionts.