The coupling effects of water deficit and nitrogen supply on photosynthesis, WUE, and stable isotope composition in Picea asperata

Water stress and nitrogen (N) availability are the two main factors limiting plant growth, and the two constrains can interact in intricate ways. Moreover, atmospheric N depositions are altering the availability of these limiting factors in many terrestrial ecosystems. Here, we studied the combined effects of different soil water availability and N supply on photosynthesis and water-use efficiency (WUE) in Picea asperata seedlings cultured in pots, using gas exchange, and stable carbon and nitrogen isotope composition (delta C-13 and delta N-15). Photosynthesis under light saturation (A(sat)) and stomatal conductance (g(s)) of P. asperata decreased as the soil moisture gradually diminished. Under severe water-stress condition, N addition decreased the Asat and gs, whereas the positive effects were observed in moderate water-stress and well-watered conditions. The effect of N addition on the intrinsic WUE (WUEi) deduced from gas exchange was associated with soil water availability, whereas long-term WUE evaluated by leaf delta C-13 only affected by soil water availability, and it would be elevated with soil moisture gradually diminished. Water deficit would restrict the uptake and further transport of N to the aboveground parts of P. asperata, and then increasing delta N-15. Therefore, delta N-15 in plant tissues may reflect changes in N allocation within plants. These results indicate that the effect of N enrichment on photosynthesis in P. asperata is largely, if not entirely, dependent on the severity of water stress, and P. asperata would be more sensitive to increasing N enrichment under low soil water availability than under high soil moisture

Data from: Allocation to male vs. female floral function varies by currency and responds differentially to density and moisture stress

Allocation of finite resources to separate reproductive functions is predicted to vary across environments and affect fitness. Biomass is the most commonly measured allocation currency; however, in comparison with nutrients it may be less limited and express different environmental and evolutionary responses. Here, we measured carbon, nitrogen, phosphorus, and biomass allocation among floral whorls in recombinant inbred lines of Brassica rapa in multiple environments to characterize the genetic architecture of floral allocation, including its sensitivity to environmental heterogeneity and to choice of currency. Mass, carbon, and nitrogen allocation to female whorls (pistils and sepals) decreased under high density, whereas nitrogen allocation to male organs (stamens) decreased under drought. Phosphorus allocation decreased by half in pistils under drought, while stamen phosphorus was unaffected by environment. While the contents of each currency were positively correlated among whorls, selection to improve fitness through female (or male) function typically favored increased allocation to pistils (or stamens) but decreased allocation to other whorls. Finally, genomic regions underlying correlations among allocation metrics were mapped, and loci related to nitrogen uptake and floral organ development were located within mapped quantitative trait loci. Our candidate gene identification suggests that nutrient uptake may be a limiting step in maintaining male allocation. Taken together, allocation to male vs female function is sensitive to distinct environmental stresses, and the choice of currency affects the interpretation of floral allocation responses to the environment. Further, genetic correlations may counter the evolution of allocation patterns that optimize fitness through female or male function