Light- and CO₂-saturated net CO₂ assimilation rate (<i>A</i>_max), maximum carboxylation rate (<i>V</i>_cmax), and maximum electron transport rate (<i>J</i>_max) in 10 Jianfengling tree species leaves.

<p>Light- and CO₂-saturated net CO₂ assimilation rate (<i>A</i>_max), maximum carboxylation rate (<i>V</i>_cmax), and maximum electron transport rate (<i>J</i>_max) in 10 Jianfengling tree species leaves.</p

The average PNUE and related factors for Leguminosae and Fagaceae tree species, and a sensitivity analysis to assess the relative importance of each of these factors in explaining the difference in PNUE.

<p>The average PNUE and related factors for Leguminosae and Fagaceae tree species, and a sensitivity analysis to assess the relative importance of each of these factors in explaining the difference in PNUE.</p

Fagaceae tree species allocate higher fraction of nitrogen to photosynthetic apparatus than Leguminosae in Jianfengling tropical montane rain forest, China - Fig 2

<p><b>Regression analysis of the fraction of leaf nitrogen allocated to (a) the photosynthetic apparatus (<i>P</i></b>_<b>P</b><b>), (b) light-harvesting components (<i>P</i></b>_<b>L</b><b>), (c) Rubisco (<i>P</i></b>_<b>R</b><b>), and (d) bioenergetics (<i>P</i></b>_<b>B</b><b>) with photosynthetic-nitrogen use efficiency (PNUE) in 10 Jianfengling tree species leaves.</b> The determination coefficient (<i>R</i>²) and <i>P</i>-value are shown. The lines fitted separately for Leguminosae and Fagaceae families are significantly different in plots <b>b</b> (<i>P</i><0.05) according to the result of a one-way ANCOVA with PNUE as a dependent variable, families as fixed factors, and <i>P</i>_L as a covariate.</p

Fagaceae tree species allocate higher fraction of nitrogen to photosynthetic apparatus than Leguminosae in Jianfengling tropical montane rain forest, China

<div><p>Variation in photosynthetic-nitrogen use efficiency (PNUE) is generally affected by several factors such as leaf nitrogen allocation and leaf diffusional conductances to CO₂, although it is still unclear which factors significantly affect PNUE in tropical montane rain forest trees. In this study, comparison of PNUE, photosynthetic capacity, leaf nitrogen allocation, and diffusional conductances to CO₂ between five Fagaceae tree species and five Leguminosae tree species were analyzed in Jianfengling tropical montane rain forest, Hainan Island, China. The result showed that PNUE of Fagaceae was significantly higher than that of Leguminosae (+35.5%), attributed to lower leaf nitrogen content per area (<i>N</i>_area, –29.4%). The difference in nitrogen allocation was the main biochemical factor that influenced interspecific variation in PNUE of these tree species. Fagaceae species allocated a higher fraction of leaf nitrogen to the photosynthetic apparatus (<i>P</i>_P, +43.8%), especially to Rubisco (<i>P</i>_R, +50.0%) and bioenergetics (<i>P</i>_B +33.3%) in comparison with Leguminosae species. Leaf mass per area (LMA) of Leguminosae species was lower than that of Fagaceae species (-15.4%). While there was no significant difference shown for mesophyll conductance (<i>g</i>_m), Fagaceae tree species may have greater chloroplast to total leaf surface area ratios and that offset the action of thicker cell walls on <i>g</i>_m. Furthermore, weak negative relationship between nitrogen allocation in cell walls and in Rubisco was found for <i>Castanopsis hystrix</i>, <i>Cyclobalanopsis phanera</i> and <i>Cy</i>. <i>patelliformis</i>, which might imply that nitrogen in the leaves was insufficient for both Rubisco and cell walls. In summary, our study concluded that higher PNUE might contribute to the dominance of most Fagaceae tree species in Jianfengling tropical montane rain forest.</p></div

Fraction of leaf nitrogen allocated to Rubisco (<i>P</i>_R), bioenergetics (<i>P</i>_B), light-harvesting components (<i>P</i>_L), photosynthetic apparatus (<i>P</i>_P), cell wall (<i>P</i>_CW), and other parts (1-<i>P</i>_P-<i>P</i>_CW, <i>P</i>_Other) in 10 Jianfengling tree species leaves.

<p>Fraction of leaf nitrogen allocated to Rubisco (<i>P</i>_R), bioenergetics (<i>P</i>_B), light-harvesting components (<i>P</i>_L), photosynthetic apparatus (<i>P</i>_P), cell wall (<i>P</i>_CW), and other parts (1-<i>P</i>_P-<i>P</i>_CW, <i>P</i>_Other) in 10 Jianfengling tree species leaves.</p

Stomatal conductance (<i>g</i>_s), mesophyll conductance (<i>g</i>_m), intercellular CO₂ concentration (<i>C</i>_i), CO₂ concentration at carboxylation site (<i>C</i>_c) in 10 Jianfengling tree species leaves.

<p>Stomatal conductance (<i>g</i>_s), mesophyll conductance (<i>g</i>_m), intercellular CO₂ concentration (<i>C</i>_i), CO₂ concentration at carboxylation site (<i>C</i>_c) in 10 Jianfengling tree species leaves.</p

Light-saturated photosynthesis (<i>A</i>_max’), leaf nitrogen content per area (<i>N</i>_area), leaf mass per area (LMA) and photosynthetic-nitrogen use efficiency (PNUE) in 10 Jianfengling tree species leaves.

<p>Light-saturated photosynthesis (<i>A</i>_max’), leaf nitrogen content per area (<i>N</i>_area), leaf mass per area (LMA) and photosynthetic-nitrogen use efficiency (PNUE) in 10 Jianfengling tree species leaves.</p

Mesophyll conductance (<i>g</i>_m) in relation to photosynthetic-nitrogen use efficiency (PNUE) in 10 Jianfengling tree species leaves.

<p>There was no significant difference between <i>g</i>_m calculated by three methods, we use the mean value of three <i>g</i>_m (Harley, Ethier and Gu).</p

Image_2_The effects of ectomycorrhizal and saprotropic fungi on soil nitrogen mineralization differ from those of arbuscular and ericoid mycorrhizal fungi on the eastern Qinghai-Tibetan Plateau.jpeg

Interactions between soil fungi and soil environmental factors regulate soil nitrogen (N) mineralization rates on the eastern Qinghai-Tibetan Plateau. Some studies have also illuminated differences in soil N mineralization rate based on different mycorrhizal forests, but the associated effect of soil fungal functional guilds and soil environmental factors underlying this process are not well-understood. Three primary forests respectively dominated by Abies fargesii var. faxoniana (ectomycorrhizal, EcM), Cupressus chengiana (arbuscular mycorrhizal, AM) and Rhododendron phaeochrysum (ericoid mycorrhizal, ErM) trees were selected in this area. Meanwhile, soil net N mineralization rate, soil fungal composition and soil enzyme activity among these three mycorrhizal forests were studied. Our results showed that there were significant differences in the seasonal variation of soil net N mineralization rates among three mycorrhizal forests. Soil net N mineralization rate in the AM forest was faster. EcM fungi and saprotroph are the main functional guilds in these three mycorrhizal forests. Meanwhile, the relative abundances of soil fungal functional guilds, soil temperature and soil peroxidase activity could explain 85.0% in the difference of soil net ammonification rate among three mycorrhizal forests. In addition, soil temperature, soil water-filled pore space and soil ammonium content play a central role in controlling the differing soil net nitrification rate among three mycorrhizal forests. Our results suggest differences in soil net mineralization among different mycorrhizal forest types are driven mainly by soil net ammonification. Soil fungal functional guilds and temperature regulate the rate of soil net ammonification by modulating soil peroxidase activity.</p

Fraction of leaf nitrogen allocated to the cell wall (<i>P</i>_CW) in relation to the fraction of leaf nitrogen allocated to Rubisco (<i>P</i>_R) in 10 Jianfengling tree species leaves.

<p>The shaded zone represents the distribution area of <i>P</i>_CW and <i>P</i>_R when trade-off existed [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0192040#pone.0192040.ref018" target="_blank">18</a>].</p