Contrasting responses of soil microbial biomass and extracellular enzyme activity along an elevation gradient on the eastern Qinghai-Tibetan Plateau

Soil microbial community composition and extracellular enzyme activity are two main drivers of biogeochemical cycling. Knowledge about their elevational patterns is of great importance for predicting ecosystem functioning in response to climate change. Nevertheless, there is no consensus on how soil microbial community composition and extracellular enzyme activity vary with elevation, and little is known about their elevational variations on the eastern Qinghai-Tibetan Plateau, a region sensitive to global change. We therefore investigated the soil microbial community composition using phospholipid fatty acids (PLFAs) analysis, and enzyme activities at 2,820 m (coniferous and broadleaved mixed forest), 3,160 m (dark coniferous forest), 3,420 m (alpine dwarf forest), and 4,280 m (alpine shrubland) above sea level. Our results showed that soil microbial community composition and extracellular enzyme activities changed significantly along the elevational gradient. Biomass of total microbes, bacteria, and arbuscular mycorrhizal fungi at the highest elevation were the significantly lowest among the four elevations. In contrast, extracellular enzyme activities involved in carbon (C)-, nitrogen (N)-, and phosphorus (P)- acquiring exhibited the maximum values at the highest elevation. Total nutrients and available nutrients, especially P availability jointly explained the elevational pattern of soil microbial community, while the elevational variation of extracellular enzyme activities was dependent on total nutrients. Microbial metabolism was mainly C- and P-limited with an increasing C limitation but a decreasing P limitation along the elevational gradient, which was related significantly to mean annual temperature and total P. These results indicated a vital role of soil P in driving the elevational patterns of soil microbial community and metabolism. Overall, the study highlighted the contrasting responses of soil microbial biomass and extracellular enzyme activities to elevation, possibly suggesting the differences in adaption strategy between population growth and resource acquisition responding to elevation. The results provide essential information for understanding and predicting the response of belowground community and function to climate change on the eastern Qinghai-Tibetan Plateau

Temporal Variability in Soil Greenhouse Gas Fluxes and Influencing Factors of a Primary Forest on the Eastern Qinghai-Tibetan Plateau

Soil greenhouse gas (GHG) fluxes relate to soil carbon and nitrogen budgets and have a significant impact on climate change. Nevertheless, the temporal variation and magnitude of the fluxes of all three major GHGs (CO2, CH4 and N2O) and their influencing factors have not been elucidated clearly in primary forests on the eastern Qinghai-Tibetan Plateau. Herein, field chamber GHG fluxes from May to November, soil microbial community and enzyme activity were analyzed in a fir-dominated (Abies fargesii var. faxoniana) primary forest. The emission rates of CO2 and N2O ranged between 64.69–243.22 mg CO2 m−2 h−1 and 1.69–5.46 ug N2O m−2 h−1, exhibiting a temporally unimodal pattern with a peak in July. The soil acted as a CH4 sink, and the uptake rate varied between 52.96 and 84.67 μg CH4 m−2 h−1 with the higher uptake rates in June and November. The temporal variation in the CO2 flux was significantly correlated with the geometric mean of enzyme activities, suggesting that the soil CO2 flux was determined by microbial activity rather than soil microbial biomass. The soil N2O flux was positively related to nitrate concentration with marginal significance, probably because N2O was a byproduct of nitrification and denitrification processes. The soil CH4 uptake was closely associated with methanotrophic biomass (18:1ω7c). The results highlight divergent temporal dynamics of GHG fluxes owing to different driving mechanisms and an important CH4 sink in the primary forest soil, helping to evaluate the carbon and nitrogen budgets of primary forests on the eastern Qinghai-Tibetan Plateau

Maxent modeling for predicting impacts of climate change on the potential distribution of Thuja sutchuenensis Franch., an extremely endangered conifer from southwestern China

Objectives Detailed and reliable information about the spatial distribution of species provides important information for species conservation management, especially in the case of rare species of conservation interest. We aimed to study the consequences of climate change on geographical distributions of the tertiary rare tree species Thuja sutchuenensis Franch. (Cupressaceae) to provide reference for conservation management of this species, including priority area selection for introduction and cultivation of the species. We expect that this approach could be promising in predicting the potential distribution of other rare tree species, and as such can be an effective tool in rare tree species restoration and conservation planning, especially species with narrow distribution or raw presence-only occurrence data. Methods 107 records covering the whole distribution range of T. sutchuenensis in the Daba Mountains were obtained during a 3-year field survey. The principle of maximum entropy (Maxent) was used to model the species' potential distribution area under paleoclimate, current and future climate background. Results The Maxent model was highly accurate with a statistically significant AUC value of 0.998, which is higher than 0.5 of a null model; The location of the potential distribution for the last interglacial period is in southeastern China, with the largest optimal habitat area being only 1666 km(2). In other periods, the central location of the potential distribution is accordant with the real present distribution, but the model's predicted optimal habitat area is outside the current distribution. Conclusions Our findings can be applied in various ways such as the identification of additional localities where T. sutchuenensis may already exist, but has not yet been detected; the recognition of localities where it is likely to spread to; the priority selection area for introduction and cultivation and the conservation management of such rare tree species. (C) 2017 The Authors. Published by Elsevier B.V

Maxent modeling for predicting impacts of climate change on the potential distribution of Thuja sutchuenensis Franch., an extremely endangered conifer from southwestern China

Objectives: Detailed and reliable information about the spatial distribution of species provides important information for species conservation management, especially in the case of rare species of conservation interest. We aimed to study the consequences of climate change on geographical distributions of the tertiary rare tree species Thuja sutchuenensis Franch. (Cupressaceae) to provide reference for conservation management of this species, including priority area selection for introduction and cultivation of the species. We expect that this approach could be promising in predicting the potential distribution of other rare tree species, and as such can be an effective tool in rare tree species restoration and conservation planning, especially species with narrow distribution or raw presence-only occurrence data. Methods: 107 records covering the whole distribution range of T. sutchuenensis in the Daba Mountains were obtained during a 3-year field survey. The principle of maximum entropy (Maxent) was used to model the species’ potential distribution area under paleoclimate, current and future climate background. Results: The Maxent model was highly accurate with a statistically significant AUC value of 0.998, which is higher than 0.5 of a null model; The location of the potential distribution for the last interglacial period is in southeastern China, with the largest optimal habitat area being only 1666 km2. In other periods, the central location of the potential distribution is accordant with the real present distribution, but the model’s predicted optimal habitat area is outside the current distribution. Conclusions: Our findings can be applied in various ways such as the identification of additional localities where T. sutchuenensis may already exist, but has not yet been detected; the recognition of localities where it is likely to spread to; the priority selection area for introduction and cultivation and the conservation management of such rare tree species

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

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

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

Does Forest Soil Fungal Community Respond to Short-Term Simulated Nitrogen Deposition in Different Forests in Eastern China?

Nitrogen (N) deposition has changed plants and soil microbes remarkably, which deeply alters the structures and functions of terrestrial ecosystems. However, how forest fungal diversity, community compositions, and their potential functions respond to N deposition is still lacking in exploration at a large scale. In this study, we conducted a short-term (4–5 years) experiment of artificial N addition to simulated N deposition in five typical forest ecosystems across eastern China, which includes tropical montane rainforest, subtropical evergreen broadleaved forest, temperate deciduous broadleaved forest, temperate broadleaved and conifer mixed forest, and boreal forest along a latitudinal gradient from tropical to cold temperature zones. Fungal compositions were identified using high-throughput sequencing at the topsoil layer. The results showed that fungal diversity and fungal community compositions among forests varied apparently for both unfertilized and fertilized soils. Generally, soil fungal diversity, communities, and their potential functions responded sluggishly to short-term N addition, whereas the fungal Shannon index was increased in the tropical forest. In addition, environmental heterogeneity explained most of the variation among fungal communities along the latitudinal gradient. Specifically, soil C: N ratio and soil water content were the most important factors driving fungal diversity, whereas mean annual temperature and microbial nutrient limitation mainly shaped fungal community structure and functional compositions. Topsoil fungal communities in eastern forest ecosystems in China were more sensitive to environmental heterogeneity rather than short-term N addition. Our study further emphasized the importance of simultaneously evaluating soil fungal communities in different forest types in response to atmospheric N deposition