Soil respiration patterns and controls in limestone cedar glades

Aims Drivers of soil respiration (R s ) in rock outcrop ecosystems remain poorly understood. We investigated these drivers in limestone cedar glades, known for their concentrations of endemic plant species and for seasonal hydrologic extremes (xeric and saturated conditions), and compared our findings to those in temperate grasslands and semi-arid ecosystems. Methods We measured R s , soil temperature (T s ), volumetric soil water content (SWC), soil organic matter (SOM), soil depth, and vegetation cover monthly over 16 mo and analyzed effects of these variables on R s . Results Seasonally, R s primarily tracked T s (r2 = 0.77; P \u3c 0.01), however R s was depressed during a summer drought. SOM was highly variable spatially, and incorporating SOM effects into the R s model dramatically improved model performance. Both shallow soil and sparse vegetation cover were also associated with lower R s . Conclusions Soil depth, SOM, and vegetation cover were important drivers of R s in limestone cedar glades. Seasonal R s patterns reflected those for mesic temperate grasslands more than for semi-arid ecosystems, in that R s primarily tracked temperature for most of the year

Experimental and modeling studies of canopy radiation and water use efficiencies, soil respiration and net ecosystem carbon exchange.

Canopy radiation and water use efficiencies (RUE and WUE), soil respiration and interannual availability in net ecosystem carbon exchange (NEE) are important issues in global climate change study. This thesis summarized four independent projects. Firstly, I used a unique environmentally controlled plant growth facility, EcoCELLs, to examine the effects of elevated [CO2] on RUE and WUE of sunflowers. Results indicated that elevated [CO2] enhanced daily total canopy carbon and water fluxes by 53% and 11%, respectively, resulting in 54% increase in RUE and 26% increase in WUE. Plant canopy consumed more water but utilized water and radiation more efficiently at elevated [CO 2]. Secondly, I investigated the effects of a gradual versus step increases in [CO2] on plant photosynthesis and growth at two nitrogen (N) levels in microcosms. The step CO2 treatment resulted in an immediate increase in photosynthetic carbon fixation, leading to a decrease in N concentration, while gradual CO2 treatment induced a gradual increase in photosynthesis, and less reduction in N concentration. Both the gradual and step CO2 increases resulted in decreases in specific leaf area, leaf N concentration but an increase in plant biomass. Thirdly, I applied a modified process-based soil respiration model (PATCIS) to evaluate soil CO2 production and transport at the Duke Forest FACE site. Simulated Soil CO2 efflux showed strong seasonal variations. Root respiration contributed 53% to total soil respiration. Annual Soil CO2 efflux was enhanced by elevated CO2. CO2 transport in the soil may not be an important restraint in surface CO2 efflux. Fourthly, I integrated regression analysis with analysis of variance to partition the interannual variability in NEE. Data of eddy-flux measurements in the Duke Forest showed that effects of the functional change exist in NEE. NEE was mainly controlled by intercepted PAR, VPD, and wind speed. About 16.1% of the variation was explained by interannual variability that caused by the functional change, 1.0% by the environmental factors change, and 70.5% was explained by the seasonal environmental factors change. Long-term measurements of RE and NEE are imperative for establishing sound relationship of NEE with environmental factors and interpreting interannual variation of NEE

Quantifying the short-term dynamics of soil organic carbon decomposition using a power function model

Introduction Soil heterotrophic respiration (R h, an indicator of soil organic carbon decomposition) is an important carbon efflux of terrestrial ecosystems. However, the dynamics of soil R h and its empirical relations with climatic factors have not been well understood. Methods We incubated soils of three subtropical forests at five temperatures (10, 17, 24, 31, and 38 °C) and five moistures (20, 40, 60, 80, and 100% water holding capacity (WHC)) over 90 days. R h was measured throughout the course of the incubation. Three types of models (log-linear, exponential, and power model) were fitted to the measurements and evaluated based on the coefficient of determination (r 2) and Akaike Information Criterion (AIC) of the model. Further regression analysis was used to derive the empirical relations between model parameters and the two climatic factors. Results Among the three models, the power function model (R h = R 1 t −k) performed the best in fitting the descending trend of soil R h with incubation time (r 2 \u3e 0.69 for 26 of 30 models). Both R 1 and k generally increased linearly with soil temperature but varied quadratically with soil moisture in the three forest soils. Conclusions This study demonstrated that the power function model was much more accurate than the exponential decay model in describing the decomposition dynamics of soil organic carbon (SOC) in mineral soils of subtropical forests. The empirical relations and parameter values derived from this incubation study may be incorporated into process-based ecosystem models to simulate R h responses to climate changes

Vertical distributions of soil microbial biomass carbon: a global dataset

Soil microbial biomass carbon (SMBC) is important in regulating soil organic carbon (SOC) dynamics along soil profiles by mediating the decomposition and formation of SOC. The dataset (VDMBC) is about the vertical distributions of SOC, SMBC, and soil microbial quotient (SMQ = SMBC/SOC) and their relations to environmental factors across five continents. Data were collected from literature, with a total of 289 soil profiles and 1040 observations in different soil layers compiled. The associated environment data collectd include climate, ecosystem types, and edaphic factors. We developed this dataset by searching the Web of Sciene and the China National Knowledge Infrastructure from the year of 1970 to 2019. All the data in this dataset met two creteria: 1) there were at least three mineral soil layers along a soil profile, and 2) SMBC was measured using the fumigation extraction method. The data in tables and texts were obtained from literature directly, and the data in figures were extracted by using the GetData Graph digitizer software version 2.25. When climate and soil properties were not available from publications, we obtainted the data from the World Weather Information Service (https://worldweather.wmo.int/en/home.html) and SoilGrids at a spatial resolution of 250 meters (version 0.5.3, https://soilgrids.org). The units of all the variables were converted to the standard international units or commonly used ones and the values were transformed correspondingly. For example, the value of soil organic matter (SOM) was converted to SOC by using the equation (SOC = SOM × 0.58). This dataset can be used in predicting global SOC changes along soil profiles by using the multi-layer soil carbon models. It can also be used to analyse how soil microbial biomass changes with plant roots as well as the composition, structure, and functions of soil microbial communities along soil profiles at large spatial scales. This dataset offers opportunities to improve our prediction of SOC dynamics under global changes and to advance our understanding of the environmental controls

Nutrient Resorption and Stoichiometric Characteristics of Wuyi Rock Tea Cultivars

Nutrient resorption is an important strategy for plants to retain critical nutrients from senesced leaves and plays important roles in nutrient cycling and ecosystem productivity. As a main economic crop and soil and water conservation species, Wuyi Rock tea has been widely planted in Fujian Province, China. However, foliar nutrient resorptions of Wuyi Rock tea cultivars have not been well quantified. In this study, three Wuyi Rock tea cultivars (Wuyi Jingui, Wuyi Rougui, and Wuyi Shuixian) were selected in the Wuyishan National Soil and Water Conservation, Science and Technology Demonstration Park. Resorption efficiencies of nitrogen (NRE), phosphorus (PRE), and potassium (KRE) along with their stoichiometric characteristics were determined. PRE of the three tea cultivars was significantly higher than KRE and NRE, indicating that tea cultivars were P limited due to low P availability for the tea growth. With the exception of Wuyi Rougui, leaf N and P contents of the other two cultivars (Wuyi Jingui and Wuyi Shuixian) had strong homeostasis under the changing soil environments. Leaf thickness and specific leaf area were positively and significantly correlated with KRE, and total chlorophyll concentration was positively correlated with NRE, indicating that leaf functional traits can be used as indicators for nutrient resorption status. Wuyi Rock tea cultivars had strong adaptabilities to the environments and had high carbon sequestration capabilities; thus, they and could be introduced into nutrient-poor mountainous areas for both economic benefits and soil and water conservation

Effects of Understory Vegetation and Litter on Plant Nitrogen (N), Phosphorus (P), N∶P Ratio and Their Relationships with Growth Rate of Indigenous Seedlings in Subtropical Plantations

Establishing seedlings in subtropical plantations is very important for forest health, succession and management. Information on seedling nutrient concentrations is essential for both the selection of suitable indigenous tree species to accelerate succession of the established plantation and sustainable forest management. In this study, we investigated the concentrations of nitrogen ([N]), phosphorus ([P]), and N∶P ratio in leaves, stems and roots of seedlings of three indigenous tree species (Castanopsis chinensis, Michelia chapensis and Psychotria rubra) transplanted with removing or retaining understory vegetation and litter at two typical subtropical forest plantations (Eucalyptus plantation and native species plantation). We also measured the relative growth rate (RGR) of seedling height, and developed the relationships between RGR and leaf [N], [P] and N∶P ratio. Results showed that treatments of understory vegetation and associated litter (i.e. removal or retained) generally had no significant effects on leaf [N], [P], N∶P ratio and RGR of the transplanted tree seedlings for the experimental period. But among different species, there were significant differences in nutrient concentrations. M. chapensis and P. rubra had higher [N] and [P] compared to C. chinensis. [N] and [P] also varied among different plant tissues with much higher values in leaves than in roots for all indigenous species. RGR of indigenous tree seedlings was mostly positively correlated with leaf [N] and [P], but negatively correlated with leaf N∶P ratio. Considering the low [P] and high N∶P ratio observed in the introduced indigenous tree seedlings, we propose that the current experimental plantations might be P limited for plant growth

Antioxidant and antidiabetic properties of Chinese and Indian bitter melons (Momordica charantia L.)

Bitter melon (Momordica charantia L.) has been used for anti-diabetes treatment for decades. Indian and Chinese bitter melons (BM) are two commonly produced cultivars in the US market. This study has comparatively evaluated the effects of two processing methods (fresh and freeze-drying) on Chinese and Indian BM by measuring their bioactivity in terms of total phenolic content (TPC), total triterpene content (TTC), antioxidant activity, and antidiabetic properties using the DPPH free radical scavenging and reducing power assays, and the α-amylase and α-glucosidase inhibition assays. The TPC (GAE mg/g dw) in freeze-dried BM were 6.03 and 6.09, and in fresh BM were 4.81 and 4.83 for Indian and Chinese BM, respectively. The TTC (OAE mg/g dw) in Indian BM were 7.25 and 5.63, and in Chinese BM were 5.88 and 3.87 for fresh and freeze-dried samples, respectively. TPC and TTC in the freeze-dried BM samples were significantly higher than that in the fresh ones (p \u3c 0.05). The DPPH IC50 of India BM was significantly lower than that of Chinese BM (p \u3c 0.05). All BM samples ranged from 9.18 to 18.6 mg/ml. The reducing power was significantly different between Indian and Chinese BM (p \u3c 0.01) for fresh samples, but after freeze-drying, there was no detectable difference in reducing power (p ≥ 0.05). The Indian BM showed a significantly stronger α-glucosidase inhibition effect as compared to the Chinese BM. TTC was positively correlated with reducing power (p \u3c 0.05). TPC was negatively correlated with α-amylase inhibition efficiency (p \u3c 0.05)

Differential Responses and Controls of Soil CO2 and N2O Fluxes to Experimental Warming and Nitrogen Fertilization in a Subalpine Coniferous Spruce (Picea asperata Mast.) Plantation Forest

Emissions of greenhouse gases (GHG) such as CO2 and N2O from soils are affected by many factors such as climate change, soil carbon content, and soil nutrient conditions. However, the response patterns and controls of soil CO2 and N2O fluxes to global warming and nitrogen (N) fertilization are still not clear in subalpine forests. To address this issue, we conducted an eight-year field experiment with warming and N fertilization treatments in a subalpine coniferous spruce (Picea asperata Mast.) plantation forest in China. Soil CO2 and N2O fluxes were measured using a static chamber method, and soils were sampled to analyze soil carbon and N contents, soil microbial substrate utilization (MSU) patterns, and microbial functional diversity. Results showed that the mean annual CO2 and N2O fluxes were 36.04 ± 3.77 mg C m−2 h−1 and 0.51 ± 0.11 µg N m−2 h−1, respectively. Soil CO2 flux was only affected by warming while soil N2O flux was significantly enhanced by N fertilization and its interaction with warming. Warming enhanced dissolve organic carbon (DOC) and MSU, reduced soil organic carbon (SOC) and microbial biomass carbon (MBC), and constrained the microbial metabolic activity and microbial functional diversity, resulting in a decrease in soil CO2 emission. The analysis of structural equation model indicated that MSU had dominant direct negative effect on soil CO2 flux but had direct positive effect on soil N2O flux. DOC and MBC had indirect positive effects on soil CO2 flux while soil NH4+-N had direct negative effect on soil CO2 and N2O fluxes. This study revealed different response patterns and controlling factors of soil CO2 and N2O fluxes in the subalpine plantation forest, and highlighted the importance of soil microbial contributions to GHG fluxes under climate warming and N deposition

Effects of the Interception of Litterfall by the Understory on Carbon Cycling in Eucalyptus Plantations of South China

For the purposes of forest restoration, carbon (C) fixation, and economic improvement, eucalyptus (Eucalyptus urophylla) has been widely planted in South China. The understory of eucalyptus plantations is often occupied by a dense community of the fern Dicranopteris dichotoma, which intercepts tree canopy leaf litter before it reaches the ground. To understand the effects of this interception of litterfall on C cycling in eucalyptus plantations, we quantified the mass of intercepted litter and the influences of litterfall interception on litter decomposition and soil respiration. The total mass of E. urophylla litterfall collected on the understory was similar to that collected by the traditional litter trap method. All of the eucalyptus litterfall is intercepted by the D. dichotoma canopy. Of the litterfall that was intercepted by D. dichotoma, 20–40% and 60–80% was intercepted by the top (50–100 cm) and bottom (0–50 cm) of the understory canopy, respectively. Intercepted litterfall decomposed faster at the bottom of understory canopy (at the base of the plants) than at the top, and decomposition was slower on the soil surface in the absence of understory than on any location in the understory canopy. Soil respiration was highest when both the understory and litter were present and was lowest when both the understory and litter were absent. These results indicate that litterfall interception changed carbon flow between aboveground and belowground through litter decomposition and soil respiration, which changed carbon cycling in eucalyptus plantations. The effects of the understory on litter decomposition and soil respiration should be considered in ecosystem carbon models