Depth-driven responses of microbial residual carbon to nitrogen addition approaches in a tropical forest: Canopy addition versus understory addition.

Canopies play an important role in nitrogen (N) redistribution in forest ecosystems, and ignoring the canopy's role might bias estimates of the ecological consequences of anthropogenic atmospheric N deposition. We investigated the effects of the approach of N addition (Canopy addition vs. Understory addition) and level of N addition (25 kg N hayr vs.

Leaf hydraulic acclimation to nitrogen addition of two dominant tree species in a subtropical forest.

Plant hydraulic traits have been shown to be sensitive to changes in nitrogen (N) availability in short-term studies largely using seedlings or saplings. The extent and the magnitude of N-sensitivity of the field grown mature trees in long-term experiments, however, are relatively unknown. Here, we investigated responses of leaf water relations and morphological and anatomical traits of two dominant tree species (Castanopsis chinensis and Schima superba) to a six-year canopy N addition in a subtropical forest.

Effects of urbanization on plant phosphorus availability in broadleaf and needleleaf subtropical forests.

Urbanization, the migration of populations from rural to urban areas, has been causing great stress on natural environments, leading to air pollution and nitrogen (N) deposition, negatively affecting forest health. Although there is evidence that urbanization has changed forest N cycling, little is known about whether urbanization also changes the availability of phosphorus (P), which is important for plant growth and forest productivity. To address this question, we carried out a survey in the Pearl River Delta region, the world's largest urban area in southern China, using two types of representative forests, the evergreen broadleaf forests (BFs) and pine plantations (PPs).

Sulfur deposition still contributes to forest soil acidification in the Pearl River Delta, South China, despite the control of sulfur dioxide emission since 2001.

Sulfur dioxide emissions have been regulated at a global scale; sulfur (S) deposition no longer contributes to soil acidification instead of an alleviation effect in temperate regions; however, it remains unclear whether S deposition still contributes to soil acidification in the tropics. The Pearl River Delta (PRD), South China, has been suffering serious soil acidification, but the contribution of S deposition was ignored because of the regulation of S emission since 2001. Here, we chose the evergreen broadleaf forests, which are the typical forest type at the regional scale in PRD to examine the contribution of S deposition and its characteristics in this acidification, based on an established urban-rural gradient in the range of 260 km.

Alterations in leaf nitrogen metabolism indicated the structural changes of subtropical forest by canopy addition of nitrogen.

Globally, nitrogen deposition increment has caused forest structural changes due to imbalanced plant nitrogen metabolism and subsequent carbon assimilation. Here, a 2 consecutive-year experiment was conducted to reveal the effects of canopy addition of nitrogen (CAN) on nitrogen absorption, assimilation, and allocation in leaves of three subtropical forest woody species (Castanea henryi, Ardisia quinquegona, and Blastus cochinchinensis). We hypothesized that CAN altered leaf nitrogen absorption, assimilation and partitioning of different plants in different ways in subtropical forest.

Consistent effects of canopy vs. understory nitrogen addition on the soil exchangeable cations and microbial community in two contrasting forests.

Anthropogenic N deposition has been well documented to cause substantial impacts on the chemical and biological properties of forest soils. In most studies, however, atmospheric N deposition has been simulated by directly adding N to the forest floor. Such studies thus ignored the potentially significant effect of some key processes occurring in forest canopy (i.

[Water recharge through nighttime stem sap flow of Schima superba in Guangzhou region of Guangdong Province, South China: affecting factors and contribution to transpiration].

To understand the nighttime water recharge of tree through its sap flow is beneficial to the precise estimation of total transpiration and canopy stomatal conductance, and to the further understanding of the time lag between canopy transpiration and stem sap flow. By using Granier's thermal dissipation probe, this paper measured the stem sap flow of Schima superba, and synchronously measured the main environmental factors including air temperature, relative humidity, photosynthetically active radiation, and soil moisture content, and also analyzed the water recharge through nighttime stem flow of S. superba at daily and seasonal scales.

[Effects of tree diameter at breast height and soil moisture on transpiration of Schima superba based on sap flow pattern and normalization].

The eigenvalues of continuous sap flow pattern, i. e. , skewness and kurtosis, were used to investigate the water usage of Schima superba with different diameter at breast height (DBH), and the method of normalization was firstly applied to eliminate the effects of strong affecting factor (photosynthetic active radiation, PAR) to explore the possible relationship between weak affecting factor (soil moisture) and sap flow.

[Net CO2 exchange and carbon isotope flux in Acacia mangium plantation].

By using stable carbon isotope technique, the leaf-level 13C discrimination was integrated to canopy-scale photosynthetic discrimination (Deltacanopy) through weighted the net CO2 assimilation (Anet) of sunlit and shaded leaves and the stand leaf area index (L) in an A. mangium plantation, and the carbon isotope fluxes from photosynthesis and respiration as well as their net exchange flux were obtained. There was an obvious diurnal variation in Deltacanopy, being lower at dawn and at noon time (18.

[Caloric value and ash content of dominant plants in plantation communities in Heshan of Guangdong, China].

Different parts of twenty dominant plant species in five plantation communities on the subtropical hilly lands in Heshan of Gunagdong as well as the litters from three of the five plantation communities were sampled, and their gross caloric value (GCV) and ash content were measured by using a PARR-1281 oxygen bomb calorimeter and a muffle furnace. Based on the measurements, the ash-free caloric value (AFCV) of the samples was calculated, and the characteristics of caloric value and ash content of the samples, according to plant part, individual, and plant growth form, were analyzed. The results showed that the GCV and AFCV of leaf, branch, stem wood, stem bark, and root were in the range of 10.

[Effects of tree height on whole-tree water use of Acacia mangium].

By using Granier's thermal dissipation probe, the sap flow of 14 sample trees in a 22-year old Acacia mangium forest in hilly land of South China was continuously measured in 2004. Environmental factors including the photosynthetically active radiation, air temperature, and air humidity above canopy and the water content in 0-30 cm soil layer were monitored simultaneously. Combining with the tree morphological features and sap flux density, the whole-tree transpiration, canopy stomatal conductance, and ratio of leaf area to sapwood area were calculated by simplified Whitehead and Jarvis equation, and the effects of tree height on these three parameters were analyzed.

High-nitrogen and low-irradiance can restrict energy utilization in photosynthesis of successional tree species in low subtropical forest.

Responses of photosynthesis and the partition of energy utilization to high-nitrogen importation and high-light intensity in leaves of three dominant tree species of subtropical forest, including sun plant or early-successional species Schima superba, mesophyte or intermediate-successional species Canstanopsis hystrix, and shading-tolerant plant or late-successional species Cryptocarya concinna were studied by using the CO(2) exchange system and chlorophyll fluorescence method. Our results showed that, regardless of plant species, net photosynthetic rate (P (n)) was higher in high-nitrogen supply and high irradiance (HNHL) plants than in low-nitrogen supply and high irradiance (LNHL) plants, implying that low-nitrogen importation would limit P (n) of plants grown under high irradiance. However, high-nitrogen supply and low irradiance (HNLL) plants had a lower P (n).

[Time lag effect between stem sap flow and photosynthetically active radiation, vapor pressure deficit of Acacia mangium].

Based on the measurement of the stem sap flow of Acacia mangium with Granier' s thermal dissipation probe, and the cross-correlation and time serial analysis of the sap flow and corresponding photosynthetically active radiation and vapor pressure deficit, this paper studied the time lag effect between the stem sap flow of A. mangium and the driving factors of the tree canopy transpiration. The results indicated that the main driving factors of the transpiration were photosynthetically active radiation (PAR) and vapor pressure deficit (VPD).

[Responses of canopy stomatal conductance of Acacia mangium forest to environmental driving factors].

Employing Granierś probes, this paper measured the sap flow of 14 sample trees in an Acacia mangium forest on the Heshan hilly lands of Guangdong Province, and recorded the photosynthetic active radiation (PAR), air relative humidity (RH) , and air temperature (T) above the forest canopy. The whole-tree transpiration (E), stand transpiration (Et), and mean canopy stomatal conductance (gc) were calculated, and the relationships between tree morphological characters and whole-tree water use as well as the responses of gc to PAR and vapor pressure deficit (D) were analyzed. The results showed that the whole-tree transpiration had logarithmical positive correlations with tree diameter at breast height (DBH) (P < 0.

[Effects of nitrate application on alleviating photosynthesis restriction of Cinnamomum burmannii leaves under elevated CO2 concentration and enhanced temperature].

In this study, potted C. burmannii saplings were cultured in a top-closed chamber with elevated CO2 (+ CO2, 731 micromol x mol(-1)) and ambient CO2(CO2, 365 micromol x mol(-1)), and at diurnal temperature (day/night) 25/23 degrees C and 32/25 degrees C, respectively. The gas exchange, calculated photosynthesis parameter, Rubisco content, and activated state of Rubisco were examined.

[Ecological and biological characteristics of Wikstroemia indica].

Wikstroemia indica was the common shrub with medicine use in subtropical and tropical zones. The studies on the biological and physiological characteristics, population dynamics, biomass, nutrient composition of Wikstroemia indica showed that Wikstroemia indica was widely dispersed over hilly lands and opened forests. It was heliophytes and grew well on improverished soil.

[Ecological restoration technologies for mined lands: a review].

Mining activities usually cause catastrophic and extensive environmental changes, and eventually cause major damages to the whole ecosystem. The natural restoration for mine lands and tailings is a very slow process, and even can hardly reach their original states. Therefore, how to develop rapid and efficient approaches to accelerate restoration of mined lands has been highlighted by restorationists and environmental engineers during the past two decades.