Soil warming effect on net ecosystem exchange of carbon dioxide during the transition from winter carbon source to spring carbon sink in a temperate urban lawn

The significant warming in urban environment caused by the combined effects of global warming and heat island has stimulated widely development of urban vegetations. However, it is less known of the climate feedback of urban lawn in warmed environment. Soil warming effect on net ecosystem exchange （NEE） of carbon dioxide during the transition period from winter to spring was investigated in a temperate urban lawn in Beijing, China. The NEE （negative for uptake） under soil warming treatment （temperature was about 5~C higher than the ambient treatment as a control） was -0.71 ~mol/（m2.sec）, the ecosytem was a CO2 sink under soil warming treatment, the lawn ecosystem under the control was a CO2 source （0.13 Ixmol/（mE.sec））, indicating that the lawn ecosystem would provide a negative feedback to global warming. There was no significant effect of soil warming on nocturnal NEE （i.e., ecosystem respiration）, although the soil temperature sensitivity （Q10） of ecosystem respiration under soil warming treatment was 3.86, much lower than that in the control （7.03）. The CO2 uptake was significantly increased by soil warming treatment that was attributed to about 100% increase of ct （apparent quantum yield） and Amax （maximum rate of photosynthesis）. Our results indicated that the response of photosynthesis in urban lawn is much more sensitive to global warming than respiration in the transition period.

Warming effects on plant biomass allocation and correlations with the soil environment in an alpine meadow,China

Alpine meadow ecosystem is fragile and highly sensitive to climate change.An understanding of the allocation of above-and below-ground plant biomass and correlations with environmental factors in alpine meadow ecosystem can result in better protection and effective utilization of alpine meadow vegetation.We chose an alpine meadow in the Qinghai-Tibetan Plateau of China as the study area and designed experimental warming plots using a randomized block experimental design.We used single-tube infrared radiators as warming devices,established the warming treatments,and measured plant above- （AGB） and below-ground biomass （BGB） during the growing seasons （May to September） in 2012 and 2013.We determined the allocation of biomass and the relationship between biomass and soil environment under the warming treatment.Biomass indices including above-ground biomass,below-ground biomass and the ratio of root to shoot （R/S） ,and soil factors including soil moisture and soil temperature at different depths were measured.The results showed that （1） BGB of the alpine meadow had the most significant allometric correlation with its AGB （y=298.7x~ （0.44） ,P〈0.001） ,but the relationship decreased under warming treatment and the determination coefficient of the functional equation was 0.102 which was less than that of 0.188 of the unwarming treatment （control） ; （2） BGB increased,especially in the deeper soil layers under warming treatment （P〉0.05） .At 0–10 cm soil depth,the percentages of BGB under warming treatment were smaller than those of the control treatment with the decreases being 8.52% and 8.23% in 2012 and 2013,respectively.However,the BGB increased 2.13% and 2.06% in 2012 and 2013,respectively,at 10–50 cm soil depths; （3） BGB had significant positive correlations with soil moisture at 100 cm depth and with soil temperature at 20–100 cm depths （P〈0.05） ,but the mean correlation coefficient of soil temperature was 0.354,greater than the 0.245 of soil moisture.R/S ratio had a significant negative correlation with soil temperature at 20 cm depth （P〈0.05） .The warmer soil temperatures in shallow layers increased the biomass allocation to above-ground plant parts,which leading to the increase in AGB;whereas the enhanced thawing of frozen soil in deep layers causing by warming treatment produced more moisture that affected plant biomass allocation.

Topsoil organic carbon mineralization and CO_2 evolution of three paddy soils from South China and the temperature dependence

Carbon mineralization and its response to climatic warming have been receiving global attention for the last decade. Although the virtual influence of temperature effect is still in great debate, little is known on the mineralization of organic carbon （SOC） of paddy soils of China under warming. SOC mineralization of three major types of China＇s paddy soils is studied through laboratory incubation for 114 d under soil moisture regime of 70% water holding capacity at 20℃ and 25℃ respectively. The carbon that mineralized as CO2 evolved was measured every day in the first 32 d and every two days in the following days. Carbon mineralized during the 114 d incubation ranged from 3.51 to 9.22 mg CO2-C/gC at 20℃ and from 4.24 to 11.35 mg CO2-C/gC at 25℃ respectively; and a mineralizable C pool in the range of 0.24 to 0.59 gC/kg, varying with different soils. The whole course of C mineralization in the 114 d incubation could be divided into three stages of varying rates, representing the three subpools of the total mineralizable C： very actively mineralized C at 1-23 d, actively tnineralized C at 24--74 d and a slowly mineralized pool with low and more or less stabilized C mineralization rate at 75-114 d. The calculated Q10 values ranged from 1.0 to 2.4, varying with the soil types and N status. Neither the total SOC pool nor the labile C pool could account for the total mineralization potential of the soils studied, despite a well correlation of labile C with the shortly and actively mineralized C, which were shown in sensitive response to soil warming. However, the portion of microbial C pool and the soil C/N ratio controlled the C mineralization and the temperature dependence. Therefore, C sequestration may not result in an increase of C mineralization proportionally. The relative control of C bioavailability and microbial metabolic activity on C mineralization with respect to stabilization of sequestered C in the paddy soils of China is to be further studied.

Stabilized effects of L-S cement-mixed batter pile composite foundation for existed warm frozen soil subgrade

In permafrost regions with warm frozen soil,subgrade thaw-collapse phenomenon commonly occurs,facing thaw collapse problems of the existed frozen soil subgrade,thus it is difficult to use traditional methods such as active cooling and passive protection technology to stabilize the existed warm frozen soil subgrade.This study derives a novel stabilizer method,a long-short(L-S)cement-mixed batter pile composite foundation to stabilize the existed warm frozen soil subgrade.To solve the thawcollapse problems in warm frozen soil subgrade,high water content and large compressibility characteristics were compared between soft soil and warm frozen soils.Theoretical analysis of heat conduction and numerical simulation of finite element model were used to study the freeze–thaw process and evaluate the stabilized effects of the L-S cement-mixed batter piles on the warm frozen soil foundation of the Qinghai-Tibet Highway.Furthermore,the thaw process and mechanical properties of foundation and piles were analyzed by introducing the hydration heat factor in the thermodynamic control equation.The results indicate that the thawing displacement of the existed warm frozen soil subgrade was reduced owing to the“support”and“grasp”effects of the L-S cement-mixed batter piles on the surrounding soil.The composite ground formed by strengthening the warm frozen ground with batter piles could considerably improve the bearing capacity of the existed warm frozen ground,effectively restrain the deformation of the upper embankment,and improve the strength of the ground.The analysis can provide method for the construction design of cement mixing batter pile foundation in cold regions.

Stress relaxation of warm frozen soil under drained or undrained conditions

To investigate the influence of drainage conditions on stress relaxation characteristics of warm frozen soil, a series of laboratory tests were carried out under drained and undrained conditions. The results indicate that confining pressure obviously influences the relaxation process of warm frozen soil. Under undrained condition, with increase in confining pressure, the critical relaxation du- ration tends to grow as well as instantaneous relaxation. But the relaxation rate is sensitive to confining pressure in the initial stage, and with further development, the effect tends to diminish. Under drained condition, the relaxation rate is greater than that under tmdrained condition in the initial stage but with the development of relaxation, the difference decreases. The volumetric defor- mation of warm frozen clay under drained condition is much larger than that under undrained condition.

Effects of elevated carbon dioxide concentration and soil temperature on the growth and biomass responses of mountain maple (Acer spicatum) seedlings to light availability

Aims Some shade-tolerant understory tree species such as mountain maple(Acer spicatum L.)exhibit light-foraging growth habits.Changes in environmental conditions,such as the rise of carbon dioxide concentration([CO_(2)])in the atmosphere and soil warming,may affect the performance of these species under different light environments.We investigated how elevated[CO_(2)]and soil warm-ing influence the growth and biomass responses of mountain maple seedlings to light availability.Methods The treatments were two levels of light(100%and 30%of the ambient light in the greenhouse),two[CO_(2)](392μmol mol^(−1)(ambient)and 784μmol mol^(−1)(elevated))and two soil tempera-tures(Tsoil)(17 and 22℃).After one growing season,we measured seedling height,root collar diameter,leaf biomass,stem biomass and root biomass.Important findings We found that under the ambient[CO_(2)],the high-light level increased seedlings height by 70%and 56%at the low Tsoil and high Tsoil,respectively.Under the elevated[CO_(2)],however,the high-light level increased seedling height by 52%and 13%at the low Tsoil and high Tsoil,respectively.The responses of biomasses to light generally followed the response patterns of height growth under both[CO_(2)]and Tsoil and the magnitude of biomass response to light was the lowest under the elevated[CO_(2)]and warmer Tsoil.The results suggest that the elevated[CO_(2)]and warmer Tsoil under the projected future climate may have negative impact on the colonization of open sites and forest canopy gaps by mountain maple.

Effects of Temperature and Moisture on Soil Organic Matter Decomposition Along Elevation Gradients on the Changbai Mountains, Northeast China

Decomposition of soil organic matter(SOM) is of importance for CO_2 exchange between soil and atmosphere and soil temperature and moisture are considered as two important factors controlling SOM decomposition. In this study, soil samples were collected at 5 elevations ranging from 753 to 2 357 m on the Changbai Mountains in Northeast China, and incubated under different temperatures(5, 10, 15, 20, 25, and 30?C) and soil moisture levels(30%, 60%, and 90% of saturated soil moisture) to investigate the effects of both on SOM decomposition and its temperature sensitivity at different elevations. The results showed that incubation temperature(F = 1 425.10, P < 0.001), soil moisture(F = 1 327.65, P < 0.001), and elevation(F = 1 937.54, P < 0.001) all had significant influences on the decomposition rate of SOM. The significant effect of the interaction of incubation temperature and soil moisture on the SOM decomposition rate was observed at all the 5 sampling elevations(P < 0.001). A two-factor model that used temperature and moisture as variables fitted the SOM decomposition rate well(P < 0.001) and could explain 80%–93% of the variation of SOM decomposition rate at the 5 elevations. Temperature sensitivity of SOM decomposition, expressed as the change of SOM decomposition rate in response to a 10?C increase in temperature(Q_(10)), was significantly different among the different elevations(P < 0.01), but no apparent trend with elevation was discernible. In addition, soil moisture and incubation temperature both had great impacts on the Q_(10) value(P < 0.01), which increased significantly with increasing soil moisture or incubation temperature. Furthermore, the SOM decomposition rate was significantly related to soil total Gram-positive bacteria(R^2= 0.33, P < 0.01) and total Gram-negative bacteria(R^2= 0.58, P < 0.001). These findings highlight the importance of soil moisture to SOM decomposition and its Q_(10) value,which needs to be emphasized under warming climate scenarios.

Adjustment of Forest Ecosystem Root Respiration as Temperature Warms

Adjustment of ecosystem root respiration to warmer climatic conditions can alter the autotrophic portion of soil respiration and influence the amount of carbon available for biomass production. We examined 44 published values of annual forest root respiration and found an increase in ecosystem root respiration with increasing mean annual temperature （MAT）, but the rate of this cross-ecosystem increase （Q10 = 1.6） is less than published values for short-term responses of root respiration to temperature within ecosystems （Q10 = 2-3）. When specific root respiration rates and root biomass values were examined, there was a clear trend for decreasing root metabolic capacity （respiration rate at a standard temperature） with increasing MAT. There also were tradeoffs between root metabolic capacity and root system biomass, such that there were no instances of high growing season respiration rates and high root biomass occurring together. We also examined specific root respiration rates at three soil warming experiments at Harvard Forest, USA, and found decreases in metabolic capacity for roots from the heated plots. This decline could be due to either physiological acclimation or to the effects of co-occurring drier soils on the measurement date. Regardless of the cause, these findings clearly suggest that modeling efforts that allow root respiration to increase exponentially with temperature, with Q10 values of 2 or more, may over-predict root contributions to ecosystem CO2 efflux for future climates and underestimate the amount of C available for other uses, including net primary productivity.

Coupling model and optimal combination scheme of water,fertilizer,dissolved oxygen and temperature in greenhouse tomato under drip irrigation

Water-fertilizer coupling technology has been widely used in the world.Poor soil aeration,low temperature or high temperature can affect the rate of nutrient uptake by crop roots.Aiming at the interaction between water,fertilizer,dissolved oxygen and temperature(WFOT)coupling model and irrigation flux of tomato in greenhouse,using these four factors with a five-level uniform-precision rotatable central composite design,a mathematical model was established among the four factors affecting tomato yield in a greenhouse,and the optimal combination scheme of WFOT was obtained.Within the test range,tomato yields increased with increasing irrigation quotas(X_(1)),fertilization amount(X_(2)),dissolved oxygen(X_(3))and geothermal pipe water temperature(X_(4)).The magnitude of the effect of each factor of WFOT on tomato yield was in the following order:X_(1),X_(2),X_(4),X_(3)(spring and summer),and X_(1),X_(3),X_(2),X_(4)(autumn and winter).The interaction between high water-low heat and low water-high heat were beneficial for yield increase(spring and summer),the high fertilizer-low heat and low fertilizer-high heat interactions were beneficial to yield increase(autumn and winter).If WFOT agronomic measures were adopted according to the 95%confidence interval,there was a 95%probability that the spring-summer tomato yield will be higher than 89902 kg/hm^(2).The WFOT coupling scheme was X_(1)of 4808-5091 m3/hm^(2),X_(2)(N-P_(2)O_(5)-K_(2)O)of 171-57-84 to 186-62-89 kg/hm^(2),X_(3)of 7.9-8.2 mg/L,and X_(4)of 34.9°C-37.0°C.There was a 95%probability of tomato yield higher than 85209 kg/hm^(2)in autumn and winter,and the WFOT coupling scheme was X_(1)of 5270-5416 m3/hm^(2),X_(2)(N-P_(2)O_(5)-K_(2)O)of 151-50-76 to 167-56-82 kg/hm^(2),X_(3)of 8.0-8.2 mg/L,and X_(4)of 34.1°C-36.2°C.Overall,and the model had a very good simulation effect,with application value.The relative error between spring-summer and autumn-winter yields ranged from 1.12%to 25.34%.The results of the study can provide a theoretical basis for improving the quality and efficiency of greenhouse tomatoes.