Straw ^(14)C Decomposition and Distribution in Humus Fractions as Influenced by Soil Moisture Regimes

14C-tracer technique and closed incubation method were used to study straw 14C decomposition and distribution in different fractions of newly formed humus under different moisture regimes. Decomposition of straw 14C was faster during the initial days, and slower thereafter. Decay rate constants of straw 14C varied from 3.29x10-3 d-1 to 7.06x10-3 d-1. After 112 d incubation, the amount of straw 14C mineralized was 1.17～1.46 times greater in submerged soils than in upland soils. of the soil residual 14C, 9.08%～15.73%was present in humic acid (HA) and 31.01%～37.62% in fulvic acid (FA). Submerged condition favored the formation of HA, and HA/FA ratio of newly formed humus (labelled) was greater in submerged soils than in upland soils. Clay minerals affected the distribution of straw 14C in different humus fractions. Proportion of 14C present in HA to 14C remaining in soil was greater in Vertisol than in Ultisol.

Predicting and delineating soil temperature regimes of China using pedotransfer function

Soil temperature regime(STR)is important for soil classification and land use.Generally,STR is delineated by estimating the mean annual soil temperature at a depth of 50 cm(MAST50)according to the Chinese Soil Taxonomy(CST).However,delineating the STR of China remains a challenge due to the difficulties in accurately estimating MAST50.The objectives of this study were to explore environmental factors that influence the spatial variation of MAST50 and generate an STR map for China.Soil temperature measurements at 40 and 80 cm depth were collected from 386 National Meteorological Stations in China during 1971–2000.The MAST50 was calculated as the average mean annual soil temperature(MAST)from 1971–2000 between 40 and 80 cm depths.In addition,2048 mean annual air temperature(MAAT)measurements from 1971 to 2000 were collected from the National Meteorological Stations across China.A zonal pedotransfer function(PTF)was developed based on the ensemble linear regression kriging model to predict the MAST50 in three topographic steps of China.The results showed that MAAT was the most important variable related to the variation of MAST50.The zonal PTF was evaluated with a 10%validation dataset with a mean absolute error(MAE)of 0.66°C and root mean square error(RMSE)of 0.78°C,which were smaller than the unified model with MAE of 0.83°C and RMSE of 0.96°C,respectively.This study demonstrated that the zonal PTF helped improve the accuracy of the predicted MAST50 map.Based on the prediction results,an STR map across China was generated to provide a consistent scientific base for the improvement and application of CST and land use support.

Microbial community structure and functional metabolic diversity are associated with organic carbon availability in an agricultural soil

Exploration of soil environmental characteristics governing soil microbial community structure and activity may improve our understanding of biogeochemical processes and soil quality. The impact of soil environmental characteristics especially organic carbon availability after 15-yr different organic and inorganic fertilizer inputs on soil bacterial community structure and functional metabolic diversity of soil microbial communities were evaluated in a 15-yr fertilizer experiment in Changping County, Beijing, China. The experiment was a wheat-maize rotation system which was established in 1991 including four different fertilizer treatments. These treatments included： a non-amended control（CK）, a commonly used application rate of inorganic fertilizer treatment（NPK）; a commonly used application rate of inorganic fertilizer with swine manure incorporated treatment（NPKM）, and a commonly used application rate of inorganic fertilizer with maize straw incorporated treatment（NPKS）. Denaturing gradient gel electrophoresis（DGGE） of the 16 S r RNA gene was used to determine the bacterial community structure and single carbon source utilization profiles were determined to characterize the microbial community functional metabolic diversity of different fertilizer treatments using Biolog Eco plates. The results indicated that long-term fertilized treatments significantly increased soil bacterial community structure compared to CK. The use of inorganic fertilizer with organic amendments incorporated for long term（NPKM, NPKS） significantly promoted soil bacterial structure than the application of inorganic fertilizer only（NPK）, and NPKM treatment was the most important driver for increases in the soil microbial community richness（S） and structural diversity（H）. Overall utilization of carbon sources by soil microbial communities（average well color development, AWCD） and microbial substrate utilization diversity and evenness indices（H＇ and E） indicated that long-term inorganic fertilizer with organic amendments incorporated（NPKM, NPKS） could significantly stimulate soil microbial metabolic activity and functional diversity relative to CK, while no differences of them were found between NPKS and NPK treatments. Principal component analysis（PCA） based on carbon source utilization profiles also showed significant separation of soil microbial community under long-term fertilization regimes and NPKM treatment was significantly separated from the other three treatments primarily according to the higher microbial utilization of carbohydrates, carboxylic acids, polymers, phenolic compounds, and amino acid, while higher utilization of amines/amides differed soil microbial community in NPKS treatment from those in the other three treatments. Redundancy analysis（RDA） indicated that soil organic carbon（SOC） availability, especially soil microbial biomass carbon（Cmic） and Cmic/SOC ratio are the key factors of soil environmental characteristics contributing to the increase of both soil microbial community structure and functional metabolic diversity in the long-term fertilization trial. Our results showed that long-term inorganic fertilizer and swine manure application could significantly improve soil bacterial community structure and soil microbial metabolic activity through the increases in SOC availability, which could provide insights into the sustainable management of China＇s soil resource.

Characteristics of the active-layer under the China-Russia Crude Oil pipeline

Active layer is a key component for permafrost environment studies as many subsurface biological,biogeochemical,ecological,and pedogenic activities prevail in this layer.This study focuses on active layer temperature monitoring in an area with sporadic permafrost at two adjacent sites along China-Russia Crude Oil Pipeline(CRCOP),NorthEast China.Site T1 is located in disturbed ground on the right-of-way(on-ROW)2 m away from the center of the oil pipeline.T2 is located in a natural and undisturbed site,around 16.6 m off-ROW.Our objective was to study seasonal variability of the active layer depth and thermal regime from October 2017 to September 2018.The monitoring sites consist of soil temperature probes arranged in a vertical array at different depths at both sites.The following parameters were computed:number of isothermal days(ID),freezing days(FD),thawing days(TD),freezing degree days(FDD),thawing degree days(TDD),number of freeze-thaw days(FTD).The mean air temperature in the monitoring period reached-3.2℃.The temperature profile indicates that the maximum active layer thickness observed during the study period was 10 m at T1 and 2 m at T2.The majority of the soil temperatures were above or close to 0℃,resulting in great values of TDD,especially in the first 4 m depth.TDD for T1 were predominant and ranged between 600-1160℃·days(0-4 m depth)reflecting the influence of oil temperature from the pipeline.In T2 borehole FDD were predominant for all the soil layer depths resulting in less permafrost degradation.This comparison emphasizes the significant influence of vegetation removal and the dispersed heat from the pipeline on the active layer thickness.

Seasonal Transpiration and Biomass Production

This paper presents a method for estimating plant production as a function of the seasonal transpiration total. Transpiration was calculated retrospectively with the HYDRUS-ET software package. This approach is based on empirical relationships between seasonal transpiration totals of particular canopy and biomass production （yield） grown under standard conditions. Novelty of this approach is the development of the tool to evaluate the biomass production as related to the seasonal transpiration. The cumulative frequency distribution of seasonal transpiration was chosen as the basic characteristic of the soil water regime. This approach allows one to estimate cumulative frequency curves of actual and potential yields. The difference between these two curves is the cumulative frequency distribution of possible yield increase by optimization of the soil water regime. The method permits a cost-benefit analysis by comparing expected yield increases to the investment and operational expenses of the newly designed irrigation/drainage system, or of newly invoked water management practices,

Decoupling between Plant Productivity and Growing Season Length under a Warming Climate in Canada’s Arctic

Given the short duration of growing season in the Arctic, a strong correlation between plant productivity and growing season length (GSL) is conventionally assumed. Will this assumption hold true under a warming climate? In this study, we addressed the question by investigating the relationship between net primary productivity of leaves (NPPleaf) and GSL for various tundra ecosystems. We quantified NPPleaf and GSL using long-term satellite data and field measurements. Our results indicated that the relationship was not significant (i.e., decoupled) for 44% to 64% of tundra classes in the southern Canadian Arctic, but significant for all classes in the northern Canadian Arctic. To better understand the causes of the decoupling, we further decomposed the relationship into two components: the correspondence of interannual variations and the agreement of long- term trends. We found that the longer the mean GSL for a tundra class, the poorer the correspondence between their interannual variations. Soil moisture limitation further decoupled the relationship by deteriorating the agreement of long-term trends. Consequently, the decoupling between NPPleaf and GSL would be more likely to occur under a warming climate if the tundra class had a mean GSL > 116 (or 123) days with a dry (or moist) soil moisture regime.

Response of soil CO_2 efflux to precipitation manipulation in a semiarid grassland

Soil CO_2efflux（SCE） is an important component of ecosystem CO_2 exchange and is largely temperature and moisture dependent, providing feedback between C cycling and the climate system. We used a precipitation manipulation experiment to examine the effects of precipitation treatment on SCE and its dependences on soil temperature and moisture in a semiarid grassland. Precipitation manipulation included ambient precipitation, decreased precipitation（- 43%）, or increased precipitation（＋ 17%）. The SCE was measured from July2013 to December 2014, and CO_2 emission during the experimental period was assessed.The response curves of SCE to soil temperature and moisture were analyzed to determine whether the dependence of SCE on soil temperature or moisture varied with precipitation manipulation. The SCE significantly varied seasonally but was not affected by precipitation treatments regardless of season. Increasing precipitation resulted in an upward shift of SCE–temperature response curves and rightward shift of SCE–moisture response curves,while decreasing precipitation resulted in opposite shifts of such response curves. These shifts in the SCE response curves suggested that increasing precipitation strengthened the dependence of SCE on temperature or moisture, and decreasing precipitation weakened such dependences. Such shifts affected the predictions in soil CO_2 emissions for different precipitation treatments. When considering such shifts, decreasing or increasing precipitation resulted in 43 or 75% less change, respectively, in CO_2 emission compared with changes in emissions predicted without considering such shifts. Furthermore, the effects of shifts in SCE response curves on CO_2 emission prediction were greater during the growing than the non-growing season.

Effects of water regime, crop residues, and application rates on control of Fusarium oxysporum f.sp.cubense

Biological soil disinfestation is an effective method to control soil-borne disease by flooding and incorporating with organic amendments, but field conditions and resources sometimes limited its practical application. A laboratory experiment was conducted to develop practice guidelines on controlling Fusarium wilt, a widespread banana disease caused by Fusarium oxysporum f. sp. cubense（FOC）. FOC infested soil incorporated with rice or maize straw at rates of 1.5 tons/ha and 3.0 tons/ha was incubated under flooded or water-saturated（100% water holding capacity） conditions at 30℃ for 30 days. Results showed that FOC populations in the soils incorporated with either rice or maize straw rapidly reduced more than 90% in the first 15 days and then fluctuated till the end of incubation, while flooding alone without organic amendment reduced FOC populations slightly. The rapid and dramatic decrease of redox potential（down to- 350 m V） in straw-amended treatments implied that both anaerobic condition and strongly reductive soil condition would contribute to pathogen inactivation. Water-saturation combined with straw amendments had the comparable effects on reduction of FOC, indicating that flooding was not indispensable for inactivating FOC. There was no significant difference in the reduction of FOC observed in the straw amendments at between 1.5 and 3 tons/ha. Therefore,incorporating soil with straw（rice or maize straw） at a rate of 3.0 tons/ha under 100%water holding capacity or 1.5 tons/ha under flooding, would effectively alleviate banana Fusarium wilt caused by FOC after 15-day treating under 30℃.