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This article is from Frontiers in Plant Science , volume 4 . Abstract Fine roots (FR) play a major role in the water and nutrient uptake of plants and contribute significantly to the carbon and nutrient cycles of ecosystems through their annual production and turnover. FR growth dynamics were studied to understand the endogenous and exogenous factors driving these processes in a 14-year-old plantation of rubber trees located in eastern Thailand. FR dynamics were observed using field rhizotrons from October 2007 to October 2009. This period covered two complete dry seasons (November to March) and two complete rainy seasons (April to October), allowing us to study the effect of rainfall seasonality on FR dynamics. Rainfall and its distribution during the two successive years showed strong differences with 1500 and 950 mm in 2008 and 2009, respectively. FR production (FRP) completely stopped during the dry seasons and resumed quickly after the first rains. During the rainy seasons, FRP and the daily root elongation rate (RER) were highly variable and exhibited strong annual variations with a total FRP of 139.8 and 40.4 mm-2 and an average RER of 0.16 and 0.12 cm day-1 in 2008 and 2009, respectively. The significant positive correlations found between FRP, RER, the appearance of new roots, and rainfall at monthly intervals revealed the impact of rainfall seasonality on FR dynamics. However, the rainfall patterns failed to explain the weekly variations of FR dynamics observed particularly during the rainy seasons. At this time step, FRP, RER, and the appearance of new FR were negatively correlated to the average soil matric potential measured at a depth of between 30 and 60 cm. In addition, our study revealed a significant negative correlation between FR dynamics and the monthly production of dry rubber. Consequently, latex harvesting might disturb carbon dynamics in the whole tree, far beyond the trunk where the tapping was performed. These results exhibit the impact of climatic conditions and tapping system in the carbon budget of rubber plantations.

Seasonal dynamics of soil water content in the typical vegetation and its response to precipitation in a semi-arid area of Chinese Loess Plateau 作者： ZHOU Tairan 1,2 HAN Chun 1,2 QIAO Linjie 1,2 REN Chaojie 1,2 WEN Tao 1,2 ZHAO Changming 1,2 作者单位： 1. State Key Laboratory of Grassland and Agro-Ecosystems, School of Life Sciences, Lanzhou University, Lanzhou 730000, China 2. Gansu Provincial Field Scientific Observation and Research Station of Mountain Ecosystems, Lanzhou University, Lanzhou 730000, China 通讯作者： ZHAO Changming Email:[email protected] 提交时间： 2021-11-10 摘要: Soil water content is a key limiting factor for vegetation growth in the semi-arid area of Chinese Loess Plateau and precipitation is the main source of soil water content in this area. To further understand the impact of vegetation types and environmental factors such as precipitation on soil water content, we continuously monitored the seasonal dynamics in soil water content in four plots (natural grassland, Caragana korshinskii, Armeniaca sibirica and Pinus tabulaeformis) in Chinese Loess Plateau. The results show that the amplitude of soil water content fluctuation decreases with an increase in soil depth, showing obvious seasonal variations. Soil water content of artificial vegetation was found to be significantly lower than that of natural grassland, and most precipitation events have difficulty replenishing soil water content below a depth of 40 cm. Spring and autumn are the key seasons for replenishment of soil water by precipitation. Changes in soil water content are affected by precipitation, vegetation types, soil evaporation and other factors. The interception effect of vegetation on precipitation and the demand for water consumption by transpiration are the key factors affecting the efficiency of soil water replenishment by precipitation in this area. Due to artificial vegetation plantation in this area, soil will face a water deficit crisis in the future. 期刊： Journal of Arid Land 分类： 地球科学 >> 地理学 引用： ChinaXiv:202112.00006 (或此版本 ChinaXiv:202112.00006V1 ) DOI:10.1007/s40333-021-0021-5 CSTR:32003.36.ChinaXiv.202112.00006.V1 推荐引用方式： ZHOU Tairan,HAN Chun,QIAO Linjie,REN Chaojie,WEN Tao,ZHAO Changming.(2021).Seasonal dynamics of soil water content in the typical vegetation and its response to precipitation in a semi-arid area of Chinese Loess Plateau.Journal of Arid Land.doi:10.1007/s40333-021-0021-5 版本历史 [V1] 2021-11-10 20:57:25 ChinaXiv:202112.00006V1 下载全文

A respirometer system was developed to study the dynamics of partial anaerobiosis and denitrification in unsaturated soil. The system enables one to measure simultaneously the distribution of water, oxygen, nitrate, nitrite, ammonium, and pH as a function of space and time in an unsaturated, artificially made, homogeneous, cylindrical aggregate and the changes in atmospheric composition as a function of time in the chamber the contains the aggregate. Except for water transport, these processes are caused by microbial activity, because roots are not present in the aggregate. The respirometer system was especially designed to generate coherent data sets to evaluate a simulation model that calculates the development of denitrification products as a function of environmental conditions. Nondestructive measurements during an experiment involve gamma-ray attenuation, gas chromatography, and polarography. Destructive measurements are executed the end of an experiment in the form of chemical analyses of soil. The reported experiment shows that hysteresis in the soil water characteristic strongly affects the water distribution in the aggregate. As a result, the oxygen supply to the interior of the aggregate is decreased to such an extent that anaerobiosis is maintained there after the oxygen is consumed. The respiratory quotient and the release of denitrification products are underestimated in the partially wet soil because of the high solubilities of carbon dioxide and nitrous oxide in soil moisture. Large amounts of nitrite have been found. Therefore, assessment of denitrification through the measurement of nitrate alone will overestimate nitrogen losses, while the measurement of nitrous oxide and molecular nitrogen alone will given an under-estimation. The consumption rate of oxygen and the production rates of carbon dioxide, nitrous oxide, and molecular nitrogen compare wel with field data. This is the result of the pretreatment of the soil, which aimed at avoiding the flush of microbial activity upon wetting. The results support the thesis that denitrification will occur in soil when at a certain place and time oxygen is absent and bacteria capable of denitrification, water, nitrate, and decomposable organic compounds are present. The respirometer system yields valuable data to evaluate the simulation model. However, full account of the interrelationships among the generated data can be achieved only by the same simulation model, because the measured variables reflect the integrated effect of biological activity and transport processes. The objective of this paper is to describe the respirometer system and its measuring devices and to report some of the measurements.

A respirometer system was developed to study the dynamics of partial anaerobiosis and denitrification in unsaturated soil. The system enables one to measure simultaneously the distribution of water, oxygen, nitrate, nitrite, ammonium, and pH as a function of space and time in an unsaturated, artificially made, homogeneous, cylindrical aggregate and the changes in atmospheric composition as a function of time in the chamber the contains the aggregate. Except for water transport, these processes are caused by microbial activity, because roots are not present in the aggregate. The respirometer system was especially designed to generate coherent data sets to evaluate a simulation model that calculates the development of denitrification products as a function of environmental conditions. Nondestructive measurements during an experiment involve gamma-ray attenuation, gas chromatography, and polarography. Destructive measurements are executed the end of an experiment in the form of chemical analyses of soil. The reported experiment shows that hysteresis in the soil water characteristic strongly affects the water distribution in the aggregate. As a result, the oxygen supply to the interior of the aggregate is decreased to such an extent that anaerobiosis is maintained there after the oxygen is consumed. The respiratory quotient and the release of denitrification products are underestimated in the partially wet soil because of the high solubilities of carbon dioxide and nitrous oxide in soil moisture. Large amounts of nitrite have been found. Therefore, assessment of denitrification through the measurement of nitrate alone will overestimate nitrogen losses, while the measurement of nitrous oxide and molecular nitrogen alone will given an under-estimation. The consumption rate of oxygen and the production rates of carbon dioxide, nitrous oxide, and molecular nitrogen compare wel with field data. This is the result of the pretreatment of the soil, which aimed at avoiding the flush of microbial activity upon wetting. The results support the thesis that denitrification will occur in soil when at a certain place and time oxygen is absent and bacteria capable of denitrification, water, nitrate, and decomposable organic compounds are present. The respirometer system yields valuable data to evaluate the simulation model. However, full account of the interrelationships among the generated data can be achieved only by the same simulation model, because the measured variables reflect the integrated effect of biological activity and transport processes. The objective of this paper is to describe the respirometer system and its measuring devices and to report some of the measurements.

Information relating to the accurate quantification of the impacts of long-term conservation tillage practices on the crop yields and water use patterns of rainfed rotational cropping systems under global climate change is urgently required. The objectives of this study were to calibrate and evaluate APSIM (Agriculture Production System sIMulator) to accurately predict crop growth and development of a maize-winter wheat-soybean rotation, and to investigate the effects of conservation tillage on grain yield, water productivity and evapotranspiration on the Loess Plateau of China. This study integrated APSIM-based simulation modelling and field-level data collected from a maize-winter wheat-soybean rotation system under conventional tillage (CT) and no tillage with stubble retention of the previous crop (NTR) in Xifeng, Gansu, China. APSIM was successfully calibrated and evaluated using the root mean square error (RMSE) and index of agreement (d), indicating good performance on simulating the crop yield, dry matter biomass and soil water dynamic of the three crops for both CT and NTR treatments. Under the long-term scenario simulations (50 a, 25 rotation phases in total), the results showed that NTR improved soil water storage by 0–159 mm (72 mm on average; P < 0.01) of soil water storage before each rotation phase. The grain yield and biomass of winter wheat were significantly improved under the NTR treatment (1805 and 4309 kg ha−1 on average), but changes in maize or soybean were not significant (P > 0.05). On a system basis, the NTR treatment had significantly greater plant transpiration (Tc) and Tc/system water supply (WSsys), but lower soil evaporation (Es), evapotranspiration (ET), and ET/WSsys than treatment CT did. Additionally, Tc and Es for maize production were not significantly different between the two treatments. Grain yield water productivity (WPY) and biomass water productivity (WPB) in wheat and soybean were substantially improved by 1.9–8.0 kg ha−1 mm−1 (P < 0.05) under treatment NTR. In general, we advocated that conservation tillage has indicated great potential for improving crop/water productivity and soil water storage under rainfed conditions in the semiarid Loess Plateau region of China.

Research was conducted on soil carbon and nitrogen dynamics at Fort Benning, GA, from October 1999 to June 2004. The objectives of the research were to (1) develop a better understanding of the effects of disturbance on key measures of soil quality at Fort Benning, and (2) determine if there are thresholds of soil quality that potentially affect ecosystem recovery or sustainability. The completed research was relevant to SERDP because it addressed several objectives in the Statement of Need No. CSSON-00-03 titled Ecological Disturbance in the Context of Military Landscapes. In particular, the research addressed the SON objective to determine whether there are thresholds in spatial extent, intensity or frequency above and/or below which the natural system cannot sustain identified ecological and/or land use disturbances.

Research was conducted on soil carbon and nitrogen dynamics at Fort Benning, GA, from October 1999 to June 2004. The objectives of the research were to (1) develop a better understanding of the effects of disturbance on key measures of soil quality at Fort Benning, and (2) determine if there are thresholds of soil quality that potentially affect ecosystem recovery or sustainability. The completed research was relevant to SERDP because it addressed several objectives in the Statement of Need No. CSSON-00-03 titled Ecological Disturbance in the Context of Military Landscapes. In particular, the research addressed the SON objective to determine whether there are thresholds in spatial extent, intensity or frequency above and/or below which the natural system cannot sustain identified ecological and/or land use disturbances.

Research was conducted on soil carbon and nitrogen dynamics at Fort Benning, GA, from October 1999 to June 2004. The objectives of the research were to (1) develop a better understanding of the effects of disturbance on key measures of soil quality at Fort Benning, and (2) determine if there are thresholds of soil quality that potentially affect ecosystem recovery or sustainability. The completed research was relevant to SERDP because it addressed several objectives in the Statement of Need No. CSSON-00-03 titled Ecological Disturbance in the Context of Military Landscapes. In particular, the research addressed the SON objective to determine whether there are thresholds in spatial extent, intensity or frequency above and/or below which the natural system cannot sustain identified ecological and/or land use disturbances.