Soil-vegetation System Research Articles

Excessive uptake of heavy metals by greenhouse vegetables

The accumulation of some harmful elements in greenhouse vegetables has caused a serious threat to human health. Comparing tests with cucumber (Cucumis sativus L.) and tomato (Lycopersicon esculentum) were conducted between greenhouse (GH) and open field (OF) cultivation with objective to determining the effects of greenhouse cultivation on transport and distribution of Cu, Zn, Fe, Mn, Pb, and Cd in soil–vegetable system. The results showed that Cd, Mn and Zn contents in most tissues of the vegetables in GH were significantly higher than those in OF, Fe contents reduction occurred in all parts of GH plants, while Pb contents decreased only in aboveground parts of GH plants. Most elements bioaccumulated in GH vegetable roots, except Fe, but exhibited lower transportation from root to aboveground parts in GH than in OF. Fe fractions extracted with ethanol and acid expressed significantly higher percentages in some parts of GH vegetables than in OF vegetables. Element interactions between Fe, Cd and Mn were significant and played an important role on metal elements transportation in vegetables. In conclusion, greenhouse cultivation could threaten vegetable production safety through changing the transportation of most metals in soil–vegetable system.

Soil quality assessment in different climate zones of China’s Wenchuan earthquake affected region

China’s 2008 8.0Ms Wenchuan earthquake and subsequent secondary geo-hazards caused widespread damage to vegetation-soil system in northwest China. In order to evaluate changes in soil quality status after damage, we established four treatments in the earthquake-affected area, including disturbed and treated sites in a dry hot climate (D-t), undisturbed sites in a dry hot climate (D-ud), disturbed and treated sites in a subtropical humid monsoon climate (S-t), and undisturbed sites in a subtropical humid monsoon climate (S-ud). Forty-eight soil samples were collected and analyzed for 27 soil physical, chemical, and biological properties. Principal components analysis (PCA) was conducted with 26 variables in significant differences except total potassium among D-t, D-ud, S-t, and S-ud. A minimum data set of soil indicators was established with available potassium (AK), K+, total salt content (TSC), and total phosphorus (TP) based on PCA results. Using the Integrated Quality Index (IQI) equation, we calculated the soil quality index (SQI). S-ud, S-t, D-ud, and D-t had mean SQI scores of 0.566, 0.275, 0.537, and 0.374, respectively. Our results showed that undisturbed sites had better soil quality compared to disturbed and treated sites based on their superior physical indicators, superior nutrient conditions, and higher microbial carbon source metabolic diversity, especially in the subtropical humid monsoon climate with frequent rainfall. The SQI reflects the variations observed in earthquake-affected area and may be considered as a suitable technique for detecting changes in soils. Our results will also supply the fundamental data for evaluating the effects, design, and implementation of restoration programs.

Calcined Eggshell Waste for Mitigating Soil Antibiotic-Resistant Bacteria/Antibiotic Resistance Gene Dissemination and Accumulation in Bell Pepper.

The combined accumulation of antibiotics, heavy metals, antibiotic-resistant bacteria (ARB)/antibiotic resistance genes (ARGs) in vegetables has become a new threat to human health. This is the first study to investigate the feasibility of calcined eggshells modified by aluminum sulfate as novel agricultural wastes to impede mixed contaminants from transferring to bell pepper (Capsicum annuum L.). In this work, calcined eggshell amendment mitigated mixed pollutant accumulation in bell pepper significantly, enhanced the dissipation of soil tetracycline, sulfadiazine, roxithromycin, and chloramphenicol, decreased the water-soluble fractions of antibiotics, and declined the diversity of ARB/ARGs inside the vegetable. Moreover, quantitative polymerase chain reaction analysis detected that ARG levels in the bell pepper fruits significantly decreased to 10(-10) copies/16S copies, indicating limited risk of ARGs transferring along the food chain. Furthermore, the restoration of soil microbial biological function suggests that calcined eggshell is an environmentally friendly amendment to control the dissemination of soil ARB/ARGs in the soil-vegetable system.

Ash-soil interface: Mineralogical composition and physical structure

Fires exert many changes on the physical, chemical, morphological, mineralogical, and biological properties of soil that, in turn, affect the soil's hydrology and nutrient flux, modifying its ability to support vegetation and resist erosion. The ash produced by forest fires is a complex mixture composed of organic and inorganic particles with varied properties. This research was conducted to study and characterized ash properties produced at different temperatures and with different soil organic matter combinations. The samples, which included two treatments of soils with underlying mixed leaves and branches composed mainly by Pinus halepensis, Pistacia lentiscus, Cistus salviifolius and typical herbaceous vegetation, versus samples of mixed leaves and branches alone. Both were exposed to 400°C and 600°C heat in a muffle furnace for 2h. The residue ash was generally grayish, consisting of mixed-sized particles that preserved almost none of the original characteristics of the fuel, and was deposited in ash layers with diverse physicochemical and textural properties. The results of this study highlight the differences between all examined samples and strongly support the assumption that ash produced from a complex vegetation-soil system is a new substance with unique structural, textural, and mineralogical properties. Moreover, the ash produced at different temperatures appeared in distinct layering patterns.

Emergent geomorphic–vegetation interactions on a subalpine alluvial fan

AbstractFollowing perturbation, an ecosystem (flora, fauna, soil) should evolve as a function of time at a rate conditioned by external variables (relief, climate, geology). More recently, biogeomorphologists have focused upon the notion of co‐development of geomorphic processes with ecosystems over very short through to very long (evolutionary) timescales. Alpine environments have been a particular focus of this co‐development. However, work in this field has tended to adopt a simplified view of the relationship between perturbation and succession, including: how the landform and ecosystem itself conditions the impact of a perturbation to create a complex spatial response impact; and how perturbations are not simply ecosystem destroyers but can be a significant source of ecosystem resources. What this means is that at the within landform scale, there may well be a complex and dynamic topographic and sedimentological template that co‐develops with soil, flora and fauna. Here, we present and test a conceptual model of this template for a subalpine alluvial fan. We combine detailed floristic inventory with soil inventory, determination of edaphic variables and analysis of historical aerial imagery. Spatial variation in the probability of perturbation of sites on the fan surface was associated with down fan variability in the across‐fan distribution of fan ages, fan surface channel characteristics and fan surface sedimentology. Floristic survey confirmed that these edaphic factors distinguished site floristic richness and plant communities up until the point that the soil–vegetation system was sufficiently developed to sustain plant communities regardless of edaphic conditions. Thus, the primary explanatory variable was the estimated age of each site, which could be tied back into perturbation history and its spatial expression due to the geometry of the fan: distinct plant communities were emergent both across fan and down fan, a distribution maintained by the way in which the fan dissipates potentially perturbing events. Copyright © 2015 John Wiley & Sons, Ltd.

Occurrence and risk assessment of phthalate esters (PAEs) in vegetables and soils of suburban plastic film greenhouses

Phthalate esters (PAEs) are suspected of having adverse effects on human health and have been frequently detected in soils and vegetables. The present study investigated their occurrence and composition in plastic film greenhouse soil–vegetable systems and assessed their potential health risks to farmers exposed to these widespread pollutants. Six priority control phthalates, namely dimethyl phthalate (DMP), diethyl phthalate (DEP), di-n-butyl phthalate (DnBP), butyl benzyl phthalate (BBP), di-(2-ethylhexyl) phthalate (DEHP) and di-n-octyl phthalate (DnOP), were determined in 44 plastic film greenhouse vegetables and corresponding soils. Total PAEs ranged from 0.51 to 7.16mgkg−1 in vegetables and 0.40 to 6.20mgkg−1 in soils with average concentrations of 2.56 and 2.23mgkg−1, respectively. DnBP, DEHP and DnOP contributed more than 90% of the total PAEs in both vegetables and soils but the proportions of DnBP and DnOP in vegetables were significantly (p<0.05) higher than in soils. The average concentrations of PAEs in pot herb mustard, celery and lettuce were >3.00mgkg−1 but were <2.50mgkg−1 in the corresponding soils. Stem and leaf vegetables accumulated more PAEs. There were no clear relationships between vegetable and soil PAEs. Risk assessment indicates that DnBP, DEHP and DnOP exhibited elevated non-cancer risk with values of 0.039, 0.338 and 0.038, respectively. The carcinogenic risk of DEHP was about 3.94×10−5 to farmers working in plastic film greenhouses. Health risks were mainly by exposure through vegetable consumption and soil ingestion.

Vegetation-soil system controls soil mechanisms for nitrogen transformations in an oligotrophic Mexican desert

Vegetation communities with high soil carbon (C) inputs, e.g. grassland ecosystems, promote N protection via microbial communities in the soil whereas communities with low soil C inputs, e.g. desert scrub ecosystems, promote nitrification and are therefore susceptible to N loss. This study examines this relationship more closely by assessing the effects of two vegetation-soil systems on soil N transformation, in a grassland-desert scrub in Cuatro Ciénegas Basin, Mexico. Metrics used in our study include: the belowground biomass of C, N and phosphorus (P) in both vegetation types; the availability of C, N and P in the soil; and the potential transformation of these nutrients by the microbial community which was characterized by 16S rRNA clone libraries. We found: (1) a higher NH4+ and microbial N concentration in the grassland soil than in the desert scrub soil, and (2) a different bacterial soil communities between both vegetation-soil systems. These findings suggest an interrelationship between nutrients in the belowground biomass, soil nutrient dynamics, and the soil bacterial community whereby grasslands promote a closed system that conserves N, whereas desert scrub vegetation exhibits an open system that sheds N.

Stoichiometric analysis of nutrient availability (N, P, K) within soils of polygonal tundra

Plant growth in arctic tundra is known to be commonly limited by nitrogen. However, biogeochemical interactions between soil, vegetation and microbial biomass in arctic ecosystems are still insufficiently understood. In this study, we investigated different compartments of the soil-vegetation system of polygonal lowland tundra: bulk soil, inorganic nutrients, microbial biomass and vegetation biomass were analyzed for their contents of carbon, nitrogen, phosphorus and potassium. Samples were taken in August 2011 in the Indigirka lowlands (NE Siberia, Russia) in a detailed grid (4 m × 5 m) in one single ice-wedge polygon. We used a stoichiometric approach, based on the N/P ratios in the vegetation biomass and the investigated soil fractions, to analyze limitation relations in the soil-vegetation system. Plant growth in the investigated polygonal tundra appears to be co-limited by nitrogen and phosphorus or in some cases only limited by nitrogen whereas potassium is not limiting plant growth. However, as the N/P ratios of the microbial biomass in the uppermost soil horizons were more than twice as high as previously reported for arctic ecosystems, nitrogen mineralization and fixation may be limited at present by phosphorus. We found that only 5 % of the total nitrogen is already cycling in the biologically active fractions. On the other hand, up to 40 % of the total phosphorus was found in the biologically active fractions. Thus, there is less potential for increased phosphorus mineralization than for increased nitrogen mineralization in response to climate warming, and strict phosphorus limitation might be possible in the long-term.

Mercury and other Heavy Metal Pollution in Soil-Vegetation System around Compact Fluorescent Lamp Production Town in China

There is an increasing concern about heavy metal contamination in farmland in China and worldwide.In order to reveal the spatial features of heavy metals in the soil-vegetable system in the CFL manufacturing area, a total of 18 pairs of soil and vegetable samples were collected from Gaohong, Southeastern China. Most of the heavy metals in soil were much higher than its corresponding background value in Zhejiang province,Most of the heavy metals in the vegetable exceeded the Safe Agricultural Product Standard in China.Compared to other heavy metals, Hg had the highest enrichment index. The CFL manufacturing companies were the main source of heavy metal Hg pollution in this area. There are strong correlation between THg in soil and vegetable.

Migration of heavy metals in vegetable farmlands amended with biogas slurry in the Taihu Basin, China

Vegetables and related soils amended with biogas slurry samples were collected from Taihu Basin to evalute current levels of local metals pollution and related migration of the metals (Cr, Mn, Co, Ni, Cu, Zn, As, Cd, Pb) in soil–vegetable system. The results showed that the concentrations of Ni, Zn, Cd and Pb in vegetables and related soils exceeded the upper limits of evaluation standards. Moreover, the concentrations of Mn, Co, Ni, Cu, Zn, As and Pb in the soils were shown significant correlations with OM (Organic Matter).The metal transfer factor (TF) was found highest for Cd followed by Zn>Cr>Pb>Mn>Cu>Ni≈Co>As, which were dependent on the vegetable species. Amaranth was observed to have a greater heavy metals absorption capacity compared with other vegetables that would pose a potential health risk to the consumers.

Evaluation of a Linear Mixing Model to Retrieve Soil and Vegetation Temperatures of Land Targets

A simple linear mixing model of heterogeneous soil-vegetation system and retrieval of component temperatures from directional remote sensing measurements by inverting this model is evaluated in this paper using observations by a thermal camera. The thermal camera was used to obtain multi-angular TIR (Thermal Infra-Red) images over vegetable and orchard canopies. A whole thermal camera image was treated as a pixel of a satellite image to evaluate the model with the two-component system, i.e. soil and vegetation. The evaluation included two parts: evaluation of the linear mixing model and evaluation of the inversion of the model to retrieve component temperatures. For evaluation of the linear mixing model, the RMSE is 0.2 K between the observed and modelled brightness temperatures, which indicates that the linear mixing model works well under most conditions. For evaluation of the model inversion, the RMSE between the model retrieved and the observed vegetation temperatures is 1.6K, correspondingly, the RMSE between the observed and retrieved soil temperatures is 2.0K. According to the evaluation of the sensitivity of retrieved component temperatures on fractional cover, the linear mixing model gives more accurate retrieval accuracies for both soil and vegetation temperatures under intermediate fractional cover conditions.

Assessment of the EUMETSAT LSA-SAF evapotranspiration product for drought monitoring in Europe

Evapotranspiration is a key parameter for water stress assessment as it is directly related to the moisture status of the soil-vegetation system and describes the moisture transfer from the surface to the atmosphere. With the launch of the Meteosat Second Generation geostationary satellites and the setup of the Satellite Application Facilities, it became possible to operationally produce evapotranspiration data with high spatial and temporal evolution over the entire continents of Europe and Africa. In the frame of this study we present an evaluation of the potential of the evapotranspiration (ET) product from the EUMETSAT Satellite Application Facility on Land Surface Analysis (LSA-SAF) for drought assessment and monitoring in Europe.To assess the potential of this product, the LSA-SAF ET was used as input for the ratio of ET to reference evapotranspiration (ET0), the latter estimated from the ECMWF interim reanalysis. In the analysis two case studies were considered corresponding to the drought episodes of spring/summer 2007 and 2011. For these case studies, the ratio ET/ET0 was compared with meteorological drought indices (SPI, SPEI and Sc-PDSI for 2007 and SPI for 2011) as well as with the anomalies of the fraction of absorbed photosynthetic active radiation (fAPAR) derived from remote sensing data. The meteorological and remote sensing indicators were taken from the European Drought Observatory (EDO) and the CARPATCLIM climatological atlas.Results show the potential of ET/ET0 to characterize soil moisture variability, and to give additional information to fAPAR and to precipitation distribution for drought assessment. The main limitations of the proposed ratio for drought characterization are discussed, including options to overcome them. These options include the use of filters to discriminate areas with a low percentage vegetation cover or areas that are not in their growing period and the use of evapotranspiration without water restriction (ETwwr), obtained as output of the LSA-SAF model instead of ET0. The ET/ETwwr ratio was tested by comparing its accumulated values per growing period with the winter wheat yield values per country published by Eurostat. The results point to the potential of using the remote sensing based LSA-SAF evapotranspiration and the ET/ETwwr ratio for vegetation monitoring at large scale, especially in areas where data is generally lacking.

Effects of Rest Grazing on Organic Carbon Storage in Stipa grandis Steppe in Inner Mongolia, China

This study was aimed to evaluate the potential effects of rest grazing on organic carbon storage in Stipa grandis steppe of Inner Mongolia, China. Using potassium dichromate heating method, we analyzed the organic carbon storage of plant and soil in Stipa grandis steppe after rest grazing for 3, 6, and 9 yr. The results indicated that as the rest grazing ages prolonged, the biomass of aboveground parts, litter and belowground plant parts (roots) of the plant communities all increased, meanwhile the C content of the biomass increased with the rest grazing ages prolonging. For RG0, RG3a, RG6a, and RG9a, C storage in aboveground vegetation were 60.7, 76.9, 82.8 and 122.2 g C m−2, respectively; C storage of litter were 5.1, 5.8, 20.4 and 25.5 g C m−2, respectively; C storage of belowground roots (0–100 cm) were 475.2, 663.0, 1 115.0 and 1 867.3 g C m−2, respectively; C storage in 0–100 cm soil were 13.97, 15.76, 18.60 and 32.41 kg C m−2, respectively. As the rest grazing ages prolonged, the organic C storage in plant communities and soil increased. The C storage of belowground roots and soil organic C was mainly concentrated in 0–40 cm soil body. The increased soil organic C for RG3a accounted for 89.8% of the increased carbon in vegetation-soil system, 87.2% for RG6a, and 92.6% for RG9a. From the perspective of C sequestration cost, total cost for RG3a, RG6a, and RG9a were 2 903.4, 5 806.8 and 8 710.2 CNY ha−1, respectively. The cost reduced with the extension of rest grazing ages, 0.15 CNY kg−1 C for RG3a, 0.11 CNY kg−1 C for RG6a and 0.04 CNY kg−1 C for RG9a. From the growth characteristics of grassland plants, the spring was one of the two avoided grazing periods, timely rest grazing could effectively restore and update grassland vegetation, and was beneficial to the sustainable use of grassland. Organic C storage for RG9a was the highest, while the cost of C sequestration was the lowest. Therefore, spring rest grazing should be encouraged because it was proved to be a very efficient grassland use pattern.

Global sensitivity analysis of the spectral radiance of a soil–vegetation system

We analyzed the sensitivity of Top-Of-Atmosphere (TOA) radiance and surface reflectance of a soil–vegetation system to input biophysical and biochemical parameters using the coupled Soil–Leaf-Canopy radiative transfer model SLC and MODTRAN. We applied variance-based global sensitivity analysis for different atmospheric conditions and observation configurations. Among 23 input parameters, crown coverage, leaf area index, leaf inclination distribution function and soil moisture were found to be the most influential parameters driving the output variance of the radiance between 400 and 2500nm with a few exceptions. Hapke's soil parameters and the canopy layer dissociation factor were recognized to have marginal influence on the output radiance. It is also found that a large portion of uncertainty in the output radiance is driven by the interaction effects among input parameters in the visible (~550nm), whereas the red-near infrared (~670nm), seems to have fewer interaction effects. The effect of solar/view direction is found to be significant on TOA radiance sensitivity to the input parameters. The results also confirmed that the sensitivities of surface reflectance are comparable to the TOA radiance sensitivities when the atmosphere is clear and visibility is high. Since coupled surface-atmosphere RT models can be computationally intensive, this work also introduces an improvement to the design and sampling of screening methods for efficient sensitivity analysis of computationally expensive models. The improvement is based on three elements: a) generating sample points by Sobol's sequence generator; b) variational analysis in the parameter space using the winding stairs method; c) use of mean and variance sensitivity measures. The results with 1200 model runs demonstrated high correlation (92%) with variance-based global sensitivity analysis using 49,152 model runs, in determining the most influential and non-influential parameters.

Lack of steady-state in the global biogeochemical Si cycle: emerging evidence from lake Si sequestration

Weathering of silicate minerals releases dissolved silicate (DSi) to the soil-vegetation system. Accumulation and recycling of this DSi by terrestrial ecosystems creates a pool of reactive Si on the continents that buffers DSi export to the ocean. Human perturbations to the functioning of the buffer have been a recent research focus, yet a common assumption is that the continental Si cycle is at steady-state. However, we have no good idea of the timescales of ecosystem Si pool equilibration with their environments. A review of modelling and geochemical considerations suggests the modern continental Si cycle is in fact characterised in the long-term by an active accumulation of reactive Si, at least partially attributable to lakes and reservoirs. These lentic systems accumulate Si via biological conversion of DSi to biogenic silica (BSi). An analysis of new and published data for nearly 700 systems is presented to assess their contribution to the accumulating continental pool. Surface sediment BSi concentrations (n = 692) vary between zero and >60 % SiO2 by weight, apparently independently of lake size, location or water chemistry. Using sediment core BSi accumulation rates (n = 109), still no relationships are found with lake or catchment parameters. However, issues associated with single-core accumulation rates should in any case preclude their use in elemental accumulation calculations. Based on lake/reservoir mass-balances (n = 34), our best global-scale estimate of combined lake and reservoir Si retention is 1.53 TMol year−1, or 21–27 % of river DSi export. Again, no scalable relationships are apparent, suggesting Si retention is a complex process that varies from catchment to catchment. The lake Si sink has implications for estimation of weathering flux generation from river chemistry. The size of the total continental Si pool is poorly constrained, as is its accumulation rate, but lakes clearly contribute substantially. A corollary to this emerging understanding is that the flux and isotopic composition of DSi delivered to the ocean has likely varied over time, partly mediated by a fluctuating continental pool, including in lakes.

Use of geophysical methods for the study of sandy soils under Campinarana at the National Park of Viruá, Roraima state, Brazilian Amazonia

Purpose The vegetation of the Campinaranas occurs in humid areas with hydromorphic sandy soils at the Amazon region. Thus, the determination and in situ monitoring of moisture content in Campinarana soils, besides the detection of subsurface layers are key measures for studying these soil–vegetation systems. Also, the application of ground penetrating radar (GPR) in deep sandy sedimentary sequence of Amazonia is a promising tool to enhance the knowledge on depositional and soil formation features.

Investigation of residual fluoroquinolones in a soil–vegetable system in an intensive vegetable cultivation area in Northern China

One of the largest vegetable cultivation field sites in Northeast China was selected to investigate the occurrence and distribution pattern of fluoroquinolones (FQs) in the soil–vegetable system. A total of 100 surface soil samples and 68 vegetable samples were collected from this study area. The antibiotic concentration was analyzed using high-performance liquid chromatography tandem mass spectrometry. Results indicated the presence of FQs in all soil samples. Ciprofloxacin (CIP) had the highest mean concentration, at 104.4μg·kg−1 in the soil, a level that represents a relatively high risk to the environment and to human health. However, in the vegetable samples, norfloxacin (NOR) was significantly higher than CIP and enrofloxacin (ENR), ranging from 18.2 to 658.3μg·kg−1. The transfer ability of NOR in soil–vegetables is greater than that of CIP and ENR. Moreover, we found that the solanaceous fruits had a higher antibiotic accumulation ability than the leafy vegetables. Taken together, these data indicate that greater attention should be paid to the region in which vegetables with higher accumulation ability are grown.

Human health risk assessment of heavy metals in soil–vegetable system: A multi-medium analysis

Vegetable fields near villages in China are suffering increasing heavy metal damages from various pollution sources including agriculture, traffic, mining and Chinese typical local private family-sized industry. 268 vegetable samples which included rape, celery, cabbages, carrots, asparagus lettuces, cowpeas, tomatoes and cayenne pepper and their corresponding soils in three economically developed areas of Zhejiang Province, China were collected, and the concentrations of five heavy metals (Pb, Cd, Cr, Hg and As) in all the samples were determined. The health risk assessment methods developed by the United States Environmental Protection Agency (US EPA) were employed to explore the potential health hazards of heavy metals in soils growing vegetables. Results showed that heavy metal contaminations in investigated vegetables and corresponding soils were significant. Pollution levels varied with metals and vegetable types. The highest mean soil concentrations of heavy metals were 70.36mgkg−1 Pb, 47.49mgkg−1 Cr, 13.51mgkg−1 As, 0.73mgkg−1 for Cd and 0.67mgkg−1 Hg, respectively, while the metal concentrations in vegetables and corresponding soils were poorly correlated. The health risk assessment results indicated that diet dominated the exposure pathways, so heavy metals in soil samples might cause potential harm through food-chain transfer. The total non-cancer and cancer risk results indicated that the investigated arable fields near industrial and waste mining sites were unsuitable for growing leaf and root vegetables in view of the risk of elevated intakes of heavy metals adversely affecting food safety for local residents. Chromium and Pb were the primary heavy metals posing non-cancer risks while Cd caused the greatest cancer risk. It was concluded that more effective controls should be focused on Cd and Cr to reduce pollution in this study area.

Dynamic response of microwave land surface properties to precipitation in Amazon rainforest

The responses of land surface microwave properties to precipitation, including the brightness temperature (Tbs) and emissivities (MLSEs) at 18.7, 23.8 and 37.0GHz, are studied by combining satellite synergetic retrievals (from AQUA AMSR-E and MODIS) with in-situ measured land surface temperature, soil moisture (SM), and precipitation at two Amazonia tropical rainforest sites Km83 and Km67. In general, Tbs and MLSEs are found to be negatively correlated to SM. Their dependences on the vegetation water content (VWC) are not monotonic: positive correlations at relatively low VWC and negative correlations at high VWC range. Although Amazon dense rainforest is the most stable vegetation regime, there are significant seasonal variations in both MLSE and Tbs, with amplitudes of about 0.025 and 7.0K, respectively. The day-to-day variation of MLSE and Tbs is larger in the wet seasons than in the dry seasons, although the mean MLSE and Tbs are lower in the wet seasons than in the dry seasons. After precipitation, the SM, VWC and canopy interception water increase and reach their peak values at different transit times. There is an equilibrium time point (about 4h in this case) at which the vegetation–soil system holds the largest amount of moisture. Consequently, Tbs and MLSEs decrease during the first several hours after the start of precipitation and then increase after the equilibrium time point. Ignoring the “turning point” may introduce significant errors in the estimation of MLSEs (up to 0.04) and Tbs (up to 10K) under rainy conditions.

INTER-ANNUAL VARIABILITY OF NET ECOSYSTEM PRODUCTIVITY OVER INDIA

Abstract. The net ecosystem productivity (NEP) is the estimates of net carbon exchanges between the vegetation-soil system and the atmosphere. Estimates of NEP could play important role in defining a terrestrial ecosystem as a net source and sink of atmospheric CO2. We model monthly NEP over India for past 26 years (1981–2006) by incorporating satellite observations of vegetation index together with other climatic parameters in to efficiency based terrestrial ecosystem model. Results depict large spatial and temporal variability of NEP over India. NEP climatology over India showed that this region sequestered annually 9.4 Tg C (at the rate of 2.54 gC m-2) and hence appeared to be a net sink of atmospheric CO2. Strength of the CO2 sequestration over the country has been increased during the study period with average linear growth rate of 1.8 TgC yr-2